Effect of the size of polycyclic aryl groups on the competition between adiabatic/diabatic photoisomerization mechanisms of cis-styrylarenes.

The occurrence of adiabatic photoisomerization in the singlet manifold directly from Z* to E* has been found to be more common than expected. This mechanism has been experimentally evidenced through a detailed fluorimetric study for a large series of styrylarenes. Its weight on the overall cis-trans photoisomerization has been determined and found to increase when increasing the size of the polycyclic chromophore.