Acid−Base Properties of the Ground and Excited States of Ruthenium(II) Bis(2,2‘-bipyridine) 3-Carboxyl-2,2‘-bipyridine

Abstract

Acid-base properties for ruthenium(II) bis(2,2'-bipyridine) 3-carboxyl-2,2'-bipyridine reveal a ground state pK(a) of 0.82 +/- 0.07 and an excited state pK(a) of 2.31 +/- 0.05, a 1.5 pH unit increase from the ground state. The excited state pK(a) is temperature independent while the ground state pK(a)(0) increases with temperature and has DeltaH(0) and DeltaS(0) values of -990 +/- 149 cm(-)(1) and -4.57 +/- 0.48 cm(-)(1) K(-)(1), respectively. The acidic form of the complex emits at lower energy than the basic form at both 296 and 77 K. The emission energy maxima are solvent dependent and decrease in energy when the solvent changes from 4:1 (v/v) 2-MeTHF-CH(2)Cl(2) to water and when the pH decreases. Changes in excited state lifetimes with emission energy follow the energy gap law with an intercept of 49 +/- 1 and a slope of (2.11 +/- 0.09) x 10(-)(3). Emission quantum yields for protonated and deprotonated species in 4:1 (v/v) 2-MeTHF-CH(2)Cl(2) are 0.023 +/- 0.001 and 0.110 +/- 0.002, respectively. The temperature dependence of the emission lifetimes gives energy barriers of 270 cm(-)(1) for the complex in aqueous solution at pH -0.5, and 990 cm(-)(1) in aqueous solution at pH 4.5, and 1920 cm(-)(1) in 4:1 (v/v) 2-MeTHF-CH(2)Cl(2.)

pH- and DNA-induced dual molecular light switches based on a novel ruthenium(II) complex

“…In practice, m B and m HB are often difficult or even impossible to obtain. A good approximation is to use the emission maxima for m B and m HB since protonation equilibrium is almost certainly established between the 3 MLCT states [57]. If the either protonated species or its conjugate base is nonluminescent, a further approximation can be made by employing MLCT absorption maxima for m B and m HB [55].…”

Synthesis and the Effect of a Peripheral N‐Arylcarbazole Moiety on theAcid‐Base and DNA Binding Properties of a Novel RuII Complex

“…An emission quantum yield for the complex in aerated H 2 O was determined to be 0.0497 by comparison with [Ru(bpy) 3 ] 2+ (φ std = 0.033) in aerated aqueous solution. [18,19] The MLCT emission maxima were bathochromically shifted on going from [Ru-(bpy) 2 2+ (λ em = 625 nm).…”

“…A good approximation is obtained by using the emission maxima for ν B and ν HB , since protonation equilibrium is almost certainly established between the 3 MLCT states. [18] By using the emission band maxima from both the protonated and deprotonated forms of the ruthenium complex for ν B and ν HB in Equation (7), two pK a * values of pK a1 * = 1.1 ± 0.1 and pK a2 * = 8.9 ± 0.1, were obtained. The excited state pK a * values are 0.7-0.8 pK a units more basic than the respective ground-state ones, indicating that the excited electron was delocalized on the cpipH moiety rather than on that of the bpy moiety.…”

A Fluorescent Chemosensor for Copper(II) Based on a Carboxylic Acid-functionalized Tris(2,2′-bipyridine)- ruthenium(II) Complex

“…The possible mechanisms for the pH-dependent luminescence of these complex were proposed to be proton-induced quenching. 20,21 These results show that the response behavior of Cu(II)-1 complex is pH independent in medium condition (pH 4.0 -8.0). From the view of sensitivity and response speed of sensor, pH 6.0 was chosen as optimum experimental condition.…”