Novel phenazine fused triphenylene discotic liquid crystals: synthesis, characterisation, thermal, optical and nonlinear optical properties

Article abstract of DOI:10.1039/c8nj03024c

A straightforward synthesis of novel phenazine fused triphenylene discotic liquid crystals (DLCs) is realized. The condensation of 3,4-diaminobenzoic acid with a triphenylene-1,2-diquinone intermediate gives an acid derivative which upon esterification with aliphatic alcohols produces the corresponding monomeric ester derivatives of the phenazine fused triphenylene discotic liquid crystals. The intermediate acid derivative exhibits a rectangular columnar phase along with a high isotropic phase transition temperature. However, the monomeric ester derivatives show a hexagonal columnar mesophase over a broad temperature range and stable when decreased to room temperature upon cooling from the isotropic phase. The mesomorphic properties of the acid and monomeric ester derivatives of the phenazine fused triphenylene DLCs were characterised by polarised optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction studies (XRD). The molecular structures of the intermediate and final compounds were characterised by spectral and elemental analysis. The photophysical properties of all the monomeric ester compounds were investigated in an anhydrous chloroform solvent and absorption bands around 291-472 nm and the corresponding emission bands at 658-661 nm were observed, respectively. The π-extended conjugation in these materials gives rise to high nonlinear optical properties. These materials have immense potential for use in electro-optical applications.

Full text of DOI:10.1039/c8nj03024c

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Novel phenazine fused triphenylene discotic liquid
crystals: synthesis, characterisation, thermal,
optical and nonlinear optical properties†
Cite this: New J. Chem., 2018,
42, 19034
Ashwathanarayana Gowda,
Sandeep Kumar
Litwin Jacob,
Nithin Joy,
Reji Philip
and
*
A straightforward synthesis of novel phenazine fused triphenylene discotic liquid crystals (DLCs) is realized.
The condensation of 3,4-diaminobenzoic acid with a triphenylene-1,2-diquinone intermediate gives an acid
derivative which upon esterification with aliphatic alcohols produces the corresponding monomeric ester
derivatives of the phenazine fused triphenylene discotic liquid crystals. The intermediate acid derivative
exhibits a rectangular columnar phase along with a high isotropic phase transition temperature. However, the
monomeric ester derivatives show a hexagonal columnar mesophase over a broad temperature range and
stable when decreased to room temperature upon cooling from the isotropic phase. The mesomorphic
properties of the acid and monomeric ester derivatives of the phenazine fused triphenylene DLCs were
characterised by polarised optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray
diffraction studies (XRD). The molecular structures of the intermediate and final compounds were
characterised by spectral and elemental analysis. The photophysical properties of all the monomeric
ester compounds were investigated in an anhydrous chloroform solvent and absorption bands around
Received 18th June 2018,
Accepted 15th October 2018
291–472 nm and the corresponding emission bands at 658–661 nm were observed, respectively. The
DOI: 10.1039/c8nj03024c
p-extended conjugation in these materials gives rise to high nonlinear optical properties. These materials
rsc.li/njc
have immense potential for use in electro-optical applications.
nematic phase (N
having only a long-range orientational order is less commonly
D
) with self-organization of disc-like molecules
1
. Introduction
Discotic liquid crystals (DLCs) are unique self-assembled supra- observed but it finds intriguing applications like optical compen-
molecular nanoarchitectures, which typically consist of a sative films used to enlarge the viewing angle of liquid crystal
1
4–18
p-conjugated disc-like polycyclic aromatic core substituted with display (LCD) devices.
three or more flexible insulating mantles of aliphatic chains.
Indeed, the functional capabilities of
1
–3
DLC smart materials have enormous advantages presumably
The anisotropic disc-shape molecules self-organize one on the because of their easy fabrication, high intrinsic charge-carrier
top of another to form columnar self-assemblies due to various mobility, spontaneous alignment between electrodes, self-healing
supramolecular weak interactions such as van der Waals forces, and self-assembled ability, which have massive potential for use in
13–26
hydrogen bonding, p–p interaction, dipolar or quadrupolar inter- device applications.
The columnar self-assembly of DLCs has
action, charge transfer interactions, etc. DLCs mainly exhibit stable find applications in active components in organic semiconductor
2
7–29
columnar and nematic mesophases. The columnar phases are devices such as organic light emitting diodes (OLED),
acquired by one-dimensional stacking arrangement of the disc-like field effect transistors (OFETs),
molecules with a long-range orientational and positional order.
organic
30–33
34–37
solar cells and sensors,
Triphenylene (TP) based DLCs are the most rigorously
etc.
They attract tremendous scientific-technological interest owing to explored scaffold in the family of DLCs exhibiting the discotic
their incredible one-dimensional charge and energy migration nematic phase along with other highly ordered columnar
4–13
1,2,38–45
properties along the columnar axis.
The least ordered discotic mesophases.
Because of strong interdisc interactions
such as p–p interactions associated with rigid, flat aromatic
structures, DLCs often exhibit stable columnar mesophases.
