Synthesis of nitropolychlorinated dibenzo-p-dioxins (NPCDDs) and their photochemical reaction with nucleophiles

1995 ◽  
Vol 73 (6) ◽  
pp. 826-834 ◽  
Author(s):  
Simona G. Merica ◽  
Nigel J. Bunce
Keyword(s):  
Excited State ◽  
Quantum Yield ◽  
Linear Relationship ◽  
Nitro Group ◽  
Photochemical Reaction ◽  
Ring Opening ◽  
Sodium Ethoxide ◽  
Chemical Yield ◽  
Triplet Excited State ◽  
High Chemical

A series of nitropolychlorodibenzo-p-dioxins (NPCDDs) was synthesized by condensation between catechols and 2,6-dinitrohalobenzene derivatives. In the presence of sodium ethoxide in anhydrous ethanol, these underwent photochemical SN2Ar* substitutions meta to the nitro group in high chemical yield and moderate quantum yield. Both ring-opening and chloride replacement reactions were observed. The reactions involved the triplet excited state of the NPCDD, and showed a linear relationship between Φ−1 and [nucleophile]−1. Analogous reactions with KCN in methanol showed similar behaviour, but the products could not be isolated. Keywords: photosubstitution, SN2Ar*, dibenzo-p-dioxins.

The mechanism of the photochemical cycloaddition reaction of N-benzoylindole with cyclopentene

1990 ◽  
Vol 68 (10) ◽  
pp. 1685-1692 ◽  
Author(s):  
Bimsara W. Disanayaka ◽  
Alan C. Weedon
Keyword(s):  
Excited State ◽  
Quantum Yield ◽  
Ground State ◽  
Mechanistic Model ◽  
Cycloaddition Reaction ◽  
Intersystem Crossing ◽  
Triplet Excited State ◽  
Excited State Lifetime ◽  
Yield Data ◽  
Counting Procedure

The mechanism of the photochemical cycloaddition reaction between N-benzoylindole, 1, and cyclopentene to give cyclobutane adducts 2 and 3 has been examined. The triplet excited state lifetime and quantum yield of intersystem crossing were determined for 1 as (2.8 ± 0.3) × 10−8 s and 0.39 ± 0.01, respectively, using the triplet counting procedure. In addition, the dependence of the quantum yield of cycloadduct formation upon the concentration of cyclopentene and upon the concentration of excited state quenchers has been determined. The results are used to propose a mechanistic model in which the triplet excited state of 1 reacts with cyclopentene to give a triplet 1,4-biradical intermediate. Following spin inversion the biradical intermediate reverts to the ground state starting materials or proceeds to the products 2 and 3; this partitioning, along with the quantum yield of intersystem crossing, gives rise to a limiting quantum yield of cycloaddition at infinite alkene concentration of 0.061. It is calculated that 84% of the biradical intermediates revert to the starting materials and 16% proceed to cycloadducts. The quantum yield data are also used to calculate two independent values of the rate constant for reaction of the triplet excited 1 with alkene; the values are (1.8 ± 0.1) × 107M−1 s−1 and (4.0 ± 0.8) × 106 M−1 s−1'. Some evidence for self quenching of the triplet excited state of 1 by ground state 1 was also observed. The quantum yield of intersystem crossing and the triplet excited state lifetime of 1 were found to vary with the solvent used; this is discussed in terms of the possible existence of a charge transfer triplet excited state. Keywords: indole, photocycloaddition, mechanism.

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.

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.

