Protonation of the excited states of ruthenium(II) complexes containing 2,2[prime]-bipyridine, 2,2[prime]-bipyrazine, and 2,2[prime]-bipyrimidine ligands in aqueous solution

Journal Article · Thu May 13 00:00:00 EDT 1993 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100121a026· OSTI ID:6258588

Sun, H; Hoffman, M Z ^[1]

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1. Boston Univ., MA (United States)

The apparent pK[sub a]* values and the rate constants for the quenching by H[sup +] of the excited states of nine homo- and heteroleptic complexes of Ru(II) that contain bpm (2,2'-bipyrimidine), bpz (2,2-bipyrazine), and bpy (2,2'-bipyridine) as ligands were determined in aqueous solution; the excited state can be described as a one-electron reduced ligand that is coordinated to a Ru(III) center with the electron localized uniquely on the most easily reduced ligand (bpz > bpm > bpy). As is the case with the one-electron reduced bpm and bpz complexes, which exhibit pK[sub a] values in the range from 6.3 to 9.2, the excited states can be protonated, resulting in spectral shifts and marked lowering of the lifetime and emission intensity. Where luminescence from the monoprotonated excited state is observable, the lifetimes and pK[sub a]* values can be directly determined; in the other cases, estimates of the deprotonation rate constants can be made. The relationship pK[sub a]-pK[sub a]* = 4.8 is obtained from the data. Correlations with the values of E[sub red][degrees] show that protonation occurs on the uniquely reduced ligand and that the bpm and bpz ligands can be distinguished. Values of pK[sub a]* for Ru(bpz)[sub 3][sup 2+] were determined as a function of temperature; activation energies for the protonation and deprotonation reactions, as well as thermodynamic parameters, were obtained from the data. 28 refs., 7 figs., 3 tabs.

• OSTI ID: 6258588
• Journal Information: Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 97:19; ISSN JPCHAX; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400500 -- Photochemistry
AQUEOUS SOLUTIONS
COMPLEXES
DATA
DISPERSIONS
ELECTRONIC STRUCTURE
ENERGY LEVELS
EXCITED STATES
EXPERIMENTAL DATA
INFORMATION
KINETICS
LIGANDS
LUMINESCENCE
MIXTURES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
PHYSICAL PROPERTIES
REACTION KINETICS
RUTHENIUM COMPLEXES
SOLUTIONS
TEMPERATURE DEPENDENCE
THERMODYNAMIC PROPERTIES
TITRATION
TRANSITION ELEMENT COMPLEXES