Synthesis and photochemical properties of stilbenophanes tethered by silyl chains. Control of (2π + 2π) photocycloaddition, cis-trans photoisomerization, and photocyclization

Article abstract of DOI:10.1021/jo050914+

Novel macrocyclic and medium-size stilbenophanes tethered by silyl chains were synthesized, and their photochemical and photophysical properties were examined. Direct photoirradiation of macrocyclic stilbenophanes gave intramolecular photocycloadducts ste

Full text of DOI:10.1021/jo050914+

Synthesis and Photochemical Properties of Stilbenophanes
Tethered by Silyl Chains. Control of (2π + 2π) Photocycloaddition,
Cis-Trans Photoisomerization, and Photocyclization
Hajime Maeda,† Ko-ichi Nishimura,† Kazuhiko Mizuno,*,† Minoru Yamaji,‡ Juro Oshima,‡ and
Seiji Tobita‡
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University,
1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan, and Department of Chemistry, Gunma University,
Kiryu, Gunma 376-8515, Japan
mizuno@chem.osakafu-u.ac.jp
Received May 9, 2005
Novel macrocyclic and medium-size stilbenophanes tethered by silyl chains were synthesized, and
their photochemical and photophysical properties were examined. Direct photoirradiation of
macrocyclic stilbenophanes gave intramolecular photocycloadducts stereoselectively, and the
efficiency increased with decreasing distance between the two stilbene units. The triplet-sensitized
photoreaction of stilbenophanes caused cis-trans photoisomerization. Photoreactions of cis-fixed
stilbenophanes under an oxygen atmosphere selectively gave phenanthrenophanes. Fluorescence
quantum yields increased with the introduction of silyl substituents, and hence those of silyl-tethered
stilbenophanes were larger than that of unsubstituted trans-stilbene. Intramolecular excimer
emission was observed when the distances between two stilbene units in the stilbenophanes were
sufficiently small.
SCHEME 1. Photochemistry of Stilbenes
Introduction
Photochemical properties and reactivities of stilbene
and its derivatives have been extensively investigated in
the last few decades.1 Three types of photochemical
reactions of stilbenes are known: (1) cis-trans photo-
isomerization,2 (2) photodimerization or cross-photocy-
cloaddition with alkenes and arenes,3 and (3) photochemi-
cal conversion to phenanthrene derivatives via oxidative
dehydrogenation of dihydrophenanthrenes4 (Scheme 1).
Among these, the cis-trans photoisomerization of stil-
phenanthrene is a reversible process, and the quantum
yield is not as high (Φ ≈ 0.1).6 However, it is a syntheti-
cally useful pathway; photoreaction of stilbene deriva-
tives at concentrations of 10-2 M or less minimizes the
competing photodimerization in the presence of oxidants
such as oxygen or iodine and gives phenanthrene deriva-
tives in high yields. Although intermolecular photo-
dimerization of stilbene and its derivatives is a promising
bene is the most frequent process (Φt-c ) 0.55, Φc-t
)
0.35).5 Photocyclization of cis-stilbene to give dihydro-
† Osaka Prefecture University.
‡ Gunma University.
(1) (a) Saltiel, J.; D’Agostino, J.; Megarity, E. D.; Metts, L.; Neu-
berger, K. R.; Wrighton, M.; Zafiriou, O. C. In Organic Photochemistry;
Chapman, O. L., Ed.; Marcel Dekker: New York, 1973; Vol. 3, pp
1-113. (b) Waldeck, D. H. Chem. Rev. 1991, 91, 415-436.
10.1021/jo050914+ CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/25/2005
J. Org. Chem. 2005, 70, 9693-9701
9693

Maeda et al.
process for synthesizing cyclobutane compounds, it is not
an efficient process in contrast to cross-photocycloaddi-
tion, even at high concentration (∼10-1 M). Moreover,
because photodimerization competes with cis-trans pho-
toisomerization, dimerized products contain a variety of
regio- and stereoisomers. To overcome these problems,
extensive efforts have been made. For example, photo-
dimerization is accelerated in hydrophilic solvents such
as water7 and methanol.8 Microcavities, for example in
zeolites9 and cyclodextrins,10 rotaxane interaction,11 stil-
bene polymers,12 and photoirradiation to stilbene crys-
tals,13 have also been employed for the acceleration of
the photodimerization.14 These results can be interpreted
as indicating that diminishing the distance between two
stilbene double bonds is necessary for accelerating the
photodimerization of stilbenes. This background prompted
us to design a selective and highly efficient set of three
types of photoreactions by use of stilbenophanes.
The synthesis, as well as the photochemical and
photophysical properties of stilbenophanes, is less
known.15,16 The only example of a photochemical study
of stilbenophanes is that of [2.2]stilbenophane reported
by Wennerstro¨m et al.,15a,b wherein attention was focused
in particular on the cis-trans photoisomerization of [2.2]-
stilbenophane, but the intramolecular photodimerization
of the stilbenophane was not investigated. We chose silyl
chains for the connection of stilbenes, because silyl
tethers can be easily removed after the event. Moreover,
because of a relatively slow intersystem crossing of
organosilicon compounds,17 selective generation of excited
singlet and triplet states is expected. We report herein
the syntheses and photochemical properties of novel
macrocyclic and medium-size stilbenophanes tethered by
silyl chains. By forcing stilbenes to be a part of cyclic
compounds by virtue of silyl tethers, we achieved selec-
tive occurrence of three types of photochemical reactions
of stilbenes. In particular, dramatic acceleration of pho-
todimerization can be developed depending on the dis-
tance between two stilbene units.
(2) (a) Saltiel, J.; Sears, D. F., Jr.; Ko, D.-H.; Park, K.-M. In CRC
Handbook of Organic Photochemistry and Photobiology; Horspool, W.
M., Song, P.-S., Eds.; CRC Press: New York, 1995; pp 3-15. (b)
Hammond, G. S.; Saltiel, J.; Lamola, A. A.; Turro, N. J.; Bradshaw, J.
S.; Cowan, D. O.; Counsell, R. C.; Vogt, V.; Dalton, C. J. Am. Chem.
Soc. 1964, 86, 3197-3217. (c) Saltiel, J.; Megarity, E. D.; Kneipp, K.
G. J. Am. Chem. Soc. 1966, 88, 2336-2338. (d) Saltiel, J. J. Am. Chem.
Soc. 1967, 89, 1036-1037. (e) Saltiel, J. J. Am. Chem. Soc. 1968, 90,
6394-6400. (f) Go¨rner, H.; Schulte-Frohlinde, D. J. Phys. Chem. 1978,
82, 2653-2659. (g) Go¨rner, H.; Schulte-Frohlinde, D. J. Phys. Chem.
1981, 85, 1835-1841.
(3) (a) Kaupp, G. In CRC Handbook of Organic Photochemistry and
Photobiology; Horspool, W. M., Song, P.-S., Eds.; CRC Press: New
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Am. Chem. Soc. 1963, 85, 1601-1605. (c) Rosenberg, H. M.; Rondeau,
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Caldwell, R. A.; Mizuno, K.; Hansen, P. E.; Vo, L. P.; Frentrup, M.;
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Results and Discussion
Synthesis of Stilbenophanes and Related Com-
pounds. Stilbenophanes 1-3 were designed and syn-
thesized as candidates having appropriate distances
between two stilbene units (Scheme 2). Stilbenophanes
4a-c were obtained as cis-fixed stilbenophanes. For
reference compounds, 4,4′-bis(trimethylsilylmethyl)stil-
bene trans-5 and 4,4′-bis(trimethylsilyl)stilbene trans-6
were also prepared.
