A/A′ where interatomic/intermolecular bonding appears only in excited states such as [A2]* (for excimers) and [AA′]* (for exciplexes). Their formation has become widely known because of their role in gas‐phase laser technologies, but their significance in general chemistry terms has been given little attention. Recent investigations in gold chemistry have opened up a new field of excimer and exciplex chemistry that relies largely on the preorganization of gold(I) compounds (electronic configuration AuI(5d10)) through aurophilic contacts. In the corresponding excimers, a new type of Au⋅⋅⋅Au bonding arises, with bond energies and lengths approaching those of ground‐state Au−Au bonds between metal atoms in the Au0(5d106s1) and AuII(5d9) configurations. Excimer formation gives rise to a broad range of photophysical effects, for which some of the relaxation dynamics have recently been clarified. Excimers have also been shown to play an important role in photoredox binuclear gold catalysis.Excimers and exciplexes are defined as assemblies of atoms or molecules  Bond formation through excitation: Linear, two‐coordinate gold(I) complexes are known to aggregate side‐on through aurophilic interactions. The resulting weak Au–Au contacts are strengthened upon UV irradiation as evidenced by a shortening of the intermetallic distance and the vibrational and electronic absorption and emission characteristics of the resulting excimers. The changes in the redox potentials make [AuI−AuI]* excimers useful intermediates in photoredox catalysis. Although this arrangement still gives free access to the central gold atoms, these metal centers are poor electrophiles, and only the strongest “soft” donors are accommodated to form complexes with CN>2. Bending of the L/X−AuI−L/X axes to accommodate an additional ligand is associated with a significant energetic cost, difficult to compensate by the energy of formation of a third or fourth AuI−L/X bond.The structural chemistry of gold(I) is largely characterized by its low coordination number CN=2) with two tightly bound electroneutral (L) or anionic ligands (X) in the three combinations  is counterintuitive considering that the Auration 5d and have− anions or [L−Au−L]+ cations to give oligomeric anions {[X−Au−X]−}n or cations {[L−Au−L]+}n is even more intriguing as it is a unique case of “anti‐electrostatic association”, that is, it occurs against the Coulomb repulsion of ions. In this sense it resembles the “anti‐electrostatic hydrogen bonding” recently summarized for the anions HCO3−, HSO4−, and H2PO4−.The aggregation of [X−Au−X]The fact that intramolecular aurophilic interactions may contribute significantly to the structural organization of di‐ or polynuclear gold(I) compounds, as well as to the assembly and packing of mono‐ and polynuclear gold(I) compounds in crystals and in solution, has many consequences for the properties of the various inorganic and organometallic systems. In recent years, mainly the solid state has been an area of widespread research activity regarding in particular the photophysical performance of gold(I)‐based materials.10–d10) affording long‐sought gold(II) complexes (d9–d9) or products with mixed oxidation states .The chemical reactivity of gold(I) compounds is also strongly influenced by aurophilic interactions because they lead to arrangements that allow for direct di‐ or multicenter reaction pathways. Scheme For mononuclear gold(I) complexes, related phenomena in solution are rare because the weak aurophilic interactions can easily be overruled by efficient solvation of the mononuclear units. However, at high concentrations of the complexes, and at low temperatures, the number of aurophilicity‐based dimers or oligomers is increased, and the association can be detected by various analytical techniques and in particular by following the UV/Vis absorption and emission properties.H: X=Cl, Br; L=PR3; overall charge 2+).As expected, intermolecular aurophilic contacts are even more pronounced for aggregates of di‐ or polynuclear gold(I) complexes where more than one Au⋅⋅⋅Au contact can be established. Early and more recent examples reflect the growing evidence for these interactions . Red lines were introduced in the formulae here and below to highlight excimer bonding—the focus of this Review.In the present Review, we direct the reader to the specific phenomenon of [Au⋅⋅⋅Au] excimer and exciplex formation, which is strongly supported by an aurophilicity‐based preorganization of the components. In these [Au−Au]* bonding in the excimers is an interesting intermediate between strong ground‐state Au0−Au0 and AuII−AuII bonding on the one hand and weak aurophilic interactions AuI⋅⋅⋅AuI on the other. The incentive for the work carried out in recent years arose from the early observations and studies by the groups of Fackler, Che, and others, but most of the long‐term advances were achieved by the groups of Patterson and Omary, complemented more recently by theoretical and experimental studies by the groups of Yam, Iwamura, Kim, Thiel, Yersin, and several others as presented below.Surprisingly, this phenomenon has been followed up only sporadically in experimental and theoretical studies, and the results have not received much attention even though early examples were first published already some 25 years ago. n}m+.The prototypes of aurophilic bonding were presented in Section 1 (106s1) and gold(II) (5d9), which both feature a covalent Au−Au bond . At the upper end, significant attraction is still observed  near 3.50 Å, which is close to the sum of two van der Waals radii of gold(I) (ca. 3.60 Å).As a first criterion for further characterization, molecular and crystal structures were analyzed in order to determine the relevant range of Au–Au distances. Surprisingly, for gold(I) complexes the lower end of about 2.75 Å is already shorter than the sum of two metallic radii  and not much larger than the distances found in diamagnetic dinuclear complexes of gold(0)  center can entertain more than one Au⋅⋅⋅Au contact and may become part of oligomeric and polymeric aggregates where the monomers are tied together by aurophilic interactions with and without ligand support.D, E). The interaction energies depend strongly on the nature of the ligands, but may reach up to 15 kcal mol−1.All of these structural observations have been confirmed by quantum‐chemical calculations on various levels of sophistication, which were aimed foremost at an estimation of the interaction energy as the most relevant criterion. Calculated energy profiles of the approach of two mononuclear model molecules L−Au−X exhibit shallow, but distinct minima for Au–Au distances in the range mentioned above and are largely insensitive to torsional constraints as exemplified by parallel (eclipsed) or perpendicular  conformations, the latter being only slightly preferred over the former (−1.3)}2 dimer was shown to have a Au–Au distance of 3.0 Å and a bond energy of 13.0 kcal mol−1.These theoretical results are in agreement with the few experimental data obtained in a series of variable‐temperature NMR studies, which cluster between 5 and 15 kcal molThis energy criterion indicates that aurophilic bonding ranks among the weak forces in chemistry, and the closest parallels are found for hydrogen bonding, where interaction energies are in a comparable range. As already mentioned, both hydrogen bonding and aurophilic interactions show a similar structural flexibility regarding contact distances and angles. There is also a degree of freedom in the number of contact partners, meaning in the aurophilicity case that several Au⋅⋅⋅Au contacts can be formed by the reference gold atom in larger aggregates (see above).3.2A–C are enclosed by solvent molecules and the energy of solvation exceeds the energy gained from aurophilic contacts. For that reason, in dilute solutions of electroneutral molecules B in nonpolar or weakly polar solvents, the molecules are not found aggregated as B2 or Bn oligomers, as shown for example, by standard molecular mass determination  or mass spectrometry studies.While for the solid state there are a plethora of examples for the aggregation of mononuclear gold(I) complexes through aurophilic interactions (see above), the situation is different for the solution state, where molecular or ionic units B in the crystals is co‐determined by aurophilic interactions, which are stronger than common van der Waals forces, as a directional element for the assembly. The aggregation of ionic counterparts A and C is largely governed by Coulomb forces favoring sequences of alternating charges +−+−+− (A⋅⋅⋅C⋅⋅⋅A⋅⋅⋅C⋅⋅⋅A⋅⋅⋅C). Other interactions such as π–π stacking or strong hydrogen bonding may also influence the mode of aggregation ruling out any Au⋅⋅⋅Au contacts. On the other hand, there are many cases where aurophilic and hydrogen bonding lend mutual support to a structure of di‐ or multinuclear aggregates.However, with the removal of the solvent, the organization of the electroneutral components 3.2.1− in crystals and solutions of the salts M+[Au(CN)2]−, M2+{[Au(CN)2]2}2−, and M3+{[Au(CN)2]3}3−. In crystals of the alkali salts , the anions are packed in sheets with all gold atoms in a common plane and with the cyanide groups extending roughly perpendicular from this plane above and below. The assembly pattern depends on the size of the counterion, and the Au⋅⋅⋅Au contacts vary across a small range around an average of 3.33 Å.2]n}n− sheet with the most common hexagonal array of gold atoms. As an example of a distorted variant, in crystals of Rb[Au(CN)2], the gold atoms are arranged in a plane composed of four‐ and eight‐membered rings.An important and most widely studied example is the  under high pressures (20 kbar). Extreme red‐shifts of the emission were observed, which are among the largest known for solid‐state compounds.2] in 197Au Mössbauer spectroscopic investigations at low temperature (4 K) and high pressure (80 kbar), which suggested a preference for Au⋅⋅⋅Au contacts in the packing.Already in many publications of early structural work it has repeatedly been assumed that “4[Au(CN)2], which separate the anions in the crystals2]− anions could be studied in the same way as in crystal matrices doped with traces of M[Au(CN)2].3P)2N]+ also no aggregation of the anions occurs.Pioneering work has also included salts with bulky cations, as in NBu13C NMR spectra (with 13C‐labeled cyanide) at various concentrations (in water and dichloromethane at room temperature) did not indicate any major effects of anion aggregation.Early studies of the vibrational spectra of dicyanoaurates(I) provided no evidence for a specific influence of the Au⋅⋅⋅Au contacts on the fundamental characteristics of the anion in solids, and solution IR and −Au]* excimers and exciplexes and a detailed study of their characteristics. Several recent quantum‐chemical calculations have followed up the early experimental work and detailed the picture of the electronic ground‐ and excited‐states, in particular of the dimers and trimers , as presented below.As already mentioned, the luminescence properties of alkali metal dicyanoaurate(I) solids have been in the focus of photophysical studies for several decades.2]− concentration, which allows for dimers, trimers, and tetramers to be studied in separate concentration ranges  and their formation and transformation to be followed. This association explains the observation of significant deviations from Beer's law in the spectra of these solutions. The absorption and luminescence excitation spectra of water or methanol solutions also show a dependence on temperature from ambient temperature to 77 K (in frozen glasses). As expected, an increase in the aggregation of the anions to oligomers was found at low temperature. From the spectral data, both the formation constant and the free energy of formation have been calculated for the dimer: K=17.9 m−1; ΔG=−1.86 kcal mol−1 (295 K). Extended Hückel calculations with relativistic parameters for the dimer (eclipsed/staggered) arrived at Au⋅⋅⋅Au binding energies of 3.04/6.87 kcal mol−1 and Au–Au distances of 3.48/2.88 Å.