Electrostatic properties of charge-transfer systems

The research carried out in this thesis focuses on the electrostatic properties of molecules that undergo photo-induced charge transfer. Electroabsorption spectroscopy is used to obtain information about the extent of charge separation and electron delocalization in the initially prepared Franck-Condon state, with respect to the ground state. Molecules that undergo excited-state intramolecular proton transfer (ESIPT) and twisted-intramolecular charge transfer (TICT), where the charge-transfer reaction is coupled to a change in geometry, are studied in this thesis. In ESIPT systems, electroabsorption spectroscopy is complemented with electronic-structure calculations and solvatochromism to gain insight into the mechanism of proton transfer. It is found that the electronic nature of ESIPT systems in the Franck-Condon region is predisposed to strongly favour proton transfer. The electroabsorption studies on the TICT molecule, p-N,N-dimethylaminobenzonitrile (DMABN), indicate that the free volume in the polymer matrix may have a significant effect on the electrostatic interactions and properties of DMABN. In addition to systems that undergo ESIPT and TICT, charge-transfer in conjugated polymeric systems has also been investigated. Both the conducting and insulating forms of polyaniline, studied using electroabsorption spectroscopy, show evidence for the influence of structural disorder on the electronic properties of these systems. The evidence for substantial geometric disorder in the non-doped, emeraldine base form of polyaniline is further substantiated with semi-empirical calculations.