2218
J. Phys. Chem. 1981, 85, 2218-2222
VIIIb) are slightly different because a nontetrahedral geometry has been used for propyne. (v) For methyl H atoms, To simplify we report only the x x elements of the tensors:
g) ,os +
dak)
a0;in
io(
~ p k ~ p k -) ,os2 a0 Po apkj
d@~l
POCH
Also in this case the tensors are formally equal for the two molecules, as required by the experimental values, and different numerical values in Table VIIIb must be ascribed to geometry. 7. Conclusions This study seems to confirm the validity of a bond ap-
proach in the study of infrared intensities of molecules containing equal groups of atoms. The satisfactory fittiqg of the observed data with a very small number of electrooptical parameters is very encouraging in the field of intensities studies. The calculated eop’s fit very well aslo the experimental polar tensors. Bop’s are also able to account for some differences between the experimental values of polar tensors referring to equivalent atoms in different molecules; this difference is due to contributions to the polar tensors by neighboring atoms. A comparison of some properties (geometrical, dynamical, and electrical) of C-H bonds in a different surrounding suggests that the eop’s are exactly transferable when the bond is the same (same strength, same length); otherwise, the eop’s change with a trend which can be easily correlated to changes of atomic distances and of stretching force constants.
Pressure Effects on the Hydrolysis of p-Nitrophenyl Esters Catalyzed by Cetyltrimethylammonlum Bromide Micelle’ Yoshihiro Taniguchi, Syoichi Makimoto, and Keiro Suruki Depattment of Chemistry, Faculty of Sclence and Engineerlng, Ritsumeikan University, Klta-ku, Kyoto, 603, Japan (Received: December 8, 1980; In Final Form: April 8, 1981)
The rates of the hydrolysis of p-nitrophenyl acetate (PNPA), propionate (PNPP), butyrate (PNPB), valerate (PNPV), and hexanoate (PNPH), catalyzed by the cetyltrimethylammonium bromide (CTAB) micelle, were measured at pressures up to 2 kbar at 25 “C and pH 8.3 in 0.05 M Tris buffer solution. Both the ester binding constant K and the rate constant of the product formation k , increased with longer alkyl chains of esters at 1 bar. The k , values were separated into the contributions of koH (hydroxide ion-catalyzed hydrolysis) and kT (Tris-catalyzed hydrolysis), which increased monotonically up to 2 kbar. But the K value decreased with increasing pressure and reached a minimum at a pressure between 1 and 1.6 kbar except for PNPA. From the pressure dependence of K , the volume change, AV, accompanying the ester binding to the CTAB micelle at 1 bar was calculated to be in the range of 0 f 2 cm3/mol for PNPA to 18 f 2 cm3/mol for PNPH. The activation volumes for the process of the product formation are -6 f 2 cm3/mol for AVOH*and -19 f 2 cm3/mol for AVT*for each ester in the micellar hydrolysis. The activation volumes for the spontaneous hydrolysis were -3 f 1 c ~ ~ / mfor o l AVO,* and -18 f 1 cm3/mol for AVT* for each ester. The results of the volume changes accompanying the formation of the micelle-substrate (MS) complex were correlated with the magnitude of the hydrophobic interaction between esters and CTAB micelles. The activation volumes of the hydroxide ion-catalyzed hydrolysis in micelles was explained by the bimolecular reaction between ester and hydroxide ion in the hydrophobic atmosphere of the micelle.
Introduction The rate of hydrolysis of esters is recognized to be markedly accelerated above the critical micelle concentration ( ~ m c ) . ~Such a an accelerating effect is explained by the incorporation of esters in the micellar phase, which is caused by the secondary forces of the electrostatic and hydrophobic interactions between esters and micelles. In the preceding s t ~ d ythe , ~ rate of hydrolysis of normal alkyl acetates catalyzed by the dodecyl hydrogen sulfate micelle has been found to decrease with compression up to -1 (1)(a) Studies of Polymer Effects under Pressure. Part 5 . (b) For Part 4, see Y. Taniguchi and K. Suzuki, Bull. Chern. SOC.Jpn., 53,1709 (1980). (2) J. Baumrucker, M. Calzadilla, and E. H. Cordes in “Reaction Kinetics in Micelles”, E. H. Cordes, Ed., Plenum Press, New York, 1973, p 25. (3) J. H. Fendler and E. J. Fendler, “Catalysis in Micellar and Macromolecular Systems”, Academic Press, New York, 1975. (4) Y. Taniguchi, 0. Inoue, and K. Suzuki, Bull. Chern. SOC.Jpn., 52, 1327 (1979).
