Liquid crystalline solvents as mechanistic probes. 6. Dynamic quenching of pyrene fluorescence by 5α-cholestan-3β-yldimethylamine in the liquid crystalline and isotropic phases of a cholesteric solvent

Valerie Anderson, Bruce B. Craig, Richard G. Weiss

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Abstract

A method is described for determining the specificity of quenching of pyrene singlets by a tertiary alkylamine, 5α-cholestan-3β-yldimethylamine (CA), in a nonpolar cholesteric liquid crystalline solvent [59.5/15.6/24.9 (w/w/w) cholesteryl oleate/cholesteryl nonanoate/cholesteryl chloride]. It is found that the pyrene-amine orientation for quenching resembles closely the probable exciplex geometry. Activation parameters for the quenching process are phase dependent: from Stern-Volmer derived quenching rate constants at low CA concentrations, the Arrhenius activation energies and preexponential factors in the cholesteric phase are calculated to be E6 = 9.9 ± 0.2 kcal mol-1 and A6 = (2.1 ± 1.3) × 1014 M-1 s-1; the isotropic phase has E6 = 5.3 ± 0.1 kcal mol-1 and A6 = (1.8 ± 0.4) × 1011 M-1 s-1. The value of E6(cholesteric) is found to change with CA concentration, approaching E6(isotropic) at high CA. A cohesive explanation of these and other results, including the previously reported photodimerization of acenaphthylene in a different cholesteric phase, is advanced.

Original languageEnglish (US)
Pages (from-to)7169-7176
Number of pages8
JournalJournal of the American Chemical Society
Volume103
Issue number24
Publication statusPublished - 1981
Externally publishedYes

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ASJC Scopus subject areas

  • Chemistry(all)

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