Elsinochrome A (EA) is one of the important perylenequinonoid photosensitizers (PQPs); however, its photophysical and photochemical properties were given less attention in comparsion with other PQPs. In view of the successful use of quantum chemical methods, especially time-dependent density functional theory (TD-DFT), in investigating the photo-physicochemical characters of various photosensitizers, we attempt to explore the photophysical and photosensitive properties of EA by theoretical methods. Firstly, the absorption spectra and lowest-lying T₁ excitation energy of EA were estimated by TD-DFT calculations. Then, the photosensitizing mechanisms of EA were explored. It was found that EA can photo-generate ¹O₂ through energy transfer in both benzene and DMSO. However, EA gives birth to O₂^.- only in DMSO, and it is E_A^.- generated from autoionization reactions that is responsible for the O₂^.--generation, which gains some deeper insights into the photosensitive behaviors of EA.

Key words: Elsinochrome A; Photosensitizing mechanisms; Reactive oxygen species; Time-dependent density functional theory.