Charge Transfer from Donor to Acceptor in Conjugated Microporous Polymer for Enhanced Photosensitization

Tailored Phototherapy Agent by Infection Site In Situ Activated Against Methicillin-Resistant S. aureus

Phototherapy, including photodynamic therapy (PDT) and photothermal therapy (PTT), is a promising treatment approach for multidrug resistant infections. PDT/PTT combination therapy can more efficiently eliminate pathogens without drug resistance. The key to improve the efficacy of photochemotherapy is the utilization efficiency of non-radiation energy of phototherapy agents. Herein, a facile phototherapy molecule (SCy-Le) with the enhancement of non-radiative energy transfer is designed by an acid stimulation under a single laser. Introduction of the protonated receptor into SCy-Le results in a distorted intramolecular charge in the infected acidic microenvironment, pH ≈ 5.5, which in turn, enhances light capture, reduces the singlet-triplet transition energies (ΔES1-T1), promotes electron system crossing, enhances capacity of reactive oxygen species generation, and causes a significant increase in temperature by improving vibrational relaxation. SCy-Le shows more than 99% bacterial killing rate against both methicillin-resistant Staphylococcus aureus and its biofilms in vitro and causes bacteria-induced wound healing in mice. This work will provide a new perspective for the design of phototherapy agents, and the emerging photochemotherapy will be a promising approach to combat the problem of antibiotic resistance.

Pyrene-Alkyne-Based Conjugated Porous Polymers with Skeleton Distortion-Mediated ⋅O2 - and 1O2 Generation for High-Selectivity Organic Photosynthesis

Reactive oxygen species (ROS) play a crucial role in determining photocatalytic reaction pathways, intermediate species, and product selectivity. However, research on ROS regulation in polymer photocatalysts is still in its early stages. Herein, we successfully achieved series of modulations to the skeleton of Pyrene-alkyne-based (Tetraethynylpyrene (TEPY)) conjugated porous polymers (CPPs) by altering the linkers (1,4-dibromobenzene (BE), 4,4'-dibromobiphenyl (IP), and 3,3'-dibromobiphenyl (BP)). Experiments combined with theoretical calculations indicate that BE-TEPY exhibits a planar structure with minimal exciton binding energy, which favors exciton dissociation followed by charge transfer with adsorbed O2 to produce ⋅O2 -. Thus BE-TEPY shows optimal photocatalytic activity for phenylboronic acid oxidation and [3+2] cycloaddition. Conversely, the skeleton of BP-TEPY is significantly distorted. Its planar conjugation decreases, intersystem crossing (ISC) efficiency increases, which makes it more prone for resonance energy transfer to generate 1O2. Therefore, BP-TEPY displays best photocatalytic activity in [4+2] cycloaddition and thioanisole oxidation. Both above reactant conversion and its product selectivity exceed 99 %. This work systematically reveals the intrinsic structure-activity relationship among the skeleton structure of CPPs, excitonic behavior, and selective generation of ROS, providing new insights for the rational design of highly efficient and selective CPPs photocatalysts.

Enhancing Photosynthesis Efficiency of Hydrogen Peroxide by Modulating Side Chains to Facilitate Water Oxidation at Low-Energy Barrier Sites

Hydrogen peroxide (H2O2) is a crucial oxidant in advanced oxidation processes. In situ, photosynthesis of it in natural water holds the promise of practical application for water remediation. However, current photosynthesis of H2O2 systems primarily relies on oxygen reduction, leading to limited performance in natural water with low dissolved oxygen or anaerobic conditions found in polluted water. Herein, a novel photocatalyst based on conjugated polymers with alternating electron donor-acceptor structures and electron-withdrawing side chains on electron donors is introduced. Specifically, carbazole functions as the electron donor, triazine serves as the electron acceptor, and cyano acts as the electron-withdrawing side chain. Notably, the photocatalyst exhibits a remarkable solar-to-chemical conversion of 0.64%, the highest reported in natural water. Furthermore, even in anaerobic conditions, it achieves an impressive H2O2 photosynthetic efficiency of 1365 µmol g-1 h-1, surpassing all the reported photosynthetic systems of H2O2. This remarkable improvement is attributed to the effective relocation of the water oxidation active site from a high-energy carbazole to a low-energy acetylene site mediated by the side chains, resulting in enhanced O2 or H2O2 generation from water. This breakthrough offers a new avenue for efficient water remediation using advanced oxidation technologies in oxygen-limited environments, holding significant implications for environmental restoration.

