Discotic triphenylene twins linked through thiophene bridges: Controlling nematic behavior in an intriguing class of functional organic materials

Article abstract of DOI:10.1021/jo3002886

Substituted triphenylenes and similar discotic molecules have a strong tendency toward columnar organization. Nematic mesophases are much less commonly observed in discotic systems. We have demonstrated a general strategy whereby discotic triphenylenes ca

Full text of DOI:10.1021/jo3002886

Article
pubs.acs.org/joc
Discotic Triphenylene Twins Linked through Thiophene Bridges:
Controlling Nematic Behavior in an Intriguing Class of Functional
Organic Materials
Liang Zhang, David L. Hughes, and Andrew N. Cammidge*
School of Chemistry, University of East Anglia, Norwich NR4 7TJ, U.K.
S
* Supporting Information
ABSTRACT: Substituted triphenylenes and similar discotic molecules have a strong tendency toward columnar organization.
Nematic mesophases are much less commonly observed in discotic systems. We have demonstrated a general strategy whereby
discotic triphenylenes can be twinned to form stable, boardlike materials that display only nematic mesophases. The dominant
structural feature that leads to nematic behavior is an enforced void region in the center of the macrocycle that results from
bridging through the triphenylene 3,6-positions. This precludes simple columnar assembly because it would lead to free space
through the center of each stack. Selection of appropriate bridging units allows materials to be designed which combine
molecular features, such as the optoelectronic properties of electron-rich triphenylenes and conjugated thiophene units, with the
processability, self-healing, and alignment features inherent in nematic mesophases. In addition, communication across twinned
structures can lead to additional enhancement of optoelectronic behavior. This is particularly apparent in fully conjugated, planar
twin 12 which is formally expected to have some antiaromatic character. This character is manifested in its spectral properties,
and particularly noteworthy is its strong, Stokes shifted emission at around 500 nm.
it combines synthetic versatility with the molecular robustness
required for device applications.6,12,13 Qualitative parameters
have been established to aid in the design of systems forming
columnar mesophases.14,15
The columnar phases of discotic materials can be likened to
the smectic mesophases formed by conventional calamitic (rod-
shaped) liquid crystals. Similarly, like their calamitic counter-
parts, discotics can also form less ordered nematic mesophases.
Unlike calamitics, however, this behavior is only rarely
observed, and structural factors leading to its formation are
poorly understood.16 Nevertheless, discotic nematics have
found very important application as optical compensating
films for liquid crystal displays.17
1. INTRODUCTION
Discotic liquid crystals, first discovered by Chandrasekhar in
1977,1 have become the subject of intense investigation.2 Early
work was mostly fundamental and curiosity-driven in nature,
leading to expansion in the number of molecular cores capable
of showing discotic liquid crystallinity.3 Although numerous
cores have been shown to give mesophases, three main classes
have received particular attention due to combinations of
molecular properties, synthetic versatility, and robustness,
namely those based on phthalocyanine,4 coronene,5 and
triphenylene6 (Figure 1). The most commonly observed and
investigated mesophases are columnar in structure,7 not least
because this unique architecture naturally lends itself to device
applications employing a combination of processability, self-
assembly/self-healing, and aligned, directional conduction of
either charge or energy.8 Molecular electronic applications of
columnar systems are diverse and include organic light-emitting
diodes,9 field-effect transistors,10 and photovoltaic systems.10c,11
A significant research effort has focused on unraveling the
structural factors that control columnar mesophase formation
in discotic systems. We and others have paid particular
attention to systems based on the triphenylene core because
2. RESULTS AND DISCUSSION
We recently communicated an unconventional molecular
architecture whereby typically columnar triphenylene sub-
structures were twinned through their 3,6-positions to create
a rigid, conjugated structure with a central void region.18
Received: February 11, 2012
Published: April 9, 2012
© 2012 American Chemical Society
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structure in Figure 3 that bridging through a 1,3-substituted
benzene moiety would lead to a twin with minimal angle strain
and an expanded cavity. A fully planar core is expected,
enforcing efficient conjugation between individual phenyl and
triphenylene units. The synthesis of the twin is shown in
Scheme 1.
Diethynyltriphenylene 318 was coupled19 with an excess of
1,3-diiodobenzene 4 to yield the bisiodophenyl intermediate 5,
which itself displayed a stable, wide range columnar mesophase.
