5190
J . Phys. Chem. 1986, 90, 5190-5193
Dealumination by steaming only occurs with acidified or ammonium-exchanged samples. AI is then extracted and deposited on the channels or on the outer surface of the crystallites as an alumina phase, as shown by the typical 27AlN M R spectrum. The solid-state 29Si N M R spectrum is highly resolved due to the absence of Si(nA1) contribution ( n C 0). Three distinct N M R lines correspond to Si(OA1) configurations of T I , T,, and T, + T3 sites, respectively. Enhancement of the 29SiN M R spectrum by cross-polarization confirms the presence of SiOH groups.
Acknowledgment. We thank Prof. E. G. Derouane for valuable discussions. We are indebted to G. Daelen for taking the N M R spectra and to F. Vallette for technical assistance. G. Debras and P. Bodart thank IRSIA-IWONL for financial support. P. A. Jacobs acknowledges NFWO-FNRS (Belgium) for a research position as "Onderzoeksleider". Registry No. AI, 7429-90-5; HCI, 7647-01-0; HN03, 7697-37-2; SiCI,, 10026-04-7.
Temperature Dependence of the Luminescence Emission of Ruthenium( I I ) Cornpiexes Containing the Ligands 2,2'-Bipyrldine and Dipyrido[ 3,2-c :2',3'-e Ipyridazine Francesco Barigelletti,ln Alberto Juris,ln*b Vincenzo Balzani,* and Alex von Zelewsky"
Peter Belser,IC
Istituto FRAE-CNR and Istituto Chimico "G. Ciamician" dell'Universitri, Bologna, Italy, and Institute for Inorganic Chemistry, University of Fribourg, Fribourg, Switzerland (Received: September 27, 1985; In Final Form: April 15, 1986)
The luminescence behavior (emission spectra and emission lifetimes) of R~(taphen),~+, Ru(bpy)(taphen)?+, and Ru(b~y)~(taphen)*+ (taphen = dipyrido[3,2-~:2',3/-e]pyridazine, bpy = 2,2'-bipyridine) has been studied in propionitrile-butyronitrile ( 4 5 v/v) solutions in the temperature range 85-350 K. The results obtained are illustrated and discussed in comparison with those previously obtained for Ru(bpy),'+. The Ru(taphen),*+ complex exhibits a very peculiar behavior. Its emission lifetime (i) decreases strongly in the temperature range of solvent melting (100-150 K), (ii) increases with increasing temperature from 150 to 230 K, and (iii) decreases again at higher temperature (230-330 K). The maximum of the emission band moves to the red and the luminescence intensity decreases in the melting region, but at higher temperatures (150-230 K) the emission maximum undergoes a blue shift and the emission intensity increases. Above 230 K the emission maximum continues to move to the blue, while the intensity decreases. Such a complicated temperature dependence of the photophysical behavior is discussed on the basis of a sequence of excited states which includes metal-to-ligand charge-transfer levels of (C, antisymmetric) $ and (Czosymmetric) x ligand orbital origin. The mixed ligand complexes exhibit a behavior qualitatively similar to that of Ru(taphen),*+, except that the emission lifetime remains approximately constant in the temperature range 150-280 K.
