Singlet Oxygen (¹Δ_g) Production by Ruthenium(II) Complexes in Microheterogeneous Systems

Abstract

Singlet oxygen (O 2 ( 1 ∆ g )) production and quenching in homogeneous and microheterogeneous media are reported for two anionic ruthenium(II) complexes ([RuL 2 L′] 2-(where L stands for (1,10-phenanthroline-4,7-diyl)bis-(benzenesulfonate) (pbbs) and L′ stands for N- (1,10-phenanthrolin-5-yl)acetamide (paa) or N-(1,10phenanthrolin-5-yl)tetradecanamide (pta)) and for the cationic complex [Ru(bpy) 3 ] 2+ (bpy: 2,2′-bipyridine). Comparative results of photosensitized 1 O 2 generation in micelles, reverse micelles, and microemulsions reveal that the nature of the ligands and the size and charge of the [RuL 3 ] complexes are important factors affecting their effective location and 1 O 2 production in these media. The rate constants of quenching of the excited state [RuL 3 ]* by molecular oxygen (k q ) are in the range of (1-3) × 10 9 M -1 s -1 . The emission lifetimes of [RuL 3 ]* and k q values depend on the nature of the ligand and on the medium. The complexes are stable singlet oxygen sensitizers, with quantum yields of singlet oxygen production (Φ ∆ ) in air-equilibrated solutions between 0.30 and 0.75. The efficiency of 1 O 2 formation (i.e., the fraction of triplet excited states quenched by oxygen yielding 1 O 2 , f ∆ T ) is a valuable probe of the interactions of the [RuL 3 ] complexes with micelles and microemulsions. The highest f ∆ T values (g0.90) were observed in micellar media based on surfactants bearing a charge opposite to that of the [RuL 3 ] complex. In the microheterogeneous systems investigated, the most probable location of the [RuL 3 ] sensitizers is the micellar interfacial region.

Singlet Oxygen in Microporous Silica Xerogel: Quantum Yield and Oxidation at the Gas–Solid Interface

“…(2) and (4)], as well as for changes in incident photon fluxes and in absorbances at the excitation wavelengths. In our case, the F D of the reference sensitizer (PN) is practically not affected by the medium, [30] in contrast to [Ru-A C H T U N G T R E N N U N G (bpy) 3 ] 2 + , [35] is much higher than that of [RuA C H T U N G T R E N N U N G (bpy) 3 ] 2 + , and all sensitizers were included in the monoliths. Therefore, errors and corrections were minimized.…”

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

“…Some recent reports concentrate on the luminescence quenching of Ru(II) complexes with 1,1′-diheptyl-4,4′-viologen [52] and oxygen [11] and dyes with DMA [53] in microheterogeneous medium. These studies indicate the role of the nature of the ligand and the size and the charge of the Ru(II)-complexes as important factors affecting the rate of luminescence quenching by electron transfer in microheterogeneous medium.…”

“…It is thus interesting to investigate ET processes in organized media to understand how the confined geometry controls the mechanism and dynamics of such reactions. The photophysics and photochemistry of ruthenium(II)-polypyridyl complexes are highly influenced by the change of solvent as well as the change of medium from homogenous to microheterogenous [6][7][8][9][10][11][12].…”

“…Davies et al studied the effects of micellar solution on the electron transfer reaction between [Co(terpyr)] 2+ and a series of Co(III)-complexes in varying ligand structure and ionic charge redox reactions of amphiphilic cobalt complexes [23]. Gutiérrez et al investigated the generation of singlet oxygen and quenching process in microheterogeneous media and reported that the nature of the ligands and the size and charge of the Ru(II) complexes are important factors affecting their effective location and singlet oxygen production in these media [11]. Though a few reports on photoinduced intermolecular electron transfer in micelles are available the systematic study with varying charge and hydrophobicity is relatively limited.…”

Static Quenching of Ruthenium(II)-Polypyridyl Complexes by Gallic Acid and Quercetin in Aqueous and Micellar Media

“…The presence of hydrophobic groups like alkyl or aryl in the 4,4'-position of 2,2'-bipyridine ligands leads to strong binding of [Ru(NN) 3 ] 2+ with micelles through hydrophobic and electrostatic interactions, the strength of binding depends on the combination of electrostatic attractions or repulsions and hydrophobic effects [9][10][11]. Many researchers have attempted a systematic investigation of binding, partitioning and photosensitization of these [Ru(NN) 3 ] 2+ complexes in both ionic and nonionic surfactant media [9][10][11][12][13][14]. In micellar solutions, reactions can be either accelerated or decelerated compared to the reactions in aqueous solutions without added co-solutes [15].…”