Crystal structure of the photo-excited state of three-coordinated gold(I) complex

Department of Chemistry and Materials Science, Tokyo Institute of Technology* Graduate School of Material Science, University of Hyogo, Japan**
○Manabu Hoshino* Hidehiro Uekusa* Yoshiki Ozawa** Koshiro Toriumi**

The three-coordinated Au(I) complexes are highly interested as new EL material. The spectroscopic and theoretical studies on these complexes suggested that the emission is due to the large structural distortion of the complexes induced by photo-excitation. In order to investigate the emission and the structural distortion relationship, the photo-excited molecular structure of three-coordinated Au(I) complex, [AuCl(PPh3)2], was determined by single crystal X-ray structural analysis.
X-ray diffraction intensity data were collected in the dark (Light-off) and under the irradiation with UV excitation light (Light-on) condition in the laboratory system. Comparing the molecular structure of Light-off and Light-on states, all Au-P, Au-Cl bonds were found to be shortened (Au-P = -0.0065(5) Å & -0.0076(5) Å, Au-Cl = -0.0052(5) Å). These bonds shortening were clearly explained by electric excitation (assigned antibonding → bonding). More precise diffraction intensity data of Light-off and Light-on states were collected by multiple-exposure IP method using low-temperature vacuum X-ray camera at SPring-8 BL02B1 beamline. Photo-difference Fourier map showed that the Au atom was slightly shifted toward the farther phosphor atom within a molecule by photo-excitation. This asymmetric shift of Au atom was also observed in the laboratory system. In conclusion, the structural distortion on the photo-excited state of [AuCl(PPh3)2] includes two types of structural change, the bond shortening and the asymmetric shift of Au atom.