Photosensitized Singlet Oxygen Research Articles

Effect of Peripheral Functionalization of Pt(II) Porphyrin(2.1.2.1) on Singlet Oxygen Generation.

Four structurally bent porphyrin(2.1.2.1) Pt(II) complexes have been obtained and verified well. Main absorbance of Pt(II) porphyrin(2.1.2.1) displayed a significant red-shift compared to that of porphyrin(1.1.1.1) Pt(II) molecules. 1O2 study indicated that electron-withdrawing group and intramolecular charge transfer effect synergistically endowed Pt(II) porphyrin(2.1.2.1) with good singlet oxygen-sensitizing capacity under blue LED light irradiation. This work presents a simple synthesis way to develop a new series of efficient porphyrinoid singlet oxygen photosensitizers for PDT through molecular engineering.

Exploiting the Potential of Iridium(III) bis-Nitrone Complexes as Phosphorogenic Bifunctional Reagents for Phototheranostics.

Cross-linking strategies have found wide applications in chemical biology, enabling the labeling of biomolecules and monitoring of protein-protein interactions. Nitrone exhibits remarkable versatility and applicability in bioorthogonal labeling due to its high reactivity with strained alkynes via the strain-promoted alkyne-nitrone cycloaddition (SPANC) reaction. In this work, four cyclometalated iridium(III) polypyridine complexes functionalized with two nitrone units were designed as novel phosphorogenic bioorthogonal reagents for bioimaging and phototherapeutics. The complexes showed efficient emission quenching, which is attributed to an efficient nonradiative decay pathway via the low-lying T1/S0 minimum energy crossing point (MECP), as revealed by computational studies. However, the complexes displayed significant emission enhancement and lifetime extension upon reaction with (1R,8S,9s)-bicyclo[6.1.0]non-4-yne (BCN) derivatives. In particular, they showed a remarkably higher reaction rate toward a bis-cyclooctyne derivative (bis-BCN) compared with its monomeric counterpart (mono-BCN). Live-cell imaging and (photo)cytotoxicity studies revealed higher photocytotoxicity in bis-BCN-pretreated cells, which is ascribed to the enhanced singlet oxygen (1O2) photosensitization resulting from the elimination of the nitrone-associated quenching pathway. Importantly, the cross-linking properties and enhanced reactivity of the complexes make them highly promising candidates for the development of hydrogels and stapled/cyclized peptides, offering intriguing photophysical, photochemical, and biological properties. Notably, a nanosized hydrogel (2-gel) demonstrated potential as a drug delivery system, while a stapled peptide (2-bis-pDIKK) exhibited p53-Mdm2 inhibitory activity related to apoptosis and a cyclized peptide (2-bis-RGD) showed cancer selectivity.

Structure-Activity Relationship of Benzophenazine Derivatives for Homogeneous and Heterogenized Photooxygenation Catalysis.

Singlet oxygen is a powerful oxidant used in various applications, such as organic synthesis, medicine, and environmental remediation. Organic and inorganic photosensitizers are commonly used to generate this reactive species through energy transfer with the triplet ground state of oxygen. We describe here a series of novel benzophenazine derivatives as a promising class of photosensitizers for singlet oxygen photosensitization. In this study, we investigated the structure-activity relationship of these benzophenazine derivatives. Akin to a molecular compass, the southern fragment was first functionalized with either aromatic tertiary amines, alkyl tertiary amines, aromatic sulfur groups, alkyl sulfur groups, or cyclic ethers. Enhanced photophysical properties (in terms of triplet excited-state lifetime, absorption wavelength, triplet state energy, and O2 quenching capabilities) were obtained with cyclic ether and sulfur groups. Conversely, the presence of an amine moiety was detrimental to the photocatalysts. The western and northern fragments were also investigated and slightly undesirable to negligible changes in photophysical properties were observed. The most promising candidate was then immobilized on silica nanoparticles and its photoactivity was evaluated in the citronellol photooxidation reaction. A high NMR yield of 97 % in desired product was obtained, with only a slight decrease over several recycling runs (85 % in the fourth run). These results provide insights into the design of efficient photosensitizers for singlet oxygen generation and the development of heterogeneous systems.

