Synthesis, thermal and photophysical studies of π–extended dibenzophenazine based discotic liquid crystals

Article abstract of DOI:10.1016/j.molliq.2020.114419

Novel π–extended dibenzophenazine based discotic mesogens tethered with alkane thiols and alkoxy phenylacetylene along with alkoxy chains have been designed and synthesised. Molecular structures of all compounds were investigated using spectral and elemen

Full text of DOI:10.1016/j.molliq.2020.114419

Journal of Molecular Liquids 320 (2020) 114419
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Synthesis, thermal and photophysical studies of π–extended
dibenzophenazine based discotic liquid crystals
c,d
Litwin Jacob a,1, Ashwathanarayana Gowda a,1, Sandeep Kumar a,b, , Victor Belyaev
⁎
a
Raman Research Institute, C.V. Raman Avenue, Sadashivanagar, Bangalore 560 080, India
Deparment of Chemistry, Nitte Meenakshi Institute of Technology (NMIT), Yelahanka, Bangalore 560 064, India
Moscow Region State University, Moscow, Russia
b
c
d
RUDN University (People's Friendship University of Russia), Moscow, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 July 2020
Received in revised form 19 September 2020
Accepted 22 September 2020
Available online 28 September 2020
Novel π–extended dibenzophenazine based discotic mesogens tethered with alkane thiols and alkoxy
phenylacetylene along with alkoxy chains have been designed and synthesised. Molecular structures of all com-
pounds were investigated using spectral and elemental analysis. The liquid crystalline properties of all the novel
compounds were characterized using polarised optical microscopy (POM) and differential scanning calorimetry
(DSC). The self-assembly of mesophase structure of discotic mesogens were examined with the help of X-ray dif-
fraction studies. All compounds exhibit stable hexagonal columnar mesophase over broad temperature range.
The photophysical properties of these compounds were studied in anhydrous chloroform solvent at room tem-
perature which exhibit absorption at 446–463 nm and corresponding emission at 578–600 nm. The high delocal-
ization of π–electrons in extended dibenzophenazine discotic mesogens may find potential applications in
devices like, solar cells, sensors, organic light emitting diodes, thin film transistors, etc.
Keywords:
Dibenzophenazine
Discotic liquid crystals
Columnar phase
Sonogashira coupling
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
structures. The self-assembly of discotic mesogens with only orienta-
tional order exhibits discotic nematic (ND) phase. The ND phase is less
Molecular shape anisotropy is among the important key factors
which determine the self-organization of molecules into liquid crystal-
line phases [1,2]. The generation of self-healing and self-aligning ability
of liquid crystals can be easily architecture through nano-segregation of
incompatible molecular subunits driven by the non-covalent weak in-
teractions such as hydrogen bonding, van der Waals forces, π–π interac-
tions, dipole–dipole interaction and charge transfer interactions etc.
[3–7]. They have application potential as novel anisotropic advanced
functional materials for technological devices [8–13]. In this regard,
discotic liquid crystals (DLCs) have been attracted considerable atten-
tion due to the formation of self-assembled ordered columnar struc-
tures [9–16]. The self-assembly of columnar structures is mainly
controlled by the stacking arrangement of disc shape molecules. The
molecular designing of discotic liquid crystals consisting of a flat, rigid
aromatic disc-like π–conjugated structure surrounded by insulating
mantle of flexible aliphatic chains. The formation of columnar structure
is depends on supramolecular interactions of discotic mesogens
[17–20]. They commonly exhibit two general classes of mesophase
commonly observed mesophase structure but it finds immense applica-
tion as an optical compensating film to enlarge wide-viewing angle in
the display devices [21–25]. The self-organized columnar mesophases
are formed when individual anisotropic discotic mesogens stack one
on top of the other to form one–dimensional columnar arrangement
and lattice arrangement of columns defines the subclass of mesophase
structure [26]. The large π–π overlap between adjacent aromatic cores
paves the road map for migration of charges along the columnar axis
[2]. Due to this peculiar behaviour, DLCs have found applications in op-
toelectronic device applications such as organic light emitting diodes
(OLEDs) [27–29], organic field effect transistors (OEFT) [30–33], photo-
voltaic solar cells [34,35] and sensors [36,37].
The presence of heterocyclic core unit in the discotic liquid crystals is
associated with their strong dipole moment, electron deficiency, etc.,
which enhance the electron transport properties for advanced materials
in semiconducting devices. Phenazine based heterocyclic compounds
have found applications in photophysical and biological sciences
[38–40]. The phenazine fused phenanthrene core leads to the construc-
tion of dibenzo[a,c]phenazine heteroaromatic polycyclic compounds.
William et al. reported the tetraalkoxy dibenzophenazine based discotic
liquid crystals containing monomeric acid and ester derivatives. The
monomeric acid derivatives form H-bonded dimers which lead to ellip-
tical shape structure and exhibit hexagonal columnar, rectangular and
⁎
Corresponding author at: Raman Research Institute, C.V. Raman Avenue,
Sadashivanagar, Bangalore 560 080, India.
E-mail address: skumar@rri.res.in (S. Kumar).
Contributed equally to this work.
1
https://doi.org/10.1016/j.molliq.2020.114419
0167-7322/© 2020 Elsevier B.V. All rights reserved.

L. Jacob, A. Gowda, S. Kumar et al.
Journal of Molecular Liquids 320 (2020) 114419
nematic phases over broad temperature [41]. Subsequently, they also
prepared several tetraalkoxydibenzo[a,c]phenazines based DLC deriva-
tives containing electron donating and electron withdrawing functional
groups present at the phenazine ring. Phenazine mesogens with elec-
tron withdrawing functional groups exhibit stable Colh phase over
broad temperature but phenazine ring containing electron donating
groups does not show any liquid crystalline behaviour [42]. Detail
investigations on the position of acid, ester and nitro functional groups
on mesomorphic properties of tetraalkoxydibenzo[a,c]phenazines
have been reported [43]. Further, the dimers of tetraalkoxydibenzo[a,
c]phenazine linking through flexible alkyl chains which self-assemble
one on top of other to form double-decker architecture and exhibit
mesomorphic properties have been realized [44]. Recently, Ong and
co-workers reported the synthesis and mesomorphic properties of
hexaalkoxydibenzo[a,c]phenazines derivatives which exhibit Colh
phase over broad temperature [45]. They also reported synthesis and
thermal properties of non-mesomorphic tetraalkoxydibenzo[a,c]phen-
azines bearing lateral metal free crown ether. However, complexation
of sodium metal crown ether containing tetraalkoxydibenzo [a,c]phen-
azines exhibit a rectangular columnar phase with C2mm symmetry [46].
Paulina and co-workers investigated the gelation and photophysical
properties of monomeric acid and its corresponding monomeric
ester derivatives of dibenzophenazine and diphenylquinoxaline
based DLCs. The acid and ester derivatives of dibenzophenazine ex-
hibit mesomorphic properties, however, the acid and ester deriva-
tives of diphenylquinoxaline do not form LC phase because of
aromatic rings are more flexible. The acid derivatives exhibit gela-
tion properties in nonpolar solvents due to H-bonding [47].
