Singlet oxygen (O-2((1)Delta(g))) production and quenching in homogeneous and microheterogeneous media are reported for two anionic ruthenium(II) complexes ([RuL2L'](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-(1,10-phenanthrolin-5-yl)tetradecanamide (pta)) and for the cationic complex [Ru(bpy)(3)](2+) (bpy: 2,2'-bipyridine). Comparative results of photosensitized O-1(2) generation in micelles, reverse micelles, and microemulsions reveal that the nature of the ligands and the size and charge of the [RuL3] complexes are important factors affecting their effective location and O-1(2) production in these media. The rate constants of quenching of the excited state [RuL3]* by molecular oxygen (k(q)) are in the range of (1-3) x 10(9) M-1 s(-1). The emission lifetimes of [RuL3]* and kq 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 (Phi(Delta)) in air-equilibrated solutions between 0.30 and 0.75. The efficiency of O-1(2) formation (i.e., the fraction of triplet excited states quenched by oxygen yielding O-1(2), f(Delta)(T)) is a valuable probe of the interactions of the [RuL3] complexes with micelles and microemulsions. The highest f(Delta)(T) values (greater than or equal to0.90) were observed in micellar media based on surfactants bearing a charge opposite to that of the [RuL3] complex. In the microheterogeneous systems investigated, the most probable location of the [RuL3] sensitizers is the micellar interfacial region.