Photoinduced Gold(I)–Gold(I) Chemical Bonding in Dicyanoaurate Oligomers

Abstract

Nicht nur σ*σ, sondern auch σ*π: Elektronenstrukturrechnungen zeigen ein σ*σ‐ und σ*π‐Bindungsmuster für AuI–AuI‐Bindungen in angeregten Zuständen und legen zwei konformationsabhängige Relaxationsmechanismen für Gold‐Dicyano‐Oligomere (n=2–5; siehe Bild) in wässriger Lösung nahe. Eine derartige elektronische Struktur der angeregten Zustände könnte auch für andere Goldkomplexe mit einem ähnlichen Goldgerüst relevant sein.

Excimer and Exciplex Formation in Gold(I) Complexes Preconditioned by Aurophilic Interactions

“…Electron structure calculations for the oligomers [Au-(CN) 2 À ] n (n = 2-5) have been carried out by Dolg, Thiel, and co-workers at the MP2 level (ground state;first excited state of the dimer), and at the DFT,R I-CC2, and MSCASPT2 levels of theory (excited states). [108] Thetheoretical results for the dimer are in full agreement with those presented by Iwamura, Tahara, and co-workers [110] for the staggered structure.I nc ontrast to the ground state,w here the eclipsed isomer is unstable,t he excited-state bonding configurations ds* 1 ps 1 and ds* 1 pp 1 of the eclipsed dimer have very similar energies in both the S 1 and T 1 states,a nd may theoretically also contribute to the absorption and emission bands.T he calculated AuÀ ÀAu bond lengths for the two conformations in both the activated singlet and triplet states do not differ significantly;t hey are both about 0.3 shorter than in the corresponding ground states.A st he 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.…”

“…[107] Later, MP2 calculations of models of the dimer yielded Au-Aud istances of 3.014 and 2.998 for the staggered dimer and trimer,r espectively. [108] Thea ggregation of dicyanoaurate(I) anions was recently also observed in ionic liquids.T ime-resolved luminescence spectra revealed the presence of different oligomers both in imidazolium and pyrrolidinium salts. [114] If the counterion of the dicyanoaurate(I) anion contains at wo-coordinate gold(I) atom, for example,w ith the bulky PTAl igand…”

“…Working at the same level of theory that had been used for interpreting the photophysics of the [Au(CN) 2 ] À dimer (see above), Fang, Dolg, Thiel, and co-workers [108] came to the conclusion that the staggered bent structure for the trimer does not exist in the vibrational ground states of the singlet or triplet excited states.Hence,the linear arrangement is already rapidly adopted during vibrational relaxation in the activated singlet state and accompanied by Au À Au À Au bond shortening ((A) in Scheme 10). Subsequently,intersystem crossing ((B) in Scheme 10) affords alow-energy triplet for the trimer, which corresponds only to the final linear structures in Schemes 10 and S1.…”

“…Several recent quantum-chemical calculations have followed up the early experimental work and detailed the picture of the electronic ground-and excited-states,i np articular of the dimers and trimers (I, J), as presented below. [108] The structural dynamics of the latter were finally followed by picosecond/femtosecond time-resolved emission and absorption spectroscopy [109,110] and femtosecond X-ray solution scattering. [111][112][113] Investigations of aqueous solutions or in polar nonaqueous solvents have shown that therein the degree of oligomerization increases stepwise with the [Au(CN) 2 ] À concentration, which allows for dimers,trimers,and tetramers to be studied in separate concentration ranges (e.g., 30 mm for the dimer,3 00 mm for the trimer in water) and their formation and transformation to be followed.…”

Generalized trajectory surface-hopping method for internal conversion and intersystem crossing

“…[34][35][36][37] One major limitation is that the original FSSH method has been formulated with a focus on nonadiabatic internal conversion processes, disregarding intersystem crossing events that are often encountered in photochemistry and may even occur on an ultrafast timescale in systems with non-negligible spin-orbit couplings. [38][39][40][41][42] To simulate these two types of nonadiabatic processes on an equal footing, it is desirable to reformulate the original FSSH method and to include spin-orbit interactions that may induce nonadiabatic intersystem crossings. Spin-orbit coupling (SOC) has previously been included in a number of classical trajectory and quantum wavepacket simulations of multi-state reaction dynamics and photodissociation dynamics, mostly with the use of precomputed potential energy surfaces and various SOC approximations.…”