Photophysical properties of beta-(1-pyrenyl)ethyl p-cyanobenzoate in binary solvents of isooctane-ethyl acetate and ethyl acetate-acetonitrile

The effects of solvent polarity on the fluorescence spectra and fluorescenc e decays of beta-(1-pyrenyl)ethyl p-cyanobenzoate (P2CN) were investigated in detail using binary solvents consisting of various mixing ratios of isoo ctane-ethyl acetate or ethyl acetate-acetonitrile (dielectric constants (ep silon) = 1.94,36.2). Whereas both the intensity and wavelength maxima of an intramolecular exciplex emission (EX) are dependent on the solvent polarit y, only the intensity of an emission from the locally excited pyrene (LE) i s dependent on the solvents used. When monitored at 377 nm, the picosecond SPC (single photon counting) measurements reveal a slow decay (> 150 ns) in addition to a fast decay (<1 ns) of the locally excited P2CN. There are al so two decays for the EX which vary the intensity ratios by the monitored w avelength. The decay rate constants, k(EX1) and k(EX2). have a good linear correlation with the dielectric constants of the solvents, indicating that there exist two kinds of exciplexes. It is suggested that the decays of the locally excited-state of P2CN are so fast due to result of the efficient e lectron transfer that the two kinds of intramolecular exciplexes are formed from the two discrete conformers in the ground state. (C) 2001 Elsevier Sc ience B.V. All rights reserved.