Heterogeneous Photosensitizers Research Articles

Synthesis of fluorescein-containing polymeric heterogeneous photocatalyst and its applications

A novel fluorescein-containing polymeric photosensitizer (FS-PHEMA) was successfully synthesized and used as an excellent heterogeneous photocatalyst for aerobic photooxidation of thioethers, hydroxylation of aryl boric acids, and oxidative self-coupling of amines. All the reactions could run smoothly upon irradiation of blue LED under aerobic conditions at room temperature. This heterogeneous photosensitizer can be easily separated, recovered, and reused at least 5 times without significant loss of catalytic activity, showing a good potential in practical applications.

One-pot synthesis of a porphyrin functionalized metal-organic frameworks as a recyclable visible-light-driven photosensitizer for efficient detoxification of a sulfur mustard simulant in air

Herein, we report a facile one-pot in situ self-assembly approach that enables a porphyrin photosensitizer, [5,10,15,20-tetrakis(4-methoxycarbonylphenyl)porphyrin]-Zn(II) (ZnTPP), to be enshrouded by a zeolitic imidazolate framework-8 (ZIF-8) to afford a novel visible-light-driven heterogeneous photosensitizer, ZnTPP@ZIF-8 composite. The ZnTTP photosensitizer was well dispersed and fully confined within the ZIF-8 crystals and the framework intactness and porosity were well maintained. The as-prepared ZnTPP@ZIF-8 composite integrates the advantages of ZIF-8 MOFs and ZnTTP photosensitizer. It not only can effectively produce both singlet oxygen (1O2) and superoxide ion (∙O2−) under visible light irradiation, but also exhibit high surface area and excellent stability. The structure characterization of ZnTPP@ZIF-8 composite was first carried out, and then this material can be used as a heterogeneous photosensitizer for the rapid and highly selective detoxification of a sulfur mustard simulant (2-chloroethyl ethyl sulfide) into the corresponding much less toxic sulfoxide product with a half-life of only 1.5 min under visible light irradiation at room temperature in air atmosphere. This catalyst can be readily recycled and reused at least six times without obvious loss of catalytic activity. This study will provide us a new strategy for the facile, rapid and environmentally friendly preparation of photosensitizer@MOFs composites and the rapid detoxification of sulfur mustard under ambient conditions in the future.

De Novo Synthesis of Acridone-Based Zn-Metal-Organic Framework (Zn-MOF) as a Photocatalyst: Application for Visible Light-Mediated Oxidation of Sulfides and Enaminones.

Acridone, a cyclic analogue of benzophenone that undergoes efficient intersystem crossing (ISC) to the triplet-excited state with near-unity quantum yield, was elaborated as a 3-connecting triacid linker, i.e., H3AcTA, to develop a photocatalytic metal-organic framework (MOF) for energy transfer applications; the triacid linker inherently features concave shapes, an attribute that is important for the construction of MOFs with significant porosity. Metal ion (Zn2+)-assisted self-assembly of the triacid yielded a Zn-MOF, i.e., Zn-AcTA, with a solvent-accessible volume of ca. 31%. The protection of the acridone chromophore in the MOF in conjunction with a wider cross-section of its absorption in the visible region renders the MOF an excellent heterogeneous photosensitizer for singlet oxygen (1O2) generation by energy transfer to the ground-state triplet oxygen (3O2). It is shown that the Zn-MOF can be applied as a photosensitizing catalyst for visible light-mediated oxidation of various sulfides to sulfoxides and enaminones to amino-esters via 1,2-acyl migration. It is further demonstrated that the photocatalyst can be easily recycled without any loss of catalytic activity and structural integrity. Based on mechanistic investigations, 1O2 is established as the reactive oxygen species in photocatalytic oxidation reactions. The results constitute the first demonstration of rational development of a photocatalytic MOF based on acridone for heterogeneous oxidations mediated by 1O2.

Heterogeneous photosensitization for water reuse in cellars: evaluation of silica, spongin, and chitosan as carrier material.

