Photochemistry of the Phenanthrene-Stilbene System. Cycloaddition and Singlet-Sensitized Isomerization

Article abstract of DOI:10.1021/ja00414a037

Photocycloaddition of phenanthrenes to stilbenes is a general and remarkably facile reaction.Two isomeric trans adducts often result with unsymmetrical phenanthrenes.The product with cis-stilbene and 9-cyanophenanthrene is the crowded cis,endo isomer.With 9-cyanophenanthrene and trans-stilbene, geometric isomerization occurs but only in a triplet process.With cis-stilbene, geometric isomerization results from the triplet, and both geometric and valence isomerizations can be induced by singlet 9-cyanophenanthrene.The reactivity of the stilbene isomers can be accounted for by an algorithm we have previously derived, as can the 20- to 30-fold enhancement of stylbenes over styrenes as a reactant in cycloaddition to phenanthrene.The possibility of singlet-sensitized valence isomerization as a mechanism for storage of solar energy is discussed.