In this article, we report the design and synthesis of some novel π–
extended dibenzophenazine based heterocyclic discotic liquid crystals.
Three series of extended tetraalkoxydibenzo[a,c]phenazines based
DLCs containing a lateral substitution of alkanethiols, symmetrical and
un-symmetrical substitution of 4-alkoxy phenylacetylene groups have
been synthesised and investigated for their liquid crystalline properties.
The intermediate and final compounds exhibit wide range of stable co-
lumnar mesophase. We discuss the synthesis, liquid crystalline charac-
terisation and photophysical properties of extended heterocyclic DLCs.
The molecular structures of intermediate and final compounds were
characterized by spectral and elemental analysis. The mesomorphic
properties were investigated using polarised optical microscopy
(POM), differential scanning calorimetry (DSC). The self-assembly of
mesophase structure was investigated with help of X-ray diffraction
(XRD) studies. The photophysical properties were investigated using
UV–Vis and emission spectroscopy.
molecular structures of all compounds were characterized using IR, 1H
NMR, 13C NMR and elemental analysis.
2.2. Thermal properties
Thermotropic liquid crystalline properties of all intermediate and
final dibenzophenazine DLC derivatives are summarized in Table 1.
The phase transition temperature (peak temperature in °C) and associ-
ated enthalpy (ΔH in kJ mol−1) values obtained from the heating and
subsequent cooling cycles of respective mesogens were determined by
DSC. The columnar textures of mesogens observed using the POM as
shown in Fig. 1.
The intermediate compound 5 was crystalline at room temperature
and melts to mesophase at 103.1 °C along with enthalpy of phase tran-
sition (ΔH) of 45.01 kJ mol−1, which further transferred to isotropic liq-
uid at 150.2 °C (ΔH = 1.93 kJ mol−1). Upon cooling, under POM, the
appearance of mosaic textures revealed the formation of hexagonal co-
lumnar phase at 148.1 °C (ESI, Figs. S1a and S2). The thiol substituted
final mesogenic compounds (6a-6c) exhibit enantiotropic hexagonal
columnar mesophase over broad temperature. Compound 6a, upon
heating melts at 55.1 °C with phase transition enthalpy (ΔH =
62.55 kJ mol−1) to hexagonal columnar phase and become isotropic liq-
uid at 121.1 °C (ΔH = 5.01 kJ mol−1) (ESI, Fig. S3). On cooling from the
isotropic liquid, it exhibits typical textures of Colh phase at 118.4 °C
under POM and become crystals at 24.3 °C (ΔH = −63.26 kJ mol−1in
DSC). As a representative example of POM texture obtained for com-
pounds, 6a is shown in Fig. 1(a). Further, compounds 6b and 6c also ex-
hibit similar trends of phase transitions from crystalline phase to Colh
phase at 77.3 °C (ΔH = 26.46 kJ mol−1) and 100.2 °C (ΔH =
29.25 kJ mol−1) respectively and Colh to isotropic liquid at 135.5 °C
(ΔH = 3.42 kJ mol−1) and 129.2 °C (ΔH = 3.02 kJ mol−1) respectively
(ESI Fig. S4). On cooling from the isotropic liquid, the Colh phase oc-
curred at 132.8 °C (ΔH = −3.50 kJ mol−1) and 126.9 °C (ΔH =
−2.89 kJ mol−1) respectively. The DSC thermogram of representative
compound 6c is shown in Fig. 2a.
The unsymmetrically substituted π–extended dibenzophenazine
based DLCs (7a–7d) exhibit similar trends of phase transition from crys-
talline phase to Colh at lower temperature and Colh phase to isotropic
phase at higher temperature. Compound 7a melts to Colh at 73.7 °C
along phase transition enthalpy 32.88 kJ mol−1 and become isotropic
liquid at 174.7 °C (ΔH = 2.0 kJ mol−1) (ESI Fig. S5). The mesophase tex-
ture was observed upon slow cooling from isotropic liquid at 171.6 °C
(ΔH = −2.0 kJ mol−1). As a representative example of POM texture ob-
tained for compounds, 7a is shown in Fig. 1(b). Compounds 7b
displayed similar phase transition from Cr to Colh at 71.9 °C (ΔH =
25.63 kJ mol−1) and Colh to isotropic phase at 152.4 °C (ΔH =
0.92 kJ mol−1) (ESI Fig. S6). The appearance of columnar texture was
observed under POM at 148.9 °C (ΔH = −0.96 kJ mol−1) (on cooling)
and become crystal phase at 14 °C (ESI Fig. S1b). The higher homologue,
compound 7c, having tetradecane alkyl chain shows monotropic phase
transition. Upon heating, compound 7c directly transferred into isotro-
pic phase at 79.6 °C (ΔH = 28.08 kJ mol−1) (ESI Fig. S7), whereas
upon cooling, dendritic textures were observed under POM at 62 °C as
shown in ESI Fig. S1c. The phase transition from isotropic phase to
Colh phase occurred at 79.5 °C (ΔH = −0.35 kJ mol−1). Compound 7d
with branched alkyl chains displayed Cr to Colh phase transition at
59.3 °C (ΔH = 25.33 kJ mol−1), which further become clear liquid at
146.3 °C (ΔH = 1.18 kJ mol−1) (ESI Fig. S8). On slow cooling from the
isotropic liquid, under POM, show appearance of dendritic textures at
143.4 °C (ΔH = −1.14 kJ mol−1).
2. Results and discussion
2.1. Synthesis and characterisation
The synthetic plan of novel dibenzophenazine based DLCs is shown
in Scheme 1. The 1,2-bis(3,4-bis(dodecylperoxy)phenyl)ethane-1,2-
dione intermediate 2 was synthesised following reported procedure
[48] and it was condensed with 4,5-dibromobenzene-1,2-diamine 3
[49] in presence of glacial acetic acid under reflux condition affording
tetraalkoxy substituted dibromoquinoxaline compound 4. An intramo-
lecular Scholl reaction was carried in presence of iron (III) chloride to
furnish the tetraalkoxy substituted dibromo-dibenzophenazine key
intermediate 5. The reaction of alkanethiols with 5 in presence of
cesium carbonate gives thiolated tetraalkoxydibenzo[a,c]phenazines
(6a–6c) DLCs. Further, Sonagashira coupling reaction of intermedi-
ate 5 with 4-alkoxy phenylacetylene [50] in presence of bis
(triphenylphosphine)palladium chloride (PdCl2(PPh3)2) and copper
iodide (CuI) gives final π–extended dibenzophenazine based DLCs
compounds (7a–7d and 8a–8c). All intermediate and final compounds
were purified by column chromatography and recrystallized from ap-
propriated solvent to ensure maximum purity of the compounds. The
The symmetrically substituted π–extended dibenzophenazine based
DLCs (8a–8c) also exhibit hexagonal columnar mesophase over broad
temperature. Compounds 8a and 8b displayed Cr to Colh phase at
82.1 °C (ΔH = 30.38 kJ mol−1) and 77.2 °C (ΔH = 29.37 kJ mol−1) re-
spectively, which further transferred to the isotropic liquid at 181.1 °C
(ΔH = 0.59 kJ mol−1) and 164.9 °C (ΔH = 0.94 kJ mol−1) respectively
2