Syntheses of stilbenophanes 1-4 and related com-
pounds 5 and 6 are shown in Schemes 3-5 and Scheme
S1 (see Supporting Information). Grignard reaction of
xylylene dichlorides 7a-c with chlorodimethylsilane gave
hydrosilanes 8a-c, which were converted to chlorosilanes
9a-c by treatment with PdCl2/CCl4 (Scheme 3). Chlo-
rosilanes 9a-c were then allowed to react with Mg and
p-vinylbenzyl chloride to give bis[(p-vinylphenyl)methyl]
derivatives 10a-c in high yields. Para-substituted mac-
rocyclic and medium-size stilbenophanes, trans,trans-1
and 4c, were prepared by ozonolysis of 10c in the
presence of Zn/AcOH followed by the McMurry coupling
reaction18 of 11c by TiCl4/Zn. Ortho- and meta-substi-
tuted medium-size stilbenophanes 4a,b were synthesized
via the McMurry coupling reaction of 11a,b.
(5) Saltiel, J.; Marinari, A.; Chang, D. W.-L.; Mitchener, J. C. J.
Am. Chem. Soc. 1979, 101, 2982-2996.
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3715.
(8) Ito, Y.; Kajita, T.; Kunimoto, K.; Matsuura, T. J. Org. Chem.
1989, 54, 587-591.
(9) Tung, C.-H.; Wu, L.-Z.; Zhang, L.-P.; Chen, A. B. Acc. Chem. Res.
2003, 36, 39-47.
(10) Herrmann, W.; Wehrle, S.; Wenz, G. Chem. Commun. 1997,
1709-1710.
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2313-2316. (b) Anger, I.; Sandros, K.; Sundahl, M.; Wennerstro¨m, O.
J. Phys. Chem. 1993, 97, 1920-1923. (c) Tsuge, A.; Nishimoto, T.;
Uchida, T.; Yasutake, M.; Moriguchi, T.; Sakata, K. J. Org. Chem.
1999, 64, 7246-7248. (d) Yamato, T.; Fujita, K.; Futatsuki, K.; Tsuzuki,
H. Can. J. Chem. 2000, 78, 1089-1099. (e) Kawase, T.; Ueda, N.;
Tanaka, K.; Seirai, Y.; Oda, M. Tetrahedron Lett. 2001, 42, 5509-5511.
(16) The chemistry of azobenzenophanes has also been developed,
but a significant difference is whether the thermal conversion of cis to
trans isomers occurs: (a) Rau, H.; Lu¨ddecke, E. J. Am. Chem. Soc.
1982, 104, 1616-1620. (b) Tamaoki, N.; Koseki, K.; Yamaoka, T.
Angew. Chem., Int. Ed. 1990, 29, 105-106. (c) Norikane, Y.; Kitamoto,
K.; Tamaoki, N. J. Org. Chem. 2003, 68, 8291-8304.
(11) Amirsakis, D. G.; Elizarov, A. M.; Garcia-Garibay, M. A.; Glink,
P. T.; Stoddart, J. F.; White, A. J. P.; Williams, D. J. Angew. Chem.,
Int. Ed. 2003, 42, 1126-1132.
(12) Herrmann, W.; Schneider, M.; Wenz, G. Angew. Chem., Int. Ed.
1997, 36, 2511-2514.
(13) (a) Coates, G. W.; Dunn, A. R.; Henling, L. M.; Ziller, J. W.;
Lobkovsky, E. B.; Grubbs, R. H. J. Am. Chem. Soc. 1998, 120, 3641-
3649. (b) MacGillivray, L. R.; Reid, J. L.; Ripmeester, J. A. J. Am.
Chem. Soc. 2000, 122, 7817-7818. (c) Varshney, D. B.; Papaefstathiou,
G. S.; MacGillivray, L. R. Chem. Commun. 2002, 1964-1965.
(14) The molecular assembly of stilbazoles is in a similar situation.
See: (a) Quina, F. H.; Whitten, D. G. J. Am. Chem. Soc. 1975, 97,
1602-1603. (b) Bartocci, G.; Mazzucato, U.; Masetti, F.; Galiazzo, G.
J. Phys. Chem. 1980, 84, 847-851.
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Steinmetz, M. G. Chem. Rev. 1995, 95, 1527-1588.
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Synthesis and Photochemical Properties of Stilbenophanes
SCHEME 2. Stilbenophanes and Related
Compounds
and trans-5 appeared at 328 nm, and shoulder peaks
were detected for both at 345 nm. These wavelengths
were shifted to a wavelength ca. 20 nm longer than those
of unsubstituted trans-stilbene. The absorbance of tran-
s,trans-1 (ꢀ(328 nm) ) 5.86 × 104 M-1 cm-1) was 1.5 times
larger than that of trans-5 (ꢀ(328 nm) ) 3.97 × 104 M-1
cm-1), and the integrated absorption of trans,trans-1
(>258 nm) was 1.64 times larger than that of trans-5,
although trans,trans-1 contains two stilbene units per
molecule. These results may be due to the rigidity of the
stilbene units in trans,trans-1.20 A UV absorption spec-
trum of stilbenophane trans,trans-2 was compared with
those of trans-6 and trans-stilbene under the same
conditions. Absorption maxima of trans,trans-2 appeared
at 310 (ꢀ ) 7.25 × 104 M-1 cm-1), 322 (ꢀ ) 6.85 × 104
M-1 cm-1), and 339 nm (ꢀ ) 3.65 × 104 M-1 cm-1). These
wavelengths were close to those of trans-6 (λmax ) 308 (ꢀ
) 3.65 × 104 M-1 cm-1), 321 (ꢀ ) 4.06 × 104 M-1 cm-1),
and 335 nm (ꢀ ) 2.44 × 104 M-1 cm-1)), but the integrated
absorption of trans,trans-2 was 1.93 times larger than
that of trans-6. These results suggest that the stil-
benophane trans,trans-2 has a more flexible structure
than trans,trans-1. A UV absorption spectrum of the
smallest stilbenophane cis,cis-3 showed a broad absorp-
tion band whose maximum appeared at 288 nm (ꢀ ) 2.33
× 104 M-1 cm-1). This spectrum resembles that of [2.2]-
(4,4′)-cis,cis-stilbenophane, whose maximun appeared at
270 nm.15b
Direct Photoreaction of Stilbenophanes. Photo-
irradiation (>280 nm) of a benzene-d6 solution containing
stilbenophane trans,trans-1 (0.02 M) by a high-pressure
mercury lamp through a Pyrex filter for 1 h gave
photocycloadducts 17 and 18 in a 10:1 ratio in an overall
yield of greater than 90% (Scheme 6). The stereochem-
istry of the products was determined by 1H NMR spectra
of the reaction mixture. During the progress of the
photoreaction of trans,trans-1 in benzene-d6, two sharp
singlet peaks appeared at 4.5 and 4.1 ppm in a 10:1
integral ratio, which is ascribable to the hydrogens
attached to the cyclobutane rings of the cis,trans,cis
isomer 17 and the all-trans isomer 18, respectively. A
similar photoreaction of trans,trans-2, whose stilbene
units are located more closely together, proceeded faster
than the reaction of trans,trans-1 to produce the
cis,trans,cis isomer 19 and the all-trans isomer 20 in a
3:1 ratio. These photoreactions also proceeded efficiently
in CH2Cl2, with similar isomeric ratios. A decrease in
absorbance during the photoreaction of trans,trans-1 in
CH2Cl2 clearly indicates the decay of the internal stilbene
units (Figure S4).
trans,trans-2 was synthesized as follows. 4,4′-Dibro-
mostilbene 12, which was prepared by McMurry coupling
of p-bromobenzaldehyde, was lithiated by t-BuLi to give
4,4′-dilithiostilbene (Scheme 4). This was then allowed
to react with 1,3-bis(chlorodimethylsilylmethyl)benzene
9b to afford stilbenophane trans,trans-2 in 2.6% yield.
