Triptycene-containing bis(phenylethynyl)benzene nematic liquid crystals

Article abstract of DOI:10.1039/b203160d

We report the synthesis of a new class of nematic liquid crystals with triptycenes built into a p-dialkoxybis(phenylethynyl)benzene mesomorphic core. Triptycenes are appended on the center or terminal ring of the mesogen, leading to symmetric liquid cryst

Full text of DOI:10.1039/b203160d

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Triptycene-containing bis(phenylethynyl)benzene nematic liquid
crystals{
Timothy M. Long and Timothy M. Swager*
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave.,
Cambridge, MA 02139, USA. E-mail: tswager@mit.edu
Received 2nd April 2002, Accepted 4th September 2002
First published as an Advance Article on the web 8th October 2002
We report the synthesis of a new class of nematic liquid crystals with triptycenes built into a p-dialkoxy-
bis(phenylethynyl)benzene mesomorphic core. Triptycenes are appended on the center or terminal ring of the
mesogen, leading to symmetric liquid crystals and reduced symmetry liquid crystals, respectively. Both types
displayed monotropic behavior, with the asymmetric compounds having unusual phase behavior, lacking
distinct crystallization transitions, and forming a glassy mesophase. A chiral analogue was found to be non-
mesomorphic, but induced chiral nematic phases when doped into achiral triptycene-containing analogues.
Rotation is physically hindered normal to the director and, hence, this new liquid crystal architecture may
allow for the synthesis of a single component liquid crystal that displays a biaxial nematic phase.
However, symmetric triptycenes with six chains were found
Introduction
to be crystalline, high melting, and had poor solubilities. All of
these materials were shown to undergo multiple phase transi-
tions and were assigned to smectic A phases with hexagonal
ordering of the triptycene cores within the lamellae.
With the discovery of a biaxial nematic phase in a lyotropic
potassium laurate–1-decanol–water system,1 serious efforts
have been invested toward the discovery of the same in a single
component thermotropic liquid crystalline system. In
a
In the new structures reported here, a classical nematogen
based upon the bis(phenylethynyl)benzene calamitic core is
appended with a triptycene on one of the benzene rings. We
considered that the attachment of the triptycene allows for
a physical ‘‘gearing’’ within the phase. Such a correlation of
triptycene motion has already been exploited in the design of
molecular gears and ratchets.10 The fact that face-to-face
disposition of the triptycenes is sterically unfavorable could
lead to local head-to-tail correlations of the triptycenes normal
to the director plane. If such ordering were induced over
extended domains, a biaxial phase could be formed.
conventional (uniaxial) nematic phase, all molecules lie, on
average, with their long axes along a single director. Due to
the inherent anisotropy in the index of refraction introduced
by this arrangement, nematic liquid crystals have long been
exploited to produce the optical effects that are the basis of
conventional liquid crystal displays.2 However, the switching
time due to the electrical switching of the nematic phase is
limited by the need to reorient the entire molecule via rotation
along its major axis. Biaxial nematic phases, which could
switch by rotation about the long axis of the molecule, offer an
opportunity to generate switching on a shorter time scale.
Molecules in a biaxial nematic phase have a preferred
organization in the direction normal to the classical nematic
director.3 This organization allows, in principle, for switching
between two optically different states by rotation around
the director, an overall faster molecular motion. A number of
groups have been in pursuit of such a phase through a variety
of designs with the hope of hindering molecular rotation to
‘‘freeze out’’ this second level of organization. However, the
existence of a biaxial nematic phase in a single component
system remains a subject of debate.4 Designs include rods
that are laterally attached to disks,5 banana-shaped molecules,
with or without laterally attached dipoles to inhibit free
rotation,6,7 and molecular-based biaxiality introduced in
metallomesogens.8
Synthesis
Two series of triptycene-based liquid crystals were synthesized,
differing only in the position of the triptycene within the
mesogen. One carries the triptycene on the center ring of a
p-bis(phenylethynyl)benzene core, yielding a symmetric meso-
gen. In the other, the triptycene is attached to one of the outer
rings, thereby reducing the symmetry of the system. This com-
parison was made to examine the effect of decreased symmetry
on the mesophase behavior.
1 Symmetric triptycene liquid crystals
The synthetic pathway to the symmetric compounds is sum-
marized in Scheme 1. Two literature compounds are coupled to
build the core of the symmetric triptycene liquid crystals:
coupling of 1,4-diiodotriptycene11 to 4-tetrahydropyranyl-1-
ethynylbenzene12 via standard Sonogashira–Hagihara13 con-
ditions at room temperature provided compound 1 in 97%
yield. Deprotection of the tetrahydropyranyl protecting
groups, with p-TsOH in a mixture of dichloromethane and
methanol, cleanly afforded the bisphenol compound 2 in 99%
yield. Alkylation of the free phenols with alkyl bromides or
iodides via modified a Williamson ether synthesis with Cs2CO3
(the Cs1 cation increases the nucleophilicity of the phenoxide
anion)9c in DMF yielded compounds CTOn (n ~ 4–14) in 41–
82% yields. A chiral analogue, CTOS, was synthesized under
During the course of our research on triptycenes and their
ability to increase molecular ordering, we became aware that
one of the compounds designed as a guest dye in our study was,
in fact, liquid crystalline. Although, this was not the first liquid
crystal based on a triptycene mesogen,9 its design is distinctly
different and could offer another entry into biaxial nematic
phases.