Photosensitization, a powerful oxidation reaction, offers significant potential for wastewater treatment in the context of industrial process water reuse. This environmentally friendly process can be crucial in reducing water consumption and industrial pollution. The ultimate goal is to complete process water reuse, creating a closed-loop system that preserves the inherent value of water resources. The photosensitized oxidation reaction hinges on three essential components: the photosensitizer, visible light, and oxygen. In this study, we assess the performance of three distinct materials-silica, chitosan, and spongin-as carrier materials for incorporating the phthalocyanine photosensitizer (ZnPcS4) in the heterogenous photosensitization process. Among the three materials under study, chitosan emerged as the standout performer in reactor hydrodynamic performance. In the photooxidation process, the photosensitizer ZnPcS4 exhibited notable efficacy, resulting in a significant reduction of approximately 20 to 30% in the remaining COD concentration of the cellar wastewater. Chitosan demonstrated exceptional hydrodynamic characteristics and displayed a favorable response to pH adjustments within the range of 8 to 10, outperforming the other two carrier materials. To further enhance the efficiency of continuous operation, exploring methods for mitigating photosensitizer bleaching within the reaction medium and investigating the impact of different pH values on the process optimization would be prudent.

Durability of Photosensitizers in a Photo-oxidation Reaction in a Novel Oscillatory Baffled Photo Reactor

AbstractWith the rapid development of novel photosensitizers/photocatalysts, photochemical transformation has become possible and practical. In this context, we report for the first time our work on testing and quantifying the durability and robustness of a heterogeneous photosensitizer, polymer-supported rose Bengal (Ps-RB) beads, in a model photo-oxidation reaction between α-terpinene and singlet oxygen (1O2). A novel photo reactor is used due to its capabilities of providing uniform suspensions of solid beads and uniform light distribution. We have proposed a methodology for quantifying the durability of the beads including the factors of loss of beads and the reduced product concentration. The results show that the durability of the Ps-RB beads has decreased by about 67% after five consecutive runs, and the half-life of the beads can be reached in less than 200 minutes. In addition, we have also identified the optimal bead mass in the novel photo reactor. Our work not only enriches the designs of new and better photosensitizers but also provides a comprehensive methodology for testing and validating photosensitizers.

Pyrene as a Triplet Acceptor Enhancing Triplet Energy Transfer of g-C3N4 in Heterogeneous Photooxidation

Triplet photosensitizers have great potential in selective photooxidation by generating 1O2 through triplet energy transfer. However, the heterogeneous bulk photosensitizers easily trap triplet excitons and inhibit photocatalysis efficiency. Previous work focused on controlling ultra-small size to reduce the transfer distance, but we propose a new strategy using triplet acceptor molecules (e.g., pyrenecarboxylic acid, PCA) with proper energy levels to modify the surface of heterogeneous photosensitizers (e.g., g-C3N4), facilitate the transfer of triplet excitons from the interior to the surface of the catalyst, and enhance catalytic reactions on its surface. In the photooxidation reaction of uric acid (UA), the conversion of UA catalyzed by pg-C3N4/PCA can reach 91.3% at 60 min, higher than that without modification (24.0%). DFT calculations and spectroscopic characterization show that the triplet acceptor in pg-C3N4/PCA could reduce the ΔEST value and grab triplet excitons in g-C3N4, thereby enhancing the 1O2 generation. This work provides another approach for high-efficiency utilization of heterogeneous triplet photosensitizers in wide applications.

Visible-light-harvesting basolite-A520 metal organic framework for photocatalytic hydrogen evolution

A heterogeneous photosensitizer Ru@dpdhpzBASF-A520 has been successfully synthesized following an unprecedented strategy based on the incorporation of surface dipyridyl-dihydropyridazine adducts by Diels–Alder reaction on the aluminum fumarate units of the highly porous metal-organic framework (MOF) BASF-A520 and their further coordination to ruthenium metal centers. The characterization of the resulting metal-organic framework, including the ruthenium bipyridine-like photosensitizer moieties attached to its linkers, has been carried out by a wide variety of techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherms, solid-state cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (13C CP/MAS NMR), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible (UV–vis) spectroscopy. The light absorption in the visible region shown by the resulting material, Ru@dpdhpzBASF-A520, has allowed its application as a single-site solid photosensitizer for photochemical reactions of hydrogen evolution in conjunction with Pt nanoparticles as catalyst, EDTA as sacrificial electron donor and MV as electron carrier. A remarkable photocatalytic activity after 72 h was achieved, with a TON of 1157 based on the heterogeneous ruthenium photosensitizer, in aqueous solution at pH 5.0, which confirmed the effective stabilization of the ruthenium dipyridyl-dihydropyridazine adducts on the MOF surface and the efficient electron injection from the photoexcited Ru@dpdhpzBASF-A520 to Pt nanoparticles mediated by MV electron carrier for hydrogen generation from water.

