EXCITATION INTENSITY-DEPENDENT FLUORESCENCE BEHAVIOR OF SOME LUMINESCENT POLYMERS

The fluorescence lifetime, fluorescence signal output and fluorescence spectral distribution of three highly diluted luminescent polymers (o ne para-phenylenevinylene and two para-phenylene-ethynylene polymers) in tetrahydrofuran are studied as a function of picosecond laser pulse excitation intensity. The results are compared with coumarin 2 in met hanol and a distyrylbenzene molecule in tetrahydrofuran. The fluoresce nce lifetime and the spectral distribution are practically independent of excitation intensity, indicating the absence of excitation-depende nt cooperative effects and the absence of emission from preferred exci ton states. The fluorescence signal saturation of the polymer solution s at high excitation intensities indicates the photoexcitation of poly mer segments (excitons or polarons) extending on average over two para -phenylene-ethynylene or four para-phenylenevinylene monomeric units. (C) 1998 Elsevier Science Ltd. All rights reserved.