J. Phys. Chem. 1985,89, 3320-3323
3320
Lumttlescence of Ruthenium( I I ) and Osmium( I I ) Polypyrldyls in Acetonitrile at High Pressures M. L. Fetterolf and H. W. Offen* Department of Chemistry and The Marine Science Institute, University of California, Santa Barbara, California 93106 (Received: January 24, 1985)
The spectra, quantum yield, and lifetime of excited Ru(I1) and Os(I1) tris(bipyridine) and tris(phenanthro1ine) complexes have been studied in acetonitrile as a function of pressure (0.1-300MPa) and temperature (2-70 "C). The radiative and nonradiative transition rates between the luminescent CT level and the ground states are generally increased by 5-10% at pressures of 300 MPa. A pressure effect of greater magnitude and opposite direction is observed for the luminescence lifetime T of Ru(1I) complexes, because a third CT LF nonradiative decay channel is thermally accessible and made inaccessible by pressure. The measurement of activation volumes for 7 at different temperatures gives A P = 11.5 mL/mol for the CT LF deactivation path of R ~ ( b p y ) ~ in C lCH3CN. ~
-
-
Introduction High-pressure luminescence is a useful method for the study of excited-state processes.' The great interest of ruthenium pyridylsZ to inorganic photochemistry has spurred this P,T investigation into the photophysical behavior of both Ru(I1) and Os(1I) complexes. The ligands employed in this study are the bidentate ?r-acceptors 2,2'-bipyridine (bpy) and 1 , l O phenanthroline (phen). The kinetic scheme of these strong-field d6 metal complexes is discussed in terms of the three-level energy diagram shown in Figure 1.2*3 Absorption by ground-state (GS) complexes leads to population of the luminescent level with unit efficiency.2 The metal-to-ligand charge-transfer state (CT) loses its excitation energy by luminescence (k,),nonradiative relaxation to GS (k2), and thermally activated decay (k,)to a ligand field state (LF), provided the lODq and Tare of appropriate magnitude. Three research groups"' have demonstrated that the observed temperature dependence of the luminescence lifetime 7 above 280 K in fluid solvents, including CH3CN, can be satisfactorily accounted for by an Arrhenius expression with a single-exponential term 7-1 = k, + k2 A3e-hEt/RT (1)
+
where the third term is the thermally activated decay, k3,and A,?? is identified with the energy barrier for crossinkg from the C T to the LF states of the coordination complex. The 1-atm 7 ( T ) dataa reveal that the 30% increase" in lODq for the heavier metal is sufficient to remove k3 as an effective decay channel in the Os complexes around 300 K, thus providing this photophysical pressure characterization with an interesting comparison. Measurements of 7 and quantum yield 0 a t fixed T lead to an evaluation of the radiative and nonradiative (k,) decay rates:
k, = 07-'
(2)
+
k, kz k3 = (1 - @P)r-l (3) In this report the volume dependence of the transition rates is deduced from 7(P)and 0 ( P ) determinations in acetonitrile.12 We (1) Drichmer, H. G. Annu. Rev. Phys. Chem. 1982, 33, 25. (2) Watts, R. J. J. Chem. Educ. 1983, 60, 834. (3) Kemp, T. J. Prop. React. Kiner. 1980, 10, 301. (4) Van Houten, J.; Watts, R. J. J. Am. Chem. Soc. 1976, 98, 4853. (5) Van Houten, J.; Watts, R.J. Inorg. Chem. 1978, 17, 3381. (6) Allsopp, S. R.; Cox, A.; Jenkins, S. H.; Kemp, T. J.; Tunstall, S. M. Chem. Phys. Letr. 1976,43, 135. (7) Allsopp, S. R.;Cox, A.; Kemp, T. J.; Reed, W. J. J. Chem. SOC., Faraday Trans. I 1978, 74, 1275. (8) Allsopp, S. R.; Cox, A.; Kemp, T. J.; Reed, W. J.; Carassitti, V.; Traverso, 0. J. Chem. Soc., Faraday Trans. 1 1979, 75, 353. (9) Durham, B.;Caspar, J. V.; Nagle, J. K.; Meyer, T. J. J. Am. Chem. Soc. 1982,104,4803. (10) Caspar, J. V.; Meyer, T. J. J. Am. Chem. Soc. 1983, 105, 5583. (1 1) Men, G. H.; White, R. P.; Rillema, D. P.;Meyer, T. J. J. Am. Chem. Soc. 1984, 106, 2613.