Photoactive Hexaazaphenalene‐based Coordination Network as a Two‐Pathway Photosensitizer for Oxidation of Alkanes

AbstractA tris(4‐pyridyl) hexaazaphenalenyl anion (TPHAP−) exhibited both energy and charge transfer processes to oxygen molecules under UV irradiation resulting in the production of reactive oxygen species (ROSs). The existence of ROSs was confirmed by spectroscopic characterization and photooxidation of a standard compound selective for the singlet oxygen, 1,5‐dihydroxynaphthalene (1,5‐DHN). In addition, a porous coordination network (PCN) consisting of TPHAP−, cadmium ions and fumarate co‐ligand was synthesized and used as a heterogeneous photosensitizer capable of ROSs generation. To take advantage of this ability, photooxidation of various saturated hydrocarbons including cyclohexane, cyclooctane and n‐octane was investigated. TPHAP‐based PCN demonstrated excellent photosensitizing ability achieving more than a hundred times higher turnover frequency than other reported coordination networks based on photoactive ligands.

Ordered heterogeneity of molecular photosensitizer toward enhanced photocatalysis

SignificanceThe photosensitizer is one of the important components in the photocatalytic system. Molecular photosensitizers have well-defined structures, which is beneficial in revealing the catalysis mechanism and helpful for further structural design and performance optimization. However, separation and recycling of the molecular photosensitizers is a great problem. Loading them into/on two/three-dimensional supports through covalent bonds, electrostatic interactions, and supramolecular interactions is a method that enhances their separation and recycling capability. Nonetheless, the structures of the resulting composites are unclear. Thus, the development of highly crystalline heterogeneity methods for molecular photosensitizers, albeit greatly challenging, is meaningful and desirable in photocatalysis, through which heterogeneous photosensitizers with well-defined structures, definite catalysis mechanisms, and good catalytic performance would be expected.

Cross-dehydrogenative Coupling of N-Aryl Tetrahydroisoquinolines Catalyzed by an Anthraquinone-containing Polymeric Photosensitizer.

This work reports the photocatalytic application of an anthraquinone-containing polymeric photosensitizer (AQ-PHEMA) in the visible light-induced cross-dehydrogenative-coupling of N-aryl tetrahydroisoquinolines with several nucleophiles, including nitromethane, 1-methyl-2-alkyl ketone and dialkyl (aryl) phosphine oxide. The results revealed that the reaction could be catalyzed by AQ-PHEMA efficiently to afford a series of 1-substituted-2-aryl-1,2,3,4-tetrahydroisoquinolines in good to excellent yields with nice substrate tolerance under aerobic conditions at room temperature. The practical application potential was also showcased by a gram-scale synthesis. More importantly, the utilization of AQ-PHEMA as a heterogeneous photosensitizer also showed nice recyclability and reusability of the catalyst, whereas AQ-PHEMA can be easily separated and reused for at least 8 times without significant loss of photocatalytic activity.

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

Photosensitization associated with light absorption and energy/electron-transfer represents the central processes for photosynthesis. However, it's still a challenge to develop a heavy-atom-free (HAF) strategy to improve the sensitizing ability of polymeric photosensitizers. Herein, we propose a new protocol to significantly improve the photosensitization by decorating mother conjugated microporous polymer (CMP-1) with polycyclic aromatic hydrocarbons (PAHs), resulting in a series of CMPs (CMP-2-4). Systematic study reveals that covalent modification with PAHs can transfer charge to Bodipy in CMP to further facilitate both intersystem crossing and electron-hole separation, which can dramatically boost energy-/electron-transfer reactions. Remarkably, CMP-2 as a representative CMP can efficiently drive the photosynthesis of methyl phenyl sulfoxide with 92 % yield, substantially higher than that of CMP-1 (32 %). Experiments and theory calculations demonstrate the structure-property-activity relationship of these CMPs, opening a new horizon for developing HAF heterogeneous photosensitizers with highly efficient sensitizing activity by rational structure regulation at a molecular level.