Crystals suitable for X-ray diffraction were obtained, and the
structure, also shown in Scheme 1, shows that the cores of the
molecules adopt an essentially planar conformation in the
crystal with the discotic molecules forming offset columnar
stacks. The target twinned structure was achieved by coupling
diiodide 5 with the precursor triphenylene diacetylene 3 under
palladium-free coupling conditions.20 It is worth noting that
this stepwise procedure proved more efficient than the single-
step coupling−macrocyclization between diacetylene 3 and 1,3-
diiodobenzene. The twinned triphenylene 6, and indeed all of
the twins described in this paper, displayed a strong tendency
to aggregation leading to broadened signals and concentration-
dependent chemical shifts observed for the aromatic protons in
some 1H NMR spectra, and it was not possible to obtain useful
13C NMR data. 1H NMR spectra were therefore recorded at the
lowest reasonable concentration (typically 10−4−10−5 M), and
sample precipitation frequently occurred on standing.
In accordance with the design feature, when heated the new
twinned structure forms only a nematic mesophase, underlining
the link between the molecular structural motif and balance
between columnar and nematic behavior. The high transition
temperature into the mesophase, which could, no doubt, be
lowered by simple side-chain modification, further indicates
efficient packing in the crystal, an observation that is not
surprising in light of the crystal structure observed for precursor
5. Although 6 is an intriguing structure that provides a strain-
free molecular void region in the center of the twin, the 1,3-
phenylene link groups do not allow communication across the
whole structure, and this results in optoelectronic properties
that essentially mirror their monomeric precursors. Conjugated
linkers are therefore required, and we first briefly investigated
the isomeric twin linked through 1,4-phenylene bridges. Such
systems would provide a strained macrocyclic twin, but it was
recognized that synthesis would be much more challenging.
Furthermore, simple molecular modeling21 indicated that 1,4-
phenylene-bridged twins could adopt a more favorable
conformation where the benzene bridges lie essentially
perpendicular to the core π-systems, breaking the conjugation
pathway and communication between the two halves of the
twin. Nevertheless, synthesis was attempted following the same
strategy developed for 1,3-phenylene-bridged twin 6
Figure 1. Three most common molecular cores that give rise to
discotic columnar mesophase formation and a cartoon of the
molecular arrangement in a columnar hexagonal mesophase.
Columnar organization of such structures would lead to free
space through the core of the column and is therefore not
possible. A switch to nematic behavior is therefore observed,
allowing side chains from one unit to occupy the void of
another. Indeed, precisely this mode of packing is observed in
the crystal structure leading to a unique zigzag arrangement
that corresponds to electronic communication in two
dimensions but not the third (Figure 2).
Twinned triphenylenes, linked through their 3,6-positions,
therefore could offer an intriguing general platform for organic
materials design due to the combination of potential
communication across the whole molecule and the incorpo-
ration of a nematogenic structural feature in the form of
enforced free space at the molecular core. This paper describes
examples of such twinned triphenylenes that were designed to
interrogate the generality of the design feature and expand the
application scope of the organic materials. To this end, we
sought to incorporate aryl bridges across triphenylene twins,
and the general structure is depicted in Figure 3. It is
immediately apparent that introduction of such bridging units
expands the central molecular cavity and the choice of bridge
will further determine whether a planar conformation is
expected through a balance between angle strain and
conjugation.
In the first materials we targeted twins linked through
phenylene bridges. It is clear from inspection of the generic
Figure 2. Columnar hexaalkoxytriphenylene 1 and its dehydroannulene twinned variant 2 that shows only nematic mesophase behavior, plus the
zigzag arrangement present in the crystal.18
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Figure 3. Triphenylene twins linked through their 3,6-positions; dehydroannulene twins (left) and arylene-bridged twins (right).
a
Scheme 1. Synthesis of 1,3-Phenylene-Bridged Twin 6 and the X-ray Crystal Structure of Intermediate 5
a
Note: there is site disorder in two of the n-hexyl chains; hexyl side chains have been omitted from the stacking diagram but they do not all lie in the
plane of the core; thermal ellipsoids and spheres are drawn at the 50% probability level.
(Scheme 2). Consequently, triphenylene diacetylene 3 was
coupled with 1,4-diiodobenzene to give diiodide intermediate 8
that again displayed a stable, wide-range columnar mesophase.
The final coupling between diiodide 8 and its precursor 3,
however, failed to yield any trace of the twin 9.
We therefore sought to design bridging units that would
reduce the overall strain (leading to achievable macro-
cyclization) but retain communication across the whole
structure so that enhanced molecular properties could be
combined with the self-assembly properties that would also be
driven by the twinning motif. Thiophene bridges were
recognized as being able to fulfill all of these requirements.
2,5-Linked thiophenes provide a near-perfect bonding angle
(Figure 4), and more importantly, oligothiophene motifs
feature in some of the most important emerging organic
materials, spanning applications across optoelectronic materi-
als.10c,22
The synthesis of thiophene-bridged twin 12 is shown in
Scheme 3 and follows a similar route to the one successfully
employed for 1,3-phenylene-bridged twin 6. The stepwise route
was once again required to synthesize the macrocylized product
with low yields obtained even under high dilution conditions.
