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

Abstract

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 D 1 -A-D 2 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 (À OMe) and the diphenyl-methylene moiety (À NMe 2 ) (λ em 680 nm). The dyes exhibited good quantum yields, large Stoke shifts (upto 293 nm) and were utilized in nitroaromatics and Cu 2 + sensing.

Silver nitrate promoted synthesis of tetraphenyl derivatives and diaryl ketones

“…(Diphenylmethylene)hydrazine (4a). 38 A mixture of benzophenone (0.2 mmol), hydrazine monohydrate (2.0 equiv. ), and acetic acid (0.06 mmol) was stirred at 100 °C for 21 h. After cooled to room temperature, solvent and volatile materials were removed under reduced pressure to afford corresponding product as a white solid (35 mg, 90%) ; mp 94-95 °C ; 1 H-NMR (400 MHz, CDCl3) δ 7.52-7.44 (m, 5H), 7.29-7.26 (m, 5H), 5.42 (bs, 2H); 13 C-NMR (100 MHz, CDCl3) δ 149.2, 138.5, 133.1, 129.5, 128.2, 126.6.…”

Aggregation-induced emission-active azines for chemosensing applications: a five-year update

“…2A]. 37 The incorporation of a hydroxybenzothiazole (HBT) unit rendered the ESIPT property in the system by keto–enol tautomerism, whereas the azine linkage along with the two phenyl units of hydrazone induces TICT property in the scaffold. The greener and cost-effective mechanochemical method afforded the azine compounds within a short time, avoiding harmful solvents and tedious workup procedures.…”

“…Similarly, our group utilized the red-emissive HBT-based unsymmetrical dyes, 8d , for the detection of nitroaromatic compounds (NACs) [Table 3, entry 2]. 37 The electron-deficient NACs in particular, picric acid, undergo noncovalent interactions with electron-rich azines resulting in the turn-off detection of NACs [Fig. 6A].…”

Grind, shine and detect: mechanochemical synthesis of AIE-active polyaromatic amide and its application as molecular receptor of monovalent anions or nucleotides

“…Despite mechanochemical synthesis and design of AIE-active compounds are emerging elds of chemistry, the reports dealing with merging these concepts are extremely sparse. 41 To the best of our knowledge, the reports mostly include very recent (2021-2023) studies on the grindinginduced synthesis of AIE-active benzothiazole-azine [42][43][44] or benzothiazole derivatives 45 (Fig. 1a).…”