PHOTOSENSITIZED CHARGE SEPARATION USING WATER-INSOLUBLE POLYMER-BOUNDRUTHENIUM(II) COMPLEX FILMS

Water-insoluble ruthenium(II) complex-containing polymer films, in whi ch bis(2,2'-bipyridine) complexes are coordinated with the imidazolyl residues on partially quaternized poly(1-vinylimidazole) (RuQPIm), hav e been prepared and characterized by spectroscopic and thermal measure ments. The photosensitized charge separation in the sacrificial system , consisting of RuQPIm film, 1,1'-dimethyl-4,4'-bipyridinium (MV2+) or 1,1'-dioctyl-4,4'-bipyridinium (C8V2+) dications, and triethanolamine (TEOA) has been investigated in aqueous solution. Here, RuQPIm film, MV2+ and C8V2+, and TEOA act as a solid polymer photosensitizer, elect ron accepters, and a sacrificial donor, respectively. The formation of viologen radical (MV.+ or C8V.+) was observed on light irradiation (l ambda > 440 nm) of the aqueous solution. With MV2+ as an acceptor, the rate of MV.+ formation decreased with increasing degree of quaterniza tion. This suggested that the rate was controlled by at least three fa ctors: (1) electrostatic repulsion, (2) pi-pi interaction between the heteroaromatic moieties of polymer and MV2+ and (3) steric hindrance o f the alkyl side chain. On the other hand, the rate of C8V.+ formation was large, and dependence of the rate on the degree of quaternization differed significantly from that of the MV2+ system. This indicated t hat the C8V2+ species had a further interaction in addition to the thr ee described above, e.g. a hydrophobic interaction between alkyl chain s in the C8V2+ and the polymer. Further, the results obtained from the photosensitized charge separation in aqueous solution containing 1 M NaCl and in CH3CN-H2O suggested that the surface morphology of the pol ymer him was also a very important factor.