L. Jacob, A. Gowda, S. Kumar et al.
Journal of Molecular Liquids 320 (2020) 114419
Scheme 1. (i) Oxalyl chloride, anhy. AlCl3, DCM, r.t, 12 h; (ii) glacial acetic acid, reflux, 6 h; (iii) FeCl3, r.t, 6 h; (iv) alkanethiol, Cs2CO3, DMAC, reflux, 24 h; (v) & (vi) 1-ethynyl-4-
alkoxybenzene, PdCl2(PPh3)2, CuI, TEA, reflux, 24 h.
(ESI Fig. S9). On slow cooling, they displayed columnar texture under
POM at 178.2 °C (ΔH = −0.45 kJ mol−1) and 161.5 °C (ΔH =
−0.89 kJ mol−1), respectively. A representative DSC thermogram of
compound 8b is shown in Fig. 2(b). Similarly, compound 8c undergoes
Cr to Colh phase at 60.1 °C (ΔH = 22.52 kJ mol−1) and become clear liq-
uid at 158.9 °C (ΔH = 0.59 kJ mol−1) (ESI Fig. S10). On slow cooling
under POM show the appearance of dendritic textures at 153.9 °C
(ΔH = −0.57 kJ mol−1) and crystallize at around room temperature
30.5 °C (ΔH = −21.72 kJ mol−1) (ESI Fig. S1d). The thiolalkyl
substituted dibenzophenazine derivatives exhibit mesophase to iso-
tropic phase transition at low temperature. However, symmetrical
and unsymmetrical substituted π–extended dibenzophenazine hav-
ing large core size exhibit mesophase to isotropic phase transition at
high temperature. This implies that increasing core size leads to a
greater propensity to form stable columnar mesophase, which is
consistent with the literature report that larger discotic mesogens
tend to form liquid crystal phases over broad temperature [51–54].
Willams et al. reported that the addition of electron-withdrawing
groups should lead to an increase in the molecular dipole moment,
which will favor the antiparallel orientation of adjacent molecules
within the columns. In our case, the dibenzophenazine derivatives
containing alkoxy chains and thioalkyl chains exhibit stable colum-
nar phase where discotic cores are self-assemble into parallel ar-
rangement [42].
Table 1
Phase transition temperature obtained from DSC (peak in DSC °C) and enthalpies
(kJ mol−1, in parentheses) of all the mesogens 5, 6a–6c, 7a–7d and 8a–8c (on heating
and cooling cycle). Cr = crystallinephase; Colh = hexagonal columnar phase; I = isotropic
phase.
Compound Phase transition peak temperature (°C); (ΔH, [kJ mol−1])
2.3. X-ray diffraction measurements
Second heating scan
Second cooling scan
The supramolecular self-assembly of dibenzophenazine based DLCs
is investigated by X-ray diffraction studies using mesogenic compounds
filled in a Lindemann capillaries. X-ray diffraction patterns were re-
corded for all the mesogens in the columnar mesophase both heating
and subsequent cooling scan as shown in Fig. 3 and ESI Fig. S11. The dif-
fraction parameters are summarized in Table 2. The mesogenic deriva-
tives (5, 6a–6c, 7a–7d & 8a–8c) exhibit increasing order of diffraction
angle along with d-spacings of the highest intensity peak in the small
angle region to the second one are in the ratio of 1:1/√3:1/2 respectively.
These d-spacing values are obtained for the occurrence of hexagonal
5
Cr 103.1 [45.01] Colh 150.2 [1.93] I I 148.1 [−1.87] Colh 74.1 [−42.29] Cr
Cr 55.1 [62.55] Colh 121.1 [5.01] I I 118.4 [−4.85] Colh 24.3 [−63.26] Cr
Cr 77.3 [26.46] Colh 135.5 [3.42] I I 132.8 [−3.50] Colh 45.32 [−27.27] Cr
Cr 100.2 [29.25] Colh 129.2 [3.02] I I 126.9 [−2.89] Colh 67.6 [−32.91] Cr
Cr 73.7 [32.88] Colh 174.7 [2.0] I I 171.6 [−2.0] Colh 9.7 [−18.12] Cr
Cr 71.9 [25.63] Colh 152.4 [0.92] I I 148.9 [−0.96] Colh 14.4 [−20.28] Cr
6a
6b
6c
7a
7b
7c
7d
8a
8b
8c
Cr 79.6 [28.08] I
I 79.5 [−0.35] Colh 39.6 [−29.38] Cr
Cr 59.3 [25.33] Colh 146.3 [1.18] I I 143.4 [−1.14] Colh 18.6 [−23.52] Cr
Cr 82.1 [30.38] Colh 181.1 [0.59] I I 178.2 [−0.45] Colh 55.4 [−32.38] Cr
Cr 77.2 [29.37] Colh 164.9 [0.94] I I 161.5 [−0.89] Colh 44.5 [−28.82] Cr
Cr 60.1 [22.52] Colh 158.9 [0.59] I I 153.9 [−0.57] Colh 30.5 [−21.72] Cr
3

L. Jacob, A. Gowda, S. Kumar et al.
Journal of Molecular Liquids 320 (2020) 114419
Fig. 1. Polarised optical micrographs taken in the hexagonal columnar phase, upon cooling from the isotropic melt. (a) Compound 6a, recorded at 109 °C, viewed at 200× magnifications.
(b) Compound 7a, recorded at 157 °C, viewed at 200× magnifications.
columnar phase. In the wide angle regime, a diffuse peak responsible for
the packing arrangement of flexible molten aliphatic chains and a weak
peak in the wide-angle region is responsible for distance between
discotic cores in the columns. The distance between adjacent columns
in the mesophase was calculated using the relation a = d10/(cos30°),
where d10 is the d-spacing of highest intensity peak occurred in the
small angle regime is shown in Table 2. The XRD pattern obtained for in-
termediate compound 5 in the columnar phase as shown in Fig. 3a (on
heating). In the small angle region, three reflections are observed with
substituted unsymmetrical tetraalkoxy dibenzophenazine DLCs
(7a-7d) exhibit similar X-ray diffraction patterns. A representative X-
ray diffraction pattern obtained for compound 7a, recorded at 120 °C
in columnar phase upon cooling from isotropic liquid, is shown in
Fig. 3c. The X-ray diffractogram shows several diffraction peaks in the
small angle regions with d-spacings of d1 = 23.51 Å, d2 = 13.56 Å and
d3 = 11.73 Å along with lattice parameter a = 27.14 Å which implies
the occurrence of hexagonal columnar phase. The broad diffused peak
at d = 4.58 Å corresponds to packing arrangement of flexible aliphatic
chains. The weak peak in wide angle region at d = 3.47 Å is attributed
to the core-core separation in the columns. The intercolumnar distance
between neighbouring columns is found to be 27.14 Å. Further, similar
diffraction pattern observed for the symmetrical substituted 4-alkoxy
phenylacetylene substituted tetraalkoxy dibenzophenazine DLCs
(8a–8c). As a representative X-ray diffractogram, recorded for 8c com-
pound at 110 °C upon heating in the mesophase, is shown in Fig. 3d.