Best Practices to Directly Assess Heterogeneous Singlet Oxygen Photosensitization by Phosphorescence

AbstractLiterature proves that the direct detection of 1O2(1Δg) at the solid gas interface is systematically performed from its phosphorescence using high intensity excitation sources (i.e., lasers), which lead to quasi‐ubiquitous chemical problems, such as sensitizer degradation, and photophysical counter‐active issues such as ultrafast exciton migration, singlet‐singlet and triplet‐triplet annihilation, and thermally activated delayed fluorescence mediated by 1O2(1Δg). To avoid these inconveniences, low excitation intensity is required but leads to serious analytical challenges. The best practices to reliably detect 1O2(1Δg) phosphorescence at various interfaces using a standard excitation source and near‐IR detector. The two main practices consist in a gas purging test for reliable identification of 1O2(1Δg), and in a particularly fine optimization of the angle made by excitation beam versus substrate plane. These practices are applied to porphyrin sensitizers H2TPP and ZnTPP, either neat or physiosorbed on glass, quartz, paper and hospital bandages, graphene oxide (GO), and embedded inside electrospun polystyrene fibers and spin coated poly(methyl methacrylate) films. Porphyrin‐based metal‐organic framework PCN‐224, freshly activated, is also examined.

First-principles design of heavy-atom-free singlet oxygen photosensitizers for photodynamic therapy.

In photodynamic therapy (PDT) treatment, heavy-atom-free photosensitizers (PSs) are a great source of singlet oxygen photosensitizer. Reactive oxygen species (ROS) are produced by an energy transfer from the lowest energy triplet excited state to the molecular oxygen of cancer cells. To clarify the photophysical characteristics in the excited states of a few experimentally identified thionated (>C=S) molecules and their oxygenated congeners (>C=O), a quantum chemical study is conducted. This study illustrates the properties of the excited states in oxygen congeners that render them unsuitable for PDT treatment. Concurrently, a hierarchy is presented based on the utility of the lowest-energy triplet excitons of thionated compounds. Their non-radiative decay rates are calculated for reverse-ISC and inter-system crossover (ISC) processes. In addition, the vibronic importance of C=O and C=S bonds is clarified by the computation of the Huang-Rhys factor, effective vibrational mode, and reorganization energy inside the Marcus-Levich-Jörtner system. ROS generation in thionated PSs exceeds their oxygen congeners as kf ≪ kISC, where radiative decay rate is designated as kf. As a result, the current work offers a calculated strategy for analyzing the effectiveness of thionated photosensitizers in PDT.

О возможности использования иттербиевого комплекса 2,4-ди (α-метоксиэтил)дейтеропорфирина IX для тераностики новообразований поверхностной локализации

The dynamics of the photosensitized singlet oxygen formation for the ytterbium 2,4-di(α-methoxyethyl)deuteroporphyrin IX complex (Yb-DMDP IX) and for its metal-free form under laser excitation on a highly sensitive laser fluorimeter was studied. It has been shown that the quantum yield of singlet oxygen generation for Yb-DMDP IX (11%) is significantly lower than in the case of DMDP IX itself (40%), which experimentally confirms the low phototoxicity of the Yb complex. However, the established 11% quantum yield of 1O2 indicates the possible presence of DMDP IX in the main substance of Yb-DMDP IX, leading to residual phototoxicity. Using high-performance liquid chromatography, the quantitative ratios of the Yb-complex and its metal-free form (10%) were established. Thus, the presented Yb-complex can also be used for cancer theranostics, since after carrying out IR luminescence diagnostics (in the 900–1100 nm spectral range), it is also possible to subsequently carry out the PDT procedure in the absorption band of the porphyrin complex metal-free form at the 630 nm wavelength. The Yb-DMDP IX effectiveness for the PDT procedure can be significantly increased by treating this compound with ascorbic acid after the IR luminescence diagnostics procedure.

Modulation of the Excited States of Ruthenium(II)-perylene Dyad to Access Near-IR Luminescence, Long-Lived Perylene Triplet State and Singlet Oxygen Photosensitization.

