A fully conjugated imidazole-fused perylene phenantroline ruthenium(II) complex in photocatalytic oxidation

In this investigation, the suitability of a specially designed imidazole-fused perylene ruthenium(II) molecule, denoted as Ru-PhP, was explored by employing the photooxidation of 1,5-dihydroxynaphthalene (DHN) to produce Juglone as a model reaction. This distinctive, entirely conjugated compound was synthesized through the reaction between perylene imide anhydride dye (1) and a ruthenium(II) phenanthroline complex (2) in the presence of a Zn(OAc)2 catalyst. Structural analyses of the compound were performed by using general spectroscopic methods including FT-IR, 1H NMR, 13C-NMR, and MALDI-TOF analyses. Various photophysical properties, including the UV-Vis absorption spectrum, fluorescence emission spectrum, and fluorescence quantum yield, were examined. The photochemical studies via indirect method endorsed Ru-PhP as an efficient photosensitizer. Furthermore, Ru-PhP proved to be highly effective in facilitating the photooxidation of DHN to yield juglone. DFT-based natural bond orbital analysis revealed intramolecular charge transfer in Ru(II) coordination environment, with a strong total stabilization energy (25.31 eV) between the ruthenium acceptor and nitrogen donors in the bipyridine and phenanthroline units. The dispersion of HOMO electrons within the imidazole-bridged perylene moiety and the localization of LUMO electrons near Ru(II)-coordinated bipyridine units were observed through Frontier Molecular Orbital and molecular electrostatic potential analyses. Ru-PhP is proposed as photocatalyst for photo redox catalytic organic reactions.