| Abstract
| - The electronic structure of bis(thiocyanato)gold(I) complexes is studied both experimentally and theoretically.Temperature-dependent photoluminescence studies for K[Au(SCN)2] reveal two unstructured luminescencebands: a strong green phosphorescence band (τ77K = 45.4 μs) and a weak blue fluorescence band (τ77K =24.4 ns) that becomes well-resolved by cooling toward 4 K or by time-resolved measurements, representinga rare case for Au(I) compounds whereby both fluorescence and phosphorescence are observed simultaneously.Quantum mechanical calculations for dimeric models indicate Au−Au covalent bond formation in the T1lowest triplet excited state (2.62 Å; υAu-Au = 180 cm-1), compared to corresponding values of 2.95 Å and 84cm-1, respectively, for the aurophilically bound S0 ground state. Intriguing structure−luminescence relationsexist for bis(thiocyanato)gold(I) complexes with different cations such as K+, Rb+, n-Bu4N+, and Cs+ inwhich the salts with shorter Au···Au nearest-neighbor separations show blue shifts in the phosphorescenceemission energies as well as smaller Stokes' shifts, contrary to the expected trends. We have also observedsignificantly red-shifted phosphorescence energies and larger Stokes shifts in frozen solutions of K[Au(SCN)]2compared to those for the crystals. The computational data suggest that the emission energy is sensitive tothe counterion, in support of the experimental photoluminescence data. Full optimizations of the T1 states forisolated dimeric models in vacuum predict a drastic rearrangement in the T1 states in contrast to the S0 groundstate and provide a physical basis for understanding the experimental photophysical results for this class ofcompounds.
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