Luminescent Hydrogel Particles Prepared by Self-Assembly of β‑Cyclodextrin Polymer and Octahedral Molybdenum Cluster Complexes

A series of luminescent octahedral molybdenum cluster complexes were obtained by treating Na₂[Mo₆I₈(OMe)₆] with icosahedral <i>closo</i>-dicarbaborane C-carboxylic acids in refluxing tetrahydrofuran. The study of the photophysical properties of Na₂[Mo₆I₈(1-OOC-1,2-<i>closo</i>-C₂B₁₀H₁₁)₆] (<b>1</b>), Na₂[Mo₆I₈(1-OOC-1,7-<i>closo</i>-C₂B₁₀H₁₁)₆] (<b>2</b>), and Na₂[Mo₆I₈(1-OOC-1,12-<i>closo</i>-C₂B₁₀H₁₁)₆] (<b>3</b>) in acetonitrile revealed a red luminescence with high quantum yields up to 0.93 for <b>2</b>, an efficient quenching of the luminescence by oxygen, and high quantum yields of singlet oxygen formation of approximately 0.7. Self-assembly between compound <b>2</b> and β-cyclodextrin polymer led to monodisperse hydrogel particles with a diameter of approximately 200 nm and unchanged luminescence spectra and kinetics features over 14 days. In contrast, bare cluster complex <b>2</b> in water formed aggregates and hydrolyzed over the time as indicated by a progressive red shift of the luminescence maxima. The invariance of key photophysical parameters of the hydrogel particles coupled with a high oxygen sensitivity of the luminescence are attractive features for long-term biological experiments involving optical oxygen probing. In addition, this hydrogel is a singlet oxygen sensitizer in water with promising properties for photodynamic therapy

Effect of Temperature on Photophysical Properties of Polymeric Nanofiber Materials with Porphyrin Photosensitizers

Electrospun nanofibers possess large surface to volume ratios, high porosity, and good mechanical properties that are necessary for biological applications. We prepared different types of photoactive polymeric nanofiber materials with encapsulated or externally bound porphyrin photosensitizers. The kinetics of formation and the decay of both singlet oxygen O₂(¹Δ_g) and porphyrin triplet states that are generated by irradiation of nanofiber materials in an air atmosphere or in an air-saturated aqueous solution were measured and evaluated by luminescence and transient absorption spectroscopy in the temperature range between 5 and 60 °C. We found shortening of the O₂(¹Δ_g) lifetime and a significant increase in singlet oxygen-sensitized delayed fluorescence at higher temperatures. These photophysical data show an increase in the diffusion coefficient for O₂(¹Δ_g) with temperature, and they are consistent with a stronger antibacterial effect of the nanofiber material on Escherichia coli at higher temperature

Antibacterial, Antiviral, and Oxygen-Sensing Nanoparticles Prepared from Electrospun Materials

A simple nanoprecipitation method was used for preparation of stable photoactive polystyrene nanoparticles (NPs, diameter 30 ± 10 nm) from sulfonated electrospun polystyrene nanofiber membranes with encapsulated 5,10,15,20-tetraphenylporphyrin (TPP) or platinum octaethylporphyrin (Pt-OEP). The NPs prepared with TPP have strong antibacterial and antiviral properties and can be applied to the photooxidation of external substrates based on photogenerated singlet oxygen. In contrast to nanofiber membranes, which have limited photooxidation ability near the surface, NPs are able to travel toward target species/structures. NPs with Pt-OEP were used for oxygen sensing in aqueous media, and they presented strong linear responses to a broad range of oxygen concentrations. The nanofiber membranes can be applied not only as a source of NPs but also as an effective filter for their removal from solution

Polystyrene Nanofiber Materials for Visible-Light-Driven Dual Antibacterial Action via Simultaneous Photogeneration of NO and O₂(¹Δ_g)

This contribution reports on the preparation, characterization, and biological evaluation of electrospun polystyrene nanofiber materials engineered with a covalently grafted NO photodonor and ionically entangled tetracationic porphyrin and phthalocyanine photosensitizers. These photofunctional materials exhibit an effective and simultaneous photogeneration of two antibacterial species such as nitric oxide (NO) and singlet oxygen, O₂(¹Δ_g) under illumination with visible light, as demonstrated by their direct detection using amperometric and time-resolved spectroscopic techniques. Dual-mode photoantibacterial action is demonstrated by antibacterial tests carried out on Escherichia coli

Lanthanide-Porphyrin Hybrids: from Layered Structures to Metal–Organic Frameworks with Photophysical Properties

