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

Abstract

The new complex [Rh 2 (phen) 2 (CH 3 CN) 6 ](BF 4 ) 4 ( 1 ) was synthesized and characterized in solution and its crystal structure was determined. Irradiation of 1 with visible light ( λ irr >590 nm) in water results in the release of two equatorial CH 3 CN ligands, CH 3 CN eq , 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)(CH 3 CN)(OH)] + and [Rh(phen)(CH 3 CN)(H 2 O) 3 (BF 4 )] + . The quantum yield for the photochemical transformation of 1 in H 2 O exceeds unity ( Φ 550 nm =1.38) indicative of dark reactions following the initial photoprocess. DNA photocleavage was observed for 1 ( λ irr >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, 1 O 2 .