Allosteric Manipulation of Photoexcited State Relaxation in (bpy)₂Ru^II(binicotinic acid)

Abstract

The emission spectrum and luminescent lifetime of (bpy) 2 Ru II (binicotinic acid) is affected by the presence of heavy metal ions in solution. As little as 1 µM Pb 2+ causes a red shift in emission, an increase in the emission quantum yield, and an increase in the room-temperature lifetime. A smaller red shift is observed in the 4,4′dicarboxy analogue in the presence of large quantities of lead; however, the emission lifetime and intensity are dimished. An X-ray determination of the ground-state geometry shows that the bipyridine rings of the binicotinic acid are twisted along the 2,2′ bond by 19.3°. The interaction between lead and the binicotinic acid complex was modeled by molecular mechanics and extended Hu ¨ckel calculations. The calculations show that interaction with lead flattens the bridged ring system of the binicotinic acid ligand, which affects the π* energy levels of the ligand, the d-orbital energies of the Ru(II), and the vibrational modes available to the substituted bipyridine ligand. The inverse energy gap law behavior observed in the binicotinic acid complex is explained in terms of an allosteric interaction between lead and the binicotinic acid complex.

Photochemical Ion Receptor Based on a Structurally Distorted Ruthenium(II) Complex Having a Crown-Ether Moiety at the 3,3′-Positions on the 2,2′-Bipyridine Ligand

“…13 On the basis of spectroscopic and X-ray crystallographic studies on an Ru(II) complex having 3,3′-R2-bpy (R = COOH), Perkovic reported that the emission quantum yield of the complex with large structural distortion became very low, as compared with that of a complex having the Oh symmetry. 6 Therefore, we think that the very low-emission quantum yield of Ru(bpy)2(CE-bpy) 2+ can be ascribed to the distorted structures of the complex as described in the preceding section.…”

“…3 As another way to incorporate a crown-ether moiety to bpy, we focused our attention on 3,3′-disubstituted-2,2′-bipyridine (3,3′-R2-bpy) and its ruthenium(II) complex. [5][6][7][8] In free 3,3′-R2-bpy, the R orient to trans with respect to one another, owing to a steric hindrance between R. When 3,3′-R2-bpy coordinates to a ruthenium ion, its structure becomes more or less distorted from octahedral (Oh) symmetry because of a steric repulsion between the Rs. 5,6 Such a circumstance in the complex brings about a non-emissive or weakly emissive property.…”

“…[5][6][7][8] In free 3,3′-R2-bpy, the R orient to trans with respect to one another, owing to a steric hindrance between R. When 3,3′-R2-bpy coordinates to a ruthenium ion, its structure becomes more or less distorted from octahedral (Oh) symmetry because of a steric repulsion between the Rs. 5,6 Such a circumstance in the complex brings about a non-emissive or weakly emissive property. In practice, Ru(II) having 3,3′-R2-bpy ligands (R = -CH3, -COOCH3, -COOC2H5, or -COOCH(CH3)2) has been demonstrated to be a very weak emitter at room temperature.…”

Differential Photoluminescent and Electrochemiluminescent Detection of Anions with a Modified Ruthenium(II)–Bipyridyl Complex

“…[39,40] These effects are much more important in the case of 3,3'-functionalized bipyridyl-Ru II complexes compared to 4,4'-functionalized analogues. [41] Indeed, steric repulsion between substituents at the 3,3'-positions of a bipyridyl ligand induces an angular twist about the carboncarbon bridge head. This angle is responsible for the disruption of the p conjugation of the bipyridyl ligand and disfavors the charge transfer between the metal center and the bipyridyl ligands.…”

“…This angle is responsible for the disruption of the p conjugation of the bipyridyl ligand and disfavors the charge transfer between the metal center and the bipyridyl ligands. [41,42] Our approach is based on the structural changes induced by the anions bonding and the resulting modification of luminescence signals. Taking into account the crucial importance of hydrogen bonding and electrostatic interactions in anion recognition, guanidinium moieties [43,44] were chosen as anion binding functions.…”