−5 m (observed for methanol glasses at 77 K). For the dimer in a staggered conformation, MP2 calculations gave an Au–Au distance of 2.960 Å and a ν(Au⋅⋅⋅Au) stretching frequency of 89.8 cm−1.Investigations of aqueous solutions or in polar non‐aqueous solvents have shown that therein the degree of oligomerization increases stepwise with the n oligomers are formed. The slim, rod‐like structure of the anions fits even into the reduced space left between the bulky PTA ligands to establish short Au⋅⋅⋅Au contacts (3.271 Å).If the counterion of the dicyanoaurate(I) anion contains a two‐coordinate gold(I) atom, for example, with the bulky PTA ligand  in [(PTA)Au(PTA)]2−]2 are trapped in supramolecular matrices offered additional means to distinguish the specific characteristics of the dicyanoaurate(I) oligomers.2) with K[AuCN)2] in water, which gave the crystalline tetrahydrate (DNP)[Au(CN)2]2⋅4 H2O. The product contains dinuclear units {[Au(CN)2]2}2− with an eclipsed  conformation with a Au⋅⋅⋅Au contact at the upper limit for aurophilic interactions =3.5108 Å), in agreement with a calculated value for this conformation, which is not the ground state in the absence of a matrix.2 and [Au(CN)2]− are non‐emissive in the visible region, (DNP)[Au(CN)2]2 shows two independent emission bands in the regions assigned to the DPN and the [Au(CN)2−]2 units, the former being a phosphorescence due to the interionic interaction of DPN with the heavy metal atoms.In this context, the design of systems where certain oligomeric units [Au(CN)2−]n can be supported by polyammonium scaffolds such as those provided by polyallylamine hydrochloride polymers, which undergo an ion exchange of [Au(CN)2]− for Cl− in water. The aggregates show tunable luminescence depending on the relative concentrations of the components. With a low supply of anions, their chains may be broken down into smaller oligomers. This process can be followed by the changes in the absorption and emission spectra with concentration.2]− anions has afforded crystalline products in which the anion is associated in symmetrical trimers (J) with Au–Au distances of 3.103 Å and a Au‐Au‐Au angle of 180°.2−]2 with an eclipsed conformation (d(Au⋅⋅⋅Au)=3.310 Å) were again found in the crystalline matrix.Polymeric strands [Au(CN)2]II(NH3)4][Au(CN)2]2.II complex [Ni(NH3)2][Au(CN)2]2, the chains of [Au(CN)2]− anions do not include the nickel atoms. These differences can again be ascribed to relativistic effects, setting, for example, Pt apart from its lighter congener Ni.The structural and electronic characteristics of crystalline dicyanoaurates(I) are strongly influenced by cations such as thallium or platinum, which appear to form heterometallophilic contacts, as in Tl[Au(CN)2]−}n appear in combination with first‐ and second‐row transition metals where the terminal N atoms of the cyanide units act as donor centers for a large variety of elements, including Co, Rh, Cu, Cd, In, and others. Chains of oligomers and polymers [Au(CN)2]−}n with the gold atoms forming angular or zigzag patterns are common in this family of structures.Extended aggregates {− has an angular structure bent at both sulfur atoms. In fundamental work in this area, the anions in crystals of bis(thiocyanato)aurates(I) with alkali or onium cations have been found by X‐ray diffraction studies to form dimers {[Au(SCN)2]−}2 almost exclusively through anti‐electrostatic aurophilic contacts. The two anions of C2 symmetry are associated in a staggered conformation, and the line connecting the two gold atoms coincides with the twofold axis (K). The Au–Au distances vary with the nature of the counterion, but all fall in the narrow range of 3.00–3.24 Å. Interestingly, this also applies to the [NnBu4]+ salt, where the Au–Au distance in the dimer is 3.07 Å. It is only in the [NMe4]+ salt that the anions are aggregated into trimers with a kinked structure . The maxima of the absorption and emission spectra of the compounds (solids at 77 K) vary with the nature of the cation, and the Au–Au distance correlates with the emission energy.In this anion, the thiocyanato ligands are attached to the gold(I) center via their sulfur atom, and the complex [Au(SCN)2]− anions is an important example of the power of aurophilic interactions. The SCN− anion has a hard (N) and a soft donor center (S) that could assist in the assembly of the anions via N→Au or S→Au donor bonds, but these alternatives are not observed. Instead, additional Au⋅⋅⋅Au contacts between the dimers can be found extending the arrangement to chains with a sequence of alternating Au⋅⋅⋅Au⋅⋅⋅⋅Au⋅⋅⋅Au⋅⋅⋅⋅Au distances.The mode of aggregation of the X2, the transannular Au–Au separations are 2.93 Å for X=Cl in the solid state and 3.08 Å for the solution in chloroform, while for X=BF4 the values are 2.90 Å in the solid and 2.97 Å in acetonitrile solution, that is, the solvent is lengthening and weakening the aurophilic interaction.A more recent report describes extended X‐ray absorption fine structure (EXAFS) investigations of a molecule with a flexible ligand carried out in solution in order to demonstrate that the conformation represented by F) may also be in equilibrium with oligomers tied up via intermolecular Au⋅⋅⋅Au contacts (O) depending on the solvent and pH value where the ligands may be deprotonated.Molecules with intramolecular aurophilic contacts . A large number of experimental and theoretical studies were dedicated to this type of assembly.UV/Vis absorption and emission properties have been the main focus of studies of transannular Au⋅⋅⋅Au interactions.Work in this area was later complemented by experimental and quantum‐chemical studies of similar cyclic cationic complexes with P,S donor ligands as further detailed below.44.1excimer was coinedAbout 100 years ago, the formation of spectroscopically observable diatomic molecules from electronically excited atoms was first achieved for gaseous mercury and the noble gases, which previously had been known as notoriously inert species.I, Pt0, PtII, and AuI, structurally privileged complexes have also shown a tendency towards excimer formation.exciplexes. Oligomeric exciplexes, some originating from weakly associated ground‐state dimers or oligomers, are also known.Finally, amongst compounds of the transition metals, and in particular those with Rh0 and AuII examples (see above): Two‐coordinate AuI atoms can also become covalently bound exclusively in the excited state. Preorganization through aurophilic interactions [Au⋅⋅⋅Au]  in the ground state assists in the formation of AuI−AuI chemical bonding in the corresponding excimers, [AuI−AuI]*, upon excitation.It therefore appears that covalent bonds formed by atomic orbital overlap between two gold atoms are not limited to Au10–d10 interactions of transition‐metal systems are repulsive. Yet, as already mentioned, metallophilic interactions of a dispersive nature tend to hold two gold atoms with this configuration together. Such interactions can only be accounted for, theoretically, by invoking excited‐state orbitals, that is, by using wave function methods in computational chemistry.10–d10 interactions by photochemical activation seems a logical consequence.According to a metal centered (MC) LCAO approach, metal–metal closed‐shell d8–d8 and d10–d10 systems can be realized by electron excitation is not new. It was proposed and explored by Gray and co‐workers during the 1970s and early 1980s for RhI and PtII complexes. Pairs of metal atoms bearing several monodentate ligands closely approach each other by metal–metal attraction in concentrated solutions,I−RhI interactions in the excited state was obtained by solution resonance Raman spectroscopy.The idea that covalent bond formation in closed‐shell d4.24.2.12(P^P)2]2+ (P^P=bis(dimethylphosphino)methane, dmpm; bis(dimethylphosphino)ethane, dmpe; bis(diphenylphosphino)methane, dppm); [Au2(P^P)3]2+ (P^P=dmpm); and [Au3(P^P^P)2]3+ (P^P^P=bis(dimethylphosphinomethyl)methylphosphine, dmmp).N), provided the impetus for related research into excimer formation to become an independent worthwhile intellectual pursuit.Inspired by the pioneering work of the Gray group, investigations led by Ludwig,I systems in solution showed that excitations resulting in luminescence are metal‐centered (MC).z2atomic orbitals of the two gold atoms  were designated dσ*. The LUMO orbitals, described as pσ, were formed by the combination of almost pure 6pz atomic orbitals.Early absorption and magnetic circular dichroism studies of the dinuclear dmpm and dmpe Auα‐SW calculations for bis(diphosphinomethane) (dpm) model complexes, [Au2(H2PCH2PH2)2]2+ , with eight‐membered rings in the elongated chair conformation, with relativistic corrections applied. Unfortunately, this work failed to explain the AuI⋅⋅⋅AuI association, and the relative energies of the unfilled orbitals were unreliable. Yet, the results agreed with more intuitive approaches. Despite the lack of solid theoretical guidance, the authors of these publicationsx2-y2‐based, MOs in the transitions, but later, with more experimental and theoretical evidence at their disposal, they accepted the general view of dσ*→pσ excitation and pσ→dσ* emission processes.Fackler and co‐workers−1) Stokes shift between the absorption and emission maxima.The one‐electron excitation from an antibonding to a bonding MO formally amounts to an increase in bond order of one, and the formation of a σ bond between the two gold atoms. The resulting molecular distortion (mainly the shortening of the Au–Au distance) is believed to be responsible for the large (ca. 17 000 cm3[dγ*1pσ1] state is proposed again for the trinuclear complex [Au3(dmpm)2]2+ (in acetonitrile), this excited configuration still implies a AuI−AuI bonding situation with pz–pz orbital overlap.2Au units results in a narrower dσ*–pσ energy gap while E(dσ*) increases; [Aun+1] units absorb at lower energy than [Aun] units.Though emission from the low‐lying 2(dppm)2]2+ complex is quenched. In redox reactions N,N,N′,N′‐tetramethyl‐p‐phenylenediamine (TMPD) served as a reductant and N,N′‐dimethyl‐4,4′‐bipyridinium  as an active oxidant:The relatively long lifetime of the triplet excited state was exploited by Che and co‐workers2(dppm)23+]*/[Au2(dppm)22+]* was estimated at −1.1 V against a saturated sodium chloride calomel electrode. Yam and co‐workers2(dmpm)23+]*/[Au2(dmpm)22+]*.The standard electrode potential of the activated couple [Au2(dppm)2]2+ is a photocatalyst for C−C bond formation with the substrates PhCH2Cl and CH3(CH2)4Br.Y2 2]−, Cl−, I−; formula N, R=Cy), subsequent to excitation, exhibit one or two triplet→singlet phosphorescence emission bands in the near‐UV and visible regions.3CN solution, all of the complexes with non‐coordinating counterions exhibit an intense, low‐energy (ca. 500 nm) emission whereas the high‐energy phosphorescence band (ca. 360–370 nm), when present, is weak. Precisely the opposite is true for the same complexes in the crystalline state. With coordinating Cl− and I− counterions, no high‐energy band is observed in solution or in the solid state. The two well separated luminescence bands have been assigned as originating, respectively, from 3[Au2(dcpm)22+]* as the lower‐energy variant of the initially formed 1[Au2(dcpm)22+]* excimer—affording the so‐called intrinsic band—and from solvated exciplexes, [Au2(dcpm)2(CH3CN)x2+]*, and/or exciplexes bearing one or more counterions, [Au2(dcpm)2(Y)nn)+. Exciplex formation of long‐lived 3[Au2(dcpm)22+]* with halides  can be straightforward complexation * and solvent makes such complexes less accessible for C−H bonds of substrates where the interaction involves an inner‐sphere mechanism.