Highly Efficient Conformer-Specific Adiabatic Cis → Trans Photoisomerization of cis-1-(2-Anthryl)-2-phenylethene in S1

Emission from cis-1-(2-anthryl)-2-phenylethene, c-APE, in toluene consists primarily (up to 76%) of fluorescence from adiabatically formed 1 t-APEB*. In this respect, the behavior of c-APE is analogous to that of the naphthyl analogue, c-NPE. However, the conformer specific adiabatic photoisomerization, c-APEB* → 1 t-APEB*, is much more efficient in c-APE than in c-NPE (≥44% vs ≥2%) although the lifetime of 1 c-APEB* is 1000-fold longer than the lifetime of 1 c-NPEB* (4.5 ± 0.5 ns vs 4 ± 1 ps). Resolution of the spectra of 1 c-APE* and 1 t-APEB* was achieved by application of principal component analysis on a matrix of sets of fluorescence spectra measured in the presence of Ar, air, and O2. The known fluorescence spectrum of t-APEB and the known Stern−Volmer constant for O2 quenching of the fluorescence of t-APEB serve as the constraints for this resolution. Sequential quenching by O2 of 1 c-APEB* and 1 t-APEB* is reflected in a quadratic Stern−Volmer plot for the latter.