Intramolecular charge transfer excitation of meso-tetrakis (1-pyrenyl) porphyrinato gold(III) acetate. Photosensitized oxidation of guanine

The novel cationic gold porphyrin complex [(TPYRP)AuIII]+CH3COO− with TPYRP = dianion of 5,10,15,20-tetrakis(1-pyrenyl)porphyrin was prepared and characterized by optical spectroscopy and high-resolution electrospray mass spectrometry. In addition to metalloporphyrin intraligand transitions, the compound shows charge transfer (CT) absorptions in the visible spectral region that are sensitive to variations of the solvent polarity. The photoreactivity of an intramolecular charge separated state of the photosensitizer populated by CT excitation was investigated in the presence of dioxygen and an excess of the purine nucleobase guanine. A photocatalytic oxidative degradation of guanine with a quantum yield of 0.03±0.01 and an initial turnover frequency of 66 per hour was observed upon irradiation with monochromatic visible light at 298 K. The potential of the cationic metallointercalator complex [(TPYRP)AuIII]+ to serve as a catalytic photonuclease for the sequence specific cleavage of DNA has been demonstrated.