The triplet potential energy surface of s-trans-2,4-hexadiene. A comparison of theory and experiment

The mechanism of s-trans-2,4-hexadiene triplet interconversion has been exp lored using the B3LYP method with 6-31+G(d,p) and cc-pVTZ basis sets. Nine stationary points are located on the T-1 surface and five on the S-0 surfac e of s-trans-2,4-hexadiene. The results are consistent with experimental ob servations that indicate that the triplet-state photoisomerization of the 2 ,4-hexadiene involves the interconversion of allylmethylene triplet interme diates. Furthermore, this equilibration is predicted to proceed via readily accessible planar triplet intermediates which are nearly isoenergetic. The accessibility of planar triplet intermediates is consistent with triplet e xcitation transfer steps between the diene isomers that are responsible for the observed quantum chain process in the photoisomerization of the 2,4-he xadienes.