Herein, we present a novel ruthenium(II)-perylene dyad (RuPDI-Py) that combines the photophysical properties of pyrrolidine-substituted perylene diimide (PDI-Py) and the ruthenium(II) polypyridine complex [Ru(phen)3]2+. A comprehensive study of excited-state dynamics was carried out using time-resolved and steady-state methods in a dimethyl sulfoxide solution. The RuPDI-Py dyad demonstrated excitation wavelength-dependent photophysical behavior. Upon photoexcitation above 600 nm, the dyad exclusively exhibits the near-infrared (NIR) fluorescence of the 1PDI-Py state at 785 nm (τfl = 1.50 ns). In contrast, upon photoexcitation between 350 and 450 nm, the dyad also exhibits a photoinduced electron transfer from the {[Ru(phen)3]2+} moiety to PDI-Py, generating the charge-separated intermediate state {Ru(III)-(PDI-Py)•-} (4 μs). This state subsequently decays to the long-lived triplet excited state 3PDI-Py (36 μs), which is able to sensitize singlet oxygen (1O2). Overall, tuning 1O2 photoactivation or NIR fluorescence makes RuPDI-Py a promising candidate for using absorbed light energy to perform the desired functions in theranostic applications.

Outcomes of folic acid esterification upon the properties of hydrophilic phenothiazinium dyes: New photosensitizers for antimicrobial photodynamic therapy

The utilization of three methylene blue analogues containing hydroxyl functionalized auxochrome units (MBA) and their corresponding novel folic acid esters (FAE) as singlet-oxygen photosensitizers for antimicrobial photodynamic therapy (aPDT) was investigated. A new environmentally friendly ultrasoundassisted procedure for the synthesis of MBA and an optimized protocol for folic acid esterification are reported. Binding of folic acid to MBA did not alter the optical absorption/emission properties of the dyes, the folates exhibiting higher or at least equal fluorescence quantum yields when compared to those of the parent dyes. The photodynamic effect of MBA and FAE was evaluated based on their singlet oxygen generation capacity. The 1O2 quantum yields, determined by the indirect detection technique using 1,3-diphenylisobenzofuran (DPBF) as a sensor, appeared to be ∼ 50 % for MBA and decreased to ∼ 20 % in the case of FAE. The antimicrobial efficacy of the new FAE on four bacterial strains (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Deinococcus radiodurans) showed remarkable results especially when combined with photodynamic therapy.

Singlet Oxygen Detection by Chemiluminescence Probes in Living Cells.

Singlet oxygen is a reactive oxygen species that causes oxidative damage to plant cells, but intriguingly it can also act as a signalling molecule to reprogram gene expression required to induce plant physiological/cellular responses. Singlet oxygen photosensitization in plants mainly occurs in chloroplasts after the molecular collision of ground-state molecular oxygen with triplet-excited-state chlorophyll. Singlet oxygen direct detection through phosphorescence emission in chloroplasts is a herculean task due to its extremely low luminescence quantum yield. Because of this, indirect alternative methods have been developed for its detection in biological systems, for example, by measuring the changes in the EPR signal or fluorescence intensity of singlet oxygen reaction-based probes. The singlet oxygen chemiluminescence (SOCL) is a chemiluminescence probe with high sensitivity and selectivity towards singlet oxygen and promising use to detect it in living cells without the inconvenience of low stability of the EPR signal of spin probes in the presence of redox compounds, spurious light scattering coming from the light source required for the excitation of fluorescence probes or the light emission of endogenous fluorescent molecules like chlorophyll in chloroplasts. The protocol presented in this chapter describes the first steps to characterizing singlet oxygen production within the biological system under study; this is accomplished through monitoring molecular oxygen consumption by SOCL using a Clark-type oxygen electrode and measuring the chemiluminescence generated by SOCL 1,2-dioxetane using a spectrofluorometer. For singlet oxygen detection within living cells, a version of SOCL with increased membrane permeability (SOCL-CPP) is described.

More is different: progressive β-thiolation induced-porphyrin aggregation switches singlet oxygen photosensitization.

Incorporating sulfur atoms into photosensitizers (PSs) has been well-established to populate triplet states and increase singlet oxygen (1O2) production when exposed to light. In this work, we found that progressive thiolation of porphyrin β-periphery does promote intersystem crossing (ISC) between triplets and singlets, as seen in the excited state dynamics in dichloromethane or PS nanoparticles in water. However, in the latter case, more sulfur substitution deactivates 1O2 photosensitization, in contrast to the expected trend observed in dichloromethane. This observation was further supported by photocytotoxicity studies, where 1O2 photosensitization was switched off in living cells and multicellular spheroids despite being switched on in in vivo mice models. To understand the inconsistency, we performed molecular dynamics simulation and time-dependent density functional theory calculations to investigate possible aggregation and related excited states. We found that the extent of thiolation could regulate molecular packing inside nanoparticles, which gradually lowers the energy levels of triplet states even lower than that of 1O2 and, in turn, alters their energy dissipation pathways. Therefore, this study provides new insights into the design of metal-free PSs and sheds light on the excited state dynamics in aqueous media beyond the molecular level.

