Journal of Photochemistry and Photobiology, A: Chemistry, 48 zyxwvutsrqponmlkjihgfedcbaZY (1989) 87 - 93 87 zyxwvut NON-RADIATIVE DEACTIVATION CHANNELS OF MOLECULAR ROTORS M. S. A. ABDEL-MOTTALEB Department of Chemistry, Faculty of Science, Ain Shams University, Abbassia, Cairo @gyp t) RAFIK 0. LOUTFY Xerox Research Centre of Canada, 2660 Speaksman Drive, Mississauga, Ontario L5K 2L 1 (Canada) R. LAPOUYADE Laboratoire de Photophysique et Photochimie Moleculaire, 351, Cours de la Liberation, F-33405 Talence Ckdex (France) (Received December 6, 1988) Summary On the basis of the fluorescence properties of a series of intramolecular charge-transfer complexes of varied structure (p-(NJV-dialkylamino) benzylidene malononitriles and coumarin laser dyes) in an inert solvent (ethyl acetate), a model of non-radiative decay is proposed. The model specifically describes the relative contributions of the possible internal relaxation channels to non-radiative energy dissipation of the Si, ct states via the free rotor mechanism. The results are consistent with the theoretical predictions based on the calculated electron density distributions and the bond-order alternation in the Si, ct state. 1. Introduction In recent years, the spectroscopic properties of a large number of donor-acceptor (D-A) intramolecular charge-transfer (ICT) complexes have received considerable attention because of their profitable applications in industry, e.g. optical recording media, switching devices, xerographic photo- receptors and solar cells [ 1 - 93. Of the donor-acceptor ICT complexes studied, the fluorescence proper- ties of a series of fluorescence probes (P-(NJV-dialkylamino) benzylidene malononitriles) which belong to a class of organic compounds known as molecular rotors have been of interest [2 - 43. The results obtained have been interpreted to indicate that the free rotor mechanism is the dominant pathway for non-radiative decay of the SiBct state of these dyes. The extremely fast deactivation rate of the Sl_ct state of these materials has been lOlO-6030/89/$3.50 0 Elsevier Sequoia/Printed in The Netherlands