Tripodal phenothiazine-based donor-acceptor type, multi-stimuli responsive derivatives displaying solvatochromism, aggregation-induced emission enhancement, and reversible acidochromism were synthesized. These act as probes for moisture and amine, show mechanofluorochromic responses and were explored for potential multi-level anti-counterfeiting application and latent fingerprint sensing.

Abstract

In this work, we designed and synthesized D-A type tripodal phenothiazine derivatives to examine the influence of different functional groups on the photophysical properties and response to external stimuli. The compounds show emission in both solution and solid-state. Intramolecular charge transfer (ICT) characteristics are evidenced by the fluorescence studies revealing positive solvatochromism in compounds. The compounds are highly thermally stable with low optical band gaps (2.1–2.55 eV). Compounds 3a-3c displayed excellent aggregation-induced emission enhancement (AIEE) phenomena in CH₃CN/DMSO and water mixtures. Compound 3e could detect moisture in three solvents, namely THF, CH₃CN, and DMSO, with the lowest detection limit of 0.018% in DMSO. The compounds show reversible acidochromism in solution and solid-state, where compound 3e containing pyridyl shows the lowest detection limit for TFA of 0.59 ppm among others. The ‘ ON-OFF-ON ’ response to TFA/TEA stimulation has been utilized for the construction of the truth table and the outcome corresponds to the IMPLICATION logic gate. The sensitive response of compound 3e to amine vapors has been utilized for monitoring food spoilage. The compounds also show mechanofluorochromism, and the phase transformation was analyzed by powder X-ray diffraction studies. These compounds are potential candidates for multi-level anti-counterfeiting applications and latent fingerprint sensing.

Acidochromism; Aggregation-induced emission enhancement (AIEE); Anti-counterfeiting; IMPLICATION logic gate; Mechanofluorochromism