In the small angle region three prominent diffraction peaks were ob-
corresponding d-spacings of d1 = 22.31 Å, d2 = 12.81 Å and d3
=
11.34 Å with increasing order of diffraction angle. These values confirm
the occurrence of two-dimensional hexagonal columnar phase and the
calculated lattice parameter, a, is found to be 25.76 Å at 120 °C. The
broad halo peak (d = 4.35 Å) in the wide-angle region obtained for
the packing arrangement of molten aliphatic chains. The intercolumnar
distance is estimated to be a = 25.76 Å (Fig. 3a) (Table 2). Similarly, the
powder XRD pattern was recorded for alkyl thiol substituted
tetraalkoxy dibenzophenazine DLCs (6a–6c). A representative and typ-
ical XRD pattern recorded for compound 6c in the columnar phase at
90 °C upon cooling from isotropic liquid is shown in Fig. 3b. The diffrac-
tion peaks observed in the small angle region with decreasing order of
d-spacings d1 = 24.73 Å, d2 = 14.33 Å and d3 = 12.41 Å along with lat-
tice parameter a = 28.55 Å corresponds to the two-dimensional hexag-
onal columnar mesophase. The diffused peaks observed at wide angle
region d = 4.55 Å corresponding to packing of aliphatic chains and
weak peak at d = 3.46 Å corresponds to core-core separation. The
distance between adjacent columns is found to be a = 28.55 Å. The
XRD pattern and corresponding lattice parameters were shown in ESI
Fig. S11 and Table 2, respectively. The 4-alkoxy phenylacetylene
served with d-spacing's of d1 = 26.48 Å, d2 = 15.28 Å and d3
=
13.25 Å along with lattice constant a = 30.57 Å which are expected
from a two dimensional hexagonal columnar phase. The weak peak at
wide angle regime with d = 3.50 Å suggests the core-core separation
in the columns. The intercolumnar distance between adjacent columns
is estimated to be 30.57 Å. The above X-ray diffraction investigations re-
veal that all the discotic mesogens (5, 6a-c, 7a-7d & 8a-8c) exhibit self-
assembled hexagonal columnar mesophase structure where disc shape
mesogens are stacked one on top of the other to form columns sur-
rounding by flexible aliphatic chains. It is apparent that the
intercolumnar distance between adjacent columns varies depending
on the central core structure and length of flexible chains.
Fig. 2. DSC thermograms of (a) compound 6c and (b) compound 8b.
4

L. Jacob, A. Gowda, S. Kumar et al.
Journal of Molecular Liquids 320 (2020) 114419
Fig. 3. XRD profiles showing the intensity against the 2θ recorded in the Colh phase upon cooling from isotropic liquid. (a) Compound 5, recorded at 120 °C. (b) Compound 6c, recorded at
90 °C. (c) Compound 7a, recorded at 120 °C. (d) Compound 8c, recorded at 110 °C.
2.4. Photophysical and self assemble properties
absorption properties of all the mesogens were investigated using chlo-
roform (10−5 M) solvent at ambient temperature to know absorption
maxima as presented in Fig. 4 and corresponding absorption values
are summarized in the Table 3. All the mesogens exhibit absorption
All the discotic mesogens (6a–6c, 7a–7d and 8a–8c) exhibit strong
absorption and photo induced light emission properties. The UV–vis
Table 2
XRD data of discotic mesogens (5, 6a-c, 7a-7d & 8a-8c). The upper script a = on heating scan and b = on cooling scan.
Compound
Temperature
(°C)a/b
2θ (degrees)
d-Spacings/Å observed
(calculated)
Miller
indexes
Phase/lattice
constant
Alkyl-chain
length (Å)
Core-core
separation (Å)
Intercolumnar
distance (a) (Å)
5
120a
115b
85a
3.96
6.90
7.79
3.80
6.56
7.58
3.70
6.40
7.40
3.56
6.16
7.11
3.75
6.50
7.53
3.67
6.37
7.35
3.59
6.24
7.21
3.59
6.24
7.21
3.56
6.22
7.19
3.41
5.90
6.82
3.33
5.77
6.66
22.31 (22.30)
12.81 (12.88)
11.34 (11.15)
23.26 (23.25)
13.46 (13.42)
11.66 (11.62)
23.91 (23.90)
13.79 (13.80)
11.93 (11.95)
24.73 (24.72)
14.33 (14.27)
12.41 (12.36)
23.51 (23.50)
13.56 (13.57)
11.73 (11.75)
24.06 (24.05)
13.84 (13.89)
12.03 (12.02)
24.55 (24.54)
14.15 (14.17)
12.24 (12.27)
24.60 (24.59)
14.15 (14.20)
12.24 (12.29)
24.73 (24.72)
14.19 (14.27)
12.27 (12.36)
25.87 (25.86)
14.95 (14.93)
12.94 (12.93)
26.48 (26.47)
15.28 (15.28)
13.25 (13.23)
100
110
200
100
110
200
100
110
200
100
110
200
100
110
200
100
110
200
100
110
200
100
110
200
100
110
200
100
110
200
100
110
200
Colh
a = 25.76
4.35
4.47
4.50
4.55
4.58
4.40
4.45
4.63
4.52
4.65
4.84
3.50
3.48
3.43
3.46
3.47
3.48
3.51
3.46
3.50
3.48
3.50
25.76
26.85
27.60
28.55
27.14
27.78
28.34
28.40
28.55
29.87
30.57
6a
6b
6c
7a
7b
7c
7d
8a
8b
8c
Colh
a = 26.85
Colh
a = 27.60
90b
Colh
a = 28.55
120b
110b
65a
Colh
a = 27.14
Colh
a = 27.78
Colh
a = 28.34
110a
100b
100a
110a
Colh
a = 28.40
Colh
a = 28.55
Colh
a = 29.87
Colh
a = 30.57
5

L. Jacob, A. Gowda, S. Kumar et al.
Journal of Molecular Liquids 320 (2020) 114419
Table 3
bands below 463 nm. The alkylthiol substituted dibenzophenazine
compounds (6a–6c) exhibit absorption bands at λmax = 451 nm.