Rare-earth layered hydroxides with intercalated tetrasulfonated porphyrins and corresponding to the chemical formula Ln₂(OH)_4.7(Por)_0.33·2H₂O (Ln = Eu³⁺, Tb³⁺; Por = 5,10,15,20-tetrakis­(4-sulfonatophenyl)­porphyrin (TPPS) and PdTPPS) have been prepared to investigate their photophysical properties. A slight variation of the synthetic procedure led to the metal–organic framework (MOF) assembled from a distorted octahedral oxometalate clusters [Eu₆(μ₆-O)­(μ₃-OH)₈(H₂O)₁₄]⁸⁺. These secondary building units (SBUs) are linked together by six distorted porphyrin units. During activation, the original SBU loses not only water molecules from the coordination sphere but also the central μ₆-O atom. The loss of the central atom results in the distortion of the octahedral [Eu₆(μ₆-O)­(μ₃-OH)₈(H₂O)₁₄]⁸⁺ SBU into a trigonal antiprismatic [Eu₆(μ₃-OH)₈(H₂O)₂]¹⁰⁺ SBU with two μ₃-OH groups nearly in plane with the europium atoms and the reduction of pores to approximately 2 × 3 Å. As a result, the MOF has no accessible porosity. This transformation was thoroughly characterized by means of single-crystal X-ray crystallographic analysis of both phases. Solid-state photophysical investigations suggest that the MOF material is fluorescent; however, in contrast to the prepared layered hydroxides, the as-prepared MOF is an effective sensitizer of singlet oxygen, O₂(¹Δ_g), with a relatively long lifetime of 23 ± 1 μs. The transition is also accompanied by variation in photophysical properties of the coordinated TPPS. The alteration of the fluorescence properties and of the O₂(¹Δ_g) lifetime presents an opportunity for preparation of MOFs with oxygen-sensing ability or with oxidation potential toward organic molecules by O₂(¹Δ_g)

X‑ray Inducible Luminescence and Singlet Oxygen Sensitization by an Octahedral Molybdenum Cluster Compound: A New Class of Nanoscintillators

Newly synthesized octahedral molybdenum cluster compound (<i>n</i>-Bu₄N)₂­[Mo₆I₈(OOC-1-adamantane)₆] revealed uncharted features applicable for the development of X-ray inducible luminescent materials and sensitizers of singlet oxygen, O₂(¹Δ_g). The compound exhibits a red-NIR luminescence in the solid state and in solution (e.g., quantum yield of 0.76 in tetrahydrofuran) upon excitation by UV–vis light. The luminescence originating from the excited triplet states is quenched by molecular oxygen to produce O₂(¹Δ_g) with a high quantum yield. Irradiation of the compound by X-rays generated a radioluminescence with the same emission spectrum as that obtained by UV–vis excitation. It proves the formation of the same excited triplet states regardless of the excitation source. By virtue of the described behavior, the compound is suggested as an efficient sensitizer of O₂(¹Δ_g) upon X-ray excitation. The luminescence and radioluminescence properties were maintained upon embedding the compound in polystyrene films. In addition, polystyrene induced an enhancement of the radioluminescence intensity via energy transfer from the scintillating polymeric matrix. Sulfonated polystyrene nanofibers were used for the preparation of nanoparticles which form stable dispersions in water, while keeping intact the luminescence properties of the embedded compound over a long time period. Due to their small size and high oxygen diffusivity, these nanoparticles are suitable carriers of sensitizers of O₂(¹Δ_g). The presented results define a new class of nanoscintillators with promising properties for X-ray inducible photodynamic therapy

Superhydrophilic Polystyrene Nanofiber Materials Generating O₂(¹Δ_g): Postprocessing Surface Modifications toward Efficient Antibacterial Effect

The surfaces of electrospun polystyrene (PS) nanofiber materials with encapsulated 1% w/w 5,10,15,20-tetraphenylporphyrin (TPP) photosensitizer were modified through sulfonation, radio frequency (RF) oxygen plasma treatment, and polydopamine coating. The nanofiber materials exhibited efficient photogeneration of singlet oxygen. The postprocessing modifications strongly increased the wettability of the pristine hydrophobic PS nanofibers without causing damage to the nanofibers, leakage of the photosensitizer, or any substantial change in the oxygen permeability of the inner bulk of the polymer nanofiber. The increase in the surface wettability yielded a significant increase in the photo-oxidation of external polar substrates and in the antibacterial activity of the nanofibers in aqueous surroundings. The results reveal the crucial role played by surface hydrophilicity/wettability in achieving the efficient photo-oxidation of a chemical substrate/biological target at the surface of a material generating O₂(¹Δ_g) with a short diffusion length

