In the current work, a copolymer of phenylene and thiophene is designed, where the phenylene ring lowers the highest occupied molecular orbital level of the polymer of visible‐light‐harvesting thiophene entities and works as a robust catalytic site for the O2 reduction to H2O2 production. The very high onset potential of the copolymer for O2 reduction  allows a H2O2 production setup with a traditional water‐oxidation catalyst, manganese oxide (MnOx), as the anode. MnOx is deposited on one face of a conducting plate, and visible‐light illumination of the copolymer layer formed on the other face aids steady O2 reduction to H2O2 with no bias assistance and a complete photocatalytic conversion rate of 14 000 mg (H2O2) gphotocat−1 h−1 or ≈0.2 mg (H2O2) cm−2 h−1. 2O2). Visible‐light‐illuminated PPT layer in combination with a manganese oxide (MnOx) catalyst exhibits the steady H2O2 production without bias voltage at pH 12 and with a very high gravimetric photocatalytic conversion rate of 14 000 mg (H2O2) gphotocat−1.Metal‐free copolymer of phenylene and thiophene (PPT) works as a visible‐light‐harvester and highly selective and robust catalyst for the oxygen reduction to hydrogen peroxide (H The oxidizing power of hydrogen peroxide (H2O2) enables the decontamination of biological contaminates, including SARS‐CoV‐2, which causes the COVID‐19 disease. H2O2 is also a promising alternative to hydrogen (H2) as a cleaner, safer energy carrier. The annual global market for H2O2 is 3 million metric tons, which is expected to double by 2022. However, the use of H2O2 as a clean chemical reagent and/or energy carrier is feasible only if it can be produced in a sustainable and on‐site manner and not via the current anthraquinone route, where high‐pressure H2 derived from methane (CH4) is used as feedstock and large amounts of aromatic solvents are required for the complicated H2O2 extraction process.Hyntheses.1 The 2O2 production from oxygen (O2) and water, a simple and green process with low energy consumption. Inorganic semiconductors for photochemical H2O2 production, such as ZnO, have long been a topic of research interest, but they have insufficient photocatalytic abilities, thus requiring the use of sacrificial agents such as formate and phenol without exception. Recent research is aimed at overcoming these difficulties. For example, the polyoxometalate cluster [PW11O39]7− was covalently combined with 3D ordered microporous graphitic carbon nitride via an organic linker to realize the highest catalytic rate of 12 mg (H2O2) gphotocat−1 h−1 without any sacrificial agents  gphotocat−1 h−1 and often determined in water under 1 atm O2). However, the performance of solar‐driven photochemical H2O2 production remains low (<15 mg (H2O2) gphotocat−1 h−1).Much effort has been directed at solar‐driven photochemical Hsumption.7 Inor2 to H2O2 have also been investigated to achieve higher catalytic rates under illumination in the presence of an additional bias potential.  The typical examples in this regard are organic epindolidione pigments and dye‐sensitized nickel oxides. Although the production rates exceed those of previous photocatalysts by one to two orders of magnitude, the corresponding devices require a significant bias voltage and must be operated at pH ≤ 7 because of the instability of the catalysts under alkaline conditions. A practical electrochemical device will require a counter electrode for the anode reaction of oxygen reduction, preferably catalytic oxygen evolution in water. As traditional water oxidation catalysts such as manganese oxide (MnOx) and CoOx function optimally at high pH, a photocatalytic cathode which can function at high pH and yield a photovoltage exceeding the voltage between O2 reduction to H2O2 and water oxidation would be ideal.Photo‐electrocatalysts or photocathodes for the reduction of Otential. 8 The π‐Conjugated polymers are emerging as appealing (photo)electrocatalytic materials. For example, we succeeded in forming polythiophene layers as a photo(electro)catalyst with an appropriate band structure and visible‐light absorption ability for the reduction of water to H2 at high pH, which relies on light to initiate the catalytic reaction. Polythiophenes have also been studied as an organic electrocatalyst for O2 reduction to H2O2 in the dark. Experimental and simulation results suggest the thiophene units as a catalytic site. Very recently, a record‐high H2O2 concentration of 110 × 10−3m was achieved with the photo‐electrocatalytic O2 reduction on polyterthiophene after the sustained reaction for 11 h at high pH. A dual‐photoelectrode device was also developed by using polythiophene, the water‐oxidation photocatalyst for NiFeOx, BiVO4, and a Nafion membrane.2 reduction to H2O2, which involves the use of a single photocatalytic π‐conjugated polymer possessing sufficient photovoltage to trigger the reduction without any bias voltage, another photocatalyst, and any suitable device configuration. One way to improve the photovoltage of the catalyst polymer is by lowering the highest occupied molecular orbital (HOMO) level of the polymer. We recently succeeded in the molecular design for lowering the HOMO level of visible‐light harvesting polythiophenes by copolymerization with an electron‐withdrawing phenylene unit, poly (PPT). Herein, we demonstrate our successful use of the purely organic PPT polymer layer as a complete photocatalyst under visible‐light for O2 reduction to steady H2O2 production with high selectivity. The very high onset potential for the O2 reduction allows a facile setup with the traditional water‐oxidation counterpart catalyst, MnOx, as the anode .11d Hen Figure .22.1The PPT polymer layers were prepared by the polymerization of 1,4‐di(2‐thienyl)benzene spin‐coated on a glassy carbon or an ITO glass plate with iodine vapor as oxidant to avoid contamination by metals. The samples were carefully washed to remove residual iodine and monomer, yielding undoped and genuine PPT layers with thicknesses of 10–210 nm . The PPT layers were deep brown in color, with a visible absorption edge at ≈570 nm . The HOMO and LUMO levels were estimated to be −5.5 and −3.3 eV and −5.2 and −3.2 eV for PPT and polyterthiophene, respectively. The HOMO level was lowered with 0.3 V by introducing the electron‐withdrawing phenylene unit in the copolymer structure of the visible‐light‐harvesting thiophene polymer.2O2 production was examined in the dark and under illumination at high pH with air bubbling (oxygen/nitrogen gas mixture). A traditional water‐oxidation catalyst worked as the counterpart in the full‐cell setup , at pH 12 under illumination  gphotocat−1 h−1 with a Faradaic efficiency of 96 ± 3% . Long‐term durability testing under illumination at pH 12 and 0 V versus Ag/AgCl showed that PPT was robust for at least one week, with a turnover number exceeding 105 and high recyclability (data for five runs are seen in Table S2 in the Supporting Information). The corresponding Raman spectra shown in Figure S3 (Supporting Information) did not show any changes in the chemical composition of PPT over the week‐long test, supporting its remarkable robustness. Figure −2. This means that, for the thicker films in Figure 2O2 concentration exceeds the oxygen concentration after ≈15–20 min and thus makes the conditions more thermodynamically difficult than suggested by the U0 values at standard conditions.In this study, H2O2 or HO2− in the dark. In situ Raman spectroscopy of PPT suggested charge transfer via the phenylene groups of PPT as the catalytic sites after the application of a potential, indicating a two‐electron reduction per the repeating unit in the presence of oxygen . That is, light illumination solely results in the input of energy (voltage) to the system, and not the creation of new catalytic sites. While thiophenes have often been reported as the catalytic active sites for H2O2 production, this experimentally proposed mechanism suggests that the benzene moiety is a more favorable site for catalytic H2O2 production than thiophene, presumably due to the chemical stability of its intermediate based on the resonance structure. The high stability of the intermediate may support the high catalytic ability of PPT at high pH. This implies the potential of the molecular design of more efficient and robust aromatic polymers as photocatalysts. The charge transfer via catalytic sites on the phenylene groups follows a completely different catalytic route from the light‐facilitated water reduction to H2 (on thiophene groups) previously reported on π‐conjugated polymers. PPT also acts as an electrocatalyst for oxygen reduction to H2O2 production at high pH.The high oxygen reduction activity and chemical robustness of the PPT polymer under illumination at high pH allowed for its combination with traditional water‐oxidation catalysts to realize photochemical H2.22O2 production at zero applied bias. Electrodeposited MnOx on a fluorine‐doped tin oxide (FTO) plate was used as a water‐oxidation catalyst and as both the counter and reference electrodes ; thus, water oxidation on MnOx was assumed to be the only oxidative reaction occurring.  The time dependence of the accumulated charge from the 0 V CA measurements, i.e., zero‐volt bias  production plots are also illustrated in Figure 2O2 on the MnOx anode must be practically absent. PPT achieved an outstanding H2O2 production rate of 11 000 mg (H2O2) gphotocat−1 h−1  even without a bias voltage.The unique properties of the PPT polymer layer make it suitable for combination with traditional high‐pH water‐oxidation catalysts. A two‐electrode photo‐electrochemical cell setup was first employed to explore the possibility of light‐driven H catalyst9 and s Figure  clearly 2O2 production by combining a photoanode and a cathode. In most cases, such combinations require the use of different electrolytes for the anode and cathode compartments, as well as metal complexes  for the key reaction of oxygen reduction. The use of PPT as a photocatalytic cathode with a sufficient photovoltage to drive both the anode and cathode reactions eliminates the need for different electrolytes and a membrane separator between the anode and cathode compartments. A similar approach to photo‐electrochemical H2O2 production employed a combination of phthalocyanine, perylene carboxylic imide, and gold as a complex and highly unstable photocathode. In contrast, our cell uses a simple and robust polymer layer formed on a thin conducting plate as the photocathode and conventional MnOx electrodeposited on another plate as the anode, thus realizing photo‐electrochemical H2O2 production using only earth‐abundant elements. Although this simple two‐electrode setup is advantageous as a measuring system, it is limited in terms of the resistance of the electrolyte and the external circuit. To significantly reduce the related energy loss, a simpler and more direct combination of PPT and MnOx was subsequently implemented.A recent study reported a photo‐electrocatalytic cell setup for H cathode.17 In 2.3x on the same electrically conductive thin plate . The performance of the PPT photocatalyst combined with MnOx at pH 12 was investigated under 1.0 Sun irradiation  gphotocat−1 h−1 (230 mg (H2O2) gphotocat−1 h−1 based on the combined weight of the anode and photocatalytic cathode catalysts; significant excess of MnOx vs the amount estimated for its single activity) or 0.20 mg (H2O2) cm−2(plate) h−1 was achieved and maintained for at least one week.To combine PPT and MnOe Figure , MnOx wan Figure , and an x. At a lower pH, this was not the case, and photocatalytic H2O2 production was therefore impossible. The LUMO level of PPT is more than 1 V higher than the theoretical potential required for the conversion of O2 to H2O2 at high pH. This leaves ample room for the design of the copolymers of phenylene and thiophene with lower‐lying LUMOs, and hence lower bandgaps, to harvest longer wavelengths from the solar spectrum.Figure 3π‐conjugated organic polymer PPT works both as a visible‐light harvester and a catalyst for oxygen reduction to H2O2 or HO2−, so that the highest photo‐electrocatalytic conversion rate of >40 000 mg (H2O2) gphotocat−1 h−1 could be achieved at 0 V versus Ag/AgCl and pH 12 with very high selectivity (>95%). PPT can be used in combination with a common and inexpensive water oxidation catalyst to produce H2O2 from oxygen and conventional alkaline water under visible light as the only energy input and air as a practical oxygen source. MnOx was used as the anode for water oxidation to yield additional oxygen. The photovoltage provided by PPT was sufficient to drive both