kbar and then to increase above 1kbar except for methyl acetate. This inversion phenomenon is related to a maximum of the cmc a t 1 kbar5-11 and is qualitatively explained by the pressure effect on the incorporation of both hydronium ions and ester molecules into the micellar phase. In order to clarify this interesting inversion phenomenon under pressure quantitatively, it is necessary to separate the pressure effects on the binding constant between esters
-
( 5 ) S. D. Hamann, J. Phys. Chern., 66, 1359 (1962). (6) R. F. Tuddenham and A. E. Alexander, J.Phys. Chem., 66,1839 (1962). (7) J. Osugi, M. Sato, and N. Ifuku, Reu. Phys. Chem. Jpn., 35, 32 (1965). (8) S. Kaneshina, M. Tanaka, T. Tomjda, and R. Matuura, J. Colloid. Interface Sci., 48, 450 (1974). (9) M. Ueno, M. Nakahara, and J. Osugi, Reu. f‘hys. Chem. Jpn., 47, 25 (1977). (10) S. D. Hamann, Reu. Phys. Chern. Jpn., 48, 60 (1978). (11)N. Nishikido, N. Yoshimura, M. Tanaka, J.Phys. Chem., 84, 558 (1980).
0022-3654/81/2085-2218$01.25/00 1981 American Chemical Society
Hydrolysis of p-Nitrophenyl Esters
The Journal
of Physical Chemistry, Vol. 85, No. 15, 1981 2219
TABLE I: Cmc, Aggregation Numbers, and p p of CTAB Micelle at Various Pressures and at 2 5 "C
2.Cl
P , kbar
0.001
10-4(cmc),M N P ,a pp,b
0.5
3.5 95 0.9
3.7 60
0.86
1 3.9 52 0.84
1.5 3.7
60 0.86
2 3.6 16 0.89
a Data of MTAB in 0.3 M NaBr at 23 'C. The ratio of the number of hydroxide ions t o surfactant i o n s in micelles is given by eq 8.
CVC
d
-O 9
10
2.0
30
Cnx1O3/mol dm-3
Flgure 1. Hydrolysis of p-nitrophenyl esters in CTAB: 1 bar, pH 8.3 (0.05 M Tris buffer), 25 'C, each ester concentration 1.0 X M.
and micelles, and the rate constant of the product formation. Therefore, the experiment must be carried out over a range of ester and micelle concentrations. The rate of the basic hydrolysis of p-nitrophenyl esters catalyzed by the CTAB micelle is well known to follow the kinetics of the Michaelis-Menten type.12J3 In the present work, the hydrolysis rate was measured under pressures up to 2 kbar a t 25 "C to obtain the pressure dependence of K and k,, which is given by both contributions of the hydroxide ion- and Tris-catalyzed hydrolysis. The reaction mechanism is discussed in terms of the volume change for the formation of the MS complex and the activation volumes for the product formation, respectively.
