Asymmetric phenothiazine derivatives modified with diphenylamine and carbazole: Photophysical properties and hypochlorite sensing

Abstract

This study reports the design, synthesis, and characterization of four asymmetric donor–acceptor (D-A) fluorescent molecules—1CAR, 1DIP, 1OOCAR, and 1OODIP—featuring phenothiazine (PTZ), diphenylamine (DIP), and carbazole (CAR) as electron donors. By oxidizing the sulfur atom in PTZ and modifying the molecular structure at the 3-position, we systematically investigated the influence of structural variations on photophysical properties. These compounds exhibit distinct solvatochromic behavior, aggregation-induced enhanced emission (AIEE), and mechanofluorochromism (MFC). Solvent-dependent fluorescence studies revealed significant red shifts with increasing polarity, confirming strong intramolecular charge transfer (ICT) characteristics, as further supported by Lippert-Mataga analysis. In aggregated states, 1CAR and 1DIP displayed remarkable AIEE, with fluorescence intensity enhancements of up to 84.1- and 9.7-fold, respectively, whereas 1OOCAR exhibited aggregation-caused quenching (ACQ) due to structural constraints. Solid-state fluorescence analysis highlighted the impact of PTZ oxidation on emission characteristics, demonstrating its critical role in tuning fluorescence properties. Additionally, the sensing capabilities of 1CAR and 1DIP toward hypochlorite ions (ClO⁻) were explored through UV–Vis and fluorescence titration experiments, revealing substantial fluorescence quenching with increasing ClO⁻ concentrations. The detection limits reached as low as 0.68 µM, underscoring their high sensitivity and selectivity. This research offers important perspectives for the rational design of multifunctional fluorescent materials for applications in chemosensing and environmental monitoring.