BASHY Dyes Are Highly Efficient Lipid Droplet-Targeting Photosensitizers that Induce Ferroptosis through Lipid Peroxidation.

Ferroptosis is an iron-dependent lipid-peroxidation-driven mechanism of cell death and a promising therapeutic target to eradicate cancer cells. In this study, we discovered that boronic acid-derived salicylidenehydrazone (BASHY) dyes are highly efficient singlet-oxygen photosensitizers (PSs; ΦΔ up to 0.8) that induce ferroptosis triggered by photodynamic therapy. The best-performing BASHY dye displayed a high phototoxicity against the human glioblastoma multiform U87 cell line, with an IC50 value in the low nanomolar range (4.40 nM) and a remarkable phototoxicity index (PI > 22,700). Importantly, BASHY dyes were shown to accumulate in lipid droplets (LDs) and this intracellular partition was found to be essential for the enhanced phototoxicity and the induction of ferroptosis through lipid peroxidation. The safety and phototoxicity of this platform were validated using an in vivo zebrafish model (Danio rerio).

Photoexcited triplet state and singlet oxygen generation of quinine, an antimalarial drug.

Energy transfer from the lowest excited triplet (T1) state of quinine (QN) to ground-state molecular oxygen produces singlet oxygen. In aqueous solutions, a neutral form QN, a singly protonated cation QNH+ and doubly protonated cation QNH22+ are present according to their pKa values. To the best of our knowledge, the pH dependence of QN-photosensitized singlet oxygen generation has not been reported. In the present study, the quantum yields of photosensitized singlet oxygen generation (ΦΔ) by QN, QNH+ and QNH22+ have been determined through the measurements of time-resolved near-IR phosphorescence. ΦΔ decreases in the following order: ΦΔ (QNH+) > ΦΔ (QNH22+) > ΦΔ (QN). The nature of the T1 states of QN, QNH+ and QNH22+ has been studied through the measurements of transient absorption, phosphorescence and EPR by changing the pH of the medium. This is the first report of EPR for the T1 state of QN. The photoexcited T1 state of 6-methoxyquinoline (6-MeOQL), a closely related component, has been studied for comparison. The observed zero-field splitting parameters, phosphorescence spectra and triplet lifetimes suggest that the nature of the T1 state of QN can be regarded as a locally excited 3ππ*state within 6-MeOQL. The two unpaired electrons localize mainly on 6-MeOQL. The nature of the T1 state of QN scarcely changes when the quinuclidine nitrogen site is protonated. Applying the Förster cycle to the T1 states of QN and its protonated cations, it was found that QNH+ becomes more basic when excited to its T1 state.

Singlet oxygen generation under optical excitation of polytetrafluoroethylene

Singlet oxygen together with radical reactions plays an important role in biochemistry of living organisms, and is one of the main active substances in photodynamic treatment of organs and body fluids. Along with traditional singlet oxygen photosensitizers based on biocompatible dyes, the singlet oxygen photogeneration ability of matrix materials such as organic solvents and metal oxide surfaces has recently been investigated. Despite a good compatibility with bio substances, polytetrafluoroethylene (also known under the trademark as Teflon®) remains unaddressed in these studies. Here we present our photoluminescence studies of singlet oxygen generation in polytetrafluoroethylene samples under ultraviolet and visible irradiation. We found a good singlet oxygen photogeneration with an efficiency no less and possibly exceeding it in carbon tetrachloride, a known singlet‑oxygen-retentive medium. Based on the results obtained, it is assumed that the phosphorescence of singlet oxygen is observed from the volume of polytetrafluoroethylene with direct optical excitation of oxygen adsorbed or dissolved in the structure of polytetrafluoroethylene by analogy with direct optical excitation of oxygen in the volume of various solvents. Cooling a PTFE sample down to −20 °C allows to enhance the singlet oxygen concentration in the polymer indicating the enthalpy of oxygen sorption of ΔHsorp = −1.51 kcal/mol. Our results can heighten medical interest to fluoropolymers and, in particular, to polytetrafluoroethylene making it a promising singlet oxygen generator for photodynamic uses.

