Optical absorption of linear-chain gold complexes under pressure: AuX2dibenzylsulfide (X2=Cl2,Br2,ClBr)

Abstract
The effect of pressure on the polarized optical absorption spectra of the quasi-one-dimensional (1D) halogen-bridged mixed-valence gold complexes AuCl2(DBS), AuBr2(DBS), and AuClBr(DBS) (with DBS denoting dibenzylsulfide) has been studied up to 6 GPa. The visible absorption edges for light polarized parallel to the chain direction, corresponding to intrachain charge-transfer transitions, exhibit exceptionally large initial red shifts ranging from -0.21 to -0.29 eV/GPa, which is interpreted as a characteristic feature of quasi-1D charge-density-wave systems. The pressure dependence of the visible absorption edges for polarization perpendicular to the chain direction supports an interpretation in terms of interchain charge-transfer transitions. The results for Au complexes are compared with those for the related 1D platinum complexes.