scholarly journals Спектральное исследование фотодинамических процессов в системе C-=SUB=-60-=/SUB=--(н-метилпирролидон)-кислород

2021 ◽  
Vol 129 (12) ◽  
pp. 1493
Author(s):  
И.М. Кисляков ◽  
И.М. Белоусова ◽  
В.М. Киселев ◽  
И.В. Багров ◽  
А.М. Стародубцев ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Singlet Oxygen ◽  
Transient Absorption ◽  
Rapid Quenching ◽  
Quenching Rate ◽  
Broadband Absorption ◽  
Laser Pumping ◽  
Time Dependencies ◽  
Quenching Rate Constant

The processes of photoexcitation and energy transfer in an air-saturated solution of fullerene C60 in n-methylpyrrolidone are studied. With femtosecond laser pumping at a wavelength л(p) = 520 nm, transient absorption spectra were obtained in the range 470-750 nm. Broadband absorption is observed at л > 650 nm as a result of aggregation of fullerene molecules, characterized by a short decay time of the picosecond scale. The analysis of the time dependencies indicates the presence of several processes. Within the proposed interpretation, we state a remarkable reduction in the time of singlet-triplet intersystem crossing with an increase of nanocluster size while the rapid quenching of the singlet state varies only slightly. The quantum yield of the triplet state can therefore increase, reaching 0.14. The phosphorescence spectra of singlet oxygen with a maximum at л = 1276 nm were measured with LED excitation at various wavelengths in the range 370-625 nm. The lifetime and quenching rate constant of singlet oxygen in n-methylpyrrolidone are determined. The combined quantum yield of triplet fullerene and singlet oxygen in n-methylpyrrolidone is estimated as 0.74. The efficiency spectra of the singlet oxygen photosensibilization in the C60-(n-methylpyrrolidone)-oxygen system are obtained, indicating the increasing role of large nanoclusters in this process during aging of the solution.

Lifetime of Singlet Oxygen and Quenching by NaN3 in Mixed Solvents

1982 ◽  
Vol 37 (5) ◽  
pp. 649-652 ◽  
Author(s):  
N. Miyoshi ◽  
M. Ueda ◽  
K. Fuke ◽  
Y. Tanimoto ◽  
M. Itoh ◽  
...  
Keyword(s):  
Activation Energy ◽  
Charge Transfer ◽  
Singlet Oxygen ◽  
Mixed Solvents ◽  
Solvent Polarity ◽  
Thermal Lensing ◽  
Partial Charge ◽  
Partial Charge Transfer ◽  
Quenching Rate ◽  
Quenching Rate Constant

Singlet oxygen was generated by the photosensitization of erythrosine. The lifetime of singlet oxygen and the quenching rate constant for singlet oxygen by NaN3 were measured by a thermal lensing method in MeOH-H2O mixed solvents. The reciprocal of the lifetime increased linearly with the increase of the H2O mole fraction. Semi-log plot of the quenching constant against the reciprocal of the solvent polarity exhibited a linear relation. The quenching of the singlet oxygen by NaN3 may proceed through a partial charge-transfer intermediate. The activation energy for the quenching reaction of N3- + 1O2 →[N3·1O2-] increased with the increase of the solvent polarity. The lifetime was also measured in MeOH-ethyleneglycol mixed solvents, and its relation with viscosity was obtained

scholarly journals Characteristics of the excited triplet states of thiolated guanosine derivatives and singlet oxygen generation

2018 ◽  
Vol 17 (10) ◽  
pp. 1469-1476 ◽  
Author(s):  
Shoma Miyata ◽  
Shunsuke Tanabe ◽  
Tasuku Isozaki ◽  
Yao-Zhong Xu ◽  
Tadashi Suzuki
Keyword(s):  
Singlet Oxygen ◽  
Triplet States ◽  
Quenching Rate ◽  
Singlet Molecular Oxygen ◽  
Excited Triplet ◽  
Oxygen Generation ◽  
Singlet Oxygen Generation ◽  
Oxygen Conditions ◽  
Quenching Rate Constant ◽  
Excited Triplet States

The long intrinsic lifetime and low self-quenching rate constant of the triplet 6,8-dithioguanosine lead to efficient singlet molecular oxygen generation under carcinomatous oxygen conditions.

scholarly journals Biradical vs singlet oxygen photogeneration in suprofen–cholesterol systems

2016 ◽  
Vol 12 ◽  
pp. 1196-1202
Author(s):  
Fabrizio Palumbo ◽  
Francisco Bosca ◽  
Isabel Maria Morera ◽  
Inmaculada Andreu ◽  
Miguel A Miranda
Keyword(s):  
Excited State ◽  
Singlet Oxygen ◽  
Near Infrared ◽  
Transient Absorption ◽  
Hydrogen Abstraction ◽  
Oxidative Degradation ◽  
Infrared Emission ◽  
Quantum Yields ◽  
Triplet Excited State ◽  
Quenching Rate

