Direct observation of electron spin polarization transfer in triplet–triplet energy transfer between porphyrins and fullerene in fluid solution

Time-resolved electron paramagnetic resonance (EPR) has been used to investigate electron spin polarization transfer in triplet–triplet (T–T) energy transfer between porphyrins (MOEP and MTPP; M=H2, Zn) and fullerene (C60) in toluene solution. EPR spectra of excited triplet (T1) states of both a donor (porphyrins) and an acceptor (C60) were directly observed. The induced spin polarizations of T1 C60 were found to be the same as those of T1 porphyrins. From the analyses of time-profiles of both triplet signals, it was shown that T1 polarizations of porphyrins are transferred to T1 fullerene with conservation of spin polarizations via T–T energy transfer.