Electronic structure and spectra of ruthenium diimine complexes by density functional theory and INDO/S. Comparison of the two methods

Density functional theory calculations have been carried out on the series [Ru(bqdi)n(bpy)3−n]2+ (bpy=2,2′-bipyridine, bqdi=o-benzoquinonediimine) to explore the extent of coupling between metal 4d and ligand π and π* orbitals. Time-dependent density-functional response theory (TD-DFRT) has been used to predict the complex electronic spectra which are compared with their experimental data. The main thrust of the paper is a comparison of these calculations with those carried out using Zernerʹs frequently used INDO/S method. Different procedures for the electron population analysis of molecular orbitals are described and discussed. The agreement in terms of orbital energies, orbital mixing and electronic spectra is remarkably good. This confirms that for these species, and probably for all non-solvatochromic species in general, INDO/S is a good model reproducing very well the results of the computationally much more demanding, but also more reliable TD-DFRT calculations.