Fluorene as the π-spacer for new two-photon absorption chromophores

Article abstract of DOI:10.1016/j.tet.2010.11.071

We report herein the design and synthesis of two new quadrupolar D-π-A-π-D chromophores containing diphenyl amine and dicyanobenzene or 2,1,3-benzothiadiazole as electron donor (D) and acceptor (A), respectively, which are bridged by fluorene linkage (π).

Full text of DOI:10.1016/j.tet.2010.11.071

Tetrahedron 67 (2011) 734e739
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Fluorene as the
p
espacer for new two-photon absorption chromophores
*
*
Jian-Zhang Cheng, Chao-Chen Lin, Pi-Tai Chou , Atul Chaskar, Ken-Tsung Wong
Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 June 2010
Received in revised form 3 November 2010
Accepted 19 November 2010
Available online 27 November 2010
We report herein the design and synthesis of two new quadrupolar De
taining diphenyl amine and dicyanobenzene or 2,1,3-benzothiadiazole as electron donor (D) and acceptor
(A), respectively, which are bridged by fluorene linkage ( ). The introduction of coplanar fluorenes is
peAepeD chromophores con-
p
highly beneficial for the enhancement of two-photon absorption (TPA), where 1b displays a TPA cross
section (s2) of up to 1975ꢀ207 GM.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Two-photon absorption
Fluorene
Quadrupolar
1. Introduction
excellent TPA property.22 In this type of system, a large s2 value has
been achieved by charge transfer from the periphery donors to the
The two-photon absorption (TPA) process, predicted theoreti-
cally in 19311 and observed experimentally in 1960s,2 is a nonlinear
absorption process invoking the simultaneous absorption of two
photons, either degenerate or nondegenerate. Ever since, it has been
receiving considerable attention due to its wide practical applica-
tions, such as three-dimensional optical data storage and micro-
fabrication,1e5 two-photon fluorescence microscopy,6e8 optical
limiting,9 and photodynamic therapy.10,11 Chromophores with high
capability of two-photon absorption are desired for all these appli-
cations, because a greater degree of excitation can be achieved while
lower laser intensity is sufficient for pumping. Thus, in order to shed
light onto the design of molecules for increasing the two-photon
absorption cross section (s2) and for tuning the position of the two-
photon absorption peak wavelength, there is an urgent need to
unveil the structureeproperty relationship for two-photon ab-
sorbing molecules. Intheory, TPAcross sections ofchromophores are
central acceptor (A) through various conjugated linkages upon
optical excitation. In an aim to enhance the TPA cross section, one
promising strategy is to maintain the coplanar conformation, which
will increase the dimension of
p electron delocalization. Adopting
the most successful molecular design strategy for highly efficient
TPA chromophores, we have strategically designed and synthesized
two new quadrupolar chromophores 1a and 1b (Scheme 1) with
high TPA cross sections.
In these new chromophores, we selected diphenyl amine as the
donor (D) and dicyanobenzene or quinonoid 2,1,3-benzothiadiazole
(BTD) as the acceptor (A), which are then bridged by fluorene
linkages (p). In particular, we incorporated the coplanar fluorene
linker in replacement for bridging units, such as the styryl group in
model compound 223 and biphenylene in molecule 3,24 since the
coplanar fluorenes are beneficial for facilitating DeA electronic
coupling and coplanar fluorene derivatives usually exhibit excellent
TPA properties.12,25e27 In addition, the 9-position of fluorene was
alkylated to enhance the solubility and to enable future function-
alization for latent applications.
governed by several factors, such as the properties of the p-conju-
gated segment, the strength of the donor and/or acceptor sub-
stituents, molecular symmetry, and the molecular dimensionality.
So far, a variety of elegant molecular structures have been designed
to improve the TPA cross section, including dipolar,12,13 quad-
rupolar,14e17 octupolar, and multipolar molecules.18e21
2. Results and discussions
Among these molecules, the quadrupolar De
ture, where D is an electron-donating group, A an electron-
accepting group, and a conjugating moiety, is highlighted by its
peAepeD struc-
2.1. Molecular structures and synthesis
p
The synthetic routes of the two new TPA chromophores are
depicted in Scheme 2.
