Effect of solvent polarizability on dual fluorescence of EE-1-phenyl,4-(1′-pyrenyl)-1,3-butadiene Original Research Article

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 solvents of different polarity and polarizability. The effect of the latter on the energy and relative position of the two lowest excited singlet states (of Bu and Ag parentage) was investigated. Dual fluorescence was observed in low polarizability solvents at room temperature. The emission from a thermally populated upper state disappears at low temperature and in higher polarizability 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.