Synthesis of the smallest stilbenophane 3, having two
stilbene units, is shown in Scheme 5. A Grignard coupling
reaction between dichlorodiphenylsilane and p-(chloro-
methyl)styrene produced 13.19 Ozonolysis of 13 followed
by McMurry coupling of 14 gave cis,cis-3 in 1.1% yield,
but the desired trans,trans isomer was not obtained (vide
infra).
See the Supporting Information about the synthesis
of trans-5 and trans-6 (Scheme S1).
Structures of Stilbenophanes. The structures of the
stilbenophanes trans,trans-1, trans,trans-2, cis,cis-3, and
4a-c were determined on the basis of their spectral and
analytical data, and confirmed by X-ray crystallographic
analysis of trans,trans-1 and cis,cis-3 (Figures S1 and S2).
X-ray crystallographic analysis of trans,trans-1 showed
a partial loss of planarity of the stilbene units (Figure
S1). The distance between two stilbene double bonds is
about 7 Å, and the two stilbene units align like stairs.
X-ray crystallographic analysis of cis,cis-3 clearly showed
its cis,cis structure (Figure S2). Geometry optimization
of trans,trans-3 via an HF/3-21G* calculation showed a
bent structure of the trans-stilbene units having 29.2 kJ/
mol higher enthalpy than that of cis,cis-3. Indeed, the
only isolable isomer was the cis,cis one in the McMurry
coupling reaction of 14.
Because the efficiency of intermolecular photodimer-
ization of stilbenes is dependent on concentration, cis-
trans photoisomerization occurs preferentially in dilute
conditions. In fact, photoreactions of trans-5 and trans-6
under the same conditions (0.02 M) did not give detect-
able amounts of photodimerized products. Only cis-trans
photoisomerization took place, giving photostationary
state mixtures in a trans-5:cis-5 ratio of 40:60 and a
trans-6:cis-6 ratio of 16:84 (Scheme S2). In the photore-
actions of stilbenophanes trans,trans-1 and trans,trans-
UV Absorption of Stilbenophanes. A UV absorption
spectrum of the stilbenophane trans,trans-1 was mea-
sured in CH2Cl2, and was compared with those of trans-5
and trans-stilbene at the same concentration (2 × 10-5
M) (Figure S3). Absorption maxima for both trans,trans-1
(18) (a) Mukaiyama, T.; Sato, T.; Hanna, J. Chem. Lett. 1973, 1041-
1044. (b) McMurry, J. E.; Fleming, M. P. J. Org. Chem. 1976, 41, 896-
897. (c) McMurry, J. E.; Fleming, M. P.; Kees, K. L.; Kreoski, L. R. J.
Org. Chem. 1978, 43, 3255-3266. (d) Detsi, A.; Koufaki, M.; Calog-
eropoulou, T. J. Org. Chem. 2002, 67, 4608-4611.
(19) Nakanishi, K.; Mizuno, K.; Otsuji, Y. J. Chem. Soc., Perkin
Trans. 1 1990, 3362-3363.
(20) For the decreased absorption of twisted stilbenes, see: Gano,
J. E.; Osborn, D. J., III; Kodali, N.; Sekher, P.; Liu, M.; Luzik, E. D.,
Jr. J. Org. Chem. 2003, 68, 3710-3713.
J. Org. Chem, Vol. 70, No. 24, 2005 9695

Maeda et al.
SCHEME 3. Synthesis of Stilbenophanes trans,trans-1 and 4a-c
SCHEME 4. Synthesis of Stilbenophane
trans,trans-2
SCHEME 5. Synthesis of Stilbenophane cis,cis-3
even with [2.2](4,4′)-trans,trans-stilbenophane.15a The
product ratios of 17:18 and 19:20 reflect the equilibrium.
Direct photoreaction of cis,cis-3 in benzene-d6 produced
the cis,trans,cis type photocycloadduct 21 quantitatively
2, the stereochemistry of the photoproducts clearly
demonstrated that the intramolecular photocycloaddition
took place faster than photoisomerization to cis isomers.
Rotation of the double bonds of trans,trans-1 and
trans,trans-2 in the ground state, as shown in Scheme
7, might be a fast process, and it should occur in solution
at room temperature, even though it involves the loss of
resonance stabilization over two benzene rings and the
double bonds.21 In fact, this equilibrium exists at 165 K
1
(Scheme 8). The stereochemistry was determined by H
NMR spectra, in which a signal due to the hydrogens on
the cyclobutane ring of 21 appeared at 4.2 ppm. The
stereochemistry of 21 clearly suggests the intermediacy
of the trans,trans-3. Changes in the UV absorption
spectra during the photoirradiation of a solution of
(21) The crankshaft motion has a precedent in the dynamic disorder
of the stilbene crystal. See: (a) Ogawa, K.; Sano, T.; Yoshimura, S.;
Takeuchi, Y.; Toriumi, K. J. Am. Chem. Soc. 1992, 114, 1041-1051.
(b) Galli, S.; Mercandelli, P.; Sironi, A. J. Am. Chem. Soc. 1999, 121,
3767-3772. (c) Saito, K.; Okada, M.; Akutsu, H.; Sorai, M. Chem. Phys.
Lett. 2000, 318, 75-78. (d) Khuong, T.-A. V.; Zepeda, G.; Sanrame, C.
N.; Dang, H.; Bartberger, M. D.; Houk, K. N.; Garcia-Garibay, M. A.
