Lateral extension induces columnar mesomorphism in crucifix shaped quinoxalinophenanthrophenazines This paper is dedicated to Professor Makhlouf J. Haddadin on the occasion of his 80th birthday and 50 years of outstanding service to the American University of Beirut

Article abstract of DOI:10.1016/j.tet.2014.11.050

Reported here is the columnar mesomorphism of board shaped dyes based on quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine (TQPP) derivatives that was induced by an increase in lateral bulk. TQPP derivatives with protons, tert-butyl and 4-tert-butyl-phenyl groups in positions 2 and 11 are compared, as well as dodecylthio, dodecyloxy, phytanylthio, and phytanyloxy side-chains. Only derivatives with 4-tert-butyl-phenyl groups display columnar liquid crystal phases over wide ranges of temperature while all other TQPPs are not liquid crystalline except for the compound with tert-butyl groups and phytanyloxy side-chains that shows a Col_r mesophase over a temperature range of 26 °C. The sole attachment of phytanyl groups does not effectively induce columnar mesophases. However, the lateral attachment of bulky groups to the TQPP core induces columnar mesomorphism because of the in-plane aspect ratio decrease and the favored twisted or helical π-stacking of the molecules in columns rather than the parallel co-planar packing.

Full text of DOI:10.1016/j.tet.2014.11.050

Tetrahedron 71 (2015) 308e314
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Lateral extension induces columnar mesomorphism in crucifix
shaped quinoxalinophenanthrophenazines
Ala’a O. El-Ballouli a, Himadri Kayal b, Chen Shuai b, Tarek A. Zeidan a, Farah S. Raad a,
,
Siwei Leng c, Brigitte Wex d, Stephen Z.D. Cheng c, S. Holger Eichhorn b
,
*
,
Bilal R. Kaafarani a
*
a Department of Chemistry, American University of Beirut, Beirut 1107-2020, Lebanon
b Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON N9B 3P4, Canada
c Institute of Polymer Science and Engineering, Department of Polymer Science, The University of Akron, Akron, OH 44325-3909, USA
d Department of Natural Sciences, Lebanese American University, Byblos, Lebanon
a r t i c l e i n f o
a b s t r a c t
Reported here is the columnar mesomorphism of board shaped dyes based on quinoxalino[20,30:9,10]
phenanthro[4,5-abc]phenazine (TQPP) derivatives that was induced by an increase in lateral bulk. TQPP
derivatives with protons, tert-butyl and 4-tert-butyl-phenyl groups in positions 2 and 11 are compared,
as well as dodecylthio, dodecyloxy, phytanylthio, and phytanyloxy side-chains. Only derivatives with 4-
tert-butyl-phenyl groups display columnar liquid crystal phases over wide ranges of temperature while
all other TQPPs are not liquid crystalline except for the compound with tert-butyl groups and phyta-
nyloxy side-chains that shows a Colr mesophase over a temperature range of 26 ꢀC. The sole attachment
of phytanyl groups does not effectively induce columnar mesophases. However, the lateral attachment of
bulky groups to the TQPP core induces columnar mesomorphism because of the in-plane aspect ratio
Article history:
Received 2 September 2014
Received in revised form 6 November 2014
Accepted 17 November 2014
Available online 21 November 2014
This paper is dedicated to Professor
Makhlouf J. Haddadin on the occasion of his
80th birthday and 50 years of outstanding
service to the American University of Beirut
decrease and the favored twisted or helical
parallel co-planar packing.
