AIE in the halogenated anils and their utilization as fluorescent probes for explosive nitro-aromatics

Abstract

AIEgens represent an intriguing class of emerging materials with interesting applications. We report three halogen-functionalized anils 1–3 and investigate the influence of interhalogen bonds on the crystal packing. Hirshfeld analyses are carried out to understand the role and contribution of the intermolecular interactions responsible for molecular aggregation and study the influence of the position and nature of the halogens on σ-hole formation. Molecular solids 1–3 are non-emissive in both the solid and solution phases, but undergo interesting emission turn-on on aggregation in the solution phase when a non-solvent is added, through the phenomenon of aggregation-induced emission (AIE). Dynamic light scattering (DLS) studies validate the AIE phenomenon as well as the direct correlation of the emission intensities with increasing particle size, as the maximum emission intensities, as well as aggregated particle size values, are observed at f_w critical values of 90, 70, and 60 for THF:water systems in 1–3, respectively. The AIEgens 1–3 exhibit 57, 70, and 60% quantum yields for the maximum emission intensity values. The AIEgens have been utilized for solution-phase sensing of common explosive nitro-compounds. 1–3 with donor tendencies interact with electron-deficient nitro-compounds through charge transfer interaction, causing quenching of the emission. AIEgen 2 has been used for sensing nitro compounds based on its better binding constant, Stern–Volmer constant, quenching constant (K_SV), and limit of detection value. Compared to the others, AIEgen 2 exhibits better L.O.D values for picric acid, plausibly due to the better donor–acceptor complexation.