Department of Materials, Eidgenössische Technische Hochschule (ETH) Zürich , Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland.
J Am Chem Soc. 2013 Sep 18;135(37):13699-709. doi: 10.1021/ja405792b. Epub 2013 Sep 6.
This study is concerned with the thermal and structural characteristics of a series of precisely defined, monodisperse, regioregular oligo(3-hexylthiophene)s (3HT)n of n = 4-36. We find that these model compounds can feature two distinctly different solid-state structures, i.e., the more classical polymorph Form I in which the hexyl side-chains are not interdigitated and Form II in which they are. The thermodynamic equilibrium melting temperatures of these phases differ as much as ~180 °C, with 116 °C for Form II and 298 °C for Form I. Furthermore, polymorph II featured an enthalpy of melting of ~3 times that of Form I and a rate of crystallization that is ~1 order of magnitude lower than that of Form I. A crossover of the thermodynamically preferred Form II into the kinetically favored Form I is observed at a number of repeat units of 12. In the regime 10 ≤ n ≤ 21 the oligo(3-hexylthiophene)s could readily be reversibly converted from one polymorph to another by appropriate processing treatments. The relevance of these findings for the polymeric form (P3HT) is discussed.
本研究关注的是一系列精确定义的、单分散的、区域规则的寡聚（3-己基噻吩）（3HT）n 的热学和结构特性，n = 4-36。我们发现，这些模型化合物可以具有两种截然不同的固态结构，即较传统的无交错构象的晶型 I 和交错构象的晶型 II。这些相的热力学平衡熔融温度差异高达约 180°C，晶型 II 的熔融温度为 116°C，晶型 I 的熔融温度为 298°C。此外，晶型 II 的熔融焓约为晶型 I 的 3 倍，结晶速率比晶型 I 低约 1 个数量级。在重复单元数为 12 的多个位置观察到热力学上更优的晶型 II 向动力学上更有利的晶型 I 的交叉。在 10≤n≤21 的范围内，通过适当的处理可以将这些寡聚（3-己基噻吩）很容易地从一种晶型可逆地转化为另一种晶型。这些发现对聚合物形式（P3HT）的相关性进行了讨论。
