Synthesis, characterization, electrochemical and spectroscopic studies of two new heteroleptic Ru(II) polypyridyl complexes

New [Ru(L1)(H2dcbpy)(NCS)2] [K30] and [Ru(L2)(H2dcbpy)(NCS)2] [K27] complexes were synthesized in a one-pot reaction starting from [RuCl2(p-cymene)]2, where the ligands (H2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine, L1 = 4,5-diazafluoren-9-one, and L2 = 1,10-phenanthroline-5,6-dione) are introduced sequentially. The resulting complexes were characterized by UV–vis, emission, IR, TGA, NMR, elemental analysis and cyclic voltammetry. The absorption and emission maxima of the two complexes are very similar to one another. The low-energy MLCT absorption maxima of the complexes appear at 524 nm, and the luminescence consists of a single band with a maximum at 700 and 720 nm, respectively, in DMF solution at 298 K. The electrochemical behaviors of the complexes have been studied in CH3CN by cyclic voltammetry. The LUMO energy levels of K27 and K30 were determined as −4.01 and −3.86 eV, respectively. The thermogravimetric analyses (TGA) of the prepared complexes show that the dyes are stable up to about 220 °C. Photodecompositions of the complexes in solution were studied in both ethanol and DMF solvents with a steady-state spectrofluorimeter in time-based mode. The photostability of the compounds in DMF was found to increase twice in comparison to ethanol. Fluorescence quenching experiments of the one simple derivative of PDIs (N,N′-bis(1-ethylpropyl)perylene-3,4,9,10-tetracarboxylic acid (EP-PDI)) in DMF were studied vs. increasing K27 and K30 concentrations to monitor donor/acceptor capability. The rate constants (kq) of EP-PDI for each complex, K27 and K30, were determined as 7.72 × 1012 and 6.52 × 1012 M−1 s−1, respectively. In addition, the free energies of exothermic photo-electron transfer (ET) processes between EP-PDI and complexes K27 and K30 were calculated to be −62.3 and −57.9 kcal mol−1, respectively.