AMPHIPHILIC COPOLYMERS AS MEDIA FOR LIGHT-INDUCED ELECTRON TRANSFER–I. ELECTROSTATIC EFFECT ON THE FORWARD REACTION AS STUDIED BY FLUORESCENCE QUENCHING

摘要: — Fluorescence quenching of amphiphilic copolymers, poly(9-vinylphenanthrene-co-sodium 2-acrylamido-2-methylpropanesulfonate) (APh) and poly(9-vinylphenanthrene-co-3-methacrylamidopropyltrimethylammonium methyl sulfate) (QPh), in aqueous solution, was studied using viologen (MV2+) or 4,4'-bipyridinium-1, 1'-bis(trimethylenesulfonate) (SPV) as oxidative quenchers. The fluorescence the excited phenanthrene groups APh found to be efficiently quenched by MV2+. apparent second-order rate constant for quenching, kq, ranged magnitude 1011 -1012M-1 s-1, which are well beyond diffusion-controlled limit. This is presumably due an increase effective concentration MV2+ around fluorophore copolymer resulting from electrostatic attraction between anionic segments APh. strong interaction also favors formation ground-state EDA (electron donor acceptor) complex residue Such striking behaviors were not observed with related model compound. Unexpectedly, SPV, a zwitterionic quencher, enhanced polymer system (kq= 2–6 × 1010M-1 s-1), suggesting presence some attractive SPV. Contrary system, corresponding cationic (QPh) strongly diminished 5 108M-1 s-1). indicates that polycation QPh effectively prevents access polymer.