Photogeneration of transient charge carriers in an alternate porphyrin-phthalocyanine Langmuir-Blodgett film
Résumé
Long-lived triplet excitons are generated by laser excitation of a zinc porphyrin Langmuir-Blodgett film. The transient T-T spectrum is similar to that obtained in the liquid phase and the triplet excitons disappear with second-order kinetics by T-T annihilation. Their half-life varies from 110±10 to 55±5 μs with increasing laser energies. In contrast, excitation of an alternate porphyrin-phthalocyanine heterolayer leads to a charge-transfer reaction. The transient optical absorption spectrum is attributed to the oxidized porphyrin and reduced phthalocyanine on the basis of the spectrum shape and the peculiar redox properties of phthalocyanine. They are the primary transient charge carriers responsible for conduction. Their half-life varies from 700 to 300 ns with increasing laser energies.