J. Am. Chem. Soc. 2004, 126, 14778-14786.
9696 J. Org. Chem., Vol. 70, No. 24, 2005

Synthesis and Photochemical Properties of Stilbenophanes
SCHEME 6. Direct Photoreaction of trans,trans-1 and trans,trans-2
SCHEME 7. Rotation of Double Bonds in
Stilbenophanes
Triplet-Sensitized Photoreaction of Stilbeno-
phanes. To understand the photochemical properties of
triplet stilbenophanes, triplet sensitization was carried
out. Photoirradiation of benzene solutions containing
trans,trans-1 by using benzophenone (ET ) 288 kJ mol-1
)
and benzil (ET ) 226 kJ mol-1) caused only cis-trans
photoisomerization, giving photostationary state mix-
tures of trans,trans-1, cis,trans-1, and cis,cis-1 in ap-
proximately 1:1:1 and 2:3:6 ratios, respectively, after
irradiation for 1 h, without any formation of intramo-
lecular photocycloadducts (Scheme 9). A similar benzil-
sensitized photoreaction of trans,trans-2 gave a photo-
stationary trans,trans-2/cis,trans-2/cis,cis-2 mixture in a
ratio of 4:28:68. Benzil-sensitized photoisomerization of
trans-5 and trans-6 gave photostationary mixtures of
trans-5 and cis-5 (20:80) and trans-6 and cis-6 (12:88),
respectively (Scheme S3). From these results, triplet
energies (ET) of trans,trans-1 and -2 and trans-5 and -6
were estimated to be lower than that of unsubstituted
trans-stilbene, and the ET values for trans,trans-2 and
trans-6 might be larger than those of trans,trans-1 and
trans-5, respectively.1a,2b,23
SCHEME 8. Direct Photoreaction of cis,cis-3
The benzophenone-sensitized photoreaction of cis,cis-3
with irradiation at wavelengths greater than 360 nm
gave only photocycloadduct 21 (Scheme 10). The stereo-
chemistry of the product was the same as that obtained
upon direct photoreaction. When the time dependence of
the benzophenone-sensitized photoreaction of cis,cis-3
was monitored by 1H NMR in C6D6 in order to detect any
intermediates, two singlet peaks (2.51 and 2.74 ppm)
appeared initially, along with the decay of a singlet peak
at 2.42 ppm, which is ascribable to the benzylic hydro-
gens on cis,cis-3; a singlet peak at 2.75 ppm then grew,
and finally, all of the peaks were converted to two doublet
peaks (2.81 and 2.95 ppm, J ) 15.0 Hz). The two singlet
peaks (2.51 and 2.74 ppm) and the singlet peak
(2.75 ppm) can be assigned to cis,trans-3 and trans,trans-
3, respectively. These results clearly suggest that
trans,trans-3, generated by the triplet isomerization of
cis,cis-3, can react intramolecularly to produce photo-
cis,cis-3 in CH2Cl2 are shown in Figure S5. In the
photoreaction of cis,cis-3, the absorption maxima of
cis,cis-3 first shifted from 288 nm to the longer wave-
length (295 nm), and then decayed. This phenomenon
corresponds to the photoisomerization from cis,cis-3 to
trans,trans-3 followed by intramolecular photocycload-
dition. Rotation of the double bonds of trans,trans-3
shown in Scheme 7 should occur, but the D2 conformation
of trans,trans-3 cannot produce an all-trans isomer,
because intramolecular photodimerization of bis[(p-vi-
nylphenyl)methyl]silanes produced only cis-fused cyclic
compounds for steric reasons.19,22
(22) (a) Mizuno, K.; Nakanishi, K.; Otsuji, Y.; Hayamizu, T.; Maeda,
H.; Adachi, T.; Ishida, A.; Takamuku, S. J. Photosci. 2003, 10, 121-
126. (b) Maeda, H.; Yagi, H.; Mizuno, K. Chem. Lett. 2004, 33, 388-
389.
(23) Herkstoeter, W. G.; Hammond, G. S. J. Am. Chem. Soc. 1966,
88, 4769-4777.
J. Org. Chem, Vol. 70, No. 24, 2005 9697

Maeda et al.
SCHEME 9. Triplet-Sensitized Photoreaction of trans,trans-1 and trans,trans-2
SCHEME 10. Triplet-Sensitized Photoreaction of
cis,cis-3
SCHEME 11. Photoreaction of 4a-c
cycloadduct 21 from its excited triplet state. In the direct
photoreaction of cis,cis-3 shown in Scheme 8, no inter-
mediates were observed in the time-dependent 1H NMR
studies, because of the rapid intramolecular photodimer-
ization.
Photocyclization to Phenanthrenophanes. The
photoreaction of the cis-fixed stilbenophanes 4a-c in the
presence of oxygen readily afforded phenanthrenophanes
22a-c (Scheme 11). In the reaction of the ortho-deriva-
tive 4a, dialdehyde 11a was obtained as an oxidation
product in small amounts together with the formation
of 22a,24 probably due to the steric factor of 22a. Ben-
zophenone-sensitized photoreactions of 4a-c were also
carried out, but trans isomers of 4a-c were not formed
at all. UV absorption and fluorescence spectra of phenan-
threnophanes 22a-c and a reference compound, 3,6-bis-
(trimethylsilylmethyl)phenanthrene 23, were measured
in cyclohexane (Figures S6 and S7). The absorption and
fluorescence spectra of 22a-c were quite similar to those
of 23, which are typical spectra corresponding to those
of phenanthrene derivatives.
excitation wavelength (291.5 nm, Abs ) 0.263); these
showed that trans,trans-1 has a greater fluorescence
intensity than trans-5 and unsubstituted trans-stilbene
(Figure S8). The fluorescence quantum yields (Φf) of
trans,trans-1 and trans-5 were determined to be 0.20 and
0.17, respectively, based on the Φf of trans-stilbene (Φf
) 0.030 in CH2Cl2).25 It is known that silyl substituents
often increase the fluorescence quantum yields of aro-
matic hydrocarbons.26 The result that the cyclized com-
pound trans,trans-1 has a higher fluorescence quantum
yield than trans-5 may be explained by a decrease of
Fluorescence of Stilbenophanes. The fluorescence
spectra of trans,trans-1 and trans-5 were measured so
that the same absorbance was obtained at the specified
(24) It is known that photooxygenation of trans- and cis-stilbene in
the presence of 9,10-dicyanoanthracene or tetraphenylporphyrin pro-
duces benzaldehyde. See: (a) Spada, L. T.; Foote, C. S. J. Am. Chem.
Soc. 1980, 102, 391-393. (b) Manring, L. E.; Kramer, M. K.; Foote, C.
S. Tetrahedron Lett. 1984, 25, 2523-2526. (c) Kwon, B.-M.; Foote, C.
S.; Khan, S. I. J. Org. Chem. 1989, 54, 3378-3382.
(25) The reported result for Φf of trans-stilbene in hexane is 0.04:
(a) Charlton, J. L.; Saltiel, J. J. Phys. Chem. 1977, 81, 1940-1944. (b)
Saltiel, J.; Waller, A. S.; Sears, D. F., Jr.; Garrett, C. Z. J. Phys. Chem.
1993, 97, 2516-2522. Φf ) 0.030 ( 0.001 in CH2Cl2 was determined
by the integral ratio of fluorescence in CH2Cl2 and hexane.
9698 J. Org. Chem., Vol. 70, No. 24, 2005

Synthesis and Photochemical Properties of Stilbenophanes
TABLE 1. Fluorescence Lifetimes, Fluorescence
Quantum Yields, and Rate Constants for Fluorescence
Radiation of Stilbenophanes and Related Compounds
come close enough to form an excimer by bond rotation
of the silyl tethers.
Fluorescence quantum yields (Φf) of these compounds
were determined in CH2Cl2 degassed by several freeze-
pump-thaw cycles in order to exclude the dissolved
dioxygen. Fluorescence quantum yields (Φf) can be
described by the equation Φf ) kfτs, where kf and τs
represent the rate constant for fluorescence radiation and
the fluorescence lifetime, respectively. The Φf values and
calculated kf values are also listed in Table 1. Fluores-
cence quantum yields and fluorescence lifetimes of silyl-
substituted trans-stilbenes are both larger than those of
unsubstituted trans-stilbene.32 The fluorescence quantum
yields and fluorescence lifetimes of macrocyclic stil-
benophanes further increased compared with those of
acyclic stilbenes.
