Singlet Oxygen Quantum Yield Determination for a Fluorene-Based Two-Photon Photosensitizer

The quantum yield, Φ_Δ, of singlet oxygen generation under two-photon excitation has been determined for a fluorene derivative. A photochemical method was developed using 1,3-diphenylisobenzofuran (DPBF), a chemical quencher of ¹O₂, and 2-(9,9-didecyl-7-nitrofluoren-2-yl)benzothiazole (1) as a two-photon photosensitizer (PS). The photochemical kinetics of the quencher was measured by two different fluorescence methods. Fluorene 1 exhibited relatively high singlet oxygen quantum yield, Φ_Δ ≈ 0.4 ± 0.1, and had a two-photon absorption cross-section of 28 ± 5 GM. Thus, 1 may have potential for use as a two-photon PS in the near-IR spectral region for biomedical applications.     

Pentacene Nanorods as Effective Photosensitizer for Photodynamic Therapy of Tumor via Singlet Fission

Singlet fission (SF), whereby a singlet exciton is converted into a pair of triplet excitons, can improve the efficiency of solar cells. Pentacene has been extensively studied as the most promising SF compound, owing to its 200% yield of triplet states. However, the easy degradation of pentacene in the presence of light and air owing to photooxidation cannot be explained by the classical ¹O₂ generation mechanism. To address this issue, in the present study, pentacene nanorods (Pc NRs) are prepared as a novel photosensitizer (PS); self-carried Pc NRs exhibited higher ¹O₂ generation capacity. Thus, a novel ¹O₂ generation mechanism is proposed based on the SF effect. The initial photon absorption occurs to access single-exciton states, S1–S3. Excited-state Pc pairs accelerate the SF effect in pentacene NRs, leading to a non-adiabatic transition to the dark D state. Dark D state is a singlet state by two triplets coupled overall, and it can transfer its energy to ³O₂ for generating ¹O₂. Using Pc NRs as PSs, photodynamic therapy (PDT) inhibits tumor growth in 4T1 tumor-bearing mice upon 405-nm-wavelength and 650-nm-wavelength laser irradiations. This study paves the way to discover novel PSs that are not considered with classical ¹O₂ generation mechanisms.     

Localized Surface Plasmon Resonance Enhanced Singlet Oxygen Generation and Light Absorption Based on Black Phosphorus@AuNPs Nanosheet for Tumor Photodynamic/Thermal Therapy

Although photodynamic therapy is an efficient therapeutic strategy for cancer treatment, it always suffers from the low singlet oxygen (¹O₂) yields owing to the weak absorption in optical transparent window of biological tissues. Herein, the black phosphorus (BP) nanosheet is integrated with gold nanoparticles (AuNPs) to simultaneously enhance the singlet oxygen generation and hyperthermia by localized surface plasmon resonance (LSPR) in cancer therapy. In the design, BP nanosheet employed as two‐dimension (2D) inorganic photosensitizer is hybridized with AuNPs through polyetherimide (PEI) as bridge to form BP‐PEI/AuNPs hybrid nanosheet. Such hybridation not only significantly increases the ¹O₂ production of BP nanosheet through maximizing the local field enhancement of AuNPs, but also significantly enhances the light absorption of BP nanosheet to promote photothermal effect by LSPR. Accordingly, about 3.9‐fold enhancement of ¹O₂ production and 1.7‐fold increasement of photothermal conversion efficiency are achieved compared with BP‐PEI alone upon single 670 nm laser irradiation. As a proof‐of‐concept model, BP‐PEI/AuNPs hybrid nanosheet with simultaneous dual‐modal phototherapy functions result in effective suppression of tumor growth with minimized side effects both in vitro and in vivo, indicating the great potential of the BP‐PEI/AuNPs hybrid nanosheet as an effective strategy to enhance the cancer therapy efficiency.     

Synthesis and Characterization of New Fluorene-Based Singlet Oxygen Sensitizers

The synthesis, photophysical characterization, and determination of singlet oxygen quantum yields (Φ_Δ) for a class of fluorene derivatives with potential application in two-photon photodynamic therapy (PDT) is reported. It has been demonstrated that these compounds possess the ability to generate singlet oxygen (¹O₂) upon excitation. A photochemical method, using 1,3-diphenylisobenzofuran (DPBF) as ¹O₂ chemical quencher, was employed to determine the singlet oxygen quantum yields (Φ_Δ) of the fluorene-based photosensitizers in ethanol. Φ_Δ values ranged from 0.35 to 0.75. These derivatives may have potential application as two-photon photosensitizers when pumped via two-photon excitation in the near-IR spectral region.     

