Synthesis of substituted dibenz[a,c]anthracenes and an investigation of their liquid-crystalline properties

Article abstract of DOI:10.1002/ejoc.201403504

We report the synthesis of a series of 2,3,5,6-tetraalkoxydibenz[ a,c]anthracenes bearing substituents (H, OCH₃, or CN) in the 11- and 12-positions and an investigation of their liquid- crystalline properties. The synthesis involved Suzuki coupling of the appropriate dibromonaphthalene and boronate ester, followed by an oxidative cyclization. Compounds 4 and 5, bearing OCH₃ and H, respectively, do not exhibit any liquid-crystalline properties. In contrast, compounds 6a-c, bearing cyano groups, assemble into columnar mesophases, suggesting that electron-withdrawing groups are important for promoting columnar mesophase assembly. Analysis of the XRD revealed that compound 6b exhibits a columnar hexagonal phase, whereas compounds 6a and 6c exhibit columnar rectangular phases. The XRD data of 6a and 6b also show reflections that are consistent with antiparallel dimers within the columnar stacks, and intercolumnar spacings suggest that molecules are tilted within the columns.

Full text of DOI:10.1002/ejoc.201403504

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DOI: 10.1002/ejoc.201403504
Synthesis of Substituted Dibenz[a,c]anthracenes and an Investigation of Their
Liquid-Crystalline Properties
Katie M. Psutka,[a] Joshua Williams,[a] Joseph A. Paquette,[a] Oliver Calderon,[b]
Kevin J. A. Bozek,[b] Vance E. Williams,[b] and Kenneth E. Maly*[a]
Keywords: Liquid crystals / Self-assembly / Pi interactions / Polycyclic aromatic compounds / Aromatic synthesis
We report the synthesis of a series of 2,3,5,6-tetraalkoxydi-
benz[a,c]anthracenes bearing substituents (H, OCH3, or CN)
in the 11- and 12-positions and an investigation of their li-
quid-crystalline properties. The synthesis involved Suzuki
coupling of the appropriate dibromonaphthalene and
mesophases, suggesting that electron-withdrawing groups
are important for promoting columnar mesophase assembly.
Analysis of the XRD revealed that compound 6b exhibits a
columnar hexagonal phase, whereas compounds 6a and 6c
exhibit columnar rectangular phases. The XRD data of 6a
boronate ester, followed by an oxidative cyclization. Com- and 6b also show reflections that are consistent with antipar-
pounds 4 and 5, bearing OCH3 and H, respectively, do not allel dimers within the columnar stacks, and intercolumnar
exhibit any liquid-crystalline properties. In contrast, com- spacings suggest that molecules are tilted within the col-
pounds 6a–c, bearing cyano groups, assemble into columnar
umns.
Introduction
phases. However, the construction of polycyclic architec-
tures with well-defined substitution patterns is often quite
challenging due to regioselectivity issues.
Polycyclic aromatic hydrocarbons bearing peripheral
flexible side chains can often self-assemble into columnar
liquid-crystal phases (mesophases) featuring extended π-
stacked arrays within the columns.[1] As a result of the ex-
tensive π-overlap, these materials can transport charge
along the columnar axis, making them promising candi-
dates as semiconducting materials in organic electronics.[2]
Numerous studies have attempted to elucidate the effect
of structural features on the self-assembly of polycyclic aro-
matic molecules into liquid-crystalline phases. Several stud-
ies have considered the nature of the aromatic core, the na-
ture and length of the side chains, as well as substituents
attached to the core and how these affect mesomorphic
properties. In terms of the core, several studies suggest that
a larger PAH core promotes assembly of stable columnar
mesophases.[3–5] Electron-withdrawing substituents on the
core or electron-deficient heteroaromatic systems also pro-
mote the formation of stable mesophases, leading to a
higher clearing point (transition from liquid crystal to iso-
tropic liquid).[3,6,7] These observations can be attributed to
improved π-stacking interactions in these systems. Conse-
quently, there is significant interest in preparing novel sub-
stituted PAHs that bear both flexible chains as well as other
substituents to promote the generation of stable meso-
Alkoxy-substituted dibenz[a,c]anthracenes are a class of
compounds that might be expected to display columnar
mesophases because of their structural similarity to hexa-
alkoxytriphenylenes, which have been studied extensively.[8]
However, there are relatively few examples of substituted
dibenzanthracenes, and the properties of this class of com-
pounds have received relatively little attention.[9–11] In 2003,
Williams and co-workers reported the synthesis and meso-
morphic properties of dimethyl-substituted hexaalkoxydi-
benzanthracene (1), showing that it does indeed form a co-
lumnar liquid-crystal phase over a relatively broad tempera-
ture range.[9] More recently, we reported the synthesis of a
series of hexaalkoxydibenzanthracenes such as 2 and 3 and
demonstrated that, although compound 2 did not display
liquid-crystalline properties, derivatives bearing substitu-
ents in the 10- and/or 13-positions such as 3, exhibited co-
lumnar phases over broad temperature ranges.[10] We have
also demonstrated that the dibenzanthracenedicarboximide
derivatives exhibit columnar hexagonal phases over broad
temperature ranges.[12] These studies underscore the re-
markable sensitivity to even minor structural changes when
considering self-assembly of these compounds.
