The Agreement of Poly-5,5’-(4,4’-Dinonyl-2,2’Bithiazole) Spectral Signatures to those of Corresponding Oligomers

Study of the electronic spectra of conjugated oligomers can provide a useful approach to obtain an analysis of the often complicated spectra of their corresponding polymers. One advantage of studying oligomers is that there is often a well defined conformational morphology and one may eliminate or reduce the spectral consequences of a distribution of conjugation lengths. In the present work, electronic spectra of some oligomers of poly-5,5’-(4,4’-dinonyl-2,2’bithiazole) were studied, both in solution and in the solid state, and the results compared with spectra of the polymer. For solution data, the plot of molar extinction coefficient vs. the number of double bonds is found to be linear, as is the Kuhn plot. This is consistent with quantum-chemical molecular modeling calculations, and closely resembles the behavior of other conjugated oligomers, such as polythiophenes and polyenes. However, the solid state spectra exhibit a large red shift in both absorption and emission. These and other results suggest the presence of strong intermolecular interactions in the solid state that significantly modify the magnitude of the homo-lumo gap of the oligothiazoles and their polymers. By comparing oligothiazoles in solution to thin film results, polymer behavior is explored.