oxygen reduction and water oxidation, thus resulting in a reaction for the overall system, i.e., only one excitation (“photon”) would be required—rather than two excitations as is, e.g., the case where both cathode and anode are photo‐electrodes and indeed in the photosynthesis. The produced H2O2 exists in the alkaline solution  in the form of HO2−, which is more stable  than H2O2 at pH 7 . HO2− in an alkaline solution is easily converted to the highly reactive H2O2 by facile neutralization. This aspect is another advantage of the proposed system for practical on‐site H2O2 production. Currently, we are preparing transparent plates composed of an electrically conducting plastic substrate sandwiched with PPT and MnOx layers and are examining the production of more concentrated H2O2 by the illumination of five‐layer stacked plates soaked in alkaline water.We demonstrated that the thiophene‐containing x is easy to fabricate, and requires no separators or membranes in the water pool, making it highly suitable for practical use. With this setup, a steady H2O2 production rate of 14 000 mg (H2O2) gphotocat−1 h−1 can be achieved. Thus, the developed photocatalyst provides a simple, sustainable, and safe H2O2 production method to meet the rapidly growing demand for decentralized H2O2 production and use.The plate combining the PPT photocatalyst and MnO4 A chlorobenzene solution of dithienylbenzene was spin‐coated onto a glassy carbon, ITO, or FTO plate, which was then placed in a pre‐heated chamber with iodine at 90 °C for 1 h. The sample was washed and soaked in acetonitrile repeatedly, dried in a vacuum chamber at 90 °C, and thereafter stored in water. To prepare PPT and MnOx on the same plate , first, one face of the plate was masked with a Kapton film, and MnOx was electrodeposited on the other face . After removal of the mask, the PPT layer (such as 149 nm) was formed on the opposite face via the iodine vapor–assisted polymerization of dithienylbenzene.1,4‐Di‐(2‐thienyl)benzene was prepared via the Suzuki–Miyaura coupling of 1,4‐dibromobenzene and 2‐thiophene, as described in the previous paper.11d A λ < 320 nm. All the measurements were performed with reproducibility. The turnover number was calculated as the molar number of produced H2O2 divided by the molar number of the dithienylbenzene unit of PPT. The weight of the PPT layer specimen was determined by the layer area (2.5 cm2), average thickness, and density of a PPT fragment.Illumination was provided by an Asahi Spectra MAX‐302 300‐W Xe lamp with an equivalent power of 1.0 Sun at the distance from the PPT plate (5 cm). Glass was used as the electrochemical cell window to filter out deep UV light at 2O2 was determined by a spectrophotometric method after adjusting the pH to 9 using the copper(I) complex of 2,9‐dimethyl‐1,10‐phenanthroline as the indicator. The calibration curve for dilute H2O2 was prepared using fresh and standard H2O2 solutions , and the pH was adjusted to 9 by an NaOH aqueous solution. The analytical errors were within ± 2%. The entire H2O2 quantification procedure was performed within 1 h.The produced amount of Hndicator.20 The2O2 quantification . The photochemical H2O2 production was examined at five cycles .Several PPT layers were prepared on a substrate, and the electrochemical tests were performed on the same PPT specimen, but a new area of the layer was employed for each (see the Supplementary Methods section in the Supporting information). The analytical errors were within ±2% in the HK.O. and B.W.‐J. contributed to experiment planning, experiment execution, data analysis, and manuscript preparation. H.N. contributed to experiment planning and manuscript preparation. All authors have reviewed and commented on the manuscript before publication.The authors declare no conflict of interest.Supporting InformationClick here for additional data file.


II complexes by systematic variation of the hydrophilic side‐chain length. A novel approach of general applicability based on complementary X‐ray diffraction and solid‐state NMR spectroscopy has allowed us to establish a clear correlation between molecular features and supramolecular ordering. Systematically increasing the side‐chain length gradually increases the steric demand and reduces the extent of aromatic interactions, thereby inducing a gradual shift in the molecular packing from parallel to a long‐slipped organization. Notably, our findings highlight the necessity of advanced solid‐state NMR techniques to gain structural information for supramolecular systems where single‐crystal growth is not possible. Our work further demonstrates a new molecular design strategy to modulate aromatic interaction strengths and packing arrangements that could be useful for the engineering of functional materials based on PtII and aromatic molecules.Understanding the relationship between molecular design and packing modes constitutes one of the major challenges in self‐assembly and is essential for the preparation of functional materials. Herein, we have achieved high precision control over the supramolecular packing of amphiphilic Pt X‐ray diffraction and advanced solid‐state NMR studies were combined as a new, general tool for detailed structural and supramolecular elucidation, using a series of amphiphilic PtII complexes as model compounds. Our approach provides an alternative for supramolecular systems where single‐crystal growth is not possible, which can be potentially applied to many other molecular and macromolecular platforms. II to π‐conjugated molecules can further extend the range of possible intermolecular interactions and enable additional applications in optoelectronics and biomedicine.Self‐assembled structures of π‐conjugated systems have long been an area of active research in materials science, where molecular assemblies in solution, in the solid state and in the liquid crystalline state can be created.II complexes. For instance, we reported the self‐assembly of two oligophenyleneethynylene (OPE)‐based bispyridyldichlorido PtII complexes featuring terminal dodecyloxy versus methoxy chains.II complexes can alter the morphologies and emission behavior of self‐assemblies in aqueous medium.II mesogens, it has been demonstrated that the variation of alkyl chains can be used to modulate the mesophases with regards to their stability and photophysical behavior.14 vs. C16 chainAs previously shown, tuning the length of peripheral alkyl chains—which are commonly used to achieve solubility of the compounds—can dramatically affect the self‐assembly behavior of PtII complexes has been scarcely investigated.II complexes featuring PEGn chains of different length was reported by the group of Manners.II complexes with ancillary ligands based on PEGn were observed to form 1D fibers (n=16) or 2D platelets (n=7) in polar solvents, depending on the PEG chain length.Apart from nonpolar alkyl chains, polar oligo‐ or poly(ethylene glycol) chains  are commonly used as hydrophilic counterparts for achieving solubility in aqueous media.II complexes by systematic variation of the hydrophilic side‐chain length. This understanding could contribute to establishing a correlation between molecular design and packing modes, which remains one of the greatest challenges in the field of self‐assembly.II complexes 1–4 featuring either three OEG chains on both termini, namely triethylene glycol , diethylene glycol , ethylene glycol , or methoxy groups  NMR in combination with 2D, “through‐space” NMR correlation techniques based on the direct magnetic dipole–dipole (or dipolar) interaction between nuclear spins to elucidate the aggregation of the methoxy‐functionalized complex 4.1H,13C correlations characteristic for certain structural motifs by comparing the 1H and 13C MAS NMR results obtained from complexes 1 to 3 with the crystallographic data. On this basis, we are able to readily identify or exclude previously observed packing structures for this specific series of OPE‐based PtII complexes, filling in the missing structural information from crystallographic data.Usually, the solid‐state structure and molecular organization are determined by single‐crystal X‐ray diffraction, and we were able to obtain suitable single crystals for complexes II complexes 1–4 were synthesized in moderate to good yields by complexation reaction of the precursor salt [PtCl2(PhCN)2] with the respective pyridine‐based ligands in toluene at 100 °C . In the following, the arrangements of the stacked molecules in the solid state will be characterized in terms of a longitudinal shift along the molecular axis as well as by a lateral offset as depicted in Scheme 1 to 3 in their crystal structures. For comparison, an excerpt of the crystal structure of previously reported analogue 5 is also shown. Relevant close intermolecular contacts are highlighted. In the crystal structure of 1  interactions and a close Pt⋅⋅⋅H contact (2.91 Å) between the central Pt atom of one molecule and the proton of the inner glycol chain of a neighboring molecule. Such Pt⋅⋅⋅H interactions have been observed in earlier reports and can be explained by donation of electron density from the dz2 orbital of the Pt to the σ* orbital of the C−H.1 . Instead, the structure formation is dominated by the TEG chains, which form a large, bulky structure surrounding the neighboring aromatic backbone in a so‐called handshake motif , which enables a more efficient π‐overlap of the OPE backbone in the crystal. The relatively short π‐system of 1 must orient in a twisted manner with a torsion angle of the two aromatic rings (phenyl and pyridine) of 53.8° to form the present structure. Stabilization of the handshake motif is achieved by intermolecular C−Harom⋅⋅⋅O interactions exhibiting distances in the range of previously observed weak hydrogen bonding for such systems (2.41–2.56 Å).1 is 9.854 Å, whereas the Pt−Pt distance illustrating the longitudinal shift of two molecules is 18.120 Å  and a slight lateral offset . The parallel displaced π‐stacking of two pyridine units has a distance of ≈3.2 Å. In contrast to the structure of 1, where the PtIICl2 fragment is surrounded by TEG chains, the PtIICl2 moiety in 2 is located on top of the C≡C bond of the next molecule in the stack. The structure is further stabilized by C−Hglycol⋅⋅⋅O (2.44 Å) as well as C−Hglycol⋅⋅⋅Carom (2.90 Å) interactions. Thus, instead of a handshake motif as in 1, the DEG side chains in 2 interdigitate with neighboring side chains . Furthermore, an intermolecular weak C−Hglycol⋅⋅⋅Cl (2.84 Å) interaction is observed within adjacent stacks .In the single crystal structure of t Figure . Althoug3 results in a similar molecular stacking to complex 2  compared to 2 (8.126 Å). Parallel displaced π–π interactions of the pyridine rings with a distance of ≈3.4 Å and C−Harom⋅⋅⋅Cl (2.86 Å) interactions stabilize the molecular packing. Additional C−Hglycol⋅⋅⋅O (2.43 Å), C−Hglycol⋅⋅⋅Carom (2.41 Å) and C−Hglycol⋅⋅⋅C≡C (2.87 Å) interactions of one stack with molecules of obliquely arranged neighboring stacks are also present .A shortening of the glycol chains to one unit (EG) in 2 Figure  with a P1–3, single crystals of 4 could not be obtained. However, considering the trend followed by 1–3, we would expect a more parallel arrangement of the molecules in 4 (shorter Pt−Pt distances) and enhanced aromatic interactions compared to 1–3 due to the lack of any side chains. Due to no available single crystal X‐ray diffraction data for complex 4, a complementary technique (solid‐state NMR) was required to elucidate the molecular arrangement in the solid state.In contrast to compounds intermolecular contacts characteristic for the packing motifs observed in 1–3 and 5. By comparing these contacts with those potentially observed  for 4, a packing arrangement for this complex can be derived. All samples used for solid‐state NMR measurements were powdered samples and were obtained under identical conditions as those used for the preparation of the single crystals discussed in the previous section (EtOAc/Et2O solutions). We therefore assumed identical (or at the very least comparable) arrangements of the molecules in the samples for solid‐state NMR studies and in the crystalline state. Additionally, we have conducted powder XRD analysis of 1–4 to further probe this assumption. A detailed summary and analysis of the XRD results can be found in the Supporting Information. Compound 1 shows the lowest crystallinity of all samples obtained by the precipitation protocol . While the positions of the reflexes are in relatively good agreement with the predicted XRD pattern , the overall intensity is greatly diminished in particular