Deactivating effect of the pyridine n,π* states on the photoreactivity of 5-[2-(pyrid-n-yl)ethenyl]oxazole (n= 2, 3 and 4)

Photocyclization of Diarylethenes: The Effect of Electron and Proton Acceptors as Additives

The effect of electron and proton acceptors on the photocyclization of diarylethenes has been studied. Without any additives, the deprotonation reaction is predominant, although other processes, including the sigmatropic shift, are not excluded. A deuterium exchange experiment has shown that a strong base (DABCO) facilitates the deprotonation reaction, thereby limiting the sigmatropic shift. In the presence of an oxidizing agent or additional sources of radicals (O₂, I₂, TEMPO), the processes of deprotonation and rearrangement (H-shift) are practically not observed, and the reaction proceeds along a radical pathway with the formation of phenanthrene or its heterocyclic analogue.

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

Adiabatic photoisomerization from ¹Z* to ¹E* has been experimentally evidenced for several styrylarenes. Its weight on the overall cis–trans photoisomerization has been found to increase upon increasing the chromophore size.