光敏化反应生成单线态氧的电子耦合计算及其分子轨道重叠描述

三重态融合反应又称三重态-三重态湮灭反应,近年来被广泛应用于光催化、太阳能电池和生物成像等前沿领域. 在光敏化生成单线态氧的反应中,三重态激发的光敏剂分子通过三重态融合反应将激发态能量传递给基态氧分子³O₂,生成单重态的激发氧分子即单线态氧. 本文以6-aza-2-thiothymine为光敏剂,通过量子化学计算得到该反应的非绝热耦合强度,然后通过分子间运动下的积分转换,得到反应的透热电子耦合强度. 最后使用光敏剂分子和O₂的前线分子轨道计算轨道重叠强度,对量子化学计算得到的电子耦合值进行拟合,验证三重态融合反应的分子轨道重叠描述. 结果表明,分子轨道重叠可以较好地描述不同间距下光敏剂-O₂三线态融合反应的电子耦合强度分布,为预测三重态融合反应电子耦合提供了一种简便而有效的新方法.     

Metal-enhanced Singlet Oxygen Generation: A Consequence of Plasmon Enhanced Triplet Yields

In this Rapid Communication, we report the first observation of Metal-Enhanced singlet oxygen generation (ME¹O₂). Rose Bengal in close proximity to Silver Island Films (SiFs) can generate more singlet oxygen, a three-fold increase observed, as compared to an identical glass control sample but containing no silver. The enhanced absorption of the photo-sensitizer, due to coupling to silver surface plasmons, facilitates enhanced singlet oxygen generation. The singlet oxygen yield can potentially be adjusted by modifying the choice of MEF (Metal-Enhanced Fluorescence) & MEP (Metal Enhance Phosphorescence) parameters, such as distance dependence for plasmon coupling and wavelength emission of the coupling fluorophore. This is a most helpful observation in understanding the interactions between plasmons and lumophores, and this approach may well be of significance for singlet oxygen based clinical therapy.     

硫代碱基与单态氧反应速率常数的时间分辨光谱测定

硫代碱基作为一类免疫抑制性药物被广泛关注,由于硫原子的取代,硫代碱基可以吸收UVA波段紫外光,并通过系间窜越至激发三重态敏化氧气生成广泛应用于光动力学治疗的活性氧物质单态氧(~1O_2).然而,硫代碱基容易与自身敏化产生的~1O_2氧化发生反应,导致光毒性.在已有关于硫代碱基与~1O_2反应机理的研究基础上,本文采用瞬态光谱方法直接测得~1O_2在1270 nm处磷光信号的衰减动力学,得到硫代碱基与单态氧反应的速率常数.通过比较6-硫代鸟嘌呤、4-硫代尿嘧啶、2,4-二硫代尿嘧啶分别在水、乙腈以及二者混合溶剂中与~1O_2的反应,发现硫代碱基与单态氧反应速率常数受溶剂的极性影响.随着溶剂极性增大,反应速率常数则减小.此外,通过对比研究,发现硫代嘧啶类碱基与~1O_2的反应速率小于硫代嘌呤类碱基,说明在光动力学治疗中以硫代嘧啶类药物作为光敏剂是较为合适的选择.     

Single-molecule Detection of Reactive Oxygen Species: Application to Photocatalytic Reactions

In this review, we have focused on the oxidation reactions of single dye molecules by reactive oxygen species (ROS). The methodologies for the single-molecule detection of ROS, such as hydroxyl radical (HO^•), singlet oxygen (O₂(a¹Δ_g)), and hydrogen peroxide (H₂O₂), have been introduced together with examples. In particular, a successful application using the single-molecule fluorescence technique for the investigation of the TiO₂ photocatalytic oxidation reactions is demonstrated in detail.     

The Efficiency of the Formation of Singlet Oxygen by a Sensitizer Based on Zinc Phthalocyanine

Using zinc octa(diethoxyphosphenylmethyl)phthalocyanine as an example, we determined experimentally the quantum yield of generation of singlet oxygen () which makes it possible to evaluate quantitatively the efficiency of photogeneration of ¹O₂ and the influence of biomolecules on this parameter. It is shown that the efficiency of generation of singlet oxygen by the sensitizers used in photodynamic therapy depends on their state in a solution and increases with disaggregation of the dye and its interaction with biomolecules. It is established that phthalocyanine in an aqueous buffer solution sensitizes the formation of ¹O₂ with the quantum yield = 0.16 ± 0.02. On introduction of the detergent Triton X100 into the buffer solution of phthalocyanine, increases up to 0.48 ± 0.07. In a microheterogeneous medium (buffer + albumin) = 0.42.     

