PH-dependent electron transfer from re-bipyridyl complexes to metal oxide nanocrystalline thin films

Chunxing She, Neil A. Anderson, Jianchang Guo, Fang Liu, Wan Hee Goh, Dai Tao Chen, Debra L. Mohler, Zhong Qun Tian, Joseph T. Hupp*, Tianquan Lian

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

62 Scopus citations


Photoinduced interfacial electron transfer (ET) from molecular adsorbates to semiconductor nanoparticles has been a subject of intense recent interest. Unlike intramolecular ET, the existence of a quasicontinuum of electronic states in the solid leads to a dependence of ET rate on the density of accepting states in the semiconductor, which varies with the position of the adsorbate excited-state oxidation potential relative to the conduction band edge. For metal oxide semiconductors, their conduction band edge position varies with the pH of the solution, leading to pH-dependent interfacial ET rates in these materials. In this work we examine this dependence in Re(L P)(CO) 3Cl (or ReC1P) [L P = 2,2′-bipyridine-4,4′-bis- CH 2PO(OH) 2] and Re-(L A)(CO) 3Cl (or ReC1A) [L A = 2,2′-bipyridine-4,4′-bis-CH 2COOH] sensitized TiO 2 and ReC1P sensitized SnO 2 nanocrystalline thin films using femtosecond transient IR spectroscopy. ET rates are measured as a function of pH by monitoring the CO stretching modes of the adsorbates and mid-IR absorption of the injected electrons. The injection rate to TiO 2 was found to decrease by 1000-fold from pH 0-9, while it reduced by only a factor of a few to SnO 2 over a similar pH range. Comparison with the theoretical predictions based on Marcus' theory of nonadiabatic interfacial ET suggests that the observed pH-dependent ET rate can be qualitatively accounted for by considering the change of density of electron-accepting states caused by the pH-dependent conduction band edge position.

Original languageEnglish (US)
Pages (from-to)19345-19355
Number of pages11
JournalJournal of Physical Chemistry B
Issue number41
StatePublished - Oct 20 2005

ASJC Scopus subject areas

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


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