Time-resolved Phosphorescence Research Articles

Integrating Full-Color 2D Optical Waveguide and Heterojunction Engineering in Halide Microsheets for Multichannel Photonic Logical Gates.

Ensuring information security has emerged as a paramount concern in contemporary human society. Substantial advancements in this regard can be achieved by leveraging photonic signals as the primary information carriers, utilizing photonic logical gates capable of wavelength tunability across various time and spatial domains. However, the challenge remains in the rational design of materials possessing space-time-color multiple-resolution capabilities. In this work, a facile approach is proposed for crafting metal-organic halides (MOHs) that offer space-time-color resolution. These MOHs integrate time-resolved room temperature phosphorescence and color-resolved excitation wavelength dependencies with both space-resolved ex situ optical waveguides and in situ heterojunctions. Capitalizing on these multifaceted properties, MOHs-based two-dimensional (2D) optical waveguides and heterojunctions exhibit the ability to tune full-color emissions across the spectra from blue to red, operating within different spatial and temporal scales. Therefore, this work introduces an effective methodology for engineering space-time-color resolved MOH microstructures, holding significant promise for the development of high-density photonic logical devices.

Singlet Oxygen Quantum Yields of Pyrogenic Dissolved Organic Matter from Lab-Prepared and Wildfire Chars.

Wildfires or prescribed fires release pyrogenic dissolved organic matter (pyDOM) into the environment, which can photochemically produce singlet oxygen (1O2) in sun-lit surface waters. 1O2 quantum yields (ΦΔ) are well-studied for non-pyrogenic DOM, but little is understood about the 1O2 generation from pyDOM, especially the ΦΔ values from real wildfire samples and their wavelength dependence. In this study, time-resolved 1O2 phosphorescence was used to determine the wavelength-dependent ΦΔ values for pyDOM generated from wildfire char and a series of lab-prepared chars produced by combusting oak and pine wood. Wildfire and most lab-prepared pyDOM generally had similar ΦΔ values (2.1-2.7%) at 365 nm compared to the reference Suwannee River Natural Organic Matter (SRNOM) isolate (2.4%). Interestingly, pyDOM from the highest combustion temperature char was found to possess extremely low ΦΔ values compared to SRNOM and other pyDOM at all excitation wavelengths. In addition, it was revealed that the predicted steady-state concentration of 1O2 from pyDOM was similar to that from SRNOM, indicating that the addition of pyDOM from wood chars may not strongly impact surface water photochemistry.

Vacuum Packaging Sensor Based on Time-Resolved Phosphorescence Spectroscopy

Intelligent food packaging with the multisensory analysis is promising as the next generation technology of food packaging. The oxygen content in food packaging is one of the crucial parameters affecting the food quality and shelf life. Caviar is among the most nutritious and costly food sources. Here, a photonic oxygen-sensing system, based on the time-resolved phosphorescence spectroscopy of a platinum complex, is developed for non-contact, non-intrusive, and real-time vacuum packaging quality control, and implemented for caviar packaging. The sensor is embedded in protective polyethylene layers and excited with a short-pulsed light emitting diode (LED) source. Integration of a blue pulsed light source, a fast and amplified silicon photodiode controlled by the Spartan-6 field programmable gate array (FPGA), and a long lifetime platinum complex results in a photonics-based oxygen sensor with a fast response and high sensitivity to the vacuum packaging damage, which is suitable for caviar. It is revealed that applying the polyethylene layers protects the caviar from the platinum complex, leaching while not interfering with the sensor functionality. Characterizing the photonic system based on its sensitivity, repeatability, stability, and long-term operation demonstrates its capability for this application.

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.

Excited-State Charge Transfer in Push-Pull Platinum(II) π-Extended Porphyrins Fused with Pentacenequinone.

