Supramolecular assemblies based on porphyrin fragments are of much interest due to their photophysical, electrochemical, catalytic properties and as model compounds to mimic biological functions. In this contribution we present the results of the investigation of photoexcited properties of a supramolecular compound based on the metalloporphyrins. The study of the exchange interaction between the photoexcited porphyrin molecule in the excited triplet state and paramagnetic ions may be crucial for search of new classes of the lightcontrolling magnetic molecular systems. One of the best tools for the investigation of the exchange interactions is electron paramagnetic resonance (EPR) spectroscopy and timeresolved EPR (TREPR) is a powerful tool to study the spin-involved processes initiated by the light irradiation. The study was carried out on the mono-substituted aza-crowned copper porphyrins (CuP) that are capable of dimerization [1]. Continuous- wave EPR investigations showed that the addition of the K+ cation to a solution of monomeric aza-crowned porphyrins led to cation-induced dimerization of these porhyrins. The magnetic resonance parameters of the monomer and dimer fragments of CuP, exchange interaction parameter and Сu-Cu distance have been obtained by the comparison of the experimental EPR spectra with the numerical computations. The change of photoinduced polarizations of aza-crowned copper porphyrins after cation–induced dimerization have been investigated by TREPR spectroscopy and numerical analysis. This research was partly supported by the Russian Foundation for Basic Research (grant no. 12-03-97078) and the grant of the President of the Russian Federation for Support of Leading Scientific Schools no. NSh-5602.2012.2.