In the presence of electron rich bis(diphenyl-phosphino)ferro-
cene (dppf) ligand, and a catalytic amount of Pd(dba)2 catalyst,
selective CeN bond formation of 9,9-dioctyl-2,7-dibromofluorene
* Corresponding authors. Tel.: þ886 2 33663894; fax: þ886 2 23695208 (P.-T.C.);
tel.: þ886 2 33661665; fax: þ886 2 33661667 (K.-T.W.); e-mail addresses: chop@
ntu.edu.tw (P.-T. Chou), kenwong@ntu.edu.tw (K.-T. Wong).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.11.071

J.-Z. Cheng et al. / Tetrahedron 67 (2011) 734e739
735
C8H17
C8H17
groups of compound 7 were subsequently transformed into amides
by reacting with SOCl2, followed by the treatment of concentrated
NH4OH to afford diamide compound 8 in 76% yield. Finally, the
dehydration of 8 with POCl3 gave the acceptor core 9 with an iso-
lated yield of 99%. The new TPA chromophores 1a and 1b were
obtained by Suzuki coupling reaction of the intermediate 6 with
acceptor 9 in 43% yield and 4,7-dibromobenzothiadiazole in 13%
yield.
NC
Ph2N
NPh2
CN
1a
S
C8H17 C8H17
C8H17 C8H17
N
N
Ph2N
NPh2
1b
C8H17 C8H17
CN
Ph2N
2.2. Optical properties characterization
NPh2
Fig. 1 depicts the single-photon absorption and emission spectra
of chromophores 1a and 1b in CH2Cl2. Pertinent photophysical data
are summarized in Table 1. The higher energy absorbing bands
NC
2
S
N
N
(310e360 nm) for both 1a and 1b can be ascribed to the
pep
*
NPh2
Ph2N
transitions of local chromophores, such as fluorene28 and 2-
aminofluorene.29
3
Scheme 1. Structures of 1a, 1b, 2, and 3.
1a UV
1.0
1a PL
1b UV
1b PL
0.8
H17C8
C8H17
H17C8
C8H17
(a)
(b)
0.6
0.4
0.2
0.0
Br
Br
Br
NPh2
5
4
H17C8
C8H17
O
B
NPh2
O
6
300
400
500
600
700
CO2H
CN
Br
CONH2
(c)
(d)
Wavelength (nm)
Br
Br
HO2C
Br
Br
Br
Fig. 1. Normalized UVevis absorption (dashed lines) and photoluminescence (solid
lines) spectra of chromophores 1a (lex¼410 nm, black) and 1b (lex¼449 nm, red) in
CH2Cl2 at 298 K.
NC
H2NOC
9
7
8
CN
Br
Br
H17C8
C8H17
NC
NC
9
Table 1
Ph2N
NPh2
6
Photophysical data for 1a, 1b, 2, and 3
(e)
CN
a
b
c
Cmpd
labs
lem
Ff
lex
S2 (TPEF)
s2 (Z-scan)
1a
H17C8 C8H17
1a
1b
2d
3e
413
449
473
422
565
610
527
657
0.17
0.61
0.73
0.14
780
800
840
780
753ꢀ82
1975ꢀ207
1370
623ꢀ28f
1620ꢀ110f
d
S
N
N
S
H17C8
C8H17
N
N
Br
Br
d
200
Ph2N
6
NPh2
a
labs: one-photon absorption maximum.
lem: emission maximum, excited at labs
lTPA: maximum of TPA spectrum.
(e)
b
c
d
e
f
.
1b
H17C8 C8H17
Compound 2: in accordance with Cho and co-workers report.23
Compound 3: in accordance with Mataka and co-workers report.24
Measured at 800 nm.