Cholesterol (Ch) is an important lipidic building block and a target for oxidative degradation, which can be induced via free radicals or singlet oxygen (1O2). Suprofen (SP) is a nonsteroidal anti-inflammatory drug that contains the 2-benzoylthiophene (BZT) chromophore and has a π,π* lowest triplet excited state. In the present work, dyads (S)- and (R)-SP-α-Ch (1 and 2), as well as (S)-SP-β-Ch (3) have been prepared from β- or α-Ch and SP to investigate the possible competition between photogeneration of biradicals and 1O2, the key mechanistic steps in Ch photooxidation. Steady-state irradiation of 1 and 2 was performed in dichloromethane, under nitrogen, through Pyrex, using a 400 W medium pressure mercury lamp. The spectral analysis of the separated fractions revealed formation of two photoproducts 4 and 5, respectively. By contrast, under the same conditions, 3 did not give rise to any isolable Ch-derived product. These results point to an intramolecular hydrogen abstraction in 1 and 2 from the C7 position of Ch and subsequent C–C coupling of the generated biradicals. Interestingly, 2 was significantly more photoreactive than 1 indicating a clear stereodifferentiation in the photochemical behavior. Transient absorption spectra obtained for 1–3 were very similar and matched that described for the SP triplet excited state (typical bands with maxima at ca. 350 nm and 600 nm). Direct kinetic analysis of the decay traces at 620 nm led to determination of triplet lifetimes that were ca. 4.1 μs for 1 and 2 and 5.8 μs for 3. From these data, the intramolecular quenching rate constants in 1 and 2 were determined as 0.78 × 105 s−1. The capability of dyads 1–3 to photosensitize the production of singlet oxygen was assessed by time-resolved near infrared emission studies in dichloromethane using perinaphthenone as standard. The quantum yields (ΦΔ) were 0.52 for 1 and 2 and 0.56 for 3. In conclusion, SP-α-Ch dyads are unique in the sense that they can be used to photogenerate both biradicals and singlet oxygen, thus being able to initiate Ch oxidation from their triplet excited states following either of the two competing mechanistic pathways.

scholarly journals Ready Access to Molecular Rotors Based on Boron Dipyrromethene Dyes-Coumarin Dyads Featuring Broadband Absorption

Molecules ◽  
2020 ◽  
Vol 25 (4) ◽  
pp. 781
Author(s):  
Ernesto Enríquez-Palacios ◽  
Teresa Arbeloa ◽  
Jorge Bañuelos ◽  
Claudia I. Bautista-Hernández ◽  
José G. Becerra-González ◽  
...  
Keyword(s):  
Molecular Rotors ◽  
Fluorescence Signal ◽  
Access Method ◽  
Broadband Absorption ◽  
Boron Dipyrromethene ◽  
Conformational Freedom ◽  
Meso Position ◽  
Photophysical Study ◽  
Ready Access

Herein we report on a straightforward access method for boron dipyrromethene dyes (BODIPYs)-coumarin hybrids linked through their respective 8- and 6- positions, with wide functionalization of the coumarin fragment, using salicylaldehyde as a versatile building block. The computationally-assisted photophysical study unveils broadband absorption upon proper functionalization of the coumarin, as well as the key role of the conformational freedom of the coumarin appended at the meso position of the BODIPY. Such free motion almost suppresses the fluorescence signal, but enables us to apply these dyads as molecular rotors to monitor the surrounding microviscosity.

scholarly journals Ruthenium-based PACT agents based on bisquinoline chelates: synthesis, photochemistry, and cytotoxicity

2021 ◽  
Author(s):  
Anja Busemann ◽  
Ingrid Flaspohler ◽  
Xue-Quan Zhou ◽  
Claudia Schmidt ◽  
Sina K. Goetzfried ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Singlet Oxygen ◽  
Cancer Cells ◽  
Cellular Uptake ◽  
Ruthenium Complex ◽  
Human Cancer ◽  
Light Irradiation ◽  
Quantum Yields ◽  
Light Activation ◽  
Human Cancer Cells

AbstractThe known ruthenium complex [Ru(tpy)(bpy)(Hmte)](PF6)2 ([1](PF6)2, where tpy = 2,2’:6’,2″-terpyridine, bpy = 2,2’-bipyridine, Hmte = 2-(methylthio)ethanol) is photosubstitutionally active but non-toxic to cancer cells even upon light irradiation. In this work, the two analogs complexes [Ru(tpy)(NN)(Hmte)](PF6)2, where NN = 3,3'-biisoquinoline (i-biq, [2](PF6)2) and di(isoquinolin-3-yl)amine (i-Hdiqa, [3](PF6)2), were synthesized and their photochemistry and phototoxicity evaluated to assess their suitability as photoactivated chemotherapy (PACT) agents. The increase of the aromatic surface of [2](PF6)2 and [3](PF6)2, compared to [1](PF6)2, leads to higher lipophilicity and higher cellular uptake for the former complexes. Such improved uptake is directly correlated to the cytotoxicity of these compounds in the dark: while [2](PF6)2 and [3](PF6)2 showed low EC50 values in human cancer cells, [1](PF6)2 is not cytotoxic due to poor cellular uptake. While stable in the dark, all complexes substituted the protecting thioether ligand upon light irradiation (520 nm), with the highest photosubstitution quantum yield found for [3](PF6)2 (Φ[3] = 0.070). Compounds [2](PF6)2 and [3](PF6)2 were found both more cytotoxic after light activation than in the dark, with a photo index of 4. Considering the very low singlet oxygen quantum yields of these compounds, and the lack of cytotoxicity of the photoreleased Hmte thioether ligand, it can be concluded that the toxicity observed after light activation is due to the photoreleased aqua complexes [Ru(tpy)(NN)(OH2)]2+, and thus that [2](PF6)2 and [3](PF6)2 are promising PACT candidates. Graphic abstract