Introduction A better knowledge of the parameters which govern the photophysical properties of transition-metal complexes2-6 is fundamental for the progress of photochemistry and essential for the design of new photo sensitizer^.^-^^ Temperature dependence studies of the luminescence behavior can yield important pieces of information concerning the energy ordering of the various excited states and the dynamics of interstate c o n v e r ~ i o n . ~ - ~ ~ 9 the ' ~ complexes of the RuContinuing our i n ~ e s t i g a t i o n s ~ Jon (11)-polypyridine family, we have recently studiedI5 the spectroscopic, electrochemical, and luminescence properties of the Ru(bpy)>"(taphen);+ complexes ( n = 0-3, bpy = 2,2'-bipyridine, taphen = dipyrid0[3,2-~:2',3'-e]pyridazine; Figure 1). We report (1) (a) Istituto FRAE-CNR. (b) Istituto Chimico 'G. Ciamician". (c) University of Fribourg. (2) For reviews, see ref 3-6. (3) Crosby, G. A. Acc. Chem. Res. 1975, 8, 231. (4) Kemp, T. J. Prog. React. Kinet. 1980, 10, 301. (5) DeArmond, M. K.;Carlin, C. M. Coord. Chem. Reu. 1981, 36, 325. (6) Demas, J. N. J. Chem. Educ. 1983, 60, 803. (7) Graetzel, M., Ed. Energy Resources through Photochemistry and Catalysis; Academic: New York, 1983. (8) Meyer, T. J. Prog. Inorg. Chem. 1983, ZZ, 94. (9) Balzani, V.; Juris, A.; Barigelletti, F.; Belser, P.; von Zelewsky, A. Riken Q. 1984, 78, 78. (10) Whitten, D. G. Acc. Chem. Res. 1980, Z3, 83. (1 1) Balzani, V.; Bolletta, F.; Ciano, M.; Maestri, M. J . Chem. Educ. 1983, 60, 447. (12) Sutin, N. Pure Appl. Chem. 1980, 52, 2717. (13) Juris, A.; Barigelletti, F.;Balzani, V.; Belser, P.; von Zelewsky, A. Inorr. Chem. 1985. 24. 202. (y4) Barigelletti, F.f Belser, P.; von Zelewsky, A,; Juris, A.; Balzani, V. J . Phys. Chem. 1985, 89, 3680. (15) Juris, A.; Belser, P.; Barigelletti, F.; von Zelewsky, A,; Balzani, V. Inorg. Chem. 1986, 25, 256.
0022-3654/86/2090-5 190$01 .50/0
now a detailed study on the temperature dependence of the luminescence emission (energy, intensity, and lifetime) of the same complexes in the temperature range 84-350 K. Experimental Section PF6- salts of the R~(bpy),_,(taphen),~+ complexes were prepared and purified as described el~ewhere.'~,'~ Two independent batches gave compounds having identical absorption, excitation, and emission spectra. All the complexes were stable in propionitrile-butyronitrile solutions for days, but for longer time periods or upon heating above 350 K they underwent a decomposition reaction. The most reactive appeared to be R~(bpy)~(taphen),+, which could not be studied above 320 K. All the experiments were carried out in a mixture of freshly distilled propionitrile and butyronitrile ( 4 5 v/v). A diluted solution (10-5-10-4 M) of each complex was sealed under vacuum in an 1-cm quartz cell after repeated freeze-pump-thaw cycles. The cell was then placed inside a Thor C 600 nitrogen flow cryostat, equipped with a Thor 3030 temperature controller and indicator. The absolute error on the temperature is estimated to be 1 2 K. The uncorrected emission spectra were obtained with a PerkinElmer MPF-44B spectrofluorimeter equipped with a Hamamatsu R 928 phototube. Emission spectra were recorded by exciting in the lowest energy absorption maximum and were independent of the excitation wavelength. Excitation spectra were performed with a Perkin-Elmer LS-5 spectrofluorimeter. Emission lifetimes were measured by a modified Applied Photophysics single-photon-counting apparatus equipped with a thyratron gated N2 lamp (337 nm) or by a JK system 2000 Nd3+:YAG DPLY4 laser. The decay was monitored at the maximum of the emission band. Data (16) Belser, P.; von Zelewsky, A . Helc. Chim. Acta 1980, 63, 1675.
0 1986 American Chemical Society
The Journal of Physical Chemistry, Vol. 90, No. 21, 1986 5191
Luminescence Emission of Ru(I1) Complexes 6
N-N
0 1.0.
264
303
252 240
-> Y
227
s
Y
214
I4
Figure 1. Structural formula of the dipyrido[3,2-~:2’,3’-e]pyridazine ligand (taphen). Atom numbering as shown.
.-5
201
UI Y
1
16 -
-& w
188
=t
-
- 0.5. (D
U
.
C
175 162 152
0.25.
d
14
-
600
700
X,nm
Figure 4. Dependence of the emission spectrum of Ru(bpy)(taphen);+ 12-
on temperature (indicated in K). 4
a
12
1000/T, K-’ 0
Figure 2. Temperature dependence of the luminescence lifetime for (a)
(c) Ru(bpy)(taphen)22+,and (d) RuRu(bpy),2+, (b) R~(taphen)~~’, (bpy)dta~hen)~’.
