Photochemical behavior of some α, β-unsaturated lactams. Dependence of reaction path on multiplicity

1969 ◽  
Vol 47 (15) ◽  
pp. 2781-2786 ◽  
Author(s):  
E. Cavalieri ◽  
S. Horoupian
Keyword(s):  
Excited State ◽  
Spectral Properties ◽  
Reaction Path ◽  
Triplet Excited State ◽  
Excited Singlet ◽  
Cleavage Reaction ◽  
Dimer Formation ◽  
Cyclobutane Dimer ◽  
Direct Irradiation ◽  
Cyclobutane Dimers

Whereas direct irradiation (2537 Å) of 5,6-dihydro-4,6,6-trimethyl-2(1H)-pyridone 1 (1a) produced almost exclusively the cleavage products 2 and 3, the acetophenone sensitized reaction (3500 Å) gave a single cyclobutane dimer. In contrast, direct (2537 Å) or sensitized (acetophenone, 3500 Å) irradiation of the homo derivative 7 of compound 1 gave approximately the same mixture of two cyclobutane dimers. It was thus demonstrated that dimer formation proceeded by way of a triplet excited state and that the cleavage reaction most probably occurred via an excited singlet state.A structure for each cyclobutane dimer in the seven-membered series was proposed on the basis of its spectral properties.

The photochemistry of 5-cyano-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene

1989 ◽  
Vol 67 (1) ◽  
pp. 82-87 ◽  
Author(s):  
Christopher Owen Bender ◽  
Douglas Dolman
Keyword(s):  
Excited State ◽  
Triplet Excited State ◽  
Deuterium Labelling ◽  
Direct Irradiation ◽  
Rearrangement Mechanism

The direct irradiation of 5-cyano-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene (18) led to 6-cyanobenzocyclooctatetraene (17; Φ = 0.00075), 6-cyanobenzosemibullvalene (14; Φ = 0.0003), and 2-cyanonaphthalene (Φ = 0.00015). The triplet excited state of 18, generated by sensitization with a variety of ketone sensitizers (e.g., Michler's ketone and acetophenone), showed no unimolecular reactivity. Compound 18 does not participate in Zimmerman di-π-methane rearrangement; the potential product from such a transformation, 8-cyanobenzosemibullvalene (19), was, however, isolated from direct (Corex filter; Φ = 0,0010) irradiation of the semibullvalene 14. Deuterium labelling experiments suggest that 14 derives from a mechanism involving initial C4—C8 bonding of 18, and that cyclooctatetraene 17 is probably formed by simple electrocyclic opening of the cyclobutene ring of 18. Keywords: photochemistry, rearrangement mechanism, di-π-methane, semibullvalenes.

trans-4-Stilbenecarboxylatoalkylpentaamminecobalt(III) Perchlorates: Synthesis and Intramolecular Energy Transfer

1996 ◽  
Vol 61 (3) ◽  
pp. 342-354 ◽  
Author(s):  
Cyril Párkányi ◽  
Lois Shiow-Chyn Yeh Huang ◽  
Sung Gun Chu ◽  
Alfred T. Jeffries III
Keyword(s):  
Energy Transfer ◽  
Excited State ◽  
Singlet State ◽  
Excitation Energy Transfer ◽  
Intramolecular Energy Transfer ◽  
Triplet Excited State ◽  
Excited Singlet ◽  
Fluorescence Studies ◽  
Methylene Groups ◽  
A Charge

Three homologs of trans-4-stilbenecarboxylic acid, viz., trans-4-stilbeneacetic acid (18), β-(trans-4-stilbene)propionic acid (19), and γ-(trans-4-stilbene)butyric acid (20) were synthesized and, together with the parent trans-4-stilbenecarboxylic acid, used to obtain the corresponding [ω-(trans-4-stilbene)carboxylatoalkylpentaamminecobalt(III) complexes, [(PhCH=CHC6H4(CH2)nCOO)Co(NH3)5]2+ (1-4), where n = 0, 1, 2, or 3. Fluorescence studies suggest that an intramolecular excitation energy transfer occurs from the first excited singlet state of the ligand to the metal giving rise to a charge-transfer triplet-excited state of the complex, based on the analogy with previous work on complex 1. The efficiency of the energy transfer seems to decrease with increasing number of the methylene groups in the ligand.