Experimental Section Materials. The CTAB (Wako Chemicals Ind.) was extracted 3 times with petroleum ether and then recrystallized 4 times from ethanol. The cmc value in aqueous solution a t 25 "C by the dye method using p-nitrophenoxide ion (A,= = 400 nm) as a probe is 0.92 X M, which corresponds to 0.82 X M by Barry14 and 0.93 X M by Ueno et aL9 PNPA was recrystallized twice from ethanol. PNPP, PNPB, PNPV, and PNPH (Sigma Chemicals Co.) were used without further purification. Apparatus and Procedure. The high-pressure apparatus is the clamp type made of SUS 630 stainless ~tee1.l~The hydrolysis was performed at pH 8.3 in a 0.05 M Tris buffer solution up to 2 kbar a t 25 f 0.5 "C. The hydrolysis under pressure was monitored by observing the change in the optical density at 400 nm due to the p-nitrophenoxide ion by means of a Shimadzu MPS-50 L type spectrophotometer directly. It takes 2-3 min a t least to compress to a certain experimental pressure after mixing esters and catalysts in the high-pressure cell. The data used from the micellar catalysis were taken during the first 15 min of each run. The pressure effect on the cmc of CTAB at pH 8.3 in 0.05 M Tris buffer solution was determined by the measurement of the absorption spectra of phenolphthalein dye (Amu = 550 nm) as a probe up to 2 kbar and by use of the same high-pressure optical cell and the same spectrophotometer. (12) C. A. Bunton, E. J. Fendler, L. Sepulveda, and K. U. Yang, J. Am. Chem. Soc., 90, 5512 (1968). (13) G. Meyer, Tetrahedron Lett., 4581 (1972). (14) B. W. Barry, J. C. Morrison, and G. F. Russel, J. Colloid Interface Sci., 33, 554 (1970). (15) K. Suzuki and M. Tsuchiya, Bull. Chem. SOC.Jpn., 48, 1701 (1975).
Results and Discussion A t 1 atm, the apparent rate constant. kepp,of the hydrolysis increases sharply a t CTAB concentrations greater than the cmc and the micellar effect on k,, increases with increasing carbon number, i.e., the hydrophobicity of the esters as shown in Figure 1. Assuming that one ester molecule is incorporated into a micelle and that the aggregation number, N , of the micelle is independent of the ester, Bunton et a1.12 showed that the scheme of the enzyme-catalyzedreaction in eq 1 is applicable to the present
M
+ s 6MS
M
+P
k,
-P (1) kinetic behavior, where M, S, MS, and P denote the micelle, esters, the micelle--ester complex, and products, respectively. The observed first-order rate constant k, p is given by eq 2, where K, k,, and k, denote the biniing ks -t- km[MlK (2) kapp = 1 [M]K
+
constant between esters and micelles and the rate constants of the product formation and the spontaneous hydrolysis. The concentration of the micelle, M, is given by eq 3, where CDis the total concentration of surface-active [MI = (C, - cmc)/N (3) agent. The cmc values a t various pressures were determined by the pressure effect on the absorption spectra of the dye-CTAB system, and they show a maximum near 1 kbar, as shown in Table I. The aggregation number, N, of the CTAB micelle at 1 bar is 95 molecules.16 Unfortunately, there are no reports of the aggregation number of detergents under pressure except for sodium dodecyl sulfate (SDS)17and for the mean hydrodynamic radius (I?) of myristyltrimethylammonium bromide (MTAB)18up to 2 kbar. Therefore, the aggregation number of CTAB under pressure, Np, is substituted for the data of MTAB in 0.3 M NaBr at 23 "C up to 2 kbar, and the NP values are calculated by eq 419for the oblate micelle, which is estiNP = N ' ( ( I ? ) P / ( R ) 1 ) 2 (4) mated from the light-scattering experiments of MTAB.20 The NP values of the CTAB micelle are listed in Table I. K and k, values are determined by least squares from the plots of l/(kapp- k,) vs. l/(CD - cmc) in eq 5, as shown 1 1 1 N =- 1 (5) k, k, K CD cmc kapp- k, h, - k, in Figures 2 (p-nitrophenyl esters a t 1 bar) and 3 (PNPB
+--
(16) P. Ekwall, L. Mandell, and P. Solyon, J . Colloid Interface Sci., 35, 519 (1971). (17) N. Nishikido, M. Shinozaki, G. Sugihara, M. Tanaka, and S. Kaneshina, J . Colloid Interface Sci., 74, 474 (1980). (18) D. F. Nicoli, D. R. Dawson, and W, Offen, Chem. Phys. Lett., 66, 291 (1976). (19) N. A. Mazer, G. B. Benedek, and M. C. Carey, J . Phys. Chem., 80, 1075 (1976). (20) R. L. Venable and R. V. Nauman, J. Phys. Chem., 68,3498 (1964).
2220
The Journal of Physical Chemistry, Vol. 85, No. 15, 1981
Taniguchl et ai.