Presently, more than 1000 DLCs derived from the TP core are
known. Accordingly, they have been described as ‘the work-
horses’ in the field of discotics. They are alluring materials
owing to their one-dimensional energy and electron transport
Raman Research Institute, C. V. Raman Avenue, Sadashivanagar,
Bangalore – 560 080, India. E-mail: skumar@rri.res.in; Fax: +91 80 23610492;
Tel: +91 80 23610122
†
Electronic supplementary information (ESI) available: The general methods,
1
13
POM images, DSC thermograms, XRD data, H NMR and C NMR spectra of
intermediate and final compounds. See DOI: 10.1039/c8nj03024c
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4
6–50
properties.
Significant synthetic efforts have been made to properties and nonlinear optical studies of new DLCs. The mole-
5
1–53
extend the TP discotic core through p-conjugation.
However, cular structures of all the compounds were examined by using
the most convenient synthetic route involves the condensation spectral and elemental analysis. The liquid crystalline properties of
of triphenylene-1,2-diquinone with o-phenylenediamine to all DLCs were investigated by polarized optical microscopy (POM),
generate heteroaromatic triphenylene DLCs. We have previously differential scanning calorimetry (DSC) and X-ray diffraction (XRD)
reported the extension of a TP core by the condensation of studies.
triphenylene-1,2-diquinone with o-phenylenediamine to produce
54,55
phenanthro[a] phenazine and phenanthro[b] phenazine DLCs.
We have also reported an imidazole fused with a TP core for the
extension of heteroaromatic p-conjugation. The heteroaromatic
imidazole fused TP DLCs exhibit a stable columnar phase and
interesting photophysical properties. Recently we have also The synthesis of an unsymmetrical monomeric ester containing
reported that, alkanethiols and alkoxy chains containing phenazine fused triphenylene derivatives is shown in Scheme 1. The
phenazine-fused triphenylene DLCs exhibit p-type (hole) mobility key intermediate monohydroxytriphenylene 4 was synthesised from
2
. Results and discussion
2.1. Synthesis and characterisation
5
6
ꢀ
4
2
ꢀ1 ꢀ1
59
of the order of 10 cm V
s
in their hexagonal columnar catechol. Oxidation of 2-hydroxy-3,6,7,10,11-pentakis(alkyloxy)-
57
phase. Cammidge et al. reported on TP twin units that were triphenylene 4 with ceric ammonium nitrate gives a triphenylene-
fused via a pyrazine heteroaromatic ring, which exhibit a stable 1,2-diquinone derivative, that is, 3,6,7,10,11-pentakis(alkyloxy)tri-
hexagonal columnar phase over a broad range of temperature.
58
60
phenylene-1,2-dione 5.
Further it was condensed with
In this article, we have designed and synthesised phenazine commercially available 3,4-diaminobenzoic acid in the
fused triphenylene based DLCs bearing a monomeric ester presence of a glacial acetic acid and toluene (7 : 3) solvent
chain. The intermediate acid derivative exhibits a rectangular medium under reflux conditions to afford the corresponding
columnar phase (Col
tives display an enantiotropic hexagonal columnar phase (Col
r
), while all the monomeric ester deriva- intermediate inseparable acid derivatives 2,3,6,7,10-penta-
alkoxyphenanthro[9,10-a]-14-carboxylic acid 6(i) and its regio-
h
)
over a broad range of temperature. We anticipated that the isomer, 2,3,6,7,10-pentaalkoxyphenanthro[9,10-a]-13-carboxylic
incorporation of a monomeric ester substituted phenazine core acid 6(ii). This mixture is designated as 6. The esterification of 6
would alter the thermal and electronic properties and, therefore with aliphatic alcohols produces an inseparable mixture of final
may be interesting materials for device applications. Here, we mesogenic ester derivatives 7(i) and 7(ii), designated as 7. The
present the synthesis, mesomorphic characterization, photophysical chromatographic purification of the intermediate and the final
2 3 3
Scheme 1 (i) alkyl halide, anhy. K CO , DMF, reflux, 24 h; (ii) anhy. FeCl , DCM, 15 min, r.t.; (iii) B-bromocatecholborane, DCM, 24 h, r.t.; (iv) ceric
ammonium nitrate, acetonitrile, r.t., 30 min; (v) 3,4-diaminobenzoic acid, acetic acid : toluene (7 : 3), 100 1C, 8 h; (vi) alkyl alcohol, EDCIꢁHCl, HOBt, DMAP,
DCM, 24 h, r.t.
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mesogens using silica gel and recrystallization with an appropriate
solvent ensure high purity. The intermediate acid derivative 6 is
sparingly soluble in organic solvents like chloroform and dichloro-
methane. However, the final compounds (7a–7e) were freely
soluble in all chlorinated solvents.
2.2. Thermal properties
The thermotropic liquid crystalline textures of all the compounds
Fig. 1 Polarised optical microscopy textures recorded in the hexagonal
(
6, 7a–7e) were investigated by POM under cross polarisers (ESI,† columnar phase, upon cooling from isotropic liquid. (a) Compound 7a at
1
76 1C, viewed at 100ꢂ magnification, scale bar = 100 mm and (b) compound
Fig. S1). The phase transition temperature (peak in 1C) along with
the enthalpy of phase transition values (DH in kJ mol ) were
examined with the help of DSC measurements upon both heating
and subsequent cooling at a scan rate of 10 1C min , under a
nitrogen atmosphere and the thermal values are summarised in
Table 1.
