Viscosity effect on the fluorescent and conformational properties of 2-N-piperidino-5-(2 ',2 '-dicyanovinyl)thiophene

The mechanism of deactivation of the electronic excitation energy of 2-N-pi peridino-5-(2',2'-dicyanovinyl)thiophene is studied by the methods of fluor escence and quantum chemical calculations. The increase in the fluorescence quantum yield from 0.0004 in n-hexane at room temperature to 1 in an EPA m ixture at 77 K is determined by an increase in the viscosity (rigidity) of the medium hindering the rotation of molecular fragments. The efficient non radiative process in a molecule with the probability less than or equal to2 .5 x 10(11) s(-1) results mainly from rotation about the C12-C13 bond and t he transition to an intermediate state with a low-lying energy level. (C) 2 001 MAIK "Nauka/Interperiodica".