Scheme 2. Synthesis of TPA chromophores of 1a and 1b. (a) 4 (1 equiv), diphenyl
amine (0.5 equiv), Pd(dba)2 (0.01 equiv), dppf (0.012 equiv), NaOtBu (1 equiv) in tol-
uene, 100 ꢂC, 5 h (70%); (b) 5 (1 equiv), n-BuLi (1.5 equiv), bis(pinacolato)diboron
(1.5 equiv) in THF (99%); (c) 7 in SOCl2, reflux, 3 h, and then remove SOCl2, added
NH4OH concd in dioxane (76%); (d) 8 in POCl3, 135 ꢂC, 12 h (99%); (e) 6 (2 equiv), 9 or
4,7-dibromothiadiazode (1 equiv), Pd(PPh3)4 (0.05 equiv), K2CO3 (2 M) in toluene,
85 ꢂC, 3 day (43% for 1a, 13% for 1b).
Compound 1a exhibits lowest-lying absorption maximum at
413 nm, whereas the absorption maximum of 1b shifts to longer
wavelength at 449 nm. Compared with a green emitting chromo-
phore of 2,1,3-benzothiadiazole core end-capped with fluorenes,
which displays an absorption maximum at 420 nm,30 the absorption
maximum of 1b can be reasonably assigned to the electronic tran-
sition of the whole conjugated backbone including the diphenyla-
mino terminus. It is noteworthy that chromophore 3, with a similar
structure to that of 1b, shows a blue-shifted absorption maximum at
422 nm, indicating that the introduction of coplanar fluorene
bridges leads to better molecular conjugation. Moreover, the red-
shifted absorption maximumof1b relative tothatof1a suggeststhat
(4) with diphenyl amine was achieved to furnish compound 5 with
an isolated yield of 70%. The bromo group of compound 5 was then
converted to boronic ester by treating it with n-BuLi at ꢁ78 ꢂC
followed by quenching with 2-isopropoxy-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane to produce the intermediate 6 in 99% yield. The
synthesis of acceptor 9 began with the oxidation of 1,4-dibromo-
2,5-dimethylbenzene to afford diacid 7 in 84% yield. The acid

736
J.-Z. Cheng et al. / Tetrahedron 67 (2011) 734e739
the steric interactions between fluorene and dicyanobenzene in 1a
leads to a twisted conformation and thus poorer -conjugation. A
Herein, the TPA cross sections (s2) were measured by both the
two-photon excited fluorescence (TPEF) and the Z-scan methods.
The upper panel of Fig. 3 illustrates the two-photon excitation
spectra of 1a (1.05ꢃ10ꢁ5 M) and 1b (9.62ꢃ10ꢁ6 M) from 720 to
900 nm in CH2Cl2, while the lower panel shows the Z-scan ex-
perimental data with the best-fitting curves for 1a (1.16ꢃ10ꢁ3 M)
and 1b (1.07ꢃ10ꢁ3 M) in CH2Cl2 at 800 nm. The obtained s2
values are also summarized in Table 1, and the results of the two
methods are mutually consistent. Chromophore 1a exhibits
maximum s2 of 753 GM at 780 nm, which is inferior to that of
the model compound 2 (s2¼1370 GM at 840 nm). The result can
once again be attributed to the twisted structure between cya-
nobenzene and fluorene in the ground state. Remarkably, the
effect of introducing coplanar fluorene linkages is clearly dem-
onstrated with an eightfold increase in the TPA cross section of
p
similar behavior was also observed in recently reported dipolar
compounds containing an internal cyanovinyl unit.31,32 In 2, such
interactions can be avoided when the cyano substituents and the
vinyl groups are in the anti configuration so that planarity can be
better maintained. On the other hand, quinoidal type chromo-
phores33,34 typically possess a more coplanar conformation. The
coplanar structural feature also renders compound 1b a red-shifted
emission maximum (610 nm) in CH2Cl2 as compared to that of 1a
(565 nm) as well as in other solvents. Apparently, the more rigid and
coplanar structure imposed by the quinoidal benzothiadiazole and
fluorene moieties suppress the nonradiative decay pathways in-
duced possibly by internal rotations. Likewise, the acceptor qui-
noidal benzothiadiazole in 1b renders less steric effect relative to
dicyanobenzene in 1a. This may result in a more planar structure for
1b. As a result, 1b exhibits a high fluorescence quantum yield
1b
s2¼200 GM at 780 nm). This suggests that the coplanarity of the
p-conjugated spacers plays an important role in enhancing the
(
s2¼1975 GM at 800 nm) as compared to that of
3
(
(
Ff¼61%) as opposed to 1a (Ff¼17%) and 3 (Ff¼14%).