To observe phosphorescence radiation, we measured
emission spectra at low temperature (Figures S10-
S13).33 However, there was negligible phosphorescence
from trans,trans-1, trans,trans-2, trans-5, and trans-6 in
MP at 77 K. To confirm the formation of triplet stilbene,
transient absorption spectra of CH2Cl2 solutions contain-
ing trans,trans-1 and trans-5 upon 308 nm laser pho-
tolysis were measured (Figures S14 and S15). A transient
absorption maximum appeared at 540 nm for both
compounds, with lifetimes of 370 µs (trans,trans-1) and
240 µs (trans-5). The lifetimes of the transient absorption
maxima were not influenced by dissolved oxygen. The
absorption bands that appeared at 540 nm can be
assigned to the radical cations of trans,trans-1 and trans-
5,34 and therefore, we were unable to observe any triplet
states in the transient absorption measurements. These
data suggest that intersystem crossing from the excited
singlet state to the excited triplet state is an unfavorable
process, and that participation of the excited triplet state
can be ruled out in experiments involving direct photo-
irradiation.
a
compound
τs
Φfb
kfc (s-1
)
trans,trans-1 863 ps (88%), 262 ps (12%)
trans,trans-2 496 ps (76%), 195 ps (24%)
0.20 2.32 × 108
0.11 2.22 × 108
cis,cis-3
8.4 ns (94.7%), 166 ps (4.7%),
19.2 ps (0.6%)
d
d
trans-5
trans-6
590 ps (96%), 141 ps (4%)
322 ps (95%), 103 ps (5%)
0.17 2.88 × 108
0.08 2.48 × 108
a Fluorescence lifetimes in aerated cyclohexane at 295 K, OD
) ca. 0.1, λex ) 266 nm (Ti- sapphire laser). b Fluorescence
quantum yield in CH2Cl2 at 301 K, degassed by freeze-pump-
thaw cycles, λex ) 291.5 nm. c Rate constant for fluorescence
radiation, calculated by kf ) Φf/τs. d Not determined.
the nonradiative decay rate due to the loss of flexibility
of stilbene units in trans,trans-1. Similar results
were obtained in the fluorescence measurements of
trans,trans-2 and trans-6. The fluorescence quantum
yields of trans,trans-2 and trans-6 were determined to
be 0.11 and 0.08, respectively.
A fluorescence spectrum of cis,cis-3 in CH2Cl2 at 2 ×
10-5 M showed a broad band whose maximum intensity
appeared at 441 nm (Figure S9). Stilbene itself is not
such an emissive molecule. Fluorescence quantum yields
of trans-stilbene and cis-stilbene are reported to be 0.0425
and <0.001,27 respectively, at room temperature.28 The
stilbene excimer has hardly been observed in general,
with the exception of the following: γ-radiation at 77 K,29
[2.2]stilbenophane,15b stilbene-linked oligonucleotides,30
and aqueous γ-cyclodextrin solution.31 To confirm whether
the observed fluorescence spectrum is based on an
intramolecular stilbene excimer or not, fluorescence
lifetimes (τs) were measured (Table 1). The observation
of a multiexponential decay suggests the existence of
different emitting conformers. From the long lifetime of
the major component (8.4 ns), the relatively long wave-
length of the fluorescence maximum, and its lack of
structure, we concluded that the emission can be assigned
to the intramolecular stilbene excimer of cis,cis-3. The
two cis-stilbene units are located in remote positions in
the X-ray crystallographic analysis (Figure S2), but it
may be possible that the cis-stilbene moieties in cis,cis-3
Conclusions
In conclusion, the intramolecular photodimerization of
stilbenes was accelerated by tethering two stilbene units
intramolecularly. The efficiency of the intramolecular
photodimerization depends on the distance between the
two stilbene double bonds. Triplet-sensitized photoreac-
tions of stilbenophanes cause cis-trans photoisomeriza-
tion, and the cis-trans ratio in the photostationary state
depends on the triplet energies of the photosensitizer.
Photoirradiation of cis-fixed stilbenophanes in the pres-
ence of oxygen gives the corresponding phenanthreno-
phanes. Fluorescence quantum yields of stilbenes in-
crease with the introduction of silyl groups. Intramolecu-
lar photodimerization via the excited triplet state and
emission of an intramolecular stilbene excimer were
observed when the silyl tethers were effectively short.
(26) (a) Declercq, D.; Delbeke, P.; DeSchryver, F. C.; Van Meervelt,
L.; Miller, R. D. J. Am. Chem. Soc. 1993, 115, 5702-5708. (b) Kyushin,
S.; Ikarugi, M.; Goto, M.; Hiratsuka, H.; Matsumoto, H. Organome-
tallics 1996, 15, 1067-1070. (c) Hiratsuka, H.; Kobayashi, S.; Mi-
negishi, T.; Hara, M.; Okutsu, T.; Murakami, S. J. Phys. Chem. A 1999,
103, 9174-9183. (d) Maeda, H.; Inoue, Y.; Ishida, H.; Mizuno, K. Chem.
Lett. 2001, 1224-1225. (e) Desvergne, J.-P.; Bonneau, R.; Do¨rr, G.;
Bouas-Laurent, H. Photochem. Photobiol. Sci. 2003, 2, 289-296. (f)
Maeda, H.; Maeda, T.; Mizuno, K.; Fujimoto, K.; Shimizu, H.; Inouye,
M. Chem.sEur. J., in press.
(27) (a) Saltiel, J.; Waller, A.; Sun, Y.-P.; Sears, D. F., Jr. J. Am.
Chem. Soc. 1990, 112, 4580-4581. (b) Saltiel, J.; Waller, A. S.; Sears,
D. F., Jr. J. Photochem. Photobiol., A 1992, 65, 29-40. (c) Saltiel, J.;
Waller, A. S.; Sears, D. F., Jr. J. Am. Chem. Soc. 1993, 115, 2453-
2465.
(28) Structurally rigid analogues of stilbenes are strongly fluorescent
even at room temperature: (a) Saltiel, J.; Zafiriou, O. C.; Megarity, E.
D.; Lamola, A. A. J. Am. Chem. Soc. 1968, 90, 4759-4760. (b) DeBoer,
C. D.; Schlessinger, R. H. J. Am. Chem. Soc. 1968, 90, 803-804.
(29) Brocklehurst, B.; Bull, D. C.; Evans, M.; Scott, P. M.; Stanney,
G. J. Am. Chem. Soc. 1975, 97, 2977-2978.
(32) For unsubstituted trans-stilbene, Φf ) 0.0400, τs ) 63.6 ps, and
kf ) 6.30 × 108 s-1 in hexane at 303.1 K. See ref 25b.
(33) Phosphorescence of stilbenes has rarely been observed, except
in cases involving the presence of heavy atoms: (a) Go¨rner, H. J. Phys.
Chem. 1989, 93, 1826-1832. (b) Ramamurthy, V.; Caspar, J. V.;
Corbin, D. R. Tetrahedron Lett. 1990, 31, 1097-1100. (c) Ramamurthy,
V.; Caspar, J. V.; Eaton, D. F.; Kuo, E. W.; Corbin, D. R. J. Am. Chem.
Soc. 1992, 114, 3882-3892.
(30) Lewis, F. D.; Wu, T.; Burch, E. L.; Bassani, D. M.; Yang, J.-S.;
Schneider, S.; Ja¨ger, W.; Letsinger, R. L. J. Am. Chem. Soc. 1995, 117,
8785-8792.
(31) Agbaria, R. A.; Roberts, E.; Warner, I. M. J. Phys. Chem. 1995,
99, 10056-10060.
(34) Hara, M.; Tojo, S.; Majima, T. J. Photochem. Photobiol., A 2004,
162, 121-128.
J. Org. Chem, Vol. 70, No. 24, 2005 9699

Maeda et al.
(s, 4 H), 2.01 (s, 4 H), 6.38 (s, 1 H), 6.73 (s, 2 H), 6.75 (dd, J )
7.5, 1.7 Hz, 2 H), 6.85 (d, J ) 8.2 Hz, 4 H), 6.97 (d, J ) 8.2 Hz,
4 H), 7.08 (t, J ) 7.6 Hz, 1 H); 13C NMR (75 MHz, CDCl3) δ
-2.0, 23.4, 24.8, 123.8, 127.5, 128.1, 129.1, 130.7, 130.8, 134.0,
138.4, 139.1; IR (KBr) 3043, 2956, 2881, 1602, 1502, 1415,
1247, 843 cm-1; MS (EI), m/z ) 73, 145, 319, 426 (M+).
