| Transient absorption experiments were used for ultrafast studies of intramolecular energy transfer in solution. In studying these energy transfer processes, three different systems are considered. The first two, xanthione and Michler's thione, are known to be exceptions to Kasha's rule and are excellent probes of upper electronic state dynamics. Both molecules are also important for illustrating the significance of solvent on intramolecular relaxation processes. The third system studied is 4-phenylbenzophenone, which has two separate chromophores. This opens up the possibility of intramolecular energy transfer from one chromophore to another.; The transient signal of xanthione was analyzed as a combination of signals originating from the S{dollar}sb2{dollar} and T{dollar}sb1{dollar} electronic states. Analysis of these signals allowed for the determination of the lifetime of the S{dollar}sb2{dollar} state and the growth of the T{dollar}sb1{dollar} state. The measured S{dollar}sb2{dollar} lifetimes appear to have a significant dependence on the nature of the solvent. For polar solvents, the faster lifetimes are explained by the stabilization of the {dollar}rmpipisp{lcub}*{rcub} Ssb2{dollar} state which leads to a more rapid {dollar}rm Ssb2to Ssb1{dollar} internal conversion. The differences in S{dollar}sb2{dollar} lifetime that are observed between linear and branched alkanes cannot be definitively explained but possible mechanisms involving collision frequencies and interactions with tertiary solvent hydrogen are proposed. Measurements of the S{dollar}sb2{dollar} lifetimes are not equivalent to the growth of the triplet state absorption which is indicative of an important relaxation process occurring. Approximate ranges for the intersystem crossing time lead to the conclusion that intersystem crossing is also dependent on the solvent.; The transient signal for Michler's thione is much simpler to analyze than xanthione due to the lack of spectral overlap; however, due to the nonrigidity of Michler's thione, it is difficult to draw quantitative comparisons between the two molecules. Qualitatively, it was observed that the triplet and singlet absorptions occur in the same general regions, and the kinetics of the singlet state shows a similar polar/nonpolar solvent dependence.; Early experiments on 4-phenylbenzophenone (PBP) suggested that there was a triplet-triplet energy transfer between the benzophenone and biphenyl chromophores. This mechanism is investigated and a new model involving a phenyl ring isomerization is discussed. The intersystem crossing time is found to be identical within error in benzophenone and PBP. Unlike benzophenone, PBP can undergo a structural change in the excited state which shuts off the intersystem crossing due to the significant decrease in potential energy, dropping the S{dollar}sb1{dollar} state below the T{dollar}sb1{dollar} state. This drop in energy also decreases the S{dollar}sb1{dollar}-S{dollar}sb0{dollar} energy, enhancing the internal conversion significantly over benzophenone. |
