Synthesis, mesomorphic properties and nonlinear optical studies of alkyl and alkoxy phenylacetylene containing phenazine fused extended triphenylene discotic liquid crystalline dyes

Article abstract of DOI:10.1016/j.dyepig.2018.07.052

Herein, we have reported the alkyl and alkoxy phenylacetylene containing phenazine fused triphenylene discotic liquid crystals (DLCs) which are obtained by the condensation reaction of triphenylene-1,2-diquinone with 1,2-diamino-4,5-dibromobenzene, followed by Sonogashira C–C coupling reaction with 4-alkyl-phenylacetylene or 4-alkoxy-phenylacetylene. Six novel derivatives were synthesized and evaluated for their thermal and optical properties. They show a broad range of hexagonal columnar phase and retain their mesophase up to room temperature upon cooling from the isotropic liquid. Thermotropic liquid crystalline properties of all the compounds were studied by polarised optical microscopy (POM), differential scanning calorimetry (DSC). The self-assembly of mesophase structure was investigated by X-ray diffraction (XRD) studies. Thermogravimetric analysis of all the mesogens shows good thermal stability over a broad temperature range. The photophysical properties of newly synthesized compounds were measured using UV–Vis absorption and photoluminescence emission spectroscopy in anhydrous chloroform solvent. The π-extended conjugation in these mesogens exhibit strong absorption bands falling around 270–487 nm and corresponding emission band at 657–663 nm respectively. The high delocalization of π– electrons in extended discotic mesogens show high nonlinear optical properties when measured under excitation by nanosecond laser pulses at 532 nm. These materials may find distinctive applications in the semiconducting devices.

Full text of DOI:10.1016/j.dyepig.2018.07.052

Accepted Manuscript
Synthesis, mesomorphic properties and nonlinear optical studies of alkyl and alkoxy
phenylacetylene containing phenazine fused extended triphenylene discotic liquid
crystalline dyes
Ashwathanarayana Gowda, Litwin Jacob, Alakananda Patra, Agnes George, Reji
Philip, Sandeep Kumar
PII:
S0143-7208(18)31383-4
10.1016/j.dyepig.2018.07.052
DYPI 6906
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 21 June 2018
Accepted Date: 28 July 2018
Please cite this article as: Gowda A, Jacob L, Patra A, George A, Philip R, Kumar S, Synthesis,
mesomorphic properties and nonlinear optical studies of alkyl and alkoxy phenylacetylene containing
phenazine fused extended triphenylene discotic liquid crystalline dyes, Dyes and Pigments (2018), doi:
10.1016/j.dyepig.2018.07.052.
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Graphical abstract:
Synthesis, mesomorphic properties and nonlinear optical studies of alkyl and alkoxy
phenylacetylene containing phenazine fused extended triphenylene discotic liquid
crystalline dyes
Ashwathanarayana Gowda, Litwin Jacob, Alakananda Patra, Agnes George, Reji Philip and
Sandeep Kumar *
Raman Research Institute, C.V. Raman Avenue, Sadashivanagar, Bangalore - 560 080, India
Phone: +91 80 23610122, Fax: +91 80 23610492, E-mail: skumar@rri.res.in

ACCEPTED MANUSCRIPT
Synthesis, mesomorphic properties and nonlinear optical studies of alkyl and
alkoxy phenylacetylene containing phenazine fused extended triphenylene
discotic liquid crystalline dyes
Ashwathanarayana Gowda, Litwin Jacob, Alakananda Patra, Agnes George, Reji Philip and
Sandeep Kumar *
Raman Research Institute, C.V. Raman Avenue, Sadashivanagar, Bangalore - 560 080, India
Phone: +91 80 23610122, Fax: +91 80 23610492, E-mail: skumar@rri.res.in
Abstract:
Herein, we have reported the alkyl and alkoxy phenylacetylene containing phenazine fused
triphenylene discotic liquid crystals (DLCs) which are obtained by the condensation reaction of
triphenylene-1,2-diquinone with 1,2-diamino-4,5-dibromobenzene, followed by Sonogashira C–
C coupling reaction with 4-alkyl-phenylacetylene or 4-alkoxy-phenylacetylene. Six novel
derivatives were synthesized and evaluated for their thermal and optical properties. They show a
broad range of hexagonal columnar phase and retain their mesophase up to room temperature
upon cooling from the isotropic liquid. Thermotropic liquid crystalline properties of all the
compounds were studied by polarized optical microscopy (POM), differential scanning
calorimetry (DSC). The self-assembly of mesophase structure was investigated by X-ray
diffraction (XRD) studies. Thermogravimetric analysis of all the mesogens shows good thermal
stability over a broad temperature range. The photophysical properties of newly synthesized
compounds were measured using UV-Vis absorption and photoluminescence emission
spectroscopy in anhydrous chloroform solvent. The π-extended conjugation in these mesogens
1

