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J. Phys. Chem. B 2006, 110, 410-419
Femtosecond Fluorescence Dynamics of Porphyrin in Solution and Solid Films: The Effects of Aggregation and Interfacial Electron Transfer between Porphyrin and TiO2 Liyang Luo,† Chen-Fu Lo,‡ Ching-Yao Lin,*,‡ I-Jy Chang,§ and Eric Wei-Guang Diau*,† Department of Applied Chemistry, Institute for Molecular Science and Center for Interdisciplinary Molecular Science, National Chiao Tung UniVersity, Hsinchu, Taiwan 300, Department of Applied Chemistry, National Chi Nan UniVersity, Puli, Nantou Hsien, Taiwan 545, and Department of Chemistry, National Taiwan Normal UniVersity, Taipei, Taiwan 116 ReceiVed: September 21, 2005; In Final Form: NoVember 4, 2005
The excited-state relaxation dynamics of a synthetic porphyrin, ZnCAPEBPP, in solution, coated on a glass substrate as solid films, mixed with PMMA and coated on a glass substrate as solid films, and sensitized on nanocrystalline TiO2 films were investigated by using femtosecond fluorescence up-conversion spectroscopy with excitation in the Soret band, S2. We found that the S2 f S1 electronic relaxation of ZnCAPEBPP in solution and on PMMA films occurs in 910 and 690 fs, respectively, but it becomes extremely rapid, ZnO, indicating a strong dependence on the nature of the semiconductor; the rate of injection depended on the redox potential of the photosensitizer, pH of the solution, and excitation energy. A two-state injection model was proposed: the rapid,
