The Mechanism for Hydrogen Abstraction by n,π* Excited Singlet States: Evidence for Thermal Activation and Deactivation through a Conical Intersection

A conical intersection along the reaction coordinate of hydrogen abstraction by molecules in n,π* excited singlet states is responsible for the solvent-induced fluorescence quenching of azoalkanes [see equation]. This novel photochemical reaction mechanism, a case of aborted hydrogen abstraction, was examined by experiment and theory. Mutually consistent results on the observed low activation energies and the deuterium isotope effects were obtained.