Thymoquinone as an electron transfer mediator to convert Type II photosensitizers to Type I photosensitizers.

The development of Type I photosensitizers (PSs) is of great importance due to the inherent hypoxic intolerance of photodynamic therapy (PDT) in the hypoxic microenvironment. Compared to Type II PSs, Type I PSs are less reported due to the absence of a general molecular design strategy. Herein, we report that the combination of typical Type II PS and natural substrate carvacrol (CA) can significantly facilitate the Type I pathway to efficiently generate superoxide radical (O2-•). Detailed mechanism study suggests that CA is activated into thymoquinone (TQ) by local singlet oxygen generated from the PS upon light irradiation. With TQ as an efficient electron transfer mediator, it promotes the conversion of O2 to O2-• by PS via electron transfer-based Type I pathway. Notably, three classical Type II PSs are employed to demonstrate the universality of the proposed approach. The Type I PDT against S. aureus has been demonstrated under hypoxic conditions in vitro. Furthermore, this coupled photodynamic agent exhibits significant bactericidal activity with an antibacterial rate of 99.6% for the bacterial-infection female mice in the in vivo experiments. Here, we show a simple, effective, and universal method to endow traditional Type II PSs with hypoxic tolerance.

Unraveling the Transformation from Type-II to Z-Scheme in Perovskite-Based Heterostructures for Enhanced Photocatalytic CO2 Reduction.

The ability to create perovskite-based heterostructures with desirable charge transfer characteristics represents an important endeavor to render a set of perovskite materials and devices with tunable optoelectronic properties. However, due to similar material selection and band alignment in type-II and Z-scheme heterostructures, it remains challenging to obtain perovskite-based heterostructures with a favorable electron transfer pathway for photocatalysis. Herein, we report a robust tailoring of effective charge transfer pathway in perovskite-based heterostructures via a type-II to Z-scheme transformation for highly efficient and selective photocatalytic CO2 reduction. Specifically, CsPbBr3/TiO2 and CsPbBr3/Au/TiO2 heterostructures are synthesized and then investigated by ultrafast spectroscopy. Moreover, taking CsPbBr3/TiO2 and CsPbBr3/Au/TiO2 as examples, operando experiments and theoretical calculations confirm that the type-II heterostructure could be readily transformed into a Z-scheme heterostructure through establishing a low-resistance Ohmic contact, which indicates that a fast electron transfer pathway is crucial in Z-scheme construction, as further demonstrated by CsPbBr3/Ag/TiO2 and CsPbBr3/MoS2 heterostructures. In contrast to pristine CsPbBr3 and CsPbBr3/TiO2, the CsPbBr3/Au/TiO2 heterostructure exhibits 5.4- and 3.0-fold enhancement of electron consumption rate in photocatalytic CO2 reduction. DFT calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy unveil that the superior CO selectivity is attributed to the lower energy of *CO desorption than that of hydrogenation to *HCO. This meticulous design sheds light on the modification of perovskite-based multifunctional materials and enlightens conscious optimization of semiconductor-based heterostructures with desirable charge transfer for catalysis and optoelectronic applications.

Color-Tunable Dual-Mode Organic Afterglow for White-Light Emission and Information Encryption Based on Carbazole Doping.

Dual-mode emission materials, combining phosphorescence and delayed fluorescence, offer promising opportunities for white-light afterglow. However, the delayed fluorescence lifetime is usually significantly shorter than that of phosphorescence, limiting the duration of white-light emission. In this study, a carbazole-based host-guest system that can be activated by both ultraviolet (UV) and visible light is reported to achieve balanced phosphorescence and delayed fluorescence, resulting in a long-lived white-light afterglow. Our study demonstrated the critical role of a charge transfer state in the afterglow mechanism, where the charge separation and recombination process directly determined the lifetime of afterglow. Simultaneously, an efficient reversed intersystem crossing process was obtained between the singlet and triplet charge transfer states, which facilitating the delayed fluorescence properties of host-guest system. As a result, delayed fluorescence lifetime was successfully prolonged to approach that of phosphorescence. This work presents a delayed fluorescence lifetime improvement strategy via doping method to realize durable white-light afterglow.

Structurally Resemblant Dopants Enhance Organic Room-Temperature Phosphorescence.

Doping has shown very promising potential in endowing room-temperature phosphorescence (RTP) properties of organic phosphors with minimal effort. Here, a new isomer design and doping strategy is reported that is applicable to dibenzothiophene (DBT) and its derivatives. Three isomers are synthesized to study the dopant effect on enhancing RTP of DBT derivatives. It is found that isomer dopants bearing close resemblance to the host with matched highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and small energy difference between singlet- and triplet-excited states can yield efficient RTP for the doped system. Meanwhile, phosphorescence color from yellow to red is achieved by varying isomer dopants used for doping the DBT derivatives. This work represents an RTP enhancement strategy based on isomer design and doping to construct luminescent organic phosphors.

