Excited state properties of donor-acceptor substituted trans-stilbenes: The meta-amino effect

Frederick D. Lewis*, Wilfried Weigel

*Corresponding author for this work

Research output: Contribution to journalArticle

86 Scopus citations

Abstract

The photochemical behavior of 3-dimethylaminostilbene (3DS), 3-amino-3′-cyanostilbene (3A3′CS), and 3-dimethylamino-4′-cyanostilbene (3DCS) has been investigated and compared to that of the analogous 4-amino derivatives. The absorption spectra of the 4-aminostilbenes display a single strong band whereas the spectra of the 3-aminostilbenes display multiple bands or lesser intensity as a consequence of configuration interaction which results from loss of symmetry. The 3-aminostilbenes have substantially higher fluorescence quantum yields and longer fluorescence lifetimes when compared to the 4-aminostilbenes. Based on analysis of the solvatochromic shifts of the absorption and fluorescence spectra, the 3- and 4-aminostilbenes have similar excited state dipole moments which are substantially larger than their ground state dipole moments. The long lifetimes of the 3-aminostilbene charge transfer singlet states are a consequence of low fluorescence rate constants and a large barrier for singlet state torsion. Thus the "meta-amino effect" reported previously for 3-aminostilbene is also observed in the case of donor-acceptor substituted stilbenes. In nonpolar solvents the 3-aminostilbenes decay predominantly by fluorescence and intersystem crossing to the triplet state which decays to yield a mixture of trans and cis isomers. In polar solvents a second nonradiative decay channel is operative and is tentatively assigned to internal conversion on the basis of its energy gap dependence. The primary 3-amino-3′-cyanostilbene displays specific solvation in alcohol solvents at room temperature and aggregation in a nonpolar solvent at low temperature.

Original languageEnglish (US)
Pages (from-to)8146-8453
Number of pages308
JournalJournal of Physical Chemistry A
Volume104
Issue number34
DOIs
StatePublished - Aug 31 2000

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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