Photochemistry and DNA photocleavage by a new unsupported dirhodium(II,II) complex

Abstract

The new complex [Rh2(phen)2(CH3CN) 6](BF4)4 (1) was synthesized and characterized in solution and its crystal structure was determined. Irradiation of 1 with visible light (λirr >590 nm) in water results in the release of two equatorial CH3CN ligands, CH3CNeq, as well as in the formation of mononuclear radical Rh(II) fragments stemming from the homolytic photocleavage of the metal-metal bond. The photoproducts, identified by electrospray ionization mass spectrometry, include [Rh(phen)(CH3 CN)(OH)] + and [Rh(phen)(CH3CN)(H2O)3(BF 4)]+. The quantum yield for the photochemical transformation of 1 in H2O exceeds unity (φ550nm = 1.38) indicative of dark reactions following the initial photoprocess. DNA photocleavage was observed for 1 (λirr >590 nm), whereas the complex is unreactive in the dark. This feature makes 1 a promising photodynamic therapy agent that does not operate via the production of singlet oxygen, 1O 2. © 2013 The Author(s) Published by the Royal Society. All rights reserved.