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Dissertation Information for Chunxing She

NAME:
- Chunxing She

DEGREE:
- Ph.D.

DISCIPLINE:
- Chemistry

SCHOOL:
- Emory University (USA) (2006)

ADVISORS:
- Tianquan Lian

COMMITTEE MEMBERS:
- Michael C. Heaven
- James T. Kindt

MPACT Status: Fully Complete

Title: Interfacial electron transfer from dyes to semiconductor nanocrystalline thin films: Effects ofpH, solvent, and cation and anchoring group

Abstract: Ultrafast IR absorption spectroscopy was employed to study the effects of pH, solvent, cation and anchoring group on photoinduced interfacial electron transfer (ET) from dyes to semiconductor nanocrystalline films, and solvation processes both in solution and at interfaces. These effects were explained based on nonadiabatic electron transfer theory by the dependencies of ET rate on density of electron-accepting states, conduction band edge, electronic coupling and reorganization energy. Solvation processes were found to be slower at interfaces due to restricted solvent motion at the interfaces. Interfacial ET from ReC1A to TiO 2 and ReC1P to SnO 2 and TiO 2 were measured as a function of pH. A sensitive dependence on pH was observed for ReC1P/TiO 2 and ReC1A/TiO 2 but not for ReC1P/SnO 2 . The sensitive dependence on TiO 2 was due to a rapidly changing density of electron-accepting states along the TiO 2 conduction band edge. The smaller dependence on SnO 2 was attributed to a much smaller variation of that change. ET dynamics from ReC1A to TiO 2 nanocrystalline thin films in different solvents and from ReC1P to TiO 2 in DMF with different amounts of adsorbed water were studied. We observed a dramatic difference in ET rate for ReC1A/TiO 2 in different solvents and attributed the difference to trace amounts of water adsorbed on TiO 2 that control the band edge of TiO 2 . The amount of adsorbed water on TiO 2 was varied to show that more adsorbed water led to a faster injection rate. We investigated ET dynamics from ReC1P to TiO 2 films in DMF with different concentrations of LiClO 4 . The half-rise injection times were >>1ns in all of these samples due to the higher conduction band edge of TiO 2 . The injection for ReC1P/TiO 2 in DMF was slightly accelerated due to a positive shift of the TiO 2 conduction band edge by 1 M LiClO 4 . ET dynamics in cis -Ru(dcbpyH 2 ) 2 (NCS) 2 /TiO 2 , cis -Ru(bpbpyH 2 ) 2 (NCS) 2 /TiO 2 , cis -Ru(dcbpyH 2 ) 2 (NCS) 2 /SnO 2 and cis -Ru(bpbpyH 2 ) 2 (NCS) 2 /SnO 2 were investigated. In cis -Ru(bpbpyH 2 ) 2 (NCS) 2 /TiO 2 , we observed a smaller amplitude of the <100 fs component and a faster injection rate for the ps component, compared to those of cis Ru(dcbpyH 2 ) 2 (NCS) 2 /TiO 2 . In cis -Ru(bpbpyH 2 ) 2 (NCS) 2 /SnO 2 , we observed a smaller amplitude of the <100 Es component and a similar injection rate for the ps component, compared to those of cis -Ru(dcbpyH 2 ) 2 (NCS) 2 /SnO 2 . Differences in electronic coupling and density of electron-accepting states were used to explain the observed rate differences. We demonstrated that ultrafast transient IR spectroscopy could be used to study the solvation dynamics of cis,trans -[Re(dmbpy)(CO) 2 (PPh 3 ) 2 ] + PF 6 - in organic solvents. We measured the vibrational peak-shift of cis,trans -[Re(dmbpy)(CO) 2 (PPh 3 ) 2 ] + PF 6 - in MeCN, DMF, C 6 H 5 CN and BuOH, and observed that the solvation dynamics in the solvents slowed in the order of MeCN > DMF > C 6 H 5 CN > BuOH. We applied ultrafast IR absorption spectroscopy to compare peak-shift dynamics in both bulk alcohol solutions and at the ZrO 2 /alcohol interface. In bulk alcohol, the peak shift amplitude decreased and dynamics slowed in longer chain alcohols. At the interface, the peak shift amplitude was smaller and dynamics were slower than that in the corresponding bulk solution. We attributed these vibrational peak-shift dynamics to solvation processes, and utilized them to compare solvation dynamics in bulk solutions and at nanoparticle/liquid interfaces.

MPACT Scores for Chunxing She

A = 0
C = 0
A+C = 0
T = 0
G = 0
W = 0
TD = 0
TA = 0
calculated 2008-03-16 15:53:50

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