−Au‐bonded [Au2(dpim)2]2+ complexes (dpim=2‐(diphenylphosphino)‐1‐methylimidazole) confirmed the dependence of the emission energy on the coordination ability of the counterion in accordance with Che's exciplex proposals.As mentioned before, exciplex formation between complexes 3(dcpm)2]Y3  in the solid state and in CH2Cl2 solution exhibit very much the same relaxation behavior as their dinuclear counterparts described above.− and SCN−—are, however, red‐shifted for trinuclear complexes and found in the respective wavelength regions 442–452 and 558–634 nm. DFT calculations support a previous result−Au exciplex bonding. Notably, no C−X bond rupture of the haloalkane solvent occurred during all of the processes in solution (see below).The linear trinuclear complexes [Au2(dcpm)2](ClO4)2 directed at the lowest energy, dipole‐allowed absorption band at about 277 nm in solution involving the generally accepted 1[dσ*pσ] excited state. By using various formalisms and the Condon approximation, it was established that the dσ*→pσ excitation is consistent with the Raman results. The change in the Au−Au bond length from the singlet ground state  to the first vibrationally relaxed singlet excited state amounts to 0.11 Å, giving a bond length of 2.81 Å for the double‐bridged excimer. The AuI−AuI σ‐bond, presumably formed by p–p overlap, is somewhat longer than the ca. 2.6 Å distance separating gold atoms in dinuclear Au0 and AuII complexes, for which a larger contribution by s‐orbitals in the bonding was invoked.Che and co‐workers2(dcpm)2]2+ complexes of copper, silver, and gold have confirmed that M−M bonds in all three complexes are strengthened upon MC excitation.Cu−Cu>ΔAg−Ag>ΔAu−Au. In the case of gold complexes, solvent complexation in the activated state apparently stimulates Au−Au bond tightening, whereas coordination by a third strong ligand donor as in complexes of the stoichiometry [M2(dmpm)3]2+, where the coordination number has increased from CN=2 to CN=3, effects Au−Au bond extension or even cleavage, both in the ground and excited states.Comparative absorption and resonance Raman spectroscopic studies of [M2(P^P)2]2+‐ and [Au2(P^S)2]2+‐type complexes were published in the early 2000s by Che and Zhang2PCH2PH2, dpm), C‐mercaptophosphinomethane , and C‐(methylsulfido)phosphinomethane  were employed2]2+ systems, and the formal 5d106s0 closed‐shell configuration of each participating gold atom is modified, allowing additional physical bonding forces to become operative. This intervention, combined with instantaneous London dispersion forces, necessitates, as mentioned earlier, the use of configuration interaction methods to correctly describe the aurophilic interaction in the ground state. The authors used an MP2‐based approach to optimize the ground‐state structures. To describe the excited states, the single‐electron configuration interaction method (CIS) was employed, which possibly suffices, in view of the more important role of orbital overlap compared to the ground state. To theoretically mimic the roles of solvent and counterions, respectively, separate calculations were carried out for the model complexes [Au2(dpm)2(CH3CN)2]2+, [Au2(mpm)2(CH3CN)2]2+, [Au2(mspm)2(CH3CN)2]2+, [Au2(dpm)2](ClO)2, and [Au2(mpm)2](ClO)2; the latter two simulate the solid‐state behavior of [Au2(P^P)2](ClO4)2‐ and [Au2(P^S)2](ClO4)2‐type complexes. The proposals made by Che and co‐workers regarding the presence and position of two prominently emitting triplet states were found to be realistic. Relative term energies for the proposed excited states of the excimer [Au2(dcpm)22+]* and its exciplexes formed by association with solvent molecules were approximately reproduced by the modelling studies.Two significant theoretical papers on [Au2(P^P)2]2+ complexes have shown that excitation in the UV region is MC, affording a 5dσ*16pσ1 electronic configuration. Covalent bond formation in the excited state is initially accomplished by pz–pz atomic orbital overlap. Two lower‐energy, long‐lived triplet states are predicted, the higher of which (the intrinsic state for an unsolvated complex) emits in the near‐UV region and corresponds to a 5dσ*1(sp)σ1 electron configuration. The stronger Au−Au bond in this instance is formed by overlap of significantly hybridized 6s and 6p atomic orbitals. Finally, linearly combined 6s orbitals are solely involved in the Au−Au bond formation for the lowest‐energy triplet state, 3[5dσ*16sσ1], explaining the appearance of short Au−Au bonds. This state corresponds to exciplex formation by complex–solvent and/or complex–counterion interactions. Overall, the bond contraction upon electron excitation was calculated to be much more significant than estimated from results of Raman experiments. According to Che and co‐workers,−Au interaction strengthens, and the solid‐state emission is red‐shifted, similar to the situation calculated for the assembly when solvent molecules are added to the model complex. Concurrent to the strengthening of the Au−Au interactions by excimer and exciplex formation, the metal–ligand bonds  are weakened and elongated. In Scheme 2(dcpm)2]2+ are combined with theoretical information pertaining to related model complexes in a Jablonski diagram, showing the trajectory of the [Au−Au]* bond length variation along the reaction coordinate. We mention that in model complexes of the general type [Au2(HSCH2PH2)2]2+, the lowest‐energy emission has a small MMLCT component.The computational results of selected [Au2(dcpm)2](ClO4)2 as a common process that proceeds at an ultrafast rate, with no solvent or phase intervention. The triplet state decays with a lifetime of 4.3 μs to the ground state. When the gold complex is dissolved in CH3CN, subsequent fast exciplex formation by sequestering of solvent molecules takes place (time constant 4.5 ps). This process illustrates the tendency of activated AuI complexes to increase their coordination number above 2. With CH2Cl2 as the solvent, the outcome  and time‐resolved emission (TRE) spectroscopic study,I⋅⋅⋅AuI‐associated complexes, Au−Au bond shortening is the most important distortion mode in the excited state, Au(PR3)3‐type complexes are rearranged upon excitation by a symmetry change from trigonal to T‐shaped.Whereas in Au4.2.3C^P ligand in coordination and spectrochemical contexts are the two exo phosphine groups, one of which is dangling in P, while all three donor groups are coordinatively involved in the linear trinuclear Au3 chain found in complex Q, [Au3L2](OTf)3, which is reminiscent of the [Au3(dmpm)2]3+ chelates investigated by Yam and Wong,Q exhibits a band of an intense, almost pure MC absorption in solution (λmax=345 nm) in addition to other bands of higher energy with ligand orbital involvement. The important role of the dσ*1pσ1 configuration and significant Au−Au covalent bonding in the excited state has been demonstrated by resonance‐enhanced Raman spectroscopy following the MC transitions, showing the excited‐state vibrations of the Au−Au bonds. Here we mainly concentrate on the results for Q. This compound displays a narrow, intense, blue‐violet radiation band at 446 nm, essentially independent of solvent polarity, state , and temperature, and with the nature of an MC 3[5dσ*6pσ] triplet state.P in the excited state, coordination of the dangling phosphine group may contribute to the stabilization of the emitting triplet state. The shortening of the Au–Au distances in the excited state of compound Q seems unambiguous, despite the use of rigid ligands. Quantitative comparison between ground‐ and excited‐state distances is not really meaningful in view of the inadequacy of DFT calculations for the ground state.An unsymmetrical dimetallacyclic complex with carbene/phosphine‐functional ligands has recently been reported by Danopoulos, Braunstein, and co‐workers.4.2.4R; double‐bridged, complex form S) as well as simpler, mononuclear, R3PAuSR′‐type complexes have been studied experimentally by various research groups.−Au]* bond formation. Under favorable, idealized conditions for Au−Au bonding, the two gold atoms are positioned in close proximity, and the initial lowest‐energy excitation is qualitatively described as S(pπ)→pσ electron transfer ,z orbitals in the Au2 unit.1[LMMCT]* and 3[LMMCT]* states and hence about progressive excimer or exciplex formation is available.Luminescent, binuclear, phosphine‐bridged gold(I) complexes that also contain thiolate ligands (SCH2S)], [Au2(H2PCH2S)2], and [Au2(HSCH2S)2], by using MP2 and CIS methods. Their results confirmed the interpretation given above regarding Au−Au bond formation and strengthening in the excited state subsequent to S(pπ)→sσ and/or pσ electron promotion. Although the assignment of the lowest‐energy emissions in the three complexes is less straightforward, they are all assumed to originate from triplet metal‐metal localized states.Importantly, structural studies in combination with luminescence spectroscopy have shown that in various phosphine‐thiolate complexes of AuT and U were investigated by experimental  and computational (time‐dependent DFT) means.The mode according to which soft heteroatom‐donor ligands contribute to covalent Au−Au bond formation at the time of UV/Vis electron excitation has been placed on a firmer footing by the results of Saillard, Liu, Boucekkine, and co‐workers.T and 3.267 Å for U are characteristic of these complexes. The structureless, lowest‐energy excitation and emission bands exhibit their low‐temperature (77 K) maxima, λmaxexc and λmaxem, in solid 2‐MeTHF at 434 and 593 nm for T, and at 471 and 565 nm for U. Solution spectra are all hypsochromically shifted. To a first approximation the excitation and emission processes can again be attributed to single‐electron transfer between the HOMO and LUMO. The former orbitals, E(pπ), are constructed by linear combinations of lone‐pair‐containing atomic orbitals at Se or S but also have 12–16 % Au d‐orbital character. The LUMO for T carries a dominant contribution from gold p orbitals whereas the LUMO of U is composed of 35 % gold  complemented by 46 % sulfur character.Very weak Au⋅⋅⋅Au interactions at intramolecular distances of 3.387 and 3.456 Å for I−AuI bond formation but that soft heteroatom‐donor ligands may also be important electron sources for such binding. On the other hand, the proposed LMMCT designation for the excitation processes perhaps underestimates the