Applications of time-resolved linear dichroism spectroscopy

This dissertation describes the applications of time-resolved spectroscopy with linearly polarized light. The ability to obtain the orientational information with polarized spectroscopy is a powerful tool in the understanding of solution dynamics, in the determination of molecular structure, and in the study of the topochemistry of bimolecular reactions in solution. Applications of polarized spectroscopy in these three areas have been considered and conclusions about the importance of experimental factors on successful accomplishment of polarized measurements have been drawn.; The first study describes a few experiments aimed at investigating the rotational relaxation of aromatic molecules in liquid hydrocarbons. The conventional Debye-Stokes-Einstein rotational model was presented and the applicability of the ellipsoidal shape approximation to these molecules was tested. Conclusions about anisotropic rotation of these molecules were made based on the results produced by this method in a series of experiments using solvents of increasing viscosity. Selective excitation and probing accessing transitions with transition moment vectors differently directed within the molecular framework provided more information on the character of molecular rotation than the fluorescence anisotropy method.; The second study describes experiments aimed at determination of transition dipole moment vectors direction in the excited state of an aromatic molecule. Complete dichroic absorption spectra of the probe molecule in the excited state were obtained and the transition moment vectors determined from the dichroism for each observed transition. The knowledge of TMVs in itself is useful in determining details about the excited state molecular structure. From the theoretical standpoint comparison of the calculated and the experimental transition moment vectors can provide an insight on the completeness of the basis set chosen for the quantum mechanical calculations.; Time-resolved linear dichroism topochemical experiments on a series of charge transfer complexes is the topic of the third study. It was generally assumed that excitation of a charge transfer complex in the charge transfer absorption band leads directly to a contact ion pair. Recent reports of rapid relaxations, "loose" ion pairs and multiple ground states suggest this model is severely oversimplified. The obtained results were found to be consistent with the relaxation process being electronic in nature rather than being purely geometric. The exact nature of the excited states involved is not totally clear at this point, but it is likely the admixing of the localized excited states to the charge-transfer excited states is taking place at least for the weaker CT complexes.