Rohde Dirk, Dunsch Lothar, Tabet Ahacine, Hartmann Horst, Fabian Jürgen
Leibniz-Institut für Festkörper- und Werkstoffforschung, Abteilung Elektrochemie und Leitfähige Polymere, Helmholtzstrasse 20, D-01069 Dresden, Germany.
J Phys Chem B. 2006 Apr 27;110(16):8223-31. doi: 10.1021/jp054401i.
A new homologous series of alpha,alpha'-bis(diphenylamino)-capped oligothiophenes, prepared by a palladium-catalyzed coupling reaction of stannylated 2-diphenylaminothiophenes with 2-mono- or 2,5-dibromothiophenes and their homologues, was studied by in situ ESR/UV-vis/NIR spectroelectrochemistry. In general, the oxidation potentials of these oligothiophenes were found to be proportional to the inverse number of thiophene units. However, the potential slope of the first oxidation is completely different from that of higher oxidation steps. Trication radicals were identified by electron spin resonance (ESR) for higher thiophene homologues in addition to monocation radicals (polarons). According to the ESR hyperfine structures, the unpaired electron is delocalized in the conjugated system. In contrast to the parent alpha,alpha'-bis(diphenylamino)-capped oligothiophenes, the UV-vis/NIR absorption maxima of the oxidized species strongly depend on the number of thiophene units. Spin-restricted and spin-unrestricted Kohn-Sham density functional calculations were used to explain and to understand these properties. Absorption wavelength and intensities were calculated by the time-dependent density functional response theory. Unrestricted density functional calculations of oligothiophene dications (bipolarons) with five or more thiophene rings result in spin-broken structures which may be considered as two-polaron biradicals (polaron pairs).
通过锡基化的2-二苯胺基噻吩与2-单溴或2,5-二溴噻吩及其同系物的钯催化偶联反应制备了一系列新的α,α'-双（二苯胺基）封端的低聚噻吩，并采用原位电子自旋共振/紫外-可见/近红外光谱电化学方法对其进行了研究。一般来说，这些低聚噻吩的氧化电位与噻吩单元的倒数成正比。然而，第一次氧化的电位斜率与更高氧化步骤的电位斜率完全不同。除了单阳离子自由基（极化子）外，通过电子自旋共振（ESR）还鉴定出了较高噻吩同系物的三阳离子自由基。根据ESR超精细结构，未成对电子在共轭体系中离域。与母体α,α'-双（二苯胺基）封端的低聚噻吩不同，氧化态物质的紫外-可见/近红外吸收最大值强烈依赖于噻吩单元的数量。采用自旋限制和自旋非限制的Kohn-Sham密度泛函计算来解释和理解这些性质。通过含时密度泛函响应理论计算吸收波长和强度。对具有五个或更多噻吩环的低聚噻吩双阳离子（双极化子）进行的非限制密度泛函计算得到了自旋断裂结构，该结构可被视为双极化子双自由基（极化子对）。
