ELECTRON-TRANSFER QUENCHING OF C-60 TRIPLETS - AN FT-EPR STUDY OF C-60-TCNE IN BENZONITRILE

A Fourier transform EPR study was made of photoinduced processes in a benzonitrile solution of C-60 and tetracyanoethylene (TCNE). It was fo und that TCNE reduces the tripIet lifetime of C-60 as had been found e arlier in a flash photolysis study. However, the experimental data sho w that this is not due to encounters between TCNE and C-3(60), but rat her stems from the presence of a trace amount of the anion radical TCN E(-). Encounters between doublet radicals and triplets can result in r eductive quenching of the tripIet, thereby causing a reversible reduct ion in, TCNE(-) concentration. Alternatively, the encounters can be no n-reactive and generate spin polarization in the paramagnetic molecule s. In the FT-EPR spectrum of TCNE(-) the spin polarization causes tran sient intensity enhancements for some of the hyperfine lines and inten sity reductions for the others. The measurements show no evidence of o xidative quenching of C-3(60).