p-stacking of the molecules in columns rather than the
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
of frontier orbital energies as well as absorption and emission
properties often dictates less symmetric molecular structures of
higher in-plane aspect ratios.40
Columnar mesophases of aromatic dyes have intrigued re-
searchers’ curiosity because of their potential applications as or-
ganic semiconductors and dyes in opto-electronic devices. Their
self-organization generates unique anisotropic structures with
distinctive properties such as self-healing of defects and high
charge-carrier mobility and exciton diffusion lengths along the
stacking axis.1e12 Columnar mesophases have been successfully
employed as organic semiconductors and absorbers in OPV,13e17
OFET,18e25 and OLED26,27 devices but most of this work has been
limited to columnar mesophases of discotic liquid crystals that
consist of disc-shaped central cores to which multiple flexible
chains are symmetrically attached. Deviation from the conven-
tional disc-shape (low in-plane aspect ratio)28 and high symmetry
has been experimentally29e33 and computationally34e39 shown to
critically affect, often diminish, columnar mesomorphism. How-
ever, the incorporation of donor-acceptor structures for the control
Typical examples with large in-plane aspect ratios are board-
shaped polyaromatic dyes, such as quinoxalino[20,30:9,10]phenan-
thro[4,5-abc]phenazine (TQPP)-based compounds that usually do
not self-organize into columnar mesophases. Lee and co-workers
reported the tuning of electronic properties and self-assembly of
TQPP-based compounds by changing the R group (Fig. 1).41 In
previous reports, Harris’ and our groups showed that sufficiently
large and branched side-chains in positions 7, 8, 15, and 16 of the
TQPP core induce high temperature mesomorphism,42,43 but not
columnar mesophases typically observed in related but less rigid
tetracatenar liquid crystals. Formation of columnar mesophases
was observed only for TQPP derivatives that have tert-butyl groups
as lateral substituents in 2 and 11 positions.44 This observation
prompted us to investigate the effect of lateral substituents in
more detail. Reported here is the mesomorphism of TQPP-based
compounds 2e5 (Fig. 1) with lateral tert-butyl and 4-tert-butyl-
phenyl groups at positions 2 and 11 and dodecylthio and phyta-
nylthio groups attached at carbons 7, 8, 15, and 16. Their meso-
morphism is compared to that of the previously reported TQPP
* Corresponding
(S.H. Eichhorn), bilal.kaafarani@aub.edu.lb (B.R. Kaafarani).
authors.
E-mail
addresses:
eichhorn@uwindsor.ca
http://dx.doi.org/10.1016/j.tet.2014.11.050
0040-4020/Ó 2014 Elsevier Ltd. All rights reserved.

A.O. El-Ballouli et al. / Tetrahedron 71 (2015) 308e314
309
afforded 949 with an overall yield of 45% over the three steps. 2,7-
Di-tert-butylpyrene was prepared by the reaction of pyrene and
tert-butylchloride in the presence of AlCl3. The synthesis and X-ray
structure of 10b are reported elsewhere.50 Briefly, 2,7-
dibromopyrene51e53,50 (10a) was synthesized by the reduction of
pyrene into tetrahydropyrene, which upon electrophilic aromatic
substitution in the presence of bromine and subsequent oxidation
in the presence of bromine and carbon disulfide, lead to 10a. The
Suzuki coupling of 2,7-dibromopyrene 10a with 4-tert-butyl-phe-
nylboronic acid afforded 10b.50 The condensation of 11 with 1,2-
dichloro-4,5-phenylenediamine 12 (commercially available) yiel-
ded 13, which upon reaction with the corresponding alkylthiol
furnished compounds 2e5. Substitution of all four chlorine atoms
with dodecylthiol is high yielding but substitution with the
branched phytanylthiol gives significantly lower yields, probably
due to steric hindrance.
Fig. 1. Chemical structures of the studied TQPP structures. Compounds 3e5 are re-
ported for the first time.
derivatives 1,45,46 6,47 and 7,44 (Fig. 1) to illustrate the influence
of lateral substituents on the formation of columnar mesophases
and to compare derivatives with oxygen and thio ether linking
groups.
2.2. Mesomorphism
Scheme 2 summarizes the thermal phase behavior of com-
pounds 1e7 based on polarized optical microscopy (POM), differ-
ential scanning calorimetry (DSC), thermal gravimetric analysis
(TGA) and variable temperature X-ray diffraction (vt-XRD)
investigations.
2. Results and discussion
2.1. Synthesis
Thermal stability of the new compounds 2e5 was probed by
thermal gravimetric analysis (TGA) under He at a heating rate of
The synthesis of compounds 1,45 2,47 6,47 and 744 has been re-
ported previously. A related approach via the 2,7-disubsituted
tetraketopyrenes 11 as key intermediates was chosen for the syn-
thesis of the new compounds 3e5 (Scheme 1). Compound 11 was
prepared by the catalytic oxidation of 2,7-disubstituted pyrene 10
using ruthenium(III) chloride and sodium(meta)periodate.48 Phy-
tanylthiol (9) was prepared by the reduction of phytol to phytanol,
which upon reaction with HBr and H2SO4 lead to phytanyl bromide.