Exploring Thioxanthone Derivatives as Singlet Oxygen Photosensitizers for Photodynamic Therapy at the Near-IR Region.

In the lowest excited triplet state, the excited photosensitizer reacts with tissue oxygen and forms reactive oxygen species (ROS), which kills tissue cells in photodynamic therapy (PDT). Metal-free thio-based pure organic molecules and analogous nucleobases can be used as photosensitizers for PDT applications. Using quantum chemical methods, we studied one- and two-photon optical absorptions, fluorescence, and other excited-state properties of substituted thioxanthone derivatives for their potential as photosensitizers for PDT. Our calculated values were compared with the available experimental data. The calculation of the intersystem crossing rate constant for these photosensitizers explains the high quantum yield of the formation of ROS, as reported experimentally. The excited triplet-state population of the photosensitizer occurs through the 1π-π* → 3n-π* channel of intersystem crossing and increases in the presence of halogen substitution.

A Novel Characteristic of a Water-soluble UV-B Absorber, 2-Phenylbenzimidazole-5-sulfonic Acid: Suppression of Riboflavin-sensitized Singlet Oxygen Generation

Abstract 2-Phenylbenzimidazole-5-sulfonic acid (PBSA) is a water-soluble UV-B absorber used in cosmetic sunscreens. Riboflavin (RF) is a water-soluble vitamin B2. RF is an efficient singlet oxygen photosensitizer. The effects of PBSA on RF-photosensitized singlet oxygen generation have been studied through measurements of transient absorption and time-resolved near-IR phosphorescence in phosphate buffer (pH 7.4). PBSA suppresses the RF-photosensitized singlet oxygen generation. The observed suppression can be ascribed to the quenching of the lowest excited triplet state of RF by PBSA.

Mixed β-γ-Cyclodextrin Branched Polymer with Multiple Photo-Chemotherapeutic Cargos.

The achievement of biocompatible platforms for multimodal therapies is one of the major challenges in the burgeoning field of nanomedicine. Here, we report on a mixed β- and γ-cyclodextrin-based branched polymeric material (βγCD-NOPD) covalently integrating a nitric oxide (NO) photodonor (NOPD) within its macromolecular scaffold, and its supramolecular ensemble with a singlet oxygen (1O2) photosensitizer (PS) Zn(II) phthalocyanine (ZnPc) and the chemodrug Lenvatinib (LVB). This polymer is highly water-soluble and generates NO under visible blue light stimuli with an efficiency of more than 1 order of magnitude higher than that of the single NOPD. The PS, which in an aqueous solution is aggregated and non-photoresponsive, can be entangled in the polymeric network as a photoresponsive monomeric species. In addition, the poorly water-soluble LVB can be co-encapsulated within the polymeric host, which increases the drug solubility by more than 30-fold compared to the free drug and more than 2-fold compared with a similar branched polymer containing only βCD units. The supramolecular nanoensemble, ca. 15 nm in diameter, retains well the photochemical properties of both the NOPD and PS, which can operate in parallel under light stimuli of different energies. Irradiation with blue and red light results in the photogeneration of NO and 1O2 associated with red fluorescence emission, without inducing any photodegradation of LVB. This result is not trivial and is due to the absence of significant, mutual interactions between the NOPD, the PS and LVB both in the ground and excited states, despite these components are confined in the same host. The proposed polymeric nanoplatform may represent a potential trimodal nanomedicine for biomedical research studies, since it combines the double photodynamic action of NO and 1O2, two species that do not suffer multidrug resistance, with the therapeutic activity of a conventional chemodrug.

Modern Applications of Porphyrin-Based MOFs in Agriculture

Nanosized metal-porphyrinic frameworks are an interesting class of porous electro- and photoactive materials finding applications in medicine (photodymanic therapy, photothermal therapy, drug delivery and chemotherapy, immunotherapy), [1], sanitary and antimicrobial devices [2], waste water purification [3], photocatalytic organic transformations [4], production of solar fuels [5], and more recently, in agriculture [6]. The fact that porphyrin derivatives are colored, they are prone for the photosensitization of singlet oxygen (1O2(g); a reactive oxygen species of type II) either at the solid state/air interfaces or in solution leading to applications listed above using visible light. In fact, they even do this efficiently. Reactive oxygen species of type I (for examples, H-O radical, HO-OH, superoxide radical, perhydroxyl radical, etc) are also photo-produced when given metals inside the porphyrins and metallic nodes in the frameworks are used, or when the metal-porphyrinic frameworks form a composite with another semiconductor. Moreover, the size of the nanoparticles can be tailored. All of these properties are cleverly exploited in the field of agriculture and include the following applications: controlled delivery of pesticides and agro-chemicals, detection of pesticides and pathogenic metals, elimination of pesticides and toxic metals, and photodynamic antimicrobial activity, and the nanosized metal-porphyrinic frameworks also have an important implication in food safety. This presentation will describe these features along with new experimental results.

