Time-Resolved Continuous-Wave and Pulse EPR Investigation of Photoinduced States of Zinc Porphyrin Linked with an Ethylenediamine Copper Complex

Electron spin dynamics of the photoexcited state of a new porphyrin system built of a zinc porphyrin molecule with a linked complex of copper ion (ZnPCu) was studied using electron paramagnetic resonance (EPR) methods. The time-resolved continuous-wave and echo-detected EPR data show that electron spins of the ZnPCu system are polarized. The shape of the EPR spectrum and the echo-detected nutation spectroscopy data indicate that there is a relatively small spin–spin interaction between two subunits, namely, less than the zero-field splitting parameter of the excited triplet ZnP molecule. Results have been interpreted assuming that the S = 1 Zn porphyrin subunit electron spins are polarized via the triplet mechanism and this polarization is transferred to the S = 1/2 copper subunit via a flip-flop process induced by the exchange interaction between these subunits. The formation of the integral spin polarization in the triplet–doublet system as a function of the value and type of the triplet–doublet interaction was analyzed.