Abstract
This dissertation employed an ultrafast time-resolved fluorescence (TRFL) spectrometer implemented by optical Kerr gating (OKG) and density functional theory calculations implemented in the Gaussian 09 program to study electron transfer dynamics in tetracyanoethylene-methylbenzene (TCNE-MBZ) complexes (MBZ = Benzene, Toluene, p-Xylene) in two solvents (CH2Cl2, CCl4) of different polarities. We used femtosecond laser to excite the TCNE-MBZ complexes to the CT-states, and the resulting TRFL spectra were measured. Analyses of the total fluorescence intensity function P(t), which describes the temporal evolution of excited state population and transition dipole moment, revealed complex relaxations associated with charge recombination (CR). We found different decay behaviors in two solvents. The fastest component which are in the similar time scale (< 0.2 ps) for the three complexes is assigned to CT2→CT1 transition, and the slowest component is ascribed to CR. The CR time constants in CH2Cl2 for TCNE-p-Xylene, TCNE-Toluene, TCNE- Benzene are 0.5, 7 and 29 ps, respectively, The CR time constants in CCl4 for TCNE-p-Xylene, TCNE-Toluene, TCNE- Benzene are 290, 820 and 150 ps, respectively. We concluded that CR time constants are consisted with the behavior in the Marcus inverted region. However the CR rates in CCl4 is reverted when the driving force(-∆G0) increase in the case of TCNE-Benzene. We use the intersecting state model (ISM) to explain this unexpected behavior. ISM accounts for structural relaxation of complex which the Marcus theory does not consider. Finally, we found that the CR rates of complexes in polar solvent is faster than in nonpolar solvent, which is mostly due to solvation effet.