J. Phys. Chem. 1984,88, 3337-3340 pyrrole films also develop increasing amounts of oxygen on the surface and become more wettable when the films are left standing in air.9 In contrast with the polythiophene films, these films are more seriously affected by the air and lose their electroa~tivity.~ The films when in the oxidized form are stable to ambient conditions. The oxygen content of the surface does not appear to change for films left standing in the open for several days. These films do show a small decrease in the contact angles with water (2-5O) and a small decrease in the electrical cond~ctivity.’~The stability of these films was checked for several days for the polyaniline films, several weeks for the polythiophene films, and 2 years for the polypyrrole films.I5 Conclusions
The results of this study shows that thin film coatings with comparable surface characteristics can be prepared by the gasphase plasma and electrochemical polymerization of aromatic (15) A. Diaz and B. Hall, IBM J . Res. Deuel., 27, 342 (1983).
3337
compounds. The films have similar surface energies and stoichiometry. The principle difference is the surface roughness, where the films produced in the plasma process are very much smoother. This difference, however, does not have a strong influence on the surface energies of the films. With regards to the electroactive films, the surface energy can be changed by switching the film from the neutral to the oxidized state. This change, however, is small and depends on the degree of oxidation of the polymer. A change was observed only when the polymer is significantly oxidized and the anion content in the film is in excess of 20%.
Acknowledgment. The authors acknowledge J. Tsay, A. Poenish, J. Coburn, J. Salem, W. Gill, and G. Ratchford (IPD, Charlotte) for their support and interest with the various aspects of this work. Registry No. Polypyrrole, 30604-8 1-0; poly(N-methylpyrrole), 72945-66-5; polythiophene, 25233-34-5; poly(3-methylthiophene), 84928-92-7; polyaniline, 25233-30-1; poly(o-trifluoromethylaniline), 76642-16-5; poly(m-trifluoromethylaniline), 76642-17-4; poly(3,S-bis(trifluoromethyl)aniline), 90269-60-6; polyphenol, 27073-41-2; poly(mcresol), 27289-33-4; poly(m-trifluoromethylphenol), 90269-61-7.
New Probe of Solvent Accessibility of Bound Photosensitizers. 2. Ruthenium(I I ) and Osmium( I I ) Photosensitizers in Triton X-1 00 Micelles Walter J. Dressick, B. L. Hauenstein, Jr., T. B. Gilbert, J. N. Demas,* Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901
and B. A. DeGraff* Department of Chemistry, James Madison University, Harrisonburg. Virginia 22807 (Received: July 18, 1983; In Final Form: January 15, 1984)
We report here an extension of our deuterium isotope method for determining F, the degree of solvent accessibility of bound photdsensitizers, to nonionic micelle systems. In particular we examine the nonionic surfactant Triton X- 100 with Ru(I1) and Os(I1) photosensitizers. A four-class system based on emission spectral shifts and F values is proposed for categorizing sensitizer-micelle interactions. A model based on competition between water and Triton for solvation of the complexes explains our results. Our present data, when combined with earlier NaLS results, provide a clearer picture of the relative importance of solvation as well as hydrophobic and electrostatic interactions in photosensitizer binding.
