Effect of solvent polarizability on dual fluorescence of EE-1-phenyl,4-(1 '-pyrenyl)-1,3-butadiene

The properties of the lowest excited states of EE-1-phenyl,4-(1'-pyrenyl)-1 ,3-butadiene were studied by absorption and emission spectrometry in solven ts of different polarity and polarizability. The effect of the latter on th e energy and relative position of the two lowest excited singlet states (of B-u and A(g) parentage) was investigated. Dual fluorescence was observed i n low polarizability solvents at room temperature. The emission from a ther mally populated upper state disappears at low temperature and in higher pol arizability solvents, such as CS2, where the lowest excited state acquires an allowed character. The excited molecule relaxes mainly by the radiative pathway. Internal conversion also plays an important role while the triplet population is scarce and photoisomerization is practically negligible. The behaviour is compared with those of related compounds. (C) 2000 Elsevier S cience B.V. All rights reserved.