The electrochemical O2 reduction to H2O2 is viable alternative with examples of the direct production of up to 20% H2O2 solutions. In that respect, we found that the dinuclear complex Cu2(btmpa) amino]methyl]‐2,2’‐bipyridine) reduces O2 to H2O2 with a selectivity up to 90 % according to single linear sweep rotating ring disk electrode measurements. Microbalance experiments showed that complex reduction leads to surface adsorption thereby increasing the catalytic current. More importantly, we kept a high Faradaic efficiency for H2O2 between 60 and 70 % over the course of 2 h of amperometry by introducing high potential intervals to strip deposited copper (depCu). This is the first example of extensive studies into the long term electrochemical O2 to H2O2 reduction by a molecular complex which allowed to retain the high intrinsic selectivity of Cu2(btmpa) towards H2O2 production leading to relevant levels of H2O2.H Optimised catalytic activity: Electrochemical H2O2 production is a promising sustainable alternative to the anthraquinone method. In that perspective, we have studied the dinuclear copper complex Cu2(btmpa) that has a high intrinsic H2O2 selectivity. By extensive, long term studies, we found that complex accumulation on the electrode increases the catalytic activity and that high potential intervals strip away deposited copper. Through this procedure we were able to reach a 60 to 70 % Faradaic efficiency during long term amperometry experiments. However, its current production method is far from environmentally friendly. Over 90 % of the worldwide H2O2 production proceeds via the anthraquinone process.4+ (Cu2(btmpa), btmpa=6,6’‐bis[[bis(2‐pyridylmethyl)amino]methyl]‐2,2’‐bipyridine) which is consisting of two Cu(tmpa) moieties fused via a covalent bond between one of the three pyridines on each moiety resulting in a bipyridine backbone (Scheme I complex [Cu2(btmpa)(MeCN)2(ClO4)2]2+ has a CuI geometry that was different from CuI(tmpa), consequently a positively shifted redox potential of the CuII/I redox couple compared to Cu(tmpa). As a result isolated and well‐characterized [CuI2(btmpa)](ClO4)2 shows a diminished reactivity towards O2 with respect to Cu(tmpa) in acetonitrile.2O2 reduction resulting in a high selectivity up to 100 % for H2O2. In addition, we performed the first systematic study of long bulk electrosynthesis of H2O2 by a molecular catalyst. By performing long term amperometry measurements, we were able to identify factors that limit the Faradaic efficiency; were able to improve the overall electrosynthesis process, and thereby achieved a record breaking Faradaic efficiency of 65 % for H2O2 over the course of 2 h.Our group reported [Cu(tmpa)(L)]) Scheme , tmpa=tre Scheme .[19] A22.12(btmpa) was synthesized from the btmpa ligand and Cu(OTf)2, while the ligand was synthesized according to an earlier reported synthesis that was slightly adjusted to increase the purity and yield (see supporting info).2+ centers of the complex . We found the copper centers of Cu2(btmpa) are reduced simultaneously in an 0.1 m phosphate buffer solution of pH 7 , similar to earlier studies in organic solvents.II/I redox potential shifted 0.3 V positively with respect to the mononuclear Cu(tmpa) towards 0.51 V versus the Reversible Hydrogen Electrode (RHE). A previously published crystal structure of a [(btmpa)Cu2(CH3CN)2(ClO4)2]2+ complex showed that the Cu−N bond of the bipyridine moiety has longer distances (2.4 Å) than the other pyridines (2.0 Å).II site is likely less electron dense than Cu(tmpa) which explains the positive shift of the CuII/I redox couple. The CuII/I redox couple of Cu2(bmpta) has a relatively large peak separation, which increases with increasing scan rate . In line with Marcus theory, in which a higher reorganization energy is linked to slower electron transfer,2(btmpa), the reduction of the mononuclear Cu(tmpa) complex is a very fast processII complex to the preferred tetragonal geometry for the CuI state by the elongation of Cu−N distance of the tertiary amine from 2.10 to 2.43 Å.II geometry of Cu2(btmpa) leans towards a more pseudo‐octahedral geometry,2(btmpa) can easily obtain the preferred tetragonal geometry for the CuI state during redox state changes.The dinuclear complex Cu2.22(btmpa) has a tendency to adsorb on the electrode. This behavior was studied in detail with electrochemical quartz crystal microbalance (EQCM) studies  from a total 4+charge to 2+charge does trigger adsorption on the electrode, whereas electrochemical oxidation triggers desorption. Although the EQCM data show that the potential‐dependent adsorption is reversible on gold electrodes, the carbon‐based GC electrode might have a stronger affinity with Cu2(btmpa).During reduction from the +II to the +I oxidation state Cu2 reduction reaction (ORR) showed that Cu2(btmpa) reduces O2 to H2O2 with an onset of 0.50 V versus RHE  and increases the reductive current when performing cyclic voltammetry (CV).Compared to Cu(tmpa) the O2 reduction and in particular the H2O2 reduction reactions mediated by Cu2(btmpa) are slow (see supporting info). This is in line with the electron transfer rates being significantly slower as well in case of Cu2(btmpa). In addition the binding affinity of dioxygen are also lower, which is most likely due to the copper +I oxidation state being relatively stable, illustrated by the higher E1/2 value of Cu2(bmpta) compared to Cu(tmpa). The slow H2O2 reduction in presence of Cu2(btmpa) results in a relatively high selectivity towards hydrogen peroxide. Whereas the rate determining step in case of the oxygen reduction reaction mediated by Cu(tmpa) is binding of dioxygen,Studies with a rotating ring disk electrode (RRDE) setup of the O2(btmpa) adsorbs at the electrode when negative potentials are applied, this allows one to significantly increase the number of active copper sites at the electrode interface over time and thereby strongly increase the peroxide productivity during amperometry measurements. Chronoamperometry in presence of Cu2(btmpa) was performed using a rotating ring disk setup . A NCE(collection efficiency of the ring electrode) of 17.5 % was determined and used to calculate the % H2O2 for this measurement . The selectivity for H2O2 production by Cu2(btmpa) initially starts at 90 %. Over the course of 15 minutes, the selectivity lowers to 70 %. A selectivity below 100 % suggests that over‐reduction of H2O2 takes place. For that purpose, H2O2 reduction by Cu2(btmpa) under argon atmosphere was studied with non‐rotating and rotating electrodes . H2O2 is reduced by Cu2(btmpa) indeed and the reducing current increases with the H2O2 concentration. However, the H2O2 reduction by Cu2(btmpa) is very sluggish which explains the high selectivity for H2O2 when performing O2 reduction. When chronoamperometry measurements were performed for a longer period, a significant drop in selectivity was observed. This is most likely linked to formation of deposited copper (depCu) at the cathode because a brown‐colored, metallic deposit could be observed on the surface of the electrode . Formation of this copper deposit inherently changes the selectivity from H2O2 to H2O over the course of time. To counter formation of depCu we applied stripping intervals, wherein the potential at the working electrode is periodically increased to 0.8 V vs RHE, which is sufficient to strip depCu from the electrode, yet insufficient to oxidize H2O2 itself .Since Cu2.32 reduction with Cu2(btmpa) was monitored over a 2 hour period in O2 saturated phosphate buffer. To do so, a rotating disk setup was used for constant diffusion of O2 saturated electrolyte at 1600 rpm rotation rate. We chose 0.0 V as the most ideal potential because a background hydrogen evolution reaction is not to be expected here, and background O2 reduction reactions on GC are still minimal at this potential, while significant currents were generated at this potential in presence of Cu2(btmpa) in amperometry experiments. Three different types of measurements were performed  was tested as blank measurement (grey line). Second, a GC electrode in 0.15 mM catalyst solution was tested while continuously applying 0.0 V (orange). Last, a GC electrode in catalyst solution was tested with intervals (blue): after 20 minutes of 0.0 V, the potential at the disk was briefly set at 0.8 V for 4 minutes  (−0.25 mA versus −0.05 mA in the first minutes) and increases gradually over the course of 2 h. In the first half hour, there is a large increase in current from −0.25 to −0.37 mA. This feature of quick increase within the first 30 minutes of the measurement is observed in all cases when catalyst is present but not in absence of the catalyst. At 0.0 V, O2 reduction by Cu2(btmpa) is still kinetically limited in a cyclic voltammetry experiment . As a result, the large increase in reductive current can be explained by an increase in active sites due to accumulation of the catalyst on the electrode. The EQCM measurements points towards this behavior as well  complex, or a reaction product thereof that still retains some form of an organic ligand, that is responsible for the two‐electron reduction of dioxygen. Heterogeneous copper species, either with Cu in the +0 oxidation state, or in a partly oxidized form are not expected to produce hydrogen peroxide in significant concentrations.Od Figure . First, 2(btmpa) largely retains on the GC electrode even when a potential of 0.8 V is briefly applied. Only thoroughly rinsing the electrode could remove most of the adsorbed catalyst and lower the O2 reduction current to the same level of a bare GC electrode in a catalyst‐free electrolyte . After 1.5 hours, the reducing current of the continuous measurement became close to the estimated diffusion limited current (−0.49 mA) that one would expect for reduction of O2 to H2O2 under these conditions. The estimation is based on the diffusion limited current that a Pt disk of the same size (0.196 cm2) reaches under the same conditions for the 4‐electron reduction of O2 to H2O, for which −0.98 mA was obtained.2O2.Interestingly, the magnitude of the current at 0.0 V after a 4‐minute 0.8 V interval is equal to the magnitude of the final part of the preceding 20 minutes amperogram. This indicates that the adsorbed Cu2 reduction at 0.0 V was alternated with short periods of depCu stripping at 0.8 V  or depCu. Two different methods were considered. The first method used the same RRDE set‐up as used for Figure S6 that utilizes the Pt ring as electrochemical H2O2 sensor. Here, we found that the ring is not suited as quantitative peroxide sensor during long‐term electrolysis . The formation of high amounts of H2O2 results in oxidation of Pt to produce PtOx resulting in deactivation of the activity of the Pt ring. .2O2 within the reaction mixture. Therefore, we applied a second method: bulk electrolysis with an RDE setup for which the bulk concentration of H2O2 was periodically determined with an enzyme based photometric analysis using a reflectometer. The Faradaic efficiency was determined for measurements with 4 minute intervals and no intervals of 0.8 V. The results of the 4‐minute interval and continuous measurement are shown in Figure depCu starts to decrease the Faradaic efficiency also in case of experiments with intervals . Here, it appears that the rising H2O2 concentration leads to a faster formation of depCu. Most likely, the ligand is  oxidized that leads to degradation of the complex (see supporting information). XPS measurements of the electrode post catalysis confirm the presence of a copper species different from Cu2(btmpa) on the electrode . Experiments wherein the electrolyte solution was spiked deliberately with hydrogen peroxide showed significant levels of overreduction, while treatment of Cu2(btmpa) with H2O2 resulted to visual color changes that can be attributed to ligand oxidation.The Faradaic efficiency for H2.42(btmpa) was found to adsorb reversibly at the electrode, and as more material deposits the activity of the ORR increases. Simultaneously the Faradaic efficiency towards formation of H2O2 decreases from >80 to >60 % during this stage. After several hours the catalytic currents increase, mostly due to more efficient reduction reaction of hydrogen peroxide, resulting in a decrease in Faradaic efficiency. Selectivity of the deposited material can be restored by stripping depCu from the electrode. These observations point to a gradual degradation process of adsorbed Cu2(btmpa) to depCu. Reactive oxidation species generated from O2 and in particular H2O2 are likely to play a role herein. We recently have shown that the reduction of peroxide mediated by Cu(tmpa) most likely proceeds via a Fenton like mechanism wherein ROS are involved.2(btmpa) to depCu is responsible for the high ORR rates leading to selective formation of H2O2. However, it is clear that this is not the final species in the sequence. Control experiments with Cu2+ salts do not lead to significant amounts of peroxide being formed,2O2. Studies with an RRDE setup  wherein the H2O2 is continuously reduced to O2 by the platinum ring displayed a high selectivity and stable catalytic rates throughout an entire 8 hour measurement, which would make these systems very suitable for flow cell chemistry.Cu3depCu formation at the electrode interface. We anticipate that our results will allow for the next step, which is the incorporating the catalyst in electrochemical flow cell devices for the direct electrochemical production of H2O2 from O2.We have shown that significant amounts of hydrogen peroxide can be produced during long term amperometry experiments employing a copper catalyst. Due to accumulation of the reduced catalysts on the electrode surface, sufficiently high currents could still be obtained which are very close to the mass transport limited currents that one in principle could reach for a two electron reduction reaction involving dioxygen with the RRDE setup of study. Periodic stripping of the cathode is important for long term selectivity, as it removes The authors declare no conflict of interest.4As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.Supporting InformationClick here for additional data file.