for the range corresponding to the long‐range order. The sterically demanding TEG chains, which adopt a highly ordered orientation in the single crystal, most likely prevent this long‐range order in the powder sample; nevertheless, a similar short‐range order could be confirmed. On the other hand, the higher crystallinity of 2 is reflected in the sharp reflexes, which match the predicted XRD pattern well . Yet, the observation of some minor discrepancies, in particular for the immediate environment of the PtII moiety, indicates that the high level of interdigitation of the DEG chains might not be perfectly transferred to the powdered sample used for solid‐state NMR studies. Nevertheless, based on the reasonably good agreement between the experimental and predicted XRD patterns, we infer that the orientation within the 1D stack is largely preserved. For the sterically least demanding compound for which single‐crystal analysis was possible (3), the predicted XRD pattern reproduces the experimental results without discrepancies . This result is logical considering the absence of significant steric effects when the chains are reduced to EG units. On this basis, we infer that the molecular orientation in the bulk as well as in the single crystal matches. For compound 4, sharp reflexes could be appreciated as well, which suggests that the sample has a highly crystalline nature, which matches the observed trend for compounds 1–3 .Our approach consisted in identifying 1H MAS NMR spectra of 1–4. Overall, broad 1H lines with few discernable details are observed due to the strong 1H,1H dipolar couplings present in the solid state. Nevertheless, apart from the broad peak around δiso(1H)=3.5 ppm assigned to the protons of the EG moieties, two signals in the aromatic region are observed: while the signal at higher ppm values (δiso(1H)=9.1 to 8.1 ppm) can be assigned to the aromatic protons adjacent to the pyridine nitrogen =7.8–6.8 ppm) corresponds to the aromatic protons Hb (Hβ‐pyridyl) and Hc. The exact position of the two peaks varies between complexes 1 to 4, going from δiso(1Ha)=9.1 ppm and δiso=7.8 ppm in complex 1, to δiso(1Ha)=8.1 ppm and δiso=6.8 ppm in complexes 2 and 3. As the moieties are structurally identical, the difference can be solely attributed to packing effects, in this case to aromatic ring current effects caused by the neighboring aromatic backbone in 2 and 3, or the lack thereof in 1. The shift to lower ppm values is often indicative of π–π interactions as observed for example in π‐conjugated polymers and other conjugated systems.Figure 4 leads to a markedly different 1H MAS NMR spectrum, cf. Figure δiso(1H)=3.5 ppm is now significantly reduced in intensity and width, and strong shifts of the 1H signals in the aromatic region are observed. The upfield shift of proton c suggests an even stronger participation of the outer ring in π–π interactions compared to complexes 2 and 3. In contrast, the 1H signal a is situated at a higher ppm value than that of 2 and 3, which might lead to the wrong conclusion that the pyridyl ring of 4 undergoes weaker aromatic interactions than that of 2 and 3. However, this effect is typical for bispyridyldichlorido PtII and PdII complexes exhibiting a pseudo‐parallel packing, and can be attributed to C−Ha⋅⋅⋅Cl interactions between the α‐pyridyl protons of one molecule and the electron‐withdrawing Cl ligands of an adjacent molecule.Replacing the EG moieties with methoxy groups as in complex 4, 2D 1H,1H double‐quantum single‐quantum correlation (DQ‐SQ) MAS NMR experiments were performed .1 to 3  are characterized by a broad auto‐correlation signal situated at δSQ=3.5 ppm and δDQ=7.0 ppm (attributed to the EG units) with some smaller auto‐correlation peaks visible at lower ppm values most likely originating from the residual trapped solvent. However, no autocorrelation signals in the aromatic region (around δSQ=7 ppm) are observed.To further probe the molecular packing of complex 1H MAS NMR spectrum, replacing the EG units with methoxy groups leads to the appearance of three aromatic 1H signals in the DQ‐SQ correlation spectra , the broad Gaussian peak associated with protons Hb at around δSQ=7 ppm is mostly obscured. In addition to the cross‐correlation between the methoxy protons and aromatic proton Hc at δDQ=9.4 ppm—which is expected due to the close spatial proximity of the methoxy groups on the same ring—a cross‐correlation between the methoxy protons and proton Ha is observed at δDQ=12.2 ppm. Interestingly, no cross‐correlation between the aromatic proton Hb and the methoxy protons is observable, though this could be related to the broad nature and comparably low amplitude of the peak at δSQ=7.0 ppm. These results suggest that the methoxy groups are placed in relatively close proximity to the complex center, though whether this is from above/below the aromatic backbone or from other neighboring complex is unclear at this point. The most significant difference between the spectra of 4 and the other three samples is the appearance of several auto‐correlation peaks in the aromatic chemical shift range . While these are barely discernible after one rotor period of DQ excitation  could lead to the shift to higher ppm. These observations fit well with a packing model similar to the pseudo‐parallel molecular arrangement observed by Allampally et al. for a longer, methoxy‐functionalized OPE‐based PtII complex.To summarize the results from 1H MAS and 1H,1H DQ‐SQ NMR correlation spectroscopy, 13C{1H} cross‐polarization (CP/MAS) and 2D 13C{1H} heteronuclear correlation (HETCOR) NMR experiments were performed . Figure 13C{1H} CP/MAS NMR spectra of complexes 1–4 along with the peak assignment. Note that the assignment uses the numbering given in Figure 1 as well as the corresponding 2D 13C{1H} HETCOR NMR data . To better visualize the changes in isotropic 13C chemical shift for the different complexes, the 13C signals associated with the OPE backbone are plotted in the lower part of Figure 4 and those of complexes 1–3 is the splitting of the broad 13C signal at δiso(13C)=129 −122 ppm, assigned to the β‐carbon of the pyridine moiety . This carbon is directly bonded to proton Hb, which was previously attributed to a broad Gaussian‐shaped peak in the 1H MAS NMR spectra (vide supra). Thus, the doublet character of this 13C signal indicates a more complex 1H line shape, with the Gaussian distribution being merely an approximation, which further explains the complex cross‐correlation peaks observed in the 1H,1H DQ‐SQ NMR spectrum of Figure C2 and Hb must be related to intermolecular packing effects. Another interesting feature of Figure C4 and C5 for complexes 2 and 3 compared to complex 1. This low‐field shift is not observed for complex 4. Because the packing mode switches from the handshake motif with a long‐shifted arrangement in complex 1 to a less shifted, staircase pattern in complexes 2 and 3 with the PtIICl2 center being close to the alkyne triple bond, we can attribute the low‐field shift to a change in packing.To confirm the results from 13C signals across all four complexes in Figure 13C signals assigned to carbon C7 at δiso(13C)=∼109 ppm, as well as those for C3, C4, and C8 in the case of complex 1. The splitting of carbons C7 and C8 can be explained by two inequivalent carbon sites in the asymmetric unit of the crystal structure. However, according to the single‐crystal XRD data, carbons C3 and C4 only occur once in the asymmetric unit of complex 1. Therefore, it is likely that the sample used for MAS NMR has a slightly different packing and additional disorder compared to the single crystal used for XRD . Figure 13C{1H} HETCOR spectra for 1, 2, and 4 acquired with 0.5 ms (green contour lines) and 3.0 ms CP contact time (black contour lines) to differentiate between directly bonded 1H–13C and intermolecular 1H–13C contacts, respectively. A comparison of these 2D HETCOR NMR datasets (green and black) allows us to identify the packing structure for each complex as illustrated by the structural fragments and corresponding assignments of 1H,13C correlations below these spectra , this also results in different intermolecular 1H–13C distances for the two positions, manifested in the 2D HETCOR NMR spectra as correlations HbC8 and HbC8′ labeled as b8 and b8′, respectively, in Figure 1). The large longitudinal shift between two molecules in 1 is also evident from the correlation HbC9, which links proton Hb (located at the complex center) to the outermost OPE carbon C9, a correlation that is only possible via intermolecular contacts. A further indicator for the magnitude of the longitudinal shift is the absence of potential intermolecular correlations HbC6 and HaC5, which would be expected for an intermediate shift , which shows numerous intermolecular correlations, most notably HbC6, HaC5, HaC4, HbC9, HcC2, and HcC1. Although HbC9 and HbC8 were also observed for complex 1, correlations HcC1, and HcC2 place the pyridine moiety close to the second phenyl ring of the OPE backbone. Interestingly, the correlations between C7 (bonded to proton Hc) and protons Ha or Hb (attached to carbons C1 and C2) are not observed. In addition, correlations HaC5 and HaC4—which were not observed for complex 1—are indicators for the PtIICl2 complex center being in the proximity to the alkyne triple bond of the neighboring molecule.Since the solid‐state 2D HETCOR NMR spectra of g Figure . As ment4 together with the proposed molecular arrangement are shown in Figure 1 and 2, none of the intermolecular correlations such as HbC9, HaC9, HaC6, HaC5, and HaC4 are observed. This can only be achieved for a structural arrangement with a parallel or nearly parallel π–π stacked arrangement of the OPE backbones, similar to the one described by Allampally et al. for the larger OPE‐based complex with methoxy functionalization.1H,1H DQ‐SQ NMR correlation data  termini of different length. A systematic length variation was achieved by gradually removing one (2), two (3) or three (4) OCH2‐CH2 units from the TEG‐substituted derivative 1. Data from single‐crystal X‐ray diffraction showed that complex 1 retained the characteristic handshake motif previously described for complex 5, which features the same TEG side chains, but has a larger aromatic surface than 1. The strong similarity between the packing motifs of 1 and 5 indicate that the TEG groups with their associated hydrophilic interactions are the primary forces dictating the solid‐state structure. However, in contrast to 5, complex 1 shows no significant aromatic interactions due to the reduced aromatic surface. Shortening the hydrophilic side chains in complexes 2 and 3 resulted in structures with longitudinally shifted molecules involving more pronounced π–π interactions, though the bulky PtIICl2 moiety in the complex center prevents efficient π–π stacking between neighboring complexes. Two‐dimensional solid‐state 1H MAS and 13C MAS NMR experiments for complexes 1, 2, 3, and 5 allowed us to identify 1H,13C through‐space correlations characteristic for each packing motif. These, in turn, led us to propose a packing motif for the only complex (4) for which single crystals could not be grown, emphasizing the potential of solid‐state NMR spectroscopy as a key tool for structural determination in the solid state. Complex 4 was found to exhibit a more parallel arrangement of the molecules stabilized by π–π interactions, most likely with a short longitudinal and lateral offset to accommodate the sterically demanding PtIICl2 moiety at the complex center. On this basis, we conclude that the steric demand of the central PtIICl2 moiety limits the effectiveness of π–π interactions; this is supported by the fact that even short mono(ethylene glycol) termini appear to prevent an efficient π‐overlap of the ligands aromatic surface. A more pronounced π‐overlap is only possible after eliminating hydrophilic interactions by replacing the ethylene glycol termini with methoxy groups. Therefore, if π–π interactions are frustrated by steric demands, hydrophilic interactions will become the dominant factor in the self‐assembly process, leading to structural aggregation. Thus, our investigations illustrate that even minor changes in the glycol chain length can be used to modulate and control aromatic interaction strengths and packing arrangements, which in turn might be useful for engineering electronic devices based on PtII and aromatic molecules.In summary, we have reported the synthesis and molecular packing of four new amphiphilic Pt1), 2004414 (2), and 2004415 (3)2004413  should be addressed to the authors.SupplementaryClick here for additional data file.


