WATER-SOLUBLE POLYSTYRENE LATEXES AS PHOTOREDOX MEDIA .2. EXCITED-STATE ELECTRON-TRANSFER FROM ANTHRACENE COVALENTLY BOUND POLY(METHACRYLIC ACID)

Poly(methacrylic acid)-co-2-(9-anthryl)ethyl methacrylate, abbreviated as PMA-A hereafter, has been adsorbed at the interface of water-soluble latexes, referred to as ''microspheres'' (abbreviated as muS). Two distinct stages of the adsorption processes of the polymer at muS interfaces are observed that depend on pH. The initial association stage is quickly achieved (<3 min) after mixing the polymer and muS in aqueous solution. The final equilibration of the polymer at the interface requires about 2 days to reach equilibrium. Excited-state quenching of PMA-A via electron transfer at interfaces of muS has been measured using a zwitterionic viologen SPV (4,4'-bipyridinyl-1,1'-bis(propanesulfonate)). The muS interface provides a unique environment for the anthracene moiety of PMA-A. Charge separation was found in all cases with the largest yield at high pH for the triplet state and at low pH for the singlet state. There is little sensitivity to the environment for triplet-state electron transfer because the dominant factor is the spin-forbidden recombination of the reactive charge pair. The efficiency of triplet-state charge separation at the muS interface was found to be comparable to homogeneous solution. For the singlet state, the efficiency of charge separation was found to be high (ca. 0.4-0.5) at high pH, in contrast with earlier results in homogeneous solution (J. Phys. Chem. 1989, 93, 1928). In all cases the ion pairs have a long lifetime, in excess of 2 ms. Thus, we have demonstrated that a solid/liquid interface of muS provides a ''compartmentalization effect'' on photoredox processes. This provides a strategy for more efficient utilization of excited-state redox processes.