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. In addition to maintaining nearly unity quantum yields and exhibiting lipid droplet bioimaging capabilities, the asymmetric BFPh-bridged derivatives exhibit a 20 nm enlargement in Stokes shift relative to their symmetric BF₂-and BPh₂bridged analogues.