Solvent effects on metal to ligand charge transfer excitations

The method for calculating solvent shifts on metal to ligand charge transfe r (MLCT) and other electronic absorption bands involving charge transfer (e .g. ligand to metal and organic charge transfer) developed by Zeng, Hush an d Reimers, henceforth named ZHR-SS, is reviewed. Also included are simple m odels 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 met hod. Results for MLCT and related processes in Fe2+(H2O)(6), Ru2+(NH3)(5)-p yridine, Ru2+ C (NH3)(5)-pyrazine, and Ru2+(NH3)(5)-pyrazine-H+ are describ ed which accommodate the (initially surprising) results of electroabsorptio n experiments within the general physical picture of MLCT processes. (C) 19 98 Elsevier Science S.A. All rights reserved.