scholarly journals Synthesis and Physicochemical Properties of [(1R,2S,5R)-2-isopropyl-5-methylcyclohexyloxy]-thiophen-5-yl-substituted Tetrapyrazinoporphyrazine with Magnesium(II) Ion

2021 ◽  
Vol 11 (6) ◽  
pp. 2576
Author(s):  
Sebastian Lijewski ◽  
Jiří Tydlitát ◽  
Beata Czarczynska-Goslinska ◽  
Milan Klikar ◽  
Jadwiga Mielcarek ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Singlet Oxygen ◽  
2D Nmr ◽  
Nmr Studies ◽  
Oxygen Formation ◽  
Nmr Techniques ◽  
Flash Column Chromatography ◽  
Photochemical Stability ◽  
Singlet Oxygen Formation ◽  
Very High

Tetrapyrazinoporphyrazine with peripheral menthol-thiophenyl substituents was synthesized using Linstead conditions and purified by flash column chromatography. The optimized synthetic and purification procedures allowed us to obtain a new macrocycle with 36% yield. Tetrapyrazinoporphyrazine derivative was characterized by UV–Vis and NMR spectroscopy, as well as MS spectrometry. Complex NMR studies using 1D and 2D NMR techniques allowed the analysis of the bulky menthol-thiophenyl substituted periphery of the new macrocycle. Further, photochemical stability and singlet oxygen quantum yield were determined by indirect method with diphenylisobenzofuran. The new tetrapyrazinoporphyrazine revealed low generation of singlet oxygen with a quantum yield of singlet oxygen formation at 2.3% in dimethylformamide. In turn, the macrocycle under irradiation with visible light presented very high stability with quantum yield for photostability of 9.59 × 10−6 in dimethylformamide, which figures significantly exceed the border for its classification as a stable porphyrinoid (10−4–10−5).

Linear and high-molecular-weight poly-porphyrins for efficient photodynamic therapy

2021 ◽  
Author(s):  
Nan Zheng ◽  
Xiahui Li ◽  
Shangwei Huangfu ◽  
Kangkai Xia ◽  
Ruofei Yue ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Photodynamic Therapy ◽  
Quantum Yield ◽  
Singlet Oxygen ◽  
High Molecular Weight ◽  
Linear Poly ◽  
High Molecular Weight Poly

A linear poly-porphyrin with high Mw and conjugated by PEG and acetazolamide was developed with enhanced singlet oxygen quantum yield, improved photo-toxicity and excellent in vivo photodynamic therapy.

scholarly journals The role of spin in the degradation of organic photovoltaics

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ivan Ramirez ◽  
Alberto Privitera ◽  
Safakath Karuthedath ◽  
Anna Jungbluth ◽  
Johannes Benduhn ◽  
...  
Keyword(s):  
Transient Absorption ◽  
Bulk Heterojunction ◽  
Critical Factor ◽  
Model Systems ◽  
Transient Absorption Spectroscopy ◽  
Triplet States ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
A Charge

AbstractStability is now a critical factor in the commercialization of organic photovoltaic (OPV) devices. Both extrinsic stability to oxygen and water and intrinsic stability to light and heat in inert conditions must be achieved. Triplet states are known to be problematic in both cases, leading to singlet oxygen production or fullerene dimerization. The latter is thought to proceed from unquenched singlet excitons that have undergone intersystem crossing (ISC). Instead, we show that in bulk heterojunction (BHJ) solar cells the photo-degradation of C60 via photo-oligomerization occurs primarily via back-hole transfer (BHT) from a charge-transfer state to a C60 excited triplet state. We demonstrate this to be the principal pathway from a combination of steady-state optoelectronic measurements, time-resolved electron paramagnetic resonance, and temperature-dependent transient absorption spectroscopy on model systems. BHT is a much more serious concern than ISC because it cannot be mitigated by improved exciton quenching, obtained for example by a finer BHJ morphology. As BHT is not specific to fullerenes, our results suggest that the role of electron and hole back transfer in the degradation of BHJs should also be carefully considered when designing stable OPV devices.

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