Metal-to-ligand charge transfer absorption in a rhenium(I) complex that contains a pi-conjugated bipyridine acceptor ligand

This Letter describes a study of the absorption and electroabsorption spect roscopy of a complex consisting of the -Re-1(CO)(3)Cl chromophore coordinat ed to the 4,4'-{bis-[2,5-(dimethoxyphenyl)ethynyl]}-2,2'-bipyridine ligand. The objective of the study is to explore whether Re --> bipyridine metal-t o-ligand charge transfer (MLCT) excitation leads to electron delocalization into the pi -conjugated 2.5-(dimethoxyphenyl)ethynylene moieties. The resu lts indicate that the two low-energy absorption bands observed for the comp lex have a strong degree of charge transfer character: however, the bands a re dominated by intraligand (IL) pi,pi* transitions. The spectroscopic data are consistent with possible configuration mixing between the lowest IL pi , pi* and MLCT transitions. (C) 2001 Published by Elsevier Science B.V.