Introduction
The photochemistry and photophysics of sensitizers bound to micelles is an area of steadily increasing importance. This interest arises in part from the utilization of these systems in energy conversion schemes. Micelles are able to selectively sequester the sensitizer, quencher, and/or reaction products. Through judicious choice of micelle, it is possible to increase the quenching efficiency and inhibit the energy-degrading back-reactions in such schemes.’ A number of factors, including the sensitizer binding mode, orientation, and solvent accessibility can radically affect the chemistry and photophysics of bound photosensitizers. However, a full understanding of these micelle-substrate interactions is currently lacking. We have embarked on a systematic study of micelle-sensitizer interactions in order to more fully understand such effects and ultimately use them to optimize existing energy conversion schemes.2 Recently we described a new method for determining the degree of solvent accessibility of micelle-bound photo sensitizer^.^ The (1) For a summary of the work in this area see: (a) Gratzel, M. Acc. Chem. Res. 1981, 14, 376. (b) Turro, J. N.; Gratzel, M.; Braun, A. M. Angew. Chem., Int. Ed. Engl. 1980,19,675. (c) Kalyanasundaram, K. Chem. SOC.Reu. 1978, 7,453. (d) Schmehl, R. H.; Whitten, D. G. J . Phys. Chem. 1981, 85, 3473. (2) Demas, J. N.; DeGraff, B. A. J . A m . Chem. SOC.1980, 102, 6169. (3) Hauenstein, B. L., Jr.; Dressick, W. J.; Buell, S. L.; Demas, J. N.; DeGraff, B. A. J . A m . Chem. SOC.1983, 105,4251,
0022-3654/84/2088-3337$01 S O / O
method exploited the solvent deuterium isotope effect on excited-state lifetimes. The solvent accessibility of a series of ruthenium(I1) and osmium(I1) complexes that exhibit metal-to-ligand charge-transfer (MLCT) luminescences was examined in sodium lauryl sulfate (NaLS) micelles. The degree of shielding of the complex from water correlated well with ligand hydrophobicity. We report here the extension of our method to the nonionic surfactant Triton X-100 (TX-100) (C8Hl,Ph(OC2H4),,,0H) with ruthenium(I1) and osmium(I1) photosensitizers. TX-100 micelles differ markedly from NaLS micelles. Both electrostatic and hydrophobic interactions are important in the binding of charged photosensitizers to NaLS micelle^.^ However, TX- 100 binds primarily by nonelectrostatic interactions, and thus studies on TX- 100 micelles permit examination of hydrophobic and hydrophilic interactions isolated from micelle/sensitizer electrostatic effect^.^ This study combined with our earlier NaLS results3 provides a clearer picture of the relative importance of these interactions in photosensitizer binding. Experimental Section
The ligands and their abbreviations are as follows: 2,2’-bipyridine (bpy), 1,lO-phenanthroline (phen), 2,2’,2”-terpyridine (terpy), 5-methyl-1,lO-phenanthroline (Me-phen), 5,6-di(4) Mandal, Krisnagopal; Hauenstein, B. L., Jr.; Demas, J. N.; DeGraff, B. A. J . Phys. Chem. 1983, 87, 328.
0 1984 American Chemical Society
3338 The Journal of Physical Chemistry, Vol. 88, No. 15, 1984
Dressick et al.
TABLE I: Properties of Photosensitizers with Triton X-100 complex Ru(bPY)32+ (bPY)20s(CNMe)22+
dH(m)l"
dH(s)l"
dD(s)l"
0.563 0.533
0.894 0.903
dD(m)l" Class I 0.544 0.895 0.558 0.890
0.962 0.140
1.100 0.235
1.040 0.147
1.389 1.320 1.243 1.680 1.790 1.810 3.30 0.076 0.048 0.223 0.995
1.940 1.710 2.201 2.190 2.770 2.140 4.56 0.152 0.082 0.422 1.510
2.264' 1.850 1.882 2.780 2.660 2.220 5.070 0.094 0.057 0.271 1.110
Kn,'
X W d
hHI,,d
1.096 f 0.007 0.870 f 0.150
617.0 588.0
618.0 588.0
Class I1 1.240 0.229
1.189 f 0.120 0.844 f 0.1 50h
602.9 726.0
611.5 719.0
Cla.ss I11 2.616' 2.100 2.299 3.040 3.050 2.250 5.600 0.129 0.070 0.326 1.260
0.291 f 0.080 0.372 i 0.071 0.275 f 0.065 0.222 f 0.077 0.243 f 0.056 0.070 f 0.254'' 0.223 f 0.071 0.439 f 0.13Ih 0.214 f 0.095* 0.292 h 0.053 0.313 f 0.076
611.5 607.1 643.0 612.4 61 1.8 608.1 634.7 727.0 677.5 676.5 612.5
618.09 614.0 646.5 620.0 617.0 613.0 645.3 733.0 692.0 689.5 620.08
Fb
4806 18 300' 26 4 0 6 52 500 57 000 102 000 561 000 23 2 0 6 36 8 0 6
OLifetimes of N2 bubble degassed solutions in microseconds at 25.0 f 0.5 "C. Errors are f 2 % unless otherwise noted. Consult the text for the meaning of the expressions in the square brackets. bCalculated from eq 1 of the text. The uncertainty was calculated by using the errors listed in the lifetime measurements listed above. CValueof the equilibrium binding constant in units of L/mol. The uncertainties are f15%. The values listed here are from ref 4 unless noted. dPosition of the emission maximum in units of nanometers. The uncertainty in the emission maxima is < f 1 . 0 nm. All values have been corrected for the variation of the detector response with wavelength. Refer to the text for the meanings of the subscripts. ~ Incomplete ~ . binding ~ of the sensitizer at [TX-1001 = 100 mM was observed. fDetermined for this work by using the eCalculated values for 7 method of ref 4. gThe emission spectrum under these conditions is a broad envelope consisting of at least two bands of nearly equal intensity. Values given in the table reflect the position of the higher energy peak. The position of the shoulder is 15 f 2 nm lower in energy than this peak. hThe large uncertainty in F is due to small changes in lifetimes upon micellization and/or short lifetimes which tax the reliability of our instrument. 'Reference 17.
