DEPENDENCE OF TRANS-1-(2-ANTHRYL)-2-PHENYLETHENE CONFORMER-SPECIFIC FLUORESCENCE-SPECTRA AND FUMARONITRILE QUENCHING RATE CONSTANTS ON TEMPERATURE

The quenching of trans-1-(2-anthryl)-2-phenylethene (t-APE) fluorescen ce by fumaronitrile (FN) was determined as a function of excitation wa velength (lambda(exc)) and temperature (5.0 less than or equal to T le ss than or equal to 80.0 degrees C). Principal component analysis with self-modeling (PCA-SM) was applied separately to the fluorescence spe ctra at each temperature. Resolved pure conformer fluorescence spectra were based on the condition that Stern-Volmer quenching constants for each conformer be lambda(exc)-independent. A shoulder at the blue edg e of the spectra of the more extended, s-trans conformer (t-APE(B)) be comes more pronounced with increasing temperature revealing fluorescen ce from a thermally populated S-2 state. Similar, but more subtle chan ges are evident in the spectra of the s-cis conformer (t-APE(A)). Both sets of resolved spectra exhibit blue shifts and broadening as the te mperature is increased. These spectral changes are reflected in the sh ape of the eigenvectors obtained from the PCA of each set of spectra a nd prevent their resolution into S-2 --> S-0 and S-1 --> S-0 component s. An earlier PCA-SM based resolution of a t-APE spectrothermal matrix into S-1 --> S-0 fluorescence of t-APE(A) and S-2 --> S-0, S-1 --> S- 0 fluorescence spectra of t-APE(B) is evaluated.