Until now, chemical carboxylation catalyzed by organometallic nucleophiles and reductants has been generally adopted particularly for the precise selectivity control of carboxylation sites. As another approach, electrochemical carboxylation has been attempted but these carboxylation reactions are limited to only a few pathways. In the case of styrene, dicarboxylation at the α‐ and β‐positions is mostly observed with electrochemical carboxylation while site‐selective hydrocarboxylations are hardly achieved. In this study, electrochemical β‐selective hydrocarboxylation of styrene using CO2 and water is developed, in which the site selectivity can be precisely controlled between β‐hydrocarboxylation and dicarboxylation without the aid of homogeneous catalysts. In this platform, water is used as proton source in the β‐hydrocarboxylation of styrene where its addition results in significant enhancement of the selectivity toward β‐hydrocarboxylation. This work provides insights into new strategies for site‐selectivity‐controllable carboxylation with CO2 using an electrochemical platform.The carboxylation of hydrocarbons using CO 2 and water are used as carbon and proton sources, respectively. The site‐selectivity of carboxylation can be precisely controlled between dicarboxylation and β‐selective hydrocarboxylation solely by providing optimal proton source in the absence of homogeneous catalysts.The carboxylation of styrene on a heterogeneously catalyzed electrochemical platform is newly demonstrated, where CO This reactions are mainly driven by reductive electrical potential on a cathode electrode.2, hydrocarboxylation of the α‐ or β‐position and dicarboxylation at both positions are feasible. Vianello and co‐workers first pioneered the electrochemical dicarboxylation of styrene to form 2‐phenylsuccinic acid (1).2 insertion to the benzylic position. It has been hypothesized that the electrochemical carboxylation of styrene is mostly carried out by the dicarboxylation pathway, whereas addition of water as protic agent can change reaction pathway to β‐hydrocarboxylation. Although these study showed that the selectivity of carboxylation can be controlled in electrochemical platform, the mechanistic study on the reaction selectivity is rarely conducted.In the carboxylation of styrene using CO3 benzylic metal species.2 later binds to the benzylic position. In the case of β‐hydrocarboxylation, CO2 insertion at the β‐position occurs prior to protonation which is the reverse order to that for α‐hydrocarboxylation as noted recently by the Jamison group[qv: 13b] and the König group.[qv: 15a] Both works achieved high selectivity for the β‐position by activating CO2 in the initial process of carboxylation using photocatalysts.In contrast, chemical carboxylation of styrene has been actively studied, ranging from dicarboxylation to hydrocarboxylation either with Markovnikov or anti‐Markovnikov regioselectivity. Notably, pioneering works have progressed to modulate site‐selectivity by developing novel chemical protocols,2 insertion to form 1  to 96% and exhibited the maximum faradaic yield of 65%. Also, the effect of other proton sources and working electrodes were investigated and mechanistic study was conducted by isotope labeling experiments. Basis on these results, we proposed a new reaction pathway for electrochemical carboxylation of styrene that can selectively carry out toward dicarboxylation and β‐hydrocarboxylation.Inspired by these predictive selectivities in chemical carboxylation, we envisioned that electrochemical carboxylation would be extended to site‐selective hydrocarboxylation by controlling the protonation process. Because β‐carboxylate is the key intermediate during electrical reduction, we thought that intentional protonation might suppress successive CO 1 Figure1, top 22 without any proton source. Three electrode systems with a Ni cathode, Mg anode and Ag/Ag+ (0.01 m)/ tetrabutylammonium tetrafluoroborate  reference electrode were used in N,N‐dimethylformamide (DMF) and TBABF4 (0.1 m) electrolyte. To investigate voltammetric behavior of styrene, linear sweep voltammetry scans were recorded at a 20 mV s−1 scan rate with IR compensation , onset potential of styrene (0.1 m) reduction reaction in Ar‐saturated electrolyte is −2.71 V (vs Ag/Ag+), which is more negative by 0.05 V compared to that of CO2 reduction reaction . Then, various concentration of styrene up to 0.2 m were added to the CO2‐saturated electrolyte. In the case of adding 5 × 10−3m styrene, the onset potential was same as that of CO2‐saturated electrolyte without styrene. As adding more styrene, the onset potential shifted positively and maintained the value at −2.50 V, while the current density gradually enhanced. The increase of current density reached saturation in the case of styrene concentration above 0.1 m because of the diffusion limitation of styrene. Therefore, the concentration of styrene was fixed to 0.1 m in the following analysis.We first performed the electrochemical carboxylation of styrene using COon Figure2a. Them at a 20 mV s−1 scan rate with IR compensation , new reduction peak which has the current density of ≈0.2 mA cm−2 was observed from the applied potential at −1.53 V (vs Ag/Ag+). These results indicate the occurrence of a new reduction reaction in the presence of water which turned out to be a hydrogen evolution reaction (HER), as will be discussed later. To determine the rate‐determining step (RDS), Tafel slopes were measured for the cases of 0, 0.05, and 0.1 m water, where a negligible shift of the onset potentials was observed . Thus, the product yield could be measured in stable electrochemical reaction condition. The carboxylate products were acidified with HCl (2 m), extracted with ether and isolated after solvent distillation. The final carboxylic acids were characterized using proton nuclear magnetic resonance spectroscopy . The 1H NMR spectra clearly showed the change in peak intensity of 1 and 2 by adding water . In the spectra, the peaks of residual styrene, DMSO‐d6, DMF and water were observed but no other peaks of by products such as polymerized or reduced styrenes are detected. In addition, α‐hydrocarboxylated products were not detected both from NMR and gas chromatography‐mass spectrometry (GC‐MS) analysis. Along with the carboxylic acids in the electrolyte, the gas products from the headspace of the reactor, such as hydrogen, carbon monoxide and methane, were analyzed by gas chromatography (GC).For the electrochemical electrolysis, 20 C of charge was passed under constant negative potential. As shown in Figure 1H NMR and GC results, the yields of each product from the styrene carboxylation were obtained based on faradaic efficiency (FE) in the presence of different amounts of water  to 1 m . This result clearly shows a change in the carboxylation pathway from dicarboxylation to β‐hydrocarboxylation. However, in terms of product yield, the maximum FE of 2 was obtained at 0.1 m water which is 1 equivalent relative to styrene  and gradually decreased to 47% when water was added up to 1 m . This decline of yield toward β‐hydrocarboxylation can be explained by the increasing gas production. In particular, FE of hydrogen significantly increased from 3.2% to 15% as the water concentration increased from 0.1 to 0.2 m  and even increased up to 44% at 1 m water . Among the CO2 reduction reactions, the production of CH4 gradually increased, exhibiting a maximum FE of 6.7% in 0.3 m water . The result indicates that excess water above 0.1 m  in the electrolyte is used mostly in the HER and partially in CH4 production. This increase in gas production also corresponds to the positive shift of the onset potential in voltammetry scans at water concentrations above 0.1 m . The selectivity of 2 was slightly enhanced in both cases using HCl, which were comparable to the cases that used a twofold amount of neutral water.In addition, the effect of water acidity on the product selectivity was investigated by using diluted HCl. In detail, the equivalent amount of 2 2 reduction reaction.2 as a carbon source in the carboxylation, CO2 molecule should not be reduced directly into hydrocarbon products such as CO and CH4. Thus, we expected that these cathodes can increase the carboxylation efficiency while suppressing CO2 reduction reaction. For the electrochemical analysis, linear sweep voltammetry scans were recorded with 0, 0.05, 0.1, and 0.4 m water at a 20 mV s−1 scan rate in CO2‐saturated DMF and TBABF4 (0.1 m) electrolyte under an atmosphere of CO2 . By adding water, the onset potentials shifted positively and new currents from HER were observed as also observed in the case of Ni cathode. Especially, Pt electrode exhibited the largest current density of HER (0.5 mA cm−2 with 0.1 m H2O) among the electrodes used in this study. The acids and gas products from the styrene carboxylation using Ti and Pt electrode were also detected under the same electrolysis condition which was used in the case of Ni electrode in Figure m water was analogous to the case of Ni electrode, where the yield of 1 decreased while that of 2 and HER increased by adding water. However, compared to a Ni electrode, both cases showed lower yield of 2 in the presence of water. In the case of Pt electrode, as also observed in the voltammetry scans, it exhibited the highest activity for HER where the FE of hydrogen reached to 38% and 61% at 0.1 and 0.4 m water while the maximum yield of 2 was only 29% at 0.4 m water. On a Ti electrode, the HER were observed by FE of 18% and 40% at 0.1 and 0.4 m water and maximum yield of 2 was 44% at 0.1 m water.The effect of electrode catalyst was investigated by using Ti and Pt cathode instead of Ni cathode. Ni, Ti, and Pt are in the metal group that prefers HER than COKa value were also used instead of water to explore the effect of proton sources on the selectivity toward 2 . The TOF further reached 38 s−1 at a 760 mV overpotential  along with the negligible change in the selectivity between 1 and 2.The influence of current density was also investigated by applying various overpotentials (η) during the electrolysis . To evaluate β‐hydrocarboxylation activity, the turnover frequency (TOF) was calculated (see the Supporting information). When the current density was below 5 mA cmFigure−1 to evaluate reduction activities. Compared to styrene, styrene derivatives bearing electron‐donating substituents such as methoxy group showed positively shifted onset potential while electron‐neutral and electron‐withdrawing styrenes possessed comparable or positively shifted onset potentials. The electrochemical carboxylation reactions were conducted with 0.1 m of each styrene derivatives and 0.1 m water on a Ni electrode in CO2‐saturated DMF and TBABF4 (0.1 m) electrolyte under 10 mA cm−2 current density. As a result, the β‐hydrocarboxylation reaction tolerated electron‐donating (2a) and electron‐neutral (2b) styrenes in good yields and fluorine‐substituted styrenes (2c and 2d) with moderate yields. In the cases of 2e and 2f, 4‐vinylbenzoic acid (3) was synthesized as a result of substitution of chlorine or trifluoromethyl group with CO2. Especially, when chlorine‐substituted styrene was used, bare styrene was observed after the electrochemical reaction and 1 and 2 were observed by FE with 16% and 59%, which clearly shows the cleavage of chlorine. However, no other styrene derivatives underwent the cleavage to styrene. Moreover, for trifluoromethyl‐substituted styrene, no products from the cleavage of fluorine‐carbon bond was observed under our detection condition using NMR and GC‐MS analysis. To further investigate the reduction of carbon‐chlorine bond, current densities during the carboxylation of chlorine‐substituted styrene were changed to 1, 10, and 20 mA cm−2. As a result, neither carboxylation toward 2e nor reduction of carbon‐chlorine bond were occurred under 1 mA cm−2 current density, and negligible change in product selectivity was observed for the cases of 10 and 20 mA cm−2 current density. The behavior of electron‐withdrawing styrenes exhibits similar trend with previous electrochemical carboxylation of styrene without proton source[qv: 12c] which also shows the cleavage (or reduction) of carbon‐chlorine bond instead of the reduction of vinyl group.After optimizing the reaction condition for the β‐hydrocarboxylation of styrene, the substrate generality of this electrochemical protocol was investigated Figure4. The 2O). In the 1H NMR spectra, D‐labeled 2 was observed with 80% deuterium incorporation at the benzylic carbon site (see the Supporting Information). Moreover, carboxylic acid products were methylated and observed in GC‐MS (see the Supporting Information). In the mass spectrum, the ion peak (M+) of D‐labeled methyl‐3‐phenylpropanoate showed a mass shift of 1 from m/z 164 to 165, which corresponds to labeling with one deuterium atom  showed a mass shift of 1. The only carbon position that these four fragments commonly contain is the benzylic carbon which indicates that deuterium labeling has been carried out at this site. Therefore, basis on the result from both 1H NMR and GC‐MS, we clearly verified that the protonation occurs at a benzylic position by using a proton of water.To verify whether the proton used in β‐hydrocarboxylation comes from water, a deuterium labeling experiment was conducted by fully replacing water with deuterium oxide  with 0.025 and 0.1 m D2O or H2O. At these proton source concentrations, the selectivity of carboxylation over gas production was above 94%, which could avoid the contribution of other unwanted proton‐involved reactions such as the HER. As shown in Figure S5 (Supporting Information), no difference was observed in the voltammetric curves between the cases using H2O and D2O. This result implies that a protonation step is not involved in the RDS of this electrochemical carboxylation. In addition, we calculated the yield of acid products from the carboxylation and found out that total FE of acids (1 + 2) were only slightly changed from 88% to 85% oxyl (TEMPO) and 5,5‐dimethyl‐pyrroline N‐oxide (DMPO) were added to the reaction solution to investigate the role of radical intermediates during the electrochemical carboxylation of styrene . In the case of using TEMPO and DMPO, the FE of 1 decreased from 26% to 8% and 13% respectively which shows the suppression of dicarboxylation in the presence of the inhibitors. Whereas, the FE of 2 showed comparable value  or even enhanced . These changes in the electrochemical carboxylation pathway in the presence of radical inhibitors indicate that radical intermediate play an essential role in this electrochemical reaction. Also, we added benzoquinone (BQ), which can act as a proton scavenger, and observed enhancement of FE toward 1 (49%) while that of 2 decreased to 27%. This shows that the supply of proton is necessary to facilitate the hydrocarboxylation pathway.Figure2 form a β‐carboxylate radical intermediate by accepting one electron. The absence of α‐hydrocarboxylated products in study supports the formation of β‐carboxylated species as an intermediate at the initial stage of the reaction. This electrical reduction step is the RDS as confirmed by the Tafel analysis and electrokinetic study. From the result that the reduction current has gradually increased by adding reactants, it can be presumed that styrene and CO2 simultaneously undergo reduction reaction at the applied potential. In terms of onset potential, CO2 reduction reaction showed more positive onset potential (−2.66 V vs Ag/Ag+) compared to the styrene reduction reaction (−2.71 V vs Ag/Ag+) by 50 mV. However, under the reaction condition used here which applies at least 320 mV overpotential, it is still ambiguous to decide the dominant pathway between these two reactions. Because the reduction potential of benzylic radicals are positioned at more positive range than the onset potential ,2 into the benzylic position of the β‐carboxylate anion intermediate. Consequently, the competition between the protonation and CO2 incorporation on the benzylic position determines the final selectivity of this electrochemical carboxylation.Based on our collective results, we proposed a reaction pathway for electrochemical β‐hydrocarboxylation of styrene in the presence of small amount of water Figure6. Firs32 was demonstrated where the site selectivity could be controlled between dicarboxylation and β‐hydrocarboxylation by inducing protonation of styrene using water. With 10 equivalents of water relative to styrene, the selectivity of β‐hydrocarboxylation toward dicarboxylation reached up to 96%. However, because excess water facilitated the HER and methane production instead of carboxylation, the highest FE of β‐hydrocarboxylation was observed when 1 equivalent of water was used, exhibiting an optimal concentration. The turnover frequency toward β‐hydrocarboxylation was enhanced up to 38 s−1 under overpotential of 760 mV, which shows that reaction rate can be controlled by applied potential without the change in the product selectivity. We revealed that the water molecule is directly consumed as a proton source in β‐hydrocarboxylation by deuterium labeling experiments. Moreover, on the basis of the kinetic study, we suggested that the protonation and incorporation of CO2 on the benzylic position of styrene competitively occurs after the formation of the β‐carboxylate intermediate. Follow‐up studies on extending substrates to general unsaturated hydrocarbons such as aliphatic olefins are in progress. We expect that our strategy will aid understanding the role of proton sources in electrochemical platforms and further exploit the desired site‐selective carboxylation reactions. Furthermore, we envision that this method can be used in hybridizing the electrochemical reduction of CO2 and carbon fixation to long‐chain hydrocarbons as photosynthetic carbon cycle.In summary, a new electrochemical carboxylation of styrene with CO4Materials: 5,5‐dimethyl‐pyrroline N‐oxide (DMPO), hydrocinnamic acid, 2‐phenylsuccinic acid, styrene, all styrene derivatives, tetrabutylammonium tetrafluoroborate (TBABF4), and tetramethylsilane (TMS) were purchased from TCI chemicals . oxyl (TEMPO), chloroform‐d (CDCl3), and dimethyl sulfoxide‐d6 (DMSO‐d6) were purchased from Acros Organics . Benzoquinone (BQ), iodomethane, and magnesium sulfate (MgSO4) were purchased from Sigma‐Aldrich . Acetic acid, acetonitrile, tert‐butanol, N,N‐dimethylformamide (DMF), diethyl ether, hydrochloric acid (HCl), methanol, phenol, potassium carbonate (K2CO3), and sodium hydroxide (NaOH) were purchased from Daejung chemicals . DMF was dried with 4 Å molecular sieve, and all other chemicals were used as received. Purified deionized water (18.2 MΩ cm−1) was used in the procedures. Nickel foil , titanium foil , platinum foil , and magnesium foil  were purchased from Alfa Aesar .Electrochemical Analysis: An undivided three‐electrode cell equipped with a gas line was used in all voltammetric measurements and electrolysis. Ni, Ti, and Pt with surface dimensions of 1 cm × 2.5 cm and Mg with surface dimensions of 1 cm × 3 cm were used as the working electrode and counter electrode, respectively. Prior to use, the metal foils were polished with sandpaper, cleaned with diluted HCl (aq.) and rinsed with distilled water. The reference electrode was Ag/Ag+ (0.01 m)/TBABF4 (0.1 m) in acetonitrile. For the electrolyte, TBABF4 (0.1 m) was put in dried DMF and saturated with CO2 by purging the gas for 1 h. Then, 4 mL of the solution was put into the reactor cell at a volume of 50 mL. The reactants were injected into the electrolyte, and the headspace of the cell was ventilated with CO2 gas for 0.5 h and closed tightly under CO2 at atmospheric pressure. All reactions were performed at room temperature under vigorous stirring of the electrolyte. After electrolysis, 1 mL of headspace gas was transferred by syringe for gas chromatography (GC) analysis. The solutions in the reactor cell were acidified with HCl  for 3 h and extracted with diethyl ether (3 × 20 mL). The organic layer was washed with distilled water, dried over MgSO4 and evaporated. The isolated products were dissolved in deuterated solvents for nuclear magnetic resonance (NMR) analysis or diethyl ether for gas chromatography‐mass spectrometry analysis.Methylation Procedure for GC‐MS Analysis: Iodomethane  and K2CO3  were mixed into the reaction solution immediately after electrolysis and stirred for 12 h under an argon atmosphere. The residues were extracted with diethyl ether (3 × 20 mL). The organic layer was washed with distilled water, dried with MgSO4 and concentrated under reduced pressure.Analytical Methods: NMR spectra were recorded on a JEOL 400 MHz NMR spectrometer (JeolJMN‐LA400) or Bruker 600 MHz NMR spectrometer (Bruker Avance 600) at room temperature. Chemical shifts were reported in parts per million (ppm) downfield of TMS (δ = 0.00 ppm). Products were dissolved into 0.7 mL of DMSO‐d6 or CDCl3. A potentiostat  was used for voltammetric measurements and bulk electrolysis. All potentials were controlled against the reference electrode and recorded after IR compensation. The quantitative measurement of the gas phase from the headspace of the electrochemical cell was performed by GC . Liquid‐ and solid‐phase products dissolved in the organic solvents were detected by GC‐MS (Agilent 5977) using an automatic liquid sampler.The authors declare no conflict of interest.Supporting InformationClick here for additional data file.


