The Journal of Physical Chemistry B
ARTICLE
the magnetic field dependence of R(B) is well-reproduced by the
SLE analysis even in the lower field of 0-0.2 T. From these
analyses, a microviscosity of Brij35 micellar solution is estimated
to be 3 cP. Although the microviscosity of the SDS micellar
solution is extensively reported,9-13 there is little reported on the
microviscosity of Brij35. Thus the present study demonstrated
that the microviscosity of Brij35 micellar solution might be
estimated using the MFE probe. From the results, complete
quenching of the MFE in the SDS micellar solution may be
explained by (1) larger microviscosity (>22 (this work) and 25
cP 35), (2) small micelle size (1.8 nm35), and (3) small Pesc (1.2 ꢀ
10-4 35). Such strong cage effects of SDS cause the frequent
reencounters which occurred on the time scale of SOC relaxa-
tion, so this may explain why the MFE is so effectively quenched
inside SDS micelles.
’ REFERENCES
(1) Steiner, U. E.; Ulrich, T. Chem. Rev. 1989, 89, 51–147.
(2) Nagakura, S.; Hayashi, H.; Azumi, T. Dynamic Spin Chemistry;
Kodansha-Wiley: Tokyo, New York, 1998.
(3) Hayashi, H. Introduction to Dynamic Spin Chemistry; World
Scientific: Singapore, 2004.
(4) Wakasa, M. J. Phys. Chem. B 2007, 111, 9434–9436.
(5) Hamasaki, A.; Yago, T.; Wakasa, M. J. Phys. Chem. B 2008, 112,
14185–14192.
(6) Hamasaki, A.; Yago, T.; Takamasu, T.; Kido, G.; Wakasa, M. J.
Phys. Chem. B 2008, 112, 3375–3379.
(7) Wakasa, M.; Yago, T.; Hamasaki, A. J. Phys. Chem. B 2009, 113,
10559–10561.
(8) Gohdo, M.; Wakasa, M. Chem. Lett. 2010, 39, 106–107.
(9) Gr€atzel, M.; Thomas, J. K. J. Am. Chem. Soc. 1973, 95, 6885–
6889. Kubota, Y.; Kodama, M.; Miura, M. Bull. Chem. Soc. Jpn. 1973, 46,
100–103.
Finally, there is a problem clarifying the location of the probe
molecule inside the micelle. Other probes for the microviscosity
such as the fluorescence depolarization technique also have the
same problem. In the present study, a simple cage model was
used. Thus the observed microviscosity may be an averaged value
in the diffusive regions of the two partners. Using the more
refined cage model such as the solvent separated radical pair
(SSRP) model, one can obtain the detail of microviscosities for
the different regions. However such specialized study is beyond
the scope of the present study for a demonstration of the MFE
probe. Otherwise the present bimolecular reaction is considered
to be a meaningful system, because the actual microviscosity
which the molecule feels during the reaction may be observed.
The MFEs are caused by the interaction between magnetic field
and unpaired electron spins. Thus only microenvironments in
the vicinity of the RP (in the range of several nanometers) can
selectively be monitored by the present MFE probe.
(10) Zachariasse, K. A. Chem. Phys. Lett. 1978, 57, 429–432. Emert,
J.; Behrens, C.; Goldenberg, M. J. Am. Chem. Soc. 1979, 101, 771–772.
Turro, N. J.; Aikawa, M.; Yekta, A. J. Am. Chem. Soc. 1979, 101, 772–774.
Turro, N. J.; Okubo, T. J. Am. Chem. Soc. 1981, 103, 7224–7228. Turley,
W. D.; Offen, H. W. J. Phys. Chem. 1985, 89, 2933–2937.
(11) Bahri, M. A.; Hoebeke, M.; Grammenos, A.; Delanaye, L.;
Vandewalle, N.; Seret, A. Collods and Surf., A 2006, 290, 206–212.
(12) Sarpal, R. S.; Belletete, M.; Durocher, G. J. Phys. Chem. 1993,
97, 5007–5013.
(13) Almgren, M.; Grieser, F.; Thomas, J. K. J. Am. Chem. Soc. 1980,
102, 3188–3193.
(14) Turro, N. J. Modern Molecular Photochemistry; Benjamin/
Cummings: Menlo Park, CA, 1978.
