吲哚并咔唑类衍生物载流子传输性质的理论研究

以密度泛函理论结合跳跃模型, 重点研究了氯原子和烷基链的引入对吲哚并咔唑类衍生物传输性质的影响. 计算结果表明, 与吲哚并[3,2-b]咔唑(1)相比, 氯原子的引入增大了2,8-二氯吲哚并[3,2-b]咔唑(2)和2,8-二氯-5,11-二己基吲哚并[3,2-b]咔唑(3)的最高占据分子轨道(HOMO)的离域程度, 而对最低未被占据分子轨道(LUMO)则无显著贡献, 但明显降低了二者的能级. 上述结果表明, 对于LUMO, 氯原子体现了吸电子效应, 而对于HOMO, 氯原子体现了共轭效应. 烷基链的引入使化合物3的空穴迁移率明显高于化合物1和2, 这主要归因于化合物3具有更加紧密的分子堆积, 尤其在跳跃路径A中, 具有更大的分子间电子耦合和轨道重叠. 同时能带结构的计算结果进一步证明, 氯原子和烷基链的同时引入大大改善了吲哚并咔唑类衍生物的电荷传输性能.

Theoretical Study on the Carrier Transport Properties of Indolo[3,2-b]carbazole Derivatives

The influence of introduction of chlorine and long alkyl side chains on the hole transport properties of indolo[3,2-b]carbazole derivatives was investigated by combining density functional theory(DFT) with Marcus theory in hopping regime. The results show that the introduction of chlorine atoms induces more delocalized HOMO of 2,8-dichloro-indolo[3,2-b]carbazole(2) and 2,8-dichloro-5,11-dihexyl-indole[3,2-b]carbazole(3) than indolo[3,2-b]carbazole(1), while the LUMO is just the opposite. Besides, both the HOMO/LUMO energy levels and the reorganization energies of compounds 2 and 3 are lower than those of compound 1, and the former is ascribed to chlorine exerting conjugate effect to HOMO but electron-withdrawing effect to LUMO. With the introduction of both chlorine and long alkyl side chains on indolo[3,2-b]carbazole derivatives, compound 3 has higher mobility, which is the result of denser intermolecular packing of dimer A in compound 3 than compounds 1 and 2, thus larger electronic coupling and higher the mobility are measured for compound 3. The results obtained from the band model are consistent with those calculated by hopping regime. Finally, our calculation clarify again in theory that rational chemical modification can improve the carrier transport property of indolo[3,2-b]carbazole derivatives.