For valence change memory (VCM)‐type synapses, a large number of vacancies help to achieve very linearly changed dynamic range, and also, the low activation energy of vacancies enables low‐voltage operation. However, a large number of vacancies increases the current of artificial synapses by acting like dopants, which aggravates low‐energy operation and device scalability. Here, mixed‐dimensional formamidinium bismuth iodides featuring in‐situ formed type‐I band structure are reported for the VCM‐type synapse. As compared to the pure 2D and 0D phases, the mixed phase increases defect density, which induces a better dynamic range and higher linearity. In addition, the mixed phase decreases conductivity for non‐paths despite a large number of defects providing lots of conducting paths. Thus, the mixed phase‐based memristor devices exhibit excellent potentiation/depression characteristics with asymmetricity of 3.15, 500 conductance states, a dynamic range of 15, pico ampere‐scale current level, and energy consumption per spike of 61.08 aJ. A convolutional neural network (CNN) simulation with the Canadian Institute for Advanced Research‐10 (CIFAR‐10) dataset is also performed, confirming a maximum recognition rate of approximately 87%. This study is expected to lay the groundwork for future research on organic bismuth halide‐based memristor synapses usable for a neuromorphic computing system. Mixed‐dimensional formamidinium bismuth iodides exhibit highly linear potentiation/depression characteristics with energy consumption as low as 61.08 aJ for the convolutional neural network (CNN) due to a large number of defects and in‐situ formed type I band alignment. In recent years, to realize the architecture and functionality for neuromorphic computing, several kinds of two‐terminal memory devices including phase‐change memory (PCM), magnetoresistive random‐access memory (MRAM) and memristor (a portmanteau of memory resistor) are suggested. Among them, memristor devices are highly suitable for neuromorphic computing because scalability, switching speed and endurance are better than those of other devices and the operating mechanism is similar to that of biological synapses. The memristor devices can be divided into two types according to resistive switching mechanisms: electrochemical metallization memory (ECM) and valence change memory (VCM). In the ECM device, resistive switching occurs by the formation and rupture of conducting filament via oxidation and reduction of metal. On the other hand, in the VCM devices, migration of defect leads to forming conducting filament or changing Schottky barrier at the interface between switching layer and metal electrode. ECM is generally not favorable to energy consumption because the operating voltage is highly dependent on the active metals such as Ag, Cu, Ni, etc. Unlike ECM devices, the VCM devices using media such as metal oxides can feature very low operating voltages, which can be further reduced to less than 1 V by generating plenty of vacancies in the metal oxide. Furthermore, vacancies are beneficial to achieving linear P/D characteristics. However, a large number of vacancies can increase the overall current of artificial synapses because charge carriers are also generated in the case that vacancies act like dopants, which is a disadvantage to energy consumption. In addition, high level of current may disturb scalable neuromorphic computing because the amount of current that flows in a wire is limited and the raised current can be saturated in artificial neurons connected with artificial synapses. Therefore, new materials for switching medium of artificial synapses are required to realize synaptic characteristics in terms of recognition accuracy, operating current, and energy efficiency. Recently, halide perovskite materials have been considered toward the memristor‐based synapses with a low operating voltage because of low activation energy for ion migration less than 1 eV. Artificial synapses with halide perovskite materials exhibited relatively low energy consumption and successfully imitated biological synapse behaviors such as P/D and spike‐timing‐dependent plasticity (STDP) characteristics. However, lead halide perovskite materials have been also suffered from behavior of vacancies acting like dopant and exhibited several problems such as small dynamic range, linearity and micro‐ampere scale current.As the amount of video, images, and other unstructured data increases exponentially, neuromorphic computing technique was suggested to process such data more efficiently, compared to serial computing based on von‐Neumann architecture.1, 23I10 (FA = formamidinium) and zero‐dimensional (0D) FA3Bi2I9 as a switching medium of artificial synapse with low energy consumption. Low crystallinity and type‐I band structure, which are achieved by combining 2D and 0D phases, induce linear P/D characteristic with considerable dynamic range and reduce the current level down to pico ampere scale while maintaining the current controllability. The crystal structure and film morphology are analyzed using X‐ray diffraction (XRD) and scanning electron microscope (SEM). We then conduct space charge limited current (SCLC) and capacitance measurements for estimating defect density and conductivity, and the temperature‐dependent electrical measurement for calculating the activation energy for ion migration. Type‐I band alignment in the mixed phase is confirmed by density functional theory (DFT) calculation. In an aspect of synaptic device operation, the exhibitory postsynaptic current (EPSC), P/D, spike‐number‐dependent plasticity (SNDP), spike‐voltage‐dependent plasticity (SVDP) and STDP characteristics are discussed, and especially, we present asymmetricity, dynamic range, and energy consumption extracted from the P/D characteristic curve. Finally, we demonstrate the applicability of our artificial synapse for convolutional neural networks via training and inference tasks for the CIFAR‐10 dataset using the “DNN+ NeuroSim” simulator and the modified National Institute of Standards and Technology (MNIST) dataset using the “NeuroSim+ MLP” simulator.Here, we report a mixed‐dimensional formamidinium bismuth iodides consisting of two‐dimensional (2D) FABisimulator25 and23 in the precursor solution. 2D layered structure (FABi3I10) is formed by FAI: BiI3 = 1: 3, while a 0D hexagonal structure with the chemical formula of FA3Bi2I9 is obtained by FAI: BiI3 = 4.5: 3. The 2D–0D mixed phase can be formed when x is between 1 and 4.5 in xFAI: BiI3. In Figure 3I10  of the (003) peak at 12.72° for the FABi3I10 film is 0.17 and that of the (101) peak at 12.30° for FA3Bi2I9 films is 0.18, while FWHMs are increased to 0.25 for the (003) peak and 0.26 for the (101) peak in the 2D–0D mixed phase. This indicates that crystallite size, estimated by Scherrer equation, is decreased from ≈45 to ≈30 nm upon mixing 2D and 0D phase  can be calculated based on trap‐filled limit voltage (VTFL) from SCLC data using Equation e is the elementary charge and L is the film thickness. Permittivity 0εε (0ε is the vacuum permittivity and ε is the dielectric constant) is related to capacitance (C) in Equation A1 stands for the device area for capacitance measurement:SCLC in Ndefect is calculated from Equation By combining Equation Ndefect is estimated to be 2.38 × 1015 cm−3, 3.46 × 1015 cm−3 and 1.55 × 1016 cm−3 for FABi3I10, the 2D‐0D mixed phase and FA3Bi2I9, respectively  for vacancy migration is thus important, which is estimated by using Nernst‐Einstein relation in Equation σ(T) and k are the temperature‐dependent conductivity and the Boltzmann constant, respectively. Ea is determined from the lnσ ‐‐ (1/T) plot in Figure Ea of 0.0836 eV than 0.2495 eV for FABi3I10 and 0.1785 eV for FA3Bi2I9. This indicates that the mixed phase is beneficial to the migration of iodide vacancy.I, A2, μ and V are the dark current density, the active area for SCLC, the carrier mobility and the applied voltage, respectively. By combining Equations μ can be estimated by Equation Characteristics of charge carrier are investigated using Mott‐Gurney's square law in Equation 33 is also evaluated from Equation  using the current of the ohmic region in SCLC,vd is the drift velocity of charge carriers and has relation with μ in Equation Based on the data listed in Table Equation 37 usiI and V in ohmic region should be used. Based on the estimated n in Table n = 6.82 × 1014 cm−3 for FABi3I10, 1.99 × 1015 cm−3 for the 2D‐0D mixed phase and 1.50 × 1015 cm−3 for FA3Bi2I9), conductivity (δ) is obtained by Equation Equation δ of FABi3I10 (2.38 × 10−7 Scm−1) and FA3Bi2I9 (2.21 × 10−5 Scm−1), the 2D‐0D mixed phase is found to demonstrate a significantly reduced δ of 1.75 × 10−10 Scm−1. Despite the increased n due to higher Ndefect, the decreased δ is mainly attributed to the five orders lower μ for the 2D–0D mixed phase than for the pure 2D and 0D phase.As compared to  To identify the type of band offset between the 0D phase and the 2D phase, we have performed first‐principles density functional theory (DFT) calculations (detailed description is shown in the Methods section in the supporting information). Our calculation based on interface super lattice model between the 0D phase and the 2D phase indicates that formation of type I band offset is possible where electrons and holes can be easily trapped at low band gap 2D phase  and FA3Bi2I9 (2.25). Moreover, when negative voltage sweeps from 0 V to −1 V and then back to 0 V, defined as one cycle, are repeated for five cycles in our memristor devices /Iinitial :poly(styrenesulfonate)). Energy consumption for EPSC is estimated to be 0.585 fJ from a peak current of 1.169 nA under a 25 µs pulse at −0.02 V (Energy consumption = |−0.02 V| × 1.169 nA × 25 µs = 0.5845 × 10−15 J ( = 0.585 fJ)). Energy consumption of 0.585 fJ is the lowest among the reported data based on halide perovskite materials  of potentiation and depression, where the method for extracting the β is well explained in Figure  In addition to P/D characteristics, emulating STDP related to Hebbian learning rule is an important requirement in artificial synapse, where STDP indicates that time interval of the spikes between pre‐ and post‐synaptic terminal determines synaptic weight in biological synapses. To mimic STDP, the shapes of two spikes are required to be the same with specific time intervals as shown in Figure  Time interval is defined to Δt (Δt = tpre − tpost). Two spikes are converted into net spikes to realize STDP in memristor devices as shown in the inset in Figure  and various shapes of input spikes for emulating the STDP are demonstrated in Figure  If the pre‐synaptic spike arrives after the postsynaptic spike (Δt > 0), the polarity of net spikes is negative and synaptic weight becomes potentiated (ΔG > 0). On the other hand, when the pre‐synaptic spike arrives later than the postsynaptic spike, the polarity of net spikes will be positive, leading to a depressed synaptic weight (ΔG < 0). Consequently, ΔG is negatively dependent on the time interval between pre‐synaptic and post‐synaptic spikes, which means the absolute value of synaptic weight is increased as Δt become closer to 0. ΔG for the mixed phase is larger than that for pure 2D and 0D phases  and pooling layers  form the feature extraction part  make the classification part  and synaptic weights (W), respectively. Here, experimentally obtained dynamic range, non‐linearity, number of conductance states, and minimum/maximum conductance values are used as synaptic characteristics for CNN simulation. For training the CIFAR‐10 dataset, two different operations are required: feed‐forward and backpropagation. In the feed‐forward operation, the input voltage signals are convolved by multiple