(15) Turro, N. J.; Ramamurthy, V.; Scaiano, J. C. Principles of
Molecular Photochemistry; University Science Books: Sausalito, CA,
2009.
(16) Scaiano, J. C. J. Photochem. 1974, 2, 81–118.
(17) Shizuka, H.; Yamaji, Y. Bull. Chem. Soc. Jpn. 2000, 73, 267–280,
and references therein..
(18) Tanaka, M.; Yago, T.; Wakasa, M. Chem. Lett. 2009, 38, 1086–
1087.
(19) Polshettiwar, V.; Kaushik, M. P. Tetrahedron Lett. 2004, 45,
6255–6257.
(20) Curphey, T. J. J. Org. Chem. 2002, 67, 6461–6473.
(21) Wakasa, M.; Hayashi, H. J. Phys. Chem. 1996, 100, 15640–
15643.
(22) Hamasaki, A.; Sakaguchi, Y.; Nishizawa, K.; Kido, G.; Wakasa,
M. Mol. Phys. 2006, 104, 1765–1771.
(23) Kumar, C. V.; Qin, L.; Das, P. K. J. Chem. Soc., Faraday Trans. 2
1984, 80, 783–793.
(24) Jeschke, G.; Wakasa, M.; Sakaguchi, Y.; Hayashi, H. J. Phys.
Chem. 1994, 98, 4069–4075.
(25) The absorptive broad spectrum could be reproduced in every
measurement and is not background drift. From the fact that the similar
’ CONCLUSION
Photochemical reactions of TBP with PhSH in alcoholic
solutions and SDS and Brij35 micellar solutions were studied
by a nanosecond laser flash photolysis. In alcoholic solutions,
appreciable MFEs were observed and analyzed by the SLE. The
MFEs observed up to 15.5 T and the viscosity dependence are
well-reproduced by the SLE analysis. The MFEs can be explained
by the ΔgM together with the spin-orbital coupling induced
direct recombination. These results indicate that the hydrogen
abstraction reaction of TBP with PhSH is useful as a new MFE
probe reaction. Using this probe reaction, it was demonstrated
that microviscosities of SDS and Brij35 micellar solutions were
estimated to be >22 and 3 cP, respectively.
MFE was observed at 450 nm for SPh, the hydrogen abstraction
3
reaction of TBP with PhSH is concluded to occur efficiently, forming
thiobenzophenone ketyl radical (TBPH ). The absorptive phase pat-
3
tern on the observed time-resolved EPR spectrum may be ascribable to
’ AUTHOR INFORMATION
the thermal populating signal of TBPH , because the signal intensity did
3
not change in the time range of 1-5 μs.
Corresponding Author
*E-mail: mwakasa@chem.saitama-u.ac.jp.
(26) Sakaguchi, Y.; Hayashi, H.; Nagakura, S. J. Phys. Chem. 1982, 86,
3177–3184.
(27) Kito, N.; Ohno, A. Bull. Chem. Soc. Jpn. 1973, 46, 2487–2489.
(28) Wakasa, M.; Nishizawa, K.; Abe, H.; Kido, G.; Hayashi, H.
J. Am. Chem. Soc. 1998, 120, 10565–10566.
(29) Wakasa, M.; Nishizawa, K.; Abe, H.; Kido, G.; Hayashi, H.
J. Am. Chem. Soc. 1999, 121, 9191–9197.
(30) Khudyakov, I. V.; Serebrennikov, Y. A.; Turro, N. J. Chem. Rev.
1993, 93, 537–570.
(31) de Kanter, F. J. J.; Kaptein, R. J. Am. Chem. Soc. 1982, 104,
4759–4766.
’ ACKNOWLEDGMENT
This work was partially supported by a Grant-in-Aid for
Scientific Research (No. 2003002) in the Priority Area ‘‘High
Field Spin Science in 100 T’’ (No. 451) from the Ministry of
Education, Culture, Sports, Science and Technology (MEXT)
and by a Grant-in-Aid for Scientific Research (B) (No.
22350003) from the Japan Society for the Promotion of Science.
1942
dx.doi.org/10.1021/jp108898a |J. Phys. Chem. B 2011, 115, 1936–1943