Stilbenophane trans,trans-2. To 12 (776 mg, 2.0 mmol)
in THF (300 mL) was added t-BuLi (1.54 M in pentane, 5.5
mL, 8.0 mmol) at -77 °C, and the mixture was stirred for 30
min. To the solution was added 9b (1.17 g, 4 mmol) in THF
(30 mmol) at -77 °C, and the mixture was stirred for an
additional 30 min. Then the solution was gradually warmed
to room temperature, and stirring was continued for 16 h.
Ether (100 mL) and saturated NaHCO3 aqueous solution were
added. The organic layer was separated, dried over Na2SO4,
and evaporated. The residue was purified by column chroma-
tography on silica gel and recycling preparative HPLC. Addi-
tion of acetone to a fraction gave a precipitate of trans,trans-2
(21 mg, 2.6%). Data for trans,trans-2: colorless solid; mp 242-
244 °C; 1H NMR (300 MHz, CDCl3) δ 0.23 (s, 24 H), 2.11 (s, 8
H), 6.19 (s, 2 H), 6.62 (dd, J ) 7.5, 1.7 Hz, 4 H), 6.95 (t, J )
7.5 Hz, 2 H), 7.09 (s, 4 H), 7.34 (d, J ) 8.1 Hz, 8 H), 7.42 (d,
J ) 8.2 Hz, 8 H); 13C NMR (75 MHz, CDCl3) δ -3.2, 26.2, 124.1,
125.6, 127.7, 128.4, 129.0, 134.2, 137.7, 137.9, 139.0; IR (KBr)
2954, 1597, 1247, 1111, 838 cm-1; TOF-MS, m/z ) 796 (M+);
HRMS (EI) calcd for C52H60Si4 796.3772, found, 796.3785.
Stilbenophane cis,cis-3. To TiCl4 (5.69 g, 30 mmol) in
DME (50 mL) was added Zn powder (3.92 g, 60 mmol) at 0 °C.
The mixture was refluxed for 1 h. After cooling the mixture to
room temperature, we added bis(4-formylphenylmethyl)dim-
ethylsilane (14, 1.26 g, 3 mmol) in DME (50 mL) dropwise,
and then stirred the mixture for 20 h under reflux. After
cooling to room temperature, we added ethanol (10 mL), and
stirring was continued. The reaction mixture was filtered
through silica gel, and then evaporated. Purification by column
chromatography on silica gel and recycling preparative HPLC
gave stilbenophane cis,cis-3 (13 mg, 1.1%). Data for cis,cis-3:
colorless solid; mp 280-282 °C; 1H NMR (300 MHz, CDCl3) δ
2.56 (s, 8 H), 6.51 (s, 4 H), 6.67 (d, J ) 8.2 Hz, 8 H), 6.90 (d,
J ) 8.1 Hz, 8 H), 7.23-7.41 (m, 20 H); 13C NMR (75 MHz,
CDCl3) δ 22.8, 127.5, 128.6, 128.6, 129.5, 129.9, 133.7, 133.8,
135.5, 136.9; IR (KBr) 3014, 2923, 1509, 837 cm-1; TOF-MS,
m/z ) 778 (M+); HRMS (EI) calcd for C56H48Si2 776.3295, found
776.3299.
The synthesis of silicon-containing macrocyclic com-
pounds has recently attracted much attention from the
synthetic and structural viewpoints as well as that of
molecular recognition.35 By virtue of silyl tethers, we can
achieve control of stilbene photochemistry.
Experimental Section
Stilbenophanes trans,trans-1 and 4c. To TiCl4 (3.68 g,
19.4 mmol) in THF (50 mL) was added Zn powder (2.42 g, 37.0
mmol) at 0 °C. The mixture was refluxed for 1 h. After cooling
the mixture to room temperature, we added 11c (800 mg, 1.8
mmol) in THF (50 mL) dropwise, and the mixture was then
stirred for 24 h under reflux. After cooling the mixture to room
temperature, we added ethanol (10 mL), and stirring was
continued. The reaction mixture was filtered through silica
gel, and then evaporated. The residue was purified by column
chromatography on silica gel followed by recycling preparative
HPLC. Addition of acetone to a fraction gave a pure precipitate
of trans,trans-1 (99 mg, 13.8%). Compound 4c was obtained
from another fraction (65 mg, 9.0%). Data for trans,trans-1:
colorless solid; mp 240-241 °C; 1H NMR (300 MHz, CDCl3) δ
-0.02 (s, 24 H), 2.05 (s, 8 H), 2.11 (s, 8 H), 6.78 (d, J ) 7.9 Hz,
8 H), 6.86 (s, 8 H), 6.92 (s, 4 H), 7.25 (d, J ) 8.1 Hz, 8 H); 13
C
NMR (75 MHz, CDCl3) δ -3.1, 24.3, 25.0, 126.1, 127.0, 128.0,
128.4, 133.3, 135.1, 139.3; IR (KBr) 3018, 2954, 2887, 1509,
1244, 968, 853 cm-1; TOF-MS, m/z ) 858 (M+); HRMS (EI)
calcd for C56H68Si4 852.4398, found 852.4402. Data for 4c: 1H
NMR (300 MHz, CDCl3) δ 0.01 (s, 12 H), 2.05 (s, 4 H), 2.18 (s,
4 H), 6.03 (s, 2 H), 6.60 (d, J ) 8.1 Hz, 4 H), 6.65 (s, 4 H), 6.80
(d, J ) 8.2 Hz, 4 H); MS (EI), m/z ) 145, 163, 219, 426 (M+).
Stilbenophane 4a. To TiCl4 (1.64 g, 8.65 mmol) in DME
(50 mL) was added Zn powder (1.13 g, 17.3 mmol) at 0 °C.
The mixture was refluxed for 1 h. After cooling the mixture to
room temperature, we added 11a (1.32 g, 2.88 mmol) in DME
(50 mL) dropwise, and then stirred for 24 h under reflux. After
cooling the mixture to room temperature, we added ethanol
(20 mL), and stirring was continued. The reaction mixture was
filtered through silica gel, and then evaporated. Purification
by column chromatography on silica gel and recycling prepara-
tive HPLC gave 4a (164 mg, 13.3%). Data for 4a: colorless
solid; mp 167-170 °C; 1H NMR (300 MHz, CDCl3) δ -0.16 (s,
12 H), 1.98 (s, 4 H), 2.10 (s, 4 H), 6.77 (d, J ) 8.2 Hz, 4 H),
6.81 (s, 2 H), 6.83 (d, J ) 8.1 Hz, 4 H); 13C NMR (75 MHz,
CDCl3) δ -3.8, 21.6, 26.5, 123.8, 127.0, 129.4, 129.8, 132.1,
134.4, 135.6, 138.2; IR (KBr) 3015, 2953, 2885, 1603, 1503,
1414, 1246, 1209, 1148, 826 cm-1; MS (EI), m/z ) 73, 145, 264,
426 (M+).
4,4′-trans-Bis(trimethylsilylmethyl)stilbene (trans-5).
To TiCl4 (5.69 g, 30.0 mmol) in DME (50 mL) was added Zn
powder (3.92 g, 60.0 mmol) at 0 °C. The mixture was refluxed
for 1 h. After cooling the mixture to room temperature, we
added 4-(trimethylsilylmethyl)benzaldehyde (16, 3.90 g, 20
mmol) in DME (50 mL) dropwise, and then stirred for 20 h
under reflux. After cooling the mixture to room temperature,
we added ethanol (10 mL), and stirring was continued. The
reaction mixture was filtered through silica gel, and then
evaporated. Purification by column chromatography on silica
gel and recycling preparative HPLC gave 4,4′-trans-bis(tri-
methylsilylmethyl)stilbene (trans-5, 382 mg, 10.7%). Data for
Stilbenophane 4b. To TiCl4 (1.52 g, 8.0 mmol) in DME
(20 mL) was added Zn powder (1.05 g, 16.0 mmol) at 0 °C.
