Design of AIE-active Schiff-bases: Mechanochromic, Thermochromic and Sensing Studies

There is a notable shift toward organic functional materials for their advantages in terms of availability, processability and biodegradability. Solid-state organic emitters, though rare, are fascinating with diverse range of applications. In this work we utilize crystal engineering principles to design Schiff bases 1 and 2, to realize solid state emission and its tuning. The products have been characterized and studied through crystallographic, Hirshfeld, and optical studies. Structural studies validate crystallization of 1 and 2 with a molecule of methanol and water, respectively, and their packing is predominantly aided by solvent assisted hydrogen bonding, while the π-π stacking interactions are absent. Crystalline solids are emissive: 1 (λ _max 474 nm, τ 0.35 ± 0.04 ns) and 2 (481 nm, 1.80 ± 0.07 ns) and aggregation induced emission (AIE) active. Mechano and thermo-fluorochromic responses of the products are attributed to phase changes triggered by grinding and desolvation, respectively. The nonemissive solutions of 1 and 2 detect presence of Pb(II) /Hg(II) through emission turn-on, with limit of detection (LOD) values in the range of 0.0017–0.0022 ppb, while picric acid sensing is reported by their AIE luminogen (AIEgen) forms with LOD values of 0.0017 ppb and 0.0034 ppb, respectively.