Synthesis of O-B ← N embedded molecules and studies on the B ← N cleavage-driven thermo- and solvatochromic properties

Abstract

Three O-B ← N embedded molecules identified as 1, 2, and 3 with different substituents and B ← N locations are synthesized to study the firmness of intramolecular B ← N coordination. After X-ray diffraction crystallography, electrochemical, and photophysical tests, in-depth B ← N cleavage-driven thermo- and solvatochromic studies were conducted. In contrast to compound 1 with phenyl side groups, compound 2 with bulky and electron-deficient perfluorophenyl substituents has twisted backbone, significantly increased fluorescence quantum yield (ΦF = 27 % vs 85 %), and most importantly, enhanced stability of B ← N coordination. Comparison to 1 and 2, whose B ← N bonds are located on the edge of fused rings, compound 3 with extended backbone conjugation and B ← N bonds embedded inside fused rings exhibits red-shifted absorption/emission, decreased ΦF = 7 %, and remarkably enhanced strength of B ← N coordination. This work discloses the effects of substituents and B ← N locations on firmness of intramolecular B ← N coordination, which are enlightening to understand the stability and application of these O-B ← N embedded molecules.