Fig. 2 depicts the absorption and emission spectra of 1a and 1b
TPA cross sections. Moreover, it is worthy to note that the TPA
maxima shift to shorter wavelength compared to one-photon
absorption, typical for centrosymmetric TPA chromophores in
which the lowest excited states are one-photon allowed but two-
photon forbidden.35 For various practical applications, such as
optical limiting, 3D microfabrication, strong TPEF agents in bio-
imaging, molecules with large TPA cross section per molecular
weight (s2/MW) or large two-photon action cross section per
molecular weight (e.g., Ffs2/MW) are highly desired.36 It has
been established that TPA active chromophores with s2/MW>1.0
are useful for these applications.4,37 Therefore, our new TPA
chromophore 1b (s2/MW¼1.9 and Ff¼0.61), with appropriate
functionalization on the pendant alkyl chains may present highly
potential application in bioimaging.
in solvents with various polarity. The absorption spectra of both 1a
and 1b show only limited solvent polarity dependence. In contrast,
the emission peak wavelength red-shifts significantly as the solvent
polarity increases, accompanied by gradual reduction in emission
quantum yield. For example, the emission maxima of 1a (474 nm)
and 1b (544 nm) in cyclohexane shift to 565 and 610 nm in CH2Cl2,
respectively. The results are the manifestation of the charge
transfer character of the corresponding electronic transition, in
which a non-equilibrated excited state species is created upon
FranckeCondon excitation, followed by solvent relaxation to the
equilibrated emitting state. As a result, it is inferred that while the
dipole moment is relatively small in the ground state, significant
charge separation (with Ddþ and Adꢁ) is present in the excited state.
(a)
7500
(a)
1.0
1a
2000
6000
1b
0.8
1500
4500
0.6
3000
0.4
1000
500
1500
0.2
0.0
0
300 350 400 450 500 550 600 650
0
725 750 775 800 825 850 875 900
Wavelength (nm)
Excitation Wavelength (nm)
(b)
(b)
2500
2000
1500
1000
500
1.0
0.8
0.6
0.4
0.2
0.0
1.00
0.98
0.96
0.94
0.92
0.90
1b
1a
pulse energy = 1.75μJ
β = 0.0175 cm GW
pulse energy = 1.25 μJ
β = 0.0420 cm GW
0.88
0
300 350 400 450 500 550 600 650 700
Wavelength (nm)
-6
-4
-2
0
2
4
6
Z (cm)
Fig. 2. UVevis absorption (dashed lines) and photoluminescence (solid lines) spectra
of chromophores 1a and 1b in cyclohexane (green), toluene (blue), THF (red), and
CH2Cl2 (black).
Fig. 3. Two-photon excitation spectra (upper) and Z-scan experimental data (lower) of
1a and 1b in CH2Cl2. Inset: the logelog plot of normalized two-photon emission in-
tensity (I/I0) versus normalized excitation power (P/P0).