TABLE 11: Kinetic Parameters of the Basic Hydrolysis of p-Nitrophenyl Esters Catalyzed by CTAB Micelle at Various Pressures and at 25 "C
P, kbar
PNPA
PNPP
0.001
0.393
0.736
0.5 1 1.5 2
0.383 0.412 0.482 0.706
0.674 0.627 0.752 0.753
PNPV
PNPH
PNPA
PNPP
104k,, s-1 PNPB
PNPV
PNPH
1.41
2.59
5.92
1.19 0.887 0.950 1.01
1.94 1.39 1.28 1.48
4.27 2.62 2.51 2.90
1.50 0.598" 2.07 3.37 4.90 7.59
1.55 0.586a 2.10 3.09 4.61 7.93
1.66 0.564a 2.36 3.68 5.62 8.91
1.87 0.484a 2.94 4.19 6.19 8.72
2.01 0.353a 2.86 4.10 6.80 10.1
1 0 - 5 ~M,- I PNPB
a The rate constant k , of the spontaneous hydrolysis at pH 8.3 (0.05 M Tris buffer) at 1 bar.
TABLE 111: Volume Changes Accompanying the Formation of MS Complex ( A V), the Activation Volumes in the Process of the Product Formation for Tris- and Hydroxide Ion-Catalyzed Hydrolysis ( A VT* and A VOH*)in Micellar and Nonmicellar Systems at 1 bar and at 25 "C volume changes, cm3/mol substrates R
VT * )mneUe
AVi 2
(
* )miceIle
AVT* (-17)' . ,
-6+2
a
AVOH* (- 3)a (- 4 p -3* 1
-182 1
Reference 29, at pH 7.8 (0.05 M Tris buffer) and a t 25 "C.
1
PNPB
* 3 '
05
3 (CD-
PNPH
-
0'
1 .o
0.5
0
( CD - CM C)'x 10-3/ rw1'dm3
10
CMC jx10"/ mol I drr3
Figure 2. Lineweaver-Burk plots for p-nitrophenyi esters in CTAB: 1 bar, pH 8.3 (0.05 M Tris buffer), 25 'C, each ester concentration 1.0 x 10-4 M.
up to 2 kbar). These values are shown in Table I1 with the data of k , a t 1bar. The binding constant, K , and the rate constant of the micellar catalyst, k,, increase with increasing hydrocarbon chain length of the ester, but k, of the spontaneous hydrolysis decreases. The values of k , / k , increase from 2.5 for PNPA (Meyer, 3.59; l3 Behme et al., 1.621)to 5.7 for PNPH (Behme et al., 4.621). The hydrophobic interaction between ester molecules and the CTAB micelle evidently plays an important role in the hydrolysis of ester catalyzed by the micelle. Ester Binding. The relationship of the logarithms of K vs. pressure in Figure 4 shows a minimum at 1 kbar except for PNPA. The inversion phenomena which correspond to the appearence of a maximum of the cmc of CTAB a t 1kbar as shown in Table I are greater for esters with longer hydrocarbon chains. The AV values accompanying the formation of MS complex at 1 atm are determined from the initial slopes of the plots of log K vs. pressure, which are summarized in Table 111. The driving force of the incorporation of p-nitrophenyl esters into the
Figure 3. Lineweaver-Burk plots for PNPB in CTAB under five pressures: pH 8.3 (0.05 M Tris buffer), 25 'C, ester concentration 1.0 X 10-4 M.
U I
Y
m
-0
-
(21) M. T. A. Behme, J. G. Fulling, R. Noel, and E. H. Cordes, J.Am. Chem. SOC.,87, 226 (1965).
0
35
1.0
1.5
20
P / kbar
Figure 4. Pressure vs. log K a t 25 'C.
micellar phase is mainly the hydrophobic interaction between ester molecules and CTAB micelle. This is supported by the following facts. (1)The binding constant increases with longer hydrocarbon chains of the acyl groups
The Journal of Physical Chemistty, Vol. 85,
Hydrolysis of p-Nitrophenyl Esters
No. 15, 1981 2221
I
1.8
t
'.O o.8
/p
tI
/p/
- 3.e
-134
ic.2
m
-3.6+,
$
1
m
I
-
0 01
P
-04 -0.2
1
3
0.5
Figure 5. Pressure vs. log k, system at 25 OC.
