Photoeffects In Thin - Fllm Molecular - Level Chromophore - Quencher Assemblies . 1 . Physlcal Characterization Nigel

Molecular-level chromophore-quencher assemblies have been prepared in precast chlorosulfonated polystyrene ( [-CHzCH(p-C6H4S02CI)]~-; PS-SOzCl) films by (1) exposing the intact film to solutions containing the chromophore [(bpy)2Ru(5-NHghen)] [PF612 (bpy is 2,2‘-bipyridine; 5-NHzphen is 5-amino1 ,IO-phenanthroline) which becomes chemically bound through sulfonamide bond formation, (2) partially hydrolyzing a portion of the remaining -S02CI sites to -SO3sites and exposing the resulting films to acetonitrile solutions containing the electron-transfer quencher paraquat (PQz+) and the reductive scavenger triethanolamine (N(CZH4OH),). The photophysical properties of the chromophore-based metal-to-ligand charge-transfer excited state have been investigated by lifetime and visible absorption and emission spectra. Although similar to related monomers, excited-state decay in the films is nonexponential. The dynamics of excited-state quenching by PQ2+ following pulsed laser excitation show that the chromophore occupies three different chemical sites within the films. At one site, which accounts for -50% of the emitted light and appears to be located near ion channels created by hydrolysis, quenching is rapid, KsV 6.8 X lo4 M-’. A second site exists that undergoes relatively slow quenching, Ksv 3 X lo3 M-I, and then only with added [NEt4](C104). A third site is present that is not quenched.