Platinum(II) π-extended porphyrins fused with pentacenequinone and dihydropentacene have been successfully synthesized. These porphyrins were investigated using various techniques including absorption, steady-state, and time-resolved phosphorescence spectroscopy and differential pulse voltammetry. UV-vis absorption spectra of pentacenequinone-fused porphyrins (SW-Pt1 and SW-Pt2) showed unusually broad and nontypical absorption patterns. Phosphorescence spectra of SW-Pt1, SW-Pt2, and SW-Pt3 displayed similar emissions in the 704-706 nm region indicating electronic transitions of similar origin; however, the triplet lifetimes were found to be quenched in the case of both SW-Pt1 and SW-Pt2, suggesting the occurrence of excited-state events. Facile reductions were obtained for both the pentacene-quinone-fused monomer (SW-Pt2) and dimer (SW-Pt1) and were identified to be located at the pentacenequinone components. The observed orbital segregations for SW-Pt2 and SW-Pt1 from DFT calculations supported the possibility of charge transfer in these push-pull systems. Interestingly, the established energy level diagram revealed that the charge transfer from the triplet excited Pt porphyrin is thermodynamically an uphill process. Systematic studies involving both femtosecond and nanosecond transient absorption techniques revealed that the singlet excited Pt porphyrins undergo an intermediate charge transfer state prior to populating the triplet state, providing a plausible explanation for phosphorescence quenching. The lifetime of the intermediate charge transfer states was found to be 25.9 and 5.68 ps, respectively, for SW-Pt1 and SW-Pt2.

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.

Singlet oxygen lifetime changes in dying glioblastoma cells.

Time-resolved phosphorescence detection was employed to determine the lifetime of singlet oxygen in live cells. Using hypericin as a photosensitizer, singlet oxygen was generated in U87MG glioblastoma cells. The phosphorescence of singlet oxygen was detected in aqueous cell suspensions following pulsed laser excitation. Our goal was to eliminate or reduce the problems associated with lifetime measurements in water-based cell suspensions. The apparatus enabled simultaneous singlet oxygen phosphorescence and transient absorption measurements, reducing uncertainty in lifetime estimation. The changes in singlet oxygen lifetime were observed during early and late apoptosis induced by photodynamic action. Our findings show that the effective lifetime of singlet oxygen in the intracellular space of the studied glioblastoma cells is 0.4 μs and increases to 1.5 μs as apoptosis progresses. Another group of hypericin, presumably located in the membrane blebs and the plasma membrane of apoptotic cells, generates singlet oxygen with a lifetime of 1.9 μs.

Photoreactivity and phototoxicity of experimentally photodegraded hair melanosomes from individuals of different skin phototypes.

Even though melanin is commonly viewed as natural photoprotectant, the pigment demonstrates residual photoreactivity, which under certain conditions could contribute to UVA-dependent melanomagenesis. Skin melanin is constantly exposed to external stressors, including solar radiation, which could induce photodegradation of the pigment. Although photodegradation of melanin pigments was studied in synthetic models and RPE melanosomes, photochemical and photobiological effects of experimental photodegradation of human skin melanin of different chemical composition remain unknown. In this work, melanosomes isolated from hair of individuals of different skin phototypes (I-III, V) were exposed to high-intensity violet light and its impact on physical and chemical properties of the pigments were analyzed using electron paramagnetic resonance (EPR), spectrophotometry and dynamic light scattering (DLS). Photoreactivity of photodegraded melanins was examined by EPR oximetry, EPR spin-trapping and time-resolved singlet oxygen phosphorescence. Antioxidant potential of the pigments was measured using the EPR DPPH assay. Cellular effect of the exposure of melanosome-loaded HaCaT cells to UV-Vis light was determined by MTT assay, JC-10 assay, and iodometric assay. The data revealed that experimental photodegradation increased photoreactivity of natural melanins, while decreasing their antioxidant capacity. Photodegraded melanin was responsible for higher cell death, a decrease in mitochondrial membrane potential and elevated levels of lipid hydroperoxides.

Phosphor thermometry for surface temperature measurements of composite materials during fire test

This study presents the implementation of phosphor thermometry method to obtain pointwise surface temperature measurements of a carbon fibers reinforced polymers composite exposed to a flame. Phosphor thermometry has previously been used to measure surface temperature in relevant applications, mainly on metallic materials. In the present study, it has been applied to measure the backside temperature of a carbon fiber Poly Phenylene Sulfide (PPS) polymer composite exposed to a flame, in order to analyze the feasibility, the limits and the advantages of the method compared to infrared thermography. Mg4FGeO6:Mn4+ thermographic phosphor is coated on the back side of the composite sample and excited with a 10 Hz repetition rate Nd:YAG laser at 355 nm. The time-resolved phosphorescence signals are processed with the lifetime approach to determine the temperature. A coating of small thickness allows the surface temperature to be measured up to 400 °C, and it is shown that this coating has no effect on the heat exchange at the surface. The comparison between the phosphor thermometry results with the ones obtained with an infrared camera shows an interesting methodology to determine the infrared emissivity of the sample at high temperature.