significant involvement of heteroatom orbitals in the LUMO acceptor orbitals. Rehybridization along the reaction coordinate is predicted by NBO analysis.During excitation, electron density is transferred from a non‐bonding to a bonding MO localized between two gold atoms; the descriptive σ p–p overlap is responsible for Au−Au bond formation (bond order≤0.5). Results of resonance Raman spectroscopy investigations have clearly confirmed Au−Au stretching motions in the resulting excited singlet and triplet states, which are completely absent in the ground states. According to DFT computations, the distance between the two gold atoms in the triplet excited state contracts by up to 25 % compared to the ground state. These results provide convincing evidence that not only Au⋅⋅⋅Au aurophilic interactions impact positively on Au4.34.3.12]− anion serve as prime and prototype examples of linear mononuclear AuI complexes participating in intermolecular excimer and exciplex formation upon excitation. Several early spectrophotometric investigations have shown that solutions of these compounds exhibit photoluminescence in concentrations ≥0.01 m. This result has been attributed to oligomerization in solution, a process ensuing from cooperative aurophilic interactions (see above).Compounds containing the [Au(CN)2−]n* , the progressively lower energy bands may be attributed to growing oligomers  formed by the successive addition of monomers to the oligomer chain .In an important and directional paper, Patterson, Fackler, and co‐workersIn the focus of the investigation were the changes in Au−Au bond length and strength that parallel the spectroscopic transitions from higher‐ to lower‐energy emission bands. It should be noted that exciplex formation by engagement with solvent, as earlier proposed for double‐bridged digold phosphine complexes in the excited state, has been ruled out because the solution‐ and solid‐state emission bands are similar in  shape and energy.2−]2 in the staggered dimer conformation as a model compound (formula I above). Upon excitation and excimer formation, the calculated Au−Au distance decreases from 2.96 Å to 2.66 Å. Simultaneously, the calculated Raman active stretching frequency, νAu−Au, almost doubles, and the force constant increases by one order of magnitude. The covalent Au−Au bond in the excited state is, again, not much longer than in well‐known unsupported AuII−AuII complexes linked by gold–gold single bonds . Extended Hückel excited‐state calculations distinctly show that the [AuI−AuI]* bonds increase in strength with increasing oligomerization along the series [Au(CN)2−]n: the exciplex [Au(CN)2−]3*, for example, is more strongly bonded (lower triplet energy) than the excimer [Au(CN)2−]2*. In addition, the Au−Au bonding is influenced by the geometry  and conformation  of a particular exciplex. These aspects are addressed in greater detail below. Interestingly, although the [Ag(CN)2]− complex photochemically generally mimics its heavier analogue, the Au⋅⋅⋅Au aurophilic interactions are stronger than the Ag⋅⋅⋅Ag argentophilic interactions in the ground state while in the corresponding excited state, the Ag−Ag interaction is stronger than the Au−Au interaction.Some of the assumptions and proposals mentioned above have been scrutinized in the same paper by MP2 chemical computation using [AuCN)2] was undertaken in Patterson's laboratory in 1986.2−]n* present in pure K[Au(CN)2] and K[Au(CN)2]/KCl doped crystals.The first study of luminescence in pure single crystals of K[Au(CN)2] and Cs[Au(CN)2] leads to the formation of sheets of gold atoms  comprises essentially 6pz orbitals, mixed with small contributions of ligand orbitals. Spectroscopic transitions are then simply described as electron transport from VB to CB or vice versa. A more complete description of spectroscopic states requires, amongst other aspects, a consideration of electron–electron (term generation), hole–electron , and exciton–lattice  interactions. The second‐order exciton–lattice interaction leads to a reduction in Au−Au distance and stronger bonding within the chains or sheets of gold atoms. A detailed theoretical description is not yet available for the [Au(CN)2]− layers in M[Au(CN)2] crystals, but has been applied to quasi one‐dimensional Mn[Pt(CN)4]⋅x H2O compounds .Association of the anions in crystalline K[Au(CN)s Figure .98 To a 2] and Cs[Au(CN)2] at room temperature.−1 kbar−1 and −200 cm−1 kbar−1, are observed. The shifts are related to the relative crystal compressibility. At a microlevel, the effect of increased pressure stems from shrinking Au−Au bonds in the excited state compared to the ground state; the band gap closes and the band energy is lowered. The broad peak shown by Cs[Au(CN)2] is resolvable at 5 K into two dominant emission peaks. The one at lower energy (454 nm) has the properties of a localized state most likely involving a cluster of only a few [Au(CN)2]− complex units in analogy to findings for Mn[Pt(CN)4] examples. The one at higher energy corresponds to the delocalized cluster states {[Au(CN)2]n}n−. The relationship of the emission energies with the Au−Au distances in the crystals is comparable to effects reported for the exciton–lattice interaction in, for example, the one‐dimensional arrays of complex anions in crystals of Ba[Pt(CN)4]⋅4 H2O.Single, broad emission peaks  have been recorded for K[Au(CN)2]) concentration within KCl crystals affords higher oligomers and stronger Au−Au bonding in the excited state, resulting in red‐shifted emission bands.An increased dopant (K[Au(CN)2]−‐doped materials strongly correlate with the photoluminescence bands of the different crystals obtained from sample batches of varying dopant concentrations. This result indicates that in the crystal, the [Au(CN)2−]n ions are found in different environments, depending on the value of n. Each of the ground‐state oligomers and the corresponding exciplexes that are formed upon excitation experience Au−Au single σ bond formation, which manifests itself in a particular emission band from a triplet excited state. It should be kept in mind that two or more emission bands may overlap when more than one exciplex with a rather similar binding energy is present.The numbers and frequencies of Raman bands observed for crystalline 2}2− units.2]− salts. At temperatures above 50 K, owing to the presence of the DNP2+ cations, rapid quenching by means of electron transfer occurs, similar to the consequences of the reaction between 3[Au2(dppm)22+]* and MV2+ [Eq. (2)].Crystals or powders of the compound (DNP)[Au(CN)2]− complex solutions and the type of excimer/exciplex formation responsible for luminescence properties, but they also cast much new light on the ultrafast structural dynamics of such activated chemical processes subsequent to initial excitation.Five recent papers not only support almost all of the results obtained in Patterson's laboratory regarding the origin and assignment of emission bands for more concentrated [Au(CN)−Au bond formation of the staggered dimer [Au(CN)2−]2 in the excited state has been clarified by femtosecond and picosecond time‐resolved transient absorption (TRTA) spectroscopy. Predominantly dimers are present in very dilute [Au(CN)2]− solutions (ca. 0.04 m) and are the only species undergoing excitation in the near‐UV region (ca. 270 nm). Relaxation transitions as well as the time constants for subsequent processes have been determined.The ultrafast dynamics of Au1 singlet state present in the femtosecond time region reflect the rapid formation of a rigid covalent Au−Au bond. Further Au−Au bond contraction occurs during subsequent intersystem crossing into a transient, low‐energy triplet state of the dimer T1 (time constant 0.21 ps). This T1 steady state slowly decays (emission at 330 nm) with a time constant of 26 ps. No further oligomerization in the excited state occurs under the selected experimental conditions.Upon photoexcitation Scheme , coheren2−]n (n=2–5) have been carried out by Dolg, Thiel, and co‐workers at the MP2 level , and at the DFT, RI‐CC2, and MSCASPT2 levels of theory (excited states).1pσ1 and dσ*1pπ1 of the eclipsed dimer have very similar energies in both the S1 and T1 states, and may theoretically also contribute to the absorption and emission bands. The calculated Au−Au bond lengths for the two conformations in both the activated singlet and triplet states do not differ significantly; they are both about 0.3 Å shorter than in the corresponding ground states. As the experimental results for the dimeric complex are in agreement with the proposed structural dynamics of the staggered isomer, the rather complex spectroscopic transitions calculated for the eclipsed form are not discussed further.Electron structure calculations for the oligomers [Au(CN)2−]n oligomers, particularly those of the trinuclear complex (n=3). Iwamura, Tahara, and co‐workers2−]3 from other interfering photochemical transitions, it was concluded that at least five different kinetic events and five complexes are required to fully explain the absorption and emission bands. Three time constants for successive transitions were determined. A decisive and coherent oscillatory motion identified in the femtosecond region has provided strong evidence for ultrafast Au−Au bond formation in the activated state.Following in the footsteps of Patterson, Fackler, and co‐workers, and relying on the latest applicable experimental and theoretical characterization approaches, other research groups have delved deeper into the solution photophysics and photochemistry of [Au(CN)2−]3 present in solutions of a given concentration under ambient conditions features a bent (non‐linear) ground‐state structure that remains unchanged in the Franck–Condon region upon excitation but relaxes immediately into a similar but covalently bonded structure. The Au−Au bond tightening is apparently completed during this vibrational relaxation (step 1). The singlet excited state S1 is fluorescent. Intersystem crossing (step 2) to form 3a[Au(CN)2−]3* is complete within 500 fs. The measurable second kinetic component (step 3) comprises simply the unfolding of the Au3 frame into a staggered linear arrangement in 3b[Au(CN)2−]*, which is then followed by oligomer growth whilst maintaining the linear arrangement of the gold atoms (step 4). The lowest energy triplet state loses energy by phosphorescence. Transient energy changes based on emissive bands and numerical time constraints have been experimentally determined, but the assignment of diverse structural changes rests on hypothesis and calculation.All of the proposed spectroscopic transitions with their time constants and the concomitant structural changes are illustrated in Schemes 2]− oligomers in aqueous solution are influenced by the molecular environment in the excited state. Surprisingly, the [Au(CN)2−]n* (n≥4) oligomers decay by dissociation into smaller excimers or exciplexes but interactions with tetraalkylammonium cations such as Et4N+ were found to stabilize the larger oligomers and enhance the lower‐energy emissions.The emission wavelengths (energies) and lifetimes of 3* 2]− dimer (see above), Fang, Dolg, Thiel, and co‐workersWorking at the same level of theory that had been used for interpreting the photophysics of the [Au(CN)2]− complex systems upon, and subsequent to, excitation by an X‐ray free‐electron laser, which allows ultrafast