Similarly, the unsymmetrical substituted phenylacetylene based
dibenzophenazine derivatives (7a–7d) show maximum absorption
band at λmax = 447 nm and symmetrical substituted phenylacetylene
based dibenzophenazine derivatives (8a–8c) exhibit absorption at
longer wavelength at λmax = 463 nm. The highly π-conjugated elec-
tronic systems and π–π* transitions in the dibenzophenazine
heteroaromatic core, extended alkoxy phenylacetylene rings and the
high molar absorption coefficients (ε = 2–2.77 × 106 L mol−1 cm−1
for compounds (6a–6c), ε = 1.98–3.69× 106 L mol−1 cm−1 for
compounds (7a–7d) and ε = 2.95–3.70 × 106 L mol−1 cm−1 for com-
pounds (8a-8c)), are attributed to the maximum absorption in these
π-extended dibenzophenazine based discotic liquid crystals. Generally,
the extent of light absorption and intensity of the peaks in the absorp-
tion spectrum largely relay on the number of molecules that absorb
light of a given wavelength. It is also known that extended conjugation
in symmetrical substitution of 4-alkoxy phenylacetylene substituted
phenazine derivatives (8a-8c) causes bathochromic shift (longer wave-
length) with respect to the unsymmetrical substituted 4-alkoxy
phenylacetylene derivatives (7a–7d) and alkylthiol substituted
dibenzophenazine compounds (6a–6c). Similarly, photoluminescence
emission studies of all the mesogens (6a–6c, 7a–7d & 8a–8c) were re-
corded using dilute solution of anhydrous chloroform solvent at ambi-
ent temperature. The dilute solutions of discotic mesogens were
excited at 450 nm and corresponding emission behaviour is shown in
Fig. 4. The thiol substituted discotic mesogens exhibit emission proper-
ties around 578–580 nm while symmetrical and unsymmetrical phena-
zine derivatives exhibit high emission properties around 597–600 nm
(Table 3).
The photophysical properties of discotic mesogens (6a–6c, 7a–7d & 8a–8c) recorded in
anhydrous chloroform solvent (10−5 M).
Compound
Absorption (λmax/nm) (ε/106 L mol−1 cm−1
)
Emission/nm
6a
6b
6c
7a
7b
7c
7d
8a
8b
8c
450 (2.0)
578
580
580
601
599
597
599
600
599
600
451 (2.35)
450 (2.77)
447 (2.83)
446 (1.98)
446 (3.69)
447 (3.77)
462 (3.70)
463 (3.41)
463 (2.95)
(6a–6c, 7a–7d and 8a–8e) were subjected to
a
heat scan of
10 °C min−1 under a nitrogen atmosphere. The discotic mesogens
(6a–6c) were thermally stable till 330 °C and initiated weight loss at
about 330 °C–340 °C and decomposes at 485 °C. Similarly, symmetrical
and unsymmetrical substituted phenazine discotic mesogens (7a–7d &
8a–8c) were thermally stable upto 355 °C and initiated weight loss
around 360–370 °C and decomposes at 510 °C. The decomposition tem-
perature of π–extended discotic mesogens are greater than correspond-
ing thiol substituted compounds. The results reveal that thermal
stability of π–extended symmetrical and asymmetrical phenazine
discotic (7a–7d & 8a–8c) is higher in comparison to thiol substituted
discotic mesogens (6a–6c) (Fig. 5). All the novel mesogens exhibit
higher thermal stability than their isotropic temperature.
4. Experimental section
3. Thermogravimetric analysis
The intermediate compounds 4,5-dibromobenzene-1,2-diamine (3)
and 1-ethynyl-4-alkoxybenzene were synthesised as reported [49,50]
and confirmed by spectral and elemental analysis.
The thermal stability of novel discotic mesogens was investigated by
thermogravimetric analysis (TGA) as shown in Fig. 5. All the samples
Fig. 4. (a) and (b) UV–Vis absorption spectra; (c) and (d) photoluminescence emission spectra of discotic mesogens (6a–6c, 7a–7d & 8a–8c).
6

L. Jacob, A. Gowda, S. Kumar et al.
Journal of Molecular Liquids 320 (2020) 114419
Fig. 5. Thermogravimetric analysis of compounds (6a–6c, 7a–7d & 8a–c).
4.1. Synthesis of 1,2-bis(3,4-bis(dodecyloxy)phenyl)ethane-1,2-dione (2)
4.3. Synthesis of 11,12-dibromo-2,3,6,7-tetrakis(dodecyloxy)dibenzo[a,c]
phenazine (5)
To a suspension of anhydrous aluminium chloride (0.29 g,
2.23 mmol) and 1,2-bis(dodecyloxy)benzene (2 g, 4.47 mmol) in dry di-
chloromethane (DCM) solvent (30 mL) under stirring, was added drop
wise solution of oxalyl chloride (0.34 g, 2.68 mmol) in dry DCM solvent
(10 mL) at 0 °C under nitrogen atmosphere. The resulting reaction mix-
ture was stirred at the same temperature for 30 min and slowly allowed
to room temperature for overnight. The reaction was quenched with
To a suspension of iron chloride (0.68 g, 4.24 mmol) in DCM solvent
(20 mL) under stirring was added dropwise solution of compound 4
(1 g, 0.84 mmol) in DCM solvent (10 mL) at 0 °C under nitrogen atmo-
sphere [56]. The reaction mixture was stirred at ambient temperature
for 30 min. The reaction mixture was quenched with methanol and
water. The resulting reaction mixture was extracted with DCM solvent
(3 × 20 mL). The organic layer was dried over Na2SO4 and concentrated
under reduced pressure. The crude compound was purified by column
chromatography using silica gel (n-hexane: ethyl acetate, 7:3) gives de-
sired compound 5. Yield: 80%. IR (film) υmax: 2926, 2914, 2895, 1606,
1
M aqueous HCl solution and extracted with DCM solvent
(3 × 20 mL). The combined extract was dried over sodium sulphate
(Na2SO4) and concentrated under reduced pressure. The crude
compound was purified by column chromatography over silica gel
(n-hexane: ethyl acetate, 9:1) and recrystallization with ethanol that
gives pure compound 2 (Yield: 50%). IR (film) υmax: 2918, 2906, 2852,
1454, 1377, 1271, 1168, 1072, 721 cm−1 1H NMR (500 MHz, CDCl3):
;
δ = 8.45 (br, 4H), 7.49 (s, 2H), 4.15 (t, J = 6 Hz, 8H), 1.90 (t, J =
6.5 Hz, 8H),1.61–1.52 (m, 8H), 1.61–1.20 (m, 64H), 0.80 ppm (t, J =
6.5 Hz, 12H); 13C NMR (125 MHz, CDCl3): δ = 152.09, 149.27, 142.36,
140.37, 132.89, 126.69, 124.79, 122.97, 108.55, 105.92, 69.46, 69.07,
31.95, 30.90, 29.78, 29.77, 29.75, 29.74, 29.71, 29.59, 29.40, 29.37,
26.24, 26.21, 22.70, 14.10 ppm, elemental analysis: C68H106N2Br2O2, cal-
culated: C, 69.49; H, 9.09; N, 2.38. % found: C, 69.37; H, 8.95; N, 2.26. 1H
and 13C NMR spectra are shown in the ESI, Fig. S14.
