Triplet-State Cis-Trans Isomerizations of a Bisstyrylcyclooctatetraene. Inefficient Processes Facilitating Observation of the Intrinsic T1-Tn Absorption Spectra of the Z,Z, E,Z, and E,E Isomers

Article abstract of DOI:10.1021/j100002a032

The mechanism for triplet-sensitized Z-E isomerizations of Z,Z-, E,Z-, and E,E-1,5-bisstyryl-3,7-dimethylcyclooctatetraene (ZZ, EZ, and EE) has been studied by quantum yield measurements and laser flash photolyses.ZZ isomerizes via EZ as a ground-state intermediate to EE with small quantum yields.At the photostationary state the isomer mixture consists of more than 99percent EE.The three E,Z isomers have different T₁-T_n absorption spectra.These results can be explained with a triplet energy surface, with local minima at geometries, in which the noncyclic double bonds are planar.The dominating decay process of ³ZZ*, ³EZ*, and ³EE*, is intersystem crossing to the corresponding ground states.Their triplet energies were estimated to be between 40 and 43 kcal/mol^-1.