Electron Transfer Induced Deazatization of Cyclic Azo Derivatives of Quadricyclane and Norbornadiene.

The photosensitized oxidation of two cyclic azoalkane derivatives (Azo-Q, Azo-N) of quadricyclane (Q) and norbomadiene (N) has been investigated using steady-state and laser flash photolysis techniques as well as chemically induced dynamic nuclear polarization (CIDNP). Irradiation of acetonitrile solutions of 9,lO-dicyanoan- thracene (DCA), 2,6,9,1O-tetracyanoanthracene (TCA), or chloranil (Chl) in the presence of Azo-Q results in rapid and efficient deazatization to afford N. Similar irradiation of DCA, TCA, and Chl in the presence of Azo-N yields N and Q. CIDNP experiments reveal that polarized N is formed as a cage product in the Chl sensitized photolysis of Azo-Q while polarized N and Q are both formed as cage products from Azo-N. The results are consistent with competitive fragmentation of Azo-"+ to N'+ and Q+, and selective deazatization of Azo-@+ to N'+. Irradiation of 1-cyanonaphthalene in the presence of Azo-Q or Azo-N affords Q andor N in chemical yields similar to those obtained from direct and naphthalene sensitized irradiations, indicative of singlet energy transfer quenching. Bimolecular rate constants for quenching by Azo-N and Azo-Q were determined by steady-state fluorescence methods for singlet sensitizers, or by laser flash photolysis (LFP) for 3Chl*.