1902
J. Phys. Chem. 1984, 88, 1902-1905
Interactions of Ruthenium( II ) Photosensitizers with Nonionic Surfactants: The Binding Region and Specific-Anion Effects B. L. Hauenstein, Jr., W. J. Dressick, T. B. Gilbert, J. N. Demas,* The Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901
and B. A. DeGraff* The Department of Chemistry, James Madison University, Harrisonburg, Virginia 22807 (Received: June 28, 1983; In Final Form: August 23, 1983)
Using excited-statelifetime measurements as a probe, we have studied the interactionsbetween a series of a-diimineruthenium(I1) photosensitizers and Triton X-100, Triton X-102, Triton X-165, Triton N-101, Brij-35, Brij-58, Brij-78, and Brij-99 nonionic surfactants. There is a good correlation between the hydrophobicity of the ligands of the Ru(I1) complex and the strength of the binding of the complexes to the micelles. A comparison of the Triton and Brij binding data shows that the photosensitizers are bound at or near the interface of the hydrated poly(ethy1ene oxide) region and the central hydrocarbon region of the micelles. Varying the counterion for the complex modifies the binding strength.
Introduction Increasingly, micelles and other organized media are used to control luminescence properties and photochemical reaction pathways.’ To date, most work has been done with ionic surfactants., Nonionic surfactants, however, can also substantially modify the courses of chemical reaction^.',^ Our preliminary results show that nonionic surfactants promise to profoundly affect luminescence and photochemical properties of transition-metal c~mplexes.~”However, in order to fully utilize the surfactants’ potential, a sound understanding of the binding and organization of micelle-sensitizer systems is required. In recent studies, we began a systematic examination of the photophysics and photochemistry of RuL3,+ (L = 2,2’-bipyridine, 1,lO-phenanthroline, and their derivatives) in i ~ n i c ~ ~and ,’,~ nonionic4” surfactant solutions. We developed a kinetic scheme that describes the binding and luminescence properties of RuL3,+ sensitizers to the nonionic Triton X-100 micelles. The binding strengths correlate well with the hydrophobicity of the ligand^.^ We left unanswered the important question of the binding site in the rather complex nonionic micelles. We report here a study which extended our knowledge of the interactions of transition-metal photosensitizers with nonionic surfactants. In particular, we address the question of the binding region by examining the interactions of RuL3,+ sensitizers with several neutral micelles. We have also examined in detail the effect of counterions on the strength of the surfactant-photosensitizer interaction. The use of suitable counterions is a well-established procedure for (1) (a) Fendler, J. H. Arc. Chem. Res. 1980, 13, 7. (b) Fendler, J. H. “Membrane Mimetic Chemistry”; Wiley: New York, 1982. (c) Fendler, J. H.; Fendler, E. J. “Catalysis in Micellar and Macromolecular Systems”; Academic Press: New York, 1975. (d) Fendler, J. H.; Hinze, W. J . Am. Chem. SOC.1981, 103, 5439. (2) (a) Dressick, W. J.; Raney, K. W.; Demas, J. N.; DeGraff, B. A. Inorg. Chem., in press. (b) Schmehl, R. H.; Whitten, D. G. J. Phys. Chem. 1981, 85, 3473. (c) Brugger, P. A,; Infelta, P. P.; Braun, M.; Gratzel, M. J . Am. Chem. Soc. 1981, 103, 320. (d) Nagamura, T.; Kurihara, T.; Matsuo, T.; Sumitani, M.; Yoshihara, K. J . Phys. Chem. 1982, 86, 4368. (3) For recent reviews, see: (a) Gratzel, M. Acc. Chem. Res. 1981, 14, 376. (b) Turro, N. J.; Gratzel, M ; Braun, A. M. Angew. Chem., In? Ed. Engl. 1980, 19, 675. (c) Yekta, A,; Aikawa, M.; Turro, N. J. Chem. Phys. Lett. 1979, 63, 543. (d) Kalyanasundaram, K. Chem. SOC.Rev. 1978, 4, 453. (e) Thomas, J. K. Acc. Chem. Res. 1977, 10, 133. (4) Mandal, K.; Hauenstein, B. L.; Demas, J. N.; DeGraff, B. A. J. Phys. Chem. 1983, 87, 328. (5) Dressick, W. J.; Demas, J. N.; DeGraff, B. A. J . Photochem. 1984, 24, 45. (6) Dressick, W. J.; Hauenstein, B. L.; Gilbert, T. B.; Demas, J. N.; DeGraff, B. A. J . Phys. Chem., accepted for publication. (7) Hauenstein, B. L.; Dressick, W. J.; Buell, S. L.; Demas, J. N.; DeGraff, B. A. J . Phys. Chem. SOC.1983, 105, 4251. 4251. (8) Dressick, W. J.; Hauenstein, B. L.; Demas, J. N.; DeGraff, B. A. J . Phys. Chem., in press.
0022-3654/84/2088-1902$01.50/0
TABLE I: IRuL,
TDM,
KDM(mon), and Icmc Values (X lo-,) for
I*’ Photosensitizers in Triton X-100and Triton X-102 Triton X-100
L bPY phen
Me-phen 5,6Me,phen 4,7Me,phen Me,phen Ph,phen
Triton X-102 icmc, mM __
TD >
PS -
0.56 0.96
