Abstract
We report in this paper in detail on the excited-state dynamics of both metal-free phthalocyanine (H2Pc) and cobalt phthalocyanine (CoPc) thin films measured by pump-and-probe experiments. Samples are excited by femtosecond laser pulses at two different photon energies, which correspond to the two maxima of the Q-band absorption. Using a test beam, we measure the differential transmission ΔT(t)/T dynamics that is spectrally resolved in the range from 1.570 to 2.470 eV (790−502 nm). When compared to a H2Pc sample, the CoPc films show a faster dynamics, which has one very fast contribution on a subpicosecond time scale, a slower part with a time constant of several picoseconds, and a subnanosecond contribution. Since the observed dynamics is independent of excitation intensity, fast exciton−exciton annihilation can be excluded for our measurements. Therefore, we attribute the observed ultrafast dynamics in CoPc to the presence of the Co atoms. In the manifold of long-living triplet states, Co atoms are resp...
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