Abstract
The Ru(phen)n(bps)3-n2n-4 (n = 0−3) complexes (phen = 1,10-phenanthroline, bps = disulfonated 4,7-diphenyl-1,10-phenanthroline) were prepared to probe the hydrophobic and electrostatic interactions with cationic DTAB (n-dodecyltrimethylammonium bromide), anionic SDS (sodium dodecyl sulfate), and neutral C12E8 (n-dodecyl octaoxyethylene glycol monoether) surfactants. The measured emission maxima and lifetimes are consistent with the population of the Ru → phen MLCT (metal-to-ligand charge transfer) excited state in Ru(phen)32+ and the lower-lying Ru → bps MLCT excited state in Ru(phen)n(bps)3-n2n-4 (n = 0−2). Premicellar aggregates with oppositely charged surfactants lead to decreased overall emission intensity for all complexes. In particular, aggregates formed by Ru(bps)34- with DTAB exhibit a 22-fold decrease in emission intensity and marked changes in the electronic absorption spectrum, with a concomitant appearance of a shorter lifetime component. The photophysical characteristics of the premicellar adduct can be explained by changes in the relative energies of the emissive 3MLCT state and the 3ππ* state of the bps ligands, such that more effective deactivation of the 3MLCT through the 3ππ* state is possible. The results show that complexes possessing at least one bps ligand do not exhibit significant changes in their spectral properties upon addition of DTAB, C12E8, and SDS micelles, compared to those observed for Ru(phen)32+, interpreted as reduced interaction between bps-containing complexes and the micellized surfactants. The interactions (inferred from changes in spectral properties) between Ru(phen)32+ and the cationic DTAB system are greater than those of Ru(bps)2(phen)2- with the anionic SDS surfactant, although both complexes possess overall charge of equal magnitude. These observations can be explained in terms of the differences in the hydrophilicity of the complexes.
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