Refluxing phytanyl bromide with thiourea in ethanol and NaOH
2
ꢀC/min. Decomposition temperatures are given as the tempera-
ture at which 0.1% wt loss has occurred because these values
agree with the long term thermal stability observed by POM and
NMR measurements of heated compounds. Values based on the
extrapolated onset of weight loss are 30e50 ꢀC higher. Thermally
most stable are compounds 2 (270 ꢀC) and 4 (274 ꢀC) with dodecyl
chains while compounds 3 (246 ꢀC) and 5 (254 ꢀC) with phytanyl
chains are slightly less stable. In contrast, the exchange of tert-butyl
groups by 4-tert-butyl phenyl groups does not significantly affect
1. Ra/Ni, H2, 40 PSI
2. H2SO4, HBr
3. Thiourea, ethanol, NaOH, H2O
OH
SH
8
9
Phytol
Phytanylthiol (45% over three steps)
Y1
Y2
Y
Y
OH
OH
B
RuCl3.XH2O; NaIO4;
MeCN; DCM
O
O
O
O
K2CO3; 18-crown-6;
Pd(PPh3)4
toluene/EtOH
Y1
10a
Y1 = Br
Y2
Y
Y
10b
10
11a. Y = t-Bu (22%)
11b. Y = 4-t-Bu-Ph (22%)
Y2 = 4-t-Bu-Ph (80%)
Y
Y
H2N
H2N
Cl
Cl
Cl
Cl
N
N
N
Cl
RS
N
N
N
N
SR
SR
acetic acid/ethanol
RSH
11a/b
+
K2CO3; DMF
Cl RS
N
12
Y
Y
13a. Y = t-Bu (90%)
2. Y = t-Bu; R = n-C12H25 (72%)
3. Y = t-Bu; R = Phytanyl (57%)
13b. Y = 4-t-Bu-Ph (80%)
4. Y = 4-t-Bu-Ph; R = n-C12H25 (84%)
5. Y = 4-t-Bu-Ph; R = Phytanyl (10%)
Scheme 1. Synthetic Scheme of compounds 2e5.

310
A.O. El-Ballouli et al. / Tetrahedron 71 (2015) 308e314
fewer and broader reflections than the sCry phases of TQPPs 1 and 2
due to the more amorphous packing of the branched phytanyl side-
chains. The structures of the sCry phases of 1 and 2 cannot be easily
deduced from the 1-dimensional XRD patterns while compound 3
most likely arranges in a layered structure. Reflections up to the 4th
order can be assigned if the smallest angle reflection of 3 is assigned
as the principle reflection of the layer spacing. However, the cal-
ꢀ
culated d-spacing of 32.6 A is 38% smaller than the length of the
extended molecule (Table 1). This difference is unlikely caused
solely by interdigitation and softening of the phytanyl side-chains.
More likely is a tilted orientation of the TQPP core with regard to
the layer normal. Diffraction studies on single crystals of TQPP 1
and related crystalline TQPP derivatives have confirmed layer
structures for several of these compounds.44
The complete absence of liquid crystal phases for compounds 2
and 3 is surprising as their oxygen ether analogs 6 and 7 display
short range liquid crystal phases.44 Exchange of oxygen ethers by
thioethers often enhances mesomorphism because of the larger
polarizability of sulfur although most experimental results for
discotic liquid crystals reveal only minimal changes to their
mesomorphism (e.g., hexaalkylthio/oxy triphenylenes and octaal-
kylthio/oxy phthalocyanines).28 The absence of liquid crystal pha-
ses for thioether compounds 2 and 3 is caused by an increase in
melting temperatures when compared to their oxygen ether ana-
logs 6 and 7. In fact, TQPP 2 melts 58 ꢀC above the isotropization
(clearing) temperature of 6 and TQPP 3 melts just 10 ꢀC below the
isotropization temperature of 7 (Scheme 2).
Scheme 2. Thermal phase behavior of compounds 1e7 based on POM, DSC, and XRD.
Transition temperatures and enthalpies based on DSC (10 ꢀC/min) are given in ꢀC and
kJ molꢂ1, respectively. Phase assignment: (s)Cry¼(soft) crystal, Colh¼hexagonal co-
lumnar mesophase, Colr¼rectangular columnar mesophase, Iso¼isotropic liquid,
Dec¼decomposition, M¼unknown mesophase. aSeveral crystal to crystal transitions
occur (see Supplementary data for details). bPeak temperature of a broad transition;
cTransition occurs above the on-set of thermal decomposition; dObserved only in the
1st-heating run; eDetermined by POM and not observed by DSC.
thermal stability. This may be expected as the phenyl rings are not
in conjugation with the TQPP core based on the similarity of the
absorption spectra of 3 and 5 above 350 nm in solution and as thin
films (Fig. 2 and Table S3).