reactions to be explored. The great advantage of TRXSS over TRTA is its sensitivity towards the global molecular structure in solution. The technique is therefore well suited to directly characterize the structures of individual dominant complex transient species with sub‐Å spatial resolution. With time limits also determinable at the sub‐ps level, information on bond contraction, covalent bond formation, bent‐to‐linear transformation, and oligomer growth can be provided along a chosen reaction coordinate.Motivated by the contrasting results described in the previous paragraph, Kim and co‐workers1→T1 (trimer) ISC within 1.6 ps before intermolecular interaction occurs, and comprises a further tightening of the Au−Au−Au bonds; C) the kinetic time constant for the spectroscopic T1(trimer)→T1(tetramer) transition by Au–Au atomic orbital overlap is 3 ns; and D) 100 ns are then available for total relaxation to the ground state, T1(tetramer)→S0.The results reported by Kim and co‐workers are in full agreement with those obtained earlier by chemical computation.2−]3 trimer occurs within 500 fsthe bent‐to‐linear transition of the 3 trimer is independent of excitation wavelengththe mechanism of Au−Au bond formation in the 3 upon Au−Au bond formation. The Au−Au breathing vibration has been measured at approximately 90 cm−1. The initial rapid growth in resonance Raman enhancement corresponding to Au−Au bond formation and intersystem crossing is followed by a gradual frequency upshift over a few picoseconds supporting a continuous structural change on the triplet potential energy surface such as the proposed bent‐to‐linear transition. Tahara and co‐workers have also discovered that even under almost ideal conditions for trimer excitation, time‐domain Raman measurements are complicated because the presence of an excited tetramer might have an impact on the contrasting X‐ray solution scattering results described above.In their most recent contribution, Tahara and co‐workers4.3.22)]− complexes in solution and in doped crystals have served as inspiration for investigations into the luminescence of M[Au(SCN)2] complexes in the solid state and in frozen solutions.+=K+, Rb+, nBu4N+, and Cs+. The major emission band is red‐shifted in frozen solutions compared to crystalline material. A shift to lower energies of the same band is also found with increasing size of the selected counterion. Notably, Ph4P+ salts, in which the [Au(SCN)2]− units are isolated from one another in the solid state, exhibit no gold‐centered emissions. A similar result was previously reported for the cyanide counterpart, nBu4N[Au(CN)2].The groundbreaking results of Patterson, Fackler, and co‐workers on excimer and exciplex formation of [Au2−]2 as the model system (formula K above). This dimeric unit is realistic as it is present in crystalline nBu4N[Au(SCN)2]. Excimeric Au−Au bonding in the excited state is predicted to occur concomitant with a significant decrease in bond length of 0.2–0.3 Å (depending on the level of theory employed). On the basis of calculations for aggregates in the gas phase that show a too large red‐shift when the dimer is oligomerized further, the authors hypothesized that discrete dinuclear excimeric units are mainly responsible for the observed luminescence. Such excited dimers, [Au2(SCN)42−]*, are then present in crystals of the various salts, independent of whether the anions are arranged as dimers, trimers, or chains in the ground state of extended structures in these solids. An influence of cation size on the spectra has been noted. The involvement of counterions is related to unspecified distortions and not to exciplex formation because the larger cations are more influential regarding their bathochromic effect. Most likely, the larger the counterion, the fewer constraints are placed on the photoinduced structural change in the excited state. Frozen solutions allow more freedom than solids.The high‐energy emission corresponds to an emitting excited singlet state (<500 nm), and the other band (>500 nm) arises from a T→Soccurs over a longer range than that in the dimer”.the spectroscopic features […] are a consequence of the supramolecular organization of molecules within the solids”. Exciplex formation and structural distortion, nevertheless, remain essential features of the excited‐state dynamics in all of these complexes (see Section 4.3.4 below).A “dimer hypothesis” has been contradicted in another study involving neutral complexes of the generic type [(RNC)AuX]. The excited‐state distortion increases and the emission energy decreases when the Au−Au bond shortening “4.3.3λmax>500 nm) at 70 K of crystalline [(Et3P)AuCl] has been attributed to gold‐centered transitions. DFT and ZINDO calculations support this hypothesis. The luminescence is completely quenched in solution.The low‐energy luminescence (3NBH2MH2)2Au]AuCl4  have been studied in the solid state.1→S0 intersystem crossing  may be manipulated: Decreasing the temperature manifests itself in a shortening of the ground state Au–Au separation; the orbital overlap in the excited state is enhanced, the band gap decreases, and a red‐shift ensues. The effect of temperature on the Au–Au distances in linear chains of gold complexes in solids to a certain extent mirrors that of increasing hydrostatic pressure as discussed above (Section 4.3.1).The emission spectra of the homoleptic, aurophilically associated cationic complexes [(Me2−]n* and [Au(SCN)2−]n* (n≥4) in solution.Regardless of the remarkable progress that has been made in understanding the photophysics and chemical transformations of excimers and exciplexes of mononuclear gold(I) complexes preorganized by aurophilic contacts, a number of issues are still unsettled and deserve further attention. These include the role of the cation size and charge in determining the structure and energy of the excited states and their lifetimes in solids and ionic liquids, the excimer characteristics arising in specific positions of a solid matrix and in one‐ or two‐dimensional arrays of gold(I) centers, and details of the relaxation profiles of * excimer fragment existing in a long‐lived triplet state appears as an active center upon irradiation of the reaction mixture with tunable light sources as proposed in the corresponding catalytic cycles. Applications in total synthesis ((±)‐triptolide in Barriault's group;The pioneering investigations of Che and co‐workers into the use of photo‐activated, phosphine‐bridged, dinuclear gold(I) complexes  complexes.Over the last 30 years, gold chemistry has been identified as a research field where for a plethora of compounds the formation and relaxation of excimers and exciplexes can readily be observed both in the solid state and in solution. This abundance is due the spontaneous aggregation of linear, two‐coordinated gold(I) complexes through side‐on aurophilic interactions. In these aggregates, the gold atoms are held in close contacts with Au–Au distances of approximately 3.0 Å. Upon UV/Vis excitation, these Au⋅⋅⋅Au contacts become significantly shortened, indicating the formation of covalent Au2]→[Au2]*, which leads to a series of singlet and triplet excited states without direct involvement of the ligands. The relaxation is generally manifested qualitatively by luminescence effects, which make the process immediately obvious and allow for detailed quantitative investigations by time‐dependent experiments. Excitation is associated with significant structural changes regarding the bonding of the metal atoms. By contrast, when the excitation involves electronic states of the ligands, that is, when the process is not strictly metal‐centered, comparable effects on the Au–Au bonding are usually less pronounced or absent.In typical examples, the UV/Vis excitation is a metal‐centered process [Au2]−, which is associated by aurophilic contacts both in the solid state and in solution. Depending on the concentration in solution or on the doping concentration in solids, dimers, trimers, and tetramers can be observed, and their transformations into excimers and exciplexes have been followed by picosecond/femtosecond time‐resolved emission and absorption spectroscopy and femtosecond solution X‐ray scattering. Resonance Raman spectroscopy has been used as an additional spectroscopic tool to characterize the Au−Au bonding in the [(NC)2Au−Au(CN)22−]* excimer.Particularly detailed information on the energy profiles of excimers and exciplexes has been compiled for the dicyanoaurate(I) complex [Au(CN)2]− have given similar results, indicating that the characteristics are very general for small gold(I) complexes.The experimental work has been complemented by extensive quantum‐chemical calculations, which have given deeper insight into the structural characteristics and photo‐induced dynamics of the excited states. Studies of the di(thiocyanato)gold(I) complex 2+ complexes produce excimers, which are key intermediates in photoredox binuclear gold catalysis for organic synthesis.The second area where gold(I) excimers have been found to be very common are dinuclear gold(I) complexes with a cyclic structure in which the intramolecular aurophilic contact is supported by bridging ligands. Upon UV/Vis excitation, the transannular Au⋅⋅⋅Au contact in, for example, an eight‐membered dimetallacyclic compound is shortened to produce a bicyclic structure where the newly generated AuThe conclusions drawn from the data accumulated in experimental work have also been confirmed in quantum‐chemical calculations, which have provided estimated characteristics of short‐lived intermediates and transition states. In polynuclear compounds with gold atoms ordered in chains by multifunctional ligands offering different donor atoms, the photophysical performance of their excitons can be tuned by the choice of the ligand characteristics.−Ag binding in the excimers was found to be even stronger, probably owing to the preference of silver(I) for higher coordination numbers, which supports the bonding in exciplexes with three‐ or four‐coordinate metal atoms. This observation shows that strong relativistic effects support more strongly the metallophilic bonding of gold(I) than of silver(I) in the ground state, but are less important for the excited states of the two coinage metals. There is still very little information on excimer formation in mercury or thallium chemistry, where metallophilic bonding to date has played a minor role. By contrast, as mentioned above, the earliest examples of excimer formation by metal complexes were found with platinum(II), where side‐on Pt⋅⋅⋅Pt contacts are formed linking a pair of square‐planar‐coordinated metal atoms thus providing the precursors for excimer formation.Selected examples of silver(I) analogues have also been probed regarding the formation of excimers, and for almost all of them, similar excitation processes have been confirmed. Even though argentophilic interactions in the precursor aggregates are generally considered to be weaker than in the gold analogues, the AgThe authors declare no conflict of interest.Hubert Schmidbaur is Professor Emeritus at the Technical University of Munich (TUM), Germany. After his studies of chemistry at the University of Munich (LMU) he held positions at the universities of Marburg and Würzburg and had numerous appointments abroad. Following work in diverse fields including the chemistry of silicon and phosphorus, π‐complexes of main group elements, the bioinorganic chemistry of magnesium and others, he has dedicated much of his research to the chemistry of gold, for which he received many prestigious awards.Helgard Raubenheimer is Professor Emeritus at the University of Stellenbosch (SUN), South Africa. He studied chemistry at SUN and later held a chair at the Rand Africaans University in Johannesburg before he returned to SUN as Head of the Department of Chemistry and Polymer Sciences. He spent sabbaticals with E. O. Fischer and H. Schmidbaur at TUM and with D. Seebach at ETH Zürich. His research focused on carbene complexes of the transition metal elements, concentrating in recent years mainly on gold chemistry, which earned him honors in South Africa and abroad.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


