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