ELECTROABSORPTION SPECTROSCOPY OF CHARGE-TRANSFER STATES OF TRANSITION-METAL COMPLEXES .2. METAL-TO-LIGAND AND LIGAND-TO-METAL CHARGE-TRANSFER EXCITED-STATES OF PENTAAMMINERUTHENIUM COMPLEXES

The absorption spectra of Ru-II(NH3)(5)L and Ru-III(NH3)(5)L (L is an aromatic N-heterocycle or nitrile) complexes in 50:50 glycerol-water g lasses at 77 K (D-s = 3.9) are a function of the applied field in the 10(6)-10(7) V/m range. Analysis of the spectra in terms of the Liptay equations yields ground-excited state dipole-moment differences rangin g from 4 to 37 D, depending upon the nature of L. The measured dipole moment differences, particularly those for the MLCT transitions, are m uch smaller than the values estimated from a simple consideration of t he electron-transfer distances. The discrepancy between the observed a nd naive dipole-moment estimates arises mainly from the multielectron nature of the response to excitation. Good agreement is obtained with the predictions of a model which includes refinement of the effective electron-transfer distance, the shift in the valence electron distribu tion in the excited state, and the effects of electron delocalization (pi-backbonding for Ru(II) and pi-bonding for the Ru(III) complexes). Other contributions, namely the dipole moment induced by the NH3 ligan ds and by the surrounding solvent molecules, are also considered.