Singlet and Triplet State Properties and Singlet Oxygen Yield of an Amino-Acyl-Quinoxalinone Yellow Dye

Amino-acyl-quinoxalinone yellow dyes are cyclised analogues of the yellow azomethine dyes developed for, and still used in, silver halide colour photography. Unlike image azomethine dyes, which are rapidly deactivated in their excited states by torsion about the azomethine bond, amino-acyl-quinoxalinone dyes have an interesting photophysics because torsion is not possible due to their cyclised structure. We report results from studies on singlet and triplet state properties, and singlet oxygen yields, of the yellow dye, 7-diethylamino-3-(2,2-dimethyl-propionyl)-5-methyl-1-phenyl-1H-quinoxalin-2-one, in polar and nonpolar solvents. The dye photophysics is characterised by a weak fluorescence, with a solvent dependent emission yield (Φ_F?≈?0.002–0.004), and short singlet state lifetime (τ_expt?≈?20–50 ps), both increasing by a factor of ≈2 in going from polar acetonitrile to non-polar dioxane as solvent. DFT ZINDO calculations show a transition involving significant electron transfer from the diethyl-amino group into the carbonyl region of the molecule. In solution, in the presence of oxygen, the triplet state decays almost exclusively by oxygen quenching, and singlet oxygen is produced in high yield (Φ_??≈?0.5–0.55). The triplet state absorbs across the 450–750 nm region with maxima around 480 and 650 nm, and moderate molar absorption coefficients (ca. 6000–8000 M^?1 cm^?1). In a glass at 77 K, triplet decay gives a red phosphorescence, with λ_max?≈?640–650 nm, and a ?≈?0.25 s lifetime. If singlet oxygen yields are a good indication of triplet yields, then internal conversion and intersystem crossing occur with roughly equal efficiency.

     

Preliminary study on singlet oxygen production using CeF3:Tb3+@SiO2-PpIX

Luminescent properties and singlet oxygen production using CeF₃:Tb³⁺-based nanoparticles modified with SiO₂ and protoporphyrin IX (PpIX) were studied. CeF₃:Tb³⁺ nanopowder was prepared via sol–gel route, with subsequent surface coating by SiO₂ layer and the conjugation with photosensitive PpIX molecules. Radioluminescence spectra suggest an energy transfer from Ce³⁺ to Tb³⁺ ions and from Tb³⁺ to molecules of PpIX photosensitizer. The energy transfer was confirmed by photoluminescence decay curves. Singlet oxygen production was detected using a reaction of ¹O₂ with 3’-(p-aminophenyl) fluorescein (APF) chemical probe after X-Ray excitation. Qualitative changes in time resolved photoluminescence spectra in the region of 520 nm indicate ¹O₂ generation. Studied nanocomposites may be good candidates for the application in X-ray induced photodynamic therapy.     

Oxygen sensing by fluorescence quenching of [Cu(btmgp)I]

A fluorescence study of acetonitrile solutions of bis(tetramethylguanidine)propane, copper(I)-iodide and [Cu(btmgp)I] was performed and the chemical reaction of the latter species with O₂ was investigated at room temperature. The actual quenching process via O₂ gassing was studied and an exponential dependence of the fluorescence intensity with respect to the complex concentration was observed.Furthermore the survey was deepened on time resolved fluorescence properties of solved [Cu(btmgp)I] in a wider concentration range. The applicability of this complex for O₂ sensing inside a microreactor system was proven by confocal fluorescence measurements. It was shown that the investigated system can be used for oxygen sensing in the copper concentration range from 10⁻² to 10⁻⁹ mol/l.     

Luminescence Study of Singlet Oxygen Production by Meso-Tetraphenylporphine

The research in the field of the photodynamic therapy of cancer (PDT) is focused on a development of photosensitizers exhibiting high quantum yield of singlet oxygen production. Direct time-resolved spectroscopic observation of singlet oxygen phosphorescence can provide time constants of its population and depopulation as well as photosensitizer phosphorescence lifetime and relative quantum yields. In our contribution, a study of time and spectral resolved phosphorescence of singlet oxygen photosensitized by meso-tetraphenylporphine in acetone together with the photosensitizer phosphorescence is presented. Time constants of singlet oxygen population and depopulation were determined at wide range of photosensitizer concentrations. The time constant of singlet oxygen generation (0.28 ± 0.01) s is slightly shorter then the lifetime of photosensitizer's triplet state (0.32 ± 0.01) s. It is caused by lower ability of TPP aggregates to transfer excitation energy to oxygen. The lifetime of singlet oxygen (50 s) decreases with increasing photosensitizer concentration. Therefore, the photosensitizer acts also as a quencher of oxygen singlet state, similarly to the effects observed in [A. A. Krasnovsky, P. Cheng, R. E. Blankenship, T. A. Moore, and D. Gust (1993). Photochem. Photobiol. 57, 324–330; H. Küpper, R. Ddic, A. Svoboda, J. Hála, and P. M. H. Kroneck (2002). Biochim. Biophys. Acta Gen. Subj. 1572, 107–113]. Moreover, the increasing concentraion of the photosensitizer causes a slight hypsochromic shift of the singlet oxygen luminescence maximum.     

