Molecular engineering of B/N substituents in asymmetrical salicylaldimine-based boranils for tuning solid-state emission and cellular lipid-droplet imaging

Abstract

Boranil derivatives have rapidly emerged as readily synthesized and strongly emissive materials. While their properties can be easily tuned by varying the salicylaldimine precursor, little attention has been paid to the effect of substituents on the boron atom. In this work, a series of asymmetrical BFPh-bridged boranil derivatives were synthesized, and their photophysical properties in solution and solid state were investigated. X-ray crystallographic analysis confirmed that five second-period elements (from B to F) were incorporated into a single molecule within this family of asymmetrical BFPh-bridged compounds. These derivatives not only retain nearly unity quantum yields and show potential for lipid droplet imaging, but also display Stokes shifts that are 20 nm larger than those of the corresponding symmetric BF₂- and BPh₂-bridged analogues.