Previous triptycene-based liquid crystals contained five long
paraffinic chains distributed among the three aromatic rings.9
{Electronic supplementary information (ESI) available: spectroscopic
data for CTO4–14, CTOS, and ETO6–12. See http://www.rsc.org/
suppdata/jm/b2/b203160d/
DOI: 10.1039/b203160d
J. Mater. Chem., 2002, 12, 3407–3412
This journal is # The Royal Society of Chemistry 2002
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the same alkylation conditions using (3S)-3,7-dimethyl-1-
bromooctane.
2 Reduced symmetry triptycene liquid crystals
Triptycene-based liquid crystals with reduced symmetry were
produced by a slightly longer but convergent synthesis. This
synthetic pathway is summarized in Scheme 2. The general
synthetic strategy centered on the palladium-catalyzed cou-
pling of compounds 5 and 6 to build the mesomorphic core.
Compound 5 was synthesized in three steps from the readily
available 1,4-triptycene quinone.14 Slow addition of lithium
trimethylsilylacetylide at low temperature, followed by the
trapping of the intermediate adduct with trimethylsilyl chloride
and reduction with zinc dust in the presence of acetic acid,
afforded compound 3 in high yield and in one pot.15 Protection
of the free phenol as the tetrahydropyranyl ether, 4, and
removal of the trimethylsilyl group with potassium carbonate
in tetrahydrofuran and methanol yielded acetylene 5.
Compound 6 can be easily prepared under standard
Sonogashira coupling conditions starting from 4-tetrahydro-
pyranyl-1-iodobenzene12 and commercially available 4-bromo-
1-ethynylbenzene. Coupling of 5 and 6 in the presence of
catalytic Pd2(dba)3 and CuI, with the addition of triphenylphos-
phine, in triethylamine in a sealed tube at 100 uC gave 7 in 73%
yield, despite coupling to an electron-rich aryl bromide. Removal
of the tetrahydropyranyl ethers in the presence of catalytic
p-TsOH gives the free bisphenol, 8, which was alkylated under
the same conditions as for the symmetric triptycenes, to give
the corresponding asymmetric triptycene compounds ETOn
(n ~ 6–12).
Scheme 1 (a) PdCl2(PPh3)2, CuI, THF, iPr2NH, 97%; (b) p-TsOH,
CH2Cl2, MeOH, 99%; (c) RX, Cs2CO3, DMF, 41–82%.
Results and discussion
Mesomorphic behavior
1 Symmetric triptycene liquid crystals (CTOn). All sym-
metric compounds displayed monotropic behavior, indicating
Scheme 2 (a) 1. Lithium trimethylsilylacetylide, THF; 2. TMSCl; 3. Zn, AcOH, 86%; (b) dihydropyran, p-TsOH, CH2Cl2, 64%; (c) K2CO3, THF,
MeOH, 99%; (d) PdCl2(PPh3)2, CuI, THF, Pr2NH, 68%; (e) 5, Pd2(dba)3, PPh3, CuI, Et3N, 73%; (f) p-TsOH, CH2Cl2, MeOH, 80%; (g) RX,
Cs2CO3, DMF, 63–86%.
i
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Fig. 1 Marbled texture exhibited by CTO8 on cooling (1006
magnification, 133 uC).
Fig. 2 Chiral nematic phase at the boundary of a contact preparation
of CTO8 and CTOS (2006 magnification, 128 uC).
calamitic element, our materials only show highly fluid nematic
phases. We believe that this difference in phase behavior is due
to the extension of the mesomorphic core, via incorporation
of the triptycene into a bis(phenylethynyl)benzene core. Any
organization in a layered phase would generate large degrees of
internal free volume. Free volume is not energetically favored
so the system organizes to efficiently fill space in the liquid
crystalline phases. This is consistent with our previous demon-
strations that triptycenes have a propensity to ‘‘nest’’ other
molecules in the convex surfaces defined by faces of their
aromatic rings.19 This is also consistent with previous appro-
aches toward introducing structural anisotropy, such addition
of lateral alkyl chains20 or metal carbonyl fragments.21
Packing considerations, as shown in Scheme 3, of the steri-
cally bulky triptycenes may also have an effect. Tail-to-tail
packing [Scheme 3(A)] is more sterically crowded and creates
free volume, thereby prohibiting smectic phase formation.
Head-to-tail packing [Scheme 3(B)] displays steric complemen-
tarity and spacial regularity. This bias in packing is a potential
mechanism for inducing a biaxial nematic phase with a pre-
ferred head-to-tail arrangement of triptycenes.
