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Activatable photosensitizers (PSs) generating 1 O 2 only under specific conditions can minimize concomitant injury to normal tissues. Heavy-atom-free PSs hold the merits of low dark toxicity, long triplet-state lifetimes, good photostability, and relatively low cost. PSs with emission in the second near-infrared (NIR-II) window are highly valuable for deep-tissue, high-contrast imaging. Herein, we have designed and synthesized a series of heavy-atom-free PSs by a one-step reaction between an easily accessible rhodamine derivative and commercially available thiophene aldehydes. One of the as-prepared PSs, 2b-3T , exhibits emission maxima at 810 nm and tails to the NIR-II region at 1140 nm, together with large Stokes shift (178 nm). Importantly, the newly developed PSs, featuring functional carboxylic acid groups, present promising opportunities as versatile platforms for creating activatable PSs. To validate our concept, we developed Cu 2+ /pH-activatable PSs using the spirocyclization mechanism of rhodamine. Ultimately, we showcased the effectiveness of these innovative PSs in photodynamic therapy through in vitro experiments.

Type I photosensitizers offer an advantage in photodynamic therapy (PDT) due to their diminished reliance on oxygen levels, thus circumventing the challenge of hypoxia commonly encountered in PDT. In this study, we present the synthesis and comprehensive characterization of a novel type I photosensitizer derived from a cyclometalated Ir(III)-rhodamine complex. Remarkably, the complex exhibits a shift in absorption and fluorescence, transitioning from "off" to "on" states in aprotic and protic solvents, respectively, contrary to initial expectations. Upon exposure to light, the complex demonstrates the effective generation of O 2 - and ·OH radicals via the type I mechanism. Additionally, it exhibits notable photodynamic antibacterial activity against both Gram-positive and Gram-negative bacteria, demonstrated through in vitro and in vivo experiments. This research offers valuable insights for the development of novel type I photosensitizers.

Hypochlorous acid (HOCl) plays important roles in many pathological and physiological processes. Herein we present a novel strategy to develop HOCl probe by one-step synthesis of rhodamine-thiophene dyad, rho-T. Unexpectedly, the thiophene moiety did not cause the fluorescence quenching of the xanthene moiety. Upon addition of HOCl, the ClO− anion attacks the carbon 9 position of rho-T and chlorinate the xanthene ring, resulting in fluorescence and absorption quenching of rho-T. rho-T exhibits linear response with increasing concentration of HOCl (R2 = 0.9875) with high sensitivity (Limit of Detection (LOD) = 2.36 nM) and selectivity in a fast response time (10 s). Finally, rho-T was successfully employed to detect HOCl in living cells and mice. Rhodamine-thiophene dyad for colorimetric and fluorescent sensing HOCl based on a novel mechanism. [Display omitted] • Rhodamine-thiophene dyad was synthesized through one-step reaction for HOCl sensing. • Excellent sensitivity, selectivity and fast response toward HOCl. • New sensing mechanism for HOCl was proposed. • The chemoprobe is capable of detecting HOCl in living cells and mice. [ABSTRACT FROM AUTHOR]