kernels, resulting in the convolved feature maps composed of the current signals (I = V × W). These current signals then pass through the ReLU (ReLU = Rectified linear unit) activation function, where this activation process converts the convolved feature maps to the activation feature maps consisting of the voltage signals (V = fReLU(I)). The activation feature maps are transferred to the next convolution layer (the 2nd layer), and other activation feature maps are generated by repeating the previous convolution process and activation process. After that, the activation feature maps are passed to the pooling layer, where the feature maps are reduced and highlighted via max‐pooling operation. These pooled feature maps are passed to the next convolution layer (the 3rd layer), converted into voltage signals through the ReLU activation function as before, and transferred to the 4th convolution layer. After completing the feature extraction by repeating the process from the 1st layer to the 3rd layer once more, the pooled feature maps consisting of various features of the input image are extracted from the last pooling layer (the 6th layer) and these feature signals are flattened into a 1 × 8912 array for the classification process. The fully connected layers consist of input/hidden/output neuron layers and synapse layers (the 7th and 8th layers) in the classification part  go through the 7th synapse layer, converting to current signals. These current signals are then transformed to voltage signals via the ReLU activation function in the hidden neuron layer. Finally, the voltage signals from the hidden layer pass through the last synapse layer (the 8th layer) and the output neuron. In the backpropagation operation, is calculated by the difference between the label values (K) and the output signals (VO). The synaptic weights, which exist in the feature extraction process (kernels) and classification process (7th and 8th synapse layers), are updated from the last output layer to the first convolution layer.Finally, we have conducted training and inference tasks for the CIFAR‐10 dataset to confirm the feasibility of our memristor‐based synaptic device toward CNN. The “DNN+ NeuroSim”, which is an integrated framework to benchmark compute‐in‐memory (CIM) accelerators for deep neural networks, is used for this work.25 As t Figure . The fla3I10‐, and 0D FA3Bi2I9‐based synaptic devices. The maximum recognition rate for the mixed phase is approximately 87%, which is significantly higher than the other two cases (approximately 40%). This result is attributed to the P/D characteristics such as dynamic range and asymmetricity, As aforementioned, the high dynamic range and low asymmetricity for the mixed phase‐based synapse contribute to a high recognition rate, while relatively low recognition rates for pure 2D FABi3I10 and 0D FA3Bi2I9 are due to insufficient dynamic range and high asymmetricity. We have additionally fabricated 3 memristor devices employing the mixed phase to investigate synaptic behavior more in detail  patterns using the NeuroSim+ MLP simulator (Figure After the training task for 50 000 CIFAR‐10 training images, we compare the recognition rates for the mixed phase with pure 2D and 0D materials via the inference simulation with 10 000 inference images. As shown in Figure etricity,65 As il Table . Exploit33I10 and 0D FA3Bi2I9, low crystallinity due to phase miscibility was found to be beneficial to lowering activation energy for migration of iodide vacancies. Despite low activation energy and high carrier density, conductivity of the mixed phase was much lower than those of the pure 2D and 0D phases because of the is‐situ formed Type‐I band structure. Thus, the developed mixed phase with low crystallinity was found to be beneficial to not only energy consumption and scalability due to low conductivity but also linearity and dynamic range due to large defect density and low activation energy for migration of iodide vacancies, which eventually realized the recognition rate accuracy of 87% in CNNs. Our unique design of switching materials suggests direction for manufacturing memristor devices to realize characteristic for neuromorphic computing.In case of general oxides and halide perovskite materials, defects for large dynamic range and good linearity act as dopant, which leads to an increase in overall current and thereby an increase in energy consumption. Thus, novel materials are required to fulfill low energy consumption in spite of high defect density. We developed the 2D‐0D mixed phase based on organic bismuth iodide enabling large dynamic range, superior linearity and low energy consumption for highly efficient neuromorphic computing. As compared to highly crystalline 2D FABiThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.


BioMed Research International has retracted the article titled “Potentiated Osteoinductivity via Cotransfection with BMP-2 and VEGF Genes in Microencapsulated C2C12 Cells” [Following the publication of the article, concerns have been identified by the authors with figures of the article and also raised on Pubpeer :The authors raised that in Figure 1(a), the image of ADSCs was incorrectly selected by them.In addition, Figure 2(b) 1w ADSCs, Figure 2(b) 4w SMSCs and Figure 2(c) 4w C2C12 were selected inappropriately.While assessing these concerns, it was also found that Figure 2(b) ADSCs at 1 week is the same as Figure 2(c) NIH/3 T3 at 1 week, with the contrast and exposure adjusted. This was not raised by the authors during their correction request.The concerns are related to Figures 1 and 2:The authors did not provide a satisfactory response. Hence, this article is being retracted with the agreement of the editorial board.


As compared to the O3‐type LiCoO2, the O2‐type LiCoO2 exhibits significantly improved cycle performance in neutral aqueous electrolyte. It is found that the structural degradation caused by electrophilic attack of proton can be effectively mitigated in O2‐type layered structure. With O2 stacking, CoO6 octahedra in LiCoO2 possess stronger Co—O bonds while Co migration from Co layer to Li layer is strongly hampered, resulting in enhanced structural stability against proton attack and prolonged cycle life in aqueous electrolyte. The findings in this work reveal that regulating oxygen stacking sequence is an effective strategy to improve the structural stability of layered materials for ALIBs.Despite the high energy density of O3‐type layered cathode materials, the short cycle life in aqueous electrolyte hinders their practical applications in aqueous lithium‐ion batteries (ALIBs). In this work, it is demonstrated that the structural stability of layered LiCoO m Li2SO4 aqueous electrolyte. With stronger Co─O bonds, the O2‐LiCoO2 exhibits enhanced Co confinement in CoO6 octahedra. Meanwhile, the face‐sharing local environments of cations in O2‐LiCoO2 effectively suppress Co migration to Li layers, thus inhibiting the layered‐to‐spinel phase transition.By altering the oxygen stacking sequence from O3 to O2, the layered structure stability can be significantly improved in the 1  In terms of cathode materials, the layered LiMO2  with suitably high electrode potential and large specific capacity are considered as promising cathode candidates for ALIBs. The O3‐type layered LiMO2 cathodes, where O represents Li+ occupied octahedral sites and the number 3 represents the oxygen stacking in “ABCABC” sequence, have achieved dramatic success in lithium‐ion batteries with organic electrolytes. However, these layered materials suffer from structural instability and rapid capacity decay upon cycling in aqueous electrolytes, which hampers the practical development of ALIBs. Recently, our group investigated the degradation mechanism of O3‐type LiCoO2 in aqueous electrolyte and found that the irreversible layered‐to‐spinel phase transition accelerated by proton attack is the main cause for structural degradation and fast capacity fading. Therefore, it is of great importance for ALIBs to develop strengthened layered structures that can suppress the layered‐to‐spinel phase transition during cycling.The aqueous lithium‐ion batteries (ALIBs) have recently attracted intense attention owing to the intriguing merits of aqueous electrolytes including high safety, nonflammability, environmental benignity, high ionic mobility, and low cost.1 The 2 proceeds through the M migration from octahedral sites at M layer to octahedral sites at Li layer via tetrahedral intermediate sites. A recent work by Kang et al. demonstrated that by developing O2‐type lithium‐rich nickel manganese oxide with oxygen stacking in “BABCBA” sequence, the transition metal ions are difficult to migrate to the octahedral sites in the Li layer, which remarkably improves the reversibility of the transition metal ion migration and thereby dramatically enhances the structural stability during cycling. In O2‐type layered structure, the transition metal ion migration to the octahedral site in Li layer is demonstrated to be unfavorable due to the large electrostatic repulsion between face‐shared cations, which could effectively suppress the layered‐to‐spinel phase transition. It is therefore speculated that similar structural regulation strategy could be implemented for layered LiMO2 cathodes to improve their cycle performance in aqueous electrolyte. Nevertheless, no direct study has been reported for investigating the electrochemical properties of O2‐type LiMO2 in aqueous electrolytes by far.The layered‐to‐spinel phase transition in O3‐type LiMO cycling.6 In O2 (O2‐LCO) and explored its structural and electrochemical stability in neutral aqueous electrolyte (1 m Li2SO4) in comparison with O3‐type LiCoO2 (O3‐LCO). It has been demonstrated that significantly improved cycle performance can be achieved in aqueous electrolyte for LiCoO2 via altering the oxygen stacking sequence from O3 to O2. Through structural characterizations, we disclosed that the O2‐LCO possesses stronger Co─O bonds than O3‐LCO, which can help O2‐LCO resist the electrophilic attack of H+ on lattice oxygen. Meanwhile, the face‐sharing local environments of cations in O2‐LCO can effectively suppress Co migration to Li layers, thus inhibiting the layered‐to‐spinel phase transition. As a result, the O2‐LCO exhibits remarkably enhanced structural stability and greatly attenuated electrochemical degradation as compared to the O3‐LCO in aqueous electrolyte. The demonstration of enhanced structure stability of O2‐type layered material in aqueous electrolyte provides valuable insights in structural regulation to develop high performance cathodes for ALIBs.In the present work, we synthesized O2‐type LiCoO22.10.7CoO2 (P2‐NCO) by a hydrothermal ion‐exchange method. The X‐ray diffraction (XRD) patterns and Rietveld‐refined results in FigureP63/mmc and BAABBA oxygen stacking, Figure P63mc and BABCBA oxygen stacking, Figure 2 slabs in P2‐NCO, which is driven by the replacement of prismatic Na sites by octahedral Li sites. To investigate whether Na+ ions remained in O2‐LCO after hydrothermal Li/Na ion exchange reaction of P2‐NCO, we further performed solid‐state 23Na magic angle spinning (MAS) NMR on the O2‐LCO. As shown in Figure 23Na MAS NMR signal located around 435 ppm, which can be attributed to the Fermi contact shift induced by spin‐transfer from paramagnetic Co4+ to the prismatic Na+ ions in the residual of NaxCoO2 phase. Compared with prismatic Na+, octahedral Na+ ions have stronger Fermi contact with Co4+. However, we did not detect the signal of the octahedral Na+ ions at the low field, demonstrating no Na+ ions exist in O2‐LCO. Therefore, Na+ ions could exist in the trace amount of residual P2‐NCO phase but are unlikely to exist in the O2‐LCO after ion exchange. In addition, we