AIE-Active Blue-to-Green Fluorescent Aroylhydrazone-BF₂ Mesogens for Latent Fingerprint Detection and...

A series of small, two-ring system aroylhydrazone-based boron difluoride complexes, designated as ML_m,_n-BF₂, were synthesized and investigated for their mesomorphic and photophysical properties. These compounds exhibited smectic or nematic liquid crystalline phases, modulated by variations in the terminal alkyl chain lengths (m = 12; n = 10, 12, 14, and 16). Among them, the ML_12-12-BF₂ complex (m = n = 12) with a moderate chain length was studied in detail for its solid- and solution-state photophysical behavior and forensic applications. This complex displayed blue-to-green fluorescence (λ_max ≈ 450 nm), with significantly enhanced emission intensity at high water fractions (60%-100%), confirming aggregation-induced emission (AIE) activity. Furthermore, ML_12-12-BF₂ enabled high-contrast, UV-vis latent fingerprint detection on various surfaces without requiring specialized equipment and also demonstrated strong potential as an anti-counterfeiting ink due to its bright luminescence, solution processability, and stability. The combination of tunable mesomorphic behavior and AIE characteristics, along with multifunctional applicability within a single small molecular system, highlights these boron difluoride complexes as promising candidates for next-generation forensic and security applications.