Like 6, and further verifying the design protocol, the 2,5-
thiophene-bridged twin 12 shows only nematic behavior when
heated, giving a highly mobile schlieren texture when observed
by polarizing optical microscopy. The molecular properties of
the two compounds 6 and 12, however, differ significantly as a
result of the conjugation that is possible in the latter twin. The
conjugation pathway mapped across the macrocycle and cores
gives a 4n electron count and describes a formally antiaromatic
pathway. One 36e pathway is shown in red on twin 12 in
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Scheme 2. Attempted Synthesis of 1,4-Phenylene-Bridged Twin 9
Figure 4. Triphenylene twin linked through 2,5-thiophene bridges and a simple molecular model showing the expected planar conformation.
Scheme 3. Synthesis of 2,5-Thiophene-Bridged Twin 12 and Its Nematic Texture Viewed by Polarizing Optical Microscopy
Scheme 3, but all others similarly give a 4n electron count. This
character can be used as one way to rationalize the observed
spectroscopic data. In the proton NMR spectrum of 12, a
significant downfield shift is observed for the proton located
inside the macrocycle compared to its position in the precursor,
consistent with antiaromatic character (Figure 5). Furthermore,
the conjugated twin is highly luminescent and gives a large
Stokes shift (ca. 60 nm difference between λmax of the longest
wavelength absorption band and the high-intensity emission
band) indicative of significant reorganization in the excited state
(Figure 6).
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1
Figure 5. Comparison of the H NMR spectra of formally antiaromatic twin 12 with its precursor 11.
the inner proton (Supporting Information). The absorption
spectrum is broad, and fluorescence is weaker in 17 compared
to both 12 and, significantly, its precursor 15, showing two
broad but distinct bands of almost equal intensity with the
second one again significantly Stokes shifted (Supporting
Information).
A strategy to encourage planarity, and therefore conjugation
across the complete framework, would be to design a twin with
a macrocylic aromatic system. This requires an unsymmetrical
core with a 4n + 2 electron count, such as the one depicted in
Figure 7.
Figure 6. Absorption (6.6 × 10−7 M) and emission (6.6 × 10−8 M)
spectra of twin 12 (excitation at 380 nm) recorded in dichloro-
methane.
The synthesis of such unsymmetrical twins is clearly more
complex than their symmetrical counterparts, and two general
macrocyclization sequences were considered (Figure S1,
Supporting Information). Simple modeling again indicated
that the proposed twin would have modest strain, and therefore
the two approaches were considered equally viable. The
synthesis of unsymmetrical twin 26 is shown in Scheme 6.
The synthesis required initial preparation of a singly protected
triphenylene diacetylene derivative 22, and this synthesis is
shown in Scheme 5. 3,6-Dibromotriphenylene 19 was coupled
first with 2-propanol-protected acetylene and then with TMS-
acetylene to give the differentially protected analogue 21.
Treatment with sodium hydroxide in dry toluene smoothly
afforded the (mono) TMS-protected derivative 22. Two
equivalents of 22 reacted with 5,5′-diiodo-2,2′-bithiophene 13
to give the protected open twin 23 that was easily deprotected
by treatment with potassium carbonate in THF−methanol
(giving 24). The final macrocyclization was achieved by careful
coupling with bis(iodothiophenyl)acetylene 25,23 albeit again in
low yield even under high dilution conditions.
The design protocol was pushed a further step forward by
inserting bithiophene bridges to form the twin. Conjugation in
such a system would be expected to shift the absorption and
fluorescence deeper into the red and open the cavity within the
macrocycle. In these structures, however, the bond angles are
no longer ideal in the planar conformation. Synthesis was
straightforward (Scheme 4) following our established method-
ology and sequence and produced twin 17 that failed to melt
below 300 °C. As previously stated, successful protocols for
tuning-phase transition temperatures are established, and in our
case simply extending the alkoxide side chains (replacing
hexyloxy- by decyloxy-) lowered the melting point sufficiently
to reveal that nematic mesophase behavior is also exclusively
observed in these greatly expanded twinned derivatives. It is
unlikely, however, that these expanded systems favor a planar
(and therefore conjugated) conformation. The proton NMR
spectra of the twins show only a marginal downfield shift for
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Scheme 4. Synthesis of Expanded 5,5′-Bithiophene-Bridged Twins 17 and 18
bridging through the triphenylene 3,6-positions which
precludes simple columnar assembly because it would lead to
free space through the middle of each stack. In this study, we
have focused on the use of thiophene units to bridge between
the discotic triphenylenes, and this leads to interesting and
potentially important organic materials that can combine the
known, favorable properties associated with oligothiophenes
with the processability, alignment, and self-healing qualities of
nematic mesophases. In addition, communication across
twinned structures can lead to enhanced and novel features
to optimize optoelectronic behavior. This is particularly
apparent in twin 12 which is clearly fully conjugated and
therefore is formally expected to have some antiaromatic
character. This character is manifested in its spectral properties,
and particularly noteworthy is its strong, Stokes-shifted
fluorescence at around 500 nm. The structural motif can
therefore be exploited for designing processable organic
materials for targeted optoelectronic applications.
