Non-emissive RuII Polypyridyl Complexes as Efficient and Selective Photosensitizers for the Photooxidation of Benzylamines

Five new Ru(II)polypyridyl complexes bearingN-(arylsulfonyl)-8-amidoquinolate ligands and three of their biscyclometalated Ir(III)congeners have been prepared and employed as photocatalysts (PCs) in the photooxidation of benzylamines with O-2. In particular, the new Ru(II)complexes do not exhibit photoluminescence, rather they harvest visible light efficiently and are very stable in solution under irradiation with blue light. Their non-emissive behavior has been related to the low electrochemical energy gaps and rationalized on the basis of theoretical calculations (DFT analysis) that predict low S-0 <- T(1)energy values. Moreover, the Ru(II)complexes, despite being non-emissive, display excellent activities in the selective photocatalytic transformation of benzylamines into the corresponding imines. The presence of an electron-withdrawing group (-CF3) on the arene ring of theN-(arylsulfonyl)-8-amidoquinolate ligand improves the photocatalytic activity of the corresponding photocatalyst. Furthermore, all the experimental evidence, including transient absorption spectroscopy measurements suggest that singlet oxygen is the actual oxidant. The Ir(III)analogues are considerably more photosensitive and consequently less efficient photosensitizers (PSs).