ꢀ
1
7d at 122 1C, and viewed at 200ꢂ magnification, scale bar = 50 mm,
respectively.
ꢀ1
ꢀ1
isotropic phase at 207.2 1C (DH = 8.12 kJ mol ) and 155.2 1C
ꢀ
1
(
DH = 1.12 kJ mol ), respectively (ESI,† Fig. S4). Upon cooling
under a POM from the isotropic phase, compounds 7b and 7c
showed the appearance of a Col texture at 205.7 1C and
54.1 1C, respectively. Similarly, branched chain compounds
d and 7e exhibit an enantiotropic phase transition from the Cr
The intermediate acid derivative 6 exhibits an enantiotropic
r
phase over a broad range of temperature along with two
Col
types of endothermic phase transitions from the Cr phase to
Col at lower temperature and Col to the isotropic phase at
h
1
7
r
r
higher temperature. The peak temperature at 95.3 1C along
with the corresponding enthalpy of phase transition (DH =
phase to the Col
h
ꢀ
phase at a lower temperature of 69.7 1C
1
ꢀ1
(DH = 67.66 kJ mol ) and 43 1C (DH = 54.61 kJ mol ), respectively,
ꢀ1
45.30 kJ mol ) is attributed to the crystalline phase to Colr
and a phase transition from the Col phase to the isotropic phase at
h
ꢀ
1
ꢀ1
phase transition while the peak temperature at 237.4 1C
191.7 1C (DH = 0.58 kJ mol ) and 173.1 1C (DH = 8.31 kJ mol ),
ꢀ
1
(
r
DH = 25.40 kJ mol ) is referred to the Col phase to isotropic
respectively (ESI,† Fig. S5 and S6). Under a POM, compound 7d
exhibits a fan shaped texture with large domains, upon slow
cooling from the isotropic liquid phase as shown in Fig. 1b, viewed
at 200ꢂ magnification. On the other hand, compound 7e displayed
the mesophase at 171.4 1C, upon cooling from isotropic liquid.
Eventually, it can be noticed that the acid derivative shows a
much higher isotropic temperature in comparison to the ester
derivatives, which could be due to the formation of H-bonding.
As a representative, the DSC thermograms of compound 7b are
shown in Fig. 2.
liquid transition (ESI,† Fig. S2). Upon slow cooling under a
POM, the appearance of a microscopic texture at 232.7 1C
revealed the existence of the Col
r
phase, which crystallizes at
8
4 1C. The Col phase structure was confirmed by XRD inves-
r
tigations as discussed later.
Similarly, all the ester derivatives (7a–7e) exhibit two types of
61
endothermic phase transitions from Cr to Col
perature and Col to isotropic phase at higher temperature. The
Col phase is retained up to room temperature, upon cooling
from the isotropic liquid phase. Compound 7a exhibited a
h
at lower tem-
h
h
ꢀ1
crystal–crystal transition at 46.4 1C (DH = 10.40 kJ mol ) and
melted to the Colh phase at 68 1C with an enthalpy change
2.3. X-ray diffraction studies
ꢀ
1
(
2
DH = 40.52 kJ mol ) and transformed to isotropic liquid at The mesophase structures of the acid and other ester deriva-
ꢀ
1
00.1 1C (DH = 4.31 kJ mol ) (ESI,† Fig. S3). Upon cooling tives (6 and 7a–7e) were investigated with the help of X-ray
under a POM, the appearance of rectilinear defect textures was diffraction studies using unoriented liquid crystal samples
observed, which are characteristics of the hexagonal columnar filled in Lindemann capillaries. The XRD data were recorded
mesophase as shown in Fig. 1a, viewed at 100ꢂ magnification. On in the columnar mesophase at both heating and cooling
the other hand, compounds 7b and 7c show the Cr and Col
at 71.1 1C (DH = 47.88 kJ mol ) and 63.4 1C (DH = 46.17 kJ mol ), ESI† Fig. S7, respectively. The XRD diffractogram obtained for
h
phases temperatures and the values are summarised in Table 2 and
ꢀ
1
ꢀ1
respectively, and a phase transition from the Col phase to the acid compound 6 at 120 1C upon cooling is shown in Fig. 3a
h
r
Table 1 Phase transition temperatures of all the mesogens 6 & 7a–7e (both heating and cooling cycles). Cr = crystalline phase; Col = rectangular
h
columnar phase; Col = hexagonal columnar phase; I = isotropic phase
ꢀ1
Phase transition peak temperature (1C); (DH, [kJ mol ])
Compound
Second heating scan
Second cooling scan
6
Cr 95.3 [45.30] Col
Cr 46.4 [10.40] Cr
Cr 71.1 [47.88] Col
Cr 63.4 [46.17] Col
Cr 69.7 [67.66] Col
Cr 43.0 [54.61] Col
r
237.4 [25.40] I
68.0 [40.52] Col
207.2 [8.12] I
155.2 [1.12] I
191.7 [0.58] I
173.1 [8.31] I
I 232.7 [ꢀ23.80] Col
r
84 [ꢀ30.53] Cr
16.9 [ꢀ53.31] Cr