Figure 7. Unsymmetrical, expanded twin structure with formally
aromatic electron count.
Unsymmetrical twin 26 does not display any mesophase
behavior below 300 °C. Its transition temperatures could again
be reduced through chain modification, and nematic behavior
would again be expected, but this was not considered useful
because the molecular properties of 26 show little evidence for
communication across the structure. In the proton NMR
spectrum, the signals for the inner protons appear at essentially
the same chemical shift as the equivalent proton in formally
antiaromatic twin 17, suggesting that both systems lack
significant conjugation (Supporting Information). The absorp-
tion and fluorescence spectra are broad and featureless
supporting this conclusion (Supporting Information).
4. EXPERIMENTAL SECTION
General Procedure for the Synthesis of Intermediate
Bis(iodoarylethynyl)triphenylenes 5, 8, 11, 15, and 16. Diiodide
(4, 7, 10, 13) (ca. 4 mmol) and Pd(PPh3)3Cl2 (0.06 mmol) in a
mixture of freshly distilled triethylamine (10 mL) and THF (5 mL)
were stirred at room temperature for 15 min. CuI (ca. 0.2 mmol) was
then added, followed by triphenylene diacetylene 3 or 14 (ca. 0.6
mmol) dissolved in THF (5 mL). After addition, the mixture was
heated at 50 °C for 17−24 h and then evaporated to dryness in vacuo.
The residue was subjected directly to purification by silica gel
chromatography to yield the title compounds.
3. SUMMARY AND OUTLOOK
We have demonstrated a general strategy whereby discotic
triphenylenes, which have a strong tendency toward columnar
organization, can be twinned to form stable, boardlike materials
that display only nematic mesophases. The dominant structural
feature that leads to nematic behavior is an enforced void
region in the center of the macrocycle that results from
2,7,10,11-Tetrakis(hexyloxy)-3,6-bis[(3-iodophenyl)ethynyl]-
triphenylene (5): pale yellow solid (385 mg, 48%); transition
temperatures Cr 89 °C Colh 262 °C I; IR (ATR, cm−1) 3017, 2970,
2925, 2857, 2212, 1608, 1582, 1427, 1376; 1H NMR (400 MHz,
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Scheme 5. Synthesis of Singly Protected Triphenylene Intermediate 22
Scheme 6. Synthesis of the Formally Aromatic, Unsymmetrical Twin 22
CDCl3) δ 8.52 (s, 2H), 7.98 (t, J = 1.6 Hz, 2H), 7.76 (s, 2H), 7.68 (m,
2H), 7.65 (s, 2H), 7.56−7.58 (m, 2H), 7.12 (t, J = 8.0 Hz, 2H), 4.27−
4.22 (m, 8H), 2.02−1.91 (m, 8H), 1.70−1.58 (m, 8H), 1.49−1.38 (m,
16H), 0.96−0.92 (m, 12H); 13C NMR (100 MHz, CDCl3) δ 157.7,
149.9, 140.1, 137.0, 130.7, 130.1, 129.8, 128.2, 125.9, 124.3, 122.1,
112.2, 107.1, 104.1, 93.7, 92.0, 88.0, 69.5, 68.9, 31.8, 31.7, 29.41, 29.37,
26.0, 25.9, 22.8, 22.7, 14.14, 14.07; MALDI-MS 1080.45 (M+). Anal.
Calcd for C58H66I2O4: C, 64.45; H, 6.15. Found: C, 64.40; H, 6.10.
2,7,10,11-Tetrakis(hexyloxy)-3,6-bis[(4-iodophenyl)ethynyl]-
triphenylene (8): yellow solid (465 mg, 53%); transition temper-
atures Cr 114 °C Colh 271 °C I; IR (ATR, cm−1) 3017, 2924, 2856,
2212, 1609, 1425, 1377; 1H NMR (300 MHz, CDCl3) δ 8.55 (s, 2H),
7.78 (s, 2H), 7.72 (d, J = 8.4, 2H), 7.67 (s, 2H) 7.34 (d, J = 8.4, 2H),
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4.28−4.21 (m, 8H), 2.02−1.90 (m, 8H), 1.69−1.55 (m, 8H), 1.46−
1.32 (m, 16H), 0.97−0.91 (m, 12H); 13C NMR (100 MHz, CDCl3) δ
157.9, 150.1, 137.6, 133.2, 130.2, 128.4, 124.5, 123.4, 122.3, 122.2,
112.6, 107.5, 104.4, 93.9, 92.9, 88.0, 69.6, 69.0, 31.6, 29.3, 25.8, 25.76,
22.59, 22.56, 13.9; MALDI-MS 1080.43 (M+). Anal. Calcd for
C58H66I2O4: C, 64.45; H, 6.15. Found: C, 64.51; H, 6.25.
