Time-Resolved and Pulse EPR Study of Conjuncted Porphyrin Trimer

The short-lived states of the photoexcited conjuncted porphyrin trimer, in which two side zinc porphyrin fragments differ from the central fragment, have been studied by time-resolved continuous-wave and pulse electron paramagnetic resonance (EPR) in X- and Q-bands. It was shown that the observed spectra are the sum of the spectra of two types of porphyrin components. This was particularly evident in the echo-detected spectra at the relatively large time delay between echo-forming microwave pulses when not all the signals were detected due to the anisotropy of phase relaxation times of porphyrin systems. The parameters of the excited triplet states were determined and it was shown that the two types of excited triplet states were characterized by the same values of the g-factors but different values of the zero-field splitting. The anisotropy of the g-tensors of triplet states was estimated from the frequency dependence of the EPR spectra.