0022-3654/85/2089-3320%01.50/0
TABLE I: CH3CN Solvent Properties"
P,MPa 50 100 150
200 300
plpob
elcob
1.05 1.08 1.11 1.13 1.17
1.08 1.11 1.13 1.18
1.05
n2/(n0)lc 1.03 1.05 1.06 1 .08 1.10
71qQd
1.19 1.40 1.93 2.69
"Thedensity p, dielectric constant e, refractive index n, and viscosity Superscript 0 refers to 0.1-MPa values. bReference 16; 25 OC. cEstimated from the Lorenz-Lorentz equation. dReference 17;30 OC. 7.
find that hydrostatic compression is an effective means to shut off the activated k3 process.
Experimental Methods The high-pressure optical cells and associated pressure equipment have been described.13 Solutions are prepared fresh each day and bubbled with scrubbed and dried Nz for 1 h before loading into a cylindrical quartz capsule. A movable, stainless-steel piston separates the sample in the capsule from the pressure-transmitting solvent in the optical cell. Temperature control to f0.2 O C was accomplished with a Peltier thermoelectric device. Compression experiments were performed in the 0.1-300-MPa pressure range (1 MPa = 10 bar = 10.1 atm) at 25 OC as well as in the 2-70 "C temperature interval. The 5 X M solutions were stored in the dark and minimally exposed to light during lifetime and spectral measurements. Absorption spectra at room temperature were recorded on a Cary 14 spectrophotometer at fmed pressures. Luminescence spectra and intensities were detected at 90° with a 0.5-m Jarrell-Ash monochromator and EM1 95558B PMT, amplified, and recorded on a strip chart. Excitation at 436 nm was accomplished with a 200-W Osram Hg lamp coupled wth a Bausch and Lomb high-intensity monochromator. The lifetime station has been described e l s e ~ h e r e . ' ~ -Oscilloscope '~ traces were recorded on film and graphically analyzed, and the data were fit by a linear least-squares regression program. Good fits indicated single exponential decays at all T and P for the polypyridine complexes in water and acetonitrile. Precision is limited to 6% in spectra and intensities and 3% in lifetimes. The Os(bpy)3Z+ion luminescence is weak, so that the concentration had to be doubled for intensity measurements. Acetonitrile, obtained from Mallinckrodt (SpectrAR grade), was used from newly opened bottles without further purification. (12) Offen, H. W.; Turley, W. D.; Fetterolf, M.L. In "High Pressure in Science and Technology"; Homan, C., MacCrone, R. K., Whalley, E.,Eds.; Elsevier: New York, 1984; Materials Research Society Symposia Proceedings Vol.22, Part 11, p 155. (13) Dawson, D. R.; Offen, H. W. Rev. Sci. Instrum. 1980, 51, 1349. (14) Watts, R. J.; Harrington, J. S.; Van Houten, J. J . Am. Chem. SOC. 1977, 99, 2 119. (15) Turley, W. D.; Offen, H. W. J . Phys. Chem. 1984, 88, 3605.
