Photophysical and electrochemical properties of new ortho-metalated complexes of rhodium(III) containing 2,2′-dipyridylketone and 2,2′-dipyridylamine. An experimental and theoretical study

Two new ortho-metalated rhodium(III) complexes of the formula [Rh(ppy)2(L)]+, ppy = 2-phenylpyridine and L = 2,2′-dipyridylketone (dpk) (1), 2,2′-dipyridylamine (HDPA) (2) have been synthesized and subjected to X-ray diffraction crystal structural, photophysical and electrochemical studies. Density functional theory calculations have also been performed to get rationalizations of the optical orbitals and redox orbitals concerning photophysical and electrochemical data. Complex 1 exhibits the triplet ligand-to-ligand charge transfer (3LLCT) [π(ppy)–π*(dpk)] phosphorescence at 77K (520 nm) and at room temperature (555 nm), while complex 2 shows triplet ligand centred (3LC) [π–π*(ppy)] phosphorescence only at 77K (460 nm). Both complexes 1 and 2 have similar irreversible oxidation potentials (+1.19 V for 1 and +1.15 V for 2vs. Fc/Fc+). These two complexes show different characteristics in the reduction process: a reversible process occurs for 1 at −1.31 V, while an irreversible process is observed for 2 at −1.85 V.