Chemistry Letters 2001
971
(δ 7.88), though higher fields than those in 4 (δ 8.67). Thus,
the H4 protons of anti-3 suffer from much less shielding effect
by the opposite phenanthrene ring than H1 and H2. These
observations are rather different from those for anti-2, where
the H4 as well as H1 and H10 resonates at high fields relative to
syn-2 and the two phenanthrene rings overlap mainly at the sin-
gle six-membered ring on the cyclobutane side. These results
obviously indicate that anti-3 possesses a less overlapped struc-
ture than anti-2; the overlap in anti-3 is only about half of the
six-membered ring on the cyclobutane side. Although single
crystals suitable for X-ray crystallographic analysis have not
been obtained, MM2 calculations demonstrated such overlap
between the two phenanthrene rings, which are arranged almost
in parallel with a distance of ca. 3.5 Å.12
difference in the extent of overlap between anti-3 and anti-2.
Therefore, it is definitely concluded that the excimer formation
of phenanthrene requires at least the overlap at one six-mem-
bered ring of two phenanthrene nuclei, provided that they are
arranged almost in parallel with a distance of ca. 3.5 Å.
In summary, novel anti-[2.3](3,10)phenanthrenophane 3
was prepared by the intramolecular [2 + 2] photocycloaddition
of 4 and successfully isolated from the syn-isomer.
Intriguingly, anti-3 exhibited monomer-like emission due to the
smaller overlap between phenanthrene rings than in anti-2.
This work was financially supported by the Grant-in-Aid
from the Ministry of Education, Culture, Sports, Science, and
Technology, Japan.
The absorption spectra of syn- and anti-3 in cyclohexane
exhibited considerable broadening and a red shift relative to
that of phenanthrene, though their shapes were rather different
from each other.13
Dedicated to Prof. Hideki Sakurai on the occasion of his
70th birthday.
References and Notes
The fluorescence spectra of syn- and anti-3 were measured
upon 280 nm excitation in cyclohexane at room temperature
(Figure 1). The spectrum of syn-3 is composed of a broad
structureless and red-shifted emission with a maximum at 420
nm similar to syn-2, though weak emission is also observed
around 370 nm. This broad emission is reasonably assignable
to the excimer fluorescence, as in the other cases.4–6 The latter
weak emission is probably due to photodecomposition prod-
ucts, since the relative intensity increased with repeated meas-
urements. On the other hand, anti-3 affords vibrational struc-
tures characteristic of monomer fluorescence, which shows the
mirror image of the longest absorption band. Although the con-
tribution of excimer fluorescence cannot be completely exclud-
ed, it is reasonable to assume that the observed emission is
derived predominantly from monomer fluorescence. This
behavior is in a remarkable contrast with that in anti-2, which
afforded distinct excimer fluorescence without vibrational
structures. Such difference is apparently ascribed to the slight
1
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2
3
4
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8
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9
10 The spectral data of syn- and anti-3 are as follows. syn-3: mp 255
˚C (dec.); 1H NMR (500 MHz, CD2Cl2) δ 8.03 (2H, dd, J = 7.8 and
0.8 Hz, H5), 7.88 (2H, d, J = 1.6 Hz, H4), 7.42 (2H, d, J = 8.5 Hz,
H1), 7.26 (2H, dd, J = 7.6 and 1.5 Hz, H8), 7.10 (2H, s, H9), 7.04
(4H, m, H6 and H7), 6.67 (2H, dd, J = 8.6 and 2.0 Hz, H2), 4.45
(2H, m, cyclobutane methine), 3.56 (2H, m, one of ArCH2CH2),
2.94 (3H, m, one of ArCH2CH2 and one of ArCH2CH2), 2.16 (1H,
m, one of ArCH2CH2); 13C NMR (125.65 MHz, CD2Cl2) δ 131.87,
134.80, 131.78, 131.10, 129.38, 129.14, 128.88, 127.66, 126.81,
126.06, 125.33, 124.60, 122.12, 121.83, 47.44, 35.97, 25.95, 20.84;
HRMS (FAB) found: m/z 448.2192. Calcd for C35H28: M+,
448.2191. anti-3: mp 255 ˚C (dec.); 1H NMR (500 MHz, CDCl3) δ
8.74 (1H, dd, J = 7.7 and 0.6 Hz, H5), 8.60 (1H, dd, J = 7.9 and 1.8
Hz, H5), 8.48 (1H, s, H4), 8.15 (1H, d, J = 1.2 Hz, H4), 7.92 (1H,
dd, J = 8.4 and 1.5 Hz, H8), 7.87 (1H, dd, J = 8.2 and 2.1 Hz, H8),
7.71 (1H, s, H9), 7.67 (1H, s, H9), 7.62 (4H, m, H6, H6, H7 and
H7), 6.34 (1H, d, J = 8.5 Hz, H1), 6.28 (1H, d, J = 8.6 Hz, H1), 6.13
(1H, dd, J = 8.7 and 1.4 Hz, H2), 5.75 (1H, dd, J = 8.6 and 1.5 Hz,
H2), 4.51 (1H, m, one of cyclobutane methine), 4.23 (1H, m, one of
cyclobutane methine), 2.78 (7H, m), 2.52 (3H, m); 13C NMR
(125.65 MHz, CDCl3) δ 139.11, 138.07, 135.99, 135.85, 131.94,
131.91, 130.01, 129.96, 129.83, 129.63, 129.53, 129.50, 128.54,
127.92, 127.86, 126.10, 125.51, 125.47, 124.41, 124.12, 123.80,
123.47, 123.26, 122.88, 122.72, 122.65, 119.56, 47.54, 46.70,
31.69, 24.38, 24.19, 21.48, 19.44; HRMS (FAB) found: m/z
448.2174. Calcd for C35H28: M+, 448.2191.
11 The isomer possessing a cyclobutane ring directed to the H2-side
seems to be only slightly formed, but its isolation and characteriza-
tion has been unsuccessful.
12 MM2 calculations were performed by CS Chem 3D Pro Version 4.0
(Cambridge Soft Corporation).
13 Absorption and fluorescence spectra were measured for the solu-
tions in the range of 10–5–10–4 M. The fluorescence excitation
spectra were in good agreement with the corresponding absorption
spectra in all cases.