Sensitized luminescence in dinuclear lanthanide(iii) complexes of bridging 8-hydroxyquinoline derivatives with different electronic properties

Abstract

Three new dinuclear lanthanide(III) complexes {Eu(hfac)₃(H₂O)}₂(μ-HPhMq)₂ (2) and {Ln(hfac)₃(H₂O)}₂(μ-HMe₂NC₆H₄Mq)₂ (Ln = Eu, 3; Nd, 4) with 8-hydroxylquinoline derivatives in μ-phenol mode were synthesized and characterized, where hfac⁻ = hexafluoroacetylacetonate, HPhMq = 2-methyl-5-phenylquinolin-8-ol, and HMe₂C₆H₄Mq = 5-(4-(dimethylamino)phenyl)-2-methylquinolin-8-ol. Compared with that (400 nm) for {Eu(hfac)₃}₂(μ-HMq)₂ (1, HMq = 2-methy-8-hydroxylquinoline), the excitation wavelength for sensitized lanthanide luminescence is extended to ca. 420 nm for 2, and 500 nm for 4 by introducing a phenyl or 4-(dimethylamino)phenyl to 8-hydroxylquinoline. These dinuclear lanthanide(III) complexes exhibit distinctly fluoride-induced lanthanide(III) emission enhancement in both intensity and lifetime due to replacing coordination water molecules or formation of strong O–H⋯F hydrogen bonds with coordinated H₂O and μ-phenol, thus suppressing significantly the non-radiative O–H oscillators.