J.-Z. Cheng et al. / Tetrahedron 67 (2011) 734e739
737
3. Conclusion
4.2.2. The open aperture Z-scan experiments were conducted with
the experimental setup and procedure described in literature39. In
this study, a mode-locked Tiesapphire laser (Tsunami, Spectra
Physics) produced a single Gaussian pulse, which was then coupled
to a regenerative amplifier that generated a w180 fs, 1 mJ pulse
(800 nm, 1 kHz, Spitfire Pro, Spectra Physics). The pulse energy,
In summary, we have synthesized two new quadrupolar
DepeAepeD chromophores by incorporating diphenylamino
groups as the electron donor, dicyanobenzene (1a) or 2,1,3-ben-
zothiadiazole (1b) as the electron acceptor, and fluorenes as the
coplanar
served for 1a and 1b clearly indicates that charge separation in the
excited state is efficient through the linkers. The red-shifted ab-
sorption maximum and high fluorescence quantum yield of 1b
suggest better coplanarity and rigidity as compared to 1a, which is
also manifested in a remarkable enhancement of TPA cross section
p
-conjugation linkers. The significant solvent effect ob-
after proper attenuation, was reduced to 1.00e2.00 mJ and the
repetition rate was further reduced to 20 Hz. After passing through
an f¼30 cm lens, the laser beam was focused and passed through
a 1.00 mm cell filled with the sample solution and the beam radius
at the focal position was 5.09ꢃ10ꢁ3 cm. When the sample cell was
translated along the beam direction (z-axis), the transmitted laser
intensity was detected by a photodiode (PD-10, Ophir). The TPA-
induced decrease in transmittance, T(z), can be fitted with Eqs. 3
p
(
s2¼1975 GM) as compared to those of 1a (s2¼753 GM) and 3
(s2¼200 GM). The successful increase in s2 values demonstrates
the key of fluorene linkers in TPA chromophores to achieve
and 3, in which the TPA coefficient (b) is incorporated:
a greater degree of excitation.
n
X
ðꢁqÞ
N
TðzÞ ¼
(3)
(4)
n¼0n þ 13=2
4. Experimental
4.1. General procedures
bI0L
q ¼
z2
1 þ z2
0
Unless otherwise noted, all reagents were used as received and
without further purification. Tetrahydrofuran (THF) and toluene
were distilled under N2 from sodium/benzophenone immediately
prior to use. Chromatography was carried out with Merck silica gel
for flash columns, and preparative thin-layer chromatography (TLC)
where n is an integer number from 0 to N and has been truncated
at n¼1000, L is the sample length, I0 is the input intensity, z rep-
resents the sample position with respect to the focal plane, and z0
denotes the diffraction length of the incident beam (Rayleigh
was conducted on 1000
m
m Whatman plates. 1H and 13C NMR
range). After obtaining the TPA coefficient (b), TPA cross section (s2)
spectra were collected on a 400 MHz spectrometer at room tem-
perature. High-resolution mass spectrometry (HRMS) was per-
formed with Micromass ProSpec using fast atom bombardment
(FAB).
can be deduced with Eq. 5:
s2NAd ꢃ 10ꢁ3
b
¼
(5)
h
y
where NA is the Avogadro constant, d is the sample concentration,
and h is the incident photon energy.
y
4.2. Spectroscopic measurements
Photophysical properties were collected at room temperature
4.3. Synthesis
with 5ꢃ10ꢁ6 M CH2Cl2 solutions of 1a and 1b. The TPA cross section
(
s2) values were measured by both the TPEF and Z-scan method.
4.3.1. 7-Bromo-9,9-dioctyl-N,N-diphenyl-9H-fluoren-2-amine
(5). The mixture of 2,7-dibromo-9,9-dioctyl-9H-fluorene (10.0 g,
15.4 mmol), diphenyl amine (1.3 g, 7.7 mmol), bis-(dibenzylide-
neacetone) palladium (88 mg, 0.153 mmol), bis(diphenylphos-
phine)ferrocene (102 mg, 0.184 mmol), sodium tert-butoxide
(1.48 g, 15.4 mmol), and toluene (50 mL) was stirred under nitrogen
at 100 ꢂC for 5 h. The mixture was cooled and partitioned between
toluene and brine. The organic layer was separated and dried over
MgSO4, concentrated under vacuum to give a brown liquid. The
crude was purified by chromatography over silica gel (elution with
hexane) to afford the pure product as a orange-red oil (3.88 g, 70%).
