T. Majima et al.
(Continuum, RGA69-10; 30 ps fwhm, 10 Hz) as the second laser. A delay
time of two laser flashes was adjusted to 1 ms by using a four channel dig-
ital delay/pulse generator (Stanford Research Systems, DG 535). The
breakdown of Xe gas generated by the fundamental pulse of the second
laser was used as a probe light. Transient absorption spectra and kinetic
traces were measured by using a streak camera (Hamamatsu Photonics,
C7700) equipped with a CCD camera (Hamamatsu Photonics, C4742-98)
and were stored by using a personal computer. To avoid stray light and
pyrolysis of the sample by the probe light, suitable filters were employed.
Each sample was poured into a transparent rectangular quartz cell (1.0
0.52.0 cm) at room temperature.
the ionization of 2HC(D1), 3HC(D1), and 4HC(D1) was not ob-
served under the present experimental conditions, it is sug-
À
gested that the main chemical reaction process was the O
H bond cleavage. The optimized geometry of 2HC(D1) calcu-
lated at the HF/6-31G** level[9] is shown in Figure 8. The
Compounds 1, 2, 3, and 4 were purchased from Kanto Chemical, Tokyo
Kasei, Aldrich, and Lancaster, respectively. 1 was recrystallized from eth-
anol before use. The other compounds were used as received. Sample so-
lutions were deoxygenated before irradiation by bubbling with argon gas
for 30 min.
Figure 8. Optimized geometry of 2HC(D1).
phenyl ring of 2HC is twisted and the hydrogen atom of the
hydroxyl group is close to the phenyl ring in the excited
state. The distance between these two parts was calculated
to be 3.1 , which is suitable for OH–p hydrogen-bond for-
mation between benzene and the alcohol.[10] It is suggested
Acknowledgements
This work has been partly supported by a Grant-in-Aid for Scientific Re-
search on Priority Area (417), 21st Century COE Research, and the Min-
istry of Education, Culture, Sports, Science and Technology (MEXT) of
the Japanese government.
À
that the OH–p interaction promotes the O H bond-cleav-
age process from 2HC(D1).
The kC value of 4HC(D1) is smaller than that of 3HC(D1).
The O H bond-cleavage process from 4HC(D1) is inefficient
owing to the small conformational change between the D0
and D1 states. Because 4HC(D1) had a larger (kr +knr) value
than that of 3HC(D1), according to the energy-gap law we
suggest that this difference reflects the difference of DE(D1–
D0).[1]
[1] a) N. J. Turro, Modern Molecular Photochemistry, Benjamin/Cum-
mings, Melco Park, CA, 1978; b) P. Suppan, Chemistry and Light,
The Royal Society of Chemistry, Cambridge, 1994.
À
[2] a) V. Ramamurthy, K. S. Schanze, Molecular and Supramolecular
Photochemistry Vol. 2, Marcel Dekker, New York, 1994; b) J. C.
Scaiano, L. J. Johnston, W. G. McGimpsey, D. Weir, Acc. Chem. Res.
1988, 21, 22; c) M. Y. Melnikov, V. A. Smirnov, Handbook of Photo-
chemistry of Organic Radicals, Begell House, New York, 1996.
[3] a) B. W. Hodgson, J. P. Keene, E. J. Land, A. J. Swallow, J. Chem.
Phys. 1975, 63, 3671; b) K. Razi Naqvi, U. P. Wild, Chem. Phys. Lett.
1976, 41, 570; c) K. Obi, H. Yamaguchi, Chem. Phys. Lett. 1978, 54,
Conclusion
ˇ
448; d) H. Baumann, K. P. Schumacher, H. J. Timpe, V. Rehꢁk,
Chem. Phys. Lett. 1982, 89, 315; e) M. C. Thurnauer, D. Meisel,
Chem. Phys. Lett. 1982, 92, 343; f) V. Nagarajan, R. W. Fessenden,
Chem. Phys. Lett. 1984, 112, 207; g) H. Baumann, C. Merckel, H. J.
Timpe, A. Graness, J. Kleinschmidt, I. R. Gould, N. J. Turro, Chem.
