Photocycloaddition des hydrocarbures aromatiques polynucleaires en solution—iv: Etude de la fluorescence et de la photoreactivite de l'acenaphtylene et du cyano-1 acenaphtylene

The fluorescence of acenaphthylene follows a Stern-Volmer relationship in air-saturated ether giving a self-quenching constant K_F=0.12M^?1, indicating that the syn photodimer originates from the singlet state of acenaphthylene. By comparison, 1-cyanoacenaphthylene undergoes a more efficient self-quenching (K_F= 2.8 M^?1) in air-saturated ether. No excimer fluorescence was detected for 1-cyanoacenaphthylene nor the parent compound in solution. The triplet state of 1-cyanoacenaphthylene, obtained by sensitization or induced by heavy atom solvent (EtI), was shown to generate exclusively the head-to-head anti photodimer in a high chemical yield. Regiospecificity and stereospecificity observed in this reaction indicates the influence of the acenaphthylenic ring and the cyano group in stabilizing the diradicaloïd transition state.