J . Phys. Chem. 1986, 90, 1593-1598
1593
Redistribution of Excitation Energy between Nonequilibrated Electronic Excited Levels of Zinc( I I ) Complexes R. C. Highland, J. G . Brummer, and C. A. Crosby* Department of Chemistry, Washington State University, Pullman, Washington 99164-4630 (Receiced: September 17, 1985)
Luminescence from crystals of zinc(I1) complexes containing both 1,lo-phenanthroline and substituted benzenethiol ligands has been resolved into at least two emitting bands with widely different energies, decay times, and orbital parentages. Barriers to energy migration between 'aa* and ligand-ligand charge-transfer levels have been demonstrated by steady-state, flash, and heat pulse experiments. A state model, including an Arrhenius expression for interconfigurational energy migration, has been proposed.
Introduction Colored complexes of zinc(I1) are obtained when this closedshell ion is coordinated with two anions of benzenethiol or an aromatic dithiol and one N,N-dinitrogen heterocy~1e.I~Previous investigators'x2 have attributed these colors to a low-energy absorption band associated with charge transfer from the thiol ligand(s) to the nitrogen heterocycle through the metal ion. Consistent with the dIo configuration of zinc(I1) no transitions of ligand-field parentage were observed. By altering the energies of the a-donor and a-acceptor orbitals in the complexes via substituent changes, one can tune this low energy absorption band over the visible region.',* Recently Truesdell and Crosby3 reported dual luminescence from this same class of mixed ligand chelates in rigid glass media at low temperatures (
