Non-radiative excitation energy transfer with participation of tetrapyrrolic macrocycles: Some peculiarities and relaxation pathways

In this review paper, we discuss the basic results obtained by our teams for chlorophyll and its derivatives in concentrated solutions (up to C = 2 × 10[Formula: see text] 2 × 10[Formula: see text] M) as well as multiporphyrin complexes of various structures: chemical dimers, self-assembled triads and polymeric ordered aggregates. This discussion is based on steady-state, pico/femtosecond time-resolved measurements including also site selection spectroscopy at 1.8 K. The adequacy of various theoretical models describing the mechanisms of the non-radiative relaxation pathways (the energy transfer especially) at short interchromophoric distances is substantiated. In concentrated solutions, basic processes involving excited singlet and triplet states of pigments are considered (fluorescence concentration depolarization, the directed energy transfer in conditions of inhomogeneous broadening, the distant energy transfer with participation of excited triplet molecules at powerful excitation, etc.). For porphyrin chemical dimers at intercenter distances R[Formula: see text]1.0 ÷ 1.26 nm, it is quantitatively shown, that the effective singlet-singlet energy transfer is fully described by the inductive resonance model and takes place without quantum losses. For porphyrin chemical dimers of various types, basic energy relaxation processes are considered: exchange d-[Formula: see text] effects, the exchange-resonance triplet-triplet energy transfer, and the directed energy transfer in conditions of inhomogeneous broadening. It is shown that in self-assembled porphyrin triads, the energy transfer and photoinduced charge separation are basic processes of electronic excitation energy relaxation. In polymeric-ordered aggregates of photosynthetic pigments, the incoherent “hot” migration with pair jump time of t[Formula: see text] [Formula: see text] 1 ÷ 6 ps under conditions of strong electron-phonon coupling takes place in the absence of dynamic correlation between the donor and the acceptor. Finally, we will give a short overview of related research work.