Table 1 Mesophase behavior of symmetric triptycene derivatives
CTOna
TIb/uC (DH/
TNc/uC (DH/
Compound
CTO4e
kJ mol21; |DS/R|)
kJ mol21; |DS/R|)
TKd/uC
205.3 (31.0)
209.2 (23.6)
181.8 (44.7)
177.2 (42.6; 12.3)
147.7 (39.6; 11.3)
145.4 (43.3; 12.5)
141.4 (55.2; 16.0)
138.9 (43.2)
—
187.8
178.8
158.5
122.5
108.1
102.6
110.5
93.0
CTO6
CTO8
CTO10
CTO12
CTO14
CTOS
158.5f
143.8 (22.3; 0.7)
134.6 (22.2; 0.7)
122.1 (22.3; 0.7)
114.9 (24.7; 1.5)
—
aAll compounds display monotropic behavior. bClearing temperature
on heating. cTransition temperature from isotropic melt to nematic
phase on cooling. dTypical crystallization temperature on cooling.
eCrystal–crystal transitions on heating and cooling. fPhase visible
under polarized microscopy; nematic transition does not resolve on
DSC.
that all liquid crystalline phases are kinetically accessible, but
not thermodynamically stable. Only nematic mesophases were
displayed and polarized microscopy revealed classic droplet
formation and coalescence to give marbled textures, character-
istic of a nematic phase, as shown for CTO8 in Fig. 1. The
mesophase behavior of the series CTOn is summarized in
Table 1. Increasing the alkyl chain length decreased the
clearing temperatures, although at a chain length longer than
ten carbons, the effect drops off dramatically. In all cases, there
is a hysteresis on cooling ranging from 13 to 33 uC. On cooling,
transitions from the isotropic to liquid crystalline state were
found to be typical for an isotropic to nematic transition,
falling in the range 2–4 kJ mol21. As the isotropic to biaxial
nematic transition has been predicted to be second order,16
transition entropies (DS/R) were determined and found to be
quite low, ranging from 0.7 to 1.5, at the lower limit of values
(0.5–6.0) found for isotropic to nematic transitions in the
literature.17
2 Reduced symmetry triptycene liquid crystals (ETOn). To
decrease the symmetry of the CTOn series, the triptycene was
moved to one of the terminal benzene rings in the bis(phenyl-
ethynyl)benzene system. It was hoped that this decreased
symmetry would extend the mesophase range. The mesophase
behavior of the ETOn series was found to be highly complex.
On heating, cold crystallization peaks could be observed before
The range over which nematic mesophases persist is narrow
in the case of CTO6 and CTO14. For CTO6, the nematic phase
can be observed with polarized microscopy on cooling, but
rapidly crystallized on standing. This was also reflected in its
differential scanning calorimetry (DSC) measurements, as the
nematic transition was not resolved from the crystallization
peak. The hexyl side chains were the shortest length that
displayed mesophases; CTO4 crystallized on cooling. Interest-
ingly, CTOS, containing chiral (3S)-3,7-dimethyloctyl groups,
also crystallized on cooling. However, a contact preparation of
CTOS with CTO8 yielded a chiral nematic phase at the contact
boundary, exhibiting the plane texture shown in Fig. 2.
The parent bis(phenylethynyl)benzene liquid crystals are
known from the literature to show a number of uncharacter-
ized smectic phases.18 Unlike the previously reported tripty-
cene-based smectic liquid crystals, in which the mesogen lacks a
Scheme 3 R ~ 4-Alkoxyphenylethynyl. (A) Steric hindrance and free
volume created by tail-to-tail orientation of triptycenes (rotation or
translation of either triptycene yields head-to-tail packing). (B) More
facile packing of head-to-tail orientation.
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Table 2 Mesophase behavior of reduced symmetry triptycene deriva-
tives, ETOna
by triptycene. Triptycenes also provide a convenient location
for further funcationalization to incorporate dipoles into the
molecules to aid in switching and further inhibit rotation.
Continuing studies in our laboratories seek to develop new
materials that exploit the potential of triptycene elements in
liquid crystals.
TIb/uC (DH/
TNc/uC (DH/
TKd/uC (DH/
Compound kJ mol21; |DS/R|) kJ mol21; |DS/R|) kJ mol21
)
ETO6
ETO8
ETO10
ETO12
179.4 (39.2; 10.4) 140.1 (21.5; 0.4) 46.3 br (234.3)
164.3 (46.0; 12.7) 134.3 (21.8; 0.5) 87.1 br (218.5)
129.3 (39.9; 11.9) 121.6 (22.4; 0.7) 36.8 (24.1)
136.0 (50.5; 14.8) 119.5 (22.1; 0.6) 40.8 br (224.1)
Experimental
aAll compounds display monotropic behavior. bClearing temperature
on heating. cTransition temperature from isotropic melt to nematic
phase on cooling. dTypical crystallization temperature on cooling; br,
broad transition.