Chryseobacterium were characterised. The first enzyme yielded the new compound chryseodiene that closely resembles the known fusicoccane diterpenes from fungi, but its experimentally and computationally studied cyclisation mechanism is fundamentally different to the mechanism of fusicoccadiene synthase. The second enzyme produced wanjudiene, a diterpene hydrocarbon with a new skeleton, besides traces of the enantiomer of bonnadiene that was recently discovered from Allokutzneria albata.Two bacterial diterpene synthases (DTSs) from  Two diterpene synthases from the bacterial genus Chryseobacterium making the new compounds chryseodiene and wanjudiene are reported. The enzyme mechanisms were investigated in detail through a combination of experimental and computational approaches. Streptomyces. A few examples from cyanobacteria,Chryseobacterium (flavobacteria). Here we report on two new diterpene synthases (DTSs) from C. polytrichastri DSM 26899 and C. wanjuense DSM 17724, structure elucidation of their products and investigations on the enzyme mechanisms by labelling experiments and computational chemistry.Terpene synthases (TSs) are remarkable enzymes that convert the oligoprenyl diphosphates geranyl (GPP), farnesyl (FPP), geranylgeranyl (GGPP) and geranylfarnesyl diphosphate (GFPP) into complex, usually polycyclic terpenes with multiple stereocentres.C. polytrichastri (WP_073290622) did not yield a product from GPP, FPP and GFPP, but efficiently converted GGPP into a diterpene . The compound was isolated for structure elucidation by NMR spectroscopy , resulting in the new compound chryseodiene .Two TS genes were cloned into the expression vector pYE‐Express1 was determined using stereoselectively deuteriated terpene precursors. Incubation of (E)‐ and (Z)‐isopentenyl diphosphateStreptomyces cyaneofuscatus1 with stereoselective deuteriation at C4 and C12 . The additional 13C‐label at these carbons allowed for a sensitive analysis by HSQC spectroscopy. The introduced stereochemical anchors of known configuration gave access to the absolute configuration of 1 as shown in Scheme 1 was confirmed by similar experiments with (R)‐ and (S)‐IPP,Serratia plymuthica,The absolute configuration of nd (Z)‐4‐C,4‐2Hiso1 starts from GGPP by a 1,11‐10,14‐cyclisation to cation A, followed by a 1,5‐hydride shift to B and a third cyclisation to C. A subsequent 1,2‐hydride migration to D and deprotonation yields 1. This mechanism was experimentally supported by twenty 13C‐labelling experiments with introduction of labelling into each carbon of 1, using the corresponding synthetic (13C)GGPP isotopomers .A to B was evident from the incubation experiments with DMAPP and (E)‐ and (Z)‐IPP, resulting in a stereoselective deuterium labelling at C8. The hydride migration from C8 into the iPr group of 1 can be followed by its cleavage during EI‐MS fragmentation, demonstrating the specific migration of the 8‐pro‐R hydrogen introduced from (Z)‐IPP , while the 8‐pro‐S hydrogen from (E)‐IPP remains bound to C8, as shown by a vanished crosspeak in the HSQC spectrum . The 1,2‐hydride transfer from C to D (Ha) was investigated by incubation of GGPP13C‐NMR spectrum that indicated a direct 13C−2H bond for the obtained product . The final deprotonation proceeds with loss of the hydrogen from C6 of GGPP (Hb), as followed by incubation of (2‐2H)FPP and IPP with GGPPS and CpCS and product analysis by GC/MS .The proposed cyclisation mechanism for C can be inferred from the structure of 1, because the subsequent 1,2‐hydride migration to D must proceed suprafacially, the configuration at C6 is based on DFT calculations for the cyclisation to 1. Two conformers of A can explain the correct stereochemistry at C2 of C  that is the required precursor of the hypothetical intermediate 6‐epi‐C. The DFT calculations further reveal a low transition state (TS) barrier for the 1,5‐hydride shift from A (DD) to B Phomopsis amygdali (PaFS) and Alternaria brassicicola (AbFS),3) formed by CotB2 in Streptomyces melanosporofaciens,4) made by the DTS SdnA in Sordaria araneosa,5) produced by the DTS MgMS in Myrothecium graminearum.6), the product of AcOS in Aspergillus clavatus,E which may be identical to A or resemble its C14 epimer, in both cases with the same configuration at C11 ,10(14)‐diene (7)a yields the main product 2. The mechanistic and stereochemical differences are also reflected by the weak identity (15 %) between CpCS and the TS domain of PaFS, suggesting that these enzymes have evolved independently. Unrelated DTSs are also known for phomopsene from fungi and bacteria,Notably, s Scheme  A, incluC. wanjuense (WP_089795910) did not accept GPP, FPP or GFPP, but efficiently converted GGPP into an unkown diterpene 8, besides traces of bonnadiene (9) for which the bonnadiene synthase (BdS) was recently discovered from Allokutzneria albata (Scheme 8) and characterised the DTS as Chryseobacterium wanjuense wanjudiene synthase (CwWS). The absolute configuration of 8 was established through stereoselective deuteriation by conversion of DMAPP and (E)‐ and (Z)‐IPP , and (R)‐ and (S)‐IPP  with GGPPS and CwWS. All experiments pointed to the absolute configuration for 8 as shown in Scheme The second enzyme from d (Z)‐4‐1C,4‐2HIPP8 starts with the isomerisation of GGPP to GLPP, followed by 1,14‐cyclisation to I. The isomerisation to GLPP is required to explain the Z configured double bond in I. A subsequent 1,3‐hydride shift to J is followed by 1,10‐cyclisation to K (path a). The downstream steps include a 1,2‐hydride migration to L, 6,10‐cyclisation to M, another 1,2‐hydride shift to N and final deprotonation. Alternatively, cation J can react by 1,6‐cyclisation to O (path B), followed by 1,2‐hydride shift to P, 6,10‐cyclisation to Q and deprotonation to the side product 9. The cyclisation mechanism to 8 was investigated by enzymatic conversion of all twenty isotopomers of (13C)GGPP with CwWS, resulting in the incorporation of labelling into the expected positions in all cases . The 1,3‐hydride shift from I to J was followed using (11‐13C)FPP with (R)‐ and (S)‐(1‐2H)IPP, GGPPS and CwWS, resulting in a triplet for C15 in the 13C‐NMR due to 13C–2H spin coupling for the product from (S)‐(1‐2H)IPP, while a singlet was observed with the R enantiomer, indicating specific migration of the 1‐pro‐S hydrogen of GGPP . Also for the side product 9 the 1‐pro‐S hydrogen of GGPP shifts into the iPr group, which is evident from its EIMS fragmentation with loss of deuterium for labelled 9 from (S)‐(1‐2H)IPP, while EIMS cleavage of the iPr group for labelled 9 from (R)‐(1‐2H)IPP proceeds with retainment of deuterium . Notably, for 9 obtained with BdS from Allokutzneria albata the opposite outcome with a shift of the 1‐pro‐R hydrogen of GGPP into the iPr group was observed,9 from BdS and the side product from CwWS are enantiomers .The proposed cyclisation mechanism from GGPP to 8 from K to L was evident from the incubation of GPP and IPP with GGPPS and CwWS, yielding labelled 8 with a slightly upfield shifted triplet for C11 . Similarly, the enzymatic conversion of FPP and IPP with GGPPS and CwWS gave a strongly enhanced and upfield shifted triplet for C7, giving experimental support for the 1,2‐hydride transfer from M to N . Finally, the stereospecificity of the deprotonation from N to 8 was elucidated from the incubation of CwWS with (R)‐ and (S)‐IPP, showing an enhanced HSQC signal for C5 from the R enantiomer, while no signal is observed when using (S)‐IPP .The second hydride migration in the biosynthesis of C. polytrichastri and C. wanjuense was investigated by collecting the volatiles on charcoal filter traps using a closed‐loop stripping apparatus (CLSA),C. polytrichastri did not produce 1 or any other diterpene , suggesting that the CpCS gene is not expressed under laboratory growth conditions, while C. wanjuense emitted 8 as one of the major volatiles .The production of diterpenes by R)‐linalool with ca. 60 % ee was reported from C. polytrichastri,1) through a mechanism that was elucidated by a combination of experimental and computational work and that is distinct from the mechanism of other fusicoccane‐type DTSs. The second DTS (CwWS) catalyses the formation of wanjudiene (8), a diterpene with a previously unknown skeleton, and also provides the enantiomer 9 of the known compound bonnadiene as a side product. This surprising result coincides with a large phylogenetic distance between CwWS and BdS , but also suggests that some terpene structures may be privileged and may be more easily accessible by enzyme reactions than others. Future studies will presumably show more of such surprises, emphasising the importance of continuous thorough investigations on the intriguing and complex mechanisms of terpene synthases.Recently a linalool synthase producing mainly  should be addressed to the authors.SupplementaryClick here for additional data file.


