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.

Synthesis, photophysicochemical studies of adjacently tetrasubstituted binaphthalo-phthalocyanines

2005 ◽  
Vol 09 (05) ◽  
pp. 316-325 ◽  
Author(s):  
Itumeleng Seotsanyana-Mokhosi ◽  
Ji-Yao Chen ◽  
Tebello Nyokong
Keyword(s):  
Excited State ◽  
Quantum Yield ◽  
Triplet State ◽  
Singlet Oxygen ◽  
Photophysical Properties ◽  
Zinc Phthalocyanine ◽  
Quantum Yields ◽  
Triplet Excited State ◽  
General Increase ◽  
Photochemical Behavior

Adjacent binaphthalo-phthalocyanines tetra-substituted with phenoxy (4a), 4-carboxyphenoxy (4b) and 4-t-butylphenoxy (4c) groups, as well as the di-substituted 4-carboxyphenoxy (5b) have been synthesized and characterized. The photophysical and photochemical behavior of 4a-c, were compared with those of the corresponding di-substituted derivatives, (5a-c). The secondary substituents on the phenoxy ring have an influence on the aggregation of the molecules and hence on their photophysical properties. All of the complexes exhibit a relatively good conversion of energy from the triplet-excited state to the singlet oxygen. The less aggregated molecule (4c), has the highest singlet oxygen quantum yield. For all the molecules, fluorescence yields are low and they all have relatively shorter triplet lifetimes compared with the unsubstituted zinc phthalocyanine. Increasing the number of ring substituents on these rigid MPc complexes (from complexes 5 to 4) showed a general increase in the triplet state lifetimes and singlet oxygen quantum yields, and a decrease in stability.

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.

scholarly journals Photoexcitation of Ge9− Clusters in THF: New Insights into the Ultrafast Relaxation Dynamics and the Influence of the Cation

Molecules ◽  
2020 ◽  
Vol 25 (11) ◽  
pp. 2639
Author(s):  
Nadine C. Michenfelder ◽  
Christian Gienger ◽  
Melina Dilanas ◽  
Andreas Schnepf ◽  
Andreas-Neil Unterreiner
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Conduction Band ◽  
Near Infrared ◽  
Transient Absorption ◽  
Time Window ◽  
Excess Electron ◽  
Cluster Core ◽  
Relaxation Dynamics ◽  
Additional Time

We present a comprehensive femtosecond (fs) transient absorption study of the [Ge9(Hyp)3]− (Hyp = Si(SiMe3)3) cluster solvated in tetrahydrofuran (THF) with special emphasis on intra- and intermolecular charge transfer mechanisms which can be tuned by exchange of the counterion and by dimerization of the cluster. The examination of the visible and the near infrared (NIR) spectral range reveals four different processes of cluster dynamics after UV (267/258 nm) photoexcitation related to charge transfer to solvent and localized excited states in the cluster. The resulting transient absorption is mainly observed in the NIR region. In the UV-Vis range transient absorption of the (neutral) cluster core with similar dynamics can be observed. By transferring concepts of: (i) charge transfer to the solvent known from solvated Na− in THF and (ii) charge transfer in bulk-like materials on metalloid cluster systems containing [Ge9(Hyp)3]− moieties, we can nicely interpret the experimental findings for the different compounds. The first process occurs on a fs timescale and is attributed to localization of the excited electron in the quasi-conduction band/excited state which competes with a charge transfer to the solvent. The latter leads to an excess electron initially located in the vicinity of the parent cluster within the same solvent shell. In a second step, it can recombine with the cluster core with time constants in the picosecond (ps) timescale. Some electrons can escape the influence of the cluster leading to a solvated electron or after interaction with a cation to a contact pair both with lifetimes exceeding our experimentally accessible time window of 1 nanosecond (ns). An additional time constant on a tens of ps timescale is pronounced in the UV-Vis range which can be attributed to the recombination rate of the excited state or quasi conduction band of Ge9−. In the dimer, the excess electron cannot escape the molecule due to strong trapping by the Zn cation that links the two cluster cores.

scholarly journals Red and Near-Infrared Absorbing Dicyanomethylene Squaraine Cyanine Dyes: Photophysicochemical Properties and Anti-Tumor Photosensitizing Effects

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2083
Author(s):  
Tiago D. Martins ◽  
Eurico Lima ◽  
Renato E. Boto ◽  
Diana Ferreira ◽  
José R. Fernandes ◽  
...  
Keyword(s):  
Singlet Oxygen ◽  
Near Infrared ◽  
Cyanine Dyes ◽  
Quantum Yields ◽  
Squaraine Dyes ◽  
Photodynamic Activity ◽  
Photochemical Properties ◽  
Radiation Treatments ◽  
Species Production

Photodynamic therapy is a medical modality developed for the treatment of several diseases of oncological and non-oncological etiology that requires the presence of a photosensitizer, light and molecular oxygen, which combined will trigger physicochemical reactions responsible for reactive oxygen species production. Given the scarcity of photosensitizers that exhibit desirable characteristics for its potential application in this therapeutic strategy, the main aims of this work were the study of the photophysical and photochemical properties and the photobiological activity of several dicyanomethylene squaraine cyanine dyes. Thus, herein, the study of their aggregation character, photobleaching and singlet oxygen production ability, and the further application of the previously synthesized dyes in Caco-2 and HepG2 cancer cell lines, to evaluate their phototherapeutic effects, are described. Dicyanomethylene squaraine dyes exhibited moderate light-stability and, despite the low singlet oxygen quantum yields, were a core of dyes that exhibited relevant in vitro photodynamic activity, as there was an evident increase in the toxicity of some of the tested dyes exclusive to radiation treatments.

Triplet Excited State Distortions in a Pyrazolate Bridged Platinum Dimer Measured by X-ray Transient Absorption Spectroscopy

2010 ◽  
Vol 114 (48) ◽  
pp. 12780-12787 ◽  
Author(s):  
Jenny V. Lockard ◽  
Aaron A. Rachford ◽  
Grigory Smolentsev ◽  
Andrew B. Stickrath ◽  
Xianghuai Wang ◽  
...  
Keyword(s):  
Excited State ◽  
Absorption Spectroscopy ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Triplet Excited State ◽  
X Ray

Efficient intersystem crossing using singly halogenated carbomethoxyphenyl porphyrins measured using delayed fluorescence, chemical quenching, and singlet oxygen emission

2015 ◽  
Vol 17 (43) ◽  
pp. 29090-29096 ◽  
Author(s):  
Dawn M. Marin ◽  
Sonia Payerpaj ◽  
Graham S. Collier ◽  
Angy L. Ortiz ◽  
Gaurav Singh ◽  
...  
Keyword(s):  
Excited State ◽  
Singlet Oxygen ◽  
State Formation ◽  
Delayed Fluorescence ◽  
Intersystem Crossing ◽  
Fluorescence Lifetimes ◽  
Triplet Excited State

Singly halogenated carbomethoxyphenylporphyrins show decreased singlet fluorescence lifetimes and increased rates of triplet excited state formation.

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