Attachment of lateral tert-butylphenyl groups in TQPPs 4 and 5
induces columnar liquid crystal phases that are stable over wide
ranges of temperature (>100 ꢀC) as confirmed by POM, DSC, and
160000
0.7
3
5
3
5
140000
0.6
120000
100000
80000
60000
40000
20000
0
0.5
0.4
0.3
0.2
0.1
0.0
250
300
350
400
450
500
550
250
300
350
400
450
500
550
Wavelength (nm)
Wavelength (nm)
Fig. 2. Absorption spectra of TQPPs 3 and 5 in solution (left, DCM) and as thin films on quartz (right).
TQPP derivatives 1 to 3 display crystal phases that melt into
isotropic liquids at or below the onsets of their thermal de-
composition. Their crystal phases, however, are best categorized as
soft crystal (meso)phases because the crystallites easily deform
under pressure similar to a fluid of high viscosity.54 X-ray diffrac-
tion patterns (see Supplementary data) and the high enthalpies of
the melting transitions are in agreement with the assigned phases
and phase transitions in Scheme 2. Attachment of phytanyl side-
chains with multiple branching points in TQPP 3 lowered the
melting point by 130 ꢀC in comparison to TQPP 2 but did not fully
suppress crystallization and neither induced a liquid crystal phase.
Diffraction patterns of the three solid phases of compounds 1 to
3 show a larger number of reflections in the small and wide-angle
ranges, which is consistent with 3-dimensionally ordered soft
crystal phases rather than 2-dimensionally ordered liquid crystal
phases. However, the sCry phase of TQPP 3 shows significantly
XRD (Scheme 2). TQPP 4 melts into a hexagonal columnar meso-
phase at 200 ꢀC and clears at 350 ꢀC, 75 ꢀC above its onset of
thermal decomposition. Both, dendritic fan-shaped defect textures
with pseudo-isotropic areas of homeotropic domains and the dif-
fraction patterns containing an intense (10) reflection and weak
(11) and (20) reflections of relative lattice spacings 1:O3:2 confirm
the hexagonal symmetry of the plane group of the columnar
mesophase (Fig. S16 and Table S1 in the Supplementary data). The
broadness of the (10) reflection indicates a rather disordered
packing of the columns that is likely caused by the elliptical shape
of the molecules. Less affected by the elliptical shape is the intra-
columnar packing order as indicated by the intense broad reflection
ꢀ
at 0.35 nm (3.5 A).
A lattice parameter of 2.93 nm was calculated for the hexagonal
plane lattice of TQPP 4 at 538 K (265 ꢀC), which gives an area per
molecule Shex of 7.43 nm2 (Shex¼a2ꢁO3/2) and a volume per

A.O. El-Ballouli et al. / Tetrahedron 71 (2015) 308e314
311
Table 1
Estimated and measured molecular dimensions for TQPPs 1e7
Comp.
Lmax (nm)
Wmax (nm)
A.R.
Smax (nm2)
Vmax (nm3)
Vliq (nm3)
SXRD (nm2)
VXRD (nm3)
1
2
3
4
5
6
7
4.7
4.7
5.2
4.8
5.2
4.7
5.2
0.9
1.1
1.1
2.0
2.0
1.1
1.1
5.2
4.3
4.7
2.4
2.6
4.3
4.7
4.23
5.17
5.72
9.60
10.40
5.17
5.72
1.48
1.81
2.00
3.36
3.64
1.81
2.00
2.23
2.38
3.18
2.53
n.a.
n.a.
n.a.
7.43
9.10
n.a.
n.a.
1.73b
n.a.
n.a.
2.60
3.11
n.a.
3.32
s. t. 2a
s. t. 3a
n.a.
Lmax¼maximum length of molecule with extended side-chains. Wmax¼maximum width of the aromatic core. A.R.¼maximum aspect ratio in the plane of the aromatic core
calculated as Lmax/Wmax. Smax¼maximum area of molecule calculated as LmaxꢁWmax. Vmax¼Smaxꢁ0.35¼maximum volume per molecule based on a stacking distance of
0.35 nm. Vliq is the more realistic volume per molecule in the liquid phase calculated as the sum of volumes of the core and aliphatic side-chains as described in the
Supplementary data. Core volumes are estimated from single crystal data and experimental volume increments and the volumes of aliphatic side chains in their liquid phases
at a given temperature are calculated based on empirical equations derived from dilatometric measurements.55 Values for TQPPs 1, 2 and 4 were calculated for a temperature
of 265 ꢀC and values for TQPPs 3 and 5 for a temperature of 120 ꢀC to allow comparison with the values obtained from the XRD data of the Colh mesophases of TQPPs 4 and 5.
