FEMTOSECOND EXCITED-STATE DYNAMICS IN FLUOROALUMINUM AND CHLOROALUMINUM PHTHALOCYANINE THIN-FILMS

Photoinduced absorption on the high-energy side of the Q-band has been observed and time-resolved in polycrystalline/amorphous thin films of both fluoroaluminum and chloroaluminum phthalocyanine. The films were pumped with almost-equal-to 100-fs optical pulses at various wavelengths inside the inhomogeneously broadened Q-band, including 620 and 760 nm. The induced absorption signal is accompanied by a bleaching signal on the low-energy edge of the Q-band. The bleaching signal resembles a blue-shifted monomer absorbance spectrum. The induced absorption signal develops as the absorption bleaching signal decays, suggesting exciton decay into a subgap state. The different bimolecular decay dynamics observed for the absorption bleaching (tau(eff) almost-equal-to 700 fs) and induced absorption (tau(eff) almost-equal-to 2 ps) signals support this conclusion. Analyses of the results and possible origins of the indicated subgap state are discussed.