Resonance-Raman Study of Intermolecular Interaction Between Electronically Excited Copper Porphyrins and Molecular Environment in Solutions

Abstract

The study of interaction between metalloporphyrins (MeP) and environment molecules permits to make an insight into diverse dynamic processes occurring in biological species at molecular level. Of the particular interest are copper porphyrins (CuP) having as a central atom copper ion with unfilled 3d⁹ electronic shell. CuP are on the margin between nonluminescent porphyrins with 3d⁴...3d⁸ configuration of inner d-shell of the central ion and luminescent ones with the filled shell. The half-filled dx² -y² -orbital determines the high CuP’s sensitivity to the axial binding of the solvent molecules which can donate the electronic density. Such types of complexes were extensively studied, for example, the interactions between CuP and nitrogen(N) -containing molecules were considered in [1–3]. The studies revealed that CuP in N-containing solvents can form intermolecular complex both in the ground and excited electronic states. Simultaneously the lifetimes of the electronic excitations are strongly decreased comparing to the noncomplexed porphyrin, dropping to the value of 100 ps. The effect is driven by the perturbation of the porphyrin π-electronic system resulting from the axial binding of N-containing molecule by CuP. It puts the charge transfer (CT) state near the lowest triplet one thus facilitating the dramatic decrease of the ^2,4T₁ excited triplet states lifetime.