methyl-1,lO-phenanthroline(5,6-Me2phen), 4,7-dimethyl- 1,lOphenanthroline (4,7-Me2phen), 3,4,7,8-tetramethyl-1,10phenanthroline (Me4phen), 4,7-diphenyl-1 ,IO-phenanthroline (Ph2phen), and cis-bis( 1,2-diphenylphosphino)ethylene(DPPene). The bpy, phen, and terpy ligands were from G. F. S. Chemical Co. and were used without further purification. The phosphine ligand was used as received from Strem Chemicals, Inc. [Ru(Ph2phen),]C12 was prepared and purified by the method of Watts and C r ~ s b y . ~[Ru(bpy),]C12 was recrystallized from water. The other Ru(I1) complexes were prepared and purified by using literature methodse6 The Os(I1) complexes were prepared as described previ~usly.~TX- 100 was used as received from Sigma Chemical Co. For the solvent accessibility measurements, 100 m M TX-100 was used, which gives a micelle concentration, [MI, of >700 pM.* This TX-100 concentration ensured that >99% binding occurred for most of the complexe~.~ Sensitizer concentrations of 5-10 pM gave adequate luminescence intensity for the lifetime measurements and ensured that no multiple sensitizer occupation of the micelles o c c ~ r r e d . Solutions ~ were prepared with deionized water
distilled from alkaline KMn04 or with Aldrich Gold Label D20. The lifetime determinations were made at 25.0 f 0.5 "C by using a temperature controller described elsewhere.1° All solutions were deaerated with solvent-saturated nitrogen by using a cell described previously." Lifetime measurements were made on equipment described previously.12 Decays were exponential over at least two half-lives. The mean lifetimes, 7's, were calculated from the slope of a semilogarithmic plot of intensity vs. time by using a least-squares fit. The reported lifetimes are averages of at least three measurements that typically agreed to f2%.
Results Table I summarizes the results of our lifetime measurements. Binding constants (KDM) for many of the ruthenium(I1) complexes and corrected emission maxima for all sensitizers in aqueous (AH(s)) and 100 mM TX-100 (A,) solutions are also listed. The solvent exposure factor, F, is the fraction of the surface of the photosensitizer that is exposed to the aqueous solvent. Fs were calculated from F = (~[H(s)]-l- ~ [ D ( s ) l - ' ] / { ~ [ H ( m ) l - ' .[D(m)]-')
(5) Watts, R. J.; Crosby, G. A. J . Am. Chem. SOC.1971, 93, 3184. (6) Dressick, W. J.; Hauenstein, B. L., Jr.; Demas, J. N.; DeGraff, B. A. Inorg. Chem., 1984, 23, 1107. (7) (a) Kober, E. M.; Sullivan, B. P.; Dressick, W. J.; Caspar, J. V.; Meyer, T. J. J . Am. Chem. SOC.1980, 102, 7383. (b) Allen, G. H.; Sullivan, B. P.; Meyer, T. J. J . Chem. SOC.,Chem. Commun. 1981, 793. (8) The micelle concentration, [MI, is defined by the relation:
(1)
where T[H(s)] and T[D(s)] are the lifetimes of the complex in surfactant-free medium using either pure H 2 0 or D 2 0 as the solvent. r[H(m)] and 7[D(m)] are the lifetimes of the micellebound complex in pure H 2 0 or D 2 0 solutions, respectively. KDM's are defined by4
[MI = ([SI - ICMC)/n where [SI is the total surfactant concentration, n = 1408a" is the micelle aggregation number for Triton X-100, and ICMC is the critical micelle concentration observed in the presence of the sensitizer: All concentrations are in mol/L. For the complexes in Table I for which ICMC's have been determined, the maximum value observed is 1.61 mM for R ~ ( M e - p h e n ) ~ ~ + . For our experiments with [SI = 100 mM, these values give [MI > 700 wM. (a) Helenius, A,; Simons, K. Eiochirn. Eiophys. Acta 1975, 415, 29. (b) Kushner, L. M.; Hubbard, W. D. J . Phys. Chem. 1954, 58, 1163. (c) law, K. Y. Photochem. Photobiol. 1981, 33, 799. (d) Fendler, J. H; Fendler, E. J. "Catalysis in Micellar and Macromolecular Systems"; Academic Press: New York, 1975. (9) The occupation number of a micelle by a solute is governed by Poisson statistics for [solute]/[M] < 5.'b,8d Under our conditions [sensitizer]/[M] < 0.015 so that >99% of the micelles which bind sensitizer contain only one sensitizer molecule.
