Photoinduced single- versus double-bond torsion in donor-acceptor-substituted trans-stilbenes

Jye Shane Yang, Kang Ling Liau, Chung Yu Hwang, Chin Min Wang

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51 Scopus citations

Abstract

The electronic absorption and fluorescence spectra, quantum yields for fluorescence (Φf) and trans -cis photoisomerization ( tc), and fluorescence lifetimes of trans-4-(N-arylamino)-4′-cyanostilbenes (2H, 2Me, 2OM, 2CN, and 2Xy with aryl = phenyl, 4-methylphenyl, 4-methoxyphenyl, 4-cyanophenyl, and 2,5-dimethylphenyl, respectively), trans-4-(N-methyl-N-phenylamino)-4′-cyanostilbene (2MP), trans-4-(N,N-diphenylamino)-4′-cyanostilbene (2PP), trans-4-methyl-N-phenylamino-4′-nitrostilbene (3MP), and three ring-bridged analogues 2OMB, 2MPB, and 3MPB are reported. Whereas fluorescence and torsion of the central double bond account for the excited decay of the majority of these donor-acceptor substituted stilbenes in both nonpolar and polar solvents (i.e., Φf + 2Φtc ∼ 1), exceptions are observed for 2OM, 3MP, and 3MPB in solvents more polar than THF and for 2Me and 2MP in acetonitrile as a result of the formation of a weakly fluorescent and isomerization-free twisted intramolecular charge transfer (TICT) state (i.e., Φf + 2Φtc ≪ 1). The TICT state for 2OM, 2Me, and 2MP results from the torsion of the stilbenyl-anilino C-N single bond, but the torsion of the styryl-anilino C-C bond is more likely to be responsible for the TICT state formation of 3MP and 3MPB. In conjunction with the behavior of aminostilbenes 1, a guideline based on the values of Φf and Φtc for judging the importance of a TICT state for trans-stilbenes is provided. Accordingly, the TICT state formation is unimportant for the excited decay of trans-4-(N,N-dimethylamino)-4′-cyanostilbene (DCS). In contrast, our results support the previously proposed TICT state for trans-4-(N,N-dimethylamino)-4′-nitrostilbene (DNS).

Original languageEnglish
Pages (from-to)8003-8010
Number of pages8
JournalJournal of Physical Chemistry A
Volume110
Issue number26
DOIs
StatePublished - 6 Jul 2006

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