Synthesis and photophysical studies of triazine-linked porphyrin–perylene bisimide dyad with long-lived perylene triplet state

• Porphyrin–perylene bisimide dyad linked with a triazine group was synthesized and characterized.
• Photoinduced energy electron transfer from excited perylene moiety to the porphyrin moiety caused a decrease of perylene fluorescence emission.
• Charge-separated state formed due to photoinduced intramolecular electron transfer.
• A triplet–triplet energy transfer from the porphyrin to the perylene moiety resulted in a long-lived perylene triplet state.

Porphyrin–perylene bisimide dyad containing a triazine group as the linker was synthesized and characterized. The absorption spectra reveal that there is no appreciable interaction between the ground-state porphyrin and ground-state perylene. The fluorescence spectra illustrate that photoinduced energy transfer takes place from the excited perylene to ground-state porphyrin moiety when excited at 491 nm, while enhanced photoinduced electron transfer occurs from the porphyrin singlets to ground-state perylene moiety in the case of excitation at 423 nm. The kinetic analysis indicates that a long-lived perylene triplet state (146 μs) forms via triplet–triplet energy transfer from the porphyrin to perylene moiety, showing potential applications in the photodynamic therapy. These photochemical events are explained with an energy-level diagram.