where [D] is the concentration of the unbound sensitizer, [DM] is the concentration of the micelle-bound sensitizer, and [MI is the total micelle concentration. Equation 1 assumes that the binding is sufficiently tight that DM is the dominant species. If this assumption is not correct, then one measures an F averaged over D and D M where D has (10) Buell, S . L.; Demas, J. N. Anal. Chem. 1982, 54, 1214. (11) Buell, S . L.; Demas, J. N. Reu. Sci. Instrum. 1982, 53, 1298. (12) (a) Hauenstein, B. L., Jr.; Dressick, W. J.; DeGraff, B. A,; Demas, J. N. J . Phys. Chem., in press. (b) Turley, T. J., M. S . Thesis, University of Virginia, Charlotteville, VA, 1980.
Solvent Accessibility of Bound Photosensitizers 100% exposure to water. For nonbinding complexes we would then expect F = 1. Futher, for KDM3 20000 and [MI 3 700 pM the F value obtained will be essentially independent of the sensitizer resident time in the m i ~ e l l e . ~ The complexes listed in Table I exhibit F values ranging from nearly zero to unity. With the exception of R ~ ( b p y ) , ~and + (bpy)20s(CNMe)22+,discernible shifts in the emission maxima are observed for all complexes on binding. The sensitizers may be categorized according to their F values and emission wavelength shifts, AA, on going from the surfactant free to the micellar solutions. These parameters can be used to assess the nature and extent of photosensitizer binding.
Discussion We group the complexes of Table I into three classes. Class I molecules exhibit large solvent exposures (Le., F > O S ) and negligible spectral shifts (Le., AA < 1 nm); these include Ru( b p ~ ) , ~and + (bpy),Os (CNMe)22+. Class I1 molecules exhibit large solvent exposures ( F > 0.5) and appreciable spectral shifts (AA > 1 nm); these include R ~ ( p h e n ) , ~and + (terpy)20s2+. Class I11 molecules exhibit low solvent exposures ( F < 0.5) and appreciable spectral shifts (AA > 1 nm); these include the remaining sensitizers. Class IV molecules would exhibit small solvent exposures and negligible spectral shifts. None of the current systems fall into class IV. This classification scheme is extendable to other combinations of interacting species, but the limits of F and AA may have to be adjusted for different systems. In the class I systems the negligible spectral shifts coupled with the near unity Fs indicate that the environment around these complexes is essentially pure water. These results leave little doubt that 1he class I complexes are noninteracting or weakly interacting with either the TX-100 monomer or micelles. Thus, class I systems are largely unbound. Class I1 systems exhibit some sensitizer surfactant interactions. In class I11 the small Fs indicate a large degree of shielding of the photosensitizer from the solvent by the surfactant. This, coupled with the large spectral shifts, indicates a favorable interaction between the surfactant and sensitizer. The F values of the class IV systems indicate a favorable interaction with the surfactant; however, binding does not affect the emission spectra. Class I11 and IV species would be bound to the micelles. We deal specifically with these various cases below. The two class I complexes are R ~ ( b p y ) , ~and + (bpy),Os(CNMe)22+. Both complexes contain bpy, which is less hydrophobic and more open than the phen ligands. Also, the 2+ charge of the complexes favors solvation by H 2 0 rather than TX-100. These two factors provide a reasonable explanation for the observed lack of interaction between these complexes and TX-100. We propose the following simplified model to rationalize our results for the remaining classes. Unlike the anionic NaLS micelle^,^-^^'^ binding with TX- 100 is due largely to hydrophobic interactions between the sensitizer’s ligands and the micelle since electrostatic interactions are absent. Also, TX-100 exhibits an interesting structural complexity. TX-100 micelles consist of two distinct regions. The central micelle core is relatively dry and consists of the phenyl groups and the aliphatic chain. The remainder of the micelle is a relatively wet outer sheath of partially hydrated polar ethoxy units.14 We have shown that binding of the sensitizers occurs predominantly at the interface of the dry core and the wet ethoxy region of the mi~e1le.l~ Figure 1 is a schematic representation of two limiting binding mechanisms for the sensitizers with TX-100 micelles. Path A represents a deep burial of the sensitizer in the dry hydrocarbon core of the micelle. In this model significant distortions occur and water exposure arises due to the presence of fjords and cleft-trapped solvent. Path B shows the binding of the sensitizer at the hydrocarbon-poly(ethy1ene oxide) interface. Water ex(13) Dressick, W. J.; Raney, K. W.; Demas, J. N.; DeGraff, B. A. Znorg. Chem., 1984, 23, 875. (14) Tanford, C.; Nozaki, Y . ;Rhode, M. F. J . Phys. Chem. 1977, 81, 1555. (15) Hauenstein, B. L., Jr.; Dressick, W. J.; Gilbert, T. B.; Demas, J. N.; DeGraff, B. A. J . Phys. Chem., 1984, 88, 1902.