Benzo[A]Pyrene and Benzo[E]Pyrene: Photoreactivity and Phototoxicity toward Human Keratinocytes.

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds derived mostly from the incomplete combustion of fossil fuels and biomass. Human skin can absorb PAHs and the uptake increases with their molar mass and lipophilicity. Benzopyrene is high molecular weight PAH frequently appearing in ambient pollution. It exists in two isomeric forms: benzo[a]pyrene (BaP) and benzo[e]pyrene (BeP), which exhibit different biological activity. Although certain properties of benzopyrenes suggested photoreactivity of the compounds, no direct measurements were previously conducted to characterize their photochemical activity. In this study, quantum yield and action spectra of singlet oxygen photogeneration by BaP and BeP were measured by time-resolved near-infrared phosphorescence, and the ability of both compounds to photogenerate superoxide anion was assessed by electron paramagnetic resonance (EPR) spin-trapping. The measurements revealed high efficiency of benzopyrenes to photogenerate singlet oxygen and their ability to photogenerate superoxide anion. Using HaCaT cells as single-layer skin model, we demonstrated concentration-dependent and light-dependent cytotoxicity of BaP and BeP. The compounds induced damage to the cell mitochondria and elevated the levels of intracellular reactive oxygen species.

CsCu2I3 Nanoparticles Incorporated within a Mesoporous Metal-Organic Porphyrin Framework as a Catalyst for One-Pot Click Cycloaddition and Oxidation/Knoevenagel Tandem Reaction.

Metal-organic frameworks (MOFs) and metal halide perovskites are currently under much investigation due to their unique properties and applications. Herein, an innovative strategy has been developed combining an iron-porphyrin MOF, PCN-222(Fe), and an in situ-grown CsCu2I3 nontoxic lead-free halide perovskite based on an earth-abundant metal that becomes incorporated within the MOF channels [CsCu2I3@PCN-222(Fe)]. Encapsulation was designed to decrease and control the particle size and increase the stability of CsCu2I3. The hybrid materials were characterized by various techniques including FE-SEM, elemental mapping and line scanning EDX, TEM, PXRD, UV-Vis DRS, BET surface area, XPS, and photoemission measurements. Hybrid CsCu2I3@PCN-222(Fe) materials were examined as heterogeneous multifunctional (photo)catalysts for copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) and one-pot selective photo-oxidation/Knoevenagel condensation cascade reaction. Interestingly, CsCu2I3@PCN-222(Fe) outperforms not only its individual components CsCu2I3 and PCN-222(Fe) but also other reported (photo)catalysts for these transformations. This is attributed to cooperation and synergistic effects of the PCN-222(Fe) host and CsCu2I3 nanocrystals. To understand the catalytic and photocatalytic mechanisms, control and inhibition experiments, electron paramagnetic resonance (EPR) measurements, and time-resolved phosphorescence were performed, revealing the main role of active species of Cu(I) in the click reaction and the superoxide ion (O2•-) and singlet oxygen (1O2) in the photocatalytic reaction.

Singlet oxygen generation in aerosol jet and on biological surfaces.

The paper presents steady-state and time-resolved experiments on photophysical processes associated with photodynamic inactivation of infections provided by nebulization of Radachlorin photosensitizer solution. As models of surfaces subjected to photodynamic inactivation we used glass, plant leaf, mushroom cap peel and superficial fascia of chicken and salmon skin flaps. The oxygen content in the photosensitizer solution was varied by blowing with atmospheric air and with pure oxygen. It was shown that singlet oxygen was generated efficiently in the aerosol jet and that its amount increased noticeably at higher oxygen concentrations. The kinetics of photosensitizer photobleaching on different surfaces were found to be significantly different with characteristic decay times varying from seconds for leaf and glass to minutes for fascial flaps. This observation was attributed to much faster oxygen depletion on rough crumbly surfaces of biological samples due to effective oxidation reactions occurred. The singlet oxygen generation and degradation times, and the relative quantum yield were determined on different surfaces by recording time-resolved phosphorescence at about 1270nm under normoxic and hyperoxic conditions and analyzed on the basis of the set of master equations. The results obtained provide reference marks for choosing optimal irradiation durations for photodynamic inactivation of pathogenic infectious agents (bacteria, mycobacteria, fungi, viruses) on mucous membranes, including the tracheobronchial tree.

