A New Series of D1‐A‐D2‐type ESIPT‐TICT‐AIE Active Orange‐to‐red Emissive Unsymmetrical Azines: Their All‐throughout Mechanochemical Synthesis and Exploration of Photophysical Properties

Azines are interesting compounds exhibiting aggregation‐induced‐emission (AIE) and twisted‐intramolecular‐charge‐transfer (TICT) properties that have exciting prospects in chemosensing and bioimaging applications. They commonly have symmetrical structures and there is no report on red‐emissive unsymmetrical azines. Herein, we report a novel class of orange‐to‐red emissive hydroxybenzothiazole(HBT)‐based unsymmetrical azines (BTDPA) with triple photophysical characteristics of ESIPT‐TICT‐AIE. The dyes were synthesized by an all‐throughout mechanochemical route in a sustainable way. They displayed D1‐A‐D2 character and fluoresce strongly both in organic solvents due to ESIPT and in the solid state by AIE via TICT. The incorporation of different electron‐withdrawing groups (EWGs) and electron‐donating groups (EDGs) at either HBT or diphenyl‐methylene moiety resulted in tunable fluorescence properties. The red‐emissive character was achieved by keeping EDG both at HBT (−OMe) and the diphenyl‐methylene moiety (−NMe2) (λem 680 nm). The dyes exhibited good quantum yields, large Stoke shifts (upto 293 nm) and were utilized in nitroaromatics and Cu2+ sensing. A novel class of hydroxybenzothiazole‐based unsymmetrical azine dyes (BTDPA) with triple photophysical characteristics of ESIPT‐TICT‐AIE has been synthesized adopting an all‐throughout mechanochemical route in a sustainable way. They displayed D1‐A‐D2 character and fluoresce strongly both in organic solvents and in solid state with large stoke shifts (upto 293 nm).