16.51 *
I
oooo
i
o o
40.6
>
228 216
1.0- 2 4 0
.-VI 2
252
4.l
H
.-5
204
264
192
274
180
UI
g
.E d
1
0.5
5
284
.-E
15.0-
303
0.6
0
3 I 5 14.5--
294
00 0
.-VI
0
15.0600
700
.-
-
’P
0.25t I
0
0.
168
‘E Y
,X 15.5E
0
I
0
X,nm
Figure 3. Dependence of the emission spectrum of R ~ ( t a p h e n ) ~ on~ + temperature (indicated in K).
treatment was carried out with a PDP/ 1 1 Digital microcomputer. Standard iterative nonlinear programs were employed to analyze the decay curves.17 In all cases, the analysis indicated a single-exponential decay. The quality of the fit was assessed by the x2 values close to unity, and the residuals were regularly distributed along the time axis. The experimental error on the emission lifetimes is estimated to be 68%. The relative emission intensities at the various temperatures were obtained from the area of the emission bands. Because of the change in the transparency of the matrix as well as in other parameters, no quantitative analysis was performed on the intensity data in the temperature range corresponding to the rigid-fluid transition. Results The absorption spectra (at 293 K) and the emission spectra complexes have been (at 77 K) of the Ru(bpy),-,(taphen);+ reported in a previous paper.I5 The corrected excitation spectra matched the absorption spectrum, and the emission lifetimes were independent of the excitation wavelength (532 and 355 nm). Figure 2 shows the temperature dependence of the luminescence (17) Bevington, P. R. Data Reduction and Error Analysis for Physical Sciences; McGraw-Hill: New York, 1969.
0
14.0
,
4
0.2
O m0
8
12
1000/T, K - l
Figure 5. Schematic diagrams showing the changes in the energy and intensity of the emission maximum of Ru(bpy)32+(A), Ru(taphen)?’ (B), and Ru(bpy)(taphen);+ (C) as a function of temperature: open circles, emission energy; full circles, emission intensity.
decay for the fQur complexes. For R ~ ( b p y ) ~the ~ ’solid line in the figure is the result of the curve fitting according to eq 1‘3,’4 (vide infra), while for the complexes containing taphen it merely represents a simple connection of the experimental points. Figures 3 and 4 show the temperature dependence of the emission spectra of Ru(taphen)32+ and Ru(bpy)(taphen)22’ above the melting temperature of the solvent. The behavior of R~(bpy),(taphen)~+ is not reported because it was quite similar (up to 320 K) to that of Ru(bpy)(taphen)?’. The spectral variations in the temperature range of the glass-fluid transition are not shown for clarity reasons and also because of the large uncertainty in the values of the emission intensities in that region (see Experimental Section). Anyway, during the melting of the solvent the emission maximum moved toward lower energies and lower intensities as the temperature increased. The changes in the position of the emission maximum and in the emission intensity are summarized in Figure 5 , where the same quantities for Ru(bpy),*’ are also shown.
Barigelletti et al.
5192 The Journal of Physical Chemistry, Vol. 90, No. 21, 1986
Discussion On the basis of electrochemical and spectroscopic results, we have shown in a previous paperI5 that the luminescence emission of R ~ ( t a p h e n ) , ~and + of the mixed ligands R ~ ( b p y ) ( t a p h e n ) ~ ~ + and Ru(b~y),(taphen)~+ complexes takes place from Ru taphen charge-transfer (MLCT) excited states. This conclusion is based on the following observations: (i) the ligand-centered (LC) emissions of taphen and bpy are expected to occur at 20000 and 23 100 cm-l, respectively, Le., at much higher energy than that of the luminescent emission of the taphen-containing complexes (C16000 cm-I); (ii) the lowest metal-centered (MC) excited state, which is thought to lie at =21 OOO cm-' for Ru(bpy)?+, is expected to move to higher energy upon substitution of taphen for bpy because taphen has the same pK, as bpy'* (Le., the same u donor properties) and better T* acceptor ~r0perties.l~ The temperature dependence of the luminescence decay of Ru(bpy)?+ has been reported p r e v i ~ u s l y . ~ ~The ~ ~essential '~~'~~~ features are (Figure 2, curve a) (a) an Arrhenius-type behavior of the luminescence decay in the rigid glass region (84-100 K), (b) a discontinuity in the glass-fluid transition region (=100-1 50 K), (c) an Arrhenius-type behavior in the 150-250 K temperature range with essentially the same parameters as in the rigid glass; and (d) another steeper Arrhenius-type region for T > 250 K. This complex behavior was accounted for by eq 1, where kd is
0.56
(N
-0.56
N = N, 0.11 -
-0.19 . 3
0
m -0.11 1
+
1/7 =
0.32
-N0.12
0.12
0.04
0.04
-0.32
(1Q
N=N
~~~
0.25 - 0
'
3
0.27 -0.44
m
;
2 -0.39 5
-0.44
Figure 6. Lowest energy n* orbitals for taphen ligand according to EHT26A; x(LUM0) orbital; B, $(1 eV higher in energy) orbital. The numbers are the atomic contributions (p orbitals) to the MO. Skeleton bond lengths are taken to be 1.36 A.
