Synthesis and Isomeric Effects of Ladder-Type Alkylated Terbenzodithiophene Derivatives

A new class of heptacyclic ladder-type terbenzodithiophene (TBDT) structures merging three fused benzodithophenes was developed. Two TBDT conjugated isomers, named as syn-TBDT and anti-TBDT, where the two thienyl rings in the outmost BDT units are in the syn- and anti-fashion, are designed. Two decyl groups are introduced to their 6,13 and 7,14-positions to form four isomeric 6,13-syn-TBDT, 7,14-syn-TBDT, 6,13-anti-TBDT, and 7,14-anti-TBDT structures which are constructed by the DBU-induced 6-benzannulation involving propargyl-allenyl isomerization of the dieneyne moieties in the corresponding precursors followed by 6π-electrocyclization/aromatization, while isomeric TD-syn-TBDT and TD-anti-TBDT with four decyl groups substituted at 6,7,13,14-positions are synthesized via palladium-catalyzed dialkylacetylene insertion/C–H arylation of the corresponding iodobiaryl precursors. The intrinsic properties can be modulated by molecular manipulation of the main-chain and side-chain isomeric structures. anti-TBDT derivatives exhibit higher melting points, larger bandgaps, stronger intermolecular interactions, and higher mobility than the corresponding syn-TBDT analogues. These molecules can be further utilized as building blocks to make various TBDT-based materials for optoelectronic applications.

本研究开发了一类由三个稠合苯并二噻吩融合而成的七环梯形三联苯并二噻吩（terbenzodithiophene, TBDT）结构。研究人员设计了两种TBDT共轭异构体，分别命名为顺式-TBDT（syn-TBDT）与反式-TBDT（anti-TBDT）；两类异构体中最外侧的苯并二噻吩（benzodithiophene, BDT）单元内的两个噻吩环分别呈顺式与反式空间构型。随后在这两种异构体的6,13位与7,14位各引入两个癸基，得到四种异构体：6,13-顺式-TBDT（6,13-syn-TBDT）、7,14-顺式-TBDT（7,14-syn-TBDT）、6,13-反式-TBDT（6,13-anti-TBDT）以及7,14-反式-TBDT（7,14-anti-TBDT）；上述四种异构体均通过1,8-二氮杂双环[5.4.0]十一碳-7-烯（DBU）诱导的6-苯并环化反应构建，该反应过程涉及对应前驱体中二炔烯片段的炔丙基-联烯异构化，随后依次发生6π电环化与芳构化步骤。而在6,7,13,14位带有四个癸基取代的异构体TD-顺式-TBDT（TD-syn-TBDT）与TD-反式-TBDT（TD-anti-TBDT），则通过钯催化的二烷基乙炔插入/C–H芳基化反应，以相应的碘代联芳前驱体为原料合成。通过对这类分子主链与侧链的异构体结构进行分子调控，可调节其本征物理性质。相较于对应的顺式-TBDT类似物，反式-TBDT衍生物展现出更高的熔点、更大的带隙、更强的分子间相互作用以及更高的载流子迁移率。这类分子可进一步作为构筑单元，用于制备各类基于TBDT的光电功能材料。