2,7,10,11-Tetrakis(hexyloxy)-3,6-bis[2-(5-iodothiophene-2-
yl)ethynyl]triphenylene (11): yellow solid (172 mg, 27%);
transition temperatures Cr 64 °C Colh 296 °C dec; IR (ATR, cm−1)
3017, 2970, 2924, 2856, 2212, 1607, 1583, 1427, 1377; 1H NMR (300
MHz, CDCl3) δ 8.45 (s, 2H), 7.75 (s, 2H), 7.63 (s, 2H), 7.19 (d, J =
3.6 Hz, 2H), 6.99 (d, J = 3.6 Hz, 2H), 4.23 (t, J = 6.3 Hz, 8H), 2.01−
1.89 (m, 8H), 1.68−1.56 (m, 8H), 1.46−1.38 (m, 16H), 0.96−0.92
(m, 12H); 13C NMR (75 MHz, CDCl3) δ 158.2, 157.7, 150.1, 137.3,
133.1, 130,4, 130.32, 130.26, 129.4, 128.0, 124.55, 124.49, 122.3,
122.2, 112.2, 111.7, 107.4, 104.4, 92.5, 85.9, 81.5, 80.7, 69.7, 69.24,
69.2, 31.92, 31.87, 29.6, 29.5, 29.4, 26.1, 26.0, 22.93, 22.89, 22.86,
14.33, 14.29; MALDI-MS 1092.46 (M+). Anal. Calcd for
C54H62I2S2O4: C, 59.34; H, 5.72. Found: C, 59.39; H, 5.75.
4H), 7.85 (s, 4H), 7.77 (s, 4H), 7.17 (s, 4H), 4.31 (t, J = 6.4 Hz, 8H),
4.25 (t, J = 6.4 Hz, 8H), 2.11−1.89 (m, 16H), 1.65−1.54 (m, 16H),
1.46−1.39 (m, 32H), 0.97−0.91 (m, 24H); UV−vis (CH2Cl2) λmax
(log ε) 277 (5.54), 389 (5.65), 416 (5.45), 434 (5.36) nm; MALDI-
MS 1514.31 (M+).
Twin 17: orange solid (10 mg, 10%); mp > 300 °C; IR (ATR,
1
cm−1) 2922, 2854, 2194, 1607, 1425, 1376; H NMR (400 MHz,
CD2Cl2) δ 8.65 (s, 4H), 7.82 (s, 4H), 7.72 (s, 4H), 7.27 (m, 8H), 4.29
(t, J = 6.4 Hz, 8H), 4.25 (t, J = 6.4 Hz, 8H), 2.11−1.89 (m, 16H),
1.65−1.54 (m, 16H), 1.46−1.39 (m, 32H), 0.97−0.91 (m, 24H); UV−
vis (CH2Cl2) λmax (log ε) 294 (5.06), 373 (5.10), 419 (5.17) nm;
MALDI-MS 1677.95 (M+).
Twin 18: orange solid (12 mg, 9%); transition temperatures Cr 210
1
°C ND; IR (ATR, cm−1) 2920, 2851, 2193, 1605, 1424, 1375; H
NMR (400 MHz, CD2Cl2) δ 8.61 (s, 4H), 7.76 (s, 4H), 7.66 (s, 4H),
7.24 (s, 8H), 4.26 (t, J = 6.4 Hz, 8H), 4.22 (t, J = 6.4 Hz, 8H), 2.04−
1.89 (m, 16H), 1.74−1.55 (m, 16H), 1.46−1.24 (m, 96H), 0.98−0.93
(m, 24H); MALDI-MS 2126.03 (M+).