Phys. Lett. 1984, 103, 497; h) H. Hiratsuka, T. Yamazaki, Y. Maeka-
wa, T. Hikida, Y. Mori, J. Phys. Chem. 1986, 90, 774; i) L. J. John-
ston, D. J. Lougnot, V. Wintgens, J. C. Scaiano, J. Am. Chem. Soc.
1988, 110, 518; j) R. W. Redmond, J. C. Scaiano, L. J. Johnston, J.
Am. Chem. Soc. 1992, 114, 9768; k) M. R. Topp, Chem. Phys. Lett.
1976, 39, 423; l) J. C. Scaiano, M. Tanner, D. Weir, J. Am. Chem.
Soc. 1985, 107, 4396; m) A. Bromberg, K. H. Schmidt, D. Meisel, J.
Am. Chem. Soc. 1985, 107, 83; n) L. J. Johnston, J. C. Scaiano, J.
Am. Chem. Soc. 1985, 107, 6368; o) S. Wada, Y. Matsushita, K. Obi,
J. Phys. Chem. A 1997, 101, 2423; p) S. Hamatani, K. Tsuji, A.
Kawai, K. Shibuya, Phys. Chem. Chem. Phys. 2003, 5, 1370; q) E. F.
Hilinski, D. Huppert, D. F. Kelley, S. V. Milton, P. M. Rentzepis, J.
Am. Chem. Soc. 1984, 106, 1951; r) K. Tokumura, N. Mizukami, M.
Udagawa, M. Itoh, J. Phys. Chem. 1986, 90, 3873; s) M. Sakamoto,
X. Cai, M. Hara, S. Tojo, M. Fujitsuka, T. Majima, J. Phys. Chem. A
2004, 108, 8147; t) M. Sakamoto, X. Cai, M. Hara, S. Tojo, M. Fujit-
suka, T. Majima, J. Phys. Chem. A 2005, 109, 2452; u) J. C. Netto-
Ferreira, W. F. Murthy, R. W. Redmond, J. C. Scaiano, J. Am. Chem.
Soc. 1990, 112, 4472; v) M. Sakamoto, X. Cai, M. Hara, S. Tojo, M.
Fujitsuka, T. Majima, J. Am. Chem. Soc. 2005, 127, 3702; w) M. Sa-
kamoto, X. Cai, M. Fujitsuka, T. Majima, J. Phys. Chem. A 2005,
109, 6830; x) W. Adam, F. Kita, R. S. Oestrich, J. Photochem. Photo-
biol. A 1994, 80, 187.
In the present work, the properties of 1HC(D1), 2HC(D1),
3HC(D1), and 4HC(D1) were investigated by using nanosec-
ond–picosecond two-color two-laser flash photolysis. The
properties of these ketyl radicals in the excited state were
significantly affected by the size and electronic properties of
the aromatic ring systems. For 1HC(D1), 3HC(D1), and
4HC(D1), tf0 becomes longer with a decrease of the nss value.
Although 2HC had a smaller nss value than that of 1HC, its tf
value was shorter. It is suggested that the OH–p interaction
À
in the excited state promotes the O H bond-cleavage pro-
cess of 2HC(D1). Bimolecular reactions between ketyl radi-
cals in the excited state and several quenchers were ob-
served. Ketyl radicals in the excited state showed reactivity
with N,N-diethylaniline. It was found that 1HC(D1) was effi-
ciently quenched by the ground-state parent molecule.
Experimental Section
The two-color two-laser flash photolysis experiments were carried out by
using the third (355 nm) harmonic oscillation of
a nanosecond
Nd3+:YAG laser (Quantel, Brilliant; 5 ns fwhm) as the first laser and the
second harmonic oscillation (532 nm) of a picosecond Nd3+:YAG laser
[4] a) Y. Matsushita, Y. Kajii, K. Obi, J. Phys. Chem. 1992, 96, 4455;
b) S. Arimitsu, H. Masuhara, N. Mataga, H. Tsubomura, J. Phys.
1616
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 1610 – 1617