Multifaceted Regioregular Oligo(thieno[3,4‑<i>b</i>]thiophene)s Enabled by Tunable Quinoidization and Reduced Energy Band Gap

Thiophene-based materials have occupied a crucial position in the development of organic electronics. However, the energy band gaps of oligo- and polythiophenes are difficult to modulate without resorting to push–pull electronic effects. We describe herein a new series of monodisperse oligo­(thieno­[3,4-b]­thiophene) derivatives with well-defined regioregular structures synthesized efficiently by direct C–H arylation. These compounds show a unique palette of colors and amphoteric redox properties with widely tunable energy band gaps. The capacity to stabilize both cations and anions results in both anodic and cathodic electrochromism. Under excitation, these compounds can produce photoionized states able to interconvert into neutral triplet or form these through singlet exciton fission or intersystem crossing. These features arise from a progressive increase in quinoidization on a fully planar platform making the largest effective conjugation length among hetero-oligomers. Oligo­(thieno­[3,4-b]­thiophene)­s might represent the more distinctive family of oligothiophenes of this decade.基于噻吩（Thiophene）的材料在有机电子学的发展进程中占据了至关重要的地位。然而，若不借助推拉电子效应，难以对低聚噻吩与聚噻吩的能带隙进行有效调控。本文报道了一系列全新的单分散低聚(噻吩并[3,4-b]噻吩)衍生物，其具备明确的区域规整结构，可通过直接C–H芳基化（direct C–H arylation）反应高效合成。该类化合物兼具独特的色彩谱系与两性氧化还原特性，其能带隙可实现大范围调控。由于同时具备稳定阳离子与阴离子的能力，它们可同时展现阳极与阴极电致变色效应。在激发条件下，这类化合物可产生光电离态，该态既能够转化为中性三线态，也可通过单线态激子裂变或系间窜越过程生成中性三线态。上述特性源于其全平面骨架上逐步增强的醌型化作用，使其成为杂环低聚物中有效共轭长度最大的一类材料。低聚(噻吩并[3,4-b]噻吩)有望成为近十年内最具特色的低聚噻吩家族成员。