Synthesis and Optical Properties of Phenanthroline-Derived Schiff Base-Like Dinuclear RuII -NiII Complexes

Abstract

Two phenanthroline-derived Schiff base-like ligands with a covalently linked ruthenium(II) phosphorescent unit were synthesised and converted into bimetallic Ru^II -Ni^II complexes. The optical properties were studied to examine a possible photoluminescence quenching through a nonradiative energy-transfer upon a coordination-induced spin-state switch (CISSS) at the nickel(II) centre. Therefore, the metalloligands and the nickel(II) complexes were studied using UV/Vis absorbance, steady-state, and time-resolved emission spectroscopy in solutions of MeCN and pyridine. It is demonstrated that the nature of the bridging ligand between the ruthenium(II) donor and the nickel(II) acceptor strongly influences the photophysical behaviour upon CISSS. For the complex with a phenazine bridge, photoluminescence quenching is observed in the presence of a paramagnetic nickel(II) centre.

Keywords: Schiff bases; heterometallic complexes; luminescence; phenantroline; spin-state switch.