CH2OPh, J 5 5.6 Hz), 7.01 (d, 4Ar-H, o to OCH2, J 5 8.8 Hz),
Results and discussion
7.64–7.79 (m, 19Ar-H).
The synthesis of molecules with branched aromatic rods was
outlined in Scheme 1. A flexible ether-type dibranched coil was
prepared according to the procedures described previously.5
The synthesis of a branched rod building block was performed
by using an aromatic coupling reaction with a Pd(0) catalyst.6
Commercially available 1,3,5-tribromobenzene, which was
selected as an aromatic branching point, was coupled with
2 equiv. of anisole boronic acid by a Suzuki aromatic coupling
reaction. The resulting terphenylene compound 4 was elon-
gated by coupling with 4-trimethylsilyl-49-biphenylboronic
acid and yielded compound 5a. The silyl group of 5a was
subsequently substituted into iodine which is the most active
group for the next aromatic coupling. To increase the
solubility, flexible coil should be attached to the rod building
blocks at the penta phenylene step prior to further extension of
the rod block. However, through treatment with boron
tribromide, compound 5b was demethylated to 5c and then
coupled with the flexible coil R1 in acetonitrile in the presence
of potassium carbonate to give rise to 5d, which shows good
solubility in common organic solvents such as chloroform,
ethyl acetate and ethanol. The molecule 1 with a short
branched aromatic rod was obtained by aromatic homo
coupling of precursor molecule 5d in a catalytic amount of
Pd. Also, 5d could be elongated further by repeating the
Suzuki coupling reaction with a boronic acid derivative and
consecutive substitution with iodine monochloride. For
example, 6a was prepared from the Suzuki coupling reaction
of 5d with 4-trimethylsilylphenylboronic acid. The trimethylsi-
lyl group was substituted with iodide, and then the subsequent
homo aromatic coupling reaction of 6b produced 2.
Synthesis of compounds 6b and 7b. Compounds were
synthesized using the same procedure.
A representative
example is described for 7b. To a solution of compound 7a
(2.0 g, 1.43 mmol) in CH2Cl2 at 278 uC was added dropwise a
1.0 M solution of ICl in CH2Cl2 (3 ml). The reaction mixture
was stirred over 1 h under nitrogen. 1 M aqueous Na2S2O5
solution was added and stirred over 1 h. The layers were
separated, and the aqueous layer was washed twice with
CH2Cl2. The combined organic layer was dried over anhy-
drous MgSO4 and filtered. The solvent was removed in a
rotary evaporator, and the crude product was purified by
column chromatography (silica gel, ethyl acetate followed by
THF) to yield 1.5 g (72%) of a colorless oil; 1H-NMR
(250 MHz, CDCl3, d/ppm) 2.40–2.44 [m, 2H, C(CH2)3H], 3.36
(s, 12H, OCH3), 3.50–3.66 (m, 56H, OCH2), 4.09 (m, 4H,
CH2OPh, J 5 5.6 Hz), 7.00 (d, 4Ar-H, o to OCH2, J 5 8.7 Hz),
7.41 (d, 2Ar-H, o to I, J 5 8.4 Hz), 7.60–7.81 (m, 21Ar-H).
Compound 6b. Yield 68%; 1H-NMR (250 MHz, CDCl3,
d/ppm) 2.38–2.44 [m, 2H, C(CH2)3H], 3.36 (s, 12H, OCH3),
3.50–3.67 (m, 56H, OCH2), 4.09 (m, 4H, CH2OPh, J 5 5.6 Hz),
7.03 (d, 4Ar-H, o to OCH2, J 5 8.5 Hz), 7.40 (d, 2Ar-H, o to I,
J 5 8.1 Hz), 7.58–7.80 (m, 17Ar-H).
Synthesis of compounds 1, 2, and 3. Compounds were
synthesized using the same procedure.
A representative
example is described for 3. Compound 7b (0.7 g, 0.48 mmol),
and TDAE (0.2 g 1.0 mmol) were dissolved in DMF (30 ml).