carried out XRD measurements on both fresh O2‐LCO sample and old O2‐LCO sample stored in a plastic bag for nearly one year. As shown in Figure R‐3m and ABCABC oxygen stacking). Owing to different oxygen stacking sequences, the local environments of Li sites in O2 and O3 are very different: LiO6 octahedra share both edges on one side and faces on the other side with CoO6 octahedra in O2 while LiO6 octahedra share edges with CoO6 octahedra in O3. Despite different layered structures, the O3‐LCO and O2‐LCO electrodes exhibit comparative specific capacities (≈135 mAh g−1 at 1 C) and similar cycle performance (≈88% capacity retention after 100 cycles) when cycled between 3 and 4.2 V (vs Li/Li+) in organic electrolyte  measurements to monitor the electrode mass change of the O3‐LCO and O2‐LCO electrodes during charge/discharge processes in aqueous electrolyte. As shown in Figure 2.2Figure3O4 and the reflection of (2−20) represents the Co occupancy at 8a tetrahedral sites in spinel. By contrast, the O2‐LCO maintains the well‐resolved layered structure at both surface and subsurface regions after cycling in aqueous electrolyte . The obtained XRD patterns of O3‐LCO and O2‐LCO electrodes after 100 cycles are presented in Figure e Figure . The lat3,2‐edges, corresponding to excitations of the 2p electrons to 3d orbitals, are sensitive to monitor the valence change of Co in O3‐LCO and O2‐LCO cycled in aqueous electrolyte. The EELS line‐scans were performed from surface to subsurface regions for both samples as indicated in high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) images in Figure 3,2‐edge spectra show red shift of both L3‐ and L2‐edges toward the surface for O3‐LCO  and Co3O4 (Co2.66+) standards, the average oxidation state of Co for O3‐LCO near the surface is estimated to be 2.66+, agreeing well with the formation of spinel Co3O4 surface layer as indicated by HRTEM result. In comparison, the L3/L2 ratio of O2‐LCO remains nearly constant at ≈2.2, which corresponds to Co3+ in LCO, demonstrating its stable surface in aqueous electrolyte. In addition, the X‐ray photoelectron spectroscopy (XPS) depth profile analysis  spectra of Co LO Figure  while suO Figure . The red  and 796 eV (Co 2p1/2) with satellite peaks at 790 eV (Co 2p3/2) and 805 eV (Co 2p1/2). During charge process, the broadening of main peaks and decrease of satellite peaks can be attributed to the oxidation process of Co3+. During discharge process, the XPS spectra of O3‐LCO show Co2+ feature with the satellite peaks shifting towards the main peaks, suggesting the formation of Co3O4 impurity phase in O3‐LCO. In comparison, the XPS spectra of O2‐LCO during discharge only show narrowing of main peaks and increase of satellite peaks without peak shifting, demonstrating highly reversible Co3+/4+ redox reaction during charge/discharge processes.To investigate the redox reactions of cobalt ions of O3‐LCO and O2‐LCO during charge/discharge in aqueous electrolyte, we have performed ex situ XPS measurements. As shown in Figure  of Co3+.13 Durg and A1g Raman bands for O3‐LCO, several new bands appear during the initial charge process, which can be attributed to the spinel LiCoO2 (S‐LCO) and Co3O4 phases, indicating the layered‐to‐spinel phase transition occurs even at the first charge process. The Raman spectra of the O3‐LCO after 10, 50, and 100 cycles of charge/discharge in Figure 3O4 during subsequent charge/discharge processes. For O2‐LCO, the in situ Raman spectra in Figure st, 50th, and 100th cycles. It is noticed that the charge transfer resistance, corresponding to the semicircle, of the O3‐LCO electrode increases quickly with the cycle numbers, indicating the poor Li+ conductive nature of the formed surface spinel phase (S‐LCO and Co3O4). By contrast, the charge transfer resistance of the O2‐LCO electrode only displays minimal increase with cycling, demonstrating greatly enhanced surface stability in aqueous electrolyte. Based on the structural evolution analysis, we can see O3‐LCO is highly unstable when cycled in aqueous electrolyte, and its structural degradation proceeds through the layered‐to‐spinel phase transition associated with Co dissolution into the electrolyte. The formed spinel Co3O4 surface layer is electrochemically inactive and severely reduces the electrode kinetics, resulting in fast capacity fading in aqueous electrolyte. It's interesting to discover the remarkably enhanced structural stability and improved electrochemical performance of O2‐LCO in aqueous electrolyte. Although slight Co dissolution still persists in O2‐LCO, no layered‐to‐spinel phase transition can be detected on the O2‐LCO surface during cycling.The in situ Raman spectra were further used to investigate the structure evolutions of O3‐LCO and O2‐LCO during the initial charge and discharge processes. As shown in Figure  During the charge process, the O21 phase (002 at 18.4°) transforms into the O22 (002 at 17.7°) phase, and the O6 phase appears together with O22 at high potential. (006 at 17.9°). Such phase transition is highly reversible during the subsequent discharge process. In the aqueous electrolyte, O2‐LCO undergoes the same phase transition from O21 to O22 during the charge process. However, the O6 phase appears earlier during the charge process and exists in a wider potential range than that in the organic electrolyte. Nevertheless, it returns to the O21 phase at the end of the discharge, showing good reversibility of the phase transition. It is speculated that the difference of O6 phase formation during phase transition of O2‐LCO in aqueous and organic electrolytes is probably caused by protonation of the material in aqueous electrolyte.Although the O2‐LCO shows improved layered structure stability than O3‐LCO in aqueous electrolyte, its capacity retention after 100 cycles (72.7%) is smaller than that in organic electrolyte (≈88%). In addition to the surface structure evolution, the bulk phase transition mechanism of O2‐LCO in aqueous electrolyte and organic electrolyte needs to be further explored. We have performed in situ XRD on O2‐LCO electrodes in both aqueous electrolyte and carbonate‐based electrolyte as shown in Figure 15 Dur2.3+ in aqueous electrolyte, it is important to further understand proton's influence on layered structures with different oxygen stackings. As revealed in recent studies, the H+ ions are electrophilic reagents and they may attack the lattice oxygen of the transition metal oxides. To investigate the interaction between proton and lattice oxygen, the O 1s XPS spectra of the O3‐LCO and O2‐LCO electrodes cycled in aqueous electrolyte and organic electrolyte are compared in Figure The absence of the 531 eV peak in O 1s XPS spectra of the cycled electrodes in organic electrolyte further suggests the existence of proton attack on lattice oxygen for both two samples in aqueous electrolyte. To explore the influence of proton attack on the structural stability, the density functional theory (DFT) calculations have been carried out on the two‐layered structure models. Based on the calculated total charge density distributions in Co─O planes of O3‐LCO and O2‐LCO . The TOF‐SIMS 18O/16O surface maps  for O3‐LCO and O2‐LCO with and without H+ attack by using DFT to evaluate the Co migration capability in these circumstances. Specifically, Ef(VCo) can be defined as follows:Ea and Eb denote the total energies of the structures with and without Co vacancy, respectively. in denotes the number of element i that have been incorporated into (in>0) or removed from (in<0) the b structure. iµ denotes the chemical potential of element i. As shown in Figure2O formation with proton attack, an oxygen vacancy will be created in the CoO6 octahedron. The Co vacancy formation energies for O3‐LCO and O2‐LCO supercells with adjacent lattice O vacancy are −7.99 and −2.34 eV, respectively, indicating more favorable Co vacancy formation with the assistance of O vacancy. Under this circumstance, the O3‐LCO has higher probability for Co migration than O2‐LCO, further demonstrating enhanced structural stability of O2‐LCO. The Co vacancy formation energies in the half‐delithiated phases are calculated and presented in Figure Since both the layered‐to‐spinel phase transition and Co dissolution depend on the capability of Co migration out of the CoO6 octahedra that can impede Co migration. To further analyze the structural difference between O3‐LCO and O2‐LCO, the Co K‐edge X‐ray absorption near edge structure (XANES) spectra of two samples were measured and are shown in Figure e to the c axis is either parallel (e∥c) or perpendicular (e⊥c). According to previous works in literature, the absorption peak at ≈7728 eV could be attributed to both (e∥c) and (e⊥c) transitions, while the peak at ≈7733 eV could be mainly attributed to the (e⊥c) transition. Due to the different oxygen stacking sequences, the O3‐LCO with transition probability from the (e∥c) transition shows increased absorption intensity at ≈7728 eV in comparison to that for O2‐LCO. The Fourier transforms of Co extended X‐ray absorption fine structure (EXAFS) spectra in Figure σ2) has been reported as a practical measure of local bond strength. As shown in Table σ2 of Co—O bonds for O3‐LCO and O2‐LCO are 0.32 and 0.28, respectively, demonstrating stronger Co─O bond strength of O2‐LCO than O3‐LCO. The stronger Co─O bond strength of O2‐LCO indicates increased energy barrier for Co migration, agreeing well with its improved structural stability in aqueous electrolyte.DFT calculations suggest O2‐LCO possesses reinforced CoOansition.21 Due6 octahedra highly depends on the Co—O bond strength. As compared in Figure 6 and CoO6 octahedra makes the migration of Co to Li site unfavorable because of the large electrostatic repulsion between face‐shared cations. But for O3‐LCO, the edge‐sharing configuration between LiO6 and CoO6 octahedra affords easier path for Co migration, thus favoring the layered‐to‐spinel phase transition. Owing to the beneficial structural features, the O2‐LCO exhibits superior structural stability to O3‐LCO in aqueous electrolyte, resulting in prominent extension of cycle life for layered materials in ALIBs.Based on the above analyses, the distinct difference in structural stability of O3‐LCO and O2‐LCO in aqueous electrolyte originates from the different Co—O bond strengths and oxygen stacking sequences for two layered structures. The O3 and O2 layered structures with different structural features are illustrated in Figure  cations.6 But 3In summary, we demonstrate the disparate structural stabilities of layered lithium cobalt oxide polymorphs of O3‐LCO and O2‐LCO in aqueous electrolyte. The O3‐LCO exhibits fast capacity fading due to the instant layered‐to‐spinel phase transition initiated at the particle surface associated with Co dissolution during cycling. In contrast, the O2‐LCO well maintains its layered structure with suppressed Co dissolution during cycling, leading to notable extension of cycle life in aqueous electrolyte. It is demonstrated that protonation occurs in both layered structures when cycled in aqueous electrolyte, and the formation of H—O bond could weaken the neighboring Co—O bond, increasing structural instability with enhanced Co migration probability. With shortened Co—O bond length, the O2‐LCO exhibits greatly improved resistibility to the electrophilic proton attack and enhanced Co confinement capability in octahedra. By altering the oxygen stacking sequence, face‐sharing local configuration between cations can be engineered to further impede Co migration to Li layers, effectively suppressing the layered‐to‐spinel phase transition. The present work provides new opportunities for designing layered cathode materials with both high energy density and long cycle life for