Cyclic voltammetry and differential cyclic voltabsorptometry of soluble oligothiophenes: evidence for a four-fold charged π-dimer in duodecithiophene

Abstract Cyclic voltammetry (CV) and differential cyclic voltabsorptometry (DCVA) measurements have been carried out on solutions of alkyl-substituted oligothiophenes ( n T, where n is the number of thiophene rings) with n = 1, 2, 3, 4, 6, 8, and 12. For 4 ⩽ n ⩽ 8, the CV curves present two oxidation waves, which are attributed to the successive formation of the radical cation and the dication. The DCVA curve of 6T shows similar behavior. In the case of 12T, the CV curve also presents two irreversible oxidation peaks, whereas only one peak is obtained with DCVA. This last behavior is consistent with previously reported measurements on chemically oxidized 12T. When plotted as a function of the reversed number of rings, the first and second oxidation peak potentials align along two straight lines that tend to merge at n → ∞. The single oxidation potential of 12T, estimated from DCVA, aligns with the first oxidation potential of shorter oligothiophenes. By combining these results with previously published optical and ESR measurements on chemically oxidized 6T and 12T, we suggest a model where oxidized 12T molecules condense into four-fold charged π-dimers.

[1]  D. Fichou,et al.  Stoichiometric control of the successive generation of the radical cation and dication of extended α-conjugated oligothiophenes: a quantitative model for doped polythiophene , 1990 .

[2]  J. Tour,et al.  Electrooxidation of Soluble Alpha, Alpha-Coupled Thiophene Oligomers , 1992 .

[3]  D. Corbin,et al.  Preparation and spectroscopic characterization of polarons and bipolarons of thiophene oligomers within the channels of pentasil zeolites : the evolution of organic radical ions into conducting polymers , 1991 .

[4]  J. Pernaut,et al.  Electrochemical Evidence of .pi.-Dimerization with Short Thiophene Oligomers , 1994 .

[5]  A. Bard,et al.  Electron transfer to and from molecules containing multiple, noninteracting redox centers. Electrochemical oxidation of poly(vinylferrocene) , 1978 .

[6]  J. Tour,et al.  Chain-length dependence of electrochemical and electronic properties of neutral and oxidized soluble .alpha.,.alpha.-coupled thiophene oligomers , 1992 .

[7]  Gilles Horowitz,et al.  Synthesis and characterization of a tetra‐alkylated alpha‐conjugated duodecithiophene , 1992 .

[8]  C. Visy,et al.  Cyclic spectrovoltammetry: a new method to study the redox processes in conductive polymers , 1992 .

[9]  M. Mehring,et al.  Didodecylsexithiophene—A Model Compound for the Formation and Characterization of Charge Carriers in Conjugated Chains , 1993 .

[10]  A. Yassar,et al.  Effects of steric factors on the electrosynthesis and properties of conducting poly(3-alkylthiophenes) , 1987 .

[11]  E. Lous,et al.  Metal-insulator-semiconductor Schottky-type diodes of doped thiophene oligomers , 1994 .

[12]  Peter Bäuerle,et al.  End-capped oligothiophenes—new model compounds for polythiophenes† , 1992 .

[13]  S. Hotta,et al.  Alkyl-substituted oligothiophenes: crystallographic and spectroscopic studies of neutral and doped forms , 1991 .

[14]  J. Roncali,et al.  Electro-oxidation of substituted conjugated sexithienyls , 1993 .

[15]  B. Servet,et al.  Molecular engineering of organic semiconductors: design of self-assembly properties in conjugated thiophene oligomers , 1993 .

[16]  Zuppiroli,et al.  Stability of transverse bipolarons in conducting polymers. , 1994, Physical review. B, Condensed matter.

[17]  Wei Wan-zhi,et al.  Differential linear sweep and differential cyclic voltabsorptometry in a long-path-length spectroelectrochemical cell: Eqr, Eir and ErCi′ , 1993 .

[18]  M. Mehring,et al.  Electronic structure of mono- and dimeric cation radicals in end-capped oligothiophenes , 1993 .

[19]  L. Nie,et al.  Derivative linear sweep and derivative cyclic voltabsorptometry of the long-path-length spectroelectrochemical cell: The single reversible electrode reaction , 1993 .

[20]  R. L. Elsenbaumer,et al.  Handbook of conducting polymers , 1986 .

[21]  Gilles Horowitz,et al.  Electrochemical coupling of dialkylated sexithiophene , 1992 .

[22]  E. E. Bancroft,et al.  Derivative linear sweep and derivative cyclic voltabsorptometry , 1981 .

[23]  Gilles Horowitz,et al.  Crystal structure of α,ω‐bis(triisopropylsilyl)‐sexithiophene: Unusual conjugated chain distortion induced by interchain steric effects , 1994 .

[24]  D. Fichou,et al.  Polaron and bipolaron formation on isolated model thiophene oligomers in solution , 1990 .

[25]  M. Hill,et al.  Photochemical Formation of Oligothiophene Cation Radicals in Acidic Solution and Nafion , 1992 .

[26]  M. Hill,et al.  Oligothiophene Cation Radicals. π-Dimers as Alternatives to Bipolarons in Oxidized Polythiophenes , 1992 .

[27]  M. Hill,et al.  Oligothiophene cation radical dimers. An alternative to bipolarons in oxidized polythiophene , 1992 .

[28]  D. Leeuw.  Stable solutions of doped thiophene oligomers , 1993 .

[29]  G. Horowitz,et al.  ESR and optical spectroscopy evidence for a chain-length dependence of the charged states of thiophene oligomers. Extrapolation to polythiophene , 1994 .

[30]  G. Zotti,et al.  Thiophene oligomers as polythiophene models. 1. Anodic coupling of thiophene oligomers to dimers: a kinetic investigation , 1993 .