Tetramethylalloxazines as efficient singlet oxygen photosensitizers and potential redox-sensitive agents

Tetramethylalloxazines (TMeAll) have been found to have a high quantum yield of singlet oxygen generation when used as photosensitizers. Their electronic structure and transition energies (S0 → Si, S0 → Ti, T1 → Ti) were calculated using DFT and TD-DFT methods and compared to experimental absorption spectra. Generally, TMeAll display an energy diagram similar to other derivatives belonging to the alloxazine class of compounds, namely π,π* transitions are accompanied by closely located n,π* transitions. Photophysical data such as quantum yields of fluorescence, fluorescence lifetimes, and nonradiative rate constants were also studied in methanol (MeOH), acetonitrile (ACN), and 1,2-dichloroethane (DCE). The transient absorption spectra were also analyzed. To assess cytotoxicity of new compounds, a hemolytic assay was performed using human red blood cells (RBC) in vitro. Subsequently, fluorescence lifetime imaging experiments (FLIM) were performed on RBC under physiological and oxidative stress conditions alone or in the presence of TMeAll allowing for pinpointing changes caused by those compounds on the intracellular environment of these cells.

Periodate-Mediated Aerobic Oxidation of Sulfides over a Bifunctional Porphyrin-polyoxometalate Catalyst: Photosensitized Singlet Oxygen Oxidation of Iodate to Periodate.

Regeneration of terminal oxidants by molecular oxygen in metal-catalyzed oxidations of organic substrates has the advantage of avoiding the use of stoichiometric amounts of hazardous and/or expensive reagents to meet (some of) the green chemistry requirements. In the present study, photosensitized singlet oxygen oxidation of iodate to periodate has been used to regenerate the oxidant in polyoxometalate (POM)-catalyzed oxidation of sulfides to sulfoxides with periodate in water. To the best of our knowledge, it is the first report on singlet oxygen oxidation of iodate to periodate. In order to determine the contribution of photooxidation and oxidation pathways in the formation of sulfoxide, the oxidation of diphenyl sulfide with a very low reactivity toward aerobic photooxidation was studied; a sevenfold increase in the conversion of the sulfide to the diphenyl sulfoxide was observed for the reaction conducted in the presence of H2TMPyP-PW12O40/IO3-/O2/hν compared to that in the presence of H2TMPyP-PW12O40/O2/hν. Also, under the same conditions, a ca. 1.5-fold increase was observed in the case of methyl phenyl sulfide, which shows high reactivity toward both the oxidation and photooxidation reactions. A porphyrin-POM nanocomposite formed by the electrostatic immobilization of meso-tetra(N-methylpyridinium-4-yl)porphyrin (H2TMPyP) on PW12O40 was employed for the one-pot oxidation and photooxidation reactions. Field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), diffuse-reflectance UV-vis spectroscopy, thermal gravimetric analysis, and Fourier transform infrared were used to characterize the formation of the hybrid compound. An average particle size of 42 nm was estimated for H2TMPyP-PW12O40 from XRD peak broadening using the Scherrer equation. Also, FESEM images showed the formation of nearly spherical nanoparticles with a size of ca. 200 nm. The redshift of the Soret band of H2TMPyP upon immobilization on POM was attributed to strong N-H···O hydrogen-bond interactions between POM and porphyrin.

Bis[1]benzothieno[1,4]thiaborins as a Platform for BODIPY Singlet Oxygen Photosensitizers.

Invited for the cover of this issue are Krzysztof Durka and co-workers at Warsaw University of Technology, University of Warsaw, Silesian University of Technology and Heinrich-Heine-Universität. The image depicts the generation of singlet oxygen by the BODIPY photosensitizer. Read the full text of the article at 10.1002/chem.202300680.