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

This Letter describes a study of the absorption and electroabsorption spectroscopy of a complex consisting of the –ReI(CO)3Cl chromophore coordinated 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-to-ligand charge transfer (MLCT) excitation leads to electron delocalization into the π-conjugated 2,5-(dimethoxyphenyl)ethynylene moieties. The results indicate that the two low-energy absorption bands observed for the complex have a strong degree of charge transfer character; however, the bands are dominated by intraligand (IL) π,π* transitions. The spectroscopic data are consistent with possible configuration mixing between the lowest IL π,π* and MLCT transitions.