Journal of the American Chemical Society, Vol.120, No.32, 8150-8158, 1998
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 Angstrom (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 (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 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-mar, 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.
Keywords:OLIGOTHIOPHENE CATION RADICALS;EFFECTIVE CONJUGATION LENGTH;END-CAPPED OLIGOTHIOPHENES;LIGHT-EMITTING DEVICES;THIOPHENE OLIGOMERS;SOLID-STATE;POLY(P-PHENYLENE VINYLENE);POLY(THIENYLENE VINYLENE);ELECTRICAL-PROPERTIES;CONDUCTING POLYMERS