2,7,10,11-Tetrakis(hexyloxy)-3-bromo-6-(3-methyl-3-
hydroxybutynyl)triphenylene (20). Dibromotriphenylene 19 (1.00
g, 1.27 mmol), Pd(PPh3)3Cl2 (45 mg, 0.0635 mmol), and CuI (12 mg,
0.0635 mmol) in freshly distilled triethylamine (20 mL) were heated at
50 °C for 20 min. 2-Methyl-3-butyn-2-ol (118 mg, 1.40 mmol) was
added dropwise and the suspension was heated at 50 °C for 3 h. The
reaction mixture was evaporated to dryness in vacuo, and the residue
subjected directly to silica gel chromatography (DCM/petroleum
ether = 1:1−9:1) to yield the title compound 20 as an off-white solid
(0.34 g, 34%): transition temperatures Cr 45 °C Colh 192 °C I; IR
(ATR, cm−1) 3413 (br), 2954, 2926, 2858, 2330 (w), 1604, 1497,
1424; 1H NMR (300 MHz, CDCl3) δ 8.50 (s, 1H), 8.29 (s, 1H), 7.76
(s, 1H), 7.75 (s, 1H), 7.64 (s, 1H), 7.58 (s, 1H), 4.26−4.17 (m, 8H),
2.18−1.91 (m, 8H), 1.72 (s, 6H), 1.65−1.53 (m, 8H), 1.45−1.35 (m,
16H), 0.96−0.92 (m, 12H); 13C NMR (100 MHz, CDCl3) δ 157.8,
153.7, 149.9, 149.84, 129.9, 128.9, 128.1, 127.6, 124.3, 124.2, 123.6,
121.5, 112.5, 112.2, 107.58, 107.51, 105.3, 104.0, 98.5, 79.1, 70.0, 69.7,
69.5, 68.9, 65.9, 51.1, 32.0, 31.93, 31.88, 31.8, 29.6, 29.4, 26.1, 26.0,
22.93, 22.90, 22.87, 14.33, 14.28; HRMS (ES) m/z [M + H]+ calcd for
C47H65BrO5 789.4088, found 789.4082. Anal. Calcd for C47H65BrO5:
C, 71.46; H, 8.29. Found: C, 71.37; H, 8.33.
2,7,10,11-Tetrakis(hexyloxy)-3,6-bis[(5′-iodo-2,2′-bithio-
phene-5-yl)ethynyl]triphenylene (15): yellow solid (415 mg,
17%); transition temperatures Cr 134 °C Colh 221 °C I; IR (ATR,
cm−1) 3068, 2920, 2853, 2196, 1607, 1537, 1425, 1378; 1H NMR (400
MHz, CD2Cl2) δ 8.60 (s, 2H), 7.85 (s, 2H), 7.76 (s, 2H), 7.22 (d, J =
4.0 Hz, 2H), 7.20 (d, J = 4.0 Hz, 2H), 7.08 (d, J = 4.0 Hz, 2H), 6.91
(d, J = 4.0 Hz, 2H), 4.29 (t, J=6.4 Hz, 4H), 4.24 (t, J = 6.4 Hz, 4H),
2.01−1.88 (m, 8H), 1.69−1.52 (m, 8H), 1.47−1.36 (m, 16H), 0.96−
0.92 (m, 12H); 13C NMR (75 MHz, CD2Cl2) δ 157.5, 150.0, 142.6,
137.9, 137.3, 132.4, 130.0, 127.7, 125.4, 124.1, 124.0, 123.0, 121.9,
112.0, 106.9, 104.0, 91.9, 86.3, 72.3, 69.2, 68.8, 31.52, 31.47, 29.2, 29.1,
25.7, 25.6, 22.5, 22.4, 13.62, 13.55; MALDI-MS 1256.32 (M+).
2,7,10,11-Tetrakis(decyloxy)-3,6-bis[(5′-iodo-2,2′-bithio-
phene-5-yl)ethynyl]triphenylene (16): yellow solid (643 mg,
15%); transition temperatures Cr 67 °C Colh 238 °C I; IR (ATR,
cm−1) 3066, 2917, 2850, 2194, 1603, 1535, 1423; 1H NMR (300
MHz, CDCl3) δ 8.56 (s, 2H), 7.80 (s, 2H), 7.70 (s, 2H), 7.22 (d, J =
3.9 Hz, 2H), 7.17 (d, J = 3.9 Hz, 2H), 7.04 (d, J = 3.9 Hz, 2H), 6.88
(d, J = 3.9 Hz, 2H), 4.23 (m, 8H), 2.04−1.88 (m, 8H), 1.71−1.56 (m,
8H), 1.51−1.19 (m, 48H), 0.96−0.92 (m, 12H); 13C NMR (100
MHz, CDCl3) δ 157.4, 149.7, 142.8, 137.7, 137.3, 132.4, 129.90, 127.6,
125.2, 124.2, 123.9, 123.1, 122.0, 112.0, 106.9, 103.9, 92.1, 86.7, 72.5,
69.4, 68.8, 32.0, 29.78, 29.76, 29.7, 29.67, 29.5, 29.4, 26.33, 26.30, 22.7,
14.18, 14.16; MALDI-MS 1480.55 (M+).
General Procedure for the Synthesis of Twinned Tripheny-
lenes 6, 12, 17, and 18. CuI (5.7 mg, 0.03 mmol), PPh3 (7.8 mg,
0.03 mmol), and K2CO3 (41.5 mg, 0.30 mmol) in freshly distilled
DMF (60 mL) were stirred at room temperature for 15 min.