1664, 1583, 1462, 1377, 1265, 1074, 723 cm−1 1H NMR (500 MHz,
;
CDCl3): δ = 7.56 (s, 2H), 7.42 (d, 2H, J = 8.5 Hz), 6.84 (d, 2H, J = 8 Hz),
4.05 (t, 8H, 6 Hz), 1.83 (br, 8H), 1.46 (br, 8H), 1.35–1.26 (m, 64H),
0.88 ppm (t, 12H, J = 7 Hz); 13C NMR (125 MHz, CDCl3): δ = 193.78,
155.01, 149.33, 126.24, 126.09, 112.40, 111.65, 69.27, 69.14, 31.92,
29.70, 29.67, 29.65, 29.62, 29.58, 29.39, 29.36, 29.09, 28.94, 26, 25.93,
22.68, 14.10 ppm, elemental analysis: C62H106O6, calculated: C, 78.59; H,
11.28. % found: C, 78.48; H, 11.09. 1H and 13C NMR spectra are shown in
the ESI, Fig. S12.
4.4. Synthesis of 2,3,6,7-tetrakis(dodecyloxy)-11,12-bis(alkylthio)dibenzo
[a,c]phenazine (6a–6c)
4.2. Synthesis of 2,3-bis(3,4-bis(dodecyloxy)phenyl)-6,7-dibromoquinoxaline
(4)
To a solution of intermediate compound 5 (0.5 g, 1 equiv) and
anhydrous cesium carbonate (5 equiv) in dry N, N-dimethylacetamide
solvent (DMAc) (20 mL) under stirring was added alkanethiol
(2.2 equiv). The resulting reaction mixture was refluxed for 24 h. After
cooling to room temperature, ice cold water was added and extracted
with DCM solvent (3 × 20 mL). The combined extracts were dried
over Na2SO4 and concentrated under reduced pressure gives crude
compound. The residue was purified by column chromatography
using silica gel (n-hexane/DCM 9:1) which affords pure compound. Re-
crystallization of the pure product with cold ethanol gives final desired
compound (6a–6c) in about 65% yield.
A mixture of compound 2 (1 g, 1.05 mmol) and 4,5-dibromobenzene-
1,2-diamine 3 (0.28 g, 1.06 mmol) in glacial acetic acid (20 mL) was
refluxed for overnight under nitrogen atmosphere [55]. After the comple-
tion of reaction, the reaction mixture was poured into ice cold water and
extracted with DCM (3 × 20 mL). The organic layer was dried over Na2SO4
and concentrated under reduced pressure. The crude compound was pu-
rified by column chromatography using silica gel (n-hexane: ethyl
acetate, 7:3) and recrystallization with ethanol to give pure compound
(3). Yield: 85%. IR (film) υmax: 2949, 2920, 2899, 1600 1518, 1454, 1377,
1269, 1139, 721 cm−1 1H NMR (500 MHz, CDCl3): δ = 8.42 (s, 2H),
;
7.08 (m, 4H), 6.82 (d, J = 8.5 Hz, 2H), 3.99 (t, J = 6.5 Hz, 4H), 3.82 (t,
J = 6.5 Hz, 4H), 1.84–1.82 (m, 4H), 1.80–1.69 (m, 4H), 1.47–1.26 (m,
72H), 0.88 ppm (t, J = 6 Hz, 12H); 13C NMR (125 MHz, CDCl3): δ =
154.27, 150.33, 148.76, 140.23, 133, 131.06, 125.72, 122.92, 115.22,
113.06, 69.22, 69.18, 31.94, 31.80, 30.89, 30.04, 29.77, 29.71, 29.68,
29.66, 29.47, 29.43, 29.40, 29.38, 29.23, 29.15, 26.35, 26.04, 22.83, 22.70,
22.56, 14.11 ppm, elemental analysis: C68H108N2Br2O6, calculated: C,
69.37; H, 9.25; N.2.38. % found: C, 69.21; H, 9.05; N. 2.21. 1H and 13C
NMR spectra are shown in the ESI, Fig. S13.
4.4.1. 2,3,6,7-Tetrakis(dodecyloxy)-11,12-bis(hexylthio)dibenzo[a,c]phen-
azine (6a)
IR (film) υmax: 2953, 2922, 2852, 1608, 1508, 1454, 1377, 1271,
1166, 771 cm−1; 1H NMR (500 MHz, CDCl3): δ = 8.63 (s, 2H), 7.90 (s,
2H), 7.62 (s, 2H), 4.25 (br, 4H), 4.18 (br, 4H), 3.11 (t, J = 7 Hz, 4H),
1.89 (br, 8H), 1.78–1.19 (br, 88H), 0.80 ppm (t, J = 6.5 Hz, 18H); 13
C
NMR (125 MHz, CDCl3): δ = 151.58, 149.44, 141.12, 140.19, 140.03,
129.46, 126.65, 126.33, 124.28, 123.89, 108.53, 106.48, 69.65, 69.15,
33.42, 32.60, 31.94, 31.42, 31.38, 30.90, 30.01, 29.75, 29.71, 29.70,
7

L. Jacob, A. Gowda, S. Kumar et al.
Journal of Molecular Liquids 320 (2020) 114419
29.55, 29.43, 29.39, 28.84, 28.70, 28.63, 28.25, 26.22, 26.18, 22.70, 22.55,
14.11, 14.04 ppm; elemental analysis: C80H132N2O4S2, calculated: C,
76.87; H, 10.64; N, 2.24; S, 5.13, % found: C, 76.77; H, 10.56; N, 2.31; S,
4.91. 1H and 13C NMR spectra are shown in the ESI, Fig. S15.
106.05, 96.12, 87.13, 69.51, 69.08, 67.84, 31.95, 31.26, 29.78, 29.72,
29.60, 29.41, 26.24, 26.21, 22.70, 19.25, 14.11, 13.85 ppm; elemental
analysis: C80H119N2BrO5, calculated: C, 75.73; H, 9.45; N,2.21. % Found:
C, 75.66; H, 9.36, 2.29. 1H and 13C NMR spectra are shown in the ESI,
Fig. S18.