Laser-Induced Fluorescence Molecular Beam Investigation of New Singlet and Triplet Electronic States of Yttrium Monohydride

The yttrium monohydride spectrum in the range 12 500-25 000 cm⁻¹ has been studied by various laser-induced fluorescence (LIF) techniques. YH (YD) molecules have been produced in a free jet molecular beam apparatus by a laser vaporizing yttrium metal in the presence of He doped with H₂ (D₂) or NH₃ (ND₃). Low-resolution (∼0.04 cm⁻¹) excitation spectra have been recorded in the entire studied range. Four green bands (19 300-19 900 cm⁻¹) of the YH isotopomer have been studied in more detail: (1) high-resolution (∼120 MHz, ∼0.004 cm⁻¹) excitation spectra have been recorded, (2) dispersed fluorescence spectra have been obtained, and (3) lifetimes of the selected rotational levels of the upper states have been measured. Our observations have confirmed that the ground state of yttrium monohydride has ¹Σ⁺ symmetry and have provided a link between the singlet and triplet manifolds. The upper states of the observed transitions have been tentatively assigned to five electronic states, d0⁺, f³Π, f′1, D¹Π, E0⁺, and Fl. The low-energy excited electronic state observed in the dispersed fluorescence experiment has been assigned as the a³Δ state.     

Sonocatalytic degradation of an anthraquinone dye using TiO2-biochar nanocomposite

TiO₂-biochar (TiO₂-BC) nanocomposite was synthesized by sol-gel method. The characteristics of the prepared nanocomposite were examined using X-ray fluorescence, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and N₂ adsorption-desorption analysis. The performance of synthesized TiO₂-BC nanocomposite as efficient sonocatalyst was studied for the degradation of Reactive Blue 69 (RB69). Sonocatalytic degradation of RB69 in the presence of TiO₂-BC nanocomposite could be explained by the mechanisms of hot spots and sonoluminescence. The optimized values for main operational parameters were determined as pH of 7, TiO₂-BC dosage of 1.5 g/L, RB69 initial concentration of 20 mg/L and ultrasonic power of 300 W. Furthermore, the effect of OH, h⁺ and O₂⁻ scavengers on the RB69 degradation efficiency was studied. Gas chromatography-mass spectroscopy analysis was used to identify intermediate compounds formed during the RB69 degradation. The results of repeated applications of TiO₂-BC in the sonocatalytic process verified its stability in long-term usage.     

Color tunable emission from (GdxY1−x)2O3: Er3+, Yb3+ phosphor prepared by combustion method

The (Gd_xY_1?x)₂O₃: Er³⁺, Yb³⁺ [x=0.0, 0.1, 0.5, 0.9, 1.0] phosphor samples with 0.5 mol% concentration of Er³⁺ and 3.0 mol% of Yb³⁺, have been prepared using combustion route. The effect of variation of composition on the morphology, crystallinity and photoluminescence characteristics of the material has been investigated. The samples were post-heated at a temperature 1200 °C, for 5 h. We find systematic color tunability from red to green with an increase of Gd₂O₃ content in Y₂O₃ lattice. Further, the post-heated samples show an enhancement of fluorescence intensity for more than fifteen times. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence measurement and Fourier transform infrared (FTIR) techniques in order to find out the structural changes in host lattice. An increase in crystallite size has been marked with increasing Gd content while FTIR analysis explains the reason of variation in the fluorescence of rare earth ions in different host matrices.     

