A new liquid crystalline derivative of dibenzotetraaza[14]annulene: synthesis, characterization and the preliminary evaluation of mesomorphic properties

Article abstract of DOI:10.1016/j.tetlet.2006.09.134

A new dibenzotetraaza[14]annulene ligand has been synthesized that contains two 2-hydroxybenzoyl and four 3,7-dimethyloctyloxy peripheral substituents. Its mesomorphic textures were observed by means of a polarizing optical microscopy.

Full text of DOI:10.1016/j.tetlet.2006.09.134

Tetrahedron Letters 47 (2006) 8209–8213
A new liquid crystalline derivative of
dibenzotetraaza[14]annulene: synthesis, characterization and
the preliminary evaluation of mesomorphic properties
a
b
a,
*
´
Jarosław Grolik, Lesław Sieron and Julita Eilmes
aDepartment of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krako´w, Poland
_
Institute of General and Ecological Chemistry, Technical University of Ło´dz´, Zeromskiego 116, 90-924 Ło´dz´, Poland
b
Received 2 August 2006; revised 11 September 2006; accepted 22 September 2006
Abstract—A new dibenzotetraaza[14]annulene ligand has been synthesized that contains two 2-hydroxybenzoyl and four 3,7-di-
methyloctyloxy peripheral substituents. Its mesomorphic textures were observed by means of a polarizing optical microscopy.
ꢀ 2006 Elsevier Ltd. All rights reserved.
It has been well established for over 28 years from Chan-
drasekhar’s early work1 that many compounds com-
posed of disc-shaped molecules exhibit liquid
crystalline properties. The conventional mesogenic
molecule has a rigid core, usually flat and aromatic,
and is equipped with several (4–8) flexible aliphatic side
chains that surround the core. A remarkable number of
known liquid crystalline materials are based on macro-
cyclic systems such as porphyrins, phthalocyanines,
azacrowns and macrocyclic Schiff bases.2 Among them,
transition metal complexes of substituted dibenzotetra-
aza[14]annulenes3 have been found to exhibit liquid
crystalline properties. Hunziker4 and Veber and co-
workers5 have studied their mesomorphic behaviour as
a function of the structure, length and number of
peripheral groups. An optical storage effect was later
demonstrated in one of these mesomorphic nickel
complexes.6
The properties-directed design of 7 was based on the
known crystal structure8 of meso-bis(2-hydroxy-
benzoyl)dibenzotetraaza[14]annulene precursor 1.9 As
shown in Figures 1 and 2, 1 is nearly flat and is rich in
p delocalized areas, and therefore seemed to be well sui-
ted to play the role of a disc-shaped building block. In
addition, aromatic pÁ Á Áp stacking interactions, involving
planar central moieties and meso phenyl rings of neigh-
bouring molecules, are clearly evidenced by the crystal
structure (Fig. 3). Recent detailed studies on mesomor-
phic materials10 have established that in the most often
encountered columnar mesophases, the disc-like mole-
cules self-assemble into columns by stacking one upon
another and self-organize into various arrangements
that differ in the degree of order and in the two-dimen-
sional symmetry of the column packing. Accordingly,
the columnar mesophases can be further sub-classified
into those referred to as hexagonal, rectangular and
oblique. Within discotic liquid crystals, there are also less
common and less ordered nematic mesophases.
We have recently elaborated synthetic routes to various
peripherally functionalized dibenzotetraaza[14]annu-
lenes.7 Herein, we describe a new liquid crystal based
on a metal-free dibenzotetraaza[14]annulene macrocycle
bearing two meso 2-hydroxybenzoyl substituents and
four 3,7-dimethyloctyloxy groups attached to o-phenyl-
ene moieties (compound 7 in Scheme 1).
In designing mesogens it is of importance, that self-
assembly and self-organisation, crucial for inducing
mesomorphic behaviour to discotic materials, are
mostly influenced by the structure and number of flexi-
ble pendant chains that surround the discotic units.
Therefore, in order to generate such supramolecular
processes in our product, we introduced four additional
peripheral substituents to the macrocyclic core of the
precursor 1, by incorporating them onto the benzenoid
rings. We chose 3,7-dimethyloctyloxy groups, since, as
Keywords: Dibenzotetraaza[14]annulene; Liquid crystal; Discotic; Tex-
tures; Polarizing optical microscopy; pÁ Á Áp Stacking.
*
Corresponding author. Tel.: +48 12 6632294; fax: +48 12 6340515;
e-mail: jeilmes@chemia.uj.edu.pl
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.09.134

