A novel strategy for designing highly efficient and activatable photosensitizers that can effectively generate reactive oxygen species (ROS) under both normoxia and hypoxia is proposed. Replacing both oxygen atoms in conventional naphthalimides (RNI-O) with sulfur atoms led to dramatic changes in the photophysical properties. The remarkable fluorescence quenching (Φ PL ≈ 0) of the resulting thionaphthalimides (RNI-S) suggested that the intersystem crossing from the singlet excited state to the reactive triplet state was enhanced by the sulfur substitution. Surprisingly, the singlet oxygen quantum yield of RNI-S gradually increased with increasing electron-donating ability of the 4-R substituents (MANI-S, Φ Δ ≈ 1.00, in air-saturated acetonitrile). Theoretical studies revealed that small singlet−triplet energy gaps and large spin−orbit coupling could be responsible for the efficient population of the triplet state of RNI-S. In particular, the ROS generation ability of MANI-S was suppressed under physiological conditions due to their self-assembly and was significantly recovered in cancer cells. More importantly, cellular experiments showed that MANI-S still produced a considerable amount of ROS even under severely hypoxic conditions (1% O 2 ) through a type-I mechanism.

Organic thermally activated delayed fluorescence (TADF) materials are emerging as potential candidates for time-resolved fluorescence imaging in biological systems. However, the development of purely organic TADF materials with bright aggregated-state emissions in the red/near-infrared (NIR) region remains challenging. Here, we report three donor–acceptor-type TADF molecules as promising candidates for time-resolved fluorescence imaging, which are engineered by direct connection of electron-donating moieties (phenoxazine or phenothiazine) and an electron-acceptor 1,8-naphthalimide (NI). Theoretically and experimentally, we elucidate that three TADF materials possessed remarkably small ΔE ST to promote the occurrence of reverse intersystem crossing (RISC). Moreover, they all exhibit aggregation-induced red emissions and long delayed fluorescence lifetimes without the influence of molecular oxygen. More importantly, these long-lived and biocompatible TADF materials, especially the phenoxazine-substituted NI fluorophores, show great potential for high-contrast fluorescence lifetime imaging in living cells. This study provides further a molecular design strategy for purely organic TADF materials and expands the versatile biological application of long-lived fluorescence research in time-resolved luminescence imaging.

We designed and investigated novel mitochondria-targeting heavy-atom-free BODIPY photosensitizers (R-BODs) that possessed considerable singlet oxygen generation abilities and good fluorescence properties for imaging-guided photodynamic therapy (PDT).

Selective fluorescence imaging of biomarkers in vivo and in situ for evaluating orthotopic hepatocellular carcinoma (HCC) chemotherapyremains agreat challenge due to current imaging agents suffering from the potential interferences of other hydrolases.H erein, we observed that carbamate unit showed ah igh selectivity towardt he HCC-related biomarker carboxylesterase (CE) for evaluation of treatment. An earinfrared two-photon fluorescent probe was developed to not only specially image CE activity in vivo and in situ but also target orthotopic liver tumor after systemic administration. The in vivo signals of the probe correlate well with tumor apoptosis, making it possible to evaluate the status of treatment. The probe enables the imaging of CE activity in situ with ah ighresolution three-dimensional view for the first time.This study may promote advances in optical imaging approaches for precise imaging-guided diagnosis of HCC in situ and its evaluation of treatment.

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Acetylcholinesterase (AChE) is an extremely critical hydrolase tightly associated with neurological diseases. Currently, specific substrates available for imaging AChE activity still remain a great challenge due to the interference from...

Novel thiocarbonyl derivatives (NIS and CRNS) with excellent ROS generation abilities are synthesized and studied as potential photosensitizers for one- and two-photon excited photodynamic therapy. In particular, NIS-Me and CRNS...

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