Synthesis, structure, photophysical property, stability of tetraphenylethylene-based boranil, and applications in cell imaging

A new family of tetraphenylethylene-based N,O-chelated boranil complexes (TPE-BAs) with aggregation-induced emission (AIE) characteristics were developed. X-ray crystallographic analysis indicated that the terminal substituents on the aniline moiety significantly affected the intermolecular stacking mode, thereby influencing the photophysical properties. The stabilities of these compounds are closely related to the substituents on the aniline moiety. Electron-donor-substituted TPE-BA-OMe exhibited the best stability, whereas the electron-acceptor-substituted compounds exhibited poor stability. Benefitting from its AIE properties and suitable lipophilicity, TPE-BA-OMe served as an excellent fluorescent probe for the specific bioimaging of lipid droplets in living cells.

Two Tetra-Nuclear Ln-Substituted Prazine Dicarboxylic Acid-Functionalized Selenotungstates with Catalytic Oxidation of Thioether Properties

Two two-dimensional Ln-substituted prazine dicarboxylic acid-functionalized selenotungstates Na3H9[(H2N(CH3)2]2{(Se4W27O100)[Ln4(H2O)8(Hpzdc)2(pzdc)]}·26H2O [Ln = Nd (1) and Ce (2)]; H2pzdc = 2,3-pyrazine dicarboxylic acid) have been synthesized by one-pot self-assembly strategy, in which the basic polyanion [Se4W27O100]22-was composed of two [SeW8O31]10- fragments, a [SeW9O33]8- segment and an intriguing {SeO} group, simultaneously tetra-nuclear Ln3+ ions with H2pzdc pendants were embedded. Compounds 1 and 2 showed excellent catalytic oxidation of thioether properties within a short time (20 min) with high 100% conversion and 98.9% selectivity. In addition, the pioneering Ln-substituted selenotungstates were used as catalysts to degrade sulfur mustard simulant 2-chloroethyl ethyl sulfide at room temperature with 99% conversion and 100% selectivity. The chemical kinetic experiment studies revealed that the catalytic reaction was in compliance with the first-order reaction, and the kinetic half-life (t1/2) values were 3.814 and 3.849 min, respectively.

Reacting Molecular Oxygen with Butanone under Visible Light Irradiation: A General Aerobic Oxidation of Alkenes, Sulfides, Phosphines, and Silanes

Here, we present a novel oxidation technique by reacting molecular oxygen with butanone under visible light irradiation. This method enables the mild oxidation of various functionalized compounds, including olefins, sulfides, phosphines, and silanes. Preliminary mechanistic experiments and theoretical calculations suggest that visible light triggers molecular oxygen to produce singlet oxygen in butanone. This singlet oxygen then reacts with butanone, producing an active oxidizing species.

Photoactive conjugated microporous polymer@C60 with quencher on tailed Y-triangular DNA structure for high-performance signal-off photoelectrochemical biosensing

Herein, we synthesized a conjugated microporous polymer (CMP) decorated C₆₀ (CMP@C₆₀) with high photoelectric conversion efficiency, in which continuously repeated donor-acceptor (D-A) π electron unit within one molecule of CMP on C₆₀ could not only effectively increase the mobility of photogenerated carriers with improved electron transmission, but also constitute the cascade energy band matching with reduced electron-hole recombination. Based on the high-performance of CMP@C₆₀ for producing exciting initial photoelectrochemical (PEC) signal, a sensitive signal-off sensing platform was designed for lead ion (Pb²⁺) assay by coupling with quencher methylene blue (MB) interacting on efficient long tailed Y-triangular DNA structure (LYTD). The proposed LYTD with a tripod structure could generate six long tails in situ on its side at the same time via a simple hybridization chain reaction (HCR), providing notably grooves on electrode to accommodate quencher MB to significantly depress the signal for sensitive detection of Pb²⁺. As a result, the proposed PEC biosensor revealed excellent analysis capability with a low detection limit of 0.3 fM (S/N = 3). Additionally, it also showed satisfactory stability in the detection of tap water samples, lake water samples and clinical serum samples, manifesting great application prospect in the areas of environmental pollutant detection.

