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 (ΔE) and band gap (Eg) which
reach values significantly smaller than that of the parent polymer. Plots of ΔE and Eg 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.