The key parameters, such as the total 3D TiO2 film and thin‐shell thicknesses, are precisely optimized by finite element analysis. Collectively, this fundamental design leads to ultrahigh chemoresistive response to NO2 with a theoretical detection limit of ≈200 ppt. The demonstration of high responses with visible light illumination proposes a future perspective for light‐activated gas sensors based on semiconducting oxides.One of the well‐known strategies for achieving high‐performance light‐activated gas sensors is to design a nanostructure for effective surface responses with its geometric advances. However, no study has gone beyond the benefits of the large surface area and provided fundamental strategies to offer a rational structure for increasing their optical and chemical performances. Here, a new class of UV‐activated sensing nanoarchitecture made of highly periodic 3D TiO 2 gas sensors using 3D TiO2 nanostructures are achieved by the unique light harvesting properties of the nanoporous structures. The light scattering effects from optical maze‐like nanostructures and numerous intermediate energy states from atomic layer deposition of the film electronically activate 3D TiO2 and enhance its gas sensing performance under UV illumination.The high‐performance light‐activated NO The IoE application requires the gas sensors to exhibit a low power consumption for their installation in mobile devices, not to mention an excellent gas‐sensing performance. To achieve low power consumption, the heaters, more than anything else, should be removed from the current chemoresistive‐type gas sensor structures. The heaters operate at ≈200–400 °C with temperature uncertainty, thermally degrade the neighboring electronic components during operation, raise issues upon the miniaturization of device, and have also been a primary reason for the low reliability of the current sensor systems. Therefore, numerous studies have focused on discovering alternative materials capable of operation at near room‐temperature or other chemical‐activation routes for sensing that consume less power than the thermal heaters.The semiconductor or chemoresistive‐type gas sensor based on metal oxides has been one of the most intensively studied and developed technologies with a growing demand from the internet of everything (IoE) market.1 The  Considering the high‐performance requirements for gas sensors in IoE applications, further modifications of the sensory materials, other than just relying on their bulk properties, should precede the full utilization of the given light energy. In response, there have been numerous efforts reported to date with various strategies for light‐activated gas sensors including i) heterojunction engineering, ii) noble metal decoration, iii) utilization of nonoxide materials , iv) incorporation of plasmonic nanoparticles, and v) development of effective nanostructures. Despite their active gas‐sensing performances, few studies suggest the possibility of improving the sensor's performance by adding structural factors to maximize the optoelectronic properties of the light‐activated gas sensors.One of the notable research directions in low temperature gas sensors is the use of light sources, particularly light‐emitting diodes (LEDs), for energy‐efficient activation of semiconducting sensor materials. Light sources with higher energy than the bandgap energy of the semiconductors can excite internal charge carriers to participate in the chemical reaction and accelerate the interaction between the semiconductor and the gas molecules. The previous studies on light‐activated gas sensors have repeatedly reported relatively improved gas responses and faster recovery characteristics under light illumination.7, 82 nanostructures (denoted as “3D TiO2”) whose symmetry is body‐centered tetragonal (BCT) and the shell thickness is 30 nm. The nanostructure can make unique use of light by multiple scatterings within the optimal total thickness of 6 µm, which is first proven by finite element analysis (FEA) of the electromagnetic field (E‐field) distribution over 3D TiO2 by unit cell modeling. The optimized light‐scattering effects by 3D thin‐shell TiO2 on the enhancement of NO2 gas‐sensing performance were verified through the measurement of resistance change. The thin‐shell and film thickness of 3D TiO2 were precisely controlled for the optimization . As a result, the fabricated 3D TiO2 exhibited significantly increased light absorption compared to that of the planar TiO2 thin film, with a thickness of 6 µm, yielding dramatically enhanced light‐activated gas responses with faster and complete recovery characteristics toward 5 ppm NO2. More interestingly, the gas response was further enhanced up to 4 times under a relative humidity of 50% due to the neutralization of hydroxyl groups under UV illumination. Finally, a notable observation is that the fabricated 3D TiO2 exhibited light‐activated characteristics even under visible light illumination due to the defective nature of the atomic layer deposition (ALD)‐coated TiO2 thin‐shell, such as O vacancies, interstitial Ti, and carbon residues. To the best of our knowledge, there has been no systematic attempt to design a structural platform for the effective utilization of the illuminated LED light (<800 µW) for gas sensor applications operating in a highly humid environment at room temperature. The light‐activated, ultrasensitive  level) gas‐sensing properties of 3D TiO2 proven by the optical simulation in this study will certainly open a new perspective toward future chemoresistive‐type gas sensors operating at room temperature without any heating unit.In this study, we systematically designed highly periodic 3D thin‐shell TiOmination.16 FinFigure 2. In brief, the optic system with a conformal phase mask for 3D nanofabrication, which generates light diffraction and interference in a proximity‐field, provides 3D periodic intensity distribution of the incident light through a prefabricated photopolymer thin film by the Talbot effect . The details can be found in the Experimental Section. Compared to other competing techniques such as self‐assembly, electrospinning, and many other bottom‐up methods, one of the notable technical advantages of this microelectromechanical system‐integrated method is the direct patterning of 3D scaffolds on the electrodes. Therefore, the further TiO2 deposition using ALD can be done without any additional transferring steps, which generally lead to poor contact issues between the electrodes and the deposited functional materials. To apply 3D TiO2 to gas sensors, we fabricated 3D TiO2 on a SiO2/Si substrate with Pt interdigitated electrodes (IDEs). Figure 2 on the IDEs‐patterned SiO2/Si substrates and gas‐sensing measurement system, respectively. The active area is 1 × 1 mm2 and the number of interdigitated fingers is 20 with 5 µm interspacing. The cross‐sectional scanning electron microscopy (SEM) images of the fabricated 3D TiO2 on a SiO2/Si substrate with Pt IDEs show the direct construction of the sensory material without any structural degradation, such as collapse and delamination  images were carefully obtained, and they present a highly periodic BCT symmetry of 3D TiO2  and 0.27 nm for d(110) with a fast Fourier transform (FFT) pattern in Figure n Figure . For a ce Figure ,e. After2 thin‐shell network with the periodicity of 600 nm offers the three major factors for ideal gas‐sensing performance: i) utility factor, ii) transducer function, and iii) receptor function. As the BCT unit cell of 3D TiO2 consists of two types of embodiments, a hollow ellipsoid core (center) and eight internecks connecting with the neighboring 1/8 parts of the hollow ellipsoids, these thin‐shell internecks allow the target gases to access both the exterior and interior surfaces of the 3D nanostructure (utility factor). It is noted that Sanger et al. reported the contribution of the hollow tubular structure with high‐aspect‐ratio to the significant improvement of the NO2 molecule collision frequency, which directly corresponds with our unprecedented enhancement of the sensing performances. In addition, the internecks in the unit cell also play an important role in the enhancement of the semiconducting performances of the TiO2. The junctions between the TiO2 thin‐shell networks narrow the conduction channels with double‐Schottky junctions originated from the depletion layers formed by the adsorption of ionized oxygen from the air. The internecks further narrow the conduction channel, which significantly enhances a transducer function that contributes to more efficient modulation of the electrical resistance upon exposure to target gases  simulation software . It is noteworthy that this numerical approach for finding the optimal conditions was valid owing to the exceptional structural uniformity, which is one of the distinctions of this work. Overall simulation data dependent on the film thickness of the 3D TiO2  confirms that the E‐field enhancement in UV by the 3D TiO2 is significantly improved owing to its optical maze‐like architecture that leads to effective UV light absorption. In particular, the periodicity of the structure and the refractive index mismatch at the interfaces between air (refractive index ≈ 1) and TiO2 (refractive index ≈ 1.7) induce the light interference resulting in an active E‐field enhancement along the 3D nanostructure. In fact, there is a saturation point to utilize the incident UV light through 3D TiO2 because of the considerable scattering effect from a thicker 3D nanostructure. For example, the degree of E‐field enhancement in UV intensively increases until the total thickness reached 6 µm, but beyond that total thickness, this effect is saturated at ≈70% . It indicates that the excess of film thickness over 6 µm is not useful for photoactivation. Thus, there should be an effective total thickness between 3 and 15 µm, and it is controlled as 6 µm in this work.To effectively utilize the large surface area of 3D TiO2 thin‐shell thickness affects the effective refractive index and porosity of 3D TiO2, which significantly contribute to both the E‐field enhancement and gas accessibility. Thus, we controlled the TiO2 thin‐shell thickness in the range from 30 to 100 nm by varying the deposition cycles of the ALD. The variation of light‐matter interaction from the controlled TiO2 thin‐shell thicknesses generates complex E‐field intensity distributions  and planar TiO2 thin films are calculated with each thin‐shell thickness . The light confinement is defined as the sum of intensity values in 5 nm cubic voxels consisting of TiO2 regions in the FDTD simulation. As the thin‐shell thickness increases, the increments in total E‐field are more prominent for 3D TiO2 than for the planar TiO2 films, which is originated from the porosity differences between the planar TiO2 thin films and 3D TiO2. Therefore, the overall light‐activated gas‐sensing performance should be determined considering both the nanostructural and light‐scattering effects.The TiOive index29 ands Figure . As the 2 using various combinations with the total film thickness of 3, 6, and 15 µm and thin‐shell thickness of 30, 50, 70, and 100 nm, 3D TiO2 was exposed to 5 ppm NO2 under ultraviolet (UV) illumination at room temperature to investigate its gas‐sensing properties. An illumination power to the sample of less than 800 µW from a commercial 5 mm UV micro‐LED was sufficient to photoactivate the sensor. It is worth mentioning that no illumination result on TiO2 chemoresistors has ever achieved high performance under this illumination condition. The extremely low energy consumption is a key factor for miniaturization and integration to IoE devices. Figure 2 with 30, 50, 70, and 100 nm thin‐shell thickness. A clear decrease in porosity can be verified for the thicker TiO2 thin‐shells and is expected to significantly affect the gas‐sensing properties along with the light‐scattering effects. Figure 2 for each 3D TiO2. The resistance increased instantly upon the initial exposure to the NO2, which indicates the behavior of an n‐type semiconductor. Compared to the planar TiO2 thin film exhibiting almost no gas response under the dark condition and a very little response under UV illumination, 3D TiO2 exhibited significantly improved gas response and full recovery to the baseline resistance . In addition, both samples exhibited decreased base resistance under UV illumination compared to that under dark condition, which indicates the photogeneration of electron–hole pairs. The trends in base resistance exhibited increment for thicker TiO2 thin‐shell thickness of each 3D TiO2 film up to 70 nm and decrement after 70 nm, except for 3D TiO2 with 15 µm, which exhibited continuous