An oxygen-carrying and lysosome-targeting BODIPY derivative for NIR bioimaging and enhanced multimodal therapy against hypoxic tumors

Cancer treatment modalities have gradually shifted from monotherapies to multimodal therapies. It is still a challenge to develop a synergistic chemo-phototherapy system with relieving tumor hypoxia, specific targeting, and real-time fluorescence tracking. In this study, we designed a multifunctional BODIPY derivative, FBD-M, for synergistic chemo-phototherapy against hypoxic tumors. FBD-M was composed of four parts: 1) The BODIPY fluorophore selected as a theranostic core, 2) A pentafluorobenzene group modified on meso-BODIPY to carry oxygen, 3) A morpholine group hooked to one side of BODIPY served as a lysosome-targeting unit for enhancing antitumor effect, and 4) An aromatic nitrogen mustard group introduced on other side of BODIPY to achieve chemotherapy. After introducing the morpholine and aromatic nitrogen mustard in BODIPY, the conjugate system of BODIPY was also expanded to realize near-infrared (NIR) phototherapy. Finally, FBD-M was obtained by a rational design, which possessed with NIR absorbance and emission, photosensitive activity, oxygen-carrying capability for relieving tumor hypoxia, high photothermal conversion efficiency, good photostability, lysosome targeting, low toxicity, and synergistic chemo-phototherapy against hypoxic tumors. FBD-M had been successfully applied for anticancer in vitro and in vivo. Our study demonstrates that FBD-M can serve as an ideal multifunctional theranostic agents.

Benzotrithiophene-based Covalent Organic Framework Photocatalysts with Controlled Conjugation of Building Blocks for Charge Stabilization

Covalent organic frameworks have recently shown high potential for photocatalytic hydrogen production. However, their structure-property-activity relationship has not been sufficiently explored to identify a research direction for structural design. Herein, we report the design and synthesis of four benzotrithiophene (BTT)-based covalent organic frameworks (COFs) with different conjugations of building units, and their photocatalytic activity for hydrogen production. All four BTT-COFs had slipped parallel stacking patterns with high crystallinity and specific surface areas. The change in the degree of conjugation was found to rationally tune the rate of photocatalytic hydrogen evolution. Based on the experimental and calculation results, the tunable photocatalytic performance could be mainly attributed to the electron affinity and charge trapping of the electron accepting units. This study provides important insights for designing covalent organic frameworks for efficient photocatalysts.

Dual Molecular Oxygen Activation Sites on Conjugated Microporous Polymers for Enhanced Photocatalytic Formation of Benzothiazoles

Oxidative formation of high value compounds involving active oxygen species using heterogeneous polymeric photocatalysts has become a useful tool in catalysis. Controlling the interaction between the active sites on polymer photocatalysts and oxygen molecules is still challenging due to the rather large polymer backbone structure. Here, we design a triazine-containing donor acceptor-type conjugated microporous polymer (CMP) containing dual major active sites at F and N atoms for molecular oxygen activation. Introducing fluorine atoms on the CMP backbone led to a combined effect of enhanced adsorption and electron transfer of oxygen. Time-resolved photoluminescence, electronic paramagnetic resonance spectra, and DFT calculation revealed favorable absorption energy and electron transfer kinetics between the CMP and oxygen molecules, thus efficiently generating superoxide radicals (O₂^•-) and singlet oxygen (¹O₂) as main active oxygen species. The photocatalytic activity, selectivity, and reusability of the CMP was demonstrated by the photocatalytic formation of a variety of benzothiazoles.

Polymerization-Enhanced Photophysical Performances of AIEgens for Chemo/Bio-Sensing and Therapy

AIE polymers have been extensively researched in the fields of OLEDs, sensing, and cancer treatment since its first report in 2003, which have achieved numerous breakthroughs during the years. In comparison with small molecules, it can simultaneously combine the unique advantages of AIE materials and the polymer itself, to further enhance their corresponding photophysical performances. In this review, we enumerate and discuss the common construction strategies of AIE-active polymers and summarize the progress of research on polymerization enhancing luminescence, photosensitization, and room-temperature phosphorescence (RTP) with their related applications in chemo/bio-sensing and therapy. To conclude, we also discuss current challenges and prospects of the field for future development.