Fluorophotometric Determination of Hydrogen Peroxide with Fluorescin in the Presence of Cobalt (II) and Reaction Against Other Reactive Oxygen Species

A fluorophotometric method for the determination of hydrogen peroxide (H₂O₂) using fluorescin was developed. This method was based on the oxidative reaction of fluorescin, a colorless, non-fluorescent lactoid fluorescein, by H₂O₂ to give highly fluorescein fluorescence emission. In the determination of H₂O₂, the calibration curve exhibited linearity over the H₂O₂ concentration range of 1.5–310 ng mL⁻¹ at an emission wavelength of 525 nm with an excitation of 500 nm and with relative standard deviations (n = 6) of 2.51%, 2.48%, and 1.31% for 3.1 ng mL⁻¹, 30.8 ng mL⁻¹, and for 308 ng mL⁻¹ of H₂O₂, respectively. The detection limit for H₂O₂ was 1.9 ng mL⁻¹ six blank determinations was performed (ρ = 6). This proposed method was applied to detection of other reactive oxygen species and nitrogen species (ROS/RNS) such as singlet oxygen (¹O₂), hydroxyl radical (^•OH), peroxynitrite (ONOO⁻) etc., and it was possible to detect them with a high sensitivity. In addition, this proposed method was applied to the recovery tests of H₂O₂ in calf serum, human saliva, rain water, and wheat noodles; the results were satisfactory.     

银团簇上吸附氧原子与氢气作用的研究

The interactions between Ag_nO^-(n=1-8) and H₂ (or D₂) were explored by combination of the mass spectroscopy experiments and density function theory (DFT) calculations. The experiments found that all oxygen atoms in Ag_nO^-(n=1-8) are inert in the interactions with H₂ or D₂ at the low temperature of 150 K, which is in contrast to their high reactivity with CO under the same condition. These observations are parallel with the preferential oxidation (PROX) of CO in excess hydrogen catalyzed by dispersed silver species in the condensed phase. Possible reaction paths between Ag_nO^-(n=1-8) and H₂ were explored using DFT calculations. The results indicated that adsorption of H₂ on any site of Ag_nO^-(n=1-8) is extremely weak, and oxidation of H₂ by any kind of oxygen in Ag_nO^-(n=1-8) has an apparent barrier strongly dependent on the adsorption style of the "O". These experiments and theoretical results about cluster reactions provided molecule-level insights into the activity of atomic oxygen on real silver catalysts.     

Photooxidation of different organic dyes (RB, MO, TB, and BG) using Fe(III)-doped TiO2 nanophotocatalyst prepared by novel chemical method

The nano-structured Fe(III)-doped TiO₂ photocatalysts with anatase phase have been developed for the oxidation of non-biodegradable different organic dyes like methyl orange (MO), rhodamine B (RB), thymol blue (TB) and bromocresol green (BG) using UV-Hg-lamp. The different compositions of Fe_xTi_1−xO₂ (x = 0.005, 0.01, 0.05, and 0.1) nanocatalysts synthesized by chemical method (CM), have been characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectra, specific surface area (BET), transmission electronic microscopy (TEM) analysis, XPS, ESR and zeta potential. From XRD analysis, the results indicate that all the compositions of Fe(III) doped in TiO₂ catalysts gives only anatase phase not rutile phase. For complete degradation of all the solutions of the dyes (MO, RB, TB, and BG), the composition with x = 0.005 is more photoactive compared all other compositions of Fe_xTi_1−xO₂, and degussa P25. The decolorization rate of different dyes decreases as Fe(III) concentration in TiO₂ increases. The energy band gap of Fe(III)-doped TiO₂ is found to be 2.38 eV. The oxidation state of iron has been found to be 3+ from XPS and ESR show that Fe³⁺ is in low spin state.     

The Influence of Human Serum Albumin on The Photogeneration of Singlet Oxygen by meso-Tetra(4-Sulfonatophenyl)Porphyrin. An Infrared Phosphorescence Study

meso-Tetra(4-sulfonatophenyl)porphyrin (TPPS₄) is a water soluble photosensitizer, which is currently clinically tested as a PDT drug. In our contribution, we present IR spectral- and time-resolved phosphorescence data reflecting the influence of human serum albumin (HSA) on singlet oxygen photogeneration by TPPS₄. IR emission of TPPS₄ was studied in samples containing various concentrations of HSA in phosphate buffer. The observed changes in spectral and temporal behaviour of TPPS₄ and singlet oxygen phosphorescence caused by the addition of HSA are equivalent to the effect of nitrogen purging of HSA-free solutions of TPPS₄. The main feature induced by addition of HSA appears to be the occurrence of a long-lived (tens of microseconds) photosensitizer phosphorescence at 900 nm besides ordinary short-lived (≈2 μs) one at 820 nm. It is accompanied by presence of a long-lived component of singlet oxygen emission with lifetime roughly corresponding to that of the long photosensitizer phosphorescence component. Moreover, the quantum yield of singlet oxygen phosphorescence decreases with increasing HSA concentration, while total quantum yield of TPPS₄ phosphorescence rises. These facts are explained by a shielding effect of HSA on bound molecules of TPPS₄ against quenching by oxygen which is analogous to oxygen removal by nitrogen purging.