4.2.1. The setup for TPEF measurements is similar to that used by Xu
and co-workers27b. First, a femtosecond mode-locked Tiesapphire
laser (Spectra Physics) generates 120 fs pulses at 80 MHz repetition
rate (700e1000 nm). The laser beam is focused on the sample cell
(1 cm) by a lens with a focal length 15 cm. Two-photon induced
fluorescence is then detected in the direction perpendicular to
excitation. To minimize re-absorption, the excitation beam is fo-
cused as close as possible to the side of the quartz cell, which faces
the entrance slit of the imaging spectrograph. The emission is fo-
cused by a lens with a focal length 8 cm into a monochromator
(SP2300i, Acton Research Corporation) in conjunction with a CCD
(PI-MAX camera, Princeton Instruments Inc.). TPEF spectra of
Coumarin 480 (1.02ꢃ10ꢁ5 M in MeOH, s2¼160 GM) were measured
under the same experimental conditions as the reference.38 TPA
cross sections (s2) are evaluated with Eqs. 1 and 2:
IR (neat)
n 3064, 3034, 2924, 2892,1592,1491,1456,1432,1340, 812,
752, 696 cmꢁ1; 1H NMR (CDCl3, 400 MHz)
d
7.51 (d, J¼8.4 Hz, 1H),
7.44e7.40 (m, 3H), 7.26e7.22 (m, 4H), 7.12e7.09 (m, 5H), 7.02e6.99
(m, 3H), 1.84 (t, J¼5.6 Hz, 4H), 1.28e1.07 (m, 20H), 0.86 (t, J¼7.2 Hz,
6H), 0.67e0.64 (m, 4H); 13C NMR (CDCl3, 100 MHz)
d 152.9, 151.8,
147.9,147.6,140.0,135.1,130.0,129.3,126.1,124.0,123.5,122.7,120.6,
120.5, 120.2, 119.2, 55.6, 40.4, 32.1, 30.2, 29.6, 29.5, 24.1, 23.0, 14.5;
MS (m/z, FABþ) 635 (18); HRMS (m/z, FABþ) calcd for C41H50BrN
635.3127, found 635.3127.
FnrCr
FrnC
sTPE
s2
¼
sTPE;r
(1)
(2)
ꢃ
Ff
¼
sTPE
4.3.2. 7-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-di-octyl-
N,N-diphenyl-9H-fluoren-2-amine (6). To the solution of 7-bromo-
9,9-dioctyl-N,N-diphenyl-9H-fluoren-2-amine (0.8 g, 1.26 mmol) in
THF (30 mL) was added n-butyl lithium (1.6 M solution in hexanes,
1.2 mL, 1.9 mmol) at ꢁ78 ꢂC and stirred for 30 min, and then to the
solution was added 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxa-
where subscript r stands for the reference, F represents the in-
tegrated emission intensity, n denotes the refractive index of the
solvent, and C is the sample concentration. The spectra were
recorded in a regime where the emission intensity is quadratically
dependent on excitation power to ensure a pure TPA process.
borolane (5 M solution in THF, 378 mL, 1.89 mmol), stirred for 1 h

738
J.-Z. Cheng et al. / Tetrahedron 67 (2011) 734e739
after warming to room temperature. The mixture was quenched
with brine, extracted into ether, dried over MgSO4, concentrated
under vacuum to give yellow oil. The crude was purified by chro-
matography over silica gel (elution with hexane/ethyl acetate¼98/
palladium (6 mg, 0.004 mmol) was added the solution of 7-(4,4,5,5-
tetramethyl-1,3,2- dioxaborolan-2-yl)-9,9-dioctyl-N,N-diphenyl-
9H-fluoren-2-amine (117 mg, 0.171 mmol) in toluene (6 mL) and
K2CO3 (2 M, 3 mL) under nitrogen, and then stirred for 3 days at
85 ꢂC. The mixture was partitioned between ether and brine, dried