a consequent decrease in lifetime and intensity. Once the glass is completely melted, the slightly activated Arrhenius behavior continues because the emission always originates from the same cluster of MLCT excited states. At higher temperature, a M C a temperature-independent term; the second term takes care emexcited state which lies about 4000 cm-] above the emitting levels pirically of the behavior in the glass-fluid transition region, and becomes a c ~ e s s i b l e . ~Since ~ ~ ~ this ~ ~ 'level is strongly distorted the two exponential terms account for the Arrhenius behavior at compared with the ground-state geometry, it undergoes very fast low and high temperature. radiationless decay (which includes ligand substitution21 and Curve b of Figure 2 shows that the temperature dependence racemization reaction^^^,^^). Note that a fourth MLCT excited of the luminescence decay of R ~ ( t a p h e n ) , ~is+ even more comstate (lying about 800 cm-' above the lowest one)24which has a plicated than that of R ~ ( b p y ) , ~ +Essentially, . there is a larger larger singlet character does not play any role in the temperature effect of the glass-fluid transition (100-150 K) and an increase dependence behavior because it is "masked" by the surface crossing of the lifetime with increasing temperature in the 150-230 K to 3MC.25 region, which is indeed a quite unusual feature. Clearly, such The more complex behavior shown by the taphen-containing a complicated non-Arrhenius behavior cannot be fit with a reacomplexes suggests the involvement of different orbitals and/or sonably simple mathematical equation. The more complex temthe presence of different orbital ordering. According to EH-type perature behavior of the Ru(taphen)32+luminescence compared calculations26for bpy (as well for other polypyridine-type ligands) with that of R ~ ( b p y ) , ~is+also apparent from Figure 5, where the lowest ? T * ~orbital has $ symmetry (antisymmetric in C,), the shift in the emission maximum and the changes in the emission while the next higher (1 .O eV) orbital has x symmetry (symmetric intensities as a function of temperature are shown. As one can in C2"). By contrast, for taphen the lowest r*Lorbital has x see, for both complexes there is a noticeable red shift of the symmetry and is substantially centered on the 5,6-N atoms emission maximum in the temperature range of the rigid-fluid (Figures 1 and 6A), with the J. orbital (largely centered on the transition; the shift, however, is larger for R ~ ( t a p h e n ) , ~(+N 1200 1,lO-N atoms, Figures 1 and 6B) lying about 1 eV higher. Since cm-I, Figure 5B) than for R ~ ( b p y ) , ~(-800 + cm-I, Figure SA). the $ orbital overlaps better the metal orbital^,^' the spin-orbit In fluid solution the emission maximum of R ~ ( b p y ) , ~moves + splitting of the states originating from the d transition slightly to the blue ( E 150 cm-', Figure 5A), while that of Ruis expected to be larger than that of the states originating from ( N 1000 cm-I, Figure 5B). ( t a ~ h e n ) ~undergoes ~' a large blue shift T * ~ ( x )transition. As a consequence the and X-type the d The emission intensity decreases strongly for both complexes in triplets, ,($ state) and ,(x state), should be very close in energy, the rigid-fluid transition region (not shown in Figure 5). In fluid and they should also exhibit different intrinsic lifetimes. In a solution, it is almost constant in the range 150-230 K and then previous paper15we have shown that these arguments can account decreases sharply for Ru(bpy)?+ (Figure SA). For R ~ ( t a p h e n ) ~ ~ + , for the absorption, emission, and electrochemical results for tathere is a noticeable increase in the emission intensity from 150 phen-containing complexes. It should also be noted that, compared to 230 K, followed by a sharp decrease at higher temperatures with the ground-state geometry, the states deriving from the x (Figure 5B). orbital are distorted essentially along the N5-N6 vibrational coThe temperature behavior of the R ~ ( b p y ) , ~emission + has been ordinate, while those deriving from the $ orbital are distorted along accounted for as follows. Emission originates from a cluster of the Ru-N, (Nlo) metal-ligand coordinates. Thus, for Ru(taclosely spaced ( A E 100 cm-I) MLCT levels having similar but hen),^' the interconversion between ,(x state) and ,(+ state) not identical decay proper - tie^.^ When the matrix melts, largeamplitude (low-frequency) vibrational modes come into play which enhance the rate of radiationless deactivation processes,I4 with (22) Hoanard. P. E.: Porter. G. B. J . Am. Chem. SOC.1978. 100. 1457.