Thermal studies were carried out via differential scanning
calorimetry (DSC) and measured on a Perkin-Elmer DSC 7
under argon at a scan rate of 10 uC min21. Microscopic textures
were viewed on a Leica DM RXP optical microscope, with
a Linkham 350 hot stage controlled by a Linkham TP 92 tem-
perature controller used to vary the sample temperature. All
synthetic manipulations were performed under an argon or
nitrogen atmosphere in flame-dried glassware. High resolution
mass spectra were obtained at the MIT Department of
Chemistry Instrumentation Facility (DCIF) using a peak
matching protocol to determine the mass and error range of
the molecular ion.
General procedure for alkylation of bisphenols
To a solution of 100 mg (0.206 mmol) of a bisphenol in 2 ml
DMF was added 3–6 equivalents of the appropriate 1-iodo-
or 1-bromoalkane and the solution purged with Ar. Cs2CO3
(167 mg, 0.618 mmol) was added and the solution was heated
at 75 uC for 3 h. After cooling, the solution was diluted with
dichloromethane and washed sequentially with water, NH4Cl
(aq.), dilute NaOH (aq.), water, and saturated NaCl (aq.).
After drying over MgSO4 and filtration, removal of the solvent
in vacuo yielded the crude product. Purification can be effected
by either repeated recrystallization from acetone (twice; sym-
metric triptycenes) or adsorbtion onto silica gel (asymmetric
triptycenes) followed by column chromatography with 5 : 1
hexanes–dichloromethane eluent. All yields are reported after
purification.
Fig. 3 Marbled texture exhibited by ETO10 on cooling (2006
magnification, 116 uC).
melting to an isotropic phase. There was a subtle decrease in
the clearing temperatures with respect to the same length chain
in the symmetric series. The mesophase behavior of the series
ETOn is summarized in Table 2. However, we did not succeed
in obtaining enantiotropic behavior. The hysteresis on cooling
remained in the range 8 to 39 uC. A typical marbled texture
exhibited by this series is shown in Fig. 3.
The reduced symmetry of this series does appear to change
the crystallization behavior. No members of the series dis-
played a distinct crystallization exotherm on cooling, exhibit-
ing only broad transitions in their DSC thermograms. The
phases remain fluid over a wide range before becoming highly
viscous. Under polarized microscopy, regions of local crystal-
lization were seen throughout and were very slow to advance
into the fluid regions. Isotropic to nematic transition entropies
in the series were found to be lower than for the CTOn series,
ranging from 0.4-0.7, indicating a lower first-order nature to
the transition. When cooled rapidly (30 uC min21) from the
nematic phase, ETOn was trapped in a glassy state, as evident
from the Tg step transition on reheating followed by a cold
crystallization. The presence of a glassy phase was also indi-
cated by the large difference in melting versus crystallization
enthalpies in ETO8–12.
1,4-Bis(4@-tetrahydropyranyloxyphenylethynyl)-9,10[1’,2’]-
benzeno-9,10-dihydroanthracene (1). 1,4-Diiodotriptycene
(1.518 g, 3 mmol), 4-tetrahydropyranyloxy-1-ethynylbenzene
(1.30 g, 6.5 mmol), PdCl2(PPh3)2 (105 mg, 0.15 mmol), and
CuI (30 mg, 0.15 mmol) were combined and placed under Ar.
Sequentially, 15 ml THF and 3 ml diisopropylamine were
added. The solution was stirred at room temperature for 2.5 h.
The reaction solution was then filtered through Celite and the
Celite was rinsed with dichloromethane. After removal of the
solvent in vacuo, the residue was flushed through a plug of
silica gel with dichloromethane to remove the catalyst.
Removal of the solvent in vacuo yielded an orange solid
that was heated with 100 ml acetone, cooled, and filtered off,
to yield 1 (1.28 g) as a tan solid. Evaporation of the filtrate in
vacuo yielded a brown solid that was purified via gradient
column chromatography with 1 : 1 hexanes–dichloromethane
to pure dichloromethane to yield an additional 640 mg of 1
(total yield: 1.92 g, 97%). 1H NMR (300 MHz, CDCl3): d 7.57
(d, 4H, J ~ 8.7), 7.43 (dd, 4H, J ~ 5.3, 3.1), 7.09 (d, 4H, J ~
8.7), 7.00 (dd, 4H, J ~ 5.3, 3.1), 5.96 (s, 2H), 5.49 (t, 2H, J ~
3.0 Hz), 3.91 (m, 2H), 3.64 (m, 2H), 2.02 (m, 2H), 1.95–1.55
(m, 10H). 13C NMR (75 MHz, CDCl3): d 157.4, 146.9, 144.8,
133.1, 127.9, 125.5, 124.1, 118.7, 116.7, 116.3, 96.4, 94.1, 86.0,
62.3, 52.4, 30.6, 25.5, 19.0. FT-IR (KBr) n/cm21: 2941, 2870,
2202, 1602, 1510, 1239, 960. HRMS (ESI) m/z: calcd. for
C46H38O4, 655.2843 ([M 1 H]1), found 655.2840. M.p. 230–
233 uC (with decomp.).
