Stimuli-Responsive Phenothiazine–Tetraphenylethylene Hybrid Luminogens: Mechano- and Piezochromic Properties with Anticancer Applications

Abstract

Mechanochromic and piezochromic luminogens represents a class of stimuli responsive materials, in which the emission colour or intensity changes reversibly in response to external mechanical stimuli such as grinding, pressing or stretching. Herein, we have reported the solid state photophysical properties of (PTZ)3, PTZO2-(PTZ)2, PTZ-(TPE)2, and PTZO2-(TPE)2 under external mechanical stimuli, exhibiting reversible changes in emission colour. The incorporation of two phenothiazine units or two tetraphenylethylene units on the vinylic carbon atom produces steric crowding which causes non-planarity and results in enhanced emission in the solid state. The compounds (PTZ)3, PTZO2-(PTZ)2, PTZ-(TPE)2, and PTZO2-(TPE)2 were evaluated for biological activities, exhibiting bright fluorescence suitable for the imaging and notable cytotoxicity against different cancer cell lines, indicating the potential anticancer activity. The compound (PTZ)3 shows moderate anticancer effect, likely mediated through lysosomal autophagic pathways, while its oxide form PTZO2-(PTZ)2 significantly reduces this effect. These results highlight the multifunctional potential of these molecules, integrating the stimulus-responsive luminescence with anticancer functionality.