-
-
+-
-
__
(18) Belser, P., to be submitted for publication. (19) Van Houten, J.; Watts, R. J. J . Am. Chem. SOC.1976, 98, 4853. (20) Elfring, W. H., Jr.; Crosby, G. A. J. Am. Chem. Soc. 1981,103,2683. (21) Durham, B.; Caspar, J. V.; Nagle, J. K.; Meyer, T. J. J. Am. Chem. SOC.1982, 104. 4803.
Porter; G . : 6 Sparks, k.H. J.'Photochem. 1980, 13, 123. (23) Liebich, C. Diplomarbeit, University of Fribourg, Fribourg, Switzerland, 1980. (24) Yersin, H.; Gallhuber, E. J . Am. Chem. SOC.1984, 106, 6582. (25) Kober, E. M.; Meyer, T. J. Inorg. Chem. 1984, 23, 3877. (26) Daul, C., private communication. (27) Day, P.; Sanders, N. J . Chem. SOC.A 1967, 1530.
J. Phys. Chem. 1986, 90, 5193-5196 requires the overcoming of a noticeable nuclear barrier. On the basis of the above considerations, a tentative explanation of the temperature dependence of the Ru(taphen)?+ luminescence could be as follows. In rigid matrix, emission originates from 3($ state) populated from I($ state), which is the one mostly involved in absorption. The slightly shorter lifetime compared with Ru( b ~ y ) can ~ ~ simply + be accounted for by the energy gap law.28 At comparable or even slightly lower energy is the 3(x state), with a smaller overall deactivation rate constant because of the smaller spin-orbit coupling and orbital overlap. These two types of levels do not communicate at low temperature because they are separated by the nuclear barrier described above. When the glass melts, radiationless deactivation of the 3(J, state) is enhanced by the coming into play of previously ”frozen” large-amplitude (lowfrequency) metal-ligand vibrations, as it happens for R ~ ( b p y ) , ~ + . I ~ As the temperature increases, the nuclear barrier between the two types of levels can be overcome. If the levels originating from ) have a longer intrinsic lifetime (vide supra), the T * ~ ( xorbital an increase of the lifetime of the luminescence emission in the temperature range 150-230 K (curve b in Figure 2) would follow. For example, if one assumes that 3(J, state) and 3(x state) are almost isoenergetic and separated by an activation energy of 1700 cm-I, using the kinetic scheme
3te state)
kll
k3
3 ( state) ~
k4
Ik2
with k3 and k4 having a frequency factor of 10l2 s-l, the experimentally observed increase in lifetime from 350 ns at 150 K to 450 ns at 230 K is accounted for by T~ = l / k 2 = 625 ns. In this temperature range, upper lying levels having comparable intrinsic lifetime but larger radiative rate constants could also be reached.29 ~~~
~
(28) Caspar, J. V.; Sullivan, B. P.; Kober,E. M.; Meyer, T. J. Chem. Phys. Lett. 1982, 91, 91 and references therein.