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J. Grolik et al. / Tetrahedron Letters 47 (2006) 8209–8213
O
O
i
ii
OH
OTs
3
2
4
l
k
g
b
e
a
j
O
O
NO2
d
i
f
O
O
NH2
NH2
iii
iv
NO2
q
6
5
u
p
OH
r
n
O
s
m
t
7
k
l
8
6
5
g
e
10
13
b
4
9
a
j
f
O
O
N
N
O
d
i
v
H
11
12
3
2
H
N
N
O
14
18
1
15
17
16
O
7
OH
Scheme 1. Reagents and conditions: (i) py, TosCl, rt, (84%); (ii) catechol, K2CO3/DMF, 80 ꢁC, (56%); (iii) CH2Cl2/HNO3, H2SO4, rt, (81%); (iv)
10% Pd/C, NaBH4, MeOH, Ar and (v) 3-formylchromone, MeOH, reflux, (41%).
OH
O
N
N
N
N
H
H
1
O
OH
Figure 3. Packing diagram viewed down the c axis, showing pÁ Á Áp
stacking interactions between adjacent molecules.
Figure 1. 7,16-Bis(2-hydroxybenzoyl)-5,14-dihydrodibenzo[b,i][1,4,8,11]-
tetraazacyclotetradecine 1.9
Figure 2. X-ray crystal structure of compound 1: (a) top-view; (b) side-view. Displacement ellipsoids for non-H atoms are drawn at the 50%
probability level.
previously reported, this kind of flexible aliphatic chain
To the best of our knowledge, 7 is the first mesomorphic
metal-free dibenzotetraaza[14]annulene synthesized in a
reasonable yield (41%). Previously, Veber and Forget
appeared
capable
of
inducing
mesomorphic
properties.11

