Spectral and photophysical properties of trans-2-styrylanthracene rotamers, derived by kinetic fluorescence analysis. A comparison with the results obtained by statistical procedures

Dependence of trans-1-(2-Anthryl)-2-phenylethene Conformer-Specific Fluorescence Spectra and Fumaronitrile Quenching Rate Constants on Temperature

“…The combination coefficients of these pure component spectra fall within the range of acceptable LS spectra in both cases but are far from the combination coefficients of the LS outer limit spectrum that was assigned to t -APE B first by Spalletti et al 3d. and more recently by Bartocci et al Having confirmed our initial spectral assignments, we conclude, once again, that at least in toluene, the alternative assignments of Spalletti, Bartocci, and co-workers are not valid. 3d, The discrepancies are due to the arbitrary assumptions that were made by these workers concerning the widths of the regions of spectral nonoverlap between the fluorescence spectra of the two conformers at the onset and tail portions of the spectra. Incorrect identification of the pure component combination coefficients on the normalization line leads to incorrect fractional contributions of the components, x A and x B , to the experimental spectra, and, in turn, to incorrect pure component fluorescence excitation spectra. , …”

“…In their investigation of the discrepancies between the spectral resolutions in refs d and , Bartocci et al also applied an independent resolution method based on quantitative kinetic fluorescence analysis (KFA) . Since the KFA approach yielded resolved spectra in nearly exact agreement with those based on their PCA-SM resolution, it is important to consider how these two seemingly independent approaches may lead to identical erroneous spectra.…”

“…Since the KFA approach yielded resolved spectra in nearly exact agreement with those based on their PCA-SM resolution, it is important to consider how these two seemingly independent approaches may lead to identical erroneous spectra. As applied in ref , the KFA procedure 18 requires identification of isoemissive wavelengths, λ‘ em , at which the decay kinetics are monitored. Since at these wavelengths the two conformers contribute equally to the observed fluorescence intensity, independent of λ exc , identification of λ‘ em requires measurement of accurate composite fluorescence quantum yields, φ f , as a function of λ exc .…”

“…Fumaronitrile, FN, a strong electron acceptor, was substituted for O 2 in applying the SV constant criterion in these resolutions because its concentration is easier to control at different temperatures and because the results may be valuable in a future study of site and conformer selectivity in its photoreactions with t -APE. The independent determination of the fluorescence spectrum of t- APE A should resolve the controversial aspects of this assignment. − Finally, determination of the temperature effects on the t -APE A and t -APE B fluorescence spectra, separately, should allow a more meaningful evaluation of the earlier attempt to resolve t -APE B fluorescence into S 2 → S 0 and S 1 → S 0 components 3d…”

Temperature and solvent effects on rotamer-specific photobehaviour of the cis and trans isomers of 2-styrylanthracene

“…The short-lived component, assigned to the A rotamer, is practically independent of solvent polarity, in q F, tvA ,10,16 agreement with both the nature of and a 1(L a ÈB u ) S 1 / F, tvA value of about 1 for this rotamer. 16 The lifetime of the longerlived component, assigned to the B rotamer, q F, tvB ,10,16 decreases with increasing polarity. On the contrary, the Ñuorescence decay, observed at nm, where the A j em \ 400 rotamer does not emit, was found to be mono-exponential.…”