ALIBs.42CO3 and Co3O4 (with Na/Co ratio of 0.7) at 850 °C for 12 h in air. The O2‐LCO was prepared by a hydrothermal ion exchange reaction. Typically, 1 g P2‐NCO was added into a 40 mL of LiCl (2.5 m) and LiOH (2.5 m) solution by continuous stirring. The solution was then sealed in a Teflon‐lined stainless steel autoclave and heated at 120 °C for 3 h. The O3‐LCO was prepared by heating a mixture of Li2CO3 and Co3O4 (with Li/Co ratio of 1.01) at 900 °C for 12 h in air.The P2‐NCO was prepared by heating a mixture of Naα radiation) was used to investigate the crystal structures of different samples. For the in situ XRD measurements in organic electrolyte, an in situ XRD cell (LIB‐XRD) with a Be window was used. The O2‐LCO film  and Li metal were used as cathode and anode, respectively. For the in situ XRD measurements in aqueous electrolyte, an in situ XRD cell (WB‐XRD) with a Kapton tape sealed window was used. The O2‐LCO electrode and active carbon electrode  were used as cathode and anode, respectively. The galvanostatic charge/discharge measurements were carried out on a potentiostat (Ivium Vertex) at a current density of 0.1 A g−1. The XRD Rietveld refinement analysis was carried out by using the GSAS program. The solid‐state 23Na MAS NMR was recorded on Agilent 600 DD2 spectrometer  at 158.64 MHz. The powder samples were placed in a pencil‐type zirconia rotor of 4.0 mm o.d. The spectra were obtained at a spinning speed of 10 kHz. The Na signal of tetramethylsilane (TMS) at 0 ppm was used as the reference of 23Na chemical shift. XPS  was applied to investigate the surface composition changes of different samples. HRTEM (JEOL JEM‐2100F) and Raman  were used to investigate the structural evolutions of different samples. For STEM‐EELS measurements, the beam energy was 200 kV and the resolution was about 1 eV. For isotope labeling, 100 mg of prepared powders (O2‐LCO or O3‐LCO) were added into a 1 m H2SO4 solution  and stirred at 25°C for 12 h. The obtained samples were centrifuged and washed several times by distilled water and dried at 60°C for 12 h. The TOF‐SIMS  was employed for the analyses of 18O and 16O ions. The analyzed areas for depth profiling and high‐resolution mapping are typically 10 µm × 10 µm with the pixel of 512 × 512. For the in situ Raman measurements, a three‐electrode in situ Raman cell (EC‐RAIR‐H) with a thin quartz window  was used. The as‐prepared cathode (was placed at the top of the glassy carbon electrode nearing the quartz window), Pt wire, and Ag/AgCl electrode were used as working electrode, counter electrode, and reference electrode, respectively. The galvanostatic charge/discharge measurements were carried out on a potentiostat (Ivium Vertex) at a current density of 1 A g−1. The power of laser beam delivered to the electrode surface was ≈10% of the maximum 50 mW laser to avoid its damage to the sample. The acquisition time was 10 s with no accumulation and the frequency range was selected from 200 to 1800 cm−1. The spectral resolution of Raman spectra in the study was ca. 1.0 cm−1. The Co K‐edge XAFS spectra were carried out at the 44A beamline of National Synchrotron Radiation Research Center (NSRRC). The samples were ground and uniformly daubed on the special adhesive tape. The data were collected in fluorescence mode using a Lytle detector. The obtained EXAFS data were processed using the ATHENA module in the Demeter software packages. The post‐edge background was subtracted from the overall absorption and then normalized with respect to the edge‐jump step. To quantify the atomic structure parameters, least‐squares curve parameter fitting was performed using the ARTEMIS module of Demeter software packages.XRD  using the three‐electrode cell, in which the prepared cathodes were used as the working electrodes, a carbon cloth supported active carbon (with mass loading of ≈12 mg cm−2) was used as the counter electrode, and SCE was used as the reference electrode. 1 m Li2SO4 solutions with pH values of 7 and 11 (adjusted by adding LiOH) were used as aqueous electrolytes. The EQCM  measurements were applied to determine the mass change (∆m) of the electrode accompanied with charge/discharge tests. The exchanged molecular weight of ion (Mw) was calculated by Mw=ΔmnFΔQ, where F is Faraday constant (96 485 C mol−1), n is the valence number of ions, and ∆Q is the charge quantity passed through the electrode in Coulombs.The obtained O3‐LCO and O2‐LCO were used as active materials to prepare electrodes by using carbon cloth as current collector. Typically, the active material, acetylene black, and polyvinylidene fluoride in 8:1:1 mass ratio were mixed in N‐methylpyrrolidone to form a slurry. Then, the slurry was coated on carbon cloth and dried in a vacuum at 100 °C for 24 h. The mass loadings of the active materials were kept in the range of 3–4 mg cm The generalized‐gradient approximation (GGA) in the form of Perdew‐Burke‐Ernzerhof (PBE) describes the exchange‐correction energy. The projector‐augmented wave (PAW) pseudopotential was chosen to describe the electron‐ion interaction. To correct the self‐interaction of Co 3d electrons, the Hubbard U of 4.91 eV was used, in line with previous literature. The cutoff energy was set to 650 eV. The 4×4×2 and 3×3×1 girds of k‐points sampling were adopted for bulk and surface calculations, respectively. All atoms were optimized to their equilibrium positions under a force convergence of 0.03 eV Å−1. Spin‐polarized calculations were performed for all calculations.All first‐principles calculations within the framework of DFT were performed using the Vienna Ab Initio Simulation Package (VASP).24 TheThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.


Microtubules are key players in several stages of the cell cycle and are also involved in the transportation of cellular organelles. Microtubules are polymerized by α/β tubulin dimers with a highly dynamic feature, especially at the plus ends of the microtubules. Therefore, understanding the interactions among tubulins is crucial for characterizing microtubule dynamics. Studying microtubule dynamics can help researchers make advances in the treatment of neurodegenerative diseases and cancer. In this study, we utilize a series of computational approaches to study the electrostatic interactions at the binding interfaces of tubulin monomers. Our study revealed that among all the four types of tubulin-tubulin binding modes, the electrostatic attractive interactions in the α/β tubulin binding are the strongest while the interactions of α/α tubulin binding in the longitudinal direction are the weakest. Our calculations explained that due to the electrostatic interactions, the tubulins always preferred to form α/β tubulin dimers. The interactions between two protofilaments are the weakest. Thus, the protofilaments are easily separated from each other. Furthermore, the important residues involved in the salt bridges at the binding interfaces of the tubulins are identified, which illustrates the details of the interactions in the microtubule. This study elucidates some mechanistic details of microtubule dynamics and also identifies important residues at the binding interfaces as potential drug targets for the inhibition of cancer cells. Microtubules are cytoskeletal structures that play an important role in shaping eukaryotic cell structure ,2. They Currently, it is known that kinesin motors bind certain cargo and move along the microtubules in anterograde axonal transport ,15. Yet Computational methods have been widely used to study the functions of biomolecules ,27,28,29Hydrogen bonds are significant to the stability of microtubules. Ayoub et al. (2014) revealed that lateral hydrogen bonds are significantly stronger than longitudinal ones . HoweverIn this work, we took two tubulin-containing structures  accessed on 31 December 2022. The calculated electrostatic surface potential was visualized with USCF Chimera . On the surface of α tubulin within the α/β tubulin complex, only ARG390 forms both a salt bridge (of any occupancy) and a hydrogen bond with occupancy greater than 80%. Three other residues  from α tubulin also form salt bridges and hydrogen bonds, but the hydrogen bonds for these have lower occupancies. Residues LYS96 and GLU97 play a role in salt bridge formation, but these do not form hydrogen bonds with other residues. On the binding interface of β tubulin within the α/β complex, residues LYS252, GLU343, and ARG46 are likely key in forming the complex because these also form both hydrogen bonds and salt bridges. In addition, they interact with multiple residues when forming hydrogen bonds and salt bridges.The β/α tubulin complex has the second strongest interaction based on the comprehensive analysis of MD simulations and electrostatic feature results. On the binding interface of the complex, all salt bridge pairs form hydrogen bond pairs, including two salt bridge pairs with occupancies above 80% [GLU181 (β-tubulin) and LYS352 (α-tubulin) as well as LYS103 (β-tubulin) and GLU254 (α-tubulin)]. In particular, the residue LYS352 on the surface of α tubulin is noteworthy, as it interacts with multiple residues to form multiple salt bridges and hydrogen bonds. In addition, residue ASP345 on the surface of the α interface also has a high occupancy (94.7%) when forming hydrogen bonds, though it is not involved in the formation of salt bridges. Some residues  also play an important role in the formation of salt bridges and hydrogen bonds, although the occupancy rate is not very high.The β/β tubulin interfaces have the weakest hydrogen bond network followed by the α/α tubulin interfaces. The weaker interactions of α/α and β/β tubulin complexes are consistent with our electrostatic feature analysis, including the electrostatic potential on their binding domains, the electric field lines, and the electrostatic forces between the interfacial surfaces. However, α/α or β/β tubulin complexes have a high occupancy of salt bridges on their surfaces , which means salt bridges play the most significant role in holding α/α or β/β tubulin complex. For the α/α tubulin complex, these high occupancy salt bridge pairs are GLU90 and LYS280, ARG64 and GLU284, and ARG123 and GLU297. For the β/β complex, the high occupancy salt bridge pairs are ASP88 and ARG282, ASP118 and LYS297, and GLU125 and LYS336.We investigated and analyzed the electrostatic interactions among tubulins for different interfaces. Four possible binding interfaces were found for tubulin/tubulin interactions. The interactions at the interfaces were analyzed utilizing various computational tools. Electrostatic features indicate that the strongest attractive forces are found in the α/β tubulin complex, while β/α complex has weaker attraction and β/β complex has the weakest attraction; The interaction between α/α tubulins is repulsive.Furthermore, residues forming salt bridges and hydrogen bonds were identified by MD simulations. Our results show that the α/β tubulin complex has the strongest electrostatic attractive interactions followed by the β/α tubulin complex, while β/β and α/α tubulin complexes have weak attractive and repulsive electrostatic interactions, respectively. The key forces between α and β tubulins are the hydrogen bonds on the interface of the two tubulins, which is consistent with our previous work . While sThis study used several approaches to study the electrostatic features of microtubules based on the interactions of tubulins. It reveals the mechanisms of tubulin-tubulin interactions which demonstrates the assembly and dynamics of the microtubule. The key residues forming hydrogen bonds and salt bridges are potential drug targets for the inhibition of cancerous cells and may help researchers in the quest to develop novel therapeutic ,52,53.


