INTRAMOLECULAR BINAPHTHYL FORMATION FROM RADICAL CATIONS OF TRI-1-NAPHTHYL PHOSPHATE AND RELATED-COMPOUNDS IN PHOTOINDUCED ELECTRON-TRANSFER REACTIONS SENSITIZED BY 9,10-DICYANOANTHRACENE

The photoinduced electron transfer of tri-l-naphthyl phosphate and rel ated compounds sensitized by 9,10-dicyanoanthracene (DCA) in acetonitr ile produces 1,1'-binaphthyl and the corresponding biaryl. The quenchi ng rate constant of the DCA fluorescence is calculated to he equal to the diffusion-controlled rate constant from the Stern-Volmer analysis and the fluorescence lifetime measurement. The free energy change calc ulated from the redox potentials and excitation energy of the singlet excited DCA indicates that the quenching process occurs exergonically to give the tri-l-naphthyl phosphate radical cation and DCA radical an ion through electron transfer from tri-1-naphthyl phosphate to the sin glet excited DCA at the diffusion-controlled rate. On the basis of spe ctroscopic and kinetic studies with laser flash photolysis, pulse radi olysis, and gamma-radiolysis, the radical cation of tri-l-naphthyl pho sphate forms an intramolecular pi-dimer radical cation with face-to-fa ce interaction between the two naphthyl groups within 8 ns of the elec tron pulse. The 1,1'-binaphthyl radical cation is eliminated at the ra te constant of k(r) = 5.3 x 10(5) s(-1) from the intramolecular pi-dim er radical cation. Branching ratios of the reaction pathways are estim ated for the reactive intermediates such as the tri-l-naphthyl phospha te radical cation and its intramolecular pi-dimer radical cation from the rate constants and quantum yields. The electron-withdrawing charac ter of the P(O) group in the O-P(O)-O spacer is responsible for the el imination of the binaphthyl radical cation. The DCA-sensitized photoin duced electron-transfer reaction of the tri-l-naphthyl phosphate is co mpared with the direct photoreaction.