22.6 [ꢀ47.45] Cr
31.6 [ꢀ62.89] Cr
21.8 [ꢀ57.55] Cr
21 [ꢀ57.51] Cr
7
7
7
7
7
a
b
c
d
e
1
2
h
200.1 [4.31] I
I 197.1 [ꢀ4.41] Col
I 205.7 [ꢀ7.41] Col
I 154.1 [ꢀ2.52] Col
I 180.4 [ꢀ0.63] Col
I 171.4 [ꢀ7.96] Col
h
h
h
h
h
h
h
h
h
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shoulder peak at 3.63 Å were observed, which correspond
to the average distance between the alkyl chains (h ) and the
a
core–core separation of the columnar stacks. Similarly, an XRD
pattern was obtained for the ester derivatives (7a–7e) in the
hexagonal columnar phase (Fig. 3b) (Table 2). All the ester
derivatives show an ascending order of the diffraction angle
along with d-spacings of the first reflection to the second
reflection in a ratio of 1 : 1/O3 : 1/2 : 1/O7, respectively. These
diffraction values correspond to the two-dimensional hexagonal
columnar phase. The broad halo peak at the wide angle region
corresponds to the average distance between the alkyl chains, and
the shoulder peak shows the average distance between core–core
separation. The intercolumnar distance (a) can be calculated by
adopting the relation a = d10/(cos 301), where the d10 spacing
corresponds to the highest intensity peak in the small angle region
(Table 2). As a representative, the XRD diffractogram obtained for
compound 7e in the hexagonal columnar phase at 70 1C upon
cooling is shown in Fig. 3b. The highest intensity peak in the small
angle region shows d-spacing, d1 = 25.68 Å and other three
d-spacings corresponding to a lower intensity was observed at
Fig. 2 DSC thermograms obtained for compound 7b.
(
Table 2). Compound 6 showed two strong reflections in the d = 14.81 Å, d = 12.85 Å and d = 9.70 Å, respectively. All the
2 3 4
small angle region with a high intensity and several additional values agree with the hexagonal columnar lattice parameters.
weak reflections in the wide angle regions of low intensity The broad halo peak in the wide angle region at approximately
(Fig. 3a). In the XRD pattern, the d-spacings of the first peak 4.52 Å corresponds to the average distance between the alkyl
and the third peak, and the second peak and the fourth peak chains. The prominent peak at 3.50 Å was assigned to the p–p
are in the ratio of 1 : 1/2 owing to the lamellar arrangement of stacking of the aromatic discotic cores.
the discotic structure in two different directions. The two
intense peaks located in the small angle region are most
commonly detected for the rectangular columnar phase. These
reflections were characterised as (200), (110), (400), (020), (220)
3
. Photophysical properties
and (600) of a two-dimensional rectangular lattice with lattice The photophysical properties of the monomeric ester deriva-
spacings a = 69.36 Å and b = 29.47 Å, respectively. In the wide tives (7a–7e) were investigated by UV-Vis and photolumines-
angle region, a broad halo reflection around 4.76 Å and a cence spectroscopy (PL) in a very dilute solution as shown in
Table 2 XRD data of compounds 6 and 7a–7e
Temperature
Compound (1C)
d-spacings/Å
Miller
Phase (lattice
Alkyl-chain Core–core
length (Å) separation (Å) distance (a) (Å)
Intercolumnar
2y (degrees) observed (calculated) indeces constant)
6
120
2.63
33.65
27.14
200
110
400
020
220
600
100
110
200
100
110
200
210
100
110
200
210
100
110
200
100
110
200
210
Col
r
a = 69.36, b = 29.47 4.76
3.63
31.32
3
5
6
6
7
.25
.11
.01
.56
.69
17.24 (17.34)
14.68 (14.73)
13.45 (13.56)
11.48 (11.56)
24.54 (24.53)
14.13 (14.16)
12.23 (12.26)
25.10 (25.09)
14.44 (14.48)
12.50 (12.54)
9.45 (9.48)
26.48 (26.47)
15.28 (15.27)
13.24 (13.23)
10.14 (10.00)
25.41 (25.40)
14.50 (14.66)
12.57 (12.70)
25.68 (25.67)
14.81 (14.82)
12.85 (12.83)
9.70 (9.70)
7
7
a
130
110
3.59
Col
Col
h
h
a = 28.33
a = 28.98
4.64
4.58
3.55
3.52
28.33
28.98
6
7
.24
.21
b
3.51
6
7
9
.11
.06
.34
7
c
110
3.332
Col
h
a = 30.57
4.84
3.58
30.57
5
6
8
.77
.66
.71
7
7
d
e
85
70
3.51
Col
Col
h
h
a = 29.34
a = 29.65
4.53
4.52
3.50
3.50
24.64
29.65
6
7
.11
.06
3.43
5
6
9
.95
.87
.10
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Fig. 3 XRD diffractograms of (a) acid derivative 6, recorded at 120 1C upon cooling in the Col
r
phase, (b) ester derivative 7e recorded at 70 1C upon
h
cooling in the Col phase.
