Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima, 739-8527, Japan.
Dalton Trans. 2010 Oct 21;39(39):9314-20. doi: 10.1039/c0dt00224k. Epub 2010 Aug 4.
Star-shaped compounds with three or four oligothiophene units linked by an organosilicon core were prepared and their hole-transport capabilities were studied. A top-contact type thin film transistor (TFT) with a vapour-deposited film of tris[(ethylterthiophenyl)dimethylsilyl]methylsilane (3T(3)Si(4)) showed field-effect mobility (μ(FET)) of 4.4 × 10(-5) cm(2) V(-1) s(-1), while the device with the carbon centred analogue tris[(ethylterthiophenyl)dimethylsilyl]methane (3T(3)Si(3)C) showed no TFT activity. Intrinsic intramolecular hole mobility of 3T(3)Si(4) and 3T(3)Si(3)C was determined by time-resolved microwave conductivity measurements to be 8 × 10(-2) and 2 × 10(-2) cm(2) V(-1) s(-1), respectively, arising from higher degree of σ-π interaction in 3T(3)Si(4). To know more about the effects of the organosilicon core structures on the intermolecular hole mobility, we calculated internal reorganization energies for hole transfer at the (U)B3LYP/6-311+G(d,p)//(U)B3LYP/6-31G(d) level, which suggested smoother intermolecular charge transfer in the silicon derivative than the carbon and germanium analogues. Star-shaped compounds with quarterthiophene units behave in a different manner from the terthiophene derivatives and tris[(ethylquarterthiophenyl)dimethylsilyl]methane (4T(3)Si(3)C) showed higher TFT mobility of μ(FET) = 1.2 × 10(-3) cm(2) V(-1) s(-1) than its silicon analogue (4T(3)Si(4): μ(FET) = 5.4 × 10(-4) cm(2) V(-1) s(-1)). This is probably due to the more condensed packing of 4T(3)Si(3)C in the film, arising from the shorter Si-C bonding. Compounds with four terthiophene units were also prepared and tetrakis[(ethylterthiophenyl)-dimethylsilyl]silane (3T(4)Si(5)) showed the mobility of μ(FET) = 2.0 × 10(-4) cm(2) V(-1) s(-1), higher than that of 3T(3)Si(4), indicating the potential of tetrakis(oligothiophenyl) compounds as the TFT materials. Tetrakis[(ethylterthiophenyl)dimethylsilyl]germane (3T(4)Si(4)Ge) was less thermally stable and could not be processed to a film by vapour-deposition, but was found to be TFT active in the spin-coated film, although the mobility was rather low (μ(FET) = 7.7 × 10(-7) cm(2) V(-1) s(-1)).
具有三个或四个通过有机硅核连接的寡噻吩单元的星形化合物被制备，并研究了它们的空穴传输能力。具有三[(乙基三噻吩基)二甲基硅基]甲基硅烷（3T（3）Si（4））蒸气沉积膜的顶接触型薄膜晶体管（TFT）显示出场效应迁移率（μ（FET））为 4.4×10（-5）cm（2）V（-1）s（-1），而具有碳中心类似物三[(乙基三噻吩基)二甲基硅基]甲烷（3T（3）Si（3）C）的器件则没有 TFT 活性。通过时间分辨微波电导率测量确定 3T（3）Si（4）和 3T（3）Si（3）C 的本征分子内空穴迁移率分别为 8×10（-2）和 2×10（-2）cm（2）V（-1）s（-1），这归因于 3T（3）Si（4）中更高程度的σ-π相互作用。为了更多地了解有机硅核结构对分子间空穴迁移率的影响，我们在（U）B3LYP/6-311+G（d，p）//（U）B3LYP/6-31G（d）水平上计算了空穴转移的内部重组能，这表明硅衍生物中的分子间电荷转移更为平滑比碳和锗类似物。具有四噻吩单元的星形化合物的行为与噻吩衍生物不同，三[(乙基四噻吩基)二甲基硅基]甲烷（4T（3）Si（3）C）的 TFT 迁移率比其硅类似物（4T（3）Si（4）高：μ（FET）= 1.2×10（-3）cm（2）V（-1）s（-1））更高。这可能是由于 4T（3）Si（3）C 在薄膜中的更密集堆积，这是由于 Si-C 键更短。还制备了具有四个噻吩单元的化合物，并且四[(乙基三噻吩基)-二甲基硅基]硅烷（3T（4）Si（5））显示出迁移率μ（FET）= 2.0×10（-4）cm（2）V（-1）s（-1），高于 3T（3）Si（4），表明四（寡噻吩基）化合物作为 TFT 材料的潜力。四[(乙基三噻吩基)二甲基硅基]锗烷（3T（4）Si（4）Ge）的热稳定性较低，无法通过蒸气沉积加工成薄膜，但在旋涂薄膜中发现具有 TFT 活性，尽管迁移率相当低（μ（FET）= 7.7×10（-7）cm（2）V（-1）s（-1））。
