Pyrene fluorescence quenching by aromatic azides

Abstract

Pyrene fluorescence quenching by phenylazide derivatives with donor and acceptor substituents has been studied by fluorescence spectroscopy and flash photolysis. The rate constants of quenching (k q) in acetonitrile ((0.2–1.2) × 1010 l mol−1 s−1) are found to be close to a diffusion limit; the rate constants were somewhat higher for perfluoro-substituted arylazides. It is found that k q does not depend on solvent polarity; the formation of the pyrene cation in the course of pyrene fluorescence quenching by tolylazide was not detected. Pyrene fluorescence quenching occurred by an energy-transfer mechanism; this is supported by the coincidence of the quantum yields of the direct and sensitized photodecomposition of tolylazide. As estimated, energy transfer in rigid media occurs at characteristic distances of about 10 A.