Fig. 4 and the data are presented in Table 3. Both absorption Table 3 Photophysical properties of the monomeric ester derivatives
(
7a–7e)
and emission spectra were recorded by dissolving the liquid
crystalline compounds in an anhydrous chloroform solvent
and recorded at room temperature. The absorption spectra of
all the monomeric ester derivatives were similar, irrespective
Molar absorption
coefficient
Absorption
abs/nm
Emission
lem/nm
ꢀ
1
ꢀ1
Compound
l
(e/L mol cm
)
6
of the number of alkyl chains with maximum absorption 7a
292, 312, 339, 352, 472 4.0714 ꢂ 10
292, 312, 338, 352, 472 4.8422 ꢂ 10
293, 312, 338, 352, 472 3.1202 ꢂ 10
292, 311, 337, 352, 472 4.5197 ꢂ 10
291, 311, 338, 352, 472 3.9871 ꢂ 10
661
658
659
659
660
6
6
6
6
7
7
7
b
c
d
bands located below 580 nm as shown in Fig. 4a. The max-
imum absorption bands at 290, 312, 338, 352 nm, along
with shoulder peaks at 240–275 nm observed at shorter 7e
wavelengths are attributed to the p–p* transition, while the
intense peak at 472 nm corresponds to the n–p* transition at a
longer wavelength. The maximum absorption at the longer compounds (7a–7e) were obtained by dissolving the com-
wavelengths may be due to the extended p-conjugation pounds in an anhydrous chloroform solvent and exciting the
of the heteroaromatic structure, which causes an increase solution of all the compounds at lex = 474 nm as shown in
in the intensity of absorption. The intensity of light absorp- Fig. 4b. The emission spectra of all the compounds show
tion eventually relies on the number of molecules that absorb strong emission bands around 658–661 nm. No significant
light at a given wavelength, which presumably causes a batho- changes were observed with increasing number of alkyl chain
chromic shift. Similarly, the emission spectra of all the lengths.
Fig. 4 (a) UV-Visible absorption and (b) photoluminescence emission spectra of all the final compounds (7a–7e).
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Fig. 5 (a) Open aperture Z-scan curves for 7a–7e compounds at an energy of 3 mJ. Solid curves are numerical fits to the experimental data obtained
using eqn (4). (b) Normalized transmission as a function of input laser fluence, calculated from the open aperture Z-scan measurements.
6
3
4
. Nonlinear optical transmission
and saturable absorption (SA). The net nonlinear absorption
coefficient is given by,
studies
a0
Nonlinear optical transmission measurements were performed
by dissolving the monomeric ester compounds (7a–7e) in an
anhydrous chloroform solvent taken in a 1 mm cuvette using
the open aperture Z-scan technique at an excitation wavelength
of 532 nm. The samples were excited using 5 ns laser pulses where I
aðIÞ ¼ ꢁ
ꢂþ bI
(3)
I
1
þ
Is
ꢀ2
s
is the saturation intensity (W m ) and b is the excited
ꢀ
2
generated from a frequency doubled Nd:YAG laser (Continuum state absorption coefficient (W m ). I
Minilite I).
by numerically fitting the light propagation equation to the
In our open aperture Z-scan experiment, the laser beam measured transmission data:
s
and b can be obtained
was focused using a plano-convex lens ( f = 10 cm). The
transmission was recorded at different positions with respect
to the beam focus (z = 0). The samples experience a different
fluence at each position, with the maximum fluence at the
focus and the linear transmission of the samples was fixed at
2
3
dI
6
a0
7
¼
ꢀ ꢁ
6
ꢂþ bI I
7
(4)
4
5
dx
I
1
þ
Is
6
5% for a wavelength of 532 nm. The Z scans measured
for all the samples at a laser pulse energy of 3 mJ are given where x is the propagation distance through the sample.
in Fig. 5. From the Z scan curve it is clear that the samples The obtained values are tabulated in Table 4.
exhibit strong optical limiting properties as the transmission
decreases at higher laser fluence.
We have observed that the excited state absorption and
saturable absorption properties of the molecules give rise to
For a spatially Gaussian laser beam, the fluence (Fin(z)) at high nonlinear optical properties. The delocalization of p
any position z can be obtained from the relation:
electrons results from extended p-conjugation in the triphenylene
fused phenazine ester derivatives, which increases the nonlinear
optical properties in these DLCs.
ꢀ
1
3
2
FinðzÞ ¼ 4ðln 2Þ2Ein p2oðzÞ
(1)
Table 4 ESA coefficient (b) and saturation intensity (Isat) calculated for the
samples (7a–7e) from the data given in Fig. 5a and b
with the beam radius o(z) given by
!
