Light harvesting a gold porphyrin-zinc phthalocyanine supramolecular donor-acceptor dyad

We reported herein the spectroscopic, electrochemical and laser photolysis studies for the newly constructed light harvesting supramolecular dyad composed of gold porphyrin (AuPpy), as an electron acceptor, and zinc phthalocyanine (ZnPc), as an electron donor, to mimic the reaction centre in the photosynthetic system. For this, gold porphyrin has been functionalized by pyridine units, which axially coordinated with zinc phthalocyanine to form the stable supramolecular AuPpy:ZnPc with a rate of 2.94 × 10⁴ M⁻¹. Steady-state fluorescence measurements showed significant quenching of the singlet excited ZnPc emission with addition of AuPpy, suggesting an electron transfer from the singlet excited ZnPc to AuPpy. The electron transfer character was confirmed by recoding the characteristic absorption band of the zinc phthalocyanine radical cation in the NIR region by a femtosecond laser photolysis technique. The findings that the AuPpy:ZnPc supramolecular dyad exhibits relatively long-lived radical-ion pairs and absorbs light in a wide range of the solar spectrum suggest that it would be useful as a photosynthetic reaction centre.