Conclusion
Two series of triptycene-containing bis(phenylethynyl)benzene
liquid crystals were synthesized and determined to display
monotropic nematic phases. Chiral variants were found to be
crystalline, but upon doping into another liquid crystal in
the series, showed a chiral nematic phase. Local gearing of
the triptycenes and threading of their sidearms through the
triptycene void spaces explain the absence of smectic phases.
Variants with reduced symmetry display slightly lower clearing
points, do not show distinct crystallization peaks on cooling,
and the order of the mesophase can be trapped by rapid cooling
in a glass. The structural elements in these compounds may be
useful for the creation of a single component biaxial liquid
crystal phase due to the physical inhibition of rotation caused
1,4-Bis(4@-hydroxyphenylethynyl)-9,10[1’,2’]-benzeno-9,10-
dihydroanthracene (2). 1 (981 mg, 1.5 mmol) was dissolved
in a mixture of 25 ml dichloromethane and 15 ml methanol.
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p-TsOH (35 mg, 0.2 mmol) was added and the solution stirred
at room temperature for 1 h. The solvent was removed in vacuo
and the residue purified via column chromatography over
silica gel with 10 : 1 dichloromethane : ethyl acetate, to yield 2
(720 mg, 99%) as an off-white solid. Analytically pure samples
of 2 were obtained by recrystallized from chloroform. 1H NMR
(300 MHz, CD3CN): d 7.59 (d, 4H, J ~ 8.7), 7.50 (dd, 4H, J ~
5.6, 3.1), 7.36 (s, 2H), 7.11 (s, 2H), 7.03 (dd, 4H, J ~ 5.1, 3.3),
6.90 (d, 4H, J ~ 8.7 Hz), 6.08 (s, 2H). 13C NMR (75 MHz,
CD3CN): d 158.5, 147.6, 145.4, 134.2, 128.5, 126.3, 124.8,
119.2, 116.5, 114.7, 95.4, 85.4, 52.5. FT-IR (KBr) n/cm21: 3419,
2968, 2208, 1605, 1514, 1164, 831. HRMS (EI) m/z: calcd. for
C36H22O2, 486.1614 (M1), found 486.1608. M.p. 240–242 uC.
in 60 ml THF over the course of 40 min. The solution was
stirred at 0 uC for 1 h. Trimethylsilyl chloride (3.0 ml,
23.6 mmol) was added and the solution stirred for 30 min.
Then, Zn dust (4.0 g, 61 mmol) and glacial AcOH (14 ml) were
added to the solution, stirred at 0 uC for 1 h, and then the
solution allowed to warm to room temperature overnight
(15 h). The solution was filtered through Celite, which was
washed with dichloromethane. The combined organic solutions
were washed with water, NaHCO3 (aq.), and NaCl (aq.). After
drying over MgSO4 and filtration, removal of the solvent
in vacuo yielded a pale yellow solid which was dried in vacuo.
Column chromatography over silica gel with dichloromethane
yielded 3 (6.32 g, 86%) as a foamy cream-colored solid.
Analytically pure 3 was obtained by recrystallization from
hexanes. 1H NMR (300 MHz, CDCl3): d 7.41 (m, 4H), 7.01 (m,
4H), 6.96 (d, 1H, J ~ 8.1), 6.35 (d, 1H, J ~ 8.1 Hz), 5.88 (s,
1H), 5.82 (s, 1H), 5.28 (s, 1H), 0.39 (s, 9H). 13C NMR (75 MHz,
CDCl3): d 150.6, 150.3, 145.0, 131.6, 129.5, 125.4, 125.3, 124.2,
123.8, 112.9, 111.6, 103.3, 99.9, 96.0, 52.6, 47.3, 0.65. FT-IR
(KBr) n/cm21: 3268, 3072, 2957, 2150, 1582, 1487, 1459, 1249,
841. HRMS (EI) m/z: calcd. for C25H22OSi, 366.1434 (M1),
found 366.1449. M.p. 94–96 uC.