1
2
ꢁ
ꢂ
Sample linear
Laser pulse transmission Beta (b)
Compounds energy (mJ) (%)
2
z
I
sat
oðzÞ ¼ o0 1 þ
(2)
ꢀ10
ꢀ1
11
ꢀ2
z0
(ꢂ10
mW ) (ꢂ10 W m
)
7
7
7
7
a
b
c
3
3
3
3
3
65
65
65
65
65
10.8
10.2
9.5
9.4
9.2
8.5
6.0
8.0
8.5
6.0
where o
given by z
has contributions from both excited state absorption (ESA)
0
is the focal spot radius, and z
0
is the Rayleigh length
2
0
= po /l. We found that the nonlinear transmission
0
d
6
2
7e
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5
. Experimental section
(t, J = 6.5 Hz, 2H), 4.25–4.19 (m, 6H), 2.12–2.11 (m, 4H), 2.09–2
(
6
m, 6H), 1.93–1.77 (m, 2H), 1.60–1.16 (m, 96H), 0.86 (t, J =
.5 Hz, 3H), 0.80 ppm (t, J = 6 Hz, 15H); C NMR (125 MHz,
5.1. General procedure for the synthesis of the intermediate
1
3
and final compounds
CDCl ): d = 165.96, 151.58, 151.11, 149.62, 148.90, 148.34,
3
The intermediate compound 3,6,7,10,11-pentakis(dodecyloxy)-
triphenylene-1,2-diones 5 were synthesised as reported previously
and confirmed by spectral and elemental analysis. The inter-
mediate 3,4-diamino benzoic acid was obtained from a commercial
source. Compound 6 is not characterised by C NMR due to
1
1
1
3
2
45.44, 141.70, 140.10, 138.37, 132.08, 131.78, 130.62, 130.17,
28.78, 127, 124.91, 124.68, 122.64, 118.16, 112.42, 108.17,
06.53, 106.34, 105.80, 69.96, 69.77, 69.64, 69.28, 68.90, 65.81,
1.95, 31.55, 29.77, 29.71, 29.69, 29.61, 29.57, 29.49, 29.41,
9.39, 29, 28.82, 26.33, 26.25, 25.77, 22.71, 22.61, 14.13 ppm;
60
1
3
insufficient solubility in the CDCl solvent.
3
146 2 7
elemental analysis: C91H N O , calculated: C, 79.19; H, 10.66;
5.1.1. Synthesis of 2,3,6,7,10-pentakis(dodecyloxy)phen-
1
13
N, 2.03. % found: C, 79.28; H, 10.73; N, 1.99. H NMR and
C
anthro[9,10-a]phenazine-13-carboxylic acid (6). A mixture of
compound 5 (0.5 g, 1 equiv.) and 3,4-diaminobenzoic acid
NMR spectra are shown in the ESI,† Fig. S9.
(1.1 equiv.) was dissolved in a mixture of glacial acetic acid :
Decyl 2,3,6,7,10-pentakis(dodecyloxy)phenanthro[9,10-a]phenazine-
toluene solvent (7 : 3). The resultant reaction mixture was 13-carboxylate (7b). IR (film) nmax: 2955, 2924, 2852, 1718, 1618,
ꢀ
1
1
refluxed at 100 1C for 8 h. After completion of the reaction, 1518, 1454, 1377, 1313, 1263, 1168, 1070 cm
;
H NMR
the reaction mixture was cooled to room temperature and (500 MHz, CDCl ): d = 10.69 (s, 1H), 8.93 (s, 1H), 8.38–8.36
3
subsequently quenched with ice cold water, and extracted with (m, 2H), 7.97 (s, 1H), 7.87–7.84 (m, 3H), 4.43 (t, J = 6.5 Hz, 4H),
dichloromethane (3 ꢂ 100 mL). The combined extracts were 4.38 (t, J = 6.5 Hz, 2H), 4.23–4.19 (m, 6H), 2.10–2.01 (m, 2H),
dried over Na SO and the solvent was evaporated under 1.93–1.89 (m, 2H), 1.89–1.78 (m, 8H), 1.62–1.57 (m, 13H),
2
4
13
vacuum. The crude compound was purified by column chromato- 1.54–1.16 (m, 91), 0.81–0.79 ppm (m, 18H); C NMR (125 MHz,
graphy using silica gel (n-hexane/dichloromethane 6 : 4). Recrystal- CDCl ): d = 165.94, 151.55, 151.09, 149.62, 148.89, 148.32, 145.43,
3
lisation of the pure product with ethanol affords a red colour solid, 141.67, 140.07, 138.35, 132.08, 131.75, 130.59, 130.13, 128.75,
6
, yield: 80%. IR (film) nmax: 2953.12, 2908.75, 2852.81, 1691.63, 126.99, 124.92, 124.66, 122.63, 118.14, 112.44, 108.17, 106.54,
ꢀ1
1
612.54, 1454.38, 1377.22, 1261.49, 1166.97, 1101.39 cm
;
106.32, 105.80, 69.95, 69.77, 69.62, 69.27, 68.89, 65.80, 31.95,
1
H NMR (500 MHz, CDCl ): d = 10.57 (s, 1H), 8.84 (s, 1H), 31.91, 29.79, 29.76, 29.74, 29.71, 29.61, 29.57, 29.51, 29.41, 29.34,
3
8.26–8.17 (m, 2H), 7.75–7.58 (m, 4H), 4.42–4.34 (m, 4 H), 4.17– 29.01, 28.87, 26.33, 26.25, 26.09, 22.70, 14.11 ppm; elemental
4
.01 (m, 6H), 2.14–2.08 (m, 4H), 1.94–1.87 (m, 8H), 1.66–1.21 analysis: C H N O , calculated: C, 79.44; H, 10.81; N, 1.95. %
95 154 2 7
1
13
(m, 91H), 0.81 pm (m, 15H); elemental analysis: C85
H
134
N
2
O
7
,
found: C, 79.50; H, 10.87; N, 1.21. H NMR and C NMR spectra
calculated: C, 78.77; H, 10.42; N, 2.16. % found: C, 78.02; are shown in the ESI,† Fig. S10.
