Non-doped, solid-state red-emitting phenothiazine-pyrene chalcones: Synthesis, aggregation-induced emission enhancement and mechanofluorochromism

We report the synthesis of a new series of red-emitting phenothiazine chalcones bearing pyrene moiety with the objective of improving the emission characteristics in the solid-state. The compounds exhibited large Stokes shift, positive solvatochromism, aggregation-induced emission enhancement, and reversible mechanofluorochromism (MFC). In contrast to the typical quenching observed in π–π stacked organic compounds, the pyrene-chalcone, Ch-H, which showed intermolecular π–π stacking through single crystal XRD studies, displayed a high quantum yield of 94.3% in solid-state, which was attributed to the crystallization-induced emission enhancement (CIEE) phenomenon. Interestingly, another pyrene-chalcone, Ch-Np, which lacked π–π stacking as observed through single crystal XRD, exhibited a poor quantum yield of 7.17% in the solid-state. The molar extinction coefficients of the solution of compounds were higher than the well-known N719 dye. The potential of highly luminescent chalcone, Ch-H, in anti-counterfeiting applications, was further demonstrated by writing and stamping on black paper, visible only under 365 nm but not under ordinary daylight. © 2024 Elsevier B.V.