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) fluorescence by fumaronitrile (FN) was determined as a function of excitation wavelength (λexc) and temperature (5.0 e T e 80.0 °C). Principal component analysis with self-modeling (PCA-SM) was applied separately to the fluorescence spectra at each temperature. Resolved pure conformer fluorescence spectra were based on the condition that Stern-Volmer quenching constants for each conformer be λexc-independent. A shoulder at the blue edge of the spectra of the more extended, s-trans conformer (t-APEB) becomes more pronounced with increasing temperature revealing fluorescence from a thermally populated S2 state. Similar, but more subtle changes are evident in the spectra of the s-cis conformer (t-APEA). Both sets of resolved spectra exhibit blue shifts and broadening as the temperature is increased. These spectral changes are reflected in the shape of the eigenvectors obtained from the PCA of each set of spectra and prevent their resolution into S2 f S0 and S1 f S0 components. An earlier PCA-SM based resolution of a t-APE spectrothermal matrix into S1 f S0 fluorescence of t-APEA and S2 f S0, S1 f S0 fluorescence spectra of t-APEB is evaluated.