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

AbstractPhotosensitization associated with light absorption and energy/electron‐transfer represents the central processes for photosynthesis. However, it's still a challenge to develop a heavy‐atom‐free (HAF) strategy to improve the sensitizing ability of polymeric photosensitizers. Herein, we propose a new protocol to significantly improve the photosensitization by decorating mother conjugated microporous polymer (CMP‐1) with polycyclic aromatic hydrocarbons (PAHs), resulting in a series of CMPs (CMP‐2–4). Systematic study reveals that covalent modification with PAHs can transfer charge to Bodipy in CMP to further facilitate both intersystem crossing and electron‐hole separation, which can dramatically boost energy‐/electron‐transfer reactions. Remarkably, CMP‐2 as a representative CMP can efficiently drive the photosynthesis of methyl phenyl sulfoxide with 92 % yield, substantially higher than that of CMP‐1 (32 %). Experiments and theory calculations demonstrate the structure‐property‐activity relationship of these CMPs, opening a new horizon for developing HAF heterogeneous photosensitizers with highly efficient sensitizing activity by rational structure regulation at a molecular level.

Doping [Ru(bpy)3]2+ into metal-organic framework to facilitate the separation and reuse of noble-metal photosensitizer during CO2 photoreduction

It is desirable to develop highly efficient and sustainable catalytic systems for CO2 photoreduction using efficient heterogeneous photosensitizers (PSs); however, this remains a great challenge. In this study, we doped [Ru(bpy)3]2+ into UiO-metal-organic frameworks (MOFs) to facilitate the separation and reuse of noble metal PS. By simply adjusting the loading amount, a series of heterogeneous photoactive MOFs, namely, UiO-Ru-1, UiO-Ru-2, and UiO-Ru-3, were constructed to act as heterogeneous PSs to drive the efficient CO2 photoreduction under visible-light irradiation. Remarkably, UiO-Ru-2 exhibited the best photosensitizing ability among the prepared MOFs in sensitizing the iron quarterpyridine catalyst (C-1), and the CO yield reached as high as 171 mmol/g with ca. 100% selectivity, which is a record value among all the MOF-based photocatalysts. This photoactive MOF can be recycled and reused three times without any obvious activity loss, signifying its good photochemical stability. Experimental investigations confirmed that the strong visible absorption, long-lived excited state, appropriate redox potential, good photocatalytic stability, and excellent collaboration with C-1 were attributable to the superior catalytic activity. This work highlights an avenue for constructing heterogeneous PSs with excellent recyclability using MOF as the platform for efficient CO2 reduction.

Porphyrin-Containing MOFs and COFs as Heterogeneous Photosensitizers for Singlet Oxygen-Based Antimicrobial Nanodevices.

Visible-light irradiation of porphyrin and metalloporphyrin dyes in the presence of molecular oxygen can result in the photocatalytic generation of singlet oxygen (1O2). This type II reactive oxygen species (ROS) finds many applications where the dye, also called the photosensitizer, is dissolved (i.e., homogeneous phase) along with the substrate to be oxidized. In contrast, metal-organic frameworks (MOFs) are insoluble (or will disassemble) when placed in a solvent. When stable as a suspension, MOFs adsorb a large amount of O2 and photocatalytically generate 1O2 in a heterogeneous process efficiently. Considering the immense surface area and great capacity for gas adsorption of MOFs, they seem ideal candidates for this application. Very recently, covalent-organic frameworks (COFs), variants where reticulation relies on covalent rather than coordination bonds, have emerged as efficient photosensitizers. This comprehensive mini review describes recent developments in the use of porphyrin-based or porphyrin-containing MOFs and COFs, including nanosized versions, as heterogeneous photosensitizers of singlet oxygen toward antimicrobial applications.

Determination of Singlet Oxygen Quantum Yield of a Porphyrinic Metal–Organic Framework

Metal–organic frameworks (MOFs) have emerged as heterogeneous photosensitizers in applications ranging from photodynamic therapy to photocatalysis. However, singlet oxygen (1O2) quantum yields of MOF photosensitizers are largely unknown. Herein, we report a reliable method to quantify the 1O2 quantum yield of a porphyrin MOF PCN-222/MOF-545 (free base). To accurately measure the optical density of the MOF suspensions in chloroform, a UV–vis spectrometer equipped with an integrating sphere detector was employed. However, no 1O2 near-infrared luminescence signal from the excited MOF could be detected and the amount of 1O2 produced by the MOF photosensitizer was quantified using a 1O2 trap 9,10-dimethylanthracene. Using C70 as a reference, the 1O2 quantum yield of PCN-222/MOF-545 (free base) was determined to be 0.35 ± 0.02. This method should be applicable to the determination of 1O2 quantum yields of other solid-state materials.