5193
This could account for the increase in the emission intensity and the blue shift of the emission spectrum in the 150-230 K temperature region. At higher temperature, the luminescence emission would be governed by the 3MC excited state as in Ru(bpy)32+. The behavior of R ~ ( b p y ) ~ ( t a p h e nand )~+R~(bpy)(taphen)~~+, though slightly different from that of Ru(taphen)z+, could perhaps be interpreted by using similar arguments.
Conclusions The anomalous temperature dependence of the luminescence properties (particularly, the non-Arrhenius behavior) of Ru(taphen)32+and other taphen-containing complexes has been discussed considering the involvement of two approximately isoenergetic 3MLCT states that originate from two different acceptor ligand orbitals (J, and x orbitals). Owing to their different symmetry and localization properties (11, orbital centered on the 1,lO-N atoms near the Ru atom, x orbital far from it, on 5- and 6-N atoms), the two states should be separated by a nucleat barrier and should also exhibit different triplet character. The low-temperature (glassy solution) emission comes from the 3(J, state). On matrix melting, nuclear rearrangements take place that allow equilibration between 3($state) and 3 ( x state). Acknowledgment. We thank C. Daul for EH-type calculations. This work was supported by the Italian National Research Council and Minister0 della Pubblica Istruzione and by the Swiss National Science Foundation. Registry No. Ru(ta~hen),~’,989 14-22-8; Ru(bpy) (taphen)?+, 98914-21-7; Ru(bpy)2(taphen)2+, 98914-20-6;R~(bpy),~+, 15158-62-0. (29) By analogy with Ru(bpy)?+ (vide supra),24a level of $ orbital origin having greater singlet character might be expected at slightly higher energy. Note that in Ru(taphen)32+ the energy gap between emitting MLCT levels and the 3MC level that is responsible for the radiationless deactivation at higher temperature is larger than in R ~ ( b p y ) ? + . ’ ~This should avoid the “masking” effect mentioned above for R~(bpy)~*+ on higher energy emissive MLCT levels in the intermediate temperature region.
Neutron and Light Scattering Study of Mixed Micelles of 2-Butoxyethanol and Cetyltrimethylammonlum Bromide in Water Francois Quirion Departement de Chimie, Universite de Sherbrooke, Sherbrooke, QuPbec, Canada J l K 2R1
and Linda J. Magid* Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996- 1600 (Received: November 14, 1985; In Final Form: April 7 , 1986)
A previous paper presented a neutron and light scattering study of cetyltrimethylammonium bromide (CTAB) in water. It was shown that CTAB micelles undergo an increase in counterion binding prior to rapid micellar growth. This paper extends that study to the effect of 2-butoxyethanol (BE) on the micelles of CTAB. At 28 OC, the addition of 0.1 m BE to CTAB in D 2 0 decreases the aggregation number ( A ) and the counterion binding at the cmc. At 0.1 m CTAB, p increases from 0.74 to 0.90 while the micellar growth starts around 0.15 m. At this concentration the aggregates become prolate ellipsoids and the micellar mole fraction of BE ( X B E decreases. ~) When BE is added to 0.03 m CTAB, the aggregates remain spherical with decreasing radius, ri, and p. The extrapolation of these quantities to pure CTAB is in very good agreement with our previous results. XsEMincreases monotonically with BE concentration. Around 0.6 m BE, the system behaves like BE in water. The model used for the analysis of small-angle neutron scattering data allowed us to get a fair estimate of the BE content of the aggregates.
Introduction The system water cetyltrimethylamonium bromide (CTAB) + 2-butoxyethanol (BE)can solubilize large amounts of benzene or decane.’ This is related to its ability to decrease the interfacial
+
(1) Desnoyers, J. E.; Quirion, F.; Hetu, D.; Perron, G. Can. J. Chem. Eng. 1983,61, 612-679.
0022-3654/86/2090-5193$01.50/0
tension between the aqueous and oil phaseq2 these properties make it an interesting system for tertiary oil recovery and tar sands extraction^.^ The role of the alcohol in such systems is not quite (2) Quirion, F.; Desnoyers, J . E. Aostra J . Res. 1984, 1, 121. (3) Sarbar, M.; Brochu, C.; Boisvert, M.; Desnoyers, J. E. Can. J . Chem. Eng. 1984, 62, 261.
0 1986 American Chemical Societv
