Effect of bulky meso-substituents on photoinduced twisted intramolecular charge transfer processes in meso-diarylamino subporphyrins

Seung Kyu Lee, Jun Oh Kim, Daiki Shimizu, Atsuhiro Osuka, Dongho Kim

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Photoexcited-state dynamics of meso-diarylamino subporphyrins 4-6 in cyclohexane, toluene, and acetonitrile have been studied by steady-state/time-resolved absorption and fluorescence experiments and quantum calculations. While 4 emits fluorescence from the locally excited state regardless of solvent polarity, the fluorescence of 5 and 6 are solvent-polarity dependent. The observed efficient fluorescent quenching of 5 and 6 has been ascribed to twisted intramolecular charge transfer (TICT), in which the two N-Cipso bonds in 5 and the Cmeso-N bond in 6 are twisted to facilitate the intramolecular electron transfer. In 2-methyltetrahydrofuran (2-MeTHF), the fluorescence of 5 and 6 are both almost completely quenched at 297 K, but restored at 77 K (below the melting point of 2-MeTHF) because of the frozen molecular twisting. Furthermore, electrochemical studies also revealed the charge separation processes of 4-6 are thermally unfavorable in nonpolar toluene and cyclohexane unless their structures change contrary to the observed efficient fluorescence quenching. These observations support the TICT mechanism. In addition, the formation of TICT state is affected by steric effect as the size of the meso-substituents increases.

Original languageEnglish
Pages (from-to)663-669
Number of pages7
JournalJournal of Porphyrins and Phthalocyanines
Issue number6
Publication statusPublished - 2016 Jun 1


All Science Journal Classification (ASJC) codes

  • Chemistry(all)

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