[[alternative]]Photopysical Properties Of Ruthenium(Ⅱ) Polypyridyl Complexes

[[abstract]]Ruthenium(II) tris(dipyridyl) complexes have been synthesized. By varying the electron-withdrawing and electron-donating abilities on each bipyridyl ligand, we have made six complexes that contain 4-carboxyl-3,3’4,’-trimethy,2’-bipyridine. These complexes are [Ru(tmbpy)2(tmcbpy)] 2+, [Ru(dmbpy)2(tmcbpy)] 2+, [Ru(phen)2(tmcbpy)] 2+, [Ru(dabpy)2(tmcbpy)] 2+, [Ru(dpphen)2(tmcbpy)] 2+, [Ru(phenNO2)2(tmcbpy)] 2+. The ground-state acid dissociation constant (pKa) were obtained from the titration curve of absorption changes. The excited-state acid dissociation constant (pKa*) were obtained from the luminescence titration curve and lifetime calibration. A positive ΔpKa (ΔpKa = pKa* - pKa) indicates the electron density of the bipyridine that contains the carboxyl group has a higher electron density in the excited state than the ground state. A negative ΔpKa indicates the carboxyl containing bipyridine has less electron density in the excited state. From the acid dissociation constant studies, the electron density in the excited state of Ruthenium(II) tris(dipyridyl) complexes can be qualitatively mapped. The experiment data forΔpKa are 1.77, 0.79, 0.64, 0.62, and -0.84 for [Ru(tmbpy)2(tmcbpy)] 2+, [Ru(dmbpy)2(tmcbpy)] 2+,[Ru(phen)2(tmcbpy)] 2+, [Ru(dabpy)2(tmcbpy)] 2+, [Ru(dpphen)2(tmcbpy)] 2+,respectively. The results indicate that if it is desired to have higher electron density in the excited state on the carboxyl containing bipyridine, [Ru(tmbpy)2(tmcbpy)] 2+ is the best choise. On the other hand, if carboxyl containing bipyridine is designated to have less electron density in the excited state , [Ru(dpphen)2(tmcbpy)] 2+ is the best candidate.