Effects of alkyl chains of thiacarbocyanine as the sensitizer for the photoreduction of methylviologen in micellar phase.

概要

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Photoinduced reduction of methylviologen (MV2+) by ethylenediaminetetraacetate was investigated with 3,3′-dialkylthiacarbocyanines as a sensitizer in the micellar solution of a nonionic surfactant, heptaethylene glycol monododecyl ether. The alkyl chains of the dyes were found to have considerable effects on the reaction rate. The fluorescence yield of a dye having two long alkyl chains, 3,3′-dioctadecylthiacarbocyanine (C18–18) in the micellar phase was larger than that of the dye having only one long alkyl chain, 3-methyl-3′-octadecylthiacarbocyanine (C1–18). This result was discussed in terms of the large effective volume associated with the intramolecular twisting motion in the excited state of C18–18. Also, from the fluorescence quenching experiments, it was found that MV2+ was of easier access to C18–18 than C1–18 in the micellar phase. Thus, the relatively higher stability of the excited state of C18–18 and the easier access of MV2+ to C18–18 were considered to be responsible for the faster reaction rate achieved by C18–18 than by C1–18 in the micellar solution.
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