Steric effects in the photoinduced electron transfer reactions of ruthenium(II)-polypyridine complexes with 2,6-disubstituted phenolate ions

Abstract

The rate constants for the photoinduced electron transfer reactions of Ru(II)-polypyridyl complexes (k q ) with 2,6-disubstituted phenolate ions in aqueous acetonitrile are highly sensitive to change in the (Ru(NN) 3 2`) bulkiness of the ligand in as well as the phenolate ion. The decrease in value with the increase in Ru(NN) 3 2`k q the size of the ligand in and the phenolate ion is ascribed to the decrease in the electronic coupling Ru(NN) 3 2m atrix element, between the donor and acceptor with the increase in the electron transfer distance. The o H DA o, hydrophobic interaction or possible pÈp stacking between the pyridine rings of and the aryl Ru(NN) 3 2m oiety of ArO~leads to less steric e †ect.

Photoinduced Electron Transfer Reactions of Ruthenium(II) Phenanthroline Complexes with Dimethylaniline in Aqueous and Micellar Media

“…The values of solvent parameters have been collected from the literature [18,[42][43][44][45][46][47][48], and radii of the Ru(II)-complexes (I-IV) were calculated from MM3 model. The value of λ o calculated using Eq.…”

Photoluminescence electron transfer quenching of ruthenium(II)-polypyridyl complexes with biologically important phenolate ions in aqueous acetonitrile solution

“…The PET reactions of ruthenium(II)-polypyridyl complexes with several ortho-, meta-and para-substituted phenolate ions are highly influenced by the change of structure of the ligands of the complex as well as the substrates. The decrease in the quenching rate constant (k q ) value with increase in the bulkiness of the ligand as well as the quencher has been explained in terms of an increase in the electron transfer distance [12][13][14][15]. The rate of ET from a donor molecule to an acceptor in a solvent is controlled by several factors and the most important of them are the free energy change (ΔG 0 ) of the reaction, the reorganization energy (λ) and the electron transfer distance (d) between the donor and acceptor [12][13][14][15]34].…”

“…Many efforts have been made in recent years to design and synthesize molecules to mimic the important light-driven process, photosystem II [27][28][29]. Realizing the importance of Ru(II)-polypyridyl complexes as model photosensitizers and phenols as electron donors in photosystem II, several researchers have investigated the photoinduced electron transfer (PET) reactions of ruthenium(II)-polypyridyl complexes with several phenols in homogeneous medium and the formation of phenoxyl radical as the transient has been established using time-resolved techniques [12][13][14][15][30][31][32][33][34]. The PET reactions of ruthenium(II)-polypyridyl complexes with several ortho-, meta-and para-substituted phenolate ions are highly influenced by the change of structure of the ligands of the complex as well as the substrates.…”

“…The generation of phenoxyl radical involves either H-atom or electron abstraction from phenol and phenolate ion, respectively. The study of the kinetic and thermodynamic aspects of electron transfer (ET) to generate phenoxyl radicals bearing bulky groups in the ortho-and para-positions may help to understand the different biological roles of phenols [12][13][14][15].The oxidation potential of a polyphenol provides an estimate of the energy required to donate an electron; the lower the oxidation potential, lesser the energy required to donate an electron, hence it undergoes oxidation easily. The mechanism of oxidation of polyphenols and their stability in solution depend on pH [16,17].…”

“…The generation of phenoxyl radical involves either H-atom or electron abstraction from phenol and phenolate ion, respectively. The study of the kinetic and thermodynamic aspects of electron transfer (ET) to generate phenoxyl radicals bearing bulky groups in the ortho-and para-positions may help to understand the different biological roles of phenols [12][13][14][15].…”