SYNTHESIS AND CHARACTERIZATION OF THE ELECTRONIC AND ELECTROCHEMICAL PROPERTIES OF THIENYLENEVINYLENE OLIGOMERS WITH MULTINANOMETER DIMENSIONS

Soluble thienylenevinylene oligomers based on 3,4-dihexylthiophene wit h chain length approaching 100 Angstrom (16-mer) have been synthesized , Optical data obtained in solution and on solution-processed thin fil ms show that chain extension produces a narrowing of the HOMO-LUMO gap (Delta E) and band gap (E-g) which reach values significantly smaller than that of the parent polymer. Plots of Delta E and E-g vs the reci procal number of carbons in the chain (1/Cn) reveal a deviation from L inearity beyond the 10-12-mer suggesting a limit of convergence around the 20-22-mer. Cyclic voltammetry shows that chain lengthening induce s a negative shift of the first redox potential, an increase of the nu mber of accessible redox states, and a decrease of the Coulombic repul sion in multicationic species. Thus, the 16-mer can be charged up to t he hexacationic state within a 0.60-V potential window. A plot of the potential of the various redox steps vs 1/Cn suggests full coalescence into a single-step process for the 20-22-mar, A single process is ind eed observed for solution cast films of 16-mer, and the respective con tributions of the intra- and intermolecular mechanisms in the recombin ation process are discussed.