Conventional processes for carbon capture from ambient air require 230 to 800 kJ thermal per mole of CO2, which accounts for most of the total cost of capture. Here, we demonstrate electrochemical direct air capture using neutral red as a redox-active material in an aqueous solution enabled by the inclusion of nicotinamide as a hydrotropic solubilizing agent. The electrochemical system demonstrates a high electron utilization of 0.71 in a continuous flow cell with an estimated minimum work of 35 kJe per mole of CO2 from 15% CO2. Further exploration using ambient air (410 ppm CO2 in the presence of 20% oxygen) as a feed gas shows electron utilization of 0.38 in a continuous flow cell to provide an estimated minimum work of 65 kJe per mole of CO2.Direct air capture of carbon dioxide is a viable option for the mitigation of CO 2 requires air-stable redox-active materials. Here, the authors present an electrochemical DAC using air-stable redox couple of neutral red with a minimum energy requirement of 65 kJe/molCO2.Electrochemical direct air capture (DAC) of CO The atmospheric CO2 concentration has increased continuously from the preindustrial level of 280 ppm to 410 ppm in 2021, induced by human activities which currently emit close to 40 billion tons of CO2 annually2. Carbon capture and storage (CCS) technologies have been recognized as one of the important strategies to slow down changes in global climate patterns by effectively lowering CO2 discharges3. Conventional CO2 capture has addressed CO2 emissions from large point sources, such as fossil-fuel power stations and chemical plants. Since a considerable portion of CO2 emissions is derived from mobile sources , direct air capture (DAC), in which CO2 is captured directly from ambient air, is considered to be an important and viable option for reducing atmospheric CO2 levels4. While there are advantages of DAC in its potential to address emissions from distributed sources, the development and application of DAC processes have been restricted by their high operation cost. Currently, the energy requirements of the leading DAC technologies are ~500 to 800 kJ thermal per mole of CO2 using sodium hydroxide scrubbing/lime causticization systems5 and ~238 to 317 kJ thermal per mole of CO2 using amine-functionalized solid sorbents6. Recent analyses suggest that the energy requirement target should be less than 400 kJ thermal per mole of CO2  by CO2-neutral power sources to be viable in order to be CO2 negative5.Increased atmospheric carbon dioxide .To overcome these limitations of high energy requirements encountered by the systems using thermal energy, electrochemical systems have come to be recognized as a feasible option due to their potentially lower energy consumption under milder conditions of room temperature and pressure, as highlighted in recent review articles  in aqueous systems. Although several efforts to engage these compounds in electrochemical direct air capture with potentially low energy consumption have been reported, these systems suffered from oxygen sensitivity and required synthetic modification to overcome low aqueous solubility10. For these reasons, none of the phenazine- and phenothiazine-based systems was reported to demonstrate capture of CO2 from ambient air, to the best of our knowledge. Direct air capture using a reversible electrochemical system with low energy consumption benefiting from the reversible PCET redox couples in an aqueous solution can be achieved by eliminating oxygen sensitivity of the redox-active compound and enhancing its aqueous solubility. Here, we report electrochemical direct air capture of CO2 using neutral red (NR), a commercial organic dye molecule, as an oxygen-insensitive organic redox-active compound , and thionin (TN) could not satisfy the need for oxygen insensitivity 26 mixture can be estimated to be 1.2 to 1.67 equivalent depending on the pH values of the starting solutions  redox system is illustrated in Fig. 25, can increase the solubility of NR in 0.5 M potassium chloride (KCl) aqueous solution from 46 mM to 306 mM . When the electrolyte solution was saturated with CO2, the voltammogram showed a positively shifted single cathodic peak at –0.65 V and an anodic peak at –0.54 V (blue curve). The second set of CV curves, shown in red, were recorded in the presence of NA. Under the N2 atmosphere, two sets of cathodic and anodic peaks appeared at –0.60 V and –0.50 V and at –0.97 V and –0.82 V, respectively (pastel red curve). These are attributed to the stepwise two single-electron transfers27. When the CO2 was introduced to the electrolyte solution with adjustment of the pH value to pH 7, the two cathodic peaks merged to show a single peak at –0.78 V with slight shifts in the two anodic peaks to –0.61 V and –0.52 V, respectively (red curve). CV curves of NR show quasi-reversibility in the redox activity of NR/NRH2 in the presence and absence of NA. The electrochemical carbon capture system in this manuscript was demonstrated using a 50 mM NR solution in the presence of 1 M NA as a hydrotropic agent.Although the aqueous solubilities of phenazines and phenothiazines would be low in electrolyte solutions, the inclusion of 1 M of NA as a hydrotropic agent, which is often used to increase the water solubility of pharmaceuticals mM Fig. . Cyclic 2 capture with the NR/NRH2 redox system . The CO2-saturated solution was then pumped to the anodic chamber where electrochemical oxidation led to regeneration of NR and release of free CO2 (path c). Then the resulting solution was transferred to the anolyte reservoir to discharge CO2 and close the flow cycle (path d). The continuous operation of the flow cell was demonstrated with 15% CO2 and ambient air.In this manuscript, we describe continuous flow electrochemical COtem Fig. . NR was 27. The first single-electron reduction peak appears at –0.61 V with the second reduction peak at –0.94 V and two single-oxidation peaks at –0.68 V and –0.52 V vs Ag/AgCl at pH 6. As the solution pH increases, the first single-electron reduction peak decreases and merges with the second electron transfer peak, which is consistent with the H e e H mechanism. The peak currents (ipc) in the CVs shown in Fig. 2 around during reduction. The minimum potential gap of 0.26 V in the cyclic system in which CO2 is dissolved in the solution is smaller based on the CV in Fig. 2 suggests that pre-association of CO2 and NR would facilitate electron transfer. The NR/NRH2 redox reaction demonstrates good reversibility and excellent redox durability, with no significant decay in the peak current after 100 CV cycles  to yield 90% reduction of the NR to NRH2. Then a 15% CO2 gas stream was introduced for 10 min to saturate the solution. The output gas flow from the CO2-saturated solution upon anodic oxidation was quantified and qualified by a CO2 flow meter and an FT-IR CO2 sensor, respectively. Plots of the amount of CO2 released by electrochemical oxidation versus electric charge are displayed in Fig. 2 release by oxidation represents the ratio between the moles of CO2 released per mole of electrons transferred. CO2 release at an electron utilization of 0.50 was obtained, accounting for the delayed release of CO2 from the cell. Combining the voltage difference (0.42 V) between the peak potentials from the CV measurements with the electrochemical electron utilization of 0.50 during CO2 release, we estimated that the minimum energy requirement of 81 kJe/mol in batch  and 45 μmol , respectively. When normalized by the inlet CO2 concentration, the curves superimpose in the initial absorption period, as shown in Fig. 2 concentrations of the inlet gas streams, as would be anticipated based on mass action kinetics. Absorption was also monitored by in situ pH measurement in 5 mL of 50 mM NRH2 solution sparged with 1, 4, and 15% CO2 stream at a flow rate of ca. 100 mL/min  and monoethanolamine (MEA), which are traditionally used for CO2 capture  during CO2 release and the potential difference obtained from the CV, the minimum work for direct air capture under the current conditions was estimated to be 123 kJe/mol (Supplementary equations e/mol with a Carnot efficiency of 0.3), which is considered to be the target for DAC technologies5. The absorption of CO2 during bubbling of air was monitored by in situ measurement of pH  and higher solubility of NR in water (50 mM in 0.5 M LiClO4 and 1 M NA vs 306 mM in 0.5 M KCl and 1 M NA) to avoid potential clogging of the tubing in the flow system. A schematic of the flow cell is shown in Fig. 2 from the CO2-rich gas stream, and one for the anolyte that contains NR from which separated CO2 would be discharged to be measured. The results of carbon capture from 15% CO2 are displayed in Fig. 2. The liquid flow rate was 0.349 mL/min, giving 6.3 min of residence time in the 2.2 mL volume of each chamber. The gas output and CO2 fraction were recorded simultaneously during the operation to show the reproducibility of CO2 capture and release over a 12 h period, which corresponds to over eight circulations of the solution through the system. The linearity of the cumulative CO2 released over time depicted in Fig. 2 capture and release, yielding a separation of ~350 mL of CO2 in 12 h. In Fig. 2 flow rate and the electric current, showed 0.41 for the first cycle and jumped to 0.71 in the second cycle with better stability. The electron utilization dropped gradually to 0.5 after 12 h. The minimum energy requirement can be estimated from the voltage gap obtained from CV experiments for the cyclic system (0.26 V) combined with the electron utility (0.71) to provide 35 kJe/mol of CO2 , a high flow rate of air was necessary to saturate the catholyte solution. In our lab scale demonstration, we used ca. 1000 mL/min of airflow for the operation at 30 mA current and 20–30 mL of catholyte solution. Due to the rapid bubbling of the solution, splashing of the catholyte and evaporation of water may have caused degradation in the lifetime of the cell. We believe that a better CO2 absorption unit design can improve CO2 absorption rate as well as the electrochemical cell’s operation time in future studies. The use of an aqueous solution of low-cost organic molecules that are stable to oxygen, air, and water implies that a carbon capture system based on this redox cycle has the potential for further development and wider applications.In this work, we demonstrated electrochemical COReactions were carried out with carbon felt (0.5 cm × 0.3 cm × 2 cm was immersed in the solution) cathode and a stainless-steel wire anode in 5 mL H-cell with #9 O-ring equipped with anion exchange membrane. In the cathodic chamber, NRH , nicotinamide  and lithium perchlorate  were added into water (4.0 mL). In the anodic chamber equipped with a needle to prevent pressurization was placed lithium perchlorate solution . The solution was bubbled with nitrogen for 10 min, after which the electrochemical potential was applied at room temperature by a constant current of –50 mA for 696 s (0.36 mmol of electrons).2 for 12 min. In the cathodic chamber equipped with a needle to prevent pressurization was placed lithium perchlorate solution . The electrochemical potential was applied at room temperature by a constant current of 50 mA for 696 s (0.36 mmol of electrons). The gas output from the anodic chamber was measured by a flow meter and FT-IR CO2 sensor.Reactions were carried out with carbon felt (0.5 cm × 0.3 cm × 2 cm was immersed in the solution) anode and a stainless-steel wire cathode in 5 mL H-cell with #9 O-ring equipped with anion exchange membrane. In the anodic chamber, the NRH2 solution  was bubbled by 15% CO2  and bubbled at a flow rate of 3.33 mL/min. An additional experiment with 15% CO2 at a lower flow rate of 1 mL/min was carried out. The gas output from the vial was measured by a flow meter and FT-IR CO2 sensor.Procedure for electrochemical reduction of NR in batch was followed with an electrochemical potential of constant current of –50 mA for 773 s (0.40 mmol of