increment after 70 nm. This can be attributed to the effects of a noneffective dead bottom volume of 3D TiO2 with 15 µm that is previously mentioned . As simulated in Figure 2 thin‐shell thickness exhibited the highest field enhancement intensity for 3D TiO2 with 6 µm and this is expected to have contributed to resistance decrease along with nanostructural effects (porosity difference). Although the simulation on 3D TiO2 with 15 µm has not been conducted for all TiO2 thin‐shell thicknesses, their impressive field enhancement will certainly be limited to the upper region of 3D TiO2 with 15 µm and cannot contribute to the conduction channel at the bottom region. As a result, bouncing back to resistance decrement from resistance increment trends up to 70 nm TiO2 thin‐shell thickness, which is highly related to light scattering effects could not happen for 15 µm 3D TiO2. These trends have been reproducible and confirmed through the fabrication of multiple batches of 3D TiO2 samples. The gas response can be calculated dividing the changes in saturated resistance before and after exposure to NO2  by the baseline resistance (Rair), expressed as (Rgas − Rair) / Rair × 100 (%). The gas responses of 3D TiO2 with the different thickness combinations toward 5 ppm NO2 under UV illumination are summarized in Figure 2 thin‐shell thickness conditions than that for 3D TiO2 with 3 and 15 µm, which is well‐matched with the simulation data. For example, low response with nonstability was observed for the 15 µm sample because of the considerable volume of the unexposed region at the bottom, which is regarded as a dead volume. The gas responses kept decreasing as the TiO2 thin‐shell thickness increased up to 70 nm but increased again as it went up to 100 nm. As the TiO2 thin‐shell thickness increases, the volume fraction of vacancy compared to the TiO2 area, calculated from the top‐view SEM images in Figure 2‐gas molecule interactions. Up to 70 nm, this nanostructural effect, a term defined as the changes in the utility factor (gas molecule accessibility) and transducer function (effective modulation of electric resistance) dominates the gas‐sensing properties of 3D TiO2, but for a thicker TiO2 thin‐shell, over 70 nm, it starts to become dominated by the light‐scattering effects from the complex 3D nanostructures. Thus, it is evident that both the levels of photoactivation and gas dynamics are crucial factors for the light‐activated gas sensors. Although the calculated total sum of intensity was the highest for 3D TiO2 with 100 nm thickness of thin‐shell, the overall gas‐sensing performance considering both the nanostructural effect and E‐field enhancement was the best for the 6 µm 3D TiO2 with 30 nm thin‐shell thickness. It has a nearly 55 times higher sum of intensity compared to that of the planar TiO2 thin film upon UV illumination, which is sufficient to take advantage of the complex 3D nanostructure designed in this study. In order to further study the strength of our 3D TiO2 nanostructures for the light activation, three other samples were prepared for the comparison, including TiO2 inverse opal  and self‐assembled TiO2 nanoparticles. It is noted that the simulations assumed a highly ordered nanostructure. Compared with 3D TiO2, it is clearly observed that the E‐field enhancement occurs at the top region of the control structures due to their restricted light penetration depth from active reflection at the top of the structures. On the other hand, the incident light through 3D TiO2 reaches to the bottom of the structure and contributes to the utilization of the whole structure. This active light scattering through the entire 3D TiO2 leads to enhanced NO2 detection performances . The highest response to 5 ppm NO2 under UV illumination was exhibited by TiO2 inverse opal with 1 µm thickness (385.88%) and it was just 2.12 times enhancement compared to dark condition. Considering our 3D TiO2 exhibiting a gas response of 3058.7% with 23.55 times enhancement by UV illumination, there is no significant light enhancement effects for the prepared three control samples.After the fabrication of 3D TiO2 with a total thickness of 6 µm and a thin‐shell thickness of 30 nm, the sample was exposed to multiple pulses of NO2 at various concentrations under UV illumination  with gas concentration as described in Figure 2 tested in this work was 400 ppb, the theoretical detection limit can be calculated by extrapolating the linear relationship to where the signal to noise ratio is equal to 3. Accordingly, the theoretical detection limit was calculated to be as low as 202 ppt, which may be advantageous for detection of extremely low concentration of target gases, such as those of explosives and narcotics. In Figure 2 to 5 ppm NO2, as high as 12 200%. While exhibiting promising gas responses under UV illumination both at dry and humid conditions, a relatively slow response time  might need to be improved for certain applications. In that case, some amount of external heating can accelerate the kinetics of gas molecules to yield faster response time, but this study will focus on light activation without any external heating.To verify further the gas‐sensing properties, such as stability and detection limit of 3D TiOn Figure 4a. The gual to 3.32 Acc3COCH3, H2, C2H5OH, NH3, and 5 ppm NO2) was tested on the 3D TiO2 sensor. As shown in Figure 2, even with the lowest concentration, was achieved. It is well‐known that the absorbed ionized oxygen species  on the surface of TiO2 are the key to the electronic interaction between 3D TiO2 and the gas molecules. Although oxygen molecules (O2(gas)) have very low chance to be ionized on the surface of TiO2 at room temperature, several studies have experimentally proved the existence of ionized oxygen species (O2(ads)−) on the surface of metal oxides even at room temperature by comparing conductance under either pure O2 and pure N2 without any photoactivation. Under UV illumination, the O2(ads)− recombine with photogenerated holes (h(photo)+) and become desorbed from the surface (h(photo)+ + O2(ads)− ↔ O2(gas)). The desorption of O2(gas) is considered advantageous to gas‐sensing properties as it supplies the available reactive sites of 3D TiO2, and the trapped electrons result in the decrease in resistance. Meanwhile, some of the photogenerated electrons (e(photo)−) can interact with the adsorbed O2(gas) to form photogenerated oxygen ions (O2(gas) + e(photo)− ↔ O2(photo)−). It should be clear that O2(ads)− desorption would overwhelm O2(photo)− adsorption. Otherwise, the resistance would not decrease under UV illumination. The O2(photo)− is expected to be weakly bound to 3D TiO2 and have higher reactivity compared to the naturally chemisorbed O2(ads)−, which is thermally stable and less reactive at room temperature. Therefore, NO2 sensing and recovery are more likely to be accelerated under UV illumination (NO2 + O2(photo)− ↔ NO2(ads)− + O2(gas)) as demonstrated in the measurement. As there are already excessive photogenerated electrons trapped in TiO2, reducing gases like CH3COCH3, H2, C2H5OH, and NH3, which produce electrons when interacting with O2(photo)−, are less likely to exhibit as much improved gas response as an oxidizing gas such as NO2, which consumes electrons, resulting in high NO2 selectivity. When in humid condition, H2O molecules become ionized on the surface of TiO2 (H2O(gas) + Ti + Olattice ↔ (Ti+ – OH−) + (OH)lattice+ + e−). Following exposure to NO2, NO2 is adsorbed on the surface of 3D TiO2 ((Ti+ – OH−) + (OH)lattice+ + e− + NO2 ↔ (Ti+ – NO2−) + H2O + Olattice). Under UV illumination, the neutralization of the hydroxyl groups (OH−) is possible with photogenerated holes (OH− + h(photo)+ ↔ OH(photo)), and OH(photo) can accelerate the above reaction and further improve NO2 gas response. That is the most‐widely accepted conduction mechanism under a moderate amount of humidity other than the hopping charge transport mechanism. When compared to other previously reported light‐activated gas sensors, the exceptional sensing performances of the fabricated 3D TiO2 greatly exceed them, as shown in Figure  In terms of IoE application, the humidity‐boosted gas‐sensing capabilities can significantly contribute to the development of disease diagnosis devices, which collect disease biomarkers from humid sources, such as the exhaled breath.The selectivity toward five different gas species . The absorbance of 3D TiO2 with normal transmittance, which contains both light scattering and actual light absorption effect, shows significant increase in broadband of visible light due to its considerable light scattering behaviors as an effective optical maze . Meanwhile, when exposed to 5 ppm NO2 under visible light, 3D TiO2 exhibited improved gas‐sensing properties compared to that under dark conditions, which should not happen considering the bandgap energy of TiO2 . As shown in Figure 2 provided an intermediate energy state in the forbidden zone of the 3D TiO2 band structure, and the excellent light scattering of 3D TiO2 leading to E‐field enhancement provided a high possibility of light absorption through the intermediate energy state. This would not have happened in a planar TiO2 thin film, which does not have any E‐field enhancement. To verify the intermediate energy state of 3D TiO2, photoluminescence (PL) spectra were acquired for the optimized 3D TiO2  and unconventional photoluminescence at several wavelengths was identified , indicating actual absorption of visible light wavelengths. Among the many deconvoluted peaks, the predominant emission peak at below 400 nm indicates the slightly shifted main peak of the TiO2 anatase phase, and the many extra peaks explain the intermediate energy states that correspond to various visible wavelengths  and oxygen vacancies (VoS) during the ALD procedure. According to the O 1s scan of the X‐ray photoelectron spectroscopy analysis, there are three major deconvoluted peaks originating from the lattice (530 eV), —OH (531 eV), and C=O (532 eV), respectively . Comparing with the planar TiO2 thin film, the suppression of the C=O peak for 3D TiO2 proves the increase in the O vacancies. In addition, the inevitable existence of the carbon atom during the heat treatment provides the additional intermediate band states that ensure that the unique activation range is extended from UV to the wide band of the visible light range. Thus, the inherent defects of 3D TiO2 facilitated light‐activated gas‐sensing properties, even at the visible wavelength, with the help of the superb light‐scattering effects of the intricate 3D TiO2 nanostructures. This implies that the photoactivation under the desired wavelength could also be achieved without any attributes from defects, but through the systematic design of the band structure through various strategies, such as catalyst decoration or formation of heterojunctions.To interpret these unusual photoactivation behaviors of 3D TiOs Figure . Accordirocedure.48 Acc2 is of fundamental significance to state‐of‐the‐art light‐activated gas sensor applications. The high degree of freedom to optimize the governing structural factors of the chemoresistive materials offers new design opportunities to overcome the bottlenecks of the conventional method for light‐activated gas sensors, which hinder the simultaneous employment of the gas dynamics and light utilization. Owing to its perfect structural uniformity, the two crucial factors, TiO2 thin‐shell thickness and total thickness, were precisely optimized as 30 nm and 6 µm, respectively, based on the FEA analysis. With these attributes, the open porous, interconnected 3D nanonetwork leads to significantly enhanced utilization of the incident light, which was experimentally verified with the exceptional NO2‐sensing performance having a theoretical detection limit of ≈200 ppt and stable operation at room temperature using low power consumption of a micro‐LED, less than 800 microwatts, for irradiation of not only UV but also visible lights. A remaining technical barrier in the application of this technology is the fabrication of denser 3D structures in terms of optical and chemical activities. The explorations of other symmetries, such as the wood‐pile structure, and material designs for controlling the band structure represent other promising research directions for the future. Therefore, the concept of the micro‐electromechanical system (MEMS) integrable 3D nanopatterning that can generate the effective light‐activated gas sensor platform presented in this work holds great promise as a rational strategy for developing general oxide‐based gas sensors in IoE applications.In conclusion, the realization of the highly periodic 3D TiOThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.