The effect of solvent polarizability on the fluorescence of trans-1-(2-naphthyl)-2-phenylethene conformers. Conformer-specific fluorescence from the cis isomer.
A matrix of trans-1-(2-naphthyl)-1-phenylethene (t-NPE) fluorescence spectra obtained from benzene solutions at 20 degrees C by varying the excitation wavelength (lambdaexc) and the oxygen concentration is resolved into pure conformer fluorescence spectra by use of principal component analysis with self-modeling based on optimum global Stern Volmer constant criteria. The resulting fractional contributions of the two components to the fluorescence spectra are combined with observed fluorescence quantum yields as a function of lambdaexc to obtain the conformer-specific quantum yields. These quantum yields and fluorescence lifetimes are used to determine conformer-specific radiative and radiationless rate constants. Comparison with results from an analogous study in methylcyclohexane reveals pronounced, diferential enhancements of all these rate constants in benzene (Bz). Preliminary measurements of emission from a cis-1-(2-naphthyl)-1-phenylethene (c-NPE) solution in Bz at 20 degrees C, under static cell conditions, are dominated by sequential two-photon-induced t-NPE fluorescence due to excitation of t-NPE formed photochemically from the cis isomer. The spectra also reveal a weak structureless broad emission, which is assigned to 1c-NPE* by comparison with the published low temperature fluorescence spectrum of c-NPE in a hydrocarbon glass. The conformational origin of this emission is addressed.
Saltiel
Jack
J
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA. saltiel@chem.fsu.edu
Krishnamoorthy
Govindarajan
G
Sears
Donald F
DF