Electron-transfer reactions and luminescent quantum yield of the triplet excited state of tetrakis[.mu.-diphosphito(2-)-p,p']diplatinate(II)

1984 ◽  
Vol 106 (4) ◽  
pp. 1163-1164 ◽  
Author(s):  
William B. Heuer ◽  
Mark D. Totten ◽  
Gary S. Rodman ◽  
Eric J. Hebert ◽  
Henry J. Tracy ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Quantum Yield ◽  
Transfer Reactions ◽  
Triplet Excited State ◽  
Electron Transfer Reactions

Photolysis of 5,5-dimethyl-4-phenyl-Δ-1,2,4-triazolin-3-one. Fragmentation to nitrogen, carbon monoxide, and isopropylidene phenyl amine

1981 ◽  
Vol 59 (21) ◽  
pp. 3087-3089
Author(s):  
Lubomira M. Cabelkova-Taguchi ◽  
John Warkentin
Keyword(s):  
Carbon Monoxide ◽  
Excited State ◽  
Quantum Yield ◽  
Triplet Excited State ◽  
Direct Photolysis ◽  
Norrish Type ◽  
Initial Cleavage

Photolysis of 5,5-dimethyl-4-phenyl-Δ1-1,2,4-triazolin-3-one (2) produces the same products as thermolysis; namely, nitrogen, carbon monoxide, and isopropylidene phenyl amine (acetone anil). The quantum yield for direct photolysis of 2 in methanol with 313 nm light is 0.066. Sensitization with benzophenone in the same solvent, and quenching with 1,3-cyclohexadiene, revealed that photolysis of 2 involves a triplet excited state. The most likely photo processes are thought to involve initial cleavage of the C3—N4 bond or the C3—N2 bond (Norrish, type 1 cleavage).

scholarly journals Ultra long‐lived triplet excited state in water at room temperature: Insights on the molecular design of tridecafullerenes

2021 ◽  
Author(s):  
Javier Ramos-Soriano ◽  
Alfonso Pérez-Sánchez ◽  
Sergio Ramírez-Barroso ◽  
Beatriz M. Illescas ◽  
Khalid Azmani ◽  
...  
Keyword(s):  
Excited State ◽  
Room Temperature ◽  
Molecular Design ◽  
Triplet Excited State

scholarly journals Triplet energies and excimer formation in meta - and para -linked carbazolebiphenyl matrix materials

2015 ◽  
Vol 373 (2044) ◽  
pp. 20140446 ◽  
Author(s):  
Sergey A. Bagnich ◽  
Alexander Rudnick ◽  
Pamela Schroegel ◽  
Peter Strohriegl ◽  
Anna Köhler
Keyword(s):  
Excited State ◽  
Triplet State ◽  
Spectroscopic Investigation ◽  
Triplet Excited State ◽  
Conjugation Length ◽  
Triplet Energy ◽  
Excimer Formation

We present a spectroscopic investigation on the effect of changing the position where carbazole is attached to biphenyl in carbazolebiphenyl (CBP) on the triplet state energies and the propensity to excimer formation. For this, two CBP derivatives have been prepared with the carbazole moieties attached at the ( para ) 4- and 4 ′ -positions ( p CBP) and at the ( meta ) 3- and 3 ′ -positions ( m CBP) of the biphenyls. These compounds are compared to analogous m CDBP and p CDBP, i.e. two highly twisted carbazoledimethylbiphenyls, which have a high triplet energy at about 3.0 eV and tend to form triplet excimers in a neat film. This torsion in the structure is associated with localization of the excited state onto the carbazole moieties. We find that in m CBP and p CBP, excimer formation is prevented by localization of the triplet excited state onto the central moiety. As conjugation can continue from the central biphenyls into the nitrogen of the carbazole in the para -connected p CBP, emission involves mainly the benzidine. By contrast, the meta -linkage in m CBP limits conjugation to the central biphenyl. The associated shorter conjugation length is the reason for the higher triplet energy of 2.8 eV in m CBP compared with the 2.65 eV in p CBP.

Investigation of the triplet excited state and application of cationic meso-tetra(cisplatin)porphyrins in antimicrobial photodynamic therapy

2021 ◽  
pp. 102459
Author(s):  
Dariane Clerici Jornada ◽  
Rafael de Queiroz Garcia ◽  
Carolina Hahn da Silveira ◽  
Lino Misoguti ◽  
Cleber Renato Mendonça ◽  
...  
Keyword(s):  
Photodynamic Therapy ◽  
Excited State ◽  
Antimicrobial Photodynamic Therapy ◽  
Triplet Excited State
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