Substituent effects in platinum(II) biphenyl bipyridine complexes

Abstract

Platinum(II) biphenyl bipyridine ligand complexes were found to exhibit emission from an excited state in the 600 nm region of the spectrum when excited in their metal-to-ligand charge transfer transition band located near 450 nm. The 2,2'-bipyridine ligands were decorated with substituents located on the 4,4'-positions of the pyridine rings. The structures of the complexes were distorted from square planarity based on single crystal structures determined for most of the complexes. Density functional theory and time dependent density functional theory gave information about the assignment of frontier orbitals, their energies and the predicted optical transitions in the series of complexes. Linear free energy correlations were determined between theoretical and experimentally obtained parameters along with correlations with substituent σp constants. We have found experimental and theoretical linear correlations between σp and emission energy maxima, emission lifetimes, absorption energy maxima and reduction potentials, between experimental and predicted absorption energy maxima and between the theoretical LUMO and experimental reduction potentials. The information obtained provides an understanding of the fundamental electronic behavior of the complexes.