In these dibenzanthracenes, and in other discotic sys-
tems, electron-withdrawing substituents appended to the
PAH core promote stable columnar mesophases as charac-
terized by high phase-transition temperatures for liquid
crystal to isotropic liquid transitions (clearing points).[10]
Given the stable columnar mesophases exhibited by hexa-
alkoxydibenzanthracenes such as 1 and 3, we sought to
characterize structurally related dibenzanthracenes with dif-
[a] Department of Chemistry and Biochemistry, Wilfrid Laurier
University,
75 University Ave.W., Waterloo, Ontario N2L 3C5, Canada
E-mail: kmaly@wlu.ca
http://wlu.ca/faculty-profiles/science/kenneth-maly.html
[b] Department of Chemistry, Simon Fraser University,
Burnaby, British Columbia V5A 1S6, Canada
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201403504.
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K. E. Maly et al.
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thracenes and related compounds with a variety of defined
substitution patterns.
ferent substitution patterns. We also aimed to examine the
importance of electron-withdrawing substituents on the
mesomorphic properties of these systems.
Results and Discussion
Herein we report the synthesis and characterization of
tetraalkoxydibenzanthracenes (4–6) bearing substituents at
The general synthetic approach to target dibenz-
the 11- and 12-positions in order to probe the effects of anthracenes involves a Suzuki cross-coupling of the appro-
substituents on the columnar mesophase range. We also priate 2,3-dibromonaphthalene derivatives (8–10) with a
demonstrate that the modular synthetic approach to these (dialkoxyaryl)boronate esters (7a–c), followed by oxidative
compounds is capable of producing polycyclic architectures cyclization (Scheme 1).
with defined substitution patterns. Specifically, we show
The (3,4-dialkoxyaryl)boronate esters (7) were prepared
that, from the appropriately substituted dibromonaphthal- as described previously.[10] 2,3-Dibromonaphthalene (9)[13]
enes and arylboronate esters, we can access dibenz[a,c]an- was prepared according to a literature procedure by
Scheme 1. Synthesis of dibenzanthracenes 4–6.
Scheme 2. Synthesis of dibromonaphthalenes 8–10.
2
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Synthesis and Study of Substituted Dibenz[a,c]anthracenes
bromination of the naphthalene–bis(hexachlorocyclopenta- Table 1. Mesophase behaviour of compounds 4–6.
diene) adduct followed by a retro-Diels–Alder reaction
(Scheme 2). Compound 10[14] was prepared by reaction of
1,2-bis(dibromomethyl)-4,5-dibromobenzene with potas-
sium iodide and fumaronitrile. The reaction proceeds by an
Compound
X, R
Transition temperatures[a] [°C]
(enthalpies of transitions [J/g])
4
5
OCH3, C10H21 Cr 97 I
H, C10H21
CN, C8H17
CN, C10H21
CN, C12H25
Cr 113 I
iodide-induced 1,4-elimination of bromine to generate the 6a
Cr 191 (34) Colr 219 (4.6) I
Cr 142 (29) Colh 218 (2.9) I
Cr 143 (31) Colr 225 (3.4) I
6b
6c
corresponding o-quinodimethane, which undergoes
a
Diels–Alder reaction with fumaronitrile, followed by rearo-
matization through elimination of HBr. Dimethoxy-di-
bromonaphthalene 8 was prepared by treatment of 5,6-di-
bromo-2,3-dihydroxynaphthalene[15] with dimethyl sulfate.
Suzuki cross-coupling of 8–10 with 7 yielded corresponding
2,3-diphenylnaphthalenes (11–13) in moderate to good
yields.
[a] Determined by DSC on heating at 5 Kmin–1, reproducible over
three heating and cooling cycles. Cr denotes a crystalline phase,
Colh denotes a columnar hexagonal phase, Colr denotes a colum-
nar rectangular phase, and I denotes an isotropic liquid.
The cross-coupling of dimethoxy derivative 8 to furnish
11 proceeded with the lowest yield, likely in part to the elec-
tron-rich nature of the substrate and also losses encoun-
tered during recrystallization. Purification of 12 proved
challenging. Consequently, 12 was used in the subsequent
step after column chromatography despite the fact that it
was impure. The oxidative cyclization using FeCl3 in DCM
proceeded in good yield for compounds 11 and 12. In con-
trast, the yields for oxidative cyclization of 13a–c under the
same conditions were poor. Moreover, when compounds
6a–c were prepared using FeCl3, purification was difficult,
due to limited solubility of the product and potential CN
complexation with residual Fe salts. A number of alterna-
tives to FeCl3 for carrying out such oxidative cyclizations
are known; these include CuCl2 or Cu(OTf)2 and AlCl3,[16]
MoCl5,[17] VOF3/BF3·Et2O,[18] and DDQ/MeSO3H.[19] We
opted to use DDQ/MeSO3H[19] for the oxidative cycliza-
tion, because we have had success with this method in the
past, and because it avoids the potential problem of nitrile–
metal coordination. Although the isolated yields under
these conditions were still modest, likely due to low product
solubility, we obtained compounds 6a–c in pure form.
