Triplet state, aromatics ethylene

Triple bond, bending, 205 Triplet, 12, 14, 180 impure, 28. 220-21, 227 Triplet energy of sensitizer, 372, 407 Triplet function, 222 Triplet state, aromatics, 76 calculation, 55 ethylene, 64... 

Response theory describes the S-T transition probabilities in unsaturated hydrocarbons quite well more than 99 % of the So - Xi transition intensity is out-of-plane polarized in agreement with experiment for aromatics in ethylene, butadiene and naphthalene the y spin-sublevel of the T state is the most active one, where y is the long in-plane axis of the molecules [134,132]. The main difference between the triplet states of aromatic and aliphatic compounds is the lack of phosphorescence for the latter. We have related this to the fact that polyenes also lack fluorescence (or have very weak fluorescence). This have been explained from the effective quenching of singlet excited (tr r ) states, which is an inherent property for the short polyenes. Our results suggest that this situation also prevails for the lowest triplet states. 

If the triplet states of 128 and 129 involve mainly single configurations with a half-occupied HOMO and a half-occupied LUMO, the pronounced regioselec-tivity may be rationalized on the basis of an interaction of the half-occupied LUMO of the aromatic moiety with the vacant LUMO of the ground-state ethylene moiety. Substitution removes the degeneracy of the benzene LUMO, and the product formed (meta or para) depends on the magnitude of the LCAO coefficients of the lower of these MOs. From Example 3.10 the MO is... 

Photoreduction of diaza-aromatics, such as DPEs, has been extensively studied by Whitten and his group [128, 130, 133, 134, 173]. It competes with fluorescence and tram - cis photoisomerization and takes place in the presence of H-atom donating solvents especially with 4,4 -DPE, its doubly protonated form (H2-DPE2+), and l,2-bis(iV-methyl-4-pyridyl)ethylene, its methylated derivative. Photoreduction probably proceeds from a low-lying planar (spectroscopically hidden) excited singlet n, n state which is evidently lower in energy than the fluorescent state. Involvement of triplet... 

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