3 years ago

Photochemistry and Photophysics of the 3-Styrylidenebenz[e]indanes

Andrew M. Kropp, David W. Eaker, V. K. Ratheesh Kumar, Jack Saltiel, Shipra Gupta
The photochemical and photophysical properties of the extended conformers of trans- and cis-1-(2-naphthyl)-2-phenylethenes (t- and c-NPEB) are strikingly different than those of their rigid analogues, trans- and cis-3-styrylidenebenz[e]indane (t- and c-BPE). The fluorescence quantum yield and lifetime at 25 °C in methylcyclohexane drop from 0.76 and 22.2 ns in t-NPEB to 0.0051 and 0.25 ns in t-BPE and there are complementary changes in the photoisomerization quantum yields. In both cases photoisomerization occurs in S2, a stilbenic excited state. The differences in behavior are traced to the diminished S1/S2 energy gap on the alkyl substitution afforded by the five-membered ring in BPE. The effect of viscosity on the torsional relaxation of t-BPE, evaluated in glycerol/methanol mixtures at 25 °C and in 95/5 and 99.9/0.1 glycerol/methanol (% v/v) as a function of T, is well accounted for by the medium enhanced barrier model. Absorption and fluorescence spectra of t-BPE in pure glycerol reveal aggregate formation. Quenching of t-BPE fluorescence in methylcyclohexane by tri-n-butylamine (TBA) leads to exciplex fluorescence. Comparison with analogous results for t-NPEB suggests that charge transfer involves primarily the naphthalenic S1 state in t-NPEB and the stilbenic S2 state in t-BPE. This article is protected by copyright. All rights reserved.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/php.12849

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