Solvent effects on metal to ligand charge transfer excitations

The method for calculating solvent shifts on metal to ligand charge transfer (MLCT) and other electronic absorption bands involving charge transfer (e.g. ligand to metal and organic charge transfer) developed by Zeng, Hush and Reimers, henceforth named ZHR-SS, is reviewed. Also included are simple models for MLCT processes in mono- and di-metal complexes and a description of key aspects of modern electroabsorption spectroscopic techniques used to study MLCT transitions. The rationale behind ZHR-SS is summarized, as are other schemes currently available for the evaluation of solvent effects on electronic spectra. Initial test calculations are described in which ZHR-SS is used to predict solvent effects on (n, pi*) transitions of azines: the physical processes involved closely resemble those involved in MLCT spectra, but a much larger range of experimental data is available to test the method. Results for MLCT and related processes in Fe2+(H2O)(6), Ru2+(NH3)(5)-pyridine, Ru2+ C (NH3)(5)-pyrazine, and Ru2+(NH3)(5)-pyrazine-H+ are described which accommodate the (initially surprising) results of electroabsorption experiments within the general physical picture of MLCT processes. (C) 1998 Elsevier Science S.A. All rights reserved.