The mesomorphic properties of compounds 4–6 were
evaluated using polarized optical microscopy and differen-
tial scanning calorimetry. Compounds 4 and 5, which bear
OCH3 and H, respectively, at the 11- and 12-positions of
the dibenzanthracene core did not display any liquid-crys-
talline phases. In contrast, compounds 6a–c, bearing cyano
groups, displayed columnar mesophases over broad tem-
perature ranges (Table 1). These results are consistent with
the findings of other studies where cyano substituents have
been shown to stabilize columnar mesophases.[7,10,20] The
textures observed by polarized optical microscopy are con-
sistent with columnar mesophases (Figure 1). It is note-
Figure 1. Representative polarized optical micrographs of (a) com-
pound 6a at 219 °C, (b) 6b at 210 °C, and (c) 6c at 223 °C, on cool-
ing.
Table 2. Summary of XRD data for compounds 6a–c.
Compound
6a
Observed [Å] Assignment
Predicted [Å]
Colr (p2gg)
25.7
(110)/(200)[b] 25.9
a = 51.4; b = 29.7 19.4
(210)
(001)
19.4
Z ≈ 8[a]
6.5
6b
Colh a = 26.8 Å
Z ≈ 2
23.2
13.6
6.7
(100)
(110)
(001)
23.9
13.8
4.9
alkyl halo
6b
Colr (p2gg)
a = 59.8; b = 34.5 22.6
Z ≈ 4
29.9
(110)/(200)[b] 29.9
(210) 22.6
(310)/(020)[c] 17.3
17.3
13.6
4.7
(410)
alkyl
(001)
13.7
3.5
[a] Calculation assumes that (001) = thickness (h) and has a density
of ca. 1. [b] In the pseudohexagonal phase, (110) and (200) peaks
are coincident. [c] In the pseudohexagonal phase, (310) and (020)
peaks are coincident.
worthy that compound 6a has a tendency to align homeo- hibits two peaks in the low-angle region, the ratio of the
tropically as shown by polarized optical microscopy, distances of these peaks is 1:1.32, rather than 1:1.73 ex-
whereas compounds 6b and 6c both show planar alignment. pected for the (100)/(110) of a Colh phase. These d-spacings
In order to probe the structure of the mesophases, com- could be indexed to the (200) and (210) peaks of a pseudo-
pounds 6a–c were studied by variable-temperature powder hexagonal phase [i.e. a columnar rectangular phase (Colr,
X-ray diffraction (VT-XRD). The diffractogram for com- p2gg) in which a = b√3 (a = 51.4 Å and b = 29.7 Å)]. Com-
pound 6b, bearing decyloxy chains, shows two peaks in the pound 6c could similarly be indexed to a pseudo-hexagonal
low-angle region, which index to the (100) and (110) reflec- phase with lattice parameters a = 59.8 Å and b = 34.5 Å;
tions of a columnar hexagonal phase (Colh) with an inter- additional peaks were also observed that helped confirm
columnar spacing of 26.8 Å (Table 2). Although 6a also ex- this assignment. In the pseudo-hexagonal phase, the mo-
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lecules adopt a tilted orientation with respect to the colum- the columns, it is difficult to establish an unambiguous
nar axis (Figure 2). Phases of this type were originally re- packing model.
ported by Guillon and co-workers in 1991,[21] and several
examples have been reported in the interim.[22]
A comparison of compounds 6a–c with the correspond-
ing tetraalkoxydicyanotriphenylenes (14) reported by Ichih-
ara et al.[26] allows us to assess the effect of extending the
aromatic core by one fused benzene ring upon mesophase
stability. Several studies have suggested that increasing the
size of the PAH core promotes stable mesophases.[3,4] How-
ever, there are very few examples where a change in the core
size is not accompanied by other structural modifications,
and therefore direct comparisons are difficult.
Figure 2. Schematic representation of the (a) columnar hexagonal
phase (Colh) and (b) columnar rectangular phase [Colr, (p2gg)]
viewed looking along the columnar axis.
The columnar mesophase temperature range of series 14
A particularly interesting feature of the diffraction pat- reported by Ichihara et al.[26] exhibits crystalline to colum-
terns of compounds 6a and 6b is the presence of a broad nar melting transition-phase transitions that are strikingly
reflection corresponding to a periodicity of 6.5–6.7 Å. This similar to those of compounds 6a–c. In contrast, the clear-
reflection, which is approximately twice that observed for ing points for compounds 14 are approximately 187–190 °C,
typical π-stacking between aromatic cores, suggests that whereas the corresponding dibenzanthracene series 6a–c
there is an antiparallel stacking of compounds within the shows clearing points ranging from approximately 219 °C
columns.[23] This antiparallel stacking is presumably a con- to 225 °C. Thus, the dibenzanthracenes 6a–c exhibit
sequence of the large dipole moment in these compounds, broader mesophase ranges than the corresponding tri-
and has been proposed for other dipolar discotic meso- phenylenes as well as higher clearing points, suggesting that
gens.[3,11,24] In most cases, there is little direct evidence for extending the aromatic core in this series of compounds
this packing arrangement. Here, the observation of the does indeed stabilize the mesophase. When the XRD lattice
broad reflection at 6.5–6.7 Å provides experimental evi- parameters of triphenylene (14) to dibenzanthracene (6) are
dence in support of antiparallel stacking. However, for 6c, compared, there are marked differences that suggest very
this reflection is not observed. Rather, a reflection at ca. different packing arrangements. Triphenylene 14 bearing
3.5 Å is observed, which is typical for π-stacking and sug- decyl chains shows a lattice parameter a of 29.8 Å, which
gests that, as the chain length is increased, the ordering corresponds to the columnar diameter, whereas the corre-
within columns is compromised.
