A Resonating B, N Covalent Bond and Coordination Bond in Aromatic Compounds and Conjugated Polymers

We herein report an organoboron compound (SBN-1) based on N-B <- N units with a balanced resonance hybrid of B, N single bond (B-N) and B, N coordination bond (B <- N). Despite the different chemical environments of the two nitrogen atoms in the N-B <- N unit, the single-crystal structure reveals that the two B, N bonds have similar bond lengths of ca. 1.55 angstrom and are almost equivalent. The resonance nature of the two B, N bonds contributes to the excellent chemical stability and photostability of SBN-1. The N-B <- N units in SBN-1 show a strong electron-withdrawing capability and large dipole, resulting in a red-shifted absorption spectrum, downshifted LUMO/HOMO energy levels, and drastically altered molecular packing behaviors in solid state. SBN-1 can be used as a building block to construct small band gap conjugated polymers. The resonance of B, N bonds discovered in this work provides new insight into the design of stable organoboron small molecules and polymers for practical applications.

Automated summary

In this study, an organoboron compound based on N-B <- N units was reported. The resonance nature of the two B, N bonds in the compound was discovered, which contributes to its excellent chemical and photostability. The compound can be used to construct small band gap conjugated polymers. This discovery provides new insights into the design of stable organoboron small molecules and polymers for practical applications.