And then Pd(PhCN)2Cl2 (10 mg, 25 mmol) was added. The
mixture was heated at 50 uC for 4 h with stirring under
nitrogen. After being cooled to room temperature, the DMF
solvent was removed under vacuum distillation, and the crude
product was purified by column chromatography (silica gel,
ethyl acetate followed by THF) and precipitated by CH2Cl2
and n-hexane to yield 0.48 g (75%) of a waxy solid: mp .
Compound
3 could be synthesized by using a similar
procedure, except that 4-trimethylsilyl-49-biphenylboronic acid
was used in place of 4-trimethylsilylphenylboronic acid. All of
the resulting molecules were purified by column chromato-
graphy (silica gel) and subsequent recrystallization, and
characterized by 1H-NMR spectroscopy, gel permeation
chromatography, elemental analysis and MALDI-TOF mass
spectroscopy, and were shown to be in full agreement with the
structures presented.
300 uC; GPC Mw/Mn 5 1.04; 1H-NMR (250 MHz, CDCl3,
d/ppm) 2.43–2.48 [m, 4H, C(CH2)3H], 3.37 (s, 24H, OCH3),
3.52–3.66 (m, 112H, OCH2), 4.11 (d, 8H, CH2OPh, J 5 5.5 Hz),
7.03 (d, 8Ar-H, o to OCH2, J 5 8.7 Hz), 7.62–7.80 (m, 46Ar-H).
MALDI-TOF-MS m/z (M + H + Na)+ 2675.35; Calc.
2675.40; Anal. calc. for C156H202O36: C, 70.62; H, 7.67.
Found C, 70.60; H, 7.54%.
¯
¯
The thermotropic phase behavior of the molecules was
studied by
a combination of thermal optical polarized
microscopy (OPM), differential scanning calorimetry (DSC),
and X-ray diffraction (XRD). Molecule 1 exists only as an
isotropic liquid, most probably due to relatively weak
interactions between the short rod blocks. In contrast, 2,
based on an elongated rod block, shows an ordered bulk-state
structure with bright birefringence which transforms it into an
isotropic liquid at 105 uC [Fig. 2(a)]. On slow cooling from the
isotropic liquid the formation of unique domains, which grow
in four directions and coalesce into a mosaic texture, could
easily be observed under OPM [Fig. 2(b)]. The DSC curves and
optical texture preliminarily confirmed the presence of an
ordered phase, which could be attributed to the rigidity of
elongated phenylene rod segments. To identify the detailed
aggregation structures, X-ray scattering studies were per-
formed. Small-angle X-ray scattering (SAXS) in the ordered
state of 2 revealed a number of well-resolved reflections, as
Compound 1. Yield 60%; GPC Mw/Mn 5 1.04; 1H-NMR
(250 MHz, CDCl3, d/ppm) 2.44–2.48 [m, 4H, C(CH2)3H], 3.37
(s, 24H, OCH3), 3.52–3.66 (m, 112H, OCH2), 4.11 (d, 8H,
CH2OPh, J 5 5.5 Hz), 7.03 (d, 8Ar-H, o to OCH2, J 5 8.6 Hz),
7.54–7.90 (m, 30Ar-H). MALDI-TOF-MS m/z (M + H + Na)+
2371.66; Calc. 2371.27; Anal. calc. for C132H186O36: C, 67.50;
H, 7.98. Found C, 67.46; H, 7.95%.
¯
¯
¯
¯
Compound 2. Yield 78%; mp 105 uC; GPC Mw/Mn 5 1.03;
1H-NMR (250 MHz, CDCl3, d/ppm) 2.42–2.46 [m, 4H,
C(CH2)3H], 3.36 (s, 24H, OCH3), 3.52–3.64 (m, 112H,
OCH2), 4.10 (d, 8H, CH2OPh, J 5 5.4 Hz), 7.02 (d, 8Ar-H,
o to OCH2, J 5 8.5 Hz), 7.46–7.80 (m, 38Ar-H). MALDI-
TOF-MS m/z (M + H + Na)+ 2523.24; Calc. 2523.33; Anal.
calc. for C144H194O36: C, 69.15; H, 7.82. Found C, 69.10; H,
7.86%.
This journal is ß The Royal Society of Chemistry 2005
J. Mater. Chem., 2005, 15, 419–423 | 421