3982
J. Phys. Chem. A 2002, 106, 3982-3990
Quenching by Oxygen of the Lowest Singlet and Triplet States of Pyrene and the Efficiency of the Formation of Singlet Oxygen in Liquid Solution under High Pressure Masami Okamoto*,† and Fujio Tanaka‡ Faculty of Engineering and Design, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan, and College of Integrated Arts and Sciences, Osaka Prefecture UniVersity, Gakuencho, Sakai 599-8531, Japan ReceiVed: October 2, 2001; In Final Form: December 20, 2001
Quenching by oxygen of the lowest singlet (S1) and triplet (T1) states of pyrene at pressures up to 400 MPa in liquid solution was investigated. The rate constant of the S1 state, kqS, decreased significantly with increasing pressure, while that of the T1 state, kqT, was nearly independent of pressure at the lower pressure region (300 MPa) in MCH. The latter evidence in MCH implies that the enhanced viscosity induced by pressure causes participation of the intersystem crossing between the encounter complex pairs, as observed previously for the oxygen quenching of the T1 state of 9-acetylanthracene34 and the triplet-triplet annihilation of 2-acetonaphthone.17 Pressure Dependence of f∆T and f∆S. From eqs 9 and 18, one may derive eq 19.
f∆ ) T
(
ketT,bim,0
(kdiff/γ) + ketT,bim,0
(
)/
ketT,bim,0
+ T,bim,0
(kdiff/γ) + ket
Figure 8. Pressure dependence of kdiff (O), kS,bim (b), kqS(obs) (4), and kqS(calc) (3) for quenching by oxygen of the S1 state of pyrene in three solvents.
(18)
3kicT,bim,0 (kdiff/γ) + kicT,bim,0
)
(19)
The values of f∆T at 0.1 MPa, calculated by using those of ketT,bim,0, kicT,bim,0 (Table 5), and kdiff/γ, decrease moderately with increasing pressure; for example, they decrease from 0.60 ( 0.23, 0.78 ( 0.06, and 0.78 ( 0.05 to 0.32 ( 0.04, 0.54 ( 0.04, and 0.53 ( 0.02 in MCH, n-pentane, and n-hexane, respectively, when pressure increases from 0.1 to 400 MPa. The
Oxygen Quenching of S1 and T1 States of Pyrene
J. Phys. Chem. A, Vol. 106, No. 15, 2002 3989
values of f∆T in MCH thus calculated agree qualitatively with those measured as a function of pressure in this work. The values 0.1 MPa are also in agreement with those in cylohexane (1.0)28 and benzene (0.65).29 Finally, in the light of the present approach, f∆S defined by eq 7 may be expressed by eq 20 using the bimolecular rate constants for the S1 state at 0.1 MPa (see eq 15), kicS,bim,0 and ketS,bim,0.
f∆ )
ketS,bim
S
kicS,bim + ketS,bim
)
ketS,bim,0 kS,bim,0
(20)
Thus, f∆S should be independent of pressure. This is because singlet encounter complex pair alone in the quenching of the S1 state is involved in the quenching (see Scheme 3). The overall quantum yield of singlet oxygen, Φ∆, in air-saturated solvent and its pressure dependence, which can be calculated by using f∆S, f∆T, and the parameters involved in eqs 6 and 8 according to eq 10, together with the reasonable assumption that ketS,bim,0 is approximately equal to ketT,bim,0, agrees qualitatively with the results shown in Figure 5 although the errors are large (the maximum error is ca. 40%). Summary It has been shown that the quenching by oxygen of the S1 state in nonpolar solvents examined in this work is not fully but nearly diffusion-controlled. The contribution of diffusion was analyzed from the pressure-induced viscosity dependence of the quenching rate constant of the S1 state, kqS, which