4.4.2. 2,3,6,7-Tetrakis(dodecyloxy)-11,12-bis(octylthio)dibenzo[a,c]phen-
azine (6b)
4.5.2. 11-Bromo-2,3,6,7-tetrakis(dodecyloxy)-12-((4-(octyloxy)phenyl)
ethynyl)dibenzo[a,c]phenazine (7b)
IR (film) υmax: 2953, 2920, 2852, 1608, 1504, 1462, 1377, 1271,
1166, 767 cm−1; 1H NMR (500 MHz, CDCl3): δ = 8.65 (s, 2H), 7.92 (s,
2H), 2 (s, 2H), 4.27 (br, 4H), 4.19 (br, 4H), 3.13 (t, J = 7 Hz, 4H), 1.89
(br, 8H), 1.79–1.20 ppm (m, 96H), 0.80 (m, 18H); 13C NMR (125 MHz,
CDCl3): δ = 151.61, 149.46, 141.17, 140.23, 140.07, 126.35, 124.34,
123.92, 108.56, 106.53, 69.66, 69.17, 33.45, 31.94, 31.82, 30.91, 29.75,
29.69, 29.54, 29.42, 29.3929.20, 29.19, 29.17, 28.29, 26.21, 26.18,
22.69, 14.11, 14.09 ppm; elemental analysis: C84H140N2O4S2, calculated:
C, 77.24; H, 10.80; N, 2.14; S, 4.91, % Found: C, 77.34; H, 10.96; N, 2.23; S,
5.06. 1H and 13C NMR spectra are shown in the ESI, Fig. S16.
IR (film) υmax: 2953, 2922, 2852, 2210, 1606, 1511, 1456, 1375,
1271, 1166, 771, 721 cm−1; 1H NMR (500 MHz, CDCl3): 8.38–8.33 (m,
3H), 8.22 (s, 1H), 7.58 (d, J = 7 Hz, 2H), 7.37 (br, 2H), 6.91 (d, J =
7 Hz, 2H), 4.21 (br, 8H), 3.99 (br, 2H), 1.96 (br, 8H), 1.81–1.28 (m,
84H), 0.86 ppm (br, 15H); 13C NMR (125 MHz, CDCl3): δ = 159.80,
151.89, 151.78, 149.15, 149.10, 142.16, 141.87, 140.95, 139.82, 133.35,
132.65, 131.92, 126.57, 126.38, 125.71, 124.82, 123.13, 123.03, 114.73,
114.68, 108.48, 105.81, 105.68, 87.17, 69.42, 69.38, 69.03, 68.17, 31.96,
31.84, 29.80, 29.74, 29.71, 29.65, 29.43, 29.26, 29.24, 26.27, 26.23,
26.06, 22.71, 22.68, 14.12 ppm; elemental analysis: C84H127N2BrO5,
calculated: C, 76.15; H, 9.66; N, 2.11. % Found: C, 76.26; H, 9.78, N,
2.23. 1H and 13C NMR spectra are shown in the ESI, Fig. S19.
4.4.3. 2,3,6,7-Tetrakis(dodecyloxy)-11,12-bis(dodecylthio)dibenzo[a,c]
phenazine (6c)
IR (film) υmax: 2953, 2918, 2850, 1608, 1510, 1462, 1377, 1271,
1166, 1074, 721 cm−1 1H NMR (500 MHz, CDCl3): δ = 8.67 (s, 2H),
;
4.5.3. 11-Bromo-2,3,6,7-tetrakis(dodecyloxy)-12-((4-(tetradecyloxy)phe-
nyl) ethynyl)dibenzo[a,c]phenazine (7c)
7.94 (s, 2H), 7.67 (s, 2H), 4.28 (br, 4H), 4.20 (br, 4H), 3.14 (t, J =
6.5 Hz, 4H), 1.89 (br, 8H), 1.81–1.19 (m, 112H), 0.80 ppm (br, 18H);
13C NMR (125 MHz, CDCl3): δ = 151.85, 151.60, 149.27, 141.83,
141.25, 140.58, 139.47, 132.06, 131.22, 130.39, 126.66, 126.16, 123.49,
108.59, 106.08, 69.52, 69.12, 69.03, 33.17, 29.78, 29.61, 29.41, 27.85,
22.71, 14.11 ppm; elemental analysis: C92H156N2O4S2, calculated: C,
77.91; H, 11.09; N, 1.98; S, 4.52, % Found: C, 77.79; H, 11.25; N, 2.18; S,
4.65. 1H and 13C NMR spectra are shown in the ESI, Fig. S17.
IR (film) υmax: 2953, 2920, 2866, 2216, 1606, 1506, 1456, 1377,
1271, 1168, 771, 721 cm−1; 1H NMR (500 MHz, CDCl3): 8.53–8.49 (br,
2H), 8.43 (s, 1H), 8.34 (s, 1H), 7.58 (d, J = 8 Hz, 2H), 7.51 (Br, 2H),
6.92 (d, J = 8 Hz, 2H), 4.25 (br, 8H), 3.99 (t, J = 6 Hz, 2H), 2.01–1.93
(m, 8H), 1.84–1.27 (m, 96H), 0.88 ppm (t, J = 6.5 Hz, 15H); 13C NMR
(125 MHz, CDCl3): δ = 159.82, 152, 151.89, 149.25, 142.04, 141.07,
139.95, 133.36, 132.68, 131.98, 126.70, 126.50, 125.88, 124.98, 123.27,
123.19, 114.68, 114.68, 108.57, 106.06, 96.13, 87.13, 69.48, 69.07,
68.18, 31.95, 29.78, 29.72, 29.61, 29.41, 29.37, 29.23, 26.24, 26.05,
22.70, 14.11 ppm; elemental analysis: C90H139N2BrO5, calculated: C,
4.5. Synthesis of symmetrical and unsymmetrical dibenzophenazine based
discotic mesogen (7a–7d and 8a–8c)
76.72; H, 9.94; N,1.99. % Found: C, 76.84; H, 10.10; N, 2.13. 1H and 13
NMR spectra are shown in the ESI, Fig. S20.
C
All the final discotic mesogens were obtained by Sonogashira
C\\C bond coupling reaction between 11,12-dibromo-2,3,6,7-
tetrakis(dodecyloxy)dibenzo[a,c]phenazine (5) with 1-ethynyl-4-
alkoxybenzene in the presence of PdCl2(PPh3)2 and CuI in anhydrous
triethylamine solvent [57,58]. The general method is described as
follows.
4.5.4.
2,3,6,7-tetrakis(dodecyloxy)dibenzo[a,c]phenazine (7d)
IR (film) υmax: 2951, 2922, 2852, 2210, 1608, 1506, 1456, 1375,
1271, 1168, 771, 721 cm−1 1H NMR (500 MHz, CDCl3): 8.40 (s, 1H),
11-Bromo-12-((4-((3,7-dimethyloctyl)oxy)phenyl)ethynyl)-
;
To a mixture of bis(triphenylphosphine) palladium dichloride
(0.04 eq.) and CuI (0.06 eq.) was added compound 5 (0.5 g, 1 eq.) in an-
hydrous triethylamine solvent under nitrogen atmosphere and allowed
to stir at room temperature for 10 min. To the above reaction mixture, 1-
ethynyl-4-(alkoxy)benzene (1.2 eq.) in anhydrous triethylamine was
added under nitrogen flow. The resulting reaction mixture was heating
to 75 °C for 24 h. The residue was diluted with diethyl ether and filtered
through celite pad. The filtrate was washed with water and then ex-
tracted with diethyl ether (3 × 40 mL). The combined extracts were
dried over Na2SO4 and concentrated under reduced pressure. The
crude compound was purified by column chromatography using silica
gel (hexane: ethylacetate 8:2) gives desired compound 7a–7d. Simi-
larly, symmetrical discotic mesogens (8a–8c) were obtained by using
compound 5 (0.5 g, 1 eq.), PdCl2(PPh3)2 (0.08 eq.), CuI (0.09 eq.) and
1-ethynyl-4-(alkoxy)benzene (2.5 eq.) respectively.