This method enables the simple synthesis of conjugated and halogenated enynes in yields of up to 90 %. Notably, quantum chemical calculations reveal an exceptional interplay between the place of the attack at the chloroacetylene: No matter which C−C bond is formed, the same enyne product is always formed. This is only possible through rearrangement of the corresponding skeleton. Hereby, one reaction pathway proceeds via a chloronium ion with a subsequent aryl shift; in the second case the corresponding vinyl cation is stabilized by a 1,3‐chlorine shift. 13C‐labeling experiments confirmed that the reaction proceeds through both reaction pathways.Haloalkynylation reactions provide an efficient method for the simultaneous introduction of a halogen atom and an acetylenic unit. For the first time, we report a gold(I)‐catalyzed haloalkynylation of aryl alkynes that delivers exclusively the  One way or another: A gold(I)‐catalyzed haloalkynylation of aryl alkynes was developed that delivers exclusively the cis addition product. This method enables the synthesis of conjugated and halogenated enynes in yields of up to 90 % yield. Notably, attack at the chloroacetylene can occur at either of two carbon atoms, but owing to rearrangement of the corresponding skeleton, the same enyne product is always formed. The use of an appropriate concentration of the chloroarylacetylene 1 a is essential since higher concentrations accelerate the dimerization,1 a and 11 a) and 5 mol % [JohnPhos(AuNCMe)]SbF6,1H NMR spectrum of the crude product shows no significant formation of byproducts. An analysis by one‐ and two‐dimensional NMR spectroscopy indicates that the reaction product is the conjugated cis‐addition product 12 a .For investigation of the haloalkynylation reaction, chloroarylacetylene 11 a to 1.5 increased the yield of 12 a, so this ratio was initially kept for further catalyst screening (entry 2). Starting from JohnPhos‐type ligands, we first varied the counterion1 a and 11 (entries 17–19) showed that the ideal ratio of 1 a and 11 is 1:2 .Raising the equivalents of 11 has no significant impact on the yield (12 a to 12 c). When the alkyne 11 bears a substituent at the para position of the aryl unit, the yield increases only with electron‐donating substituents (12 d to 12 f) which gave yields up to 90 % (12 f). In the case of electron‐withdrawing substituents attached to the para position of the alkyne 11, for example, for 11 e, no selective formation of the corresponding enyne product could be observed. The substitution pattern (para vs. ortho) of the aromatic unit of the chloroarylacetylene is not important since the yields for 12 g and 12 h are almost the same. By contrast, the electronic nature of the substituent attached to the aromatic unit of the chloroarylacetylene 1 is crucial: Chloroarylacetylenes 1 with electron‐withdrawing substituents lead to high yields of the corresponding enynes 12, whereas electron‐donating groups decrease the yield (12 f to 12 j). For chloroarylacetylenes with strong electron‐donating groups, for example, for chloroarylacetylene 1 f, an unselective reaction was observed that delivered the enyne product in significant lower yields (<20 %).In the second part, we performed the reaction on a preparative scale (0.4 mmol) in order to evaluate the scope of the chloroalkynylation Scheme  under th12 n to 12 r). Furthermore, the analogous reaction of bromoarylacetylenes 4 led to similar yields (13 a and 13 b).To our delight, the scope of the reaction could be extended to both terminal aryl alkynes and diaryl alkynes. Here again, only one regioisomer was obtained (11 a) with both Me3P and JohnPhos as ligands of the gold catalyst  or C1 (route B) positions of complex 14. Both reaction pathways lead to product 20, which corresponds to the gold(I) complex of the successfully isolated enyne 12 k ‐catalyzed reaction of phenylchloroacetylene with 1‐phenyl‐1‐propyne  can be stabilized through rotation around the C2−C2′ single bond to form chloronium ion 18 . The final step is the formation of gold complex 20 through a 1,3‐chlorine shift, which has a slightly lower activation barrier  than the rearrangement of the aryl group for route A /B3//B3LYP‐D3BJ/B1) with JohnPhos as ligand of the gold catalyst for both reaction pathways  predict that route A is energetically favored compared to route B. Thus, all calculations forecast the preferred addition of alkyne 13C‐labeling of one of the starting materials should help in gaining mechanistic insights. Therefore, we synthesized a chlorophenylacetylene in which the outer acetylenic carbon atom is 13C‐labeled (13C(1)‐1 d; Scheme 11 f delivered the enyne product 13C‐12 i with a total yield of 81 %. A closer look at the 13C NMR spectrum reveals that the 13C signals for both acetylenic carbon atoms C1 and C2 are enriched with the carbon isotope 13C . According to the quantitative 13C NMR spectrum, the percentage of 13C is 14 and 98 times, respectively, higher at positions C1 and C2 than that for the quaternary carbon atom C5′ which just shows the natural abundance of the carbon isotope 13C (ca. 1 %) . Since both intensive signals of the acetylenic carbon atoms (C1 and C2) exhibit no splitting pattern (one would expect a doublet corresponding to the 1J coupling of both 13C‐labeled acetylenic carbon atoms), the 13C‐enriched carbon atoms (C1 and C2) cannot be present in the same molecule. Therefore, the isolated enyne must be a mixture of compounds 13C(2)‐12 i and 13C(1)‐12 i (Scheme 13C(2)‐12 i and 13C(1)‐12 i was determined using the integrals for the 13C‐enriched signals of C2 and C1, respectively, and amounts to 87:13 . This demonstrates that the reaction proceeds through both reaction pathways  is favored.To verify our calculations, we attempted to confirm the previously proposed reaction mechanism. We assumed that 13C‐labeling experiments show that the reaction indeed passes through both ways. This interplay could be employed for the development of future novel carbon–carbon bond‐forming reactions.In conclusion, we have developed a gold(I)‐catalyzed variant of the haloalkynylation reaction that gives direct access to conjugated and halogenated enynes with good to very good yields (up to 90 %) from readily available starting materials, while tolerating a broad range of substrates with respect to both alkyne reactants. Since the halogen pattern on both the aromatic and vinylic unit enables potential further transformations (see Scheme S1), the gold(I)‐catalyzed haloalkynylation of aryl alkynes represents an attractive method for the synthesis of more complex conjugated systems. Of particular interest is the fact that the enyne product can be formed through two complementary pathways: The regioselectivity of the C−C bond formation plays absolutely no role since rearrangement of the skeleton results in the same product. The authors declare no conflict of interest.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


MicroRNAs (miRNAs) have been found to play a key role in drug resistance. In the current study, we aimed to explore the potential role of miR‐126 in trastuzumab resistance in breast cancer cells. We found that the trastuzumab‐resistant cell lines SKBR3/TR and BT474/TR had low expression of miR‐126 and increased ability to migrate and invade. The resistance, invasion and mobilization abilities of the cells resistant to trastuzumab were reduced by ectopic expression of miR‐126 mimics. In comparison, inhibition of miR‐126 in SKBR3 parental cells had the opposite effect of an increased resistance to trastuzumab as well as invasion and migration. It was also found that miR‐126 directly targets PIK3R2 in breast cancer cells. PIK3R2‐knockdown cells showed decreased resistance to trastuzumab, while overexpression of PIK3R2 increased trastuzumab resistance. In addition, our finding showed that overexpression of miR‐126 reduced resistance to trastuzumab in the trastuzumab‐resistant cells and that inhibition of the PIK3R2/PI3K/AKT/mTOR signalling pathway was involved in this effect. SKBR3/TR cells also showed increased sensitivity to trastuzumab mediated by miR‐126 in vivo. In conclusion, the above findings demonstrated that overexpression of miR‐126 or down‐regulation of its target gene may be a potential approach to overcome trastuzumab resistance in breast cancer cells. The sensitivity to trastuzumab of these resistant cells was increased by overexpressing miR‐126 or knocking down its target gene PIK3R2. We report that the mechanism of resistance to trastuzumab by reduced miR‐126 partially involves inactivation of the PIK3R2/PI3K/AKT/mTOR signalling pathway. These results highlight novel aspects of miR‐126 and trastuzumab resistance in breast cancer that are suggestive of the use of this microRNA or its downstream targets as potential new therapeutic targets to turn the tide against resistance.22.12. Trastuzumab resistance was induced by administration of the drug at a low concentration of 5 μg/mL continuously over 6 months to SKBR3 and BT474 cells as previous study.The human breast cancer cell lines SKBR3 and BT474 were obtained from American Type Culture Collection . RPMI‐1640 supplemented with 10% foetal bovine serum  was used for cell culture at 37°C and a humidified atmosphere with 5% CO2.2Western blotting was performed as previously described2.3GenePharma was the source of mimic NC (FAM‐labelled mimic negative control), miR‐126 inhibitor, NC inhibitor, miR‐126 mimics, ex‐PIK3R2 , PIK3R2‐shRNA , shRNA control and ex‐control. Six‐well plates were used for seeding cells that were subjected to transfection with either shRNA (0.4 μg) vectors or oligonucleotides (200 pmol). Transfections were performed according to the instructions for Lipofectamine 2000 , and 48 hours later, further analysis was performed.2.4−ΔΔCt method was used to calculate the fold changes. The primers are list as follows: miR126: 5’‐TATGGTTGTTCTCGACTCCTTCAC‐3’ and 5’‐TCGTCTGTCGTACCGTGAGTAAT‐3’ and U6: 5’‐CTCGCTTCGGCAGCACA‐3’ and 5’‐AACGCTTCACGAATTTGCGT‐3’.TRIzol reagent (Invitrogen) was used to isolate total RNA. Total RNA was then subjected to spectroscopy to determine purity and concentration. Stem‐loop RT was used for mature miRNA expression, followed by real‐time PCR. The Sanger Center miRNA Registry was the source of the miR‐126 sequence that in turn was used for primer design. An ABI 7900 HT Thermal cycler was used for qRT‐PCR  in triplicate. The 22.5The probable target of human miR‐126 was predicted to be PIK3R2 using the miRDB, microRNA.org and TargetScan databases for miRNA analysis. The pmirGLO3 