0 1985 American Chemical Society
The Journal of Physical Chemistry, Vol. 89, No. 15, 1985 3321
Ru(I1) and Os(I1) Polypyridyls in Acetonitrile
'500 T
L F -
IS'L
1250
k 750
4 Figure 1. Energy level diagram for Ru(I1) and Os(I1) polypyridyls.
500
1250
-0
TABLE Ik Quantum Yield Corrections at 300 MPa' 1. Ru(bpy)Qz
11. R~(phen)~CI, 111. Os(bpy),CIz IV. Os(phen)3C1,
F
f
Ff
0.935 0.907 0.798 0.974
1.01
0.94 0.93 0.82 0.98
1.03 1.03
1.01
kS't
0
I08 200 300 PRESSURE / MPa Figure 2. Pressure dependence of the luminescence lifetimes of Ru(bpy),CI, ( 0 ) and Ru(phen)$I2 (6) in CH3CN at 15 and 45 OC. W 0 Z
1 25
'See text and eq 5 and 6 for definitions of F and f. 0
For reference, data on the pressure dependence of the density,16 1 J dielectric constant,16 refractive index, and viscosity1' are collected 15 in Table I. The convention used throughout this paper is that 0 1-atm values are indicated by the superscript zero. H 5 t The complex Ru(bpy),Cl2.6H2O was used as purchased from 0 G. F. Smith Chemical Co. The compounds R ~ ( p h e n ) ~ C 1 ~ . 3 H ~ O , ~ ~ Q 25 O~(bpy),C1~.6H~O and , ~ ~O ~ ( p h e n ) ~ C l ~ . 8 Hwere , O ~ ~prepared :0 according to reported procedures. The starting materials were RuC13.3Hz0 (G. F. Smith Chemical Co.), (NH4)@Br6 (Strem PRESSURE / MPo Chemical Co.), and the N-heterocyclic ligands 2,2'-bipyridine Figure 3. Pressure dependence of the lifetime T , expressed as the fracand1,l-phenanthroline hydrate from Aldrich Chemical Co. The , R~(bpy)~C ( 0l )~and Ru(phen),Cl, (+) in tional change ( 7 - 7 0 ) / r 0 of products were recrystallized thrice from conductivity water. The CH3CN at 15 and 45 OC. observed spectral and lifetime data in water and in acetonitrile at 25 O C are in substantial agreement with literature valthe €436 values, which represent greater pressure sensitivity, are ues. 10.18,21-23 changed by -7%, -1.576, 14%, and -1 2% for the complexes I-IV The pressure dependence of 9 was determined from corrected in the same pressure interval. The bandwidths remain unchanged intensities I within experimental errors, so that the pressure variation in 6~ is directly proportional to 6Je ds, Le. the transition probability i p / @ = (Z/P)Ff (4) for absorption. due to pressure-induced changes in the absorbed intensities and The 1-atm, 25 OC kinetic parameters +, 9, k:, and k: of the beam attenuation. The pressure dependence of the concentration luminescent C T level are collected in Table IV. The pressure and the molar extinction coefficient €436 is responsible for the responses of these parameters at 25 OC are summarized in Table correction factors F and f: V. The Ru(I1) complexes show monotonic increases in both 9 F = (1 - ,-2.303r0C09/(1 - e-2.303t~9 and T with pressure, leading to reductions in k, and k,; however, (5) the magnitudes of the pressure change are substantialy greater f = e-2.3036°8d for the phenanthroline ligands. Kirk and Porter25 found the /e- 2.303tcd (6) * R ~ ( b p y ) lifetime ~ ~ + in HzO at room temperature to decrease Here I = 0.3 cm is the average length across the luminescence by -9% for a AP = 230 MPa, which is smaller and of opposite viewing region and d = 0.07 cm is the distance from the cell sign to CH3CN at the same temperature and thus illustrative of window to the edge of the viewing port in the present apparatus. a strong solvent dependence of the observed pressure effects. We As seen from Table 11, the corrections introduced by these two factors at 300 MPa are minimal except for O ~ ( b p y ) , ~ + . verified that T and T(P) of I at 25 O C are identical for extensively dried CH3CN and freshly opened solvent