1,4-Bis(4@-butyloxyphenylethynyl)-9,10[1’,2’]-benzeno-9,10-
dihydroanthracene (CTO4). Prepared according to the general
procedure: 2 (100 mg, 0.206 mmol), 1-iodobutane (0.070 ml,
0.617 mmol), yielded CTO4 (50 mg, 41%). Representative
characterization for the CTOn series, the remaining character-
ization data are contained in the ESI. 1H NMR (300 MHz,
CDCl3): d 7.59 (d, 4H, J ~ 6.9), 7.47 (dd, 4H, J ~ 5.3, 3. Hz),
7.12 (s, 2H), 7.03 (dd, 4H, J ~ 5.4, 3.3), 6.96 (d, 4H, J ~ 6.9),
5.99 (s, 2H), 4.03 (t, 4H, J ~ 6.6), 1.82 (pent., 4H, J ~ 6.8),
1.55 (m, 4H), 1.01 (t, 6H, J ~ 7.3 Hz). 13C NMR (75 MHz,
CDCl3): d 159.7, 147.0, 145.0, 133.4, 128.0, 125.6, 124.3, 118.8,
115.3, 114.9, 94.2, 85.9, 68.0, 52.4, 31.5, 19.5, 14.1. FT-IR
(KBr) n/cm21: 2951, 2925, 2967, 2210, 1604, 1512, 1248, 1167,
833. HRMS (EI) m/z: calcd. for C44H38O2, 598.2866 (M1),
found 598.2846.
1-Tetrahydropyranyloxy-4-trimethylsilylethynyl-9,10-[1’,2’]-
benzeno-9,10-dihydroanthracene (4). Dihydropyran (1.0 ml,
11 mmol) and p-TsOH (10 mg, 0.06 mmol) were added to a
solution of 3 (3.67 g, 10 mmol) in 25 ml dichloromethane The
solution was allowed to stir at room temperature for 4 h.
Additional dihydropyran (0.25 ml) was added after 1.5 and 3 h.
The reaction was then diluted with dichloromethane and
washed with NaHCO3 (aq.) and NaCl (aq.). After drying over
MgSO4 and filtration, removal of the solvent in vacuo yielded a
pale yellow oil which was titurated with MeOH and filtered to
1,4-Bis(4@-hexyloxyphenylethynyl)-9,10-[1’,2’]-benzeno-9,10-
dihydroanthracene (CTO6). Prepared according to the general
procedure: 2 (100 mg, 0.206 mmol), 1-iodohexane (0.092 ml,
0.617 mmol), yielded CTO6 (72 mg, 53%).
1
yield 4 (2.88 g, 64%) as a white powder. H NMR (300 MHz,
CDCl3): d 7.41 (m, 4H), 7.06 (d, 1H, J ~ 8.3), 7.01 (m, 4H),
6.74 (d, 1H, J ~ 8.3), 5.91 (s, 1H), 5.89 (s, 1H), 5.24 (t, 1H,
J ~ 3.0 Hz), 3.86 (m, 1H), 3.56 (m, 1H), 2.19 (m, 1H), 1.90-1.60
(m, 5H), 0.37 (s, 9H). 13C NMR (75 MHz, CDCl3): d 151.9,
149.6, 145.3, 134.3, 129.4, 125.3, 124.1, 123.8, 123.7, 112.4,
112.3, 103.3, 96.7, 96.2, 62.3, 52.6, 47.6, 30.6, 25.5, 19.3, 0.7.
FT-IR (KBr) n/cm21: 2954, 2149, 1590, 1484, 1249, 856, 840.
HRMS (EI) m/z: calcd. for C30H30O2Si, 450.2010 (M1), found
450.2011. M.p. 191–193 uC.
1,4-Bis(4@-octyloxyphenylethynyl)-9,10[1’,2’]-benzeno-9,10-
dihydroanthracene (CTO8). Prepared according to the general
procedure: 2 (100 mg, 0.206 mmol), 1-bromooctane (0.212 ml,
1.2 mmol), yielded CTO8 (118 mg, 81%). Characterization
matches that in ref. 17.
1,4-Bis(4@-decyloxyphenylethynyl)-9,10-[1’,2’]-benzeno-9,10-
dihydroanthracene (CTO10). Prepared according to the
general procedure: 2 (100 mg, 0.206 mmol), 1-iododecane
(0.131 ml, 0.617 mmol), yielded CTO10 (106 mg, 65%).
1-Tetrahydropyranyloxy-4-ethynyl-9,10-[1’,2’]-benzeno-9,10-
dihydroanthracene (5). 4 (1.80 g, 4 mmol) was dissolved in a
mixture of 25 ml THF and 8 ml methanol and the solution
was purged with Ar for 30 min. K2CO3 (2.21g, 16 mmol) was
added and the solution stirred at room temperature for 8 h. The
solution was then filtered through Celite, which was washed
with dichloromethane. Removal of the solvent in vacuo yielded
5 (1.50 g, 99%) as a white solid. 1H NMR (300 MHz, CDCl3):
d 7.43 (m, 4H), 7.11 (d, 1H, J ~ 8.7), 7.02 (m, 4H), 6.78 (d, 1H,
J ~ 8.7), 5.94 (s, 1H), 5.93 (s, 1H), 5.44 (t, 1H, J ~ 3.0 Hz),
3.87 (m, 1H), 3.58 (m, 1H), 3.30 (s, 1H), 2.22 (m, 1H), 2.10-1.90
(m, 5H). 13C NMR (75 MHz, CDCl3): d 152.1, 149.7, 145.2,
134.4, 130.0, 125.33, 125.29, 124.2, 123.8, 123.7, 112.5, 111.1,
96.7, 81.8, 79.1, 62.3, 52.3, 47.6, 30.6, 25.5, 19.3. FT-IR (KBr)
n/cm21: 3286, 2940, 2869, 2096, 1594, 1486, 1015. HRMS (EI)
m/z: calcd. for C27H22O2, 378.1614 (M1), found 378.1626. M.p.
