Synthesis and Characterization of the Electronic and Electrochemical Properties of Thienylenevinylene Oligomers with Multinanometer Dimensions

Soluble thienylenevinylene oligomers based on 3,4-dihexylthiophene with chain length approaching 100 Å (16-mer) have been synthesized. Optical data obtained in solution and on solution-processed thin films show that chain extension produces a narrowing of the HOMO−LUMO gap (Δ E ) and band gap ( E g ) which reach values significantly smaller than that of the parent polymer. Plots of Δ E and E g vs the reciprocal number of carbons in the chain (1/Cn) reveal a deviation from linearity beyond the 10−12-mer suggesting a limit of convergence around the 20−22-mer. Cyclic voltammetry shows that chain lengthening induces a negative shift of the first redox potential, an increase of the number of accessible redox states, and a decrease of the Coulombic repulsion in multicationic species. Thus, the 16-mer can be charged up to the 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-mer. A single process is indeed observed for solution cast films of 16-mer, and the respective contributions of the intra- and intermolecular mechanisms in the recombination process are discussed.