The Journal of Physical Chemistry, VoL 88, No. 15, 1984 3339 CLEFT-TRAPPED SOLVENT----,
r\----HYDROCARBON
REGION
SOLVENT FJ ORD--
Figure 1. Schematic representation of two limiting binding modes of sensitizers to Triton micelles.
posure here is restricted and arises only from the projection of the sensitizer into the wet poly(ethy1ene oxide) region. Regardless of the details of the sensitizer -micelle structure we can make several general statements concerning the details of the water accessibility. Binding in our model involves competition between the micelle and water molecules for solvation of the sensitizer. The classification of the sensitizers according to the magnitude of the emission wavelength shift and solvent exposure in Table I reflects this competition. Binding occurs as the hydrophobic core and, to a lesser extent, the hydrated ethoxy groups interact with the polypyridyl ligands. Water associated with the solvated complex and/or the hydrated ethoxy groups of the micelle is released as binding occurs. The water may be either extruded completely from the bound complex or trapped in pockets in the micelle.I6 Molecular models indicate that solvent trapping is most likely to occur in the clefts between the ligands of the complex. Solvent trapping becomes more probable as the radius of the complex and, thus, the size of the clefts increase. The solvent accessibility parameter makes no direct statement concerning the microscopic details and the position of the sensitizer within the hydrophobic region of the micelle. Because solvent trapping is a possibility, even a deeply buried sensitizer can exhibit a large F (see Figure 1). Alternatively, a bulky sensitizer with an irregular surface might disrupt the micelle structure and create channels which permit solvent access to the sensitizer. For example, the F value of Ru(Ph2phen):+ is anomalously high relative to the much more weakly binding Ru(Me4phen)?+. This anomaly can then be explained because of the large size (1 2.5-ii radius vs. 8.6-A radius for the Me4 complex) of the Ph2phen complex.I2” A combination of trapped solvent and direct exposure to bulk or poly(ethy1ene oxide) water probably accounts for the high F. Ru(Ph,phen),,+ is a class I11 complex, as are most of the sensitizers of Table I. The low Fs coupled with the appreciable spectral shifts leave no doubt as to the close association of the bound sensitizers to the micelles. As expected, many of the complexes in this category possess hydrophobic phenanthroline or phosphine ligands conducive to favorable interactions with the micelles. (16) We do not define solvent trapping here in the sense that the water molecules are permanently trapped within a micelle-sensitizer cage. We expect that exchange can occur between water molecules at different sites located anywhere within the vicinity of the bound sensitizer. In our model, solvent exchange between the bulk solution and that area of the micelle interior at which sensitizer binding occurs is impeded (note Figure 1). The high local viscosity of the micelle near the sensitizer results in a decreased mobility of the water and inhibits exchange. Such a process also lowers the ability of substrates to reach the bound sensitizer and quench the emission.” (17) Raines, D., Snyder, S., unpublished results.