bottles. Henceforth, the four complexes are denoted I-IV as in Table 11. A comparison of Ru(I1) and Os(I1) complexes (Tables IV and V) reveals the smaller pressure sensitivity as well as opposite trends Reults in both 9 and T for complexes of the heavier metal. The decay The luminescence and absorption band maxima, ijL and vA, and kinetics of IV is similar to that of I in k,(P) but shows by contrast the 436-nm molar extinction coefficient €436 of the four complexes an increase in k,(P) of -8% at 300 MPa. The low quantum yield are listed in Table 111. The excited-state energies decrease with of I11 introduces greater uncertainties in the observed small increasing pressure, the red shift being -2-3 times greater for changes, but the marked decrease in k,(P) is considered outside the absorption than the emission a t 300 MPa, yet representing the known errors and in sharp contrast to the other three comonly a -0.5% energy shift. Such a small pressure-induced red plexes. shift of the I absorption is of comparable magnitude to the The pressure coefficient of 7 for the Ru(I1) complexes is highly measurements of Gulino and Drickamer" in water. In contrast, dependent on the temperature. As illustrated in Figure 2, the increase in lifetime for the AP = 300 MPa interval is -20% and (16) Srinivasan, K.R.; Kay, R. L. J. Solution Chem. 1977, 6, 357. -100% at 15 OC and -85% and -150% at 45 OC for I and 11, (17) Salmon, 0. A. Dim. Abstr. Int., B 1983, 43, 2974. (18) Lin, C.-T.; Bottcher, W.; Chou, M.; Creutz, C.; Sutin, N. J . Am. respectively. On the other hand, Figure 3 shows that the fractional Chem. Soc. 1976, 98,6536. increase in lifetime in acetonitrile for the 15-45 O C temperature (19) Burstall, F. H.; Dwyer, F. P.; Gyarfas, E. C. J. Chem. Soc. 1950,953. interval is much greater for I than 11. This prompts the detailed (20) Dwyer, F.P.; Gibson, N. A.; Gyarfas, E. C. J. Proc. R. SOC.N . S. T,P study of the former complex and gives the results in Table W.1952.84.68. (21) Credtz, C.; Chou, M.; Netzel, T. L.; Okumura, M.; Sutin, N. J . Am. VI. It is noted that at the lower T,P end of the table the T change Chem. SOC.1980, 102, 1309. induced by a 5 OC decrease is equivalent to a 100-MPa increase. (22) Juris, A.; Balzani, V.; Belser, P.; von Zelewsky, A. Helu. Chim. Acta
+
1981, 64, 2175. (23) Caspr, J. V.; Kober, E. M.; Sullivan, B. P.; Meyer, T. J. J. Am. Chem. SOC.1982, 104, 630.
(24) Gulino, D. A.; Drickamer, H. G. J. Phys. Chem. 1984, 88, 1173. (25) Kirk, A. D.; Porter, G. B. J . Phys. Chem. 1980, 84, 2998.
3322 The Journal of Physical Chemistry, Vol. 89, No. 15, 1985 TABLE III: Luminescence and Ahsorption Spectral Data' 1 atm iO-3~L, cm-I 10-3D,, cm-I
1. Ru(bpy),Clz 11. Ru(phen)?Cl, 111. 0s(bpy)3c12 IV. Os(phen)3C1z
16.54 16.95 14.04 14.36
Fetterolf and Offen
M-I cm-I 13.3 19.8 11.5 16.4
22.19 22.49 23.05 23.19
300 MPa AD,, cm-l
AD^, cm-I -70 -60 -50 -60
10-3e436,M-I cm-' 12.4 19.5 13.1 14.5
-190 -210 -170 -130
'In CH3CN at 25 OC. TABLE I V Kinetic Parameters in CHXN at 25 O C TO, ns $O iO-5k,0, s-I 0.73 I. R~(bpy)$I1 855 0.062' 0.106b 2.68 11. R ~ ( p h e n ) ~ C l ~396 111. Os(bpy),C12 63 0.005' 0.8 0.016c 0.71 IV. O ~ ( p h e n ) ~ C l ~224
iO-5k2, s-I 11 23 160 44
4 4 2 0 -2
$/bo
I I1 I11 IV
T / 70
krlk,o
knlk,o
I I1 111 IV I I1 I11 IV I I1 111 IV
50 1.11 1.23 0.9 1.03
o
100
o
o
0 0 0
ooooo 0
270
290 310 TEMPERATURE /
Parameters
P,MPa complex
1
4
'Reference 10. bEstimated by the Parker-Rees ratio method. Reference 23. TABLE V: Pressure Dependence of -tic
1
l2 10
1
330
K
Temperature dependence of the activation volume of r-l(AV,+) for Ru(bpy),C12 in CH3CN. F i g u r e4.
