2-Hydroxyphenyl benzimidazoles and their boron complexes: synthesis, structure, aggregation-induced emission and picric acid sensing

A series of differently substituted 2-(2-hydroxyphenyl) benzimidazoles were synthesized by a coupling reaction involving aryl dibromides and 2-hydroxyphenyl benzimidazole. These ligands react with BF3·Et2O to yield the corresponding boron complexes. The photophysical properties of the ligands (L1-L6) and the boron complexes (1-6) were studied in the solution state. Among these, the ligands L1-L4 and L6 displayed aggregation-induced emission (AIE) behavior upon the addition of water in THF resulting in a sizable enhancement of fluorescence intensity. Additionally, compound 5 was found to detect picric acid with a detection limit of 8.33 × 10-7 M.