Supramolecular photodynamic agents for simultaneous oxidation of NADH and generation of superoxide radical

Given that Type-I photosensitizers (PSs) have hypoxia tolerance, developing general approaches to prepare Type-I PSs is of great importance, but remains a challenge. Here, we report a supramolecular strategy for the preparation of Type-I photodynamic agents, which simultaneously generate strong oxidizing cationic radicals and superoxide radicals, by introducing electron acceptors to the existing Type-II PSs. As a proof-of-concept, three electron acceptors were designed and co-assembled with a classical PS to produce quadruple hydrogen-bonded supramolecular photodynamic agents. The photo-induced electron transfer from the PS to the adjacent electron acceptor occurs efficiently, leading to the generation of a strong oxidizing PS^+• and an anionic radical of the acceptor, which further transfers an electron to oxygen to form O₂^-•. In addition, these photodynamic agents induce direct photocatalytic oxidation of NADH with a turnover frequency as high as 53.7 min^-1, which offers an oxygen-independent mechanism to damage tumors.

Enhancing Built-in Electric Field via Molecular Dipole Control in Conjugated Microporous Polymers for Boosting Charge Separation

The built-in electric field (BEF) has been considered as the key kinetic factor for facilitating efficient photoinduced carrier separation and migration of polymeric photocatalysts. Enhancing the BEF of the polymers could enable a directional migration of the photogenerated carriers to accelerate photogenerated charge separation and thus boost photocatalytic performances. However, achieving this approach remains a formidable challenge, which has never been realized in conjugated microporous polymers (CMPs). Herein, we developed a molecular dipole control strategy to modulate the BEF in CMPs by varying the nature of the core. As a result, a series of CMPs with a tunable BEF were designed and prepared via FeCl₃-mediated coupling of bicarbazole with different acceptor cores. The optimized CbzCMP-9 featured the strongest BEF induced by its high molecular dipole, which grants it with a powerful driving force to accelerate exciton dissociation into electron-hole pairs and facilitates charge transfer along the backbone of CMPs to the surface, resulting in a remarkable photocatalytic performance toward thiocyano chromones and C-3 thiocyanation of indoles (up to 95 and 98% yields, respectively) and prominently surpassing many other reported photocatalysts. In brief, the proposed strategy highlights that enhancing the BEF by modulating molecular dipole can lead to a dramatic improvement in photocatalytic performance, which is expected to be employed for constructing other photocatalytic systems with high performance.

Copper-Bridged Tetrakis(4-ethynylphenyl)ethene Aggregates with Photo-Regulated 1 O2 and O2 .- Generation for Selective Photocatalytic Aerobic Oxidation

Active species regulation is a key scientific issue that essentially determines the selectivity and activity of a photocatalyst. Herein, Cu^I -bridged tetrakis(4-ethynylphenyl)ethene aggregates (T₄ EPE-Cu) with photo-regulated ¹ O₂ and O₂ ^.- generation were demonstrated for selective photocatalytic aerobic oxidation. In this system, transient photovoltage combined with the density functional theory calculations confirmed that Cu-alkynyl was the main oxygen activation site. The adsorbed O₂ tends to produce O₂ ^.- because of the potential well effect of Cu-alkynyl under high-energy light excitation. But under low-energy light, O₂ tends to produce ¹ O₂ via resonance energy transfer with Cu-alkynyl. For α-terpinene oxidation, the ratios of ¹ O₂ products to O₂ ^.- products can be controlled from 1.3 (380 nm) to 10.7 (600 nm). Furthermore, T₄ EPE-Cu exhibited ultrahigh photocatalytic performance for Glaser coupling and benzylamine oxidation, with a conversion and selectivity of over 99 %.

