Photoeffects in thin-film molecular-level chromophore-quencher assemblies. 1. Physical characterization

Molecular-level chromophore-quencher assemblies have been prepared in precast chlorosulfonated polystyrene ([-CH₂CH(p-C₆H₄SO₂Cl)]_x-; PS-SO₂Cl) films by (1) exposing the intact film to solutions containing the chromophore [(bpy)₂Ru(5-NH₂Phen)][PF₆]₂ (bpy is 2,2′-bipyridine; 5-NH₂phen is 5-amino-1,10-phenanthroline) which becomes chemically bound through sulfonamide bond formation, (2) partially hydrolyzing a portion of the remaining -SO₂Cl sites to -SO₃^- sites and exposing the resulting films to acetonitrile solutions containing the electron-transfer quencher paraquat (PQ²⁺) and the reductive scavenger triethanolamine (N(C₂H₄OH)₃). 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, K_SV ∼ 6.8 × 10⁴ M^-1. A second site exists that undergoes relatively slow quenching, K_SV ∼ 3 × 10³ M^-1, and then only with added [NEt₄](ClO₄). A third site is present that is not quenched.