sponding dibenzanthracene (6b) has a cell constant of only
The intercolumnar distances, which are determined from 26.8 Å, which is surprising given that the molecular volume
the lattice parameters (a for the Colh phase and b for the is larger by virtue of the extended core. Indeed, based on
Colr phase), have values of 29.7 Å, 26.8 Å, and 34.5 Å for the lattice parameters and estimated density of 14, Ohta
compounds 6a, 6b, and 6c, respectively. These intercolum- and co-workers propose an assembly where two molecules
nar spacings are smaller than the molecular dimensions, es- per unit cell are arranged in a head-to-head manner so that
pecially for a π-stacked dimer, which should have an ex- the opposing dipoles cancel one another (Figure 3). Al-
tended elliptical shape. The smaller intercolumnar spacing though our data support an antiparallel orientation of adja-
may be attributed, in part, to interdigitation of the alkoxy cent molecules within the columns, it appears there is a
chains of adjacent columns. However, it may also be ex- higher degree of overlap of adjacent aromatic cores for
plained by a tilt of molecules with respect to the columnar compounds 6a–c than with series 14.
axis, effectively reducing the intercolumnar spacing. Indeed,
A comparison with structurally related dibenzophen-
for compounds 6a and 6c, which exhibit the rectangular azines 15 and 16,[27] where the dimensions of the aromatic
p2gg phase, tilted molecules within the columns are ex- core are similar to those of series 6, reveals that the lattice
pected. For compound 6b, which exhibits a hexagonal parameters, and therefore columnar diameters, are smaller
phase, a circular cross-section of the columns is expected to for the dibenzophenazines: 19.0 Å and 19.6 Å, for 15 and
maintain hexagonal symmetry. In this case, it is possible 16, respectively. Although it is noteworthy that 15 and 16
that the tilted elliptical molecules project a circle onto the have shorter hexyloxy chains, the differences in columnar
columnar cross-section.[25] Since the intercolumnar spacing diameters are too large to arise only from differences in
depends on the degree of interpenetration of the side chains alkoxy chain lengths. These differences in intercolumnar
from adjacent columns, the amount of overlap in the anti- spacings suggest that there may be differences in the extent
parallel dimers, and the tilt angle of the molecules within of overlap in the stacking of adjacent molecules within the
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Synthesis and Study of Substituted Dibenz[a,c]anthracenes
Figure 3. Schematic representation of the different packing modes of compounds 14, 6, and 15.
columns. It is possible that the π-stacked dimers in 6a–c are gated. Compounds 4 and 5 do not display any meso-
somewhat offset when compared with 15 and 16 (Figure 3). morphism, whereas compounds 6a–c, bearing electron-
However, we cannot rule out the possibility that the degree withdrawing cyano groups, exhibit columnar mesophases
of interpenetration of alkoxy chains or differences in the over broad temperature ranges. Compared to the corre-
tilt of the molecules with respect to the columnar axis are sponding dicyanotriphenylenes, extension of the aromatic
responsible for the observed differences in intercolumnar core does indeed generate more stable mesophases as re-
spacings.
flected by higher clearing temperatures. XRD studies on
compounds 6a–c reveal reflections that are consistent with
antiparallel dimers and suggest that the molecules are tilted
with respect to the columnar axis. Compounds 6a–c also
show little variation in clearing point when chain length is
altered. We propose that this behaviour is the result of
strong arene–arene interactions of the core structures and
that these interactions largely dictate the observed clearing
points.
It is also noteworthy that the clearing points in series 6a–
c show very little change in response to changes in the
length of the alkoxy chains. This behavior is atypical for
columnar liquid-crystalline materials, which usually show
a decrease in the clearing point with longer alkyl chains.
However, this relative invariability in clearing point has
been observed for discotic mesogens bearing electron-with-
drawing cyano groups.[20,26] For the series of dicyanotri-
phenylenes 14, Ohta and co-workers have attributed the
lack of clearing point changes to the formation of a dimeric
disk assembly (vide supra), suggesting that the clearing
point is determined by dimer dissociation. However, this
behaviour is also observed for structurally related dibenzo-
quinoxalines[20] as well as compounds 6a–c from this study.
We propose an alternative explanation, where the columnar
phase in these systems is stabilized by strong core–core in-
teractions. With core–core interactions controlling the me-
sophase stability, side-chain lengths appear to exert little
influence on mesophase temperature ranges.
Experimental Section
General: 1H and 13C NMR spectra were recorded with a Varian
300 MHz (1H) Unity Inova NMR spectrometer, using indicated
deuterated solvents purchased from CIL Inc. All chemicals used
were purchased from Sigma–Aldrich and were used as received.
The (3,4-dialkoxyphenyl)boronate esters (7a–c) were prepared as
described previously.[10] 2,3-Dibromonaphthalene (9),[13] 2,3-di-
bromo-5,6-dicyanonaphthalene (10),[14] and 5,6-dibromo-2,3-dihy-
droxynaphthalene[15] were also prepared according to literature
procedures. Anhydrous and oxygen-free solvents were dispensed
from a custom-built solvent purification system which used purifi-
cation columns packed with activated alumina and supported cop-
per catalyst (Glasscontour, Irvine, CA). Oven- or flame-dried glass-
ware was used for all reactions. Melting points were determined
with a Barnstead Electrothermal 9100 melting-point apparatus and
are uncorrected. High-resolution MALDI, ESI, APCI, and ASAP
mass spectra were recorded at the Centre Régional de Spectromé-
trie de Masse à l’Université de Montréal using an Agilent LC-MSD
TOF spectrometer.
