Photochemical reaction of 5-dicyanomethylenebicyclo[2.2.2]oct-2-ene as a model for a light-energy conversion and storage system

Upon irradiation, 5-dicyanomethylenebicyclo2.2.2]octene ($\text{3}$) gives a highly strained compound, 2,2-dicyanotricyclo4.2.1.0^1,3]nonene ($\text{6}$) in good yield. Of additional interest is the observation that the starting material $\text{3}$ can be quantitatively regenerated from the photo-product $\text{6}$ with release of 28.8 kcal/mol.