over MgSO4, and concentrated under vacuum to get brown oil. The
brown oil was purified by chromatography over silica gel (elution
with hexane/toluene¼4/1) to afford the pure product as an orange
2) to afford the pure product as a yellow oil (0.86 g, 99%). IR (neat)
n
3061, 3035, 2955, 2926, 2854, 1595, 1492, 1467, 1415, 1354, 1275,
1144, 1113, 1081, 1029, 963, 821, 696, 622 cmꢁ1 1H NMR (CDCl3,
400 MHz)
;
d
7.78 (d, J¼7.6 Hz, 1H), 7.70 (s, 1H), 7.62e7.57 (m, 2H),
7.26e7.22 (m, 4H), 7.13e7.11 (m, 5H), 7.03e6.99 (m, 3H), 1.93e1.85
(m, 4H), 1.40 (s, 12H), 1.28e1.05 (m, 20H), 0.85 (t, J¼7.2 Hz, 6H),
solid (0.012 g, 13%). Mp¼152e153 ꢂC; IR (KBr)
n 3034, 2924, 2851,
1594, 1492, 1462, 1274, 1028, 893, 816, 752, 696, 511 cmꢁ1; 1H NMR
0.66e0.64 (m, 4H); 13C NMR (CDCl3, 100 MHz)
d
152.8, 149.8, 148.0,
(CDCl3, 400 MHz)
d
8.03 (d, J¼8.0 Hz, 2H), 7.94 (s, 2H), 7.89 (s, 2H),
147.6, 144.0, 136.1, 133.9, 129.2, 128.7, 123.9, 123.5, 122.6, 120.9,
119.4, 118.5, 83.8, 55.3, 40.4, 32.1, 30.3, 29.6, 29.5, 25.3, 24.11, 23.0,
14.5; MS (m/z, FABþ) 683 (5); HRMS (m/z, FABþ) calcd for
C47H62BNO2 683.4874, found 683.4879.
7.79 (d, J¼8.0 Hz, 2H), 7.64 (d, J¼8.8 Hz, 2H), 7.30e7.16 (m, 18H),
7.08e7.02 (m, 6H), 2.04e1.90 (m, 8H), 1.29e1.14 (m, 40H),
0.92e0.84 (m, 20H); 13C NMR (CDCl3,100 MHz)
d 154.0,152.4,150.7,
147.7, 147.0, 140.9, 135.6, 135.2, 133.3, 129.0, 128.0, 127.6, 123.8,
123.5, 123.3, 122.4, 120.5, 119.2, 119.0, 55.6, 40.7, 32.4, 30.6, 29.9,
29.8, 24.6, 23.3, 14.8; MS (m/z, FABþ) 1247 (12); HRMS (m/z, FABþ)
calcd for C88H102N4S 1247.7903, found 1247.7892.
4.3.3. 2,5-Dibromobenzene-1,4-diamide (8). The mixture of 2,5-
dibromotetrephthalic acid (1.5 g, 4.6 mmol), thionyl chloride
(20 mL), a drop of DMF was refluxed for 3 h. Thionyl chloride was
removed by co-evaporation with toluene (20 mL) with rotary
evaporation. The concentrated crude product was dissolved in di-
oxane (20 mL). Ammonium hydroxide (20 mL, concd) was added
dropwisely to the mixture and stirred overnight at room temper-
ature. The precipitate was filtered and washed with dioxane to
Acknowledgements
This work was financially supported by the National Science
Council of Taiwan.
afford the pure product as
a
white solid (1.22 g, 76%).
Supplementary data
Mp¼338e341 ꢂC; IR (KBr)
n 3176, 1653, 1615, 1527, 1483, 1393, 1352,
1319, 1264, 1205, 1153, 1125, 1057, 887, 802, 735, 662, 609,
1H and 13C NMR spectra of new compounds. Supplementary
data associated with this article can be found in online version at
doi:10.1016/j.tet.2010.11.071.
502 cmꢁ1; 1H NMR (DMSO-d6, 400 MHz)
d 7.98 (s, 2H), 7.70 (s, 2H),
7.63 (s, 2H); 13C NMR (DMSO-d6, 100 MHz)
d 166.9, 140.6, 132.1,
117.5; MS (m/z, FABþ) 321 (4); HRMS (m/z, FABþ) calcd for
C8H6Br2N2O2 320.8874, found 320.8875.
References and notes
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was heated at 135 ꢂC for 12 h. The mixture was slowly poured into
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washed with water to afford the pure product as a white solid40 (9)
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