Photophysical property of -bis(thiocyanato)aurate(I) complexes in ionic liquids

Aoyagi, Noboru   ; Shinha, Yusuke*; Ikeda, Atsushi*  ; Haga, Yoshinori   ; Shimojo, Kojiro   ; Brooks, N. R.*; Izuoka, Akira*; Naganawa, Hirochika  ; Kimura, Takaumi ; Binnemans, K.*

The photochemistry of a gold(I) thiocyanate complex has been investigated to determine the coordination structure in both the solid and liquid states. The coordination geometries of the supramolecular complex and the concomitant exciplex have mainly been analyzed by crystallographic analysis and X-ray absorption spectroscopy. The Au-S bond distance and Au-Au separation of the compound in the ground state and in the phosphorescent excited state were compared. Upon irradiation with UV light, the excimeric interactions were enhanced, resulting in a contraction of the Au-Au aurophilic distance. A broad luminescence spectrum was observed for the one-dimensional chain suprastructure. The time-resolved luminescence spectra indicated the entity of several oligomeric species in the crude liquid without neutral solvent molecules. In addition, EXAFS spectroscopy exhibited a slight change in the nearest Au-S distance due to the photo-switched transformation. The deformation of the (Au-Au)* exciplexes was not apparently promoted in the liquid state with the asymmetrical imidazoium cations having a non-local charge distribution in the present observation. This is plausibly due to a flexible molecular structure and a property in the liquid state. In conclusion, the photo-excited nature of the pseudo-one dimensional complexes is emerged in controlling bond distances among the supramolecular networks.