2,3-Dibromo-5,6-dimethoxynaphthalene (8): 5,6-Dibromo-2,3-dihy-
droxynaphthalene[15] (9.85 g, 31.0 mmol) was combined with KOH
(7.51, 134 mmol) in water (200 mL). Dimethyl sulfate was then
added dropwise over a 15 min period. The reaction mixture was
Conclusions
A series of novel tetraalkoxydibenz[a,c]anthracenes were
synthesized, and their mesomorphic properties were investi- stirred at room temperature for 20 h. The product was collected by
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filtration, washed with water, and then recrystallized from EtOH to
a brown solid (0.88 g, 60%). 1H NMR (300 MHz, CDCl3): δ = 0.89
(m, 12 H) 1.28 (m, 56 H), 1.67 (m, 4 H), 1.83 (m, 4 H), 3.73 (t, J
1
yield 7.40 g of 8 as light grey crystals (69%). H NMR (300 MHz,
CDCl3): δ = 3.97 (s, 6 H), 6.92 (s, 2 H), 7.90 (s, 2 H) ppm. 13C = 7 Hz, 4 H), 3.98 (t, J = 7 Hz, 4 H), 6.64 (s, 2 H), 6.83 (s, 4 H),
NMR (75 MHz, CDCl3): δ = 56.2, 105.3, 119.8, 129.3, 130.7,
150.6 ppm. HRMS (EI): calcd. for C12H10Br2O2 343.9048, found
343.9048.
7.96 (s, 2 H), 8.34 (s, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
14.35, 22.93, 26.26, 26.30, 29.33, 29.53, 29.62, 29.63, 29.66, 29.72,
29.90, 29.92, 29.94, 29.96, 30.01, 32.17, 69.42, 69.49, 110.01,
113.47, 115.86, 116.32, 122.33, 129.67, 132.46, 132.48, 135.75,
144.57, 148.87, 149.24 ppm. HRMS (ASAP): calcd. for
C72H110N2O4 + H 1066.8466, found 1066.8460.
2,3-Dicyano-6,7-bis(3Ј,4Ј-dioctyloxyphenyl)naphthalene (13a): 4-
Boropinacolato-1,2-bis(octyloxy)benzene (1.54 g, 3.34 mmol), 2,3-
dibromo-5,6-dicyanonaphthalene (0.45 g, 1.34 mmol), aq. 2.0 m
K2CO3 (7.00 mL), EtOH (7.00 mL), and toluene (25.0 mL) were
combined in a reaction flask, fitted with a reflux condenser, and
degassed with N2. Pd(PPh3)4 (0.080 g, 0.069 mmol) was then added
to the solution. The mixture was heated to 80 °C and stirred for a
period of 48 h. The solution was cooled to room temperature, and
dichloromethane (20 mL) was added. The organic phase was
washed with water (2ϫ 20 mL) and brine (1ϫ 20 mL). The organic
phase was dried with MgSO4, and the solvent was removed under
reduced pressure to give a brown solid. The crude product was
purified by column chromatography (9:1, hexanes/EtOAc) to yield
2,3-Dimethoxy-6,7-bis(3Ј,4Ј-didecyloxyphenyl)naphthalene (11): 4-
Boropinacolato-1,2-bis(decyloxy)benzene (3.00 g, 5.81 mmol), 2,3-
dibromo-5,6-dimethoxynaphthalene (0.89 g, 2.58 mmol), Pd(OAc)2
(0.029 g, 0.129 mmol), and PPh3 (0.068 g, 0.258 mmol) were com-
bined in a reaction flask, fitted with a reflux condenser, and purged
with N2. A solution of degassed toluene/water (12 mL:4 mL) was
added to the reaction flask. To the reaction mixture degassed was
added aq. 2.0 m K3PO4 (3.93 g, excess). The mixture was heated to
80 °C and stirred for a period of 86 h. The solution was cooled to
room temperature, and dichloromethane (20 mL) was then added.
a brown solid (0.90 g, 80%). 1H NMR (300 MHz, CDCl3): δ = 0.90 The organic phase was washed with water (2ϫ 20 mL) and brine
(m, 12 H) 1.28 (m, 56 H), 1.68 (m, 4 H), 1.83 (m, 4 H), 3.70 (t, J (1ϫ 20 mL). The organic phase was dried with MgSO4, and the
= 7 Hz, 4 H), 3.98 (t, J = 7 Hz, 4 H), 6.64 (s, 2 H), 6.83 (s, 4 H),
7.96 (s, 2 H), 8.34 (s, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = The crude product was purified by column chromatography (98:2,
14.32, 22.90, 22.92, 26.23, 26.28, 29.31, 29.51, 29.56, 29.58, 29.64, hexanes/EtOAc). The resulting product was recrystallized from
solvent was removed under reduced pressure to give a brown solid.
1
32.06, 69.41, 69.47, 110.01, 113.43, 115.81, 116.32, 122.32, 129.67, acetone to yield a brown solid (0.78 g, 31%). H NMR (300 MHz,
132.44, 132.48, 135.75, 144.57, 148.86, 149.22 ppm. HRMS CDCl3): δ = 0.88 (m, 12 H) 1.28 (m, 56 H), 1.70 (m, 4 H), 1.80 (m,
(APCI): calcd. for C56H79N2O4 843.60243, found 843.60344.