X‑ray Inducible Luminescence and Singlet Oxygen Sensitization by an Octahedral Molybdenum Cluster Compound: A New Class of Nanoscintillators

Newly synthesized octahedral molybdenum cluster compound (<i>n</i>-Bu₄N)₂­[Mo₆I₈(OOC-1-adamantane)₆] revealed uncharted features applicable for the development of X-ray inducible luminescent materials and sensitizers of singlet oxygen, O₂(¹Δ_g). The compound exhibits a red-NIR luminescence in the solid state and in solution (e.g., quantum yield of 0.76 in tetrahydrofuran) upon excitation by UV–vis light. The luminescence originating from the excited triplet states is quenched by molecular oxygen to produce O₂(¹Δ_g) with a high quantum yield. Irradiation of the compound by X-rays generated a radioluminescence with the same emission spectrum as that obtained by UV–vis excitation. It proves the formation of the same excited triplet states regardless of the excitation source. By virtue of the described behavior, the compound is suggested as an efficient sensitizer of O₂(¹Δ_g) upon X-ray excitation. The luminescence and radioluminescence properties were maintained upon embedding the compound in polystyrene films. In addition, polystyrene induced an enhancement of the radioluminescence intensity via energy transfer from the scintillating polymeric matrix. Sulfonated polystyrene nanofibers were used for the preparation of nanoparticles which form stable dispersions in water, while keeping intact the luminescence properties of the embedded compound over a long time period. Due to their small size and high oxygen diffusivity, these nanoparticles are suitable carriers of sensitizers of O₂(¹Δ_g). The presented results define a new class of nanoscintillators with promising properties for X-ray inducible photodynamic therapy

Nanoparticles with Embedded Porphyrin Photosensitizers for Photooxidation Reactions and Continuous Oxygen Sensing

We report the synthesis and characterization of sulfonated polystyrene nanoparticles (average diameter 30 ± 14 nm) with encapsulated 5,10,15,20-tetraphenylporphyrin or ionically entangled tetracationic 5,10,15,20-tetrakis­(<i>N</i>-methylpyridinium-4-yl)­porphyrin, their photooxidation properties, and the application of singlet oxygen-sensitized delayed fluorescence (SODF) in oxygen sensing. Both types of nanoparticles effectively photogenerated singlet oxygen, O₂(¹Δ_g). The O₂(¹Δ_g) phosphorescence, transient absorption of the porphyrin triplet states, and SODF signals were monitored using time-resolved spectroscopic techniques. The SODF intensity depended on the concentration of the porphyrin photosensitizer and dissolved oxygen and on the temperature. After an initial period (a few microseconds), the kinetics of the SODF process can be approximated as a monoexponential function, and the apparent SODF lifetimes can be correlated with the oxygen concentration. The oxygen sensing based on SODF allowed measurement of the dissolved oxygen in aqueous media in the broad range of oxygen concentrations (0.2–38 mg L^–1). The ability of both types of nanoparticles to photooxidize external substrates was predicted by the SODF measurements and proven by chemical tests. The relative photooxidation efficacy was highest at a low porphyrin concentration, as indicated by the highest fluorescence quantum yield (Φ_F), and it corresponds with negligible inner filter and self-quenching effects. The photooxidation abilities were sensitive to the influence of temperature on the diffusion and solubility of oxygen in both polystyrene and water media and to the rate constant of the O₂(¹Δ_g) reaction with a substrate. Due to their efficient photogeneration of cytotoxic O₂(¹Δ_g) at physiological temperatures and their oxygen sensing via SODF, both types of nanoparticles are promising candidates for biomedical applications

Designing Porphyrinic Covalent Organic Frameworks for the Photodynamic Inactivation of Bacteria

Microbial colonization of biomedical devices is a recognized complication contributing to healthcare-associated infections. One of the possible approaches to prevent surfaces from the biofilm formation is antimicrobial photodynamic inactivation based on the cytotoxic effect of singlet oxygen, O₂(¹Δ_g), a short-lived, highly oxidative species, produced by energy transfer between excited photosensitizers and molecular oxygen. We synthesized porphyrin-based covalent organic frameworks (COFs) by Schiff-base chemistry. These novel COFs have a three-dimensional, diamond-like structure. The detailed analysis of their photophysical and photochemical properties shows that the COFs effectively produce O₂(¹Δ_g) under visible light irradiation, and especially three-dimensional structures have strong antibacterial effects toward Pseudomonas aeruginosa and Enterococcus faecalis biofilms. The COFs exhibit high photostability and broad spectral efficiency. Hence, the porphyrinic COFs are suitable candidates for the design of antibacterial coating for indoor applications