or pGL3 luciferase reporter vector was used for cloning the predicted portion of the 3'‐UTR of PIK3R2, which was termed PIK3R2‐WT. pmirGLO3 was also used for cloning the 3'‐UTR of PIK3R2 containing a mutated sequence, which was termed PIK3R2‐MUT. The positive control (PC) was pmirGLO3 expressing the miR‐126 inhibitor sequence. The luciferase assay was performed using cotransfection of a reporter vector and miR‐126 mimics or mimic NC in SKBR3 cell lines. The dual‐luciferase reporter assay system was used to analyse the luciferase activity of cells that were harvested 48 hours post‐transfection.2.6Cell migration was determined by wound healing experiments, while cell invasion was assessed by transwell insert assays. The former involved the use of a pipette tip to wound cells grown to confluence. Images were obtained at zero time and time intervals to determine the wound width as a way to assess migration. The invasion assay involved the use of the lower portion of invasion inserts coated with Matrigel. Cells in serum‐free media were added to the upper chamber, and invasion towards medium with 10% FBS was assessed after 24 hours at 37°C. The cells that invaded the membrane were fixed, stained with crystal violet and imaged to be counted using ImageJ software. All the above assays were performed in triplicate.2.75 cells/well with which transfection was performed. SKBR3 cells were transfected with inhibitor negative control or miR‐126 inhibitor, while SKBR3/TR cells were transfected with negative control or miR‐126 mimic. The transfection was performed with Lipofectamine 2000 (Invitrogen) by following the manufacturer's instructions. Then, 96‐well plates were used to seed 5 × 103 cells/well 24 hours following the transfection. An MTS ‐2,5‐diphenyl‐tetrazolium bromide) assay followed by measurement of A490 (absorbance at 490 nm) was used for the cell viability study 48 hours after drug treatment. A relative survival curve was used to estimate the IC50 or drug concentration that caused 50% growth inhibition. Assays were conducted in duplicate as 3 independent experiments.Six‐well plates were used for seeding 3 × 102.85 SKBR3/TR cells in 100 μL phosphate‐buffered saline in the right flank. Seven days after inoculation with cells, 24 mice were randomly assigned into 4 groups (n = 6). Xenografts received miR‐126 agomirs and miR‐126 agomir negative control (2 nmol) every two days by direct local injection. Five milligrams/kg trastuzumab was administered every other day using intraperitoneal injection. The mice were killed at day 30 post‐treatment; the tumours were removed and weighed. Western blotting was used for the protein profile of the tumours.Nude mice received subcutaneous injections of 5 × 102.9t test and one‐way analysis of variance (ANOVA) were used to analyse statistical significance among groups with P < 0.05 considered statistically significant.Prism V was used for all statistical analyses, and data are presented as the mean ± SD. Student's 33.1Resistance to drugs has been shown to be an outcome of increased invasive ability caused by drugs used in chemotherapy.3.2To obtain a clearer picture of the role of the microRNA in resistance, the resistant cell lines SKBR3/TR and BT474/TR were transfected with miR‐126 mimics, while the parental cells were transfected with miR‐126 inhibitor. The use of mimics attenuated the trastuzumab resistance of SKBR3/TR and BT474/TR cells, while the use of miR‐126 inhibitor in SKBR3 and BT474 cells caused increased trastuzumab resistance Figure . The mig3.3The functions of miRNAs are elucidated with analyses of the genes they target. PIK3R2 was identified as a putative target of miR‐126 using target prediction programs. The 3’‐UTR of PIK3R2 was cloned (either the wild‐type: PIK3R2‐WT or a mutated sequence: PIK3R2‐MUT) downstream of the luciferase reporter gene to assess the role of the binding site that was predicted to be in the 3’‐UTR of the target gene Figure . Cotrans3.4The next step was analysis of the abilities of cells to respond to trastuzumab by using silencing and overexpression of PIK3R2. Trastuzumab sensitivity was enhanced in SKBR3/TR and BT474/TR cells when PIK3R2 was knocked down Figure . However3.5A known target of PIK3R2 is the PI3K/AKT/mTOR pathway.3.6A xenograft model was used to study the effects of miR‐126 on the sensitivity of cancer cells towards trastuzumab. Consistent with the in vitro results, the in vivo results also demonstrated that treatment with miR‐126 enhanced the sensitivity to trastuzumab in SKBR3/TR tumours Figure . Compare4Among the family of human epidermal growth factor receptors (EGFR), HER2 has been linked to the activation of PI3K/AKT as well as Ras/Raf/MEK/MAPK, which has been associated with features of several cancer types in terms of the ability to divide, migrate and differentiate.The role of modulation of resistance to trastuzumab by miRNAs in breast cancer has been demonstrated by studies.Several aspects of cancers, such as division, invasion, migration, motility and survival, involve the potential role of molecules downstream of PIK3R2.Animal studies were conducted to evaluate the anticancer effect of miR‐126 in mice that were resistant to trastuzumab. It was found that the trastuzumab sensitivity of SKBR3/TR cells was increased in the presence of this miRNA with inhibition of PIK3R2/AKT/mTOR signalling in vivo. Thus, a potential mode of addressing breast cancer resistance to trastuzumab is highlighted in this study mainly by the use of a microRNA to inhibit PIK3R2 and its associated pathway. To the best of our knowledge, this is the first study to show the role of increased levels of miR‐126 and decreased trastuzumab resistance of SKBR3 cells. To advance the study of miR‐126 and resistance to trastuzumab, research in additional cell lines is warranted, as we have conducted experiments in 2 pairs of cell lines resistant to trastuzumab.In conclusion, inhibition of PIK3R2 and its downstream PIK3R2/AKT/mTOR signalling pathway in cells resistant to trastuzumab by overexpression of miR‐126 caused a decrease in drug resistance. This study paves the way for a possible use of miR‐126 activation or inhibition of its targets as a tool to address the resistance to trastuzumab in breast cancer cell lines.The authors declare no conflict of interest.


This reaction can serve as a fast way to synthesize diazadispirocycles, which are found in the core structures of bioactive natural products. Product diversification via Suzuki–Miyaura cross coupling and application to the synthesis of 1‐oxa‐9‐azadispiro[4.2.48.25]tetradecatrienes were also conducted.Here we describe the diastereoselective synthesis of (5 Double Spirocyclization: The present reaction is the first example of double spirocyclization of N‐arylamides via dearomatization, where 1,9‐diazadispiro[4.2.48.25]tetradecatrienes were synthesized diastereoselectively. Dearomative transformations play a significant role in organic chemistry.r,8r)‐1,9‐diazadispiro[4.2.48.25]tetradecatriene scaffold, which is found in the core structures of grandilodine C (1),2),3)In this context, we planned to construct a ‐diazadispirocycle 6 b in 21% 1H NMR yield, whose stereochemistry was established by the NOESY experiment. Next, the reaction was performed with NIS and AgNO3 in various solvents (entries 2–4). Acetone or CH2Cl2 was inefficient, while MeNO2 worked efficiently and gave relatively clean crude material. Two diastereomers, 6 b and 9 b, could be separated through conventional silica gel column chromatography, and 6 b was isolated in 46% yield. The results of the solvent screening experiment indicated that polar and low‐nucleophilic solvents are suitable for the reaction. Therefore we turned to test fluorinated alcohols , which are known to enhance the halogenation of both aromatics and olefins.6 b in 54% yield with 73 : 27 dr. The amount of AgNO3 could be reduced to 0.1 equivalent without affecting the outcome (entry 8), and performing the reaction at 0 °C improved the yield by 68% (entry 9). As in entry 10, replacing the counter anion of silver reagent from nitrate to trifluoroacetate improved the yield by 75%, while the diastereoselectivity did not change. The importance of silver reagents was explored in entries 11 and 12. The reactions with catalytic nitric acid or without any catalysts did not reach completion, although retained diastereoselectivity with 75 : 25 dr. Lastly, as in entry 13, the reaction without silver catalyst in MeNO2 did not give 6 b or even intermediate 4‐Ib, resulting in the recovery of 4‐Hb. Through the optimization of the reaction conditions, the product derived from the direct spirocyclization of 4‐Hb before the formation of 4‐Ib was not detected.After synthesizing the cyclization precursor on Table . As show1 and R2 groups on diastereoselectivity . The reaction employing 4‐Hd with the p‐toluenesulfonyl group for R1 proceeded smoothly, although dr decreased to 58 : 42 (entry 3). Next, we tested the effect of the electron density of R2 on diastereoselectivity. Thus we performed cyclization with substrates bearing an electron‐donating group  or an electron‐withdrawing group (entry 6). Only slight differences were observed among the yields and selectivities among 4‐He−4‐Hg. Lastly, the size of the R2 was investigated (entries 7–10). While the methyl group showed low diastereoselectivity, the 2‐naphthylmethyl group gave high selectivity. The best result was obtained when the 1‐naphthylmethyl group was employed, providing ‐diazadispirocycle 6 k with 91 : 9 dr.With the optimized conditions in hand, we evaluated the effects of the R1 group of the side chain and the R2 or R3 group of the lactam ring. The intermediate A, leading to the desired isomer 6, would be predominant if the R2 group is more sterically hindered than the R3 group, so that the substrate 4‐Hk with the R2 group for a bulkier substituent  resulted in the high selective (91 : 9 dr) formation of the desired ‐diazadispirocycle 6. In contrast, ‐isomer was predominant when the precursor with the R3 group for a bulkier substituent  was employed. Thus, the treatment of 4‐Ph under the same reaction conditions gave 9–Ph as a major product with 60 : 40 dr, as shown in Figure The observed stereoselectivity can be explained by considering the conformation of the cationic intermediates produced by the first spirocyclization reaction Figure a. In the3)4 catalyst, Ag2O, and CsF. The reaction was completed at room temperature within 2 hours, and 6 e was converted into diarylethene 10 e–1, having two p‐nitrophenyl groups in 78% yield, while the use of an organic base such as K3PO4 instead of Ag2O resulted in partial decomposition. Next, under similar conditions, derivative 10 e–2 with two p‐methoxyphenyl groups was synthesized in 62% yield.Next, derivatization was conducted by a modification of the diiodo moiety Scheme . Thus, dr,8r)‐ and ‐diastereomers of 1‐oxa‐9‐azadispiro[4.2.48.25]tetradecatrienes ‐isomer of dispirocycle 15 as a major product in 59% isolated yield with 65 : 35 dr. Second, cyclization of phenylpropiolate 16 afforded ‐isomer of the dispirocycle 17 in 57% yield with 66 : 34 dr. The stereochemical outcome can be explained in the same way as the corresponding diazadispirocycles in Figure Finally, we extended the above‐developed method to the synthesis of both  should be addressed to the authors.SupplementaryClick here for additional data file.


