Group 15 Element (As, Sb, Bi)-Substituted Bibenzofurans with Noncovalent Conformational Locks for Enhanced Planarity

Intramolecular noncovalent interactions offer a convenient approach to design organic semiconductors with enhanced molecular planarity via conformational locks, which can readily reduce the band gaps, as evidenced by the example of a phosphorus-substituted bibenzofuran derivative (BFP) that exhibits P···O interactions, reported previously. Compared with lighter Group 15 elements, the use of heavier elements in organic chemistry has been rather limited. However, the introduction of heavier elements may result in stronger noncovalent interactions. This inspired us to prepare bismuth- and antimony-substituted bibenzofurans (BFBi and BFSb). As expected, BFBi and BFSb showed red-shifted ultraviolet–visible (UV–vis) absorption bands relative to that of BFP, suggesting the enhanced molecular planarity. Single-crystal X-ray diffraction (SXRD) studies revealed that the enhanced Bi···O and Sb···O interactions contributed to the self-planarity and rigidity of the conjugated systems. In contrast, bismuth- and antimony-substituted bibenzothiophene congeners showed blue-shifted absorption bands and twisted structures. Density functional theory (DFT) calculations and topological analysis of the electron density distribution by quantum theory of atoms in molecules (QTAIM) were performed to evaluate the bond critical points (3, −1) for the weak interactions in these structures. Noncovalent interactions in an arsine-substituted bibenzofuran compound were also evaluated.