Furano‐ and Thieno‐fused Carbazole‐Containing Azaborines and Their π‐Extension: Synthesis, Structures, and Properties

A series of carbazole‐containing azaborines, furano‐fused 1–2F and 1–3F and thieno‐fused 1–2T and 1–3T , were efficiently synthesized from a common carbazole boronic acid ester in two steps. The structural effects of the fused ring moieties and the patterns of the ring fusion were clarified. According to X‐ray crystal structure analysis, the furano‐ and thieno‐fused carbazole azaborines had planar structures and generally formed 1D columns. UV–vis analysis revealed that their absorption properties were significantly affected by the fused ring moieties. In contrast, the fluorescence properties were affected by the ring fusion patterns. π‐Extended derivatives of 1–2T and 1–3T , benzothieno‐fused 1–2BT and 1–3BT and phenyl‐substituted 1–2T‐Ph 2 and 1–3T‐Ph 2 were synthesized, and the effects of π‐extension on physical properties were also investigated. All the π‐extended compounds showed red‐shifts in absorption and fluorescence spectra compared with the pristine 1–2T and 1–3T . The color of solid‐state emission of the synthesized azaborines was tuned from purple to green without electron‐rich or ‐deficient substituents. The structural effects on the electronic structures were also discussed based on theoretical calculations.