Triphenylene diiodide (5, 8, 11, 15 or 16) (0.10 mmol) and
triphenylene diacetylene (3 or 14) (0.12 mmol) were added. The
reaction was stirred and heated at 150 °C for 24 h, and then the
mixture was poured into saturated aqueous NH4Cl (50 mL), followed
by methanol (200 mL). The product was filtered and washed
thoroughly with methanol. A portion of the solid was then subjected to
careful silica gel chromatography to yield an analytical sample of the
twin. [The samples’ low solubility and aggregation prevented
acquisition of informative 13C NMR data.]
2,7,10,11-Tetrakis(hexyloxy)-3-(trimethylsilylethynyl)-6-(3-
methyl-3-hydroxybutynyl)triphenylene (21). Triphenylene 20
(700 mg, 0.90 mmol), Pd(PPh3)3Cl2 (156 mg, 0.22 mmol), and CuI
(42.3 mg, 0.22 mmol) in freshly distilled triethylamine (20 mL) were
heated at 60 °C for 20 min. Trimethylsilyl acetylene (354 mg, 3.60
mmol) was then added dropwise. The suspension was heated at 60 °C
for 18 h. The reaction mixture was evaporated to dryness in vacuo, and
the residue was subjected directly to silica gel chromatography (DCM/
petroleum ether = 2:3−4:1) to yield the title compound 21 as an off-
white solid (645 mg, 90%): transition temperatures Cr 105 °C Colh
192 °C I; IR (ATR, cm−1) 3443 (br), 2955, 2929, 2859, 2150, 1610,
1
1503, 1468, 1426; H NMR (300 MHz, CDCl3) δ 8.57 (s, 1H), 8.52
(s, 1H), 7.82 (s, 1H), 7.80 (s, 1H), 7.69 (s, 1H), 7.67 (s, 1H), 4.26−
4.19 (m, 8H), 2.24 (s, 1H) 2.00−1.90 (m, 8H), 1.71 (s, 6H), 1.65−
1.53 (m, 8H), 1.45−1.35 (m, 16H), 0.96−0.92 (m, 12H), 0.33 (s,
9H); 13C NMR (100 MHz, CDCl3) δ 158.1, 157.7, 149.84, 149.80,
130.0, 129.8, 128.7, 128.4, 124.4, 124.3, 122.2, 122.16, 122.13, 112.7,
112.2, 107.4, 107.3, 104.3, 104.2, 101.6, 98.9, 98.2, 78.8, 69.5, 68.9,
68.8, 65.8, 31.7, 31.62, 31.60, 31.5, 29.6, 29.31, 29.28, 29.25, 25.78,
25.77, 22.62, 22.58, 14.04, 14.02, 14.0, 0.0; HRMS (ES) m/z [M + H]+
calcd for C52H74O5Si 807.5378, found 807.5383. Anal. Calcd for
C52H74O5Si: C, 77.37; H, 9.24. Found: C, 77.30; H, 9.26.
2,7,10,11-Tetrakis(hexyloxy)-3-(trimethylsilylethynyl)-6-
ethynyltriphenylene (22). Freshly powdered sodium hydroxide
(500 mg, 12.5 mmol) was added to triphenylene 21 (527 mg, 0.653
mmol) dissolved in anhydrous toluene (50 mL). The suspension was
heated under reflux for 80 min. The mixture was filtered, and the
filtrate was evaporated to dryness in vacuo. The residue was subjected
directly to silica gel chromatography (DCM/petroleum ether = 1:1) to
yield the title compound 22 as an off-white solid (440 mg, 90%):
transition temperatures Cr 99 °C Colh 157 °C dec; IR (ATR, cm−1)
Twin 6: off-white solid (16 mg, 11%); transition temperatures Cr
113 °C Cr 272 °C ND; IR (ATR, cm−1) 3016, 2927, 2854, 1609, 1425,
1378; 1H NMR (400 MHz, CDCl3) δ 8.75 (s, 4H), 8.10 (s, 2H), 7.87
(s, 4H), 7.76 (s, 4H), 7.56 (dd, J = 7.6 Hz, J = 1.6 Hz, 4H), 7.39 (t, J =
7.6 Hz, 2H), 4.32−4.25 (m, 16H), 3.38 (s, 1H), 2.06−1.93 (m, 16H),
1.76−1.57 (m, 16H), 1.51−1.26 (m, 32H), 0.99−0.93 (m, 24H); UV−
vis (CH2Cl2) λmax (log ε) 312 (5.32), 343 (5.12), 397 (4.58) nm;
MALDI-MS 1502.15 (M+).
