Photoinduced hydride transfer reaction between methylene blue and leuco crystal violet

Yingjin Liu, Shunzo Yamamoto, Yoshimi Sueishi

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The photoinduced hydride transfer reaction between methylene blue (MB+) and leuco crystal violet (CVH) was investigated spectrophotometrically under conditions of direct excitation of MB+ with steady-illumination of visible light and of photosensitization by benzophenone (BP) and α-nitronaphthalene (NNP) with UV light. It was found that upon the irradiation of the solution of MB+ and CVH with visible light, MB+ disappeared and crystal violet (CV+) formed simultaneously. The ratio of the CV+ concentration formed to that of MB+ consumed was unity. The photosensitized reactions by NNP gave similar results. From the findings that the fluorescence of MB+ was not quenched by CVH and the triplet photosensitizations were observed, it was concluded that the hydride transfer reaction in acetonitrile occurs in the triplet state of MB+. The quantum yield for the disappearance of MB+ in acetonitrile was estimated to be 1.1×10-4 and it was independent of CVH concentration. The electron transfer from CVH to triplet methylene blue (3MB+*) and the back electron transfer within the geminate radical pair must occur effectively. A spin adduct of a radical formed during the reaction was detected by the ESR method with 2-methyl-2-nitrosopropane (MNP) as a radical trap. This radical was attributed to CV·. The results can be explained by a mechanism with stepwise electron-proton-electron transfers. In tert-butyl alcohol, however, it was observed that the fluorescence of MB+ was quenched by CVH and the quantum yield of the disappearance of MB+ depended on CVH concentration. Different mechanism from that in acetonitrile was proposed for the reaction in tert-butyl alcohol.

Original languageEnglish
Pages (from-to)153-159
Number of pages7
JournalJournal of Photochemistry and Photobiology A: Chemistry
Volume143
Issue number2-3
DOIs
Publication statusPublished - Oct 10 2001

Keywords

  • Leuco crystal violet
  • Methylene blue
  • Photoinduced hydride transfer
  • Steady-illumination photolysis
  • Stepwise transfer mechanism

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Physics and Astronomy(all)

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