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, Eric Wei Guang Diau

Research output: Contribution to journalArticle

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Abstract

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→S1 electronic relaxation of ZnCAPEBPP in solution and on PMMA films occurs- in 910 and 690 fs, respectively, but it becomes extremely rapid, <100 fs, in solid films and TiO2 films due to formation of porphyrin aggregates. When probed in the Si state of porphyrin, the fluorescence transients of the solid films show a biphasic kinetic feature with the rapid and slow components decaying in 1.9-2.4 and 19-26 ps, respectively. The transients in ZnCAPEBPP/TiO2 films also feature two relaxation processes but they occur on different time scales, 100-300 fs and 0.8-4.1 ps, and contain a small offset. According to the variation of relaxation period as a function of molecular density on a TiO 2 surface, we assigned the femtosecond component of the TiO 2 films as due to indirect interfacial electron transfer through a phenylethynyl bridge attached to one of four meso positions of the porphyrin ring, and the picosecond component arising from intermolecular energy transfer among porphyrins. The observed variation of aggregate-induced relaxation periods between solid and TiO2 films is due mainly to aggregation of two types: J-type aggregation is dominant in the former case whereas H-type aggregation prevails in the latter case.

Original languageEnglish
Pages (from-to)410-419
Number of pages10
JournalJournal of Physical Chemistry B
Volume110
Issue number1
DOIs
Publication statusPublished - 2006 Jan 12

Fingerprint

Porphyrins
porphyrins
electron transfer
Agglomeration
Fluorescence
Electrons
fluorescence
Polymethyl Methacrylate
Glass
Energy Transfer
Spectrum Analysis
glass
Relaxation processes
Substrates
Excited states
Energy transfer
excitation
energy transfer
Spectroscopy
Kinetics

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

Cite this

Femtosecond fluorescence dynamics of porphyrin in solution and solid films : The effects of aggregation and interfacial electron transfer between porphyrin and TiO2. / Luo, Liyang; Lo, Chen Fu; Lin, Ching Yao; Chang, I. Jy; Diau, Eric Wei Guang.

In: Journal of Physical Chemistry B, Vol. 110, No. 1, 12.01.2006, p. 410-419.

Research output: Contribution to journalArticle

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