MULTIPLE LUMINESCENCE FROM PUSH-PULL DIPHENYL POLYENES REVEALED BY PICOSECOND SPECTROSCOPY - EVIDENCE FOR TICT AND BICIMER STATES

Picosecond time-resolved spectroscopy has been used to study the emiss ion behavior of methylaminophenyl)-4-(p-cyanophenyl)-1,3-butadiene (DC B) and hylaminophenyl)-6-(p-cyanophenyl)-1,3,5-hexatriene (DCH) in dif ferent solvents and experimental conditions (temperature, concentratio n, excitation intensity). At low concentrations (C< 10(-4) M) in polar solvents, we clearly resolved two emission bands: the first one is at tributed to the planar conformer and is the direct precursor of the se cond one attributed to the emission of a TICT state. At higher concent ration (C> 10(-4) M) and higher excitation intensity a third emission appears, assigned to a 'bicimer' species, as observed previously in st ilbene derivatives. This 'bicimer' species is formed by the associatio n of at least two excited molecules. Under certain experimental condit ions, laser action can be observed from the bicimer emission.