Direct excitation of tryptophan phosphorescence. A new method for triplet states investigation

We studied room temperature phosphorescence of tryptophan (TRP) embedded in poly (vinyl alcohol) films. With UV (285 nm) excitation, the phosphorescence spectrum of tryptophan appears at about 460 nm. We also observed the TRP phosphorescence with blue light excitation at 410 nm, well outside of the S0 →S1 absorption. This excitation reaches the triplet state of tryptophan directly without the involvement of the singlet excited state. The phosphorescence lifetime of tryptophan is in the sub-millisecond range. The long-wavelength direct excitation to the triplet state results in high phosphorescence anisotropy which can be useful in macromolecule dynamics study via time-resolved phosphorescence.

Dual-mode nanophotonic upconversion oxygen sensors.

Nanophotonic biosensors capable of being excited in the NIR spectrum have applications in various sectors. Here, we develop a 980 nm-excitable nanophotonic sensor for real-time oxygen detection in both water and air by analyzing the photoluminescence lifetime and intensity using a nanocomposite of lanthanide-doped NaYF4:Yb3+,Tm3+ upconversion nanoparticles and a PtTFPP platinum porphyrin complex in a polystyrene matrix. Excellent overlap between the emission of the upconversion nanoparticles and the excitation band of the PtTFPP guarantees 68% efficient excitation of the PtTFPP molecules with a 980 nm NIR laser. For the first time, the oxygen sensitivity of the upconversion nanoparticles alone was reported, and it was demonstrated that the PL lifetime-based sensitivity slope was boosted more than 10 times by adding PtTFPP oxygen-sensitive molecules due to the energy transfer from the upconversion nano-emitters. In addition, the functionality of the upconversion-based sensor was investigated by analyzing its sensitivity, stability, reversibility, and temperature-dependent lifetime in both water and air, and its performance was compared with that of the sensor exposed to direct excitation at 410 nm. More importantly, the sensor was implanted under the skin of a chicken, and it was demonstrated that the PL intensity was amplified more than 12 times by employing the 980 nm excitation laser instead of 410 nm laser light. Therefore, excellent emission of the sensor under the skin paves the way for the development of implantable oxygen sensor platforms.

Caviar Packaging Sensor Based on Time-Resolved Phosphorescence Spectroscopy

Caviar Packaging Sensor Based on Time-Resolved Phosphorescence Spectroscopy

Revisiting the Graphitized Nanodiamond-Mediated Activation of Peroxymonosulfate: Singlet Oxygenation versus Electron Transfer.

Graphitized nanodiamonds (ND) exhibit outstanding capability in activating peroxymonosulfate (PMS) for the removal of aqueous organic micropollutants (OMPs). However, controversial observation and interpretation regarding the effect of graphitization degree on ND's activity and the role of singlet oxygen (1O2) in OMP degradation need to be clarified. Herein, we investigated graphitized ND-mediated PMS activation. Experiments show that the activity of ND increases first and then decreases with the monotonically increased graphitization degree. Further experimental and theoretical studies unveil that the intensified surface graphitization alters the degradation mechanism from singlet oxygenation to an electron-transfer pathway. Moreover, for the first time, we applied a self-constructed, time-resolved phosphorescence detection system to provide direct evidence for 1O2 production in the PMS-based system. This work not only elucidates the graphitization degree-dependent activation mechanism of PMS but also provides a reliable detection system for in situ analysis of 1O2 in future studies.

Fine Particulate Matter-Induced Oxidative Stress Mediated by UVA-Visible Light Leads to Keratinocyte Damage.

The human skin is exposed to various environmental factors including solar radiation and ambient air pollutants. Although, due to its physical and biological properties, the skin efficiently protects the body against the harm of environmental factors, their excessive levels and possible synergistic action may lead to harmful effects. Among particulate matter present in ambient air pollutants, PM2.5 is of particular importance for it can penetrate both disrupted and intact skin, causing adverse effects to skin tissue. Although certain components of PM2.5 can exhibit photochemical activity, only a limited amount of data regarding the interaction of PM2.5 with light and its effect on skin tissue are available. This study focused on light-induced toxicity in cultured human keratinocytes, which was mediated by PM2.5 obtained in different seasons. Dynamic Light Scattering (DLS) and Atomic Force Microscopy (AFM) were employed to determine sizes of the particles. The ability of PM2.5 to photogenerate free radicals and singlet oxygen was studied using EPR spin-trapping and time-resolved singlet oxygen phosphorescence, respectively. Solar simulator with selected filters was used as light source for cell treatment to model environmental lightning conditions. Cytotoxicity of photoexcited PM2.5 was analyzed using MTT assay, PI staining and flow cytometry, and the apoptotic pathway was further examined using Caspase-3/7 assay and RT-PCR. Iodometric assay and JC-10 assay were used to investigate damage to cell lipids and mitochondria. Light-excited PM2.5 were found to generate free radicals and singlet oxygen in season-dependent manner. HaCaT cells containing PM2.5 and irradiated with UV-Vis exhibited oxidative stress features–increased peroxidation of intracellular lipids, decrease of mitochondrial membrane potential, enhanced expression of oxidative stress related genes and apoptotic cell death. The data indicate that sunlight can significantly increase PM2.5-mediated toxicity in skin cells.

