Singlet-triplet transitions polyenes, intensities

III- D Comparison of singlet-triplet transition intensities in polyenes. . ... 

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. 

---