1
H, 10.59; N, 2.32. H NMR spectra are shown in the ESI,† Fig. S8.
Hexadecyl 2,3,6,7,10-pentakis(dodecyloxy)phenanthro[9,10-a]-
5
.1.2. Synthesis of the monomeric ester discotic mesogens
7a–7e). All the mesogenic derivatives were prepared by the
esterification reaction between the intermediate acid compounds
and various aliphatic alcohols. The general method is depicted
as follows.
In a two neck-flask containing compound 6 (0.2 g, 0.154 mmol),
phenazine-13-carboxylate (7c). IR (film) nmax: 2956, 2918, 2852,
(
ꢀ1
1
718, 1616, 1518, 1454, 1377, 1338, 1263, 1182, 1078 cm ;
1
H NMR (500 MHz, CDCl
3
): d = 10.66 (s, 1H), 8.89 (s, 1H), 8.38–
6
8
4
1
1
.33 (m, 2H), 7.91 (s, 1H), 7.84–7.81 (m, 3H), 4.41–4.36 (m, 6H),
.23–4.16 (m, 6H), 2.10–2.08 (m, 2H), 2.03–2.0 (m, 2H), 1.93–
.90 (m, 6H), 1.81–1.57 (m, 2H), 1.58 (m, 8H), 1.37–1.16 (m,
alkyl alcohol (1.2 eq.) and a catalytic amount of 4-dimethylamino-
pyridine (DMAP) (0.01 g, 0.07 mmol) were added in a dry dichloro-
methane (DCM) solvent (50 mL) under argon at room temperature.
1
3
08H), 0.79 ppm (t, J = 6 Hz, 18H); C NMR (125 MHz, CDCl3):
d = 165.93, 151.49, 151.04, 149.57, 148.83, 148.26, 145.39,
141.62, 140.01, 138.28, 132.06, 131.69, 130.55, 130.10, 128.71,
0
After stirring for 10 min, N-(3-dimethylaminopropyl)-N -ethylcarbo-
1
1
2
2
26.93, 124.90, 124.61, 122.58, 118.06, 112.38, 108.06, 106.44,
06.22, 105.70, 69.89, 69.73, 69.55, 69.23, 68.86, 65.80, 31.96,
9.81, 29.78, 29.73, 29.68, 29.64, 29.60, 29.53, 29.42, 29.38,
8.87, 26.35, 26.26, 26.10, 22.71, 14.13 ppm; elemental analysis:
diimide hydrochloride (EDCꢁHCl) (0.047 g, 0.30 mmol) and
N-hydroxybenzotriazole (HOBt) (0.04 g, 0.26 mmol) were added.
The resulting mixture was stirred at room temperature for 24 h.
After completion of the reaction, water was added and extracted
with DCM (3 ꢂ 50 mL). The combined extracts were dried over
C101H166N O , calculated: C, 79.79; H, 11; N, 1.84. % found:
C, 79.86; H, 11.05; N, 1.88. H NMR and C NMR spectra are
shown in the ESI,† Fig. S11.
2
7
1
13
2 4
Na SO and concentrated under vacuum. The residue was purified
by column chromatography using silica gel (n-hexane/dichloro-
methane 9 : 1). Recrystallisation of the pure product with ethanol
affords a red colour solid, 7a–7e. Yield: 80–90%.
3
,7-Dimethyloctyl 2,3,6,7,10-pentakis(dodecyloxy)phenanthro-
9,10-a]phenazine-13-carboxylate (7d). IR (film) nmax: 2951,
924, 2852, 1716, 1618, 1518, 1454, 1377, 1313, 1263, 1182,
[
2
ꢀ
1 1
Hexyl 2,3,6,7,10-pentakis(dodecyloxy)phenanthro[9,10-a]phena- 1078 cm ; H NMR (500 MHz, CDCl ): d = 10.71 (s, 1H), 8.96 (s,
3
zine-13-carboxylate (7a). IR (film) nmax: 2951, 2918, 2852, 1716, 1H), 8.41–8.35 (m, 2H), 8.02 (s, 1H), 7.90–7.87 (m, 3H), 4.46–
ꢀ
1 1
1
(
(
560, 1518, 1454, 1377, 1340, 1263, 1182, 1071 cm ; H NMR 4.42 (m, 6H), 4.24–4.19 (m, 6H), 2.11 (m, 2H), 2.02 (m, 2H),
500 MHz, CDCl ): d = 10.70 (s, 1H), 8.95 (s, 1H), 8.41–8.35 1.93–1.89 (m, 6H), 1.62 (m, 6H), 1.59–1.16 (m, 96H), 0.80 ppm
m, 2H), 8 (s, 1H), 7.89–7.86 (m, 3H), 4.44 (t, J = 6.5 Hz, 4H), 4.38 (m, 24H); C NMR (125 MHz, CDCl
3
1
3
3
): d = 164.93, 150.57,
19040 | New J. Chem., 2018, 42, 19034--19042 This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018

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1
1
3
2
2
50.10, 148.62, 147.90, 147.34, 144.43, 139.10, 130.70, 129.15, References
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8.23, 36.22, 34.71, 30.92, 29.11, 28.74, 28.72, 28.68, 28.66,
8.57, 28.53, 28.46, 28.37, 28.35, 27.97, 26.95, 25.30, 25.21,
3.64, 21.67, 21.58, 18.67, 13.09 ppm; elemental analysis:
2
A. N. Cammidge and R. J. Bushby, in Handbook of Liquid Crystals,
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C H N O , calculated: C, 79.44; H, 10.81; N, 1.95. % found:
C, 79.68; H, 10.93; N, 2.06. H NMR and C NMR spectra are
shown in the ESI,† Fig. S12.
