Effect of molecular mass on supramolecular organisation of poly(4,4″-dioctyl-2,2′:5′,2″-terthiophene)
作者:Tomasz Jaroch、Marek Knor、Robert Nowakowski、Małgorzata Zagórska、Adam Proń
DOI:10.1039/b805066j
日期:——
The effect of the chain length on the type and extent of the 2D supramolecular organization in poly(4,4â³-dioctyl-2,2â²:5â²,2â³-terthiophene) (PDOTT) monomolecular layers deposited on highly oriented pyrolytic graphite (HOPG) is studied by scanning tunneling microscopy (STM) and analyzed in terms of molecular modeling. The strictly monodispersed fractions of increasing molecular mass used in this study were obtained by chromatographic fractionation of the crude product of 4,4â³-dioctyl-2,2â²:5â²,2â³-terthiophene oxidative polymerization. STM investigations of PDOTT layers, deposited on HOPG from poly- and monodispersed fractions, show that polydispersity can be considered as a key factor seriously limiting supramolecular ordering. This is a consequence of significant differences in the type of supramolecular order observed for molecules of different chain length. It has been demonstrated that shorter molecules (consisting of 6 and 9 thiophene units) form well-defined two-dimensional islands, while the interactions between longer molecules (consisting of 12 and 15 thiophene units) become anisotropic. Consequently, for higher molecular mass fractions, the supramolecular organization is one-dimensional and consists of more or less separated rows of ordered macromolecules. In this case an increase of the chain length leads to amplification of the intermolecular interactions proceeding via interdigitation of the alkyl substituents of adjacent molecules. Polydispersed fractions show much less ordered organization because of the incompatibility of the supramolecular structures of molecules of different molecular masses. This finding is of crucial importance for the application of polythiophene derivatives in organic and molecular electronics since ordered supramolecular organization constitutes the condition sine qua non of good electrical transport properties.
通过扫描隧道显微镜(STM)研究了链长对聚(4,4³-二辛基-2,2²:5²,2³-三噻吩)(PDOTT)单分子层二维超分子组织类型和程度的影响,并进行了分子建模分析。本研究中使用的严格单分散的分子质量增加部分是通过4,4³-二辛基-2,2²:5²,2³-三噻吩氧化聚合的粗产品的色谱分离获得的。对聚和单分散部分沉积在HOPG上的PDOTT层的STM研究表明,多分散性可被视为严重限制超分子有序的关键因素。这是由于不同链长分子观察到的超分子有序类型存在显著差异。已经证明,较短的分子(由6个和9个噻吩单元组成)形成明确的二维岛,而较长分子(由12个和15个噻吩单元组成)之间的相互作用变得各向异性。因此,对于分子质量分数较高的情况,超分子组织是一维的,由或多或少分离的、有序的大分子排组成。在这种情况下,链长的增加导致分子间相互作用通过相邻分子的烷基取代基的交互作用而放大。由于不同分子质量的分子的超分子结构不兼容,多分散部分显示出更少的有序组织。这一发现对于聚噻吩衍生物在有机和分子电子学中的应用至关重要,因为有序的超分子组织是良好的电传输