噻吩环取代掺杂一维共轭碳基材料的电子输运

Electron Transport Pathways Through One-Dimensional Conjugated Carbon Chain Doped by Thiophene Ring

一维共轭碳基材料以苯环为基本单元,具有优越的导电性,分子光电器件的发展要求其在高导电性的前提下兼具富电子或少电子特征.本工作设计了噻吩环取代掺杂一维共轭碳基材料的寡聚苯并[1,2-b:4,5-b']二噻吩(BmT)和寡聚噻吩(TnP)分子模型,利用密度泛函理论结合非平衡格林函数方法研究了掺杂位置和掺杂程度对其输运行为的影响.噻吩环在一维共轭碳基材料上的取代掺杂有效提升了材料的电子输运效率.BmT和TnP分子的导电特性随分子长度的变化表明分子的共轭程度决定了电子输运效率.反式BmT和TnP分子具有多条电子传输路径,而顺式BmT和TnP分子随着分子长度增加,经历了由单条电子传输路径至多条电子传输路径的转变.该研究结果为开发高性能碳基分子电子材料提供了重要参考.

Represented by graphene and carbon nanotubes, one-dimensional（1D） conjugated carbon materials are potential ones to be used in molecular electronic devices. The further application of 1D conjugated carbon materials in optoelectronic devices requires that they have electron-poor/electron-rich characteristics, with the premise of high conductivity. Most of 1D conjugated carbon materials are constructed by aromatic rings as the basic units. Substitutional S atoms into benzene ring is an effective method to achieve electron doping into 1D conjugated carbon materials. Herein, to simulate the doping effect of 1D conjugated carbon materials, a series of oligobenzo [1,2-b：4,5-b＇] dithiophene（BmT） and oligothiophene（TnP） molecules were designed by substitutional doping thiophene ring into conjugated carbon skeleton. The influence of doping position and concentration on the electron transport properties were studied based on the nonequilibrium Green＇s function approach and density functional theory. Static electronic properties indicate that HOMO orbitals have higher delocalization on trans-configurations of BmT and TnP molecules as compared with cis-conjugations, indicating the higher conductivity of trans-BmT and trans-TnP. Dynamic transport behaviors demonstrate that the substitutional doping of thiophene rings can significantly improve the electron transport efficiency of carbon skeleton. The conductance trend of BmT and TnP molecules indicates that the electron transport efficiency through the compounds is dependent on their conjugation. The conductance of BmT and TnP molecules are not only dependent to the chain length, but also related to the energy gaps and electron transport pathways. Trans-BmT and trans-TnP are conjugated molecules with multiple pathways, however, cis-BmT and cis-TnP are conjugated molecules that can transform from a single pathway to multiple pathways, with the increase of chain length. The diversity of the electron transport behaviors of the thiophene-doped carbon skeletons is directly dominated by the electron transport pathways. Our work gives insight into the development of novel carbon-based molecular optoelectronic materials with high performance.