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Two star‐shaped tetranuclear Ru(II) complexes containing uncoordinated imidazole groups: synthesis, characterization, photophysical and pH sensing properties
Author(s) -
Cheng Feixiang,
Yu Shiwen,
He Chixian,
Ren Mingli,
Yin Hongju
Publication year - 2016
Publication title -
luminescence
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.428
H-Index - 45
eISSN - 1522-7243
pISSN - 1522-7235
DOI - 10.1002/bio.3015
Subject(s) - imidazole , chemistry , characterization (materials science) , star (game theory) , combinatorial chemistry , medicinal chemistry , stereochemistry , nanotechnology , physics , materials science , astrophysics
Abstract Tetrapodal ligands H 4 L 1 and H 4 L 2 containing imidazole groups have been synthesized by the reaction of 1,10‐phenanthroline‐5,6‐dione with 1,2,4,5‐tetrakis[(4‐formylphenoxy)methyl]benzene and 1,2,4,5‐tetrakis[(3‐formylphenoxy)methyl]benzene, respectively, in presence of NH 4 OAc. Two star‐shaped complexes [{Ru(bpy) 2 } 4 (μ 4 ‐H 4 L 1 )](PF 6 ) 8 and [{Ru(bpy) 2 } 4 (μ 4 ‐H 4 L 2 )](PF 6 ) 8 (bpy = 2,2′‐bipyridine) have been prepared by refluxing Ru(bpy) 2 Cl 2 ·2H 2 O and each ligand in ethylene glycol. The deprotonated complexes [{Ru(bpy) 2 } 4 (μ 4 ‐L 1 )](PF 6 ) 4 and [{Ru(bpy) 2 } 4 (μ 4 ‐L 2 )](PF 6 ) 4 have been obtained by the reaction of sodium methoxide with [{Ru(bpy) 2 } 4 (μ 4 ‐H 4 L 1 )](PF 6 ) 8 and [{Ru(bpy) 2 } 4 (μ 4 ‐H 4 L 2 )](PF 6 ) 8 , respectively, in methanol. The pH effects on the UV–vis light absorption and emission spectra of both complexes have been studied, and ground‐ and excited‐state ionization constants of both complexes have been derived. The photophysical properties of both complexes are strongly dependent on the solution pH. They act as proton‐induced off–on–off luminescent sensors through two successive deprotonation processes of imidazole groups, with a maximum on–off ratio of 8 in buffer solution at room temperature. Theoretical calculations for the highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LOMO) orbitals of bridging ligand are also presented for plausible explanations of the fluorescence changes. Copyright © 2015 John Wiley & Sons, Ltd.