Affiliation:
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
Abstract
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.