L-Tyrosine Ester-Mediated Photosensitized Charge Separation - Length Effects of Alkyl Side Chains in Polymers and Alkyl Groups inL-Tyrosine Esters

Abstract

The ruthenium(II) complex- and viologen-containing partially quaternized poly(1-vinylimidazole)s with a butyl (C4RuVQPIm), an octyl (C8RuVQPIm), a dodecyl (C12RuVQPIm), and hexadecyl (C16RuVQPIm) as alkyl side chains have been prepared. The length-effects of the alkyl side chain in the polymers and the alkyl groups in the L-tyrosine esters on the L-tyrosine-ester-mediated intra-polymer photosensitized charge-separation reactions have been investigated in methanol. The L-tyrosine esters with a hexyl (C6Tyr), an octyl (C8Tyr), and a dodecyl (C12Tyr) group were used. The luminescence intensities decreased with the addition of the L-tyrosine esters, and they significantly depended on the length of the alkyl side chains on the polymers, C12RuVQPIm showed the smallest luminescence intensity. In contrast, the luminescence intensity of C4RuVQPIm depended on the length of the alkyl groups in the L-tyrosine esters, but not for CnRuVQPIms (n ≥ 8). These results were explained by a difference in the microdomain structure formed by the polymer structure between C4RuVQPIm and other polymers. During the photosensitized charge separation, the reaction proceeded through a mediated process, using L-tyrosine esters, and a direct process (without L-tyrosine esters). The initial rate of the viologen radical formation was influenced by both the alkyl side chains on the polymers and alkyl groups in the L-tyrosine esters, particularly; particularly influenced was the back reaction in the mediated process.