3340 The Journal of Physical Chemistry, Vol. 88, No. 15, 1984 (phen),Os(CO)Cl+ is clearly a bound class I11 species, but it + is structurally similar to the unbound class I R ~ ( b p y ) , ~and 0~(bpy),(CNMe),~+.On this basis binding is unexpected. The origins of this behavior undoubtedly lie in the reduction of the formal positive charge in this species vs. that of the class I species. The reduction in formal charge from 2+ to 1+ reduces the tendency for solvation of the complex by water while permitting the hydrophobic interactions with the micelle to predominate. This example provides a dramatic illustration of the role of charge in the competitive solvation leading to sensitizer micellization. Finally, consider the class I1 sensitizers R ~ ( p h e n ) , ~and + Os(te~py),~+. The nonzero shifts in the emission maxima indicate an interaction with the surfactant, but the F parameters show a very solvent-exposed structure. In the case of Os(terpy)?+, the interaction between the sensitizer and the TX-100 molecule is supported by a definite lifetime change between the aqueous and surfactant media. That binding should occur is somewhat surprising, since terpy closely resembles bpy in structure, and Ru(bpy),,+ is a noninteracting class I molecule. Given this fact and the dipositive charge of the complex, solvation by water is expected to predominate and binding should not occur. This seemingly contradictory behavior can be resolved if binding occurs in the wet ethoxy region of the micelle. Alternatively, binding might occur to individual TX- 100 molecules rather than to the micelles. The high F value observed for the complex is consistent with either explanation. Ru(phen),,+ is also a class I1 molecule and once again a seemingly inexplicable situation exists. The observed red shift in the emission maxima for the complex points to a binding interaction with the TX-100 micelle rather than with the individual surfactant molecules. A solvent accessibility parameter of near unity suggests the absence of such an interaction. However, using an intensity method, we have shown that Ru(phen)?+ does in fact bind weakly (KDM 200 M-I) to Triton X-lOO.'* Using this binding constant and a typical degree of solvent exposure of 1/3, we would expect an observed F value that is not corrected for the degree of binding of 0.92. This value is in reasonable agreement with the observed F. We therefore conclude that Ru(phen)32+ interacts with the Triton micelles. The apparent high degree of solvent exposure is due to our inability to drive the equilibrium substantially to the DM form rather than to a binding site which is highly exposed to water. This result points out the danger of interpreting Fs without some independent information about the binding constants.
-
(18) Dressick, W. J.; Demas, J. N.; DeGraff, B. A. J . Phofochem. 1983, 24, 45.
Dressick et al. An additional relationship is suggested by the F parameters and K D M values in Table I. For complexes containing methylsubstituted phenanthroline ligands, the solvent accessibility parameter generally decreases as the binding constant increases. Increases in K D M with an increasing proportion of methyl substitution reflect the increased hydrophobicity of the sensitizer. For these structurally related complexes, the observed decrease in F with increasing hydrophobicity of the molecule (as measured by K D M ) is indeed expected.
Conclusions Our results justify the following conclusions: (i) The deuterium isotope effect on sensitizer excited-state lifetimes is a valuable probe of sensitizer interactions with nonionic micelles. (ii) In binding to nonionic (e.g., Triton) micelles, nonelectrostatic interactions are most important. Binding is by competition between water and Triton for solvation of the complexes. Factors such as decreasing the sensitizer charge or increasing the ligand methylation, which increases sensitizer hydrophobicity, will enhance binding. (iii) For our systems an emission shift on going from water to surfactant is a necessary condition for interaction to occur. It does not guarantee binding to micelle since shifts could arise from binding to individual surfactants in a DS complex. (iv) Our F method gives no information about binding location or the exact nature of binding interaction at the sensitizer. The approach is to be coupled with an independent probe of structure or interactions. (v) Extrusion, solvent trapping, and the size of the sensitizer are all important in determining F but we cannot quantitate the relative extent of each effect. Our general model encompasses all these effects in order to explain the behavior of the complexes in Table I. Acknowledgment. We gratefully acknowledge the support of the National Science Foundation (CHE 82-06279), the Air Force Office of Scientific Research (Chemistry) (AFOSR 78-3590), and the donors of the Petroleum Research Fund, administered by the American Chemical Society. Registry No. Ru(bpy)32', 15158-62-0; (bpy)20s(CNMe)22t,818312 1-2; R ~ ( p h e n ) ~22873-66'~, 1 ; O~(terpy)~~', 85452-9 1- 1 ; R ~ ( p h e n ) ~ (4,7-Me2phen)", 90481-55-3; Ru(Me-phen)32+, 14975-39-4; (4,7Me2phen)2Ru(phen)2', 90481-56-4; R~(4,7-Me~phen)~~', 24414-00-4; R ~ ( 5 , 6 - M e ~ p h e n )14975-40-7; ~~+, R ~ ( M e ~ p h e n ) ~64894-64-0; ", Ru(Ph2phen)?', 63373-04-6; Os(phen),*', 3 1067-98-8; (bpy)20s(Co)C1', 80502-53-0; (phen)20s(CO)C1', 80502-75-6; (phen)zOs(DPPene)2', 75446-26-3; H20, 7732-18-5; Tx-100,9002-93-1; deuterium, 7782-39-0.