electrons) to provide 50 mM NRH2 solution. A 1 mL of the solution was transferred to a 10 mL vial that was prefilled with 1, 4, and 15% CO2 and bubbled at a flow rate of 3.33 mL/min. The gas output from the vial was measured by a flow meter and FT-IR CO2 sensor.Aqueous solutions of EDA (50 mM in 1 mL of water) and MEA (50 mM in 1 mL of water) were transferred to a 10 mL vial that was prefilled with 1, 4, and 15% CO2 sensor.The procedure for electrochemical reduction of NR in the batch was followed to provide NRH2 solution . The solution was transferred to a 20 mL vial and bubbled with air from the in-house supply at ca. 120 mL/min. After contacting to air, the solution was transferred to the anodic chamber and the procedure for electrochemical oxidation was followed. The gas output from the anodic chamber was measured by a flow meter and FT-IR CO2  at a flow rate of 100 mL/min and air at a flow rate of ca. 120 mL/min.Procedure for electrochemical reduction of NR in the batch was followed to provide NRH2 solution . The 5 mL of solution was transferred to an 8 mL vial equipped with a pH probe and bubbled with 1, 4, and 15% CO2 (flow rate of 3 mL/min), and air (flow rate of 5 mL/min). The samples were measured by UV–vis after 30 min, 2 h, and 1 d. Each time 10 µL of the samples were collected and diluted with 10 mL phosphate buffer solution (pH 6.6) to provide 50 µM solutions. After 1 day, the solutions were sealed under the contracted gas and stored at room temperature for 1 week. The 10 µL samples were collected and diluted with 10 mL phosphate buffer solution (pH 6.6) to provide 50 µM solutions that were measured by UV–vis absorption spectroscopy.Procedure for electrochemical reduction of NR in the batch was followed with an electrochemical potential of constant current of at –50 mA for 773 s (0.40 mmol of electrons) to provide 50 mM NRH2 solution. A set of 1 mL of solution in an 8 mL vial was prepared and contacted with oxygen (flow rate of 3 mL/min), nitrogen (flow rate of 3 mL/min), COReactions were carried out with carbon felt (1.5 cm × 0.3 cm × 1.5 cm was immersed in the solution) cathode and a stainless-steel wire anode in 20 mL H-cell with #20 O-ring equipped with anion exchange membrane. In the cathodic chamber, NRH , nicotinamide , and potassium chloride  were added into water (20 mL). In the anodic chamber equipped with a needle to prevent pressurization was placed potassium chloride solution . The electrochemical potential was applied at room temperature by a constant current of –100 mA for 1739 s (1.8 mmol of electrons) to provide 20 mL of 45 mM NRH2 solution.2  at a flow rate of 70 mL/min for 15 min.The 15 mL NR solution  was added to a 50 mL round bottom flask anolyte reservoir. The 15 mL NRH2 solution was transferred to a 100 mL round bottom flask catholyte reservoir equipped with a stir bar. The solution was bubbled by 15% CO2 gas stream was maintained at 20 mL/min. The output gas flow from the anolyte reservoir was measured by a flow meter and CO2 sensor.The peristaltic pump equipped with Masterflex® 14 tubing was set to 1.6 rpm for the liquid flow rate of 0.349 mL/min providing 6.3 min of residence time in each 2.2 mL chamber of the flow cell. After one residence time passed from pumping the solution, the electrochemical potential at a constant current mode of 50 mA was applied to the cell. During operation, a flow rate of 15% COThe 30 mL NR solution  was added to a 50 mL round bottom flask anolyte reservoir. The 30 mL of NRH2 solution was transferred to a 500 mL three-neck round bottom flask catholyte reservoir equipped with a stir bar. The solution was bubbled by ambient air at a flow rate of ca. 1000 mL/min for 12 h to saturate the solution. The solution pH was monitored by in situ pH probe simultaneously. The pH was maintained between 9 and 10 during the experiment.2 sensor. A syringe pump was used to add water into the catholyte reservoir at a flow rate of 1.5 mL/hour.The peristaltic pump equipped with Masterflex® 14 tubing was set to 1.0 rpm for the liquid flow rate of 0.218 mL/min providing 10.1 min of residence time in each 2.2 mL chamber of the flow cell. After one residence time passed from pumping the solution, the electrochemical potential at a constant current mode of 30 mA was applied to the cell. During operation, a flow rate of air was maintained at ca. 1000 mL/min. The output gas flow from the anolyte reservoir was measured by a flow meter and COSupplementary InformationPeer Review File


The unique connectivity of the phosphorus atom affords multipolar molecules with a variable number of arms and the electronic properties of the acceptor group. In the ion‐paired form, the transition from dipolar to quadrupolar configuration enhances the low energy migration‐induced band by providing the additional pathways for anion motion. The multipolar architecture, adjustable lengths of the π‐spacers and the nature of counterions allow for efficient tuning of the emission and achieving nearly pure white light with quantum yields around 30 %. The methyl substituent at the phosphorus atom reduces the rate of ion migration and suppresses the red shifted bands, simultaneously improving total emission intensity. The results unveil the harnessing of the multiple emission of phosphonium fluorophores by anion migration via structure and branching of donor–acceptor arms.In the emerging field of intramolecular charge transfer induced counterion migration, we report the new insights into photophysical features of luminescent donor–acceptor phosphonium dyes (D−π−) nA+[X−] have been investigated. These dyes exhibit steady‐state panchromatic luminescence attributed to the photoinduced counterion migration. The intra‐ion‐pair dynamics and the fluorescence response can be rationally tuned on the molecular level that might broaden the scope of functionalities and stimulate the development of new ionic systems.The photophysical properties of a series of multipolar donor–acceptor phosphonium fluorophores (D−π−) Light‐driven molecular motion is a fascinating property, which forms a basis for the development of unconventional materials,+ fluorophores, the CT‐modulated interactions within non‐dissociated ion pairs have been noticed to exhibit a more pronounced photophysical response.+ fluorophores with phosphonium and pyridinium acceptor A+ units ,δ+R2 site+ area (ground state location) in the direction of the transient −Nδ+R2 group (excited state target) that decreases the energy of the emissive state and leads to the evolution of a continuum of red‐shifted fluorescence bands  dye combined with a calixarene receptor leads to very fast translocation of a coordinated potassium ion within the host molecule, which is clearly reflected in time‐resolved absorption spectra.s Scheme . The res+ salts (π=−(C6H4)x−) via a new series of phosphonium dyes with various branching CT chromophores. The strategy lies in the unique connectivity and accessible quaternization of the phosphorus atom,nA+ with variable number of and length of linear donor–acceptor arms, +PPhn4‐(−π−D)n (n=1–4) and +PPh2(−π−D)(−π′−D). To probe the cationic effect, we also chemically alter the acceptor group by introducing the methyl group along the aromatic substituents in +PMePhm3‐(−π−D)m . The results elaborated below, for the first time, unveil the key role played by cation structure and donor–acceptor arms to the ESICT‐driven counterion migration and hence to the harnessing of the multiple emission.In this emerging field, herein, we aim at exploring the factors affecting the ESICT‐induced ion motion and photophysical features of emissive ion‐paired D−π−AnA+[X−] phosphonium dyes is outlined in Scheme 2‐catalyzed protocol,n3‐[−(C6H4)x−NPh2]n y−NPh2 (y=1–3),32[Br]) afford tetraaryl bromide salts, which were isolated as amorphous solids. These quaternized cationic species are designated as YnZn′[Br], where Y and Z correspond to the length of phenylene linkers and the n, n′ subscripts indicate the number of the respective donor‐containing substituents. Compounds 22[Br] and 32[Br] are obtained in good yields (77 and 80 %), and for the rest of the series the target compounds are generated with visibly smaller efficiency (34–52 %). The Pd‐catalyzed formation of phosphonium ions1L2 and Br−(C6H4)y−NPh2 give mixtures of several P‐cationic products , which are difficult to separate. Whereas selectivity of the process can be significantly improved by lowering the temperature from 140 to ca. 115 °C, the overall conversion of the starting materials does not exceed 30 %. A phenol‐promoted metal‐free approach22[Br] and 10 % for 32[Br]) because of limited solubility of the oligophenylene phosphine precursors 1L2 and 3L2. Salts 12[X] and 13[Br] have been studied by us previously.−→OTf− was performed with silver(I) triflate in a nearly quantitative manner. Methylation of phosphines 1L2, 3L2 and 3L3 was readily carried out with methyl triflate, giving salts 1Me2[OTf], 3Me2[OTf] and 3Me3[OTf] in 83–93 % yield.The preparation of (D−π−)+ mass spectra of all salts show one dominating signal that in each case corresponds to the molecular cation . The 31P, 13C and 1H NMR spectra (see the Supporting Information) are also compatible with the proposed structures (Scheme 2Cl2 appear in the ranges 22.3–23.4 ppm (aryl‐substituted ions) and 20.6–21.5 (methylated ions), which belong to a typical region for other acyclic phosphonium compounds..The composition of the products was confirmed by spectroscopic methods. The ESI Figure S. The 31Pompounds.18 The ei) compounds 2n[X] where we probe the effect of branching the multipolar cations bearing identical substituents; ii) quadrupolar compounds containing two elongated π‐spacers 23[X], and two different spacers Y1Z1[X] with competing migration pathways; iii) methylated species 1Me2[OTf] and Y3Me[OTf] with sterically and electronically different quaternized phosphorus center.To avoid complication, we segregate the dyes under study into three groups–2Cl2 and CH3CN one can neglect ion pairing effect due to efficient dissociation. In these solvents, optical properties of all titled salts are not exceptional and arise from intramolecular charge transfer (ICT) transitions expected from the D‐A architecture of these cations, being nearly independent on the counterion . The absorption profiles of 2n[X]  are close to that of 12[X]2Cl2 (373–378 nm in CH3CN), where the molar attenuation coefficient additively grows with the increase of the number n of the −π−D arms. The structureless emission bands are almost identical for the entire series 2n[X]. In addition, they all show positive solvatochromism, for which the peak wavelength shifts from 522–528 nm (Φem=0.73–0.81) in CH2Cl2 to 547–551 nm (Φem=0.25–0.39) in CH3CN with moderate to high emission quantum yields. Note that a small hypsochromic shift of the emission maxima for ca. 5 nm is identified within the series of 2n+ (n=1→4) cations, which likely arises from a combination of slight decrease of electron‐accepting strength of the phosphonium unit and an additive effect of the donor‐containing substituents. This correlation is further supported by gradually decreasing Stokes shifts , and the chemical shifts in the 31P NMR spectra; the latter indicate slight shielding of the phosphorus nuclei from n=1 to n=4 . Very close fluorescence spectral properties of 2n[X] in dichloromethane and acetonitrile suggest that the corresponding electronic transitions mostly occur within one {+P−(C6H4)2−NPh2} push‐pull arm, i.e. there is no appreciable electronic coupling between A+−D subchromophores in A+(−D)n (n=2–4) multipolar ions, which can be approximated in polar solvents as chromophores with dipolar symmetry‐broken excited state.0 geometry for the cation 22+ with density functional theory (DFT) leads in a geometry where both biphenylene spacers are somewhat twisted with estimated torsion angle of about 30°. The lowest energy absorption S0(optimized)→S1 in 22+ involves two equivalent chromophore arms and results in substantial charge transfer from the donor −NPh2 