1.0 P / kbar
15
0
2.0
1.0
15
2.0
I
P 1 kbar
and log kTfor PNPA in nonmicellar
of esters. (2) The inversion phenomena of log K under high pressure are in line with the general observation of the maximum of the cmc of ionic d e t e r g e n t P even in systems containing additives, alcoholszz and n a ~ h t h a l e n eat ,~~1 kbar. (3) The A V values for the ester binding increase in the range of 0 f 2 cm3/mol for PNPA to 18 f 2 cm3/mol for P N P H with increasing hydrophobicity of esters. The AV values per methyl or methylene group range from 2.0 cm3 for P N P P to 3.6 cm3 for PNPH, which correspond to the magnitude of AV values per methyl or methylene group accompanying the formation of the hydrophobic interaction, obtained from studying the pressure effects on the dimerization of carboxylic acids (1,5, and 8 cm3/mol for CH3, C2Hs,and C3H7,re~pectively).~~ Therefore, AV values per methyl or methylene group are explained by the dehydration of the hydrophobic hydration around acyl groups of esters for the formation of the hydrophobic interaction between ester molecules and CTAB micelles. Hydrolysis i n Micelle. The hydrolysis of p-nitrophenyl esters in the Tris buffer solution is catalyzed by both the hydroxide ion and free-amine Tris. Its pseudo-first-order rate constant, k, is described by eq 6.25 In order to sep-
-
k = k o ~ [ o H ]+ h~[TriS]
0.5
(6)
arate the k value into the contribution of the hydroxide ion and Tris catalysis, a t first we must express the k value as the function of koHIOH] or kT[Tris] only assuming that Lockyer's data of log kOH/kT (ref 26) are the same for each ester and vary linearly with pressure. Secondly, it is necessary to correct the concentrations of both hydroxide ions and Tris for the compression of the solution and for the increase in the ionization constant of water by comp r e s ~ i o n But . ~ ~ the pressure dependence of the ionization constant of Tris is negligible.28 According to the above procedure, the values of AVoH* for the hydroxide ioncatalyzed hydrolysis and AVT* for the Tris-catalyzed hydrolysis for each ester in the spontaneous hydrolysis were determined graphically from the plots of log k vs. pressure, Figure 5 shows one of the typical examples. These values of -3 f 1 cm3/mol for AVOH*and -18 f 1 cm3/mol for (22) S. Kaneshina, M. Tanaka, and R. Matuura, Mem. Fac. Sa., Kyushu Uniu., Ser. C, 9, 71 (1974). (23) Y. Taniguchi and K. Suzuki, Reu. Phys. Chem. Jpn., 49,91 (1980). (24) K. Suzuki, Y. Taniguchi, and T. Watanabe, J . Phys. Chem., 77, 1918 (1973). (25) W. P. Jencks and J. Carrivolo, J. Am. Chem. Soc., 82, 1778 (1960). (26) G. D. Lockyer, Jr., D. Owen, D. Crew, and R. C. Neuman, Jr., J . Am. Chem. SOC..96. 7303 (1974). (27) S. D. Hamann, J. Phys. Chem., 67, 2233 (1963). (28) R. C. Neuman, Jr., W. Kauzmann, and A. Zipp, J. Phys. Chem., 77, 2687 (1973).
Flgure 6. Pressure vs. log k, at 25 O C .