SXRD and VXRD are the molecular cross-sections and volumes in the hexagonal columnar mesophases determined by XRD based on one molecule per columnar slice.
a
s. t.¼similar to.
b
This value is based on the unit cell dimensions of the high temperature monoclinic crystal phase.44
molecule of 2.60 nm3 for a stacking distance of 0.35 nm. Area and
volume per molecule determined by XRD are in good agreement
with the estimated values listed in Table 1. We conclude from the
observed dimensions and the stacking model shown in Fig. 3 that
the long axes of the cores of TQPP 4 (and 5) must be at an angle to
accommodate the steric bulk of the out-of-plane tert-butylphenyl
groups. This type of arrangement also distributes the aliphatic side-
chains more evenly around the columnar stacks, which is essential
for the formation of a hexagonal columnar mesophase. The most
probable columnar structure is a helical arrangement of the mol-
ecules that has been confirmed for similar compounds.56,57 How-
ever, diffraction data of unaligned samples of TQPP 4 (and 5) do not
provide any evidence for a helical structure and no attempt was
made to study aligned monodomains of TQPPs 4 and 5. Conse-
quently, we cannot exclude other possible stacking structures with
ordered or disordered rotations of the stacking molecules with
regard to each other.
1:O3:2. These patterns and the observation of pseudo isotropic
areas of homeotropic domains (Fig. 4) confirm the presence of
a Colh phase at the given temperatures. The (10) reflection is
broadening with decreasing temperature and the (11) and (20)
reflections eventually disappear at 40 ꢀC (Fig. S18). This change is
interpreted as a gradual increase in distortion of the hexagonal
packing that eventually leads to the formation of the Colr below
21 ꢀC (Fig. 5). However, the wider range of temperature of the Colh
phase and the lesser broadening of the (10) reflection compared to
TQPP 4 confirms a much better compatibility of TQPP 5 with
a hexagonal columnar arrangement. Noteworthy is the short
stacking distance of 0.342 nm at 120 ꢀC that increases to 0.347 nm
at 200 ꢀC and in the Colr mesophase. However, the persistence
length of the stacking increases with decreasing temperature and is
the highest in the Colr mesophase as indicated by the increase in
intensity and narrowing of the wide angle (001) reflection.
Estimated molecular dimensions of TQPP 5 agree well with
observed dimensions of the columnar mesophases (Table 1). A
columnar cross section of 9.10 nm2 and a volume of 3.11 nm3 per
columnar stacking unit are calculated based on a lattice parameter
of a¼3.24 nm and a stacking distance of 0.342 nm for the Colh phase
at 120 ꢀC. Both cross section and volume decrease with tempera-
ture and the smallest values are obtained in the Colr mesophases. A
projected area per molecule of 8.36 nm2 (molecules are tilted with
regard to the stacking axis) and a volume per molecule of 2.90 nm3
are calculated based on lattice parameters of a¼7.25 nm and
ꢀ
b¼2.30 nm, a stacking distance of 3.47 A and the occupancy of 2
molecules per unit plane and cell. A reduction in the volume per
molecule is expected for a transition from a Colh to a higher ordered
Colr mesophase.58 All (hk) reflections obtained for the Colr meso-
phase satisfy the condition hþk¼2n and, consequently, the dif-
fraction data are not sufficient for a distinction between the
centered c2mm and the p2gg lattices.
A comparison of TQPPs 1, 2, and 4 shows how the lateral ex-
tension from hydrogen (TQPP 1) to tert-butyl (TQPP 2) to 4-tert-
butylphenyl (TQPP 4) first stabilizes the crystalline phase (TQPPs 1
and 2) but finally induces columnar mesomorphism in TQPP 4. This,
perhaps surprising, can be rationalized with differences in in-
termolecular interactions and a reduction of the aspect ratios in the
order 1>2>4. TQPP 1 has an aspect ratio of 4.7 and packs into
layered crystalline structures but does not form liquid crystal
phases. Instead, it melts into an isotropic liquid at a comparatively
low temperature of 167.4 ꢀC. Introduction of tert-butyl groups at the
2 and 11 positions of 2 decreases the aspect ratio to 4.3 and in-
terferes with the formation of layered structures with parallel close
co-facial packing of the molecules. Close co-facial packing of the
aromatic cores is possible only if the long-axes of the molecules are
rotated with regard to each other to generate a helical-type
Fig. 3. Cartoon illustrating the proposed helical arrangement in the Colh mesophases
of TQPPs 4 and 5.
