Hydrogen‐bonding Assisted Quantum Yield Enhancement and Chromism Activity of 4’‐Halo‐2’‐azaboranils

By replacing a carbon atom of boranils with a nitrogen atom, azaboranils were newly designed. In the 2'-azaboranils synthesized from 2-aminopyridines with 2-hydroxy-1-naphthaldehyde, the pyridine ring underwent a hydrogen-bonding interaction with the imine proton to restrain the molecular flexibility, which resulted in a significant improvement in luminescence quantum yield in both the solution state and the solid state over those for the parent boranils. The crystalline powder 4'-chloro-2'-azaboranil exhibited mechanochromism and vapochromism in the network of π-π stacking, halogen-bonding, H-F hydrogen-bonding, and CH-π interaction.