195–198 uC (with decomp.).
1,4-Bis(4@-dodecyloxyphenylethynyl)-9,10-[1’,2’]-benzeno-9,10-
dihydroanthracene (CTO12). Prepared according to the gen-
eral procedure: 2 (100 mg, 0.206 mmol), 1-bromododecane
(0.155 ml, 0.617 mmol), yielded CTO12 (139 mg, 82%).
1,4-Bis(4@-tetradecyloxyphenylethynyl)-9,10-[1’,2’]-benzeno-
9,10-dihydroanthracene (CTO14). Prepared according to the
general procedure: 2 (100 mg, 0.206 mmol), 1-bromotetra-
decane (0.357 ml, 1.2 mmol), yielded CTO14 (126 mg, 70%).
1,4-Bis{4@-[(3’’’S)-3’’’,7’’’-dimethyloctyloxy]phenylethynyl}-
9,10-[1’,2’]-benzeno-9,10-dihydroanthracene (CTOS). Prepared
according to the general procedure: 2 (100 mg, 0.206 mmol),
(3S)-3,7-dimethyl-1-bromooctane (0.250 ml), yielded CTOS
(109 mg, 69%).
1-Hydroxy-4-trimethylsilylethynyl-9,10-[1’,2’]-benzeno-9,10-
dihydroanthracene (3). A solution of trimethylsilyllithium was
prepared via dropwise addition of n-BuLi (2.5 M in hexanes,
9.5 ml, 23.8 mmol) to a solution of trimethylsilylacteylene
(3.40 ml, 24 mmol) in 60 ml THF at 240 uC. The solution
was stirred for 10 min, and then allowed to warm to 0 uC. The
trimethylsilyllithium solution was added dropwise via cannula
to a 240 uC solution of triptycene-1,4-quinone (5.68 g, 20 mmol)
1-Bromo-4-(4’-tetrahydropyranyloxy-1’-ethynylphenyl)ben-
zene (6). 4-Tetrahydropyranyloxy-1-iodobenzene (1.824 g,
6 mmol), 1-bromo-4-ethynylbenzene (1.086 g,
6 mmol),
PdCl2(PPh3)2 (210 mg, 0.3 mmol), CuI (57 mg, 0.3 mmol)
were combined and placed under Ar. To the solids was added
30 ml THF and 6 ml diisopropylamine, and the solution stirred
at room temperature for 14 h. The solvent was then removed
in vacuo and the residue flushed through a plug of silica gel with
J. Mater. Chem., 2002, 12, 3407–3412
3411

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a solution of 2 : 1 dichloromethane–hexanes to remove the
catalyst. After removal of the solvent in vacuo, the orange solid
was triturated with methanol and filtered, to yield 6 (1.45 g,
68%) as a tan solid. 1H NMR (300 MHz, CDCl3): d 7.45
(m, 4H), 7.36 (d, 2H, J ~ 8.7),7.02 (d, 2H, J ~ 8.0), 5.45 (t, 1H,
J ~ 3.0), 3.89 (dt, 1H, J ~ 10.4, 3.0 Hz), 3.62 (m, 1H),
2.10–1.55 (m, 6H). 13C NMR (75 MHz, CDCl3): d 157.5,
133.2, 133.1, 131.8, 122.8, 122.3, 116.6, 116.0, 96.4, 90.8, 87.3,
62.3, 30.4, 25.3, 18.9. FT-IR(KBr) n/cm21: 2947, 2213, 1599,
1508, 1240, 1078, 1037, 825. HRMS (ESI) m/z: calcd. for
C19H17BrO2, 379.0304 ([M 1 Na]1), found 379.0312. M.p.
119–121 uC.
68.7, 68.3, 52.6, 47.3, 31.9, 29.53, 29.47, 26.2, 26.0, 23.0, 22.9,
14.45, 14.42. FT-IR (KBr) n/cm21: 3066, 2925, 2854, 2211,
1600, 1516, 1273, 1244. HRMS (EI) m/z: calcd. for C48H46O2,
654.3492 (M1), found 654.3467.
Compound ETO8. Prepared according to the general
procedure: 8 (100 mg, 0.02 mmol), 1-bromooctane (0.212 ml,
1.2 mmol), yielded ETO8 (94 mg, 64%).
Compound ETO10. Prepared according to the general
procedure: 8 (100 mg, 0.02 mmol), 1-bromodecane (0.250 ml,
1.2 mmol), yielded ETO10 (120 mg, 76%).