motifs as well as changing polarization of the π‐spacer 2−NPh2 fragment becomes flattened and is responsible for the emission that makes 22+ behaving in a dipolar manner.In polar media such as CH2Cl2 and CH3CN, the behavior of salts 23[X], 1311[X] and 1312[X]  is dominated by the −π−D fragment with terphenylene spacer . The non‐symmetric cations 1311+ and 1312+ reveal minor hypsochromic shifts of yellow‐orange emission, and substantially higher quantum yields  than 23+ congener . The lack of dual fluorescence for 1311+ and 1312+ in polar media is in line with Kasha's rule, i.e. the emission is associated with the dipolar lowest excited state, which corresponds to the ICT occurring on the arm with the longest terphenylene spacer. The DFT‐calculated electronic transitions S0→S1/S0←S1 in cation 1312+ obtained for symmetry unconstrained geometries (C1) primarily involve the shorter chromophore component, which becomes flattened during the geometry optimization of the S1 state . However, considering an average conformation (sC) with flattened phenylene spacers on both chromophores shifts the localization of electronic transitions related to the excitation/emission mainly to the terphenylene fragment. The sC structure is energetically higher than the C1 local minimum by only 10 kJ mol−1 per phenylene group, making the sC structure an energetically feasible idealized description of the molecular conformation in solution.In CH1Me2[OTf], 3Me2[OTf] and 3Me3[OTf] in CH2Cl2 and CH3CN demonstrate modest hypsochromic shifts with respect to their tetraarylated relatives . Apparently, this energy increase, which is more pronounced in more polar acetonitrile, is caused by non‐electron accepting methyl substituent and therefore less polarizing effect of the phosphonium group.The absorption and emission signals of the methylated dyes i) 2Multipolar dyes n[X] Br In the lower polarity solvent such as toluene, where ion pairing is anticipated, branching the molecular structure of the phosphonium cations has a distinct influence on the photoluminescence characteristics. In accordance with earlier studies,2n[X] demonstrate high‐energy  and low‐energy  emission bands of variable ratio in their steady‐state spectra  are identical with the absorption profiles, confirming that they both share common ground‐state species. By analogy with 12+, the F1 band is assigned to an anion‐destabilized ICT state S1, whereas the red‐shifted F2 band emerges upon photoinduced anion migration and consequent stabilization of the initial charge separated state . The results imply completely suppressed anion migration in frozen ion pair, which is electrostatically stabilized in the ground state but destabilized in the CT excited state.gy HiE, F and low‐gy HiE, F and low‐2n[OTf]  measurements, followed by the relaxation of the excited state with τobs=2.6–3.3 ns  than the bromide congeners (Φem=0.17–0.10), while the multipolar dyes show somewhat lower intensity than dipolar compounds. The transition from dipolar (D−A+) 12+ to quadrupolar (D−A+−D) 22+ architecture in the presence of Br− anion dramatically increases the intensity of F2 band (λ=586 nm) relative to F1 band (λ=468 nm) that changes the F1/F2 ratio from 1/0.41 to 0.57/1 . Qualitatively, the same trend is observed for OTf− salts, for which the LoE signal dominates and grows for 22+ vs 12+ cation . Schematically, it can be illustrated by the symmetrically branched molecular structure of 22+ that increases the probability of photoinduced anion translocation by providing two accessible migration pathways and minimizing steric restrictions, i.e. eliminating migration‐unfavorable locations for relatively small counterions around the cationic motif . Possible delocalization of the CT excited state over three (32+) and four (42+) sites might somewhat decrease the depletion of electron density from the NPh2 groups with respect to dipolar compounds. This should disfavor the Coulomb attraction X−⋅⋅⋅ δ+NPh2 in the charge‐separated states (Scheme 2 band.Further addition of the subchromophores to the phosphorus atom in ii) 3Quadrupolar dyes 2112[A], 11[A], 1312[A], 131[A] Br Taking into account that major alterations of luminescence for 2n+ series are observed between the a) dipolar and quadrupolar ions, and b) different counterions, in the next stage we explore the tunability of the emission among the quadrupolar D−A+−D and D−A+−D′ type of dyes. As we have shown for salts 12[Br] and 13[Br],1 band (from 468 to 480 nm), but has a more drastic effect on the F2 signal, increasing its wavelength from 592 to 660 nm that is accompanied by a drop of its intensity to produce sky‐blue fluorescence. Quadrupolar configuration of 23[Br] enhances the F2 band . This results in nearly pure white light emission demonstrated by 23[OTf], Commission Internationale de l'Eclairage (CIE) coordinates , with good quantum yield of 0.29 3−NPh2 fragment  points to the common origin of the F1 and F2 fluorescence bands. Time‐resolved data , which is dominated by the longest −π−D fragment. Contrarily, in toluene these asymmetric dyes exhibit the contribution of both components into the total steady state luminescence . For detailed analyses we have chosen salt 1312[OTf], the emission spectrum of which is shown in Figure 12[OTf] and 13[OTf]. Due to similarity of HiE bands of the latter compounds (468 and 482 nm), the experimental spectrum of 1312[OTf] can be fitted with three components, which correspond to the average F1 and two migration‐induced LoE bands (F2 and F2′) assigned to the −biphenylene−NPh2 (2) and −terphenylene−NPh2 (3) motifs . Possible delocalization of the S1 state over the entire cation or the contribution of two dipolar excited configurations (i.e. 1*312+ and 131*2+) should provide two opportunities for anion migration and therefore lead to the evolution of two red shifted bands, F2 and F2′. Two other non‐symmetrical salts, 1112[OTf] and 1311[OTf], generally operate pursuant to 1312[OTf]. Their LoE bands are slightly blue shifted relative to 12[OTf] and 13[OTf], respectively . The short −phenylene−NPh2 (1) group, the emission of which is poorly responsive to anion migration,1 signal in 1112[OTf] and 1311[OTf]. On the other hand, in contrast to 22[OTf] (Φem=0.38), 1312[OTf] (Φem=0.23) and 23[OTf] (Φem=0.29), branching the dipolar phosphonium ions with chromophore 1 does not have a detrimental effect on the quantum yields, which in the case of 1112[OTf] (Φem=0.53) and 1311[OTf] (Φem=0.49) slightly exceed those of 12[OTf] (Φem=0.47) and 13[OTf]  2Methylated dyes 1Me[OTf], 23Me[OTf] and 33Me[OTf]. Tuning the electron deficient nature of the phosphonium group and its polarizing ability toward the −π−D motifs envisages the variation of the environment around the phosphorus atom. In this approach, the methylated derivatives 1Me2[OTf], 3Me2[OTf] and 3Me3[OTf] were selected to probe the effect of electronic and steric features of the −+PR3 moiety on their optical properties. Accordingly, the electron deficiency of the phosphonium group can be directly identified by the chemical shift from the 31P NMR spectrum (see above). The replacement of the phenyl in cations 12+ and 32+ for the electron‐donating methyl substituent leads to upfield shift of the phosphorus resonances from 22.3–23.4 ppm (tetraaryl‐substituted ions) to 20.6–21.5 ppm (methylated ions). Surprisingly, this simple modification of the phosphonium group transforms yellowish emission of the tetraaryl triflates 12[OTf] and 32[OTf] with dominating LoE band  into cold white‐blueish luminescence of the methylated congeners 1Me2[OTf] and 3Me2[OTf] with predominant HiE band   is achieved for multipolar configuration of 3Me2[OTf], which is opposite to arylated cations exhibiting the highest intensities among the dipolar compounds.2 band for 1Me2[OTf] and 3Me2[OTf] that correlates with much longer rise times of this LoE signal , the dipole moment of 1Me2+ (13.8 D) is visibly larger than that of 12+ (11.9 D). This is in line with ca. 30 kJ mol−1 higher ion pairing energy predicted for the optimized structures of 1Me2[OTf] and 22[OTf]. In the excited S1 state, the dipole moment of 12+ and 1Me2+ decreases to 1.7 D and 4.3 D, respectively. This implies a somewhat smaller charge redistribution for 1Me2+ compared to that for 12+ in the S1 state and could result in a less favourable anion migration along the 1Me2+ cation. Consequently, the system undergoes radiative relaxation primarily from charge destabilized S1 state , which generally supports the hypothesis. We have optimized the S0 geometry for salts 1Me2[Br] and 12[Br], see Supporting Information. In both cases the bromide anion shows attractive interactions with the H atoms of the phenyl or methyl fragments, which seem to be stronger for H(Me)⋅⋅⋅Br contact thanks to higher polarization of the Me. These secondary interactions remain in the CT state and further hinder the movement of the anion for methylated cations. The terphenylene‐based compound 3Me3[OTf] adheres the same tendency, manifested by a substantially decreased intensity of the F2 band  and additional growth of its rise time as long as 1496 ps.The time‐resolved spectra Figures B and S15nA+[X−]  to investigate the effect of molecular structure on the photophysical behavior in relation to the counterion migration proposed for non‐dissociated ion pairs in solvents of low polarity. For this purpose, we varied the amount of the constituting chromophores around the P center +PPhn4−(−π−D)n x−), combined two different donor–acceptor arms +PPh2(−π−D)(−π′−D) in the same cation, and changed the steric and electronic features of the phosphonium fragment in methylated species +PMePhm3−(−π−D)m . In polar solvents , the new compounds reveal regular fluorescence with positive solvatochromism, virtually independent on the branching of the dye cation and assigned to dipolar‐like intramolecular charge transfer (ICT) excited state, which originates primarily from the −π−D component with the largest π‐spacer. In lower polarity medium (toluene), all salts are expected to exist as ion pairs and exhibit spectral temporal evolution of multiple emissions shifting from blue to red region. The resulting steady‐state panchromatic luminescence is associated with continuous electrostatic stabilization of the excited state upon anion migration from the ground‐state location in the direction opposite to that of ICT. In the ion paired form, the transition from dipolar to quadrupolar molecular structure substantially enhances the low energy band due to stereochemical reasons by providing the additional migration pathways. The quadrupolar architecture together with the adjustable lengths of the π‐spacers, and the nature of counterions allow for efficient tuning of the emission and achieving nearly pure white light with appreciable quantum yields. On the other hand, introducing the methyl substituent to the phosphorus atom dramatically reduces the rate of ion migration and suppresses the red shifted bands simultaneously improving total emission intensity. The presented results thus point to a quite general character of fast photoinduced anion motion that occurs in ion‐paired dyes and is accompanied by the optical response. This multiple intra‐ion‐pair dynamics and the corresponding fluorescence response can be rationally fine‐tuned on the molecular level that might considerably broaden the scope of functionalities and stimulate the development of new ionic systems for molecular machinery.In summary, via utilizing the unique organophosphonium motif, which chemically combines versatile connectivity of the quaternized phosphorus atom with pronounced electron‐deficient properties, we have prepared a series of multipolar donor–acceptor ionic dyes (D−π−)Synthetic, other experimental and computational details (PDF) are given in the Supporting Information.The authors declare no conflict of interest.1As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.Supporting InformationClick here for additional data file.Supporting InformationClick here for additional data file.