Aggregation-induced emissions in the mesogenic BF₂complexes of aroylhydrazines

Herein, we report the synthesis of two new families of borondifluoride complexes derived from aroylhydrazines and the investigation of their mesomorphic and AIE properties. The crystallographic structure of the mesogenic complex1a-BF₂(n= 8) was determined by X-ray analysis; it crystallizes in theP1̄ triclinic space group and the geometry of boron atoms is tetrahedral. The crystal is considered to be linear-shaped with a length ofL∼ 33.92 Å. A relatively small dihedral angle ofca.3.30°-5.75° was observed between both neighboring phenyl groups and tetrahedral BF₂moiety. Mesomorphic properties were crucially impacted by the structure of the terminal group. Ligands1a-bwere not mesogenic; however, both the series of1a-BF₂and1b-BF₂complexes formed SmC or/and N phases. The H-bonding interactions are attributed to the occurrence of mesomorphism in compounds1-BF₂, which was supported by FT-IR spectroscopy. The optical property of the boron complexes is related to their molecular structures, and they emitted blue-to-green emissions atλ_max= 445-466 nm in CH₂Cl₂. Compounds1a-BF₂aggregated in higher water fractions (f_w), which turned on their light emission process, whereas weak PL signals were recorded atf_w< 50% because the luminogen was fully dissolved and quenched in these solvent compositions. The PL intensity was enhanced atf_w> 60% until it reached the maximum intensity atf_w∼ 90%. Thus, compound1a-BF₂is AIE active.