J. Grolik et al. / Tetrahedron Letters 47 (2006) 8209–8213
8211
reported liquid crystalline properties5c of a hexasub-
stituted dibenzotetraaza[14]annulene ligand prepared
in 5% yield via an unpractical synthetic procedure.5b It
seems therefore, that the easy and relatively efficient
synthesis described here can be of practical significance.
First of all, the procedure can be easily extended to
other derivatives of the meso bis(hydroxybenzoyl)
macrocycle, which may also be potential liquid crystals.
Moreover, subsequent metallation of these ligands could
give rise to a variety of corresponding metallomesogens.
textures are shown in Figure 4a and b, others are col-
lected in the Supplementary data. For each texture,
the sample was annealed for 15 min before a photo-
graph was taken. On cooling from the isotropic liquid,
a new texture appeared just below the clearing point
and remained stable at room temperature. This texture,
shown in Figure 5, seems to be very similar to that rec-
ognized theoretically as characteristic of discotic hexag-
onal columnar phases14 and observed experimentally for
mesogens reported recently.15 The thermal behaviour of
7 was also examined by differential scanning calorimetry
(DSC). DSC traces recorded at different scan rates and
corresponding to various temperature ranges are shown
in the Supplementary data. Since more advanced meth-
ods are required to unambiguously elucidate the exact
nature of the mesophases, a detailed study has been
undertaken including X-ray diffraction measurements
(XRD), which is currently in progress. The results will
be reported elsewhere.
The synthesis of dibenzotetraaza[14]annulene 7 is shown
in Scheme 1. The preparation is based on a general
method described elsewhere,9 involving the condensa-
tion of o-phenylenediamine with 3-formylchromone
to give meso-bis(2-hydroxybenzoyl)dibenzotetraaza[14]-
annulene 1 (Fig. 1). Here, in the last step of the synthe-
sis, 4,5-bis(3,7-dimethyloctyloxy)-o-phenylenediamine 6
is used in place of o-phenylenediamine in order to incor-
porate four additional substituents. Diamine 6 was pre-
pared in four steps starting from 3,7-dimethyl-1-octanol
2, which was initially transformed to the corresponding
tosylate 312 then used for alkylation of catechol to give
4.13 Dinitro derivative 5 was synthesized in 81% yield
by a procedure analogous to that described earlier.5a
The nitro groups of 5 were successfully reduced by means
of NaBH4/methanol in the presence of 10% Pd/C. Since
diamine 6 appeared very reactive and easily oxidizable,
the reaction mixture containing 6 was carefully filtered
under argon in order to remove the catalyst, solid by-
product and undissolved reducing agent, and immedi-
ately subjected to the reaction with 3-formylchromone.
The product 7 was obtained in a reasonable yield of
41%, after recrystallization from acetone–methanol (4:1).
The X-ray crystal structure of 1 was reported by Rihs
et al.8 The present structure has been redetermined from
new intensity data, with appreciably improved precision.
The difference in the Fourier map analysis exhibited two
peaks located in the expected positions of H amine
atoms which indicated the presence of two tautomeric
states of a tetraaza[14]annulene ring.16 The found H
atoms were disordered with a ratio of 0.39:0.61.
In the solid state, the central 14-membered ring of the
macrocycle has an almost planar conformation and lies
across the centre of inversion. The dihedral angle be-
tween the C(2–7)/N1/N2 central flat plane and C(11–
17)/O2 benzoyl group is 43.24(3)ꢁ, and between the
C(2–7)/N1/N2 and N1/C9/C8i/N2i planes it is
i
The new products 5 and 7 were fully characterized by ele-
mental analysis, ESI-MS, 1H and 13C NMR spectra. The
HETCOR spectrum of 7 used in the assignment of 13C
NMR signals is shown in the Supplementary data.
12.64(8)ꢁ (symmetry: = Àx, Ày, Àz).
The carbonyl O1 atom is involved in a strong intramo-
lecular hydrogen bond [O2–H2O = 0.94(2), H2O Á Á Á
˚
O1 = 1.67(2), O1 Á Á Á O2 = 2.5297(16) A, \O2–H2O Á Á Á
Our preliminary studies performed with the use of a
polarizing optical microscope revealed the birefringence
of 7 evidenced by the appearance of textures typical for
liquid crystals. A sample of 7 was placed between a slide
O1 = 150(2)ꢁ], and deviates from the plane of the benz-
oyl group, with a dihedral angle O1–C11–C12–C13 of
12.6(2)ꢁ.
and a coverslip and slowly heated until it melted at Tiso
=
The distance of the most outlying atom (O2) of the
benzoyl group from the centre of the molecule is about
192 ꢁC, then it was very slowly cooled to the room
temperature. A variety of textures were observed on
heating, below the clearing point. Two representative
˚
2 A. The shortest intermolecular distance between adja-
˚
cent macrocyclic rings is about 3.25 A, indicating pÁ Á Áp
Figure 4. Textures of 7 viewed on heating, under crossed polarizers: (a) at 94 ꢁC and (b) at 177 ꢁC.