and log k, for PNPA in mlcellar system
AVT* for each ester are consistent with the data of PNPA and PNPP.29 In the micellar catalyst, the hydroxide ion concentration is not thoroughly uniform in the solution but is higher near the CTAB micellar cations, while the distribution of free-amine Tris would not be influenced by the micellar effect. Therefore, the first-order rate constant for Tris, ( k ~ ) ~ iis~independent ~u~, of the concentration of Tris, and the pseudo-first-order rate constant for hydroxide ion, ( k ~ ~is given ) ~ approximately , ~ ~ by eq 7, where ( OH)mi,ne (kOH)micelle = kOH/ (OH)micelle (7) is the average concentration of the hydroxide ions near the micellar phase. If one assumes that the hydroxide ions behave like gegenions of bromine ions in micellar solution, the ratio of the number of hydroxide ions to that of CTAB ions, P P , in the micelle a t various pressures is given by eq 8, where q is the effective charge on the micelle and the /3P = 1 - q / N p (8) value for CTAB micelle is 8.6 in 0.013 M KBr solution a t 1bar.30 The P P values are listed in Table I. The values of (AVoH*)fi,, = 4 f 2 cm3/mol and for Tris (AVT*),,u, = -19 f 2 cm3/mol in Table I11 were determined graphically from the plots of log (k)micelle vs. pressure in Figure 6. The values of AVO,* in micellar and nonmicellar systems are given by the volume difference between the transition state leading to formation of the tetrahedral intermediate and the reactants in eq 9. As the solvation R-C-0
I0I
*NO2
L a-
t OH-
-
J (9)
effect of water molecules both on the reactants and on the activation complex is negligible in the hydrophobic atmosphere of the CTAB micelle, the bimolecular reaction given by eq 9 only is expected to have a negative value of ca. -10 cm3/mol (ref 31) for the formation of one covalent (29) R. C. Neuman, Jr., G. D. Lockyer, Jr., and J. Marin, J. Am. Chem. SOC.,98, 6975 (1976).
(30) K. J. Mysels, J . Colloid Interface Sci., 10, 507 (1955). (31) W. J. IeNoble, Prog. Phys. Org. Chem., 5, 207 (1967).
2222
J. Phys. Chem. 1981, 85, 2222-2226
bond, which nearly corresponds to the value of AVO,* in the micelle. In nonmicellar systems, the small negative values of AVO,* for hydrolysis of PNPA and P N P P are explained by Neuman et al.29to be the result of a balance between the negative volume change for the bimolecular reaction and the positive volume change for the difference of the solvation effect between reactants and the activation
complex. The difference in AVO,* between the more negative value of -10 cm3/mol for trimethylacetateZ9and the less negative value of -3 cm3/mol for PNPV in this work showing the same hydrophobic effect would not come from the hydrophobic (hydration) effect but from the steric effect, so that the reason for the steric effect on the AVO,* values will be clarified by further study of the steric effect on the base hydrolysis reactions.
Electron-Transfer Quenching of Excited Ru( bpy),2+ Ions Adsorbed on Ion-Exchange Surfaces Anny Slama-Schwok, Yehuda Feltelson, and Joseph Rabani" Energy Research Center and the Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem, 9 1000, Israel (Received: December 9, 1980: In Final Form: March 27, 198 1)
Both the decay of the 3CT Ru(bpy)$+ emission at 600 nm and the bleaching of Ru(bpy)$+ ground-state optical absorption have been investigated. The ionic species were adsorbed on a negative ion exchange resin (Sephadex ~~+ SP-C50) which is a tridimensional dextran gel with sulfopropyl groups attached. The 3CT R ~ ( b p y ) ions are quenched by Cu2+,Fe3+,ferric nitrilotriacetate (FeNTA), 02,benzoquinone, and Cr(acacI3 in a dynamic process. Except for 0 2 and benzoquinone, electron-transfer products are produced with quantum yields ranging from 0.1 for FeNTA and C r ( a ~ a cto ) ~0.68 for Cu2+and 1.0 for Fe3+. The rates of quenching for the positive ions, based on the total volume of the swollen resin, are higher by about one order of magnitude as compared to the appropriate rates in water. Rates of quenching by the uncharged species seem to be comparable to the rates in polyelectrolyte solutions. The reversed electron-transfer reactions were also measured for Fe3+,Cu2+, and FeNTA. In all three cases, the back-reaction is very fast, obeying fairly closely a second-order rate law (deviations indicating a possible first-order contribution are observed after >70% have reacted back). Reaction rate constants are 3.4 X los, 4.1 X lo9,and 4 X lo9M-' s- for Fe3+,Cu2+,and iron(II1)nitrilotriacetate, respectively. At sufficiently high coverage by Ru(bpy)p and sufficiently high laser pulse intensities, triplet-triplet annihilation was observed for 3CT R ~ ( b p y ) ~similarly ~+, to the effect measured previously in micelle solutions and in a polyelectrolyte solution. Unlike the complicated nature of the enhanced decay of 3CT R ~ ( b p y ) , ~in+ the polyelectrolyte,the enhanced decay in the ion-exchange resin obeys a simple second-order rate law. The results are discussed in the light of previous work in water, polyelectrolytes, and an ion exchanger.
