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Dissertation Information for John Barber Asbury

NAME:
- John Barber Asbury

DEGREE:
- Ph.D.

DISCIPLINE:
- Chemistry

SCHOOL:
- Emory University (USA) (2001)

ADVISORS:
- Tianquan Lian

COMMITTEE MEMBERS:
- Michael C. Heaven
- Ming-Chang Lin

MPACT Status: Fully Complete

Title: Interfacial electron transfer studied by femtosecond infrared spectroscopy

Abstract: "Femtosecond mid-infrared spectroscopy was used to study interfacial electron transfer dynamics from a series of Ru and Re polypyridyl sensitizers to TiO 2 and SnO 2 nanocrystalline thin films. A kinetic model describing interfacial electron transfer has been developed which allows the interfacial electron injection dynamics to be quantified. The kinetic model allows the comparison of the measured electron injection rates with classical Marcus theory for non-adiabatic electron transfer by incorporating the effects of the semiconductor conduction band and trap state distributions as well as the sensitizer excited state dynamics. The sensitizer excited state dynamics were described by a two state system so that electron injection occurred either from the energetically hot or the cooled excited states. A systematic study of the dependence of the electron transfer dynamics on excited state energy, pH, solvent, electronic coupling and pump wavelength demonstrated that the model is a good approximation of the electron transfer process. For sensitizers strongly adsorbed to TiO 2 film, the electron injection dynamics were highly non-exponential and occurred in two distinct phases. The first phase of injection occurred from the energetically hot excited state with characteristic time constant <100 fs and was relatively insensitive to the energy of the excited state relative to the conduction band. The fast injection component was estimated to contribute about 50% of the injection process. The second phase occurred with a much longer time constant from the energetically relaxed excited state. The time scale of the slow injection phase varied from the sub-picosecond to 100's of picoseconds time scales, nearly three orders of magnitude over an almost 1 eV range in driving force. The slow injection dynamics were quantified by correcting the measured electron absorption dynamics for the effect of electron absorption cross section decay in the semiconductor. The dependence of the time scales of the slow electron injection phases on driving force could be quantitatively described by non-adiabatic electron transfer theory modified for the semiconductor as the acceptor. The reorganization energy and electronic coupling were established from the model to be 0.9 eV and 145 cm -1 respectively for all the Ru sensitizers.

The dependence of interfacial electron transfer on solvent and excitation wavelength was investigated for Ru sensitizers on TiO 2 film and compared with the theory.

When the electronic coupling is low between the sensitizes and semiconductor, the two-state kinetic model predicts a single phase electron injection process from the energetically relaxed excited state."

MPACT Scores for John Barber Asbury

A = 0
C = 0
A+C = 0
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G = 0
W = 0
TD = 0
TA = 0
calculated 2009-06-14 12:04:17

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