Rapid chromium reduction by metal-free organic polymer photocatalysis via molecular engineering

The conversion of hexavalent chromium (Cr(VI)), a highly poisonous heavy metal found in natural environment, to less poisonous trivalent chromium (Cr(III)) has attracted a lot of interest. However, little interest has been paid to the development of metal-free catalysts. Here, we demonstrate for the first time a molecular engineering strategy to synthesize a range of donor-acceptor conjugated polymer photocatalysts, which can significantly increase the reduction efficiency of Cr(VI) by a factor of 5.2, corresponding to a significant change in the reduction reaction rate constant (from 0.0337 to 0.1740 min^-1). In addition, the apparent quantum efficiency (AQE) of Cr(VI) removal was obtained, and the optimized photocatalyst (Py-SO₁) could achieve the highest apparent quantum efficiency at wavelength of 420 nm in those samples. Despite the narrow light absorption of Py-SO₁ polymer, its excellent exciton separation efficiency and efficient electron output enabled it to achieve excellent performance in photoreduction of Cr(VI), surpassing that of the reported metal-free photocatalysts. The results show that the present work provides a new perspective for designing suitable environmental remediation catalysts based on molecular engineering strategies.

Polarization Engineering of Covalent Triazine Frameworks for Highly Efficient Photosynthesis of Hydrogen Peroxide from Molecular Oxygen and Water

Two-electron oxygen photoreduction to hydrogen peroxide (H₂ O₂ ) is seriously inhibited by its sluggish charge kinetics. Herein, a polarization engineering strategy is demonstrated by grafting (thio)urea functional groups onto covalent triazine frameworks (CTFs), giving rise to significantly promoted charge separation/transport and obviously enhanced proton transfer. The thiourea-functionalized CTF (Bpt-CTF) presents a substantial improvement in the photocatalytic H₂ O₂ production rate to 3268.1 µmol h^-1 g^-1 with no sacrificial agents or cocatalysts that is over an order of magnitude higher than unfunctionalized CTF (Dc-CTF), and a remarkable quantum efficiency of 8.6% at 400 nm. Mechanistic studies reveal the photocatalytic performance is attributed to the prominently enhanced two-electron oxygen reduction reaction by forming endoperoxide at the triazine unit and highly concentrated holes at the thiourea site. The generated O₂ from water oxidation is subsequently consumed by the oxygen reduction reaction (ORR), thereby boosting overall reaction kinetics. The findings suggest a powerful functional-groups-mediated polarization engineering method for the development of highly efficient metal-free polymer-based photocatalysts.

A host-guest strategy for converting the photodynamic agents from a singlet oxygen generator to a superoxide radical generator

Type-I photosensitizers (PSs) generate cytotoxic oxygen radicals by electron transfer even in a hypoxic environment. Nevertheless, the preparation of type-I PSs remains a challenge due to the competition of triplet-triplet energy transfer with O2 (type-II process). In this work, we report an effective strategy for converting the conventional type-II PS to a type-I PS by host-guest complexation. Electron-rich pillar[5]arenes are used as an electron donor and macrocyclic host to produce a host-guest complex with the traditional electron-deficient type-II PS, an iodide BODIPY-based guest. The host-guest complexation promotes intermolecular electron transfer from the pillar[5]arene moiety to BODIPY and then to O2 by the type-I process upon light-irradiation, leading to efficient generation of the superoxide radical (O2 -˙). The results of anti-tumor studies indicate that this supramolecular PS demonstrates high photodynamic therapy efficacy even under hypoxic conditions. This work provides an efficient method to prepare type-I PSs from existing type-II PSs by using a supramolecular strategy.

Porous organic polymers in solar cells

Owing to their unique porosity and large surface area, porous organic polymers (POPs) have shown their presence in numerous novel applications. The tunability and functionality of both the pores and backbone of the material enable its suitability in photovoltaic devices. The porosity induced host-guest configurations as well as periodic donor-acceptor structures benefit the charge separation and charge transfer in photophysical processes. The role of POPS in other critical device components, such as hole transporting layers and electrodes, has also been demonstrated. Herein, this review will primarily focus on the recent progress made in applying POPs for solar cell device performance enhancement, covering organic solar cells, perovskite solar cells, and dye-sensitized solar cells. Based on the efforts in recent years in unraveling POP's photophysical process and its relevance with device performances, an in-depth analysis will be provided to address the gradual shift of attention from an entirely POP-based active layer to other device functional components. Combining the insights from device physics, material synthesis, and microfabrication, we aim to unfold the fundamental limitations and challenges of POPs and shed light on future research directions.