Homolytic versus heterolytic cleavage for the photochemistry of 1-naphthylmethyl derivatives

1985 ◽  
Vol 63 (11) ◽  
pp. 3140-3146 ◽  
Author(s):  
B. Arnold ◽  
L. Donald ◽  
A. Jurgens ◽  
J. A. Pincock
Keyword(s):  
Excited Singlet ◽  
Triplet Energy ◽  
Heterolytic Cleavage ◽  
Exciplex Formation ◽  
Singlet States ◽  
Leaving Group ◽  
Excited Singlet States ◽  
Leaving Groups ◽  
Triplet Energy Transfer ◽  
Photochemical Cleavage

The photochemical cleavage of the 1-naphthylmethyl derivatives, 1–7, has been examined in methanol solvent under both direct and sensitized conditions. The competitition between homolytic and heterolytic cleavage as a function of multiplicity and leaving group has been studied in detail. Only substrates 1, 2, 3, and 7 react on sensitization with xanthone but evidence is presented that the resulting reactivity of 1, 2, and 3 may not be triplet energy transfer but rather exciplex formation. A semi-quantitative scale for photofugacities of the leaving groups from the excited singlet states has been established.

The photochemistry of indenyl alcohols and esters: Substituent effects on the competition between ion- and radical-derived products

2003 ◽  
Vol 81 (10) ◽  
pp. 1083-1095 ◽  
Author(s):  
J A Pincock ◽  
I S Young
Keyword(s):  
Excited State ◽  
Ground State ◽  
Fluorescence Emission ◽  
Substituent Effects ◽  
Sharp Contrast ◽  
Carboxylate Anion ◽  
Excited Singlet ◽  
Heterolytic Cleavage ◽  
Singlet States ◽  
Excited Singlet States

The photochemistry of the indenyl acetates 1 and pivalates 2, substituted with X = H, 5-CH3O, and 6-CH3O, have been examined in both methanol and cyclohexane. The precursor alcohols 3 were also found to be photoreactive. Although only radical-derived products were obtained in cyclohexane, both ion- and radical-derived products were formed in methanol. The absence of significant fluorescence emission from any of the substrates 1, 2, and 3 indicates that the excited singlet states are highly reactive. A mechanism is proposed for the ion-derived products that proceeds through direct heterolytic cleavage to give an indenyl cation – carboxylate anion pair. The indenyl cations generated are anti-aromatic in the ground state and their efficient generation by this photochemical solvolysis is in sharp contrast to the very low reactivity of related ground-state substrates. For the pivalate esters 2, an excited-state migratory decarboxylation is proposed for the formation of tert-butyl derived products.Key words: ester photochemistry, indenyl cations, indenyl radicals.

Quasiparticle Excitations in Polyenes and Polyacetylene

1987 ◽  
Vol 109 ◽  
Author(s):  
Paul Tavan ◽  
Klaus Schulten
Keyword(s):  
Dispersion Relations ◽  
Excited Singlet ◽  
Quasi Particle ◽  
Double Excitation ◽  
Singlet States ◽  
Excited Singlet States ◽  
Electron Excitations ◽  
Quasiparticle Excitations

ABSTRACTWe apply the Pariser-Parr-Pople Hamiltonian to study many-electron excitations in polyenes and polyacetylene. The excited singlet states of polyenes, calculated by a multireference double excitation expansion, are classified as quasi-particle excitations, namely as triplet-triplet magnons and particle-hole excitons. From finite polyene spectra we derive approximate dispersion relations for these quasi-particles in the infinite polyene, i.e. polyacetylene.

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