was separated into the rate constants for diffusion, kdiff, and for bimolecular quenching in the solvent cage. It was found for the quenching of the T1 state that the ratio of the quenching rate constant of the T1 state kqT to kdiff, kqT/kdiff, decreases over 1/9 and approaches 4/9 with increasing pressure in the solvents examined. The results of the oxygen concentration dependence of the quantum yield for the formation of singlet oxygen, Φ∆, in MCH, together with those of the quantum yield for T1 state at pressures up to 400 MPa, revealed that the branching ratio for the singlet oxygen formation in the T1 state, f∆T, decreases with increasing pressure. On the basis of Scheme 1, which involves the encounter complex pairs with singlet, triplet, and quintet spin multiplicities, the pressure dependence of kqT/kdiff and f∆T was satisfactorily interpreted by eqs 18 and 19, respectively. References and Notes (1) Birks, J. B. Photophysics of Aromatic Molecules; Wiley-Interscience: New York, 1970; p 518. (2) Saltiel, J.; Atwater, B. W. AdVances in Photochemistry; WileyInterscience: New York, 1987; Vol. 14, p 1. (3) Ware, W. R. J. Phys. Chem. 1962, 66, 455. (4) Rice, S. A. In ComrehensiVe Chemical Kinetics. Diffusion-Limited Reactions; Bamford, C. H., Tripper, C. F. H., Compton, R. G., Eds.; Elsevier: Amsterdam, 1985; Vol. 25. (5) Birks, J. B. Organic Molecular Photophysics; Wiley: New York, 1973; p 403. (6) Evans, D. F.; Tominaga, T.; Chan, C. J. Solution Chem. 1979, 8, 461. (7) Evans, D. F.; Tominaga, T.; Davis, H. T. J. Chem. Phys. 1981, 74, 1298. (8) Spernol, A.; Wirtz, K. Z. Naturforsch., A 1953, 8A, 522. (9) Gierer; A.; Wirtz, K. Z. Naturforsch., A 1953, 8A, 532. (10) Schuh, H.-H.; Fischer, H. HelV. Chim. Acta 1978, 61, 2130. (11) Saltiel, J.; Shannon, P. T.; Zafiriou, O. C.; Uriarte, K. J. Am. Chem. Soc. 1980, 102, 6799. (12) Okamoto, M. J. Phys. Chem. A 1998, 102, 4751. (13) Okamoto, M. J. Phys. Chem. A 2000, 104, 5029. (14) Okamoto, M. J. Phys. Chem. A 2000, 104, 7518.
(15) Okamoto, M.; Wada, O. J. Photochem. Photobiol., A: Chem. 2001, 138, 87. (16) Okamoto, M.; Wada, O.; Tanaka, F.; Hirayama, S. J. Phys. Chem. A 2001, 105, 566. (17) Okamoto, M.; Teratsuji, T.; Tazuke, Y.; Hirayama, S. J. Phys. Chem. A 2001, 105, 4574. (18) Yasuda, H.; Scully, A. D.; Hirayama, S.; Okamoto, M.; Tanaka, F. J. Am. Chem. Soc. 1990, 112, 6847. (19) Hirayama, S.; Yasuda, H.; Scully, A. D.; Okamoto, M. J. Phys. Chem. 1994, 98, 4609. (20) Gijzeman, O. L. J.; Kaufman, F.; Porter, G. J. Chem. Soc., Faraday Trans. 2 1973, 69, 708. (21) Wilkinson, F.; McGravey, D. J.; Olea, A. F. J. Am. Chem. Soc. 1993, 115, 12151. (22) Olea, A. F.; Wilkinson, F. J. Phys. Chem. 1995, 99, 4518. (23) Redmond, R. W.; Braslavsky, S. E. Chem. Phys. Lett. 1988, 148, 523. (24) Darmanyan, A. P.; Foote, C. S. J. Phys. Chem. 1993, 97, 5032. (25) McGravey, D. J.; Szekeres, P. G.; Wilkinson, F. Chem. Phys. Lett. 1992, 199, 314. (26) Wilkinson, F.; McGravey, D. J.; Olea, A. F. J. Phys. Chem. 1994, 98, 3762. (27) Wilkinson, F.; Abdel-Shafi, A. A. J. Phys. Chem. A 1997, 101, 5509. (28) Usui, Y.; Shimizu, N.; Mori, S. Bull. Chem. Soc. Jpn. 1992, 65, 897. (29) McLean, A. J.; McGravey, D. J.; George Truscott, T.; Lambert, C. R.; Land, E. J. J. Chem. Soc., Faraday Trans. 