8.37 (s, 1H), 8.31 (s, 1H), 8.23 (s, 1H), 7.51 (d, J = 7.5 Hz, 2H), 7.38
(br, 2H), 6.85 (d, J = 7.5 Hz, 2H), 4.16 (m, 8H), 3.97 (br, 2H), 1.90 (m,
8H), 1.8–1.2 (m, 82H), 0.90 (d, J = 6 Hz, 3H), 0.81 ppm (br, 18H); 13
C
NMR (125 MHz, CDCl3): δ = 159.80, 151.98, 151.87, 149.26, 149.22,
142.30, 142.01, 141.06, 139.93, 133.36, 132.69, 131.98, 126.68, 126.48,
125.85, 124.94, 126.26, 123.16, 114.69, 108.58, 106, 105.89, 96.11,
87.14, 69.49, 69.45, 69.07, 66.51, 39.27, 37.33, 36.15, 31.96, 29.90,
29.78, 29.75, 29.72, 29.62, 29.41, 27.99, 26.25, 26.21, 24.68, 22.71,
22.61, 19.67, 14.11 ppm; elemental analysis: C86H131N2BrO5, calculated:
C, 76.35; H, 9.76; N,2.07. % Found: C, 76.25; H, 9.64; N, 1.98. 1H and 13
NMR spectra are shown in the ESI, Fig. S21.
C
4.5.5. 11,12-Bis((4-butoxyphenyl)ethynyl)-2,3,6,7-tetrakis(dodecyloxy)
dibenzo[a,c]phenazine (8a)
IR (film) υmax: 2955, 2922, 2852, 2216, 1606, 1506, 1456, 1377,
1269, 1168, 771, 721 cm−1; 1H NMR (500 MHz, CDCl3): 8.62 (br, 2H),
8.39 (br, 2H), 7.59 (m, 6H), 6.93 (d, J = 8 Hz, 4H), 4.32–4.26 (m, 8H),
4.03 (t, J = 6.5 Hz, 4H), 1.99 (t, J = 6 Hz, 8H), 1.83–1.30 (m, 80H),
1.03 (t, J = 7 Hz, 6H), 0.89 ppm (br, 12H); 13C NMR (125 MHz,
CDCl3): δ = 159.61, 151.88, 149.36, 142.23, 140.73, 133.34, 131.85,
126.57, 125.83, 123.59, 115.15, 114.65, 108.69, 106.23, 95.39, 87.20,
69.57, 69.10, 67.83, 31.94, 31.28, 29.77, 29.71, 29.58, 29.40, 26.20,
22.70, 19.25, 14.11, 13.85 ppm; elemental analysis: C92H132N2O6, calcu-
lated: C, 81.13; H, 9.77; N,2.06. % Found: C, 81.26; H, 9.86; N, 2.18. 1H and
13C NMR spectra are shown in the ESI, Fig. S22.
4.5.1.
11-Bromo-12-((4-butoxyphenyl)ethynyl)-2,3,6,7-tetrakis
(dodecyloxy)dibenzo[a,c]phenazine (7a)
IR (film) υmax: 2951, 2924, 2852, 2214, 1606, 1510, 1454, 1377,
1273, 1166, 773, 721 cm−1 1H NMR (500 MHz, CDCl3): δ = 8.52 (s,
;
1H), 8.49 (s, 1H), 8.43 (s, 1H), 8.34 (s, 1H), 7.61 (d, J = 8 Hz, 2H), 7.50
(br, 2H), 6.95 (d, J = 8 Hz, 2H), 4.29–4.24 (br, 8H), 4.03 (t, J = 5.5 Hz,
2H), 2.0 (br, 8H), 1.83–1.30 (m, 76H), 1.03 (t, J = 6.5 Hz, 3H),
0.98 ppm (br, 12H); 13C NMR (125 MHz, CDCl3): δ = 159.82, 152,
151.89, 149.29, 149.25, 142.33, 142.04, 141.07, 139.95, 133.36, 132.70,
131.99, 126.70, 126.51, 125.88, 124.97, 123.28, 123.19, 114.68, 108.61,
8

L. Jacob, A. Gowda, S. Kumar et al.
Journal of Molecular Liquids 320 (2020) 114419
4.5.6. 2,3,6,7-Tetrakis(dodecyloxy)-11,12-bis((4-(octyloxy)phenyl)ethy-
nyl)dibenzo[a,c]phenazine (8b)
been provided in the supporting information. Supplementary data to
this article can be found online at https://doi.org/10.1016/j.molliq.
2020.114419.
IR (film) υmax: 2953, 2924, 2852, 2208, 1606, 1507, 1456, 1377,
1247, 1168, 769, 721 cm−1; 1H NMR (500 MHz, CDCl3): 8.56 (br, 2H),
8.33 (br, 2H), 7.57–7.52 (m, 6H), 6.90 (d, J = 7 Hz, 4H), 4.29–4.22 (m,
8H), 3.99 (br, 4H), 1.97 (br, 8H), 1.81–1.27 (m, 96H), 0.88 ppm (br,
18H); 13C NMR (125 MHz, CDCl3): δ = 159.61, 151.83, 149.28, 142.15,
140.69, 133.33, 131.84, 126.54, 125.78, 123.50, 115.15, 114.65, 108.64,
106.14, 95.37, 87.21, 69.54, 69.09, 68.16, 31.95, 31.83, 29.77, 29.74,
29.72, 29.60, 29.40, 29.39, 29.25, 26.22, 26.20, 26.06, 22.70, 22.67,
14.10 ppm; elemental analysis: C100H148N2O6, calculated: C, 81.47; H,
10.12; N,1.90. % Found: C, 81.59; H, 10.23; N, 2.09. 1H and 13C NMR spec-
tra are shown in the ESI, Fig. S23.
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Declaration of competing interest
We declare that we don't have any conflict of interest.
Acknowledgments
The author thanks Dr. Vijayaragavan for recording the NMR spectra,
Dr. Srinivas HT and Ms. Vasuda for their technical support. Department
of Science and Technology, Government of India, Grant INT/RUS/RFBR/
376 and Russian Foundation for Basic Projects, grant No. 19-57-
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Appendix A. Supplementary data
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