A Heterogeneous Photosensitizer Based on Zinc Oxide for Photo Cleaning of Aquatic Media

A Heterogeneous Photosensitizer Based on Zinc Oxide for Photo Cleaning of Aquatic Media

8,8'-(Benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(quinolin-4(1H)-one): a twisted photosensitizer with AIE properties.

A new benzothiadiazole (BTZ) luminogen is prepared via the Suzuki–Miyaura Pd-catalysed C–C cross-coupling of 8-iodoquinolin-4(1H)-one and a BTZ bispinacol boronic ester. The rapid reaction (5 min) affords the air-, thermo-, and photostable product in 97% yield as a yellow precipitate that can be isolated by filtration. The luminogen exhibits aggregated-induced emission (AIE) properties, which are attributed to its photoactive BTZ core and nonplanar geometry. It also behaves as a molecular heterogeneous photosensitizer for the production of singlet oxygen under continuous flow conditions.

Efficient Photooxygenation Process of Biosourced α-Terpinene by Combining Controlled LED-Driven Flow Photochemistry and Rose Bengal-Anchored Polymer Colloids

This work studies the reactivity of poly(N-vinylcaprolactam-co-vinyl acetate-co-vinylbenzyl Rose Bengal) microgels (VBRB@MG) as heterogeneous photosensitizers in a continuous-flow process for susta...

Supramolecular Porous Organic Nanocomposites for Heterogeneous Photocatalysis of a Sulfur Mustard Simulant.

Efficient heterogeneous photosensitizing materials require both large accessible surface areas and excitons of suitable energies and with well-defined spin structures. Confinement of the tetracationic cyclophane (ExBox4+ ) within a nonporous anionic polystyrene sulfonate (PSS) matrix leads to a surface area increase of up to 225 m2 g-1 in ExBox•PSS. Efficient intersystem crossing is achieved by combining the spin-orbit coupling associated to Br heavy atoms in 1,3,5,8-tetrabromopyrene (TBP), and the photoinduced electron transfer in a TBP⊂ExBox4+ supramolecular dyad. The TBP⊂ExBox4+ complex displays a charge transfer band at 450 nm and an exciplex emission at 520 nm, indicating the formation of new mixed-electronic states. The lowest triplet state (T1 , 1.89 eV) is localized on the TBP and is close in energy with the charge separated state (CT, 2.14 eV). The homogeneous and heterogeneous photocatalytic activities of the TBP⊂ExBox4+ , for the elimination of a sulfur mustard simulant, has proved to be significantly more efficient than TBP and ExBox+4 , confirming the importance of the newly formed excited-state manifold in TBP⊂ExBox4+ for the population of the low-lying T1 state. The high stability, facile preparation, and high performance of the TBP⊂ExBox•PSS nanocomposites augur well for the future development of new supramolecular heterogeneous photosensitizers using host-guest chemistry.

1O2 determined from the measured PDT dose and 3O2 predicts long-term response to Photofrin-mediated PDT

Photodynamic therapy (PDT) that employs the photochemical interaction of light, photosensitizer and oxygen is an established modality for the treatment of cancer. However, dosimetry for PDT is becoming increasingly complex due to the heterogeneous photosensitizer uptake by the tumor, and complicated relationship between the tissue oxygenation ([3O2]), interstitial light distribution, photosensitizer photobleaching and PDT effect. As a result, experts argue that the failure to realize PDT’s true potential is, at least partly due to the complexity of the dosimetry problem. In this study, we examine the efficacy of singlet oxygen explicit dosimetry (SOED) based on the measurements of the interstitial light fluence rate distribution, changes of [3O2] and photosensitizer concentration during Photofrin-mediated PDT to predict long-term control rates of radiation-induced fibrosarcoma tumors. We further show how variation in tissue [3O2] between animals induces variation in the treatment response for the same PDT protocol. PDT was performed with 5 mg kg−1 Photofrin (a drug-light interval of 24 h), in-air fluence rates (ϕair) of 50 and 75 mW cm−2 and in-air fluences from 225 to 540 J cm−2. The tumor regrowth was tracked for 90 d after the treatment and Kaplan–Meier analyses for local control rate were performed based on a tumor volume ⩽100 mm3 for the two dosimetry quantities of PDT dose and SOED. Based on the results, SOED allowed for reduced subject variation and improved treatment evaluation as compared to the PDT dose.