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J. Grolik et al. / Tetrahedron Letters 47 (2006) 8209–8213
tration through
a pad of Celite under argon.
3-Formylchromone (0.36 g, 2.1 mmol) was immediately
added to the filtrate and the mixture was allowed to re-
flux under argon for 2 h. The crude product which pre-
cipitated after cooling was filtered off and recrystallized
from acetone–methanol (4:1). Brown crystals, yield
1
0.49 g (41%), mp 192 ꢁC. H NMR (300 MHz; CDCl3,
d ppm): 0.87 (d, J = 6.6 Hz, 24H, Hj,k), 0.93 (d,
J = 6.3 Hz, 12H, H-1), 1.17 (m, 8H, Hg), 1.18 (m, 4H,
He), 1.33 (m, 8H, Hf), 1.33 (m, 4H, He), 1.54 (m,
4H, Hi), 1.60 (m, 4H, Hb), 1.66 (m, 4H, Hd), 1.84 (m,
4H, Hb), 3.96 (t, J = 6.75 Hz, 8H, Ha), 6.64 (s, 4H,
H-1,4,10,13), 6.88 (dd, J = 7.5 Hz, J = 7.5 Hz, 2H,
Hs), 7.06 (d, J = 7.8 Hz, 2H, Hq), 7.45 (dd, J = 7.8 Hz,
J = 7.8 Hz, 2H, Hr), 7.55 (d, J = 7.8 Hz, 2H, Ht), 8.34
(d, J = 6 Hz, 4H, H-6,8,15,17), 11.37 (s, 2H, Hu),
14.97 (t, J = 6.6 Hz, 2H, NH); 13C NMR (75 MHz,
CDCl3, d ppm): 19.6 (Ci), 22.6, 22.69 (Cj,k), 24.7 (Cf),
27.98 (Ci), 29.9 (Cd), 36.2 (Cb), 37.3 (Ce), 39.2 (Cg),
68.0 (Ca), 100.6 (C-1,4,10,13), 108.9 (Ch), 118.1 (Cs),
118.4 (Cq), 120.2 (C-7,16), 130.1 (C-5a,9a,14a,18a),
131.1 (Ct), 134.6 (Cr), 148.6 (C-2,3,11,12), 150.7 (C-
6,8,15,17), 161.5 (Cp), 195.9 (Cm); IR (KBr) mmax
(cmÀ1): 2954, 2927, 2869, 1565, 1216, 1009, 815; ESI-
MS (m/z) 1154.2 (M+H)+; Anal. Calcd. for
C72H104N4O8: C, 74.96; H, 9.09; N, 4.86. Found: C,
74.04; H, 9.03; N, 4.93.
Figure 5. Texture of 7 observed on cooling, at 160 ꢁC, under partially
crossed polarizers.
stacking interactions. The molecules are linked by C5–
H5 Á Á Á O1ii hydrogen bonds [C5–H5 = 0.97(2), H5 Á Á Á
ii
O1ii = 2.57(2), C5 Á Á Á O1 = 3.398(2) A, \C5-H5 Á Á Á
˚
O1ii = 144.4(13)ꢁ] (symmetry: ii = Àx, Ày, 1 À z).
3,7-Dimethyl-1-octanol 2 and 3-formylchromone were
purchased from Sigma–Aldrich and were used as re-
ceived. Products 3 and 4 were prepared according to
the procedures reported elsewhere.12,13 Compound 1
was synthesized using the previously reported proce-
dure.9 Crystals suitable for X-ray measurements were
grown from ethyl acetate.
1,2-Dinitro-4,5-bis(3,7-dimethyloctyloxy)benzene 5: A
solution of 4 (3.5 g, 9.1 mmol) in dichloromethane
(50 ml) was added dropwise to vigorously stirred con-
centrated HNO3 (20 ml) over a period of 30 min. Con-
centrated sulfuric acid (10 ml) was then added in
portions and stirring was continued for 1.5 h at room
temperature. The reaction mixture was next poured
onto crushed ice and the resultant suspension was ex-
tracted with dichloromethane (2 · 50 ml). The organic
layer was washed thoroughly with saturated aqueous so-
dium carbonate, then with water, and finally dried over
anhydrous MgSO4. The solvent was evaporated to give
a crude product which was crystallized from ethanol.
Pale-yellow crystals, yield 3.5 g (81%), mp 81–82 ꢁC.
Crystallographic data (excluding structure factors) for
the structure in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supple-
mentary publication number CCDC 616527. Copies of
the data can be obtained, free of charge, on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
[e-mail: deposit@ccdc.cam.ac.uk].
Supplementary data
The photographs of the mesomorphic textures observed
on heating, the HETCOR spectrum and DSC curves of
7 are given in the Supplementary data. Supplementary
data associated with this article can be found, in the
online version, at doi:10.1016/j.tetlet.2006.09.134.
1H NMR (300 MHz, CDCl3,
d ppm): 0.87 (d,
J = 6.6 Hz, 12H, Hj,k), 0.96 (d, J = 6.3 Hz, 6H, H-1),
1.1–2.0 (m, 20H, Hb,d,e,f,g,i), 4.13 (t, 4H, J = 5.9 Hz,
Ha), 7.31 (s, 2H, H-3); 13C NMR (75 MHz, CDCl3, d
ppm): 19.6 (C-1), 22.5, 22.6 (Cj,k), 24.6, 27.9, 29.8,
35.5, 37.1, 39.1 (Cb,d,e,f,g,i), 68.6 (Ca), 107.7 (C-3,6),
136.4 (C-1,2), 151.7 (C-4,5); IR (KBr) mmax (cmÀ1):
3072, 2958, 2926, 2870, 2845, 1538, 1221, 1048, 875;
ESI-MS (m/z) 481.4 (M+H)+; Anal. Calcd. for
C26H44N2O6: C, 64.97; H, 9.23; N, 5.83. Found: C,
65.05; H, 9.12; N, 5.86.
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