TQPP 5 forms a soft crystal phase when precipitated from so-
lution. The soft crystal phase irreversibly melts into a hexagonal
columnar liquid crystal phase at 105 ꢀC, which clears into an iso-
tropic liquid at 240 ꢀC. No soft crystal phase is formed on cooling
but, instead, the compound displays a rectangular columnar mes-
ophase below 21 ꢀC. Again, the phase assignment is confirmed by
characteristic defect textures (Fig. 4) and diffraction patterns
(Fig. 5).
Diffraction patterns at 120 ꢀC (Fig. 5) and 200 ꢀC (Fig. S18) both
show small angle reflections (10), (11), and (20) with a ratio of

312
A.O. El-Ballouli et al. / Tetrahedron 71 (2015) 308e314
Fig. 4. POM micrographs of the Colh (left) and Colr (right) phases of TQPP 5 between glass slides at 215 ꢀC and 17 ꢀC on cooling from the isotropic liquid at 2 ꢀC/min (crossed
polarizers, 200ꢁ magnification). Dark areas around the dentritic texture are homeotropically (vertically) aligned domains.
the temperature range of the columnar mesophases of TQPP 5 in
comparison to TQPP 4, but does not induce mesomorphism in TQPP
3. Clearly, the combination of lateral extension with 4-tert-butyl-
phenyl groups and the increase in packing volume of the side-
chains by the attachment of phytanyl chains is crucial for the en-
hancement of columnar mesomorphism in TQPP 5. A room tem-
perature columnar mesophase is obtained because crystallization
from the mesophase is suppressed by the branched chains and the
presence of many isomers. In fact, TQPP 5 is not a single compound
because each of the 4 phytanyl chains contains 3 racemic chiral
carbons that generate 4096 diastereomers and enantiomers. Other
advantages are the sufficiently low clearing temperature that
generates a thermally stable isotropic liquid phase as well as a more
fluid Colh phase that spontaneously aligns homeotropically
between glass substrates. Both properties are advantages for the
processing of these materials. We also note that the stacking order
in the hexagonal and, in particular, rectangular columnar meso-
phases remains high despite the incorporation of multiple
branched side-chains.
3. Conclusions
The board-shaped TQPP core is transformed into a potent co-
lumnar mesogen TQPP 5 by the lateral attachment of 4-tert-butyl-
phenyl groups at carbons 2 and 11 and the use of multiple branched
phytanyl side-chains. Lateral extension of the core to crucifix sha-
ped structures is essential for the formation of hexagonal columnar
mesophases while the incorporation of phytanyl side-chains is
most effective in the control of phase transition temperatures.
Surprisingly, TQPPs with oxygen ether linking groups show a higher
propensity for mesomorphism than their thio ether analogs.
Fig. 5. Diffraction patterns of TQPP 5 at 35 ꢀC (as precipitated; soft crystal phase), at
120 ꢀC (Colh), and after cooling from 150 ꢀC to 18 ꢀC (Colr).
4. Experimental
4.1. General synthesis
columnar stack or the molecules arrange in slipped stacks as ob-
served for some laterally substituted polyacenes.59 However, TQPP
2 does not display a liquid crystal phase mainly because its soft
crystal phase persists up to 271 ꢀC. Attachment of 4-tert-butyl-
phenyl groups in TQPP 4 significantly reduces the aspect ratio to 2.4
and promotes columnar stacking because the out-of-plane phenyl
groups sterically disfavor parallel co-facial packing. In fact, the high
clearing temperature of 349 ꢀC of the Colh mesophase of TQPP 4 is
evidence for a stabilization of the columnar mesophases that is
likely caused by a helical stacking of the molecules. Induction of
helical stacking by phenyl groups attached to the aromatic core has
been reported for other discotic liquid crystals.57
1-Dodecanethiol (C12H25SH) is commercially available. Phyta-
nylthiol (9),49 2,7-dibromopyrene (10a),52,53 2,7-di-tert-butylpyr-
ene-4,5,9,10-tetraone (11a),48 and 2,7-bis-(4-tert-butylphenyl)
pyrene (10b)50 were prepared according to literature procedures.
Syntheses of 1,45 2,47 6,47 and 744 were previously reported.