Compound 7. 5 (379 mg, 1.0 mmol), 6 (358 mg, 1.0 mmol),
Pd2(dba)3 (45 mg, 0.05 mmol), triphenylphosphine (130 mg,
0.50 mmol), and CuI (10 mg, 0.05 mmol) were combined and
placed under Ar. Triethylamine (10 ml) was added, the tube
sealed with a Teflon plug, and the solution heated to 100 uC for
24 h. The reaction solution was cooled, diluted with dichloro-
methane, and filtered through a plug of Celite, which was
rinsed with further dichloromethane. Removal of the solvent
in vacuo yielded a yellow solid which was absorbed onto silica
gel and purified via gradient column chromatography over
silica gel with 2 : 1 to 1 : 2 hexanes–dichloromethane, to yield 7
Compound ETO12. Prepared according to the general pro-
cedure: 8 (100 mg, 0.02 mmol), 1-bromododecane (0.310 ml,
1.2 mmol), yielded ETO12 (145 mg, 86%). Compound ETO12
was recrystallized from hexanes.
Acknowledgements
The authors wish to thank the National Science Foundation
(NSF) and the US Army Research Office (ARO), through a
MURI grant, for funding. T. M. L. wishes to thank Alex
Paraskos for helpful advice and discussions.
1
(471 mg, 73%). H NMR (300 MHz, CDCl3): d 7.58 (d, 2H,
J ~ 8.1), 7.52 (d, 2H J ~ 8.1), 7.47 (d, 2H, J ~ 8.7), 7.41 (m,
4H), 7.09 (d, 2H, J ~ 8.4), 7.03 (d, 1H, J ~ 8.4), 6.99 (m, 4H),
6.77 (d, 1H, J ~ 8.7 Hz), 5.93 (s, 1H), 5.91 (s, 1H), 5.43 (m, 2H),
3.87 (m, 2H), 3.58 (m, 2H), 2.16 (m, 2H), 2.10–1.55 (m, 10H).
13C NMR (75 MHz, CDCl3): d 157.3, 152.0, 149.1, 145.2,
145.1, 134.5, 13.1, 131.5, 129.5, 125.3, 124.2; 123.8, 123.4,
116.5, 116.1, 112.6, 112.1, 96.8, 96.4, 91.5, 91.2, 88.2, 62.3, 52.6,
References
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1
chloroform. H NMR (300 MHz, CDCl3): d 7.60(d, 1H, J ~
8.1), 7.55 (d, 2H, J ~ 8.1), 7.47 (d, 2H, J ~ 9.0), 7.44 (m, 4H),
7.06 (d, 1H, J ~ 8.4), 7.02 (dd, 4H, J ~ 5.1, 3.1), 6.84 (d, 2H,
J ~ 8.1), 6.45 (d, 1H, J ~ 8.7 Hz), 5.95 (s, 1H), 5.84 (s, 1H),
4.89 (s, 1H), 4.88 (s, 1H). 13C NMR (75 MHz, CD3CN): d
158.3, 152.7, 150.2, 145.9, 145.7, 133.9, 133.8, 132.5, 133.3,
132.1, 130.2, 126.1, 126.0, 124.7, 124.4, 124.0, 123.8, 116.4,
114.7, 114.1, 110.7, 92.2, 91.5, 89.6, 88.0, 52.8, 47.5. FT-IR
(KBr) n/cm21: 3399, 3069, 2965, 2212, 1606, 1517. HRMS (EI)
m/z: calcd. for C36H22O2, 486.1614 (M1), found 498.1623. M.p.
187–189 uC.
Compound ETO6. Prepared according to the general
procedure: 8 (100 mg, 0.02 mmol), 1-iodohexane (0.184 ml,
1.2 mmol), yielded ETO6 (104 mg, 77%). Representative
characterization for the ETOn series, the remaining character-
ization data are contained in the ESI. 1H NMR (300 MHz,
CDCl3): d 7.60 (d, 2H, J ~ 8.1), 7.55 (d, 2H, J ~ 8.1), 7.50
(d, 2H, J ~ 8.7), 7.45 (dd, J ~ 5.0, 3.2), 7.41 (dd, 2H, J ~ 5.0,
3.2), 7.13 (d, 1H, J ~ 8.4), 7.00 (dd, 4H, J ~ 5.3, 3.2), 6.89
(d, 2H, J ~ 9.0), 6.55 (d, 1H, J ~ 8.7 Hz), 5.94 (s, 1H), 5.92 (s,
1H), 3.99 (m, 4H), 1.83 (m, 4H), 1.60–1.30 (m, 12H), 0.94 (m,
6H).13C NMR (75 MHz, CDCl3): d 159.4, 154.2, 149.1, 145.33,
145.25, 133.8, 133.2, 131.5, 129.6, 125.3, 125.2, 124.1, 123.8,
123.4, 123.3, 115.0, 114.7, 110.9, 109.5, 91.6, 91.1, 89.4, 88.1,
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3412
J. Mater. Chem., 2002, 12, 3407–3412