Synthesis, structures and photophysical properties of luminescent cyanoruthenate(ii) complexes with hydroxylated bipyridine and phenanthroline ligands

Abstract

Treatment of (PPh₄)₂[Ru^II(PPh₃)₂(CN)₄] (1) with bpyOH and phenOH in DMF afforded two mononuclear compounds fac-(PPh₄)[Ru^II(bpyOH)(PPh₃)(CN)₃] (2) and fac-(PPh₄)[Ru^II(phenOH)(PPh₃)(CN)₃] (3), respectively (bpyOH = 6-hydroxy-2,2′-bipyridine; phenOH = 2-hydroxy-1,10-phenanthroline). These complexes have been characterized by various spectroscopic techniques. The structures of 1 and 2 have also been determined by X-ray crystallography. Their photophysical and electrochemical properties have been investigated. Compound 3 displays intense emission with much higher quantum efficiency (Φ_em = 19.4%) in solution, compared with other related ruthenate(II) diimine complexes. In addition, their solvatochromism, pH effects, and ion perturbation have also been investigated. The different photoluminescent behaviors between these complexes and the previously reported complex [Ru^II(phen)(PPh₃)(CN)₃]⁻ suggest that the introduction of the hydroxyl group into the diimine ligand would significantly affect their emission properties. Through spectrophotometric titrations, the ground state pK_a and excited state pK_a* values, as well as the dynamic pH response ranges of these complexes have been determined. Their photophysical response towards various metal ions have also been studied.