Photoreactivity of Hair Melanin from Different Skin Phototypes-Contribution of Melanin Subunits to the Pigments Photoreactive Properties.

Photoreactivity of melanin has become a major focus of research due to the postulated involvement of the pigment in UVA-induced melanoma. However, most of the hitherto studies were carried out using synthetic melanin models. Thus, photoreactivity of natural melanins is yet to be systematically analyzed. Here, we examined the photoreactive properties of natural melanins isolated from hair samples obtained from donors of different skin phototypes (I, II, III, and V). X-band and W-band electron paramagnetic resonance (EPR) spectroscopy was used to examine the paramagnetic properties of the pigments. Alkaline hydrogen peroxide degradation and hydroiodic acid hydrolysis were used to determine the chemical composition of the melanins. EPR oximetry and spin trapping were used to examine the oxygen photoconsumption and photo-induced formation of superoxide anion, and time-resolved near infrared phosphorescence was employed to determine the singlet oxygen photogeneration by the melanins. The efficiency of superoxide and singlet oxygen photogeneration was related to the chemical composition of the studied melanins. Melanins from blond and chestnut hair (phototypes II and III) exhibited highest photoreactivity of all examined pigments. Moreover, melanins of these phototypes showed highest quantum efficiency of singlet oxygen photogeneration at 332 nm and 365 nm supporting the postulate of the pigment contribution in UVA-induced melanoma.

A pilot study of the dynamics of tissue oxygenation in vivo using time-resolved phosphorescence imaging

Oxygenation of tissues plays an important role in the development and progression of tumor to treatment effects. Method of metalloporphyrines phosphorescence quenching by oxygen is one of the ways to measure dynamics of the oxygen concentration in the tissues by phosphorescence lifetime imaging of meso-tetra(sulfopheny1)tetrabenzoporphyrin Pd (II) (TBP) using the time-correlated single photon counting (TCSPC) method. It has been shown that phosphorescence lifetime of the sensor in S37 tumor in vivo varied in the range of 130 to 290 [Formula: see text]s after both topical and intravenous administration of TBP. It indicates that oxygen level in tumors was lower compared to normal tissues where TBP phosphorescence has not been detected. Phosphorescence lifetimes of TBP increased in the solid tumor and in the muscle after photodynamic therapy of solid tumor that demonstrates oxygen consumption during treatment and possibly stopping the blood flow and hence the oxygen supply to the tissues.

A Highly Sensitive "on-off" Time-Resolved Phosphorescence Sensor Based on Aptamer Functionalized Magnetite Nanoparticles for Cadmium Detection in Food Samples.

Cadmium contamination is a severe threat to food safety. Therefore, the development of sensitive and selective cadmium detection strategies is urgently required. The elimination of background autofluorescence generated from the food matrix is critical to the optical assay for cadmium detection. Herein, a time-resolved phosphorescence sensor based on an “on-off” strategy was developed for cadmium determination in food samples. The phosphorescence nanoparticles were used as a luminous material to minimize the interference of background autofluorescence. The cadmium-binding aptamer was immobilized onto the magnetic beads and combined with a black hole quencher 1 (BHQ1) with complementary DNA as the target recognition element. With the presence of cadmium, the cadmium-binding aptamer bound to cadmium specifically and resulted in the release of BHQ1. The free BHQ1 remained in the solution after magnetic separation and quenched the phosphorescence. The phosphorescence intensity was negatively related to the concentration of cadmium. Under optimal conditions, the time-resolved phosphorescence sensor showed a linear response to cadmium concentration within a range from 0.05 to 5 ng mL−1 and with a detection limit of 0.04 ng mL−1. This “on-off” time-resolved phosphorescence sensor was successfully applied for cadmium detection in spring water and clam samples, which provided a rapid and straightforward method.