Interactions of ruthenium(II) photosensitizers with surfactant media
The Journal of Physical Chemistry
Luminescent tris(a-diimine)ruthenium(II) photosensitizers exhibit complex emission intensity and lifetime curves when titrated with surfactants. The curve shapes depend on the charges and hydrophobicities of the complexes and surfactant. A simple model has been developed that accurately describes the interactions with anionic sodium dodecyl sulfate, nonionic Triton X-100, and cationic cetyltrimethylammonium bromide. The model includes binding of the sensitizer to micelles and may also require
... rmation of small premicellar aggregates. The strength of binding can be attributed to a combination of electrostatic attractions or repulsions and hydrophobic effects. Electrostatic attraction of oppositely charged species always yields tight binding. However, complexes with sufficiently hydrophobic ligands (Le., 4,7-diphenyl-l, 10-phenanthroline) can overcome electrostatic repulsions and bind to like-charged micelles. Binding of metal complexes to premicellar surfactant aggregates is normally stabilized by electrostatic interactions, and optimum aggregate size is close to the number required for charge neutralization. Results of this study can be used in the design of luminescent probes for specific microheterogeneous environments. Ruthenium(I1) complexes with cyano ligands are especially sensitive probes of local environment and show potential as luminescent probes for the rapid determination of critical micelle concentrations for anionic surfactants.