Many interesting target guest molecules have low symmetry, yet most methods for synthesising hosts result in highly symmetrical capsules. Methods of generating lower symmetry pores are thus required to maximise the binding affinity in host–guest complexes. Herein, we use mixtures of tetraaldehyde building blocks with cyclohexanediamine to access low‐symmetry imine cages. Whether a low‐energy cage is isolated can be correctly predicted from the thermodynamic preference observed in computational models. The stability of the observed structures depends on the geometrical match of the aldehyde building blocks. One bent aldehyde stands out as unable to assemble into high‐symmetry cages‐and the same aldehyde generates low‐symmetry socially self‐sorted cages when combined with a linear aldehyde. We exploit this finding to synthesise a family of low‐symmetry cages containing heteroatoms, illustrating that pores of varying geometries and surface chemistries may be reliably accessed through computational prediction and self‐sorting. A sea of expanding shapes: A combined experimental–computational approach enabled the synthesis of low‐symmetry imine cages from mixtures of tetraaldehyde building blocks. This “social self‐sorting” approach was applied to obtain a family of new cages containing heteroatoms, showing that pores of varying geometries and surface chemistries may be reliably accessed. Controlled host‐guest recognition is of crucial importance to biological processes and artificial supramolecular systems alike.A limitation of self‐sorting strategies is that they often result in the formation of highly symmetrical products.3Di6Tet tubular organic cages that were prepared through imine formation between three pseudo‐linear tetratopic aldehydes (“Tet”) and six ditopic amines (“Di”), and selected the linear tetraaldehydes as a starting point for these studies.B1 ‐trans‐1,2‐cyclohexanediamine  in the presence of trifluoroacetic acid catalyst. Each bent aldehyde was then allowed to react sequentially with the series of linear aldehyde partners and R,R‐CHDA to assess their cage‐forming and self‐sorting behaviour. All reactions were characterised by ultra‐performance liquid chromatography‐mass spectrometry (UPLC‐MS) and 1H NMR spectroscopy. Where cage species could be isolated, crystal structures were sought to confirm their identities and assess their stable conformations. The sizes of isolable low‐symmetry cages were further investigated in solution by diffusion‐ordered spectroscopy (DOSY NMR) and ion‐mobility spectrometry‐mass spectrometry (IMS‐MS). Aldehyde B1 was found to induce social self‐sorting in the studied cages, thus heteroatom‐containing analogues of B1 were synthesised and reacted using the same methods to test whether the self‐sorting behaviour was retained.To test our hypothesis, we studied imine‐based cages formed from two bent tetratopic aldehydes B1–B2 and L1–L4. The experimentally observed outcomes agreed with the relative gas‐phase formation energies of the possible 3Di6Tet products, showing the predictive power of the simple model for the self‐sorting behaviour of imine‐based organic cages.We previously used density functional theory (DFT) formation energies to explain the thermodynamically preferred cage topologies in the dynamic imine‐based self‐assembly processes.B1–B2 and L1–L4 were synthesised via Pd‐catalysed cross‐coupling reactions (see Supporting Information Section S3 for the synthetic details). The reactions of L2 and L3 with R,R‐CHDA have been reported to give tubular covalent cages [3L2] and [3L3], respectively . Indeed, the DFT formation energy for RS][3B1‐ was 20 kJ mol−1 lower than the formation energy for the enantiopure [3B1] at the M06‐2X/6–311G level of theory. B1 was the only studied aldehyde for which any preference was observed. As the reaction of B1 with R,R‐CHDA only formed the enantiopure [3B1] cage in trace amounts, we postulated that more stable cages may result from the addition of linear tetraaldehydes, enabling access to socially self‐sorted lower‐symmetry architectures. By contrast, cages including linear aldehydes and B2 would compete with the favourable formation of [3B2], leading to narcissistic self‐sorting or statistical mixtures of all possibilities.This result prompted us to computationally explore the thermodynamic preference for the formation of pseudo‐L and B families in single‐pot reactions with R,R‐CHDA under cage‐forming conditions. We expected the 3Di6Tet topology to be favoured in all cases based on our previous work.To explore self‐sorting in the system, we combined aldehydes from the 3Di6Tet cages in all possible stoichiometries of the linear and bent aldehydes. We then applied a workflow consisting of high‐temperature molecular dynamics simulations with OPLS3e force field,B1) and Table B2). These calculations are performed on isolated molecules in the gas phase, which does not consider solvent effects, and hence large energetic differences are needed to predict solution‐phase structures with confidence.For each reaction studied, we manually constructed the [L+2B] . A deuterated variant of aldehyde L3 was available from a previous study and used in reactions with B1 to allow discrimination of the resultant cages by mass in the UPLC‐MS.L4 and B2, and the reaction was characterised primarily by 1H NMR chemical shifts and UPLC retention times. Table In parallel, we attempted to address the problem synthetically by targeting the cage stoichiometry of L+B . The major product was identified as the d][2L3‐ and d + 2B1] cage, which was of significantly lower DFT energy than any competing structure in this system. In all cases, other species could be detected by mass spectrometry as trace products, including the chiral cage [3B1], but could not be isolated. The distribution of the products is affected by the length of the linear aldehydes L1–L4 in a seemingly unpredictable way, but the observed structures agree with predicted trends in the DFT formation energies. The length of L1 appears to be suitable to relieve strain in a cage containing two B1 moieties; L2 is of suitable length to relieve strain in a cage containing one B1 moiety, but L3 and L4 seem to be too long and do not form stable mixed 3Di6Tet cages with B1.Reactions of B2 and aldehydes L1–L4 also all resulted in the formation of cage compounds . However, as all products in this system have the same mass, it was not possible to unambiguously characterise the self‐sorting behaviour with mass spectrometry. While formation energies of [3L1] and [L1 + 2B2] are comparable, and the formation energy of [3L4] is higher than that of the socially‐sorted cages nL4 +[mB2], we propose that the clean narcissistic self‐sorting in those cases is a result of antagonistic coupling between the homoleptic and the heteroleptic cages in these libraries.[3B2] cage removes free B2 from solution, thus favouring the formation of [3L1] over [L1 + 2B2]. Similarly, formation of the significantly more stable [3L2] cage removes free L2 from the system, thus shifting the equilibrium towards clean formation of [3B2] over the nL4 +[mB2] structures.Reactions involving aldehyde B1, aldehyde B2 has more degrees of freedom and forms a stable [3B2] cage as well as scrambled mixtures of heteroleptic cages with other aldehydes. Chromatographic separations of the mixtures containing heteroleptic cages [2L2 + B1], nL2 +[mB2], and nL3 +[mB2] are currently under investigation. The reaction of L1 and B1 with R,R‐CHDA stands out as the only combination which produces a low‐symmetry heteroleptic organic cage as the only product detected by NMR.Contrary to B1 we synthesised thiophene (B1S) and pyridyl (B1N) derivatives that have structurally related geometries . Computational modelling predicts comparable formation energies for [L1 + 2B1X] and [3B1X] in both cases, with a slight preference for the heteroleptic structures . Inspection of the computational models suggests that [L1 + 2B1] and its analogues exhibit similar shapes and sizes. It was possible to obtain a single‐crystal X‐ray structure of [L1 + 2B1S] . Further evidence was obtained from IMS‐MS experiments, which indicated that the drift times for the three cages are similar (see Section S5), supporting the conclusion that the subtle differences in the linker structures have little effect on the overall molecular size in these systems.In both cases, the reactions of [L1 + 2B1S]. The heteroatoms themselves have little effect on the shape of the void, but do affect its electronic properties, providing a subtle yet important distinction that may have consequences for guest binding and selectivity.We performed analysis of the shapes and electronic structures of the internal cage cavities to probe the effect of using different aldehydes. Cage geometries were optimised as described previously. These structures were used to calculate the total electron density and the electrostatic potential at the M06‐2X/6–311+G level of theory. We found the 0.0004 a.u. density isosurface and selected a subsurface approximating the internal cavity of each cage . Figure L1, L4) and two non‐linear , were synthesised and treated with R,R‐CHDA to form three new 3Di6Tet organic cages: [3L1], [3L4], and [3B2]. Aldehyde B1 did not form the expected cage [3B1] when treated with R,R‐CHDA or S,S‐CHDA. However, upon co‐crystallisation of reaction mixtures containing B1 and both enantiomers of CHDA, the formation of the pseudo‐Ch3‐symmetric cage RS][3B1‐ was detected. We exploited the lack of a stable homochiral cage [3B1] to form low‐symmetry cage compounds containing mixtures of B1 and linear aldehydes L1–L4 of varying lengths. Computationally obtained formation energies of the resultant cages were able to rationalise the experimentally observed resultant cages. In particular, the heteroleptic cage [L1 + 2B1] was predicted to be more stable than the corresponding homoleptic cages [3L1] and [3B1], and was indeed preferentially formed. Two heteroatom‐containing analogues of [L1 + 2B1] were formed using this strategy, demonstrating the generality of the social self‐sorting approach to synthesis of organic cages of low symmetry. The slight change in the aldehyde geometry and the incorporation of heteroatoms did not affect the overall size of the cage molecules, while allowing for tuning of the shape and electronic properties of the internal cavity. We hope that these results will aid the design of more anisotropic organic cages for challenging separations and the selective encapsulation of biologically relevant low‐symmetry guests.Four new tetraaldehydes, two linear  should be addressed to the authors.SupplementaryClick here for additional data file.