4 H), 3.71 (t, 4 H), 3.97 (t, 4 H) 4.02 (s, 6 H), 6.67 (s, 2 H), 6.80
(s, 4 H), 7.15 (s, 2 H), 7.72 (s, 2 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 14.35, 22.94, 26.28, 26.32, 29.38, 29.61, 29.64, 29.68,
29.75, 29.85, 29.88, 29.90, 29.95, 32.17, 32.18, 56.13, 69.32, 69.51,
106.22, 113.53, 116.39, 122.27, 127.76, 128.59, 134.90, 137.49,
148.01, 148.56, 149.97 ppm. HRMS (MALDI): calcd. for
C64H100O6 964.7520, found 964.7514.
2,3-Dicyano-6,7-bis(3Ј,4Ј-didecyloxyphenyl)naphthalene (13b): 4-
Boropinacolato-1,2-bis(decyloxy)benzene (1.26 g, 2.44 mmol), 2,3-
dibromo-5,6-dicyanonaphthalene (0.33 g, 0.97 mmol), aq. 2.0 m
K2CO3 (5.00 mL), EtOH (5.00 mL), and toluene (20.0 mL) were
combined in a reaction flask, fitted with a reflux condenser, and
degassed with N2. Pd(PPh3)4 (0.055 g, 0.048 mmol) was then added
to the solution. The mixture was heated to 80 °C and stirred for a
period of 48 h. The solution was cooled to room temperature, and
dichloromethane (20 mL) was then added. The organic phase was
washed with water (2ϫ 20 mL) and brine (1ϫ 20 mL). The organic
phase was dried with MgSO4, and the solvent was removed under
reduced pressure to give a brown solid. The crude product was
purified by column chromatography (9:1, hexanes/EtOAc) to yield
6,7-Bis(3Ј,4Ј-didecyloxyphenyl)naphthalene (12): 4-Boropinacolato-
1,2-bis(decyloxy)benzene (2.00 g, 3.87 mmol), 2,3-dibromonaphth-
alene (0.48 g, 1.72 mmol), Pd(OAc)2 (0.019 g, 0.086 mmol), and
PPh3 (0.045 g, 0.172 mmol) were combined in a reaction flask, fit-
ted with a reflux condenser, and purged with N2. A solution of
degassed toluene/water (8 mL:2.50 mL) was added to the reaction
flask. To the reaction mixture was added degassed aq. 2.0 m K3PO4
a brown solid (0.73 g, 79%). 1H NMR (300 MHz, CDCl3): δ = 0.89 (2.62 g, excess). The mixture was heated to 80 °C and stirred for a
(m, 12 H) 1.28 (m, 56 H), 1.68 (m, 4 H), 1.83 (m, 4 H), 3.70 (t, J period of 86 h. The solution was cooled to room temperature, and
= 7 Hz, 4 H), 3.98 (t, J = 7 Hz, 4 H), 6.64 (s, 2 H), 6.83 (s, 4 H),
dichloromethane (20 mL) was then added. The organic phase was
7.96 (s, 2 H), 8.34 (s, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = washed with water (2ϫ 20 mL) and brine (1ϫ 20 mL). The organic
14.35, 22.93, 26.25, 26.29, 29.32, 29.51, 29.61, 29.63, 29.66, 29.72,
29.89, 29.91, 29.93, 29.95, 29.99, 32.17, 69.41, 69.47, 110.01,
113.43, 115.82, 116.33, 122.32, 129.67, 132.44, 132.48, 135.75,
phase was dried with MgSO4, and the solvent was removed under
reduced pressure to give a brown solid. The crude product was
purified by column chromatography (100% hexanes). The resulting
144.57, 148.85, 149.22 ppm. HRMS (ASAP): calcd. for product was recrystallized from hexanes and methanol to yield a
C64H94N2O4 + H 955.7277, found 955.7292. white solid. The product was used without any further purification.
2,3-Dicyano-6,7-bis(3Ј,4Ј-didodecyloxyphenyl)naphthalene (13c): 4- 11,12-Dimethoxy-2,3,6,7-tetrakis(decyloxy)dibenz[a,c]anthracene
Boropinacolato-1,2-bis(dodecyloxy)benzene (2.00 g, 3.45 mmol), (4): 2,3-Dimethoxy-6,7-bis(3Ј,4Ј-didecyloxyphenyl) naphthalene
2,3-dibromo-5,6-dicyanonaphthalene (0.47 g, 1.39 mmol), aq. 2.0 m (0.50 g, 0.52 mmol) was dissolved in dry dichloromethane (75 mL).
