Optimization of Triplet Excited State and Singlet Oxygen Quantum Yields of Picolylamine–Porphyrin Conjugates through Zinc Insertion

2013 ◽  
Vol 117 (43) ◽  
pp. 13515-13522 ◽  
Author(s):  
Betsy Marydasan ◽  
Akhil K. Nair ◽  
Danaboyina Ramaiah
Keyword(s):  
Excited State ◽  
Singlet Oxygen ◽  
Quantum Yields ◽  
Triplet Excited State

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 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.

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.

Stereochemical studies of the photochemical cycloaddition reaction of alkenes with N-benzoylindole and N-carboethoxyindole; evidence for biradical intermediacy

1991 ◽  
Vol 69 (7) ◽  
pp. 1171-1181 ◽  
Author(s):  
David J. Hastings ◽  
Alan C. Weedon
Keyword(s):  
Excited State ◽  
Rate Constant ◽  
Ground State ◽  
Addition Reaction ◽  
Cycloaddition Reaction ◽  
Adduct Formation ◽  
Quantum Yields ◽  
Triplet Excited State ◽  
Marked Contrast ◽  
Cis And Trans

The stereochemistries of the 2 + 2 cycloaddition products obtained from the photochemical addition reaction between N-benzoylindole or N-carboethoxyindole and the alkenes cyclopentene, cyclohexene, cycloheptene, cis- and trans-2-butene, and cis- and trans-4-octene are examined. The structures of the products are shown to be consistent with a photo-cycloaddition mechanism involving the intermediacy of triplet 1,4-biradical species. The quantum yields of adduct formation between N-benzoylindole and both cis- and trans-octene were measured as a function of alkene concentration. The results suggest that cis-octene reacts with the indole derivative's triplet excited state with a rate constant of (1.7 ± 0.3) × 107 M−1 s−1. The results are also consistent with the immediate products of this reaction being 1,4-biradicals, 98% of which revert to the ground state indole derivative and alkene, and only 2% of which proceed to cycloadduct. In marked contrast, the same treatment suggests that trans-octene reacts with the triplet excited state of N-benzoylindole with a rate constant estimated to be in the range of 1 × 106 and 6 × 105 M−1 s−1, and it appears that the 1,4-biradicals formed revert much less efficiently to the starting materials; it is estimated that between 67 and 100% of the 1,4-biradicals proceed to cycloadducts. In the reaction with cis-octene biradical reversion leads to the formation of trans-octene ("Schenk isomerization"); the quantum yield of this process is determined to be 0.074 ± 0.004, which may imply that approximately 75% of the biradicals collapse to cis-alkene and 25% collapse to the trans isomer. Key words: indole, photocycloaddition, 1,4-biradicals.

Successive photocyanation of highly chlorinated aromatic compounds

1999 ◽  
Vol 77 (8) ◽  
pp. 1366-1373
Author(s):  
Alexandre D Konstantinov ◽  
Andrea N Johnston ◽  
Nigel J Bunce
Keyword(s):  
Excited State ◽  
Aromatic Compounds ◽  
Sodium Cyanide ◽  
Reaction Channel ◽  
Quantum Yields ◽  
Triplet Excited State ◽  
General Reaction ◽  
Major Reaction ◽  
Chlorinated Aromatic Compounds

Successive photocyanation was found to be a general reaction when chlorinated aromatic compounds were photolyzed with sodium cyanide. The products were polycyanated hydroxychloro compounds with various degrees of chlorine replacement. Although the products from some substrates could be isolated, identified, and characterized, most reactions proceeded with low regioselectivity, which limits their synthetic potential. Quantum yields of substrate disappearance increased with the number of chlorine substituents on a substrate, and followed the expected relationship ϕ-1 is proportional to [CN-]-1. In some cases, ϕ depended also on the concentration of the chloro compound, indicating the involvement of excimers, although the major reaction channel appears to be SN2Ar*. Sensitization and quenching experiments established the triplet excited state to be reactive for all substrates tested.Key words: photocyanation, chlorinated aromatic compounds.

Roles of singlet oxygen and triplet excited state of dissolved organic matter formed by different organic matters in bacteriophage MS2 inactivation

2013 ◽  
Vol 47 (14) ◽  
pp. 4869-4879 ◽  
Author(s):  
Sahid L. Rosado-Lausell ◽  
Hanting Wang ◽  
Leonardo Gutiérrez ◽  
Ofelia C. Romero-Maraccini ◽  
Xi-Zhi Niu ◽  
...  
Keyword(s):  
Organic Matter ◽  
Excited State ◽  
Dissolved Organic Matter ◽  
Singlet Oxygen ◽  
Triplet Excited State ◽  
Organic Matters ◽  
Bacteriophage Ms2

Photolysis of polychlorinated benzenes in cyclohexane solution

1983 ◽  
Vol 61 (6) ◽  
pp. 1103-1104 ◽  
Author(s):  
Nigel J. Bunce ◽  
Patrick J. Hayes ◽  
Mary E. Lemke
Keyword(s):  
Excited State ◽  
Quantum Yield ◽  
Concentration Dependence ◽  
Quantum Yields ◽  
Intersystem Crossing ◽  
Triplet Excited State ◽  
Chlorinated Benzenes ◽  
Polychlorinated Benzenes

Quantum yields of dechlorination and of intersystem crossing have been measured in cyclohexane for a series of chlorinated benzenes. The results are compatible with the reactions occurring predominantly from the triplet excited state. The quantum yield of reaction shows a concentration dependence on [Formula: see text], but the dependence is less for the more heavily chlorinated members of the scries.

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