The photochemistry of 3,3′,4,4′-tetramethoxy-and 4-hydroxy-3,3′,4′-trimethoxystilbene — models for stilbene chromophores in peroxide-bleached, high-yield wood pulps

1996 ◽  
Vol 74 (2) ◽  
pp. 263-275 ◽  
Author(s):  
William J. Leigh ◽  
T. Johnathan Lewis ◽  
Vincent Lin ◽  
J. Alberto Postigo
Keyword(s):  
Material Balance ◽  
Radical Cations ◽  
Ethanol Solution ◽  
High Yield ◽  
Quantum Yields ◽  
Excited Singlet ◽  
Photostationary State ◽  
Direct Irradiation ◽  
Cyclobutane Dimers ◽  
Wood Pulps

The photochemistry of the title compounds has been investigated in ethanol and tetrahydrofuran solution under aerobic and anaerobic conditions. Direct irradiation of trans-3,3′,4,4′-tetramethoxystilbene (trans-1) in deoxygenated ethanol leads to the rapid establishment of a photostationary state with the cis isomer, and the slower formation of the ethyl ether corresponding to addition of ethanol across the olefinic C=C bond and cyclobutane dimers. The same products are formed upon photolysis in the presence of oxygen under the same conditions but, in addition, two isomeric tetramethoxyphenanthrenes and 3, 4-dimethoxybenzaldehyde are formed. Photolysis of trans-1 in oxygenated tetrahydrofuran leads to the same products in different relative yields. Quantum yields for cis, trans photoisomerization, phenanthrene formation, and addition of ethanol have been determined by ferrioxalate actinometry. Direct irradiation of tran-4-hydroxy-3,3′,4′-trimethoxystilbene (trans-2) in ethanol solution also results in rapid cis–trans isomerization and the formation of (three) isomeric phenanthrene derivatives in photolyses carried out in the presence of oxygen, although the material balance is low. The various products of photolysis of trans-2 have been independently synthesized by desilylation of the products isolated from photolysis of trans-4-tert-butyldimethylsiloxy-3,3′,4′-trimethoxystilbene (trans-3) under similar conditions. Fluorescence-quenching experiments have been carried out to determine the relative rates of quenching of the excited singlet states of trans-1 and trans-2 by alcohols and oxygen. The formation of aldehydes is proposed to arise via reaction of superoxide ion with stilbene radical cations, which are formed by electron-transfer quenching of the stilbene excited singlet state by oxygen. Key words: stilbenes, lignin, photochemistry, photooxidation.

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.

Electron transfer from guanosine to the lowest triplet excited state of 4-nitroindole through hydrogen-bonded complex

2021 ◽  
Vol 408 ◽  
pp. 113106
Author(s):  
Zhao Ye ◽  
Yong Du ◽  
Xinghang Pan ◽  
Xuming Zheng ◽  
Jiadan Xue
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Triplet Excited State ◽  
Hydrogen Bonded

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

A photochemical study of the triplet excited state of pyrene-4,5-dione and pyrene-4,5,9,10-tetrone derivatives

2020 ◽  
Vol 401 ◽  
pp. 112777
Author(s):  
Rodolfo I. Teixeira ◽  
Simon J. Garden ◽  
Nanci C. de Lucas
Keyword(s):  
Excited State ◽  
Triplet Excited State

Ground- and Triplet Excited-State Properties Correlation: A Computational CASSCF/CASPT2 Approach Based on the Photodissociation of Allylsilanes

2012 ◽  
Vol 116 (5) ◽  
pp. 1425-1434 ◽  
Author(s):  
Panayiotis C. Varras ◽  
Antonios K. Zarkadis
Keyword(s):  
Excited State ◽  
Triplet Excited State
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