4.1.1. TQPP-[t-Bu]2-[Cl]4
(13a). 2,7-Di-tert-butyltetraketopyrene
(11a) (1.00 g, 2.67 mmol) was added to a solution of 4,5-dichloro-
1,2-phenylenediamine (1.00 g, 0.01 mol) in ethanol:acetic acid
(1:1). The solution was refluxed for 24 h. The mixture was cooled,
filtered and the solid was triturated using hot toluene via soxhlet
extraction to obtain 13a as dark yellow solid (1.40 g, 80%), mp
>300 ꢀC. The solid was used for the next step without further
Exchange of the linear dodecyl chains by branched phytanyl
chains drastically reduces transition temperatures and broadens

A.O. El-Ballouli et al. / Tetrahedron 71 (2015) 308e314
313
purification. HRMS-MALDI (m/z): [MþH]þ Calcd for C36H27N4Cl4,
84%), mp (determined by DSC) 200.6 ꢀC. 1H NMR (300 MHz, CDCl3):
655.09; Found, 655.08.
d
9.24 (s, 4H), 7.94 (d, J¼8.1 Hz, 4H), 7.64 (d, J¼8.1 Hz, 4H), 7.62 (s,
4H), 3.21e3.16 (m, 8H),1.97e1.88 (m, 8H),1.65e1.62 (m, 8H),1.60 (s,
18H), 1.46e1.28 (m, 64H), 0.9e0.85 (t, J¼6 Hz, 12H). 13C NMR
4.1.2. TQPP-[t-Bu]2-[Sphytanyl]4 (3). The title compound was syn-
thesized according to a modified literature procedure.60 TQPP-[t-
Bu]2-[Cl]4 (13a) (1.3 g, 1.98 mmol) and K2CO3 (15.1 g, 0.11 mol) was
suspended in dry DMF and purged with argon for one hour. Dis-
tilled phytanylthiol (9) (9.35 g, 29.7 mmol) was transferred to the
reaction mixture through a syringe. The mixture was heated at
80 ꢀC for one week. The reaction mixture was cooled down, poured
onto water and neutralized with conc. HCl to pH¼5. The yellow
solid was filtered and washed with water. The product was purified
by gradient column chromatography starting from hexanes:-
chloroform 9:1 till 7:3 and the solvent was evaporated. The col-
lected solid was recrystalized from heptane/ethanol to obtain 3 as
sticky yellow solid (2.00 g, 57%), mp (determined by DSC) 142.1 ꢀC.
(75.5 MHz, CDCl3):
d 159.73, 150.28, 140.90, 140.22, 139.15, 138.14,
129.07, 127.70, 125.66, 124.82, 124.52, 122.84, 34.70, 33.25, 31.96,
31.62, 29.80, 29.74, 29.72, 29.51, 29.42, 28.16, 22.72, 14.15. Anal.
Cald. for C96H134N4S4: C, 78.31; H, 9.17; N, 3.81; S, 8.71. Found: C,
78.43; H, 9.14; N, 3.85; S, 8.75.
4.1.6. TQPP-[p-t-Bu-phenyl]2-[Sphytanyl]4 (5). The titled compound
was synthesized according to a modified literature procedure.60
TQPP-[p-t-Bu-phenyl]2-[Cl]4 (13b) (0.30 g, 0.37 mmol) and K2CO3
(2.56 g, 18.6 mmol) suspended in dry DMF. A stream of argon gas
was passed through the mixture for 1 h. Distilled phytanylthiol (8)
(1.13 g, 3.59 mol) was added. The mixture was heated at 80 ꢀC in oil
bath for one week. The reaction mixture was cooled down, poured
onto water and neutralized by conc. HCl to pH¼5. The yellow solid
was filtered and washed with water. The product was purified by
gradient column chromatography starting from hexanes:chloro-
form 9:1 till 6:4 and the solvent was evaporated. The collected solid
was recrystallized from heptane/ethanol to obtain 5 as sticky yel-
low solid (70 mg, 10%), mp (determined by POM) 239 ꢀC. 1H NMR
1H NMR (300 MHz, CDCl3):
8H), 1.92e1.82 (m, 4H), 1.76e1.74 (m, 8H), 1.75 (s, 18H), 1.40e1.18
(m, 84H), 0.98e0.97 (m, 60H). 13C NMR (75.5 MHz, CDCl3):
150.68,
d 9.74 (s, 4H), 8.10 (s, 4H), 3.34e3.27 (m,
d
142.19, 141.39, 140.67, 129.40, 125.38, 124.01, 123.90, 39.34, 37.50,
37.44, 37.39, 37.27, 37.12, 35.91, 35.19, 35.12, 32.82, 32.78, 32.56,
31.91, 31.23, 27.97, 24.80, 24.49, 24.43, 22.73, 22.63, 19.80, 19.74.
