Die Temperaturabhangigkeit der Fluoreszenzquantenausbeuten von Donator-Akzeptor-substituierten trans-Stilbenen in Losungsmitteln unterschiedlidier Polaritat

Abstract

Abstract The temperature dependence of the fluorescence quantum yield of donor-acceptor-substituted trans-stilbenes (1) in n-heptane, toluene and dimethylformamide (DMF) in the temperature range of 5-70 °C is due to twisting of the excited Si state to the perp.-S1 state. Twisting and fluorescence are the predominant deactivation processes. Within the series of 4'-acceptor-substituted substances 1g, 1b, 1h- 1k, the activation energies, Etp, in n-heptane and DMF are correlated with the Hammett constants atp of the acceptor in a way comparable to the correlaton between the twisting rate constant kt„ and Aσp. No such correlation was found with toluene. The deactivation of the S1 state results from two oppositely acting factors: the intramolecular donoracceptor interaction and the intermolecular solute-solvent interaction