1.22 1.49 0.8 1.02
150 1.29 1.71 0.8 1.02
200 1.35 1.95 0.7 1.00
300 1.42 2.38 0.7 0.95
1.08 1.21 0.93 0.98
1.18 1.41 0.93 0.98
1.25 1.62 0.91 0.98
1.30 1.68 1.03 0.95
1.39 2.13 1.01 0.93
1.04 1.02 1.0 1.05
1.04 1.05
0.9 1.04
1.03 1.06 0.8 1.04
1.04 1.16 0.7 1.05
1.03 1.12 0.7 1.03
0.93 0.80 1.1 1.02
0.84 0:66 1.1 1.02
0.78 0.57 1.1 1.02
0.75 0.53 1.0 1.05
0.70 0.39 1.0 1.08
3 2
3
3 4
T " 1 1 0 K~ - ' Figure 5. Arrhenius plot for Ru(bpy),Clz in CH3N at 0.1, 100, and 300
MPa. TABLE MI: Temwrature Dewndence of A V J (mL/mol)
T, "C
P,MPa 0.1 100 200 300
15 1155 1290 1345 1380
20 1020 1155 1235 1250
25 855 1000 1110 1155
30 730 875 995 1040
T,,"C 35 600 735 885 930
40 460 615 735 810
45 375 490 620 690
50 270 395 510 570
In parallel with the concept of activation energy in transition-state theory, the pressure dependence of a kinetic process can be expressed in terms of an activation volume A P . For example AV: = -RT[a In 7-l/aPjT
In
(7-I
- 7;)'
= A3 - @ / R T
I I1
(8)
where T ; ~ = k, + kz and equal to 5.6 X lo5 s-l for I,l0 linear plots result as illustrated in Figure 5 for three pressures. In the absence of any knowledge about 7(P)at low temperatures, we assume that
25 4.7 8.2 -1.3 -0.2
111 IV
45 8.7 9.9 -1.9
TABLE WI: Temperature Dependence of A Vat (&/mol) T, OC
(7)
Evaluation of the linear wfficieni from a least-squares quadratic fitting procedure gives AV: values at P = d.1 MPa with. an estimated error of f 1.O mL/mol. The results are shown in Table VI1 and, for I, in Figure 4. The activation volume for I rises with temperature and levels off above 50 OC to a value of 11.5 mL/mol. In the same temperature regime AV: of 11 is temperature independent within experimental errors and gives values similar to those of I at high temperatures. As previously noted, the Small and o p p i t e 7(P)data for I11 and IV give small and negative AVJ values. The temperature dependence of the luminescence decay can be analyzed according to eq 1. When the data for I in Table VI are plotted according to eq 8
15 2.9 8.8
15 10.5 10.9
I' IIb "T;~
= 5.6 X lo5 s-l (ref 10).
25 10.5 8.9 b~;'
45 11.6 10.5
= 1.9 X lo5 s-I (ref 9, normal-
ized results in CHzC12to CH3CN). r.
