SPECTROSCOPY AND PHOTOPHYSICS OF SOME OLIGOMERS AND POLYMERS DERIVED FROM THIOPHENES

A series of bithiophene and terthiophene derivatives and their respect ive polymers have been prepared. The absorption and fluorescence spect ra, quantum yields, and lifetimes of these derivatives in solution are studied and compared. The bandwidths of the absorption and fluorescen ce profiles of the different derivatives are used to discuss the geome try changes occurring from one molecule to the other in the ground and excited states. Increasing the chain length and/or substitution of bi thiophene and terthiophene at both ends of the molecule with a carbony l chloride group increases the planarity of the molecules in both thei r ground and excited states by improving the electronic delocalization throughout the molecular frame. Comparison between the absorption and fluorescence spectra has proved to be a good tool to discover conform ational changes occurring during the relaxation of the excited state. All the molecules investigated show geometrical changes from a twisted ground state to a more planar conformation in the excited state. A ra diationless torsional mechanism and intersystem crossing processes are involved in the excited state relaxation of,the various molecules. In corporation of substituted bithiophene and terthiophene units in aroma tic polyesters have been made and the optical and photophysical proper ties of these polymers are studied. It is shown that the bithiophene a nd terthiophene units are perfectly isolated in the polymeric chain. T he photophysical properties of the polyesters make these materials goo d candidates for the fabrication of efficient blue-light-emitting diod es.