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 luminescence bands: a strong green phosphorescence band (τ 77K ) 45.4 µs) and a weak blue fluorescence band (τ 77K ) 24.4 ns) that becomes well-resolved by cooling toward 4 K or by time-resolved measurements, representing a 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 T 1 lowest triplet excited state (2.62 Å; υ Au-Au ) 180 cm -1 ), compared to corresponding values of 2.95 Å and 84 cm -1 , respectively, for the aurophilically bound S 0 ground state. Intriguing structure-luminescence relations exist for bis(thiocyanato)gold(I) complexes with different cations such as K + , Rb + , n-Bu 4 N + , and Cs + in which the salts with shorter Au‚‚‚Au nearest-neighbor separations show blue shifts in the phosphorescence emission energies as well as smaller Stokes' shifts, contrary to the expected trends. We have also observed significantly red-shifted phosphorescence energies and larger Stokes shifts in frozen solutions of K[Au(SCN)] 2 compared to those for the crystals. The computational data suggest that the emission energy is sensitive to the counterion, in support of the experimental photoluminescence data. Full optimizations of the T 1 states for isolated dimeric models in vacuum predict a drastic rearrangement in the T 1 states in contrast to the S 0 ground state and provide a physical basis for understanding the experimental photophysical results for this class of compounds.

Photoluminescence and Raman results for single crystals of KCl doped with KAu(CN) 2 with different Au content are presented and compared with results for pure KAu(CN) 2 crystals. Photoluminescence spectra of the doped crystals show three major UV-vis bands that can be resolved by varying the excitation wavelength. Spectroscopic and computational evidence suggests the formation of Au-Au bonded excimers and exciplexes in this doped system. The excimer/exciplex luminescence bands can be tuned in a given crystal by siteselective excitation and their relative intensities tuned by varying the dopant concentration. Microsecond lifetimes were observed for the various luminescence bands, suggesting Au-centered phosphorescent emissions. Raman spectral analysis was used successfully to correlate with the luminescence bands observed in pure and doped crystals of