1
13
3
2-Hexyldecyl 2,3,6,7,10-pentakis(dodecyloxy)phenanthro[9,10-a]-
4
5
6
7
8
phenazine-13-carboxylate (7e). IR (film) nmax: 2953, 2924, 2852,
ꢀ1
1
720, 1614, 1514, 1454, 1377, 1303, 1263, 1182, 1078 cm ;
1
H NMR (500 MHz, CDCl
.52–8.45 (m, 2H), 8.15 (s, 1H), 8.01–7.99 (m, 3H), 4.59–4.54
m, 4H), 4.40–4.30 (m, 6H), 4.23–4.20 (m, 2H), 2.11–2.08 (m, 2H),
3
): d = 10.79 (s, 1H), 9.07 (s, 1H),
8
(
2007, 36, 1902.
2
.03–1.90 (m, 7H), 1.69–1.26 (m, 116H), 0.91–0.94 ppm (m, 21H);
9
L. Schmidt-Mende, A. Fechtenkotter, K. Mullen, E. Moons,
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1
3
C NMR (125 MHz, CDCl ): d = 166.06, 151.58, 151.13, 149.64,
3
1
1
1
6
2
2
48.92, 148.40, 145.46, 141.72, 140.17, 138.38, 132.07, 131.88,
30.62, 130.21, 128.77, 127.03, 124.91, 124.71, 122.65, 118.21,
12.41, 108.20, 106.55, 106.37, 105.83, 69.98, 69.77, 69.66, 69.29,
8.88, 68.38, 37.55, 31.95, 31.91, 31.88, 31.45, 30.01, 29.79, 29.77,
9.71, 29.68, 29.64, 29.60, 29.56, 29.49, 29.41, 29.38, 29.34, 28.99,
6.82, 26.79, 26.40, 26.24, 22.71, 22.67, 14 ppm; elemental
1
0 J. Cornil, V. Lemaur, J.-P. Calbert and J.-L. Bredas, Adv. Mater.,
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1
1
1
1
1
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analysis: C101H166N O , calculated: C, 79.79; H, 11; N, 1.84. %
found: C, 79.91; H, 11.28; N, 1.96. H NMR and C NMR spectra
are shown in the ESI,† Fig. S13.
2
7
1
13
1
1
1
112, 3270.
6
. Conclusions
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Jpn. J. Appl. Phys., 1997, 36, 143.
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Chem., 2001, 11, 302.
The synthesis and characterisation of five novel extended
p-conjugated monomeric ester containing phenazine fused
triphenylene discotic liquid crystals are reported. The inter-
mediate acid derivative 6 exhibits a rectangular columnar
2
2
2
2
0 S. Setia, S. Sidiq, J. De, I. Pani and S. K. Pal, Liq. Cryst., 2016,
r
phase (Col ) over a broad range of temperature, while the
43, 2009.
monomeric ester derivatives exhibit a hexagonal columnar
phase, which remains stable till room temperature upon
cooling from the isotropic phase. All the ester derivatives
exhibit strong photoluminescence properties in an anhydrous
chloroform solvent upon excitation at 474 nm. The p-extended
conjugation in the triphenylene fused phenazine based DLCs
enhance the nonlinear optical properties. Such ordered supra-
molecular structures may find applications in various semi-
conducting devices.
1 J. P. Schmidtke, R. H. Friend, M. Kastler and K. Mullen,
J. Chem. Phys., 2006, 124, 17.
2 G. Zucchi, B. Donnio and Y. H. Geerts, Chem. Mater., 2005,
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2
2
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2
017, 1700003.
Conflicts of interest
2
2
2
7 A. Bacher, I. Bleyl, C. H. Erdelen, D. Haarer, W. Paulus and
H. W. Schmidt, Adv. Mater., 1997, 9, 1031.
8 I. Seguy, P. Jolinat, P. Destruel, J. Farenc, R. Mamy, H. Bock,
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9 T. Hassheider, S. A. Benning, H. S. Kitzerow, M. F. Achardand
and H. Bock, Angew. Chem., Int. Ed., 2001, 40, 2060.
There are no conflicts to declare.
Acknowledgements
The authors thank Dr Vijayaragavan for recording the NMR 30 A. M. van de Craats, N. Stutzmann, O. Bunk, M. M. Nielsen,
spectra, Dr Srinivas HT and Ms Vasuda for their technical
support.
M. Watson, K. M u¨ llen, H. D. Chanzy, H. Sirringhaus and
R. H. Friend, Adv. Mater., 2003, 15, 495.
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19042 | New J. Chem., 2018, 42, 19034--19042 This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018