7-'(P) is small and identical with r ( P ) of O ~ ( p h e n ) ~at~room + tewfirature, which amounts to an -8% increase of 7;l at 300 MPa. According to eq 8, the 1-atm slope and intercept in Figure 5 correspond to hEt 4300 cm-' and A3 'v 5.6 X lo1*s-l, which are similar to the values reported p r e v i o ~ s l y . ~However, J~ both A3 and are found to be highly sensitive to the choice of 7c1, which prohibits any discussion of ASand AEf at high pressures. An alternative analysis of the k3(P,T)process considers the activation volume for that decay channel: AV3+= -RT[E) In
(7-I
- 7;')/aP],
(9)
The nearly parallel slopes of Figure 5 predict AVSt to be temperature independent (fl.O &/mol), which is confirmed in Table VI11 for the k3 decay channel of I as well as 11. Further, the
The Journal of Physical Chemistry, Vol. 89, No. 15, 1985 3323
Ru(I1) and Os(I1) Polypyridyls in Acetonitrile magnitude of the volume change is the same for both complexes and independent of the choice of T;', in contrast to the above analysis involving eq 8.
Discussion The salient feature of this work is the measurement of excited-state decay processes of the Ru(I1) and Os(I1) polypyridyls in extreme environments. The pressure dependence of each decay channel is discussed in turn. The effect of pressure on radiative transitions can be judged in terms of eq 10, based on the simplified Strickler-Berg and Birks-Dyson equations:26 Sk, = 6n2 + StL2
+ 6s'
di,
(10)
The observed variations in k, (Table V) for AP = 300 MPa of compounds I-IV are 4-376, +12%, -30%, and +3%, respectively. For comparison, the oalculated sums of the three factors in eq 10 are +3%, +WO,+24%, and -2%. In this estimate we have used Sn2 = +11% (Table I) and 6i,Lz = -1% (Table 111) and assumed that S S c di, (Table 111) is the same for the absorbing and emitting state. The electronic term in eq 10 is the modulating factor credited with the obseived variations in radiative rates of these related complexes. The correlations are excellent for I, diminish progressively for I1 and IV, and fail entirely for O s ( b ~ y ) ~ ~The +. pressure resulh for the latter compound predict that the absorbing and emitting states have dissimilar electronic structures. In this context it is rekalled that the absorption spectrum of I11 is far more complex than that of the other ions.27 Salman and DrickameP have reported that 8k, of Re(C0)3Cl(phen) is +36% for the same solvent and pressure interval; hence, generalizations about the pressure dependence of radiative transitions in d6 complexes cannot yet be made. The electronic relaxation rates k2 (CT GS), equal to k, of Os(I1) complexes, exhibit a pressure-induced increase in dk2 which is negligible for I11 and +5% at 300 MPa for IV. According to the simplest version of the energy gap law29
-
Sk2 = -In k2 Si,,
(11)
An expo,nential dependence of nonradiative rates on the energy gap is expected and has be& successfully tested with solvent and ligand substituent effect;.23,30*31The pressure-induced shift of Si,, = -0.4% for IV at $IO MPa predicts, according to eq 12, 6k2 = +7% which agrees with the observed behavior of the electronic relaxation. But I11 do& not offer such simple correlation. That is not surprising becadbe pressure is likely to affect other factors besides the energy gap in modifying radiationless transitions. In the case of Re(1) c o m p l e ~ e s ~a* .blue ~ ~ shift is accompanied by a slight decrease in k,, which is in the right direction but -20-fold less than predicted by eq 11. The pressure effect on nonradiative rates and spectral shifts between excited and ground states is too smll in the 300-MPa interval to do much better than lead to crude correlations. (26) Strickler, S. J.; Berg, R. A. J. Chem. Phys. 1962,37,814. Birks, J. d.;,Dyson,D. J,Proc. R. SOC.London A 1963, 275, 195. (27) Kober, E. M.; Meyer, T. J. Inorg. Chem. 1982, 21, 3967. (28) Salman, 0. A.; Drickamer, H. G . J . Chem. Phys. 1982, 77, 3337. (29) Robinson, G . W.; Frosch, R. P. J . Chem. Phys. 1963, 38, 1187. (30) Caspar, J. V.; Meyer, T. J. J. Phys. Chem. 1983,87,952. (31) Caspar, J. V.; Sullivan, B. P.; Kober, E. M.; Meyer, T. J. Chem. Phys. Let?. 1982, 91, 91.