Carbazole isomers induce ultralong organic phosphorescence.

Commercial carbazole has been widely used to synthesize organic functional materials that have led to recent breakthroughs in ultralong organic phosphorescence1, thermally activated delayed fluorescence2,3, organic luminescent radicals4 and organic semiconductor lasers5. However, the impact of low-concentration isomeric impurities present within commercial batches on the properties of the synthesized molecules requires further analysis. Here, we have synthesized highly pure carbazole and observed that its fluorescence is blueshifted by 54 nm with respect to commercial samples and its room-temperature ultralong phosphorescence almost disappears6. We discover that such differences are due to the presence of a carbazole isomeric impurity in commercial carbazole sources, with concentrations <0.5 mol%. Ten representative carbazole derivatives synthesized from the highly pure carbazole failed to show the ultralong phosphorescence reported in the literature1,7-15. However, the phosphorescence was recovered by adding 0.1 mol% isomers, which act as charge traps. Investigating the role of the isomers may therefore provide alternative insights into the mechanisms behind ultralong organic phosphorescence1,6-18.

Reactivity-Based Organic Theranostic Bioprobes.

Reactivity-based organic bioprobes have been increasingly designed and developed in the last couple of years to address important questions in numerous fields, particularly in biology and medicine. Contrary to the conventional lock-and-key bioprobes, which rely on molecular recognition to probe biological systems and impart sensing specificity, reactivity-based bioprobes capitalize on molecular reactivity for selective target detection. In fact, reactivity-based sensing exploits the intrinsic differences in chemical reactivity to differentiate various chemical species possessing similar size and shape in biological systems. This unique sensing mechanism has been effective for the detection of a wide range of chemical analytes in living cells, tissues, and animals, although bioprobes with additional functionalities are increasingly required in the quest to unravel and understand the complex biological systems. This is why the integration of diagnostic and therapeutic functions in one theranostic platform has become a continuous pursuit in the development of bioprobes in recent years. To this end, numerous design and synthetic approaches have been explored, notably that combining different organic materials with distinct functionalities into one integrated system, also known as "all-in-one" strategy. Nevertheless, the "all-in-one" strategy is prone to design complexity and unsatisfactory reproducibility. To minimize these undesirable hurdles, the deliberate design and engineering of simple organic molecules with multiple functionalities have been actively pursued, leading to the emergence of a unique approach known as "one-for-all" strategy. A prominent example of this approach leverages on fluorogens with aggregation-induced emission (AIE) characteristic. Through smart molecular engineering, we and other groups have recently shown that conventional organic AIE fluorogens can be specifically tailored to offer both imaging and therapeutic functionalities, such as photosensitizing ability to facilitate photodynamic therapy. The creation of this new class of versatile organic theranostic bioprobes with simultaneous imaging and therapeutic capabilities has further enabled image-guided chemotherapy and image-guided photodynamic therapy. Essentially, from this endeavor, replacing the fluorophores of conventional reactivity-based bioprobes with multifunctional molecules will yield reactivity-based organic theranostic bioprobes with enhanced capabilities and improved performance. In this Account, we summarize the latest advancement of reactivity-based theranostic bioprobes. To start with, we discuss the fundamental differences between conventional lock-and-key and reactivity-based sensing mechanisms, followed by general design routes of reactivity-based organic theranostic bioprobes. We then describe our efforts in recent years in formulating reactivity-based organic biosensing/imaging probes and multifunctional theranostic probes as well as in utilizing these bioprobes in detecting various chemical species in living systems, such as free radicals and toxins, and in diagnosing and treating cancer and bacterial infections. Finally, we highlight current challenges and opportunities in the conclusions and outlook section. With this Account, we seek to further stimulate research activities and closer collaborations among the research fields of chemistry, materials, and biology to push the boundary of this emerging field and promote reactivity-based theranostics for practical applications and clinical translations.

Simultaneous Imaging of Endogenous Survivin mRNA and On-Demand Drug Release in Live Cells by Using a Mesoporous Silica Nanoquencher.

The design of multifunctional drug delivery systems capable of simultaneous target detection, imaging, and therapeutics in live mammalian cells is critical for biomedical research. In this study, by using mesoporous silica nanoparticles (MSNs) chemically modified with a small-molecule dark quencher, followed by sequential drug encapsulation, MSN capping with a dye-labeled antisense oligonucleotide, and bioorthogonal surface modification with cell-penetrating poly(disulfide)s, the authors have successfully developed the first mesoporous silica nanoquencher (qMSN), characterized by high drug-loading and endocytosis-independent cell uptake, which is able to quantitatively image endogenous survivin mRNA and release the loaded drug in a manner that depends on the survivin expression level in tumor cells. The authors further show that this novel drug delivery system may be used to minimize potential cytotoxicity encountered by many existing small-molecule drugs in cancer therapy.