K2CO3 (7.50 mL), EtOH (7.50 mL), and toluene (30.0 mL) were
combined in a reaction flask, fitted with a reflux condenser, and
degassed with N2. Pd(PPh3)4 (0.080 g, 0.069 mmol) was added to
the solution. The mixture was heated to 80 °C and stirred for a
period of 48 h. The solution was cooled to room temperature, and
dichloromethane (20 mL) was then added. The organic phase was
washed with water (2ϫ 20 mL) and brine (1ϫ 20 mL). The organic
phase was dried with MgSO4, and the solvent was removed under
reduced pressure to give a brown solid. The crude product was
purified by column chromatography (95:5, hexanes/EtOAc) to yield
N2 was bubbled through the solution for 10 min. A degassed solu-
tion of FeCl3 (1.46 g, 8.99 mmol) in CH3NO2 (11.15 mL) was
added to the mixture. The solution was then stirred at room tem-
perature for a period of 15 min, with N2 continuously bubbled
through the solution. The solution was then poured into MeOH
(100 mL), and the resulting precipitate was collected by suction fil-
tration. The crude product was purified through a short silica plug
(100% dichloromethane), and the solvent was removed in a rotary
evaporator. The resulting product was recrystallized from acetone
to yield a light brown solid (0.28 g, 58%). 1H NMR (300 MHz,
6
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Synthesis and Study of Substituted Dibenz[a,c]anthracenes
CDCl3): δ = 0.89 (t, J = 7 Hz, 12 H) 1.41 (m, 56 H), 1.98 (m, 8 14.35, 22.93, 26.42, 29.62, 29.75, 29.86, 29.93, 32.17, 69.87, 107.23,
H), 4.08 (s, 6 H), 4.26 (m, J = 7 Hz, 8 H), 7.32 (s, 2 H), 7.79 (s, 2 107.99, 108.63, 116.62, 122.31, 122.44, 125.67, 130.25, 132.15,
H), 8.10 (s, 2 H), 8.17 (s, 2 H) ppm. 13C NMR (75 MHz, CDCl3): 136.55, 149.72, 151.46 ppm. HRMS (ESI): calcd. for C64H93N2O4
δ = 14.36, 22.94, 26.44, 26.46, 29.63, 29.74, 29.78, 29.79, 29.88,
29.95, 32.18, 56.17, 69.67, 70.02, 105.83, 107.72, 107.91, 119.73,
124.16, 124.22, 126.92, 128.19, 149.30, 149.59, 150.09 ppm. HRMS
(MALDI): calcd. for C64H98O6 962.7363, found 962.7358.
953.7115, found 953.7135.
11,12-Dicyano-2,3,6,7-tetrakis(dodecyloxy)dibenz[a,c]anthracene
(6c): 2,3-Dicyano-6,7-bis(3Ј,4Ј-didodecyloxyphenyl)naphthalene
(0.25 g, 0.23 mmol) was dissolved in dry dichloromethane
(31.0 mL) under N2. CH3SO3H (2.34 mL, 36.0 mmol) was added,
and the solution was then cooled in an ice bath. DDQ (0.057 g,
0.252 mmol) was added, and the mixture was stirred at 0 °C for a
period of 15 min. The solution was quenched slowly with saturated
NaHCO3. The organic phase was extracted and washed with water
(2ϫ 20 mL) and brine (1ϫ 20 mL). The organic phase was dried
with MgSO4, and the resulting solution was passed through a short
silica plug (100% dichloromethane). The solvent was removed in a
rotary evaporator, and the resulting product was recrystallized from
2,3,6,7-Tetrakis(decyloxy)dibenz[a,c]anthracene (5): 6,7-Bis(3Ј,4Ј-di-
decyloxyphenyl)naphthalene (3.35 g, 3.70 mmol) was dissolved in
dry dichloromethane (200 mL). N2 was bubbled through the solu-
tion for 10 min. A degassed solution of FeCl3 (10.5 g, 64.4 mmol)
in CH3NO2 (20.0 mL) was added to the mixture. The solution was
then stirred at room temperature for a period of 15 min, with N2
continuously bubbled through the solution. The solution was then
poured into MeOH (250 mL), and the resulting precipitate was col-
lected by suction filtration. The crude product was purified through
a short silica plug (100% dichloromethane), and the solvent was
removed in a rotary evaporator. The resulting product was recrys-
tallized from hexanes to yield a white solid (2.26 g, 68%, over two
1
toluene to yield a yellow solid (45 mg, 15%). H NMR (300 MHz,
CDCl3): δ = 0.89 (m, 20 H) 1.28 (m, 72 H), 1.98 (m, 8 H), 4.28 (m,
J = 5 Hz, 8 H), 7.79 (s, 2 H), 8.08 (s, 2 H), 8.56 (s, 2 H), 8.95 (s, 2
H), 8.17 (s, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 14.10,
17.38, 22.71, 26.20, 29.40, 29.71, 31.95, 69.65, 108.39, 116.41,
122.06, 125.44, 130.02, 131.91, 149.48, 151.226 ppm. HRMS
(ASAP): calcd. for C72H108N2O4 + H 1065.8368, found 1065.8387.
1
steps). H NMR (300 MHz, CDCl3): δ = 0.89 (t, J = 7 Hz, 12 H)
1.42 (m, 56 H), 1.98 (m, 8 H), 4.28 (m, 8 H), 7.54 (m, 2 H), 7.80
(s, 2 H), 8.06 (m, 2 H), 8.16 (s, 2 H), 8.89 (s, 2 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 14.36, 22.94, 26.43, 29.63, 29.68, 29.77,
29.87, 29.94, 32.17, 69.74, 69.98, 107.8, 108.0, 121.3, 124.0, 124.5,
125.7, 128.1, 128.3, 131.8, 149.3, 149.9 ppm. HRMS (MALDI):
calcd. for C62H94O4 902.7152, found 902.7147.