'
Introduction The so-called triplet state of tris(2,2'-bipyridine)ruthenium(I1) ions (3CTRu(bpy)z+) has been extensively investigated in the last decade.'+ Electron-transfer reactions from 3CT Ru(bpy)3z+to various ions, including Fe3+ the effects of and Cu2+,have been s t ~ d i e d . ~ -Recently, '~ p~lyelectrolytes'~-~~ and ion-exchange resin16 on several (1) F. E. lytle and D. M. Mercules, J . Am. Chem. SOC.,91,253 (1969). (2) D. M. Klassen and G. A. Crosby, J . Chem. Phys., 49, 1853 (1968). (3) J. N. Demas and A. U. Adamson, J . Am. Chem. SOC.,93, 1800 (1971). (4) F. Bolleta, M. Maestri, and L. Moggi, J . Phys. Chem., 77, 861 (1973). (5) J. N. Demas and A. W. Adamson, J . Am. Chem. Soc., 95, 5159 (1973). (6) G. Navon and N. Sutin, Inorg. Chem., 13, 2159 (1974). (7) H. D. Gafney and A. W. Adamson, J. Am. Chem. SOC.,94, 8238 (1972). (8)G. S. Lawrence and U. Balzani, Inorg. Chem., 13, 2976 (1974). (9) C. R. Bock, T. S. Meyer, and D. G. Whitten, J . Am. Chem. SOC., 96,4710 (1974). (10) C. T. Lin and N. Sutin, J. Phys. Chem., 80, 97 (1976). (11) C. T. Lin and N. Sutin, J . Am. Chem. SOC.,97, 3543 (1975). (12) J. N. Demas, J. W. Addington, S. H. Peterson, and E. W. Harris, J . Phys. Chem., 81, 1039 (1977). (13) D. Meisel and M. S. Matheson, J . Am. Chem. Soc., 99, 6577 (1977). ' (14) D. Meisel, J. &bani, D. Meyerstein, and M. S. Matheson, J. Phys. Chem., 82, 985 (1978). (15) D. Meyerstein, J. Rabani, D. Meisel, and M. S. Matheson, J. Phys. Chem., 82, 1879 (1978). 0022-3654/81/2085-2222$O1.25/0
3CT Ru(bpy),2+ reactions have been investigated. The triplet-triplet annihilation of 3CT Ru(bpy),2+ has been reported to be observed in both micelles17 and polyelectrolytels aqueous solutions. The absorption spectrum of R ~ ( b p y ) , ~the + , relatively ps), and its highly long lifetime of 3CT R ~ ( b p y ) , ~(-0.6 + negative redox potential made the Ru(bpy)gP+ a popular compound for the investigation of photochemical conversion and storage of solar energy. Recently, water splitting to hydrogen and oxygen using Ru(bpy),2+systems has been r e p ~ r t e d . ' ~ Among the major obstactles in the way of photochemical storage of solar energy are the following: (a) the short lifetime of most excited states; (b) the inability, in most cases, to achieve an efficient redox reaction without losing too much of the excess free energy which was obtained by the primary photolytic process; and (c) the so-called "back-reactions'' in which the ground-state reactants are regenerated from photochemical transients. Environmental effects of polyelectrolytes and micelles have been (16) A. T. Thornton and G. S. Lawrence, J . Chem. SOC.,Chem. Commun., 408 (1978). (17) U. Lachish, M. Ottolenghi, and J. Rabani, J. Am. Chem. SOC., 99, 8062 (1977). (18) S. Kelder and J. Rabani, J . Phys. Chem., submitted for publica-
tion. (19) K. Kalyanasundaram and M. Gratzel, Angew. Chem., 41, 759 (1979).
0 1981 American Chemical Society
