Interaction of Sulfonated Ruthenium(II) Polypyridine Complexes with Surfactants Probed by Luminescence Spectroscopy

• Published in: Helvetica chimica acta Vol. 84; no. 9; pp. 2708 - 2730
• Main Authors: García-Fresnadillo, David, Orellana, Guillermo
• Format: Journal Article
• Language: English
• Published: Basel Verlag Helvetica Chimica Acta 19.09.2001; Wiley
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; OXYGEN; TRIS(2,2'-BIPYRIDYL)RUTHENIUM(II); FLUORESCENCE; MECHANISM; PHOTOCHEMICAL PROPERTIES; CHROMIUM(III); MICELLAR SOLUTIONS; PHOTOSENSITIZERS; ELECTRON-TRANSFER REACTIONS; METAL-COMPLEXES
• ISSN: 0018-019X; 1522-2675
• DOI: 10.1002/1522-2675(20010919)84:9<2708::AID-HLCA2708>3.0.CO;2-M

Novel anionic [RuL2L′]2− complexes, where L stands for (1,10‐phenanthroline‐4,7‐diyl)bis(benzenesulfonate) (pbbs; 3a) or (2,2′‐bipyridine)‐4,4′‐disulfonate (bpds; 3b), and L′ is N‐(1,10‐phenanthrolin‐5‐yl)tetradecanamide (pta; 2a) or N‐(1,10‐phenanthrolin‐5‐yl)acetamide (paa; 2b), were synthesized, and their interaction with the prototypical surfactants sodium dodecylsulfate (SDS), cetyl trimethyl ammonium bromide (CTAB), and Triton X‐100 (TX‐100) was investigated by electronic absorption, luminescence spectroscopy, emission‐lifetime determinations, and O2‐quenching measurements. [Ru(pbbs)2(pta)]2− (5a) displayed cooperative self‐aggregation in aqueous medium at concentrations above 1.3 μM; the observed association was enhanced in the presence of either β‐cyclodextrin or NaCl. This amphiphilic RuII compound showed the strongest interaction with all the detergents tested: nucleation of surfactant molecules around the luminescent probe was observed below their respective critical micellar concentrations. As much as a 12‐fold increase of the emission intensity and a 3‐fold rise in the lifetime were measured for 5a bound to TX‐100 micelles; the other complexes showed smaller variations. The O2‐quenching rate constants decreased up to 1/8 of their original value in H2O (e.g., for [Ru(bpds)2(pta)]2− (6a) bound to CTAB micelles). Luminescence‐lifetime experiments in H2O/D2O allowed the determination of the metal‐complex fraction exposed to solvent after binding to surfactant micelles. For instance, such exposure was as low as 25% for pta complexes⋅CTAB aggregates. The different behaviors observed were rationalized in terms of the RuII complex structure, the electrostatic/hydrophobic interactions, and the probe environment.