Mesophase Characterization: Polarized optical microscopy studies
were carried out using an Olympus BX-51 polarized optical micro-
scope equipped with a Linkam LTS 350 heating stage and a digital
camera. Differential Scanning Calorimetry (DSC) studies were car-
ried out using a TA Instruments DSC Q200 with a scanning rate
of 5 °C/min. Variable-temperature X-ray scattering measurements
were carried out with a Rigaku RAXIS rapid diffractometer using
Cu-Kα radiation (λ = 1.5418 Å), a Fujifilm Co. curved image plate
(460 mmϫ256 mm) and a graphite monochromator. Samples were
heated to the isotropic liquid phase on a hot plate and loaded by
capillary action. The temperature for XRD measurements was con-
trolled using an in-house built capillary furnace.[28]
11,12-Dicyano-2,3,6,7-tetrakis(octyloxy)dibenz[a,c]anthracene (6a):
2,3-Dicyano-6,7-bis(3Ј,4Ј-dioctyloxyphenyl)naphthalene (0.25 g,
0.30 mmol) was dissolved in dry dichloromethane (40.0 mL) under
N2. CH3SO3H (2.96 mL, 45.6 mmol) was added, and the solution
was then cooled in an ice bath. DDQ (0.073 g, 0.320 mmol) was
added, and the mixture was stirred at 0 °C for a period of 15 min.
The solution was quenched slowly with saturated NaHCO3. The
organic phase was extracted and washed with water (2ϫ 20 mL)
and brine (1ϫ 20 mL). The organic phase was dried with MgSO4,
and the resulting solution was passed through a short silica plug
(100 % dichloromethane). The solvent was removed in a rotary
evaporator, and the resulting product was recrystallized from tolu-
ene to yield a yellow solid (135 mg, 54%). 1H NMR (300 MHz,
CDCl3): δ = 0.91 (t, J = 6 Hz, 24 H) 1.41 (m, 36 H), 1.97 (m, J =
7 Hz, 8 H), 4.30 (m, J = 6 Hz, 8 H), 7.79 (s, 2 H), 8.08 (s, 2 H),
8.56 (s, 2 H), 8.95 (s, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = ,
–14.15, 16.63, 22.72, 25.91, 26.20, 29.36, 29.49, 29.72, 31.89, 69.67,
106.94, 108.36, 109.99, 122.05, 125.44, 130.00, 131.87, 136.30,
149.48 ppm. HRMS (ESI): calcd. for C56H77N2O4 841.5905, found
841.5883.
Supporting Information (see footnote on the first page of this arti-
cle): NMR spectroscopic data and XRD data.
Acknowledgments
We are grateful to the Natural Sciences and Engineering Council
of Canada (NSERC), the ACS Petroleum Research Fund, The
Canada Foundation for Innovation, the Ontario Research Fund,
and Wilfrid Laurier University for support. K. E. M. thanks the
Ministry of Research and Innovation for an Ontario Early Re-
searcher Award. K. M. P. thanks the NSERC for a Postgraduate
Scholarship Award and the Ontario Government for an Ontario
Graduate Scholarship.
11,12-Dicyano-2,3,6,7-tetrakis(decyloxy)dibenz[a,c]anthracene (6b):
2,3-Dicyano-6,7-bis(3Ј,4Ј-didecyloxyphenyl)naphthalene (0.25 g,
0.26 mmol) was dissolved in dry dichloromethane (35.0 mL) under
N2. CH3SO3H (2.61 mL, 40.2 mmol) was added, and the solution
was then cooled in an ice bath. DDQ (0.064 g, 0.282 mmol) was
added, and the mixture was stirred at 0 °C for a period of 15 min.
The solution was quenched slowly with saturated NaHCO3. The
organic phase was extracted and washed with water (2ϫ 20 mL)
and brine (1ϫ 20 mL). The organic phase was dried with MgSO4,
and the resulting solution was passed through a short silica plug
(100 % dichloromethane). The solvent was removed in a rotary
evaporator, and the resulting product was recrystallized from tolu-
ene to yield a yellow solid (86 mg, 35 %). 1H NMR (300 MHz,
CDCl3): δ = 0.89 (t, J = 6 Hz, 12 H) 1.29 (m, 56 H), 1.99 (m, J =
7 Hz, 8 H), 4.30 (m, J = 6 Hz, 8 H), 7.79 (s, 2 H), 8.09 (s, 2 H),
8.56 (s, 2 H), 8.95 (s, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
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Received: November 20, 2014
Published Online: ᭿
8
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Date: 20-01-15 18:59:54
Pages: 9
Synthesis and Study of Substituted Dibenz[a,c]anthracenes
Dibenz[a,c]anthracenes
The synthesis of a series of novel di-
benz[a,c]anthracenes is described. The di-
cyano-substituted derivatives exhibit col-
umnar mesophases and are consistent with
antiparallel stacking and a tilted arrange-
ment within the columns.
K. M. Psutka, J. Williams, J. A. Paquette,
O. Calderon, K. J. A. Bozek,
V. E. Williams, K. E. Maly* ............. 1–9
Synthesis of Substituted Dibenz[a,c]an-
thracenes and an Investigation of Their
Liquid-Crystalline Properties
Keywords: Liquid crystals / Self-assembly /
Pi interactions / Polycyclic aromatic com-
pounds / Aromatic synthesis
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9