It is clearly evident that the large pressure effects on 7 of Ru(1) complexes are not explained by eq 10 and 11, giving additional support to the existence of a third decay channel to the nonobservable LF states. The temperature dependence of the activation volumes of the luminescence decay represents a novel perspective for the photophysical behavior and the relativevolumes of molecules in different electronic states. The three channel process gives32j33 AVJ = 0,AV; + 02AV2' + 83AV3' (12) where the quantum efficiencies ei for all channels i add to unity. The temperature dependence of AVJ appears primarily in 0 of thermally activated processes, such as O3 in this case. Since the two ruthenium c ~ m p l e x e s 'have ~ ~ different e,(T), the observed pressure change of 7 at a given Twill also be generally different. A low- and high-temperature limit is characterized by 8, 0 and e3 1, respectively. The application of eq 12 to the complexes under study leads to the following observations. The activation volumes for the radiative transition rates are -1, -2, +5, and -1 mL/mol for complexes I-IV, respectively. Since these systems are weakly luminescent, the first term makes a small to negligible contribution to the makeup of AVJ. The Os(I1) complexes, in particular, are characterized by 0, < e2and €13 < e2,so that AVJ N AVJ. The CT GS nonradiative transition rates yield activation volumes of -1 mL/mol for Os(I1) complexes (Table VII), which is of similar magnitude to the pressure coefficient of k,. The slight temperature dependence of AVJ in IV probably reflects the onset of a small contribution from k3. In Ru(I1) complexes the CT LF relaxation path dominates at high temperatures, giving the limiting value of AVJ N AVJ = 11.5 mL/mol. By use of this value for AVJ and €12and 8, from literature values for I at 25 OC in CH3CN,l0eq 12 predicts AVJ = -3 mL/mol for the nonradiative CT GS process. Thus, the complex with the lighter metal atom shrinks more in the transition state than the Os complex, according to this analysis. The lack of 1-atm values for e2and O3 of I1 in CH3CN and this temperature regime prevents the above computation; however, the results in Table VI11 suggest a similar magnitude for AV,+ of both Ru(I1) complexes. It is important to note that other e ~ i d e n c ealso ~~,~~ predicts AVJ N 10 mL/mol for the transition between the CT and LF states. Volume expansion for the CT LF process and a relatively smaller volume reduction for the CT GS process are entirely reasonable. The above discussion shows that when nonradiative, thermally activated decay paths are accessible, the pressure dependence of 7 cannot be interpreted unless measured at several temperatures. Further, the combined P,T effects on a luminescent state represent an excellent method for the diagnosis of activated decay channels which are accompanied by large activation volumes.
-
-
-
-
-
--
Acknowledgment. We gratefully acknowledge financial support of The Marine Science Institute and generous access to the lifetime instrumentation of Professor R. J. Watts. Registry No. I, 14323-06-9; 11, 23570-43-6; 111, 82872-27-3; IV, 73466-62-3; CH3CN, 75-05-8. (32) Weber, W.; van Eldik, R.; Kelm, H.; DiBenedetto, J.; Ducommon, Y.; Offen, H.; Ford, P. C. Inorg. Chem. 1983, 22, 623. (33) Kirk, A. D.; Namaslvayam, C.; Porter, G . B.; Rampi-Scandola, M. A.; Simmons, A. J . Phys. Chem. 1983, 87, 3108. (34) Weber, W.; DiBenedetto, J.; Offen, H.; van Eldik, R.; Ford, P. C. Inorg. Chem. 1984, 23, 2033.
