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

The novel cationic gold porphyrin complex [(TPYRP)Au-III](+) CH3COO- with T PYRP = dianion of 5,10,1 5,20-tetrakis(1-pyrenyl)porphyrin was prepared and characterized by optical spectroscopy and high-resolution electrospray mas s spectrometry. In addition to metalloporphyrin intraligand transitions, th e compound shows charge transfer (CT) absorptions in the visible spectral r egion that are sensitive to variations of the solvent polarity. The photore activity of an intramolecular charge separated state of the photosensitizer populated by CT excitation was investigated in the presence of dioxygen an d an excess of the purine nucleobase guanine. A photocatalytic oxidative de gradation of guanine with a quantum yield of 0.03 +/- 0.01 and an initial t urnover frequency of 66 per hour was observed upon irradiation with monochr omatic visible light at 298 K. The potential of the cationic metallointerca lator complex [(TPYRP)Au-III](+) to serve as a catalytic photonuclease for the sequence specific cleavage of DNA has been demonstrated. (C) 2001 Elsev ier Science B.V. All rights reserved.