Continuous-Wave and Time-Resolved Electron Paramagnetic Resonance Study of Dimerized Aza-Crown Copper Porphyrins

The dimerization of 5-(4’-(aza-15-crown-5)-phenyl) copper porphyrin (CuP) upon the addition of the K(SCN) salt to a solution of the CuP monomer has been proven by electron paramagnetic resonance (EPR). The magnetic resonance parameters of the CuP monomer, the exchange interaction parameter, J = +0.25 cm−1, and the Cu–Cu distance of the CuP dimer have been determined by comparing the experimental continuous-wave EPR spectra with the results of the numerical calculations. The photoexcited states have been studied in the time-resolved EPR experiments. It has been shown that the time-resolved EPR spectra of the dimerized porphyrins can be presented as a sum of two components that represent the spectra derived by integrating the dataset in the time windows of 1.1–1.3 and 2.1–2.3 μs. To describe the spectrum in the time window of 2.1–2.3 μs, it is assumed that there is an essential contribution to the signal from the excited state of the supramolecule, which is formed by the interaction between the photoexcited porphyrin in the quartet state and the neighboring non-excited porphyrin in the ground state.