| The research carried out in this thesis focuses on the determination of some very basic and important electrostatic properties that characterize the electronic states and optical transitions in molecules. Stark (Electroabsorption) Spectroscopy was used to quantitatively determine the change of the permanent dipole moment and the static electronic polarizability between the ground and excited electronic states upon optical excitation, for chromophores in the condensed phase relevant in chemistry, biology, and materials science.; Stark spectroscopic investigation on a solvatochromic probe coumarin 153, reveal that the presence of polar dopant molecules in polymer matrices can significantly alter the local polarity of cavities, especially for polar polymers having a high glass transition temperature. The observed enhancement of polarity of the local environment in such polymers is significant from the standpoint of applications in the development of non-linear optical devices. Furthermore, we have found that measured changes in electronic polarizability of dopant molecules are extremely sensitive to the rigidity and mobility of polymer and solvent glass matrices. Stark spectroscopy can thus be a valuable tool to monitor the flexibility and motions inside polymer matrices, which are important from the standpoint of photorefractive applications.; Our studies on blue copper proteins, which are involved in biological electron transfer, reveal a small value for the dipole moment changes upon electronic excitation. We obtained a large value for the ground state electron-transfer coupling matrix, similar to that observed in inorganic charge-transfer systems. This supports previous observations that the there is a high degree of ground state electron delocalization which lowers the electron transfer barrier in the proteins.; Finally, we have studied various H- and J-aggregates of cyanine dyes that were formed using double helical DNA as templates, using absorption, fluorescence and Stark spectroscopies. The control over the structure and the number of molecules constituting the aggregates enabled us to see the effect of electronic coupling and aggregate size on the extent of electronic delocalization, which was correlated to the spectroscopic aggregation number. The delocalization of the wavefunction was found to be restricted over two molecules for all the H-aggregates, in contrast to the J-aggregates where around five to six molecules were estimated to be excited collectively. (Abstract shortened by UMI.)... |