The mixture was refluxed for 1 h. After cooling the mixture to
room temperature, we added 11b (917 mg, 2.0 mmol) in DME
(30 mL) dropwise, then the mixture was stirred for 24 h under
reflux. After cooling the mixture to room temperature, we
added ethanol (10 mL), and stirring was continued. The
reaction mixture was filtered through silica gel, and then
evaporated. Purification by column chromatography on silica
gel (eluent, benzene:hexane ) 1:2) and recycling preparative
HPLC gave 4b (81 mg, 9.7%). Data for 4b: colorless solid; mp
114-117 °C; 1H NMR (300 MHz, CDCl3) δ 0.17 (s, 12 H), 1.81
1
trans-5: colorless solid; mp 137-141 °C; H NMR (300 MHz,
CDCl3) δ 0.00 (s, 18 H), 2.09 (s, 4 H), 6.97 (d, J ) 8.4 Hz, 8 H),
7.00 (s, 2 H), 7.35 (d, J ) 8.2 Hz, 4 H); 13C NMR (75 MHz,
CDCl3) δ -1.8, 27.1, 126.1, 127.0, 128.2, 133.3, 139.8; IR (KBr)
2954, 1510, 1246, 851 cm-1; MS (EI), m/z ) 73, 279, 352 (M+);
HRMS (EI) calcd for C22H28Si2 352.2042, found 352.2046.
4,4′-trans-Bis(trimethylsilyl)stilbene (trans-6). To 12
(1.14 g, 3.4 mmol) in THF (300 mL) was added t-BuLi (1.54 M
in pentane, 9.1 mL, 14.0 mmol) at -77 °C, and the mixture
was stirred for 30 min. To the solution was added Me3SiCl
(1.52 g, 14 mmol) in THF (30 mmol) at -77 °C, and stirring
was continued for an additional 30 min. The solution was then
gradually warmed to room temperature, and stirring was
continued for 16 h. Ether (100 mL) and saturated NaHCO3
aqueous solution were added. The organic layer was separated,
dried over Na2SO4, and evaporated. Recrystallization from
ethanol gave 4,4′-trans-bis(trimethylsilyl)stilbene (trans-6, 858
mg, 78%). Data for trans-6: colorless solid; mp 155-156 °C;
(35) For silicon-containing macrocyclic compounds: (a) Ko¨nig, B.;
Ro¨del, M.; Bubenitschek, P.; Jones, P. G. Angew. Chem., Int. Ed. 1995,
34, 661-662. (b) Liu, F.-Q.; Harder, G.; Tilley, T. D. J. Am. Chem.
Soc. 1998, 120, 3271-3272. (c) Yoshida, M.; Goto, M.; Nakanishi, F.
Organometallics 1999, 18, 1465-1470. (d) Kwon, E.; Sakamoto, K.;
Kabuto, C.; Kira, M. Chem. Lett. 2000, 1416-1417. (e) Me´zailles, N.;
Maigrot, N.; Hamon, S.; Ricard, L.; Mathey, F.; Le Floch, P. J. Org.
Chem. 2001, 66, 1054-1056. (f) Unno, M.; Negishi, K.; Matsumoto,
H. Chem. Lett. 2001, 340-341. (g) Kyushin, S.; Kitahara, T.; Tanaka,
R.; Takeda, M.; Matsumoto, T.; Matsumoto, H. Chem. Commun. 2001,
2714-2715. (h) Zhang, H.; Lam, K. T.; Chen, Y. L.; Mo, T.; Kwok, C.
C.; Wong, W. Y.; Wong, M. S.; Lee, A. W. M. Tetrahedron Lett. 2002,
43, 2079-2082. (i) Negishi, K.; Unno, M.; Matsumoto, H. Chem. Lett.
2004, 33, 430-431.
9700 J. Org. Chem., Vol. 70, No. 24, 2005

Synthesis and Photochemical Properties of Stilbenophanes
1H NMR (300 MHz, CDCl3) δ 0.28 (s, 18 H), 7.13 (s, 2 H), 7.48-
7.54 (m, 8 H); 13C NMR (75 MHz, CDCl3) δ -1.0, 125.7, 128.8,
133.6, 137.6, 139.9; IR (KBr) 2955, 1597, 1250, 1113, 970, 841
cm-1; MS (EI), m/z ) 73, 147, 309, 324 (M+); HRMS (EI) calcd
for C20H28Si2 324.1730, found 324.1714.
Direct Photoreaction of trans,trans-1. A C6D6 (1 mL)
solution of trans,trans-1 (1 mg) was degassed by bubbling of
argon before photoirradiation. Photoirradiation of the solution
was carried out with a 300-W high-pressure mercury lamp
through a Pyrex filter for 1 h at room temperature. Two singlet
peaks appeared at 4.52 and 4.10 ppm, with an integral ratio
of 10:1; these were assigned to hydrogens on cyclobutane rings
of 17 and 18. See Supporting Information.
Direct Photoreaction of trans,trans-2. A C6D6 (1 mL)
solution of trans,trans-2 (1 mg) was irradiated as described
above. Two singlet peaks appeared at 4.46 and 4.13 ppm, with
an integral ratio of 3:1; these were assigned to hydrogens on
cyclobutane rings of 19 and 20. See Supporting Information.
Direct Photoreaction of cis,cis-3. A C6D6 (1 mL) solution
of cis,cis-3 (1 mg) was irradiated as described above. Product
21 was obtained quantitatively. Data for 21: 1H NMR (300
MHz, C6D6) δ 2.81 (d, J ) 15.0 Hz, 4 H), 2.95 (d, J ) 15.0 Hz,
4 H), 4.21 (s, 4 H), 6.33 (dd, J ) 7.9, 1.8 Hz, 2 H), 6.54 (dd, J
) 7.9, 1.8 Hz, 2 H), 6.70 (dd, J ) 7.9, 2.0 Hz, 2 H), 6.77 (dd, J
) 8.1, 1.9 Hz, 2 H), 7.12-7.32 (m, 24 H), 7.67 (dd, J ) 7.6, 1.7
Hz, 2 H), 7.75 (dd, J ) 7.6, 1.7 Hz, 2 H).
Triplet-Sensitized Photoreaction of trans,trans-1. A
C6D6 (1 mL) solution of trans,trans-1 (1 mg) and benzophenone
(1 mg) was irradiated through a cutoff filter (>360 nm). A
singlet peak at -0.10 ppm was assigned to trans,trans-1.
Singlet peaks appearing at -0.14 and -0.02 ppm were
assigned to cis,trans-1. A singlet peak at -0.10 ppm was
assigned to cis,cis-1.
ature. Purification by chromatography on silica gel and
recycling preparative HPLC gave 22c (20 mg, 42.6%). Data
1
for 22c: colorless solid; mp 204-205 °C; H NMR (300 MHz,
CDCl3) δ 0.04 (s, 12 H), 2.16 (s, 4 H), 2.52 (s, 4 H), 7.06 (s, 4
H), 7.17 (dd, J ) 8.0, 1.6 Hz, 2 H), 7.29 (s, 2 H), 7.48 (s, 2 H),
7.61 (d, J ) 8.1 Hz, 2 H); 13C NMR (75 MHz, CDCl3) δ -1.6,
24.7, 26.6, 121.8, 124.9, 127.6, 127.8, 128.8, 129.7, 135.5, 138.2;
IR (KBr) 3015, 2949, 2884, 1604, 1511, 1250, 848 cm-1; MS
(EI), m/z ) 73, 145, 219, 409, 424 (M+); UV (cyclohexane) λmax
(log ꢀ) ) 359 (2.96), 342 (2.90), 310 (4.16), 297 nm (4.10).