Anal. Cald. for C116H190N4S4: C, 78.76; H, 10.83; N, 3.17; S, 7.25.
Found: C, 78.54; H, 10.87; N, 3.15; S, 7.13.
(300 MHz, CDCl3):
d
9.44 (s, 4H), 7.99 (d, J¼7.5 Hz, 4H), 7.76 (s, 4H),
7.66 (d, J¼7.5 Hz, 4H), 3.23e3.20 (m, 8H), 1.96e1.93 (m, 4H),
4.1.3. 2,7-Bis(4-tert-butylphenyl)-4,5,9,10-tetraketopyrene (11b). The
title compound was prepared according to a modified literature
procedure.48 2,7-Bis(4-tert-butylphenyl)pyrene (10b) (800 mg,
1.71 mmol) was dissolved together with sodium(meta)periodate
NaIO4 (2.96 g, 0.01 mol) in 50 mL (1:1; CH2Cl2:CH3CN). Ruth-
enium(III) chloride RuCl3$xH2O (0.09 g, 0.43 mmol) was added along
with 32 mL distilled water. The reaction mixture was stirred for 2
days at 40 ꢀC. The brown mixture was poured over H2O (200 mL)
and was extracted using CH2Cl2. The organic layer was dried over
MgSO4 after which it was evaporated under reduced pressure. The
collected solid was then purified using gradient column chroma-
tography 7:3 (hexanes:chloroform) till 100% chloroform as an elu-
ent, the solvent was then evaporated. The title compound 11b was
collected as red solid (200 mg, 22%), mp >300 ꢀC. 1H NMR
1.77e1.70 (m, 8H), 1.58 (s, 18H), 1.45e1.10 (m, 84H), 0.97e0.95 (m,
60H). 13C NMR (75.5 MHz, CDCl3):
d 150.52, 141.31, 141.25, 140.48,
139.62, 138.18, 129.45, 127.72, 125.78, 125.21, 124.84, 123.22, 39.36,
37.44, 37.40, 37.34, 37.29, 35.17, 34.72, 32.90, 32.80, 32.73, 31.60,
31.25, 29.71, 27.97, 24.81, 24.54, 22.72, 22.63, 19.74, 19.67, 19.58.
C128H198N4S4: C, 80.02; H, 10.39; N, 2.92; S, 6.68. Found: C, 79.86; H,
10.40; N, 3.05; S, 6.56.
Acknowledgements
This work has been supported by the ACS-PRF (Grant No. 47343-
B10), the University Research Board of the American University of
Beirut, the Natural Sciences and Engineering Research Council of
Canada (NSERC) grant (P\RGPIN-2014-05706), the Canada Foun-
dation for Innovation (CFI), and the Ontario Innovation Trust (OIT).
The authors are grateful for this support. B. R. K. and B. W. thank the
Arab Fund Scholarship Program for financial support.
(300 MHz, CDCl3):
d
8.71 (s, 4H), 7.71 (d, J¼8.4 Hz, 4H), 7.57 (d,
J¼8.4 Hz, 4H), 1.39 (s, 18H). 13C NMR (75.5 MHz, CDCl3):
d 178.13,
153.06, 143.65, 134.46, 133.91, 132.79, 131.25, 126.54, 126.38, 34.81,
31.24.
Supplementary data
4.1.4. TQPP-[4-t-Bu-phenyl]2-[Cl]4
(13b). 2,7-Di-4-tert-butylph
enyltetraketopyrene (11b) (0.10 g, 0.20 mmol) was added to a so-
lution of 4,5-dichloro-1,2-phenylenediamine (0.10 g, 0.56 mmol) in
ethanol:acetic acid (1:1). The solution was refluxed for 24 h. The
mixture was cooled down, filtered and the solid was triturated
using hot toluene via soxhlet extraction to obtain 13b as dark yel-
low solid (0.12 g, 80%), mp >300 ꢀC. The solid was used for the next
step without further purification. MALDI-TOF (m/z): [MþH]þ Calcd
for C48H35N4Cl4, 809.62; Found, 809.30.
1H NMR, 13C NMR, MALDI-TOF, TGA, DSC, Powder XRD, Calcu-
lations of dimensions, and UV of thins films are available in ESI.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2014.11.050.
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