Transient absorption spectroscopy of ruthenium and osmium polypyridyl complexes adsorbed onto nanocrystalline TiO2 photoelectrodes

Darius Kuciauskas, Jeremy E. Monat, Randy Villahermosa, Harry B. Gray, Nathan S. Lewis, James K. McCusker

Research output: Contribution to journalArticle

169 Citations (Scopus)

Abstract

Transient absorption spectroscopy has been used to probe the electron injection dynamics of transition metal polypyridyl complexes adsorbed onto nanocrystalline TiO2 photoelectrodes. Experiments were performed on photoelectrodes coated with Ru(H2L')2(CN)2, Os(H2L')2(CN)2, Ru(H2L')2(NCS)2, or Os(H2L')2(NCS)2, where H2L' is 4,4'-dicarboxylic acid-2,2'-bipyridine, to study how the excited-state energetics and the nature of the metal center affect the injection kinetics. All of these complexes exhibited electron injection dynamics on both the femtosecond and picosecond time scales. The femtosecond components were instrument-limited (<200 fs), whereas the picosecond components ranged from 3.3 ± 0.3 ps to 14 ± 4 ps (electron injection rate constants k2' = (7.1-30) × 1010 s-1). The picosecond decay component became more rapid as the formal excited-state reduction potential of the complex became more negative. Variable excitation wavelength studies suggest that femtosecond injection is characteristic of the nonthermalized singlet metal-to-ligand charge-transfer (1MLCT) excited state, whereas picosecond injection originates from the lowest-energy 3MLCT excited state. On the basis of these assignments, the smaller relative amplitude of the picosecond component for the Ru sensitizers suggests that electron injection from nonthermalized excited states competes more effectively with 1MLCT → 3MLCT conversion for the Ru sensitizers than for the Os sensitizers.

Original languageEnglish
Pages (from-to)9347-9358
Number of pages12
JournalJournal of Physical Chemistry B
Volume106
Issue number36
DOIs
Publication statusPublished - Sep 12 2002

ASJC Scopus subject areas

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

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