ELECTRON-SPIN POLARIZATION TRANSFER FROM EXCITED TRIPLET PORPHYRINS TO A NITROXIDE RADICAL VIA A SPIN-EXCHANGE MECHANISM

CIDER mechanisms in systems of excited triplet tetraphenylporphyrins (MTPP; M = H-2, Mg, Zn, Cd) and TEMPO were studied by time-resolved EPR. It was found that dominant polarizations generated on TEMPO are net emissions for H2TPP and MgTPP and net absorptions for ZnTPP and CdTPP, which are the same as the polarizations of the corresponding triplet (T-1) porphyrins. The polarizations were diminished with a spin-lattice relaxation time of TEMPO. A polarized T-1 signal of ZnTPP was observed in paraffin solution and was quenched by TEMPO. These facts clearly indicate that these polarizations are due to an electron spin polarization transfer mechanism. This is the first definitive demonstration of ESPT in triplet-doublet systems.