Preparation, characterization, and proton-induced fluorescence switching of two Ru(II) polypyridyl complexes containing different N-Heterocyclic groups

摘要

Two ligands H _2L ~1 and HL ~2 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(H _2L ~1)Ru(bpy) _2] ~(4+) and [(bpy) _2Ru(HL _2)] ~(2+) have been synthesized by the reaction of Ru(bpy) _2Cl2·2H2O with ligands H _2L ~1 and HL ~2, 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.