3,6-Bis(trimethylsilylmethyl)phenanthrene (23). A ben-
zene (10 mL) solution of trans-5 (70 mg, 1.20 mmol) was
bubbled with O2 for 10 min. Photoirradiation of the solution
was carried out with a 300-W high-pressure mercury lamp
through a Pyrex filter for 40 h at room temperature. Purifica-
tion by chromatography on silica gel and recycling preparative
HPLC gave 23 (12 mg, 17.2%). Data for 23: colorless solid;
mp 88-92 °C; 1H NMR (300 MHz, CDCl3) δ 0.04 (s, 18 H),
2.35 (s, 4 H), 7.23 (dd, J ) 8.0, 1.4 Hz, 2 H), 7.57 (s, 2 H), 7.71
(d, J ) 8.1 Hz, 2 H), 8.22 (s, 2 H); 13C NMR (75 MHz, CDCl3)
δ -1.8, 27.8, 120.7, 125.1, 127.4, 128.1, 129.1, 129.9, 138.6;
IR (KBr) 2955, 1511, 1243, 847 cm-1; MS (EI), m/z (%) ) 73,
247, 277, 350 (M+); UV (cyclohexane) λmax (log ꢀ) ) 358 (2.99),
341 (3.03), 308 (4.26), 296 nm (4.19).
Fluorescence Quantum Yields. Fluorescence quantum
yields (Φf) of stilbene derivatives were determined by com-
parison with the data (Φf(trans-stilbene) ) 0.030 ( 0.001 in
CH2Cl2). The Φf value in CH2Cl2 was determined by the
integral ratio of fluorescence in CH2Cl2 and hexane. The
reported result for Φf(trans-stilbene) was 0.04 in hexane.25 The
absorption of sample solutions was adjusted to be ca. 0.1 at
the excitation wavelength. The samples were carefully de-
gassed by freeze-pump-thaw cycles before measurement in
order to exclude the influence of dioxygen.
Fluorescence Lifetimes. The third harmonic (266 nm,
fwhm 250 fs) from a mode-locked Ti-sapphire laser (800 nm,
fwhm 70 fs, at 82 MHz) pumped by a CW green laser (532
nm, 4.5 W) was used for the excitation source. The repetition
rate was adjusted to 4 MHz by use of a pulse-picker. The
monitoring system consisted of a microchannel-plate photo-
multiplier (MCP) tube cooled at -20 °C and a single-photon
counting module. The fluorescence photon signal detected by
the MCP detector and the photon signal of the second
harmonic (400 nm) of the Ti-sapphire laser were used for the
start and stop pulses of the time-to-amplitude converter. The
instrumental response function had a half-width of 20 ps. The
fluorescence time profiles were analyzed by iterative recon-
volution with the response function.
Triplet-Sensitized Photoreaction of trans,trans-2. A
C6D6 (1 mL) solution of trans,trans-2 (1 mg) and benzil (1 mg)
was irradiated through a cutoff filter (>360 nm). A singlet peak
at 0.23 ppm was assigned to trans,trans-2. Singlet peaks
appearing at -0.01 and 0.26 ppm were assigned to cis,trans-
2. A singlet peak at 0.14 ppm was assigned to cis,cis-2.
Phenanthrenophane 22a. Photoirradiation of 4a (26 mg)
in benzene (3.1 mL) in a catalytic amount of I2 was carried
out with a 300-W high-pressure mercury lamp through a Pyrex
filter for 40 h at room temperature. Purification by chroma-
tography on silica gel and recycling preparative HPLC gave
22a (4 mg, 15.4%). Data for 22a: colorless solid; mp 144-145
1
°C; H NMR (300 MHz, CDCl3) δ 0.12 (s, 12 H), 2.18 (s, 4 H),
2.52 (s, 4 H), 7.22-7.27 (m, 4 H), 7.50-7.53 (m, 2 H), 7.55 (s,
2 H), 7.68 (d, J ) 8.1 Hz, 2 H), 7.87 (d, J ) 1.3 Hz, 2 H); 13C
NMR (75 MHz, CDCl3) δ -1.7, 19.7, 24.0, 121.6, 125.0, 125.5,
127.9, 128.0, 129.0, 129.6, 130.4, 138.0, 139.1; IR (KBr) 3014,
2919, 2887, 1602, 1512, 1249, 1149, 846 cm-1; MS (EI), m/z )
73, 145, 247, 262, 424 (M+); UV (cyclohexane) λmax (log ꢀ) )
358 (2.89), 341 (2.82), 310 (4.08), 297 nm (4.05).
Transient Absorption. The fourth harmonic (266 nm) of
an Nd3+-YAG laser (pulse width 8 ns) was used as the
excitation light source. The transient absorption spectra were
obtained with a system capable of capturing a transient
absorption spectrum with a one-shot laser pulse.
Phenanthrenophane 22b. A benzene (4.9 mL) solution of
4b (42 mg) was bubbled by O2 for 10 min. Photoirradiation of
the solution was carried out with a 300-W high-pressure
mercury lamp through a Pyrex filter for 7 h at room temper-
ature. Purification by chromatography on silica gel and
recycling preparative HPLC gave 22b (18 mg, 43.5%). Data
Acknowledgment. This work was supported by
Corporation of Innovative Technology and Advanced
Research in Evolutional Area (CITY AREA) from the
Wakayama Technology Promotion Foundation. This
work was also supported by a Grant-in-Aid for Scientific
Research on Priority Areas (412), Young Scientists (B)
(16750039), and Scientific Research (B) (15350026) from
the Ministry of Education, Culture, Sports, Science and
Technology (MEXT) of Japan.
1
for 22b: colorless solid; mp 194-198 °C; H NMR (300 MHz,
CDCl3) δ 0.21 (s, 12 H), 1.95 (s, 4 H), 2.44 (s, 4 H), 6.67 (s, 1
H), 7.12 (dd, J ) 7.7, 1.4 Hz, 2 H), 7.21 (dd, J ) 8.1, 1.6 Hz,
2 H), 7.30 (t, J ) 7.6 Hz, 1 H), 7.54 (s, 2 H), 7.57 (s, 2 H), 7.67
(d, J ) 8.1 Hz, 2 H); 13C NMR (75 MHz, CDCl3) δ -1.3, 24.0,
25.1, 122.0, 124.6, 125.0, 127.4, 127.8, 128.5, 129.0, 129.6,
132.4, 137.8, 140.2; IR (KBr) 3009, 2948, 2885, 1603, 1512,
1242, 848 cm-1; MS (EI), m/z ) 73, 145, 219, 246, 424 (M+);
UV (cyclohexane) λmax (log ꢀ) ) 358 (3.00), 341 (2.92), 310
(4.18), 297 nm (4.14).
Phenanthrenophane 22c. A benzene (5.6 mL) solution of
4c (47 mg) was bubbled with O2 for 10 min. Photoirradiation
of the solution was carried out with a 300-W high-pressure
mercury lamp through a Pyrex filter for 7 h at room temper-
Supporting Information Available: Schemes S1-S3 and
Figures S1-S15; synthetic procedures for 8-16; 1H NMR, 13
C
NMR, and TOF-MS spectra for new compounds; X-ray reports
and CIFs of trans,trans-1 and cis,cis-3; and details of fluores-
cence lifetime measurements. This material is available free
of charge via the Internet at http://pubs.acs.org.
JO050914+
J. Org. Chem, Vol. 70, No. 24, 2005 9701