Twin 12: bright yellow solid (20 mg, 13%); transition temperatures
Cr 69 °C Cr 291 °C ND 300 °C; IR (ATR, cm−1) 2925, 2856, 2197,
1
1604, 1519, 1425, 1377; H NMR (400 MHz, C6D5CD3, 85 °C) δ
8.94 (s, 4H), 8.04 (s, 4H), 7.89 (s, 4H), 4.21−4.18 (t, J = 6.4 Hz,
16H), 1.96−1.86 (m, 16H), 1.68−1.53 (m, 16H), 1.45−1.39 (m,
1
32H), 1.01−0.96 (m, 24H); H NMR (400 MHz, CD2Cl2) δ 8.88 (s,
4295
dx.doi.org/10.1021/jo3002886 | J. Org. Chem. 2012, 77, 4288−4297

The Journal of Organic Chemistry
Article
3316, 2955, 2927, 2859, 2150, 2105, 1609, 1468, 1425; 1H NMR (300
MHz, CDCl3) δ 8.59 (s, 1H), 8.54 (s, 1H), 7.80 (s, 1H), 7.79 (s, 1H),
7.68 (s, 1H), 7.67 (s, 1H), 4.27−4.19 (m, 8H), 3.38 (s, 1H) 2.00−1.90
(m, 8H), 1.68−1.57 (m, 8H), 1.43−1.37 (m, 16H), 0.96−0.91 (m,
12H), 0.33 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 158.2, 158.1,
150.0, 149.9, 130.2, 130.0, 129.4, 128.8, 124.5, 124.3, 122.2, 122.0,
112.7, 111.6, 107.4, 107.3, 104.3, 101.5, 98.9, 94.4, 81.3, 80.4, 69.52,
69.47, 69.1, 68.9, 31.7, 31.60, 31.56, 29.7, 29.31, 29.26, 29.1, 25.8, 25.7,
22.63, 22.59, 22.56, 15.0, 14.1, 14.0, 0.0; HRMS calcd for C49H68O4Si
748.4881, found 748.4880. Anal. Calcd for C49H68O4Si: C, 78.56; H,
9.15. Found: C, 78.59; H, 9.08.
1701.96 (M+). (The samples’ low solubility and aggregation prevented
acquisition of informative 13C NMR data.)
ASSOCIATED CONTENT
■
S
* Supporting Information
Characterization spectra for all new compounds including
absorption and emission spectra, polarizing optical microscopy
images for nematic materials and DSC traces, and X-ray crystal
structure of 5. This information is available free of charge via
the Internet at http://pubs.acs.org/.
5,5′-Bis[2,7,10,11-tetrakis(hexyloxy)-3-(trimethyl-
silylethynyl)triphenylen-6-yl]bithiophene (23). 5,5′-Diiodobi-
thiophene (41.8 mg, 0.10 mmol), Pd(PPh3)3Cl2 (7.0 mg, 0.01
mmol), and CuI (3.8 mg, 0.02 mmol) in freshly distilled triethylamine
(5 mL) and THF (5 mL) were stirred at 50 °C for 20 min. Compound
22 (150 mg, 0.20 mmol) in THF (15 mL) was added at the rate of 5
mL/h to the solution, and then the reaction was stirred at 50 °C for 16
h. The reaction mixture was evaporated to dryness in vacuo, and the
residue subjected directly to purification by silica chromatography
(DCM/hexane = 3:7) to yield the title compound 150 as a pale orange
semisolid (42 mg, 25%): IR (ATR, cm−1) 2926, 2857, 2150, 1608,
AUTHOR INFORMATION
■
Corresponding Author
*a.cammidge@uea.ac.uk
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the EPSRC mass spectrometry service centre,
Swansea, and Dr. Hemant Gopee for additional NMR
experiments.
1
1425, 1378; H NMR (300 MHz, CD2Cl2) δ 8.57 (s, 2H), 8.55 (s,
2H), 7.81 (s, 4H), 7.74 (s, 2H), 7.69 (s, 2H), 7.26 (d, J = 3.9 Hz, 2H),
7.18 (d, J = 3.9 Hz, 2H), 4.32−4.29 (t, J = 6.6 Hz, 4H), 4.26−4.22 (t, J
= 6.6 Hz, 12H), 2.07−1.92 (m, 16H), 1.77−1.53 (m, 16H), 1.51−1.39
(m, 32H), 0.99−0.92 (m, 24H), 0.33 (s, 18H); 13C NMR (100 MHz,
CD2Cl2) δ 158.6, 158.0, 150.3, 150.2, 138.8, 133.1, 130.4, 130.3, 129.0,
127.9, 124.6, 124.5, 124.3, 123.9, 122.4, 122.2, 112.7, 107.1, 106.9,
104.4, 102.8, 99.0, 93.0, 87.5, 69.9, 69.5, 69.2, 32.5, 32.4, 32.3, 30.14,
30.10, 30.07, 26.7, 26.5, 26.45, 23.4, 23.28, 23.26, 14.6, 14.44, 14.39;
MALDI-MS 1660.33 (M+).
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