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Z. Naturforsch. 2012,
67b, 657 – 666
doi:10.5560/ZNB.2012-0103
Preparation, Characterization, and Proton-induced Fluorescence Switching of Two Ru(II) Polypyridyl Complexes containing Different N-Heterocyclic Groups
1 College of Chemistry and Chemical Engineering, Qujing Normal University, Qujing 655011, P. R. China
2 College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P. R. China
Reprint requests to Dr. Feixiang Cheng. E-mail:
chengfx2010@163.com
Received April 13, 2012 / published online July 18, 2012
Two ligands H2L1 and HL2 containing imidazole rings and piperazine or morpholine units have been prepared by the reaction of 1,10-phenanthroline-5,6-dione with 4,4'-(1,4-piperazinediyl)bisbenzaldehyde and 4-morpholinobenzaldehyde, respectively. The Ru(II) polypyridyl complexes [(bpy)2Ru(H2L1)Ru(bpy)2]4+ and [(bpy)2Ru(HL2)]2+ have been synthesized by the reaction of Ru(bpy)2Cl2 ·2H2O with ligands H2L1 and HL2, respectively. The pH effects on the UV/Vis absorption and fluorescence spectra of both complexes have been studied. The ground-state and excited-state ionization
constants of the acid-base equilibria have been calculated according to the absorbance and emission data. The photophysical properties of both complexes are strongly dependent on the solution pH. They act as proton-induced “off-on-off” fluorescence pH sensors through protonation and deprotonation of the imidazole, piperazine or morpholine groups, with a maximum on-off ratio of 6 in buffer solution at room temperature.
Key words: Ru(II) Complex, pH Switching, UV/Vis Absorption, Fluorescence