1990, 86, 3075. (30) Abdel-Shafi, A. A.; Wilkinson, F. J. Phys. Chem. A 2000, 104, 5747. (31) Darmanyan, A. P.; Foote, C. S. J. Phys. Chem. 1992, 96, 3728. (32) Garner, A.; Wilkinson, F. Chem. Phys. Lett. 1977, 45, 432. (33) Grewer, C.; Brauer, H.-D. J. Phys. Chem. 1994, 98, 4230. (34) Okamoto, M.; Tanaka, F.; Hirayama, S. J. Phys. Chem. 1998, 102, 10703. (35) Tanaka, F.; Furuta, T.; Okamoto, M.; Hirayama, S. Chem. Lett. 2000, 768. (36) Kristiansen, M.; Scurlock, R. D.; Iu, K.-K.; Ogilby, P. R. J. Phys. Chem. 1991, 95, 5190. (37) Scurlock, R. D.; Ogilby, P. R. J. Photochem. Photobiol., A: Chem. 1993, 72, 1. (38) Okamoto, M.; Teranishi, H. J. Phys. Chem. 1984, 88, 5644. (39) Okamoto, M.; Teranishi, H. J. Am. Chem. Soc. 1986, 108, 6378. (40) Okamoto, M.; Sasaki, M. J. Phys. Chem. 1991, 95, 6548. (41) Murrov, S. L. Handbook of Photochemistry; Marcel Dekker: New York, 1973. (42) IUPAC Analytical Chemistry Division, Commission on Solubility Data. Oxygen and Ozone; Battino, R., Ed.; Solubility Data Series 7; Pergamon: Oxford, 1981. (43) Bridgman, P. W. Proc. Am. Acad. Arts Sci. 1926, 61, 57. (44) Brazier, D. W.; Freeman, G, R. Can. J. Chem. 1969, 47, 893. (45) Oliveiria, C. M. B. P.; Wakeham, W. A. Int. J. Thermophys. 1992, 13, 773. (46) Dymond, J. H.; Young, K. J.; Isdale, J. D. Int. J. Thermophys. 1980, 1, 345. (47) Jonas, J.; Hasha, D.; Huang, S. G. J. Chem. Phys. 1979, 71, 15. (48) Okamoto, M.; Tanaka, F. J. Phys. Chem. 1993, 97, 177. (49) Okamoto, M.; Tanaka, F. Phys. Chem. Chem. Phys. 2000, 2, 5571. (50) Okamoto, M.; Tanaka, F.; Teranishi, H. J. Phys. Chem. 1990, 94, 669. (51) Schmidt, R.; Sekel, K.; Brauer, H.-D Ber. Bunsen-Ges. Phys. Chem. 1990, 94, 1100. (52) In previous papers,13-16 the quenching was assumed to involve the exciplex as well as the encounter complex formed between fluorophore, 1M*, and quencher, Q. In this work, the contribution of the former is neglected since no evidence of the exciplex formation between the S1 state of pyrene and O2 in solution near room temperature has been observed. (53) The radial distribution function at the closest approach distance, rM*Q ()rM* + rQ) with the hard sphere assumption, g(rM*Q), is given by54
g(rM*Q) )
( )
( )
rred 1 2y2 rred 3y + + 1 - y (1 - y)2 rS (1 - y)3 rS
2
(A-1)
where rred ) rM*rQ/rM*Q and y is the packing fraction, given in terms of the molar volume of solvent, VS, by
y)
4NAπrS3 3VS
(A-2)
By using the values of rS, rM*, and rQ,55 together with the data of the solvent density,43-47 g(rM*Q) was calculated by eq A-1.
3990 J. Phys. Chem. A, Vol. 106, No. 15, 2002
Okamoto and Tanaka
(54) Yoshimura, Y.; Nakahara, M. J. Chem. Phys. 1984, 81, 4080. (55) Bondi, A. J. Phys. Chem. 1964, 68, 441. (56) From the approximation by Spernorl and Wirtz, one may derive eq A-3.
(
)
2RTrM*Q 1 1 kdiff ) + SW 3000η f SWr fQ r Q M* M*
(A-3)
where fiSW (i ) M* or Q) represents a microfriction factor and is given by
fiSW ) (0.16 + 0.4ri/rS)(0.9 + 0.4TSr - 0.25Tir)
(A-4)
In eq A-4, Tsr and Tir are the reduced temperatures of solvent and solute, respectively, which can be calculated by the method described elsewhere.2,8,9 By comparing with eq 1, RSW is given by
RSW )
(
)
1.2 × 104 1 1 + rM*Q fM*SWrM* fQSWrQ
-1
(A-5)
The values of RSW(full) and RSW(trunc) were evaluated by eq A-4 and by neglecting the second parenthetical quantity in eq A-4, respectively. The values of RSW(trunc) are shown in Table 5 since RSW(full) gives a negative value for the fluorophore/oxygen system.15,16
