title: Photophysical properties of ruthenium bipyridine (4-carboxylic acid-4'-methyl-2,2'-bipyridine) complexes and their acid-base chemistry.
abstract: Photophysical properties such as absorption and emission spectra, lifetimes, and redox potentials of eight ruthenium complexes, Ru(LL)2(MebpyCOOH)2+, where LL represents bpy, phen, Me2bpy, Me4bpy, (MeO)2bpy, (EtO)2bpy, Cl2bpy, and NO2phen, have been measured. The acid dissociation constants of ground and excited states have been determined. The ground-state pKa values were obtained from the pH dependence of the complex absorbance changes. The excited-state pKa* values were extracted from the emission titration curve and corrected for the excited-state lifetime of both protonated and deprotonated species. The largest DeltapKa, pKa*-pKa, found for Ru(Me2bpy)2(MebpyCOOH)2+ and Ru(Me4bpy)2(MebpyCOOH)2+ of 1.7 indicate that MebpyCOOH gains most of the MLCT excited-state electron. The big negative DeltapKa found for Ru(Cl2bpy)2(MebpyCOOH)2+, -4.2, clearly indicates the metal-to-ligand charge transfer to the Cl2bpy ligands.
authors.affiliation: Department of Chemistry, National Taiwan Normal University, 88 Tingchow Road, Section 4, Taipei 11677, Taiwan.
authors.forename: Chien-Hua
authors.initials: CH
authors.lastname: Su
authors.forename: Hsuan-Ying
authors.initials: HY
authors.lastname: Chen
authors.forename: Kelvin Yun-Da
authors.initials: KY
authors.lastname: Tsai
authors.forename: I-Jy
authors.initials: IJ
authors.lastname: Chang