RESOLUTION OF TRANS-1-(2-NAPHTHYL)-2-PHENYLETHENE FLUORESCENCE IN THEPRESENCE OF TRI-N-BUTYLAMINE INTO PAIRS OF MONOMER AND EXCIPLEX SPECTRA - SELECTIVITY IN CONFORMER QUENCHING

Fluorescence spectra of trans-1-(2-naphthyl)-2-phenylethene (NPE) obta ined at different excitation wavelengths and tri-n-butylamine (TEA) co ncentrations in methylcyclohexane are resolved into four distinct comp onents by application of principal component analysis with self-modeli ng. Two of the components are the NPE conformer fluorescence spectra, and the other two are the corresponding NPE . TBA exciplexes. Pure com ponent combination coefficients are based on optimization of global (l ambda(exc)-independent) Stern-Volmer plots for the monomers and excipl ex fluorescence plots for the exciplexes. Conformer-specific fluoresce nce quenching rate constants by the amine are obtained for the first t ime. These are indistinguishable from the corresponding exciplex forma tion rate constants. Fortuitously, the Stern-Volmer constants for the two singlet excited conformer/TBA interactions differ by only similar to 25%, revealing high conformer selectivity by TBA. This selectivity is consistent with the large shift between the lambda(max) of the two exciplex fluorescence spectra which reveals the more favorable (2.9 kc al/mol) reduction potential of NPE(A), the less extended conformer.