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exhibit strong absorption bands falling around 270−487 nm and corresponding emission band at
6
57−663 nm respectively. The high delocalization of π– electrons in extended discotic mesogens
show high nonlinear optical properties when measured under excitation by nanosecond laser
pulses at 532 nm. These materials may find distinctive applications in the semiconducting
devices.
Keywords: Discotic liquid crystals, triphenylene, Sonogashira coupling, columnar phase,
nonlinear optical transmission.
1
. Introduction
The spontaneous self-assembly of nanostructured materials generated by utilizing non-covalent
interactions such as van der Waals forces, π‒π interactions, H-bonding, charge transfer, ionic
interactions, dipolar and quadrupolar interactions and so on are extremely important in the soft
material science [1–4]. Liquid crystals (LCs) belong to this family of self-assembled
supramolecular architectures which can be used as potential anisotropic materials for commercial
applications [5]. The discovery of discotic liquid crystals (DLCs) obtained from disc-shape
molecules by S. Chandrasekhar, et al. in 1977, opens scientific evolution in the soft material
science [6–10]. The appropriate functionalization of disc-shape molecules leads to the formation
of DLCs via self-organization and self-assembly. The self-healing and self aligning ability of
DLCs are remarkable properties responsible for forming highly ordered supramolecular
architectures which have been recognized as molecular wires in various electronic device
applications [11–17]. Most of the DLCs are derived from polycyclic aromatic cores such
triphenylene (TP), anthraquinone (AQ), phthalocyanine (Pc), hexabenzocoronene (HBC) and so
2

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on, surrounded by a mantle of flexible aliphatic chains [7,18–22]. Orientational order of discs
forms the nematic phase which has found commercial applications as optical compensating films
in wide viewing LCDs [9,19,22–26]. The strong π–π interactions between aromatic cores favour
columnar stacking of the molecules, where individual molecules stacked one on top of the other
to form columns. The high charge carrier mobility in DLCs arises due to the stacking
arrangement of discs which provides facile π- electrons overlap in only one direction. The
electrons or hole migrates effectively along the columns in quasi one dimension [11–16].
Eventually, the electrical conductivity along the columns have been observed several orders of
magnitude greater than that in perpendicular direction [27–36]. Hence, due to this peculiar
behavior, DLCs have been extensively applied in organic light emitting diodes (OLEDs), [37–
3
9], organic field effect transistors (OEFT) [40–42], photovoltaic solar cells [11,43,44] and
sensors [45,46] etc.
Triphenylene is the most widely studied discotic core. The appropriate chemical modification of
triphenylene (TP) is known to exhibit various stable columnar mesophases [7,47–51]. The nature
of alkyl chains and functional groups substitutions on TP core show stable mesophases over
broad temperature range having interesting electronic properties. The electron rich nature of TP
derivatives makes them suitable for doping with electron acceptors to gives p-type of organic
semiconductors. Extension of TP discotic core significantly changes the liquid crystalline
behaviour and electronic properties. Such macromolecular macro discs exhibit wide range of
mesophase and high charge carrier mobility in the columnar phases [52,53]. Many synthetic
methods have been employed to extend the triphenylene core to produce phenanthrophenazine
[54,55], hexabenzotriphenylene [56], triphenylenophthalocyanine [57], etc. Cammidge et al.
reported TP discotic twins fused via pyrazine heteroaromatic ring and they exhibit stable
3

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hexagonal columnar phase over broad temperature range [58]. Wu et al. synthesised
triphenylene-fused triazatruxenes based π-extended discotic liquid crystals and investigated their
charge carrier mobility and gelation properties. The higher homologues in the series exhibit high
2
–1 –1
hole mobility (p-type) of 0.8 cm V s [59]. We have reported synthesis and liquid crystalline
properties of imidazole fused triphenylene discotic liquid crystals [60]. Very recently, we have
also investigated the charge carrier mobility of phenazine fused triphenylene discotic liquid
crystals containing alkanethiols and alkoxy chains. We have observed that hole mobility of the
‒
4
2
‒1 ‒1
order of 10 cm V s in its hexagonal columnar mesophase [61].
In the present investigation, we have synthesised symmetrical phenazine-fused-triphenylene
derivatives to look the effect of extension of discotic core on the liquid crystalline properties.
Here, we report alkyl and alkoxy phenylacetylene containing phenazine fused triphenylene DLCs
with enhanced π-electron conjugation. We designed and synthesized extended triphenylene
DLCs as shown in Scheme 1. We discuss the synthesis, characterisation and mesomorphic
properties of novel extended phenazine fused triphenylene derivatives. All the novel compounds
were characterised using spectral and elemental analysis. The liquid crystalline behaviour of all
the compounds was investigated by polarised optical microscopy (POM) and differential
scanning calorimetry (DSC). The mesophase structure of all the mesogens were investigated
using X-ray diffraction studies (XRD). Further, the photophysical and nonlinear optical studies
were also investigated for all the mesogens (14a–14f).
2
. Results and Discussions
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2
.1. Synthesis
The synthesis of π-extended phenazine fused triphenylene discotic liquid crystals is shown in
Scheme 1. The intermediate monohydroxytriphenylene 11 was prepared following reported
procedure starting from catechol [62]. Its oxidation with ceric ammonium nitrate (CAN)
produces 3,6,7,10,11-pentakis(dodecyloxy)triphenylene-1,2-diones 12 [63]. The another
intermediate compound 4,5-dibromobenzene-1,2-diamine 4 was synthesized using a reported
procedure [64]. Its condensed with triphenylene-1,2-diquinone in presence of glacial acetic acid
gives 13,14-dibromo-2,3,6,7,10-pentakis(dodecyloxy)phenanthro[9,10-a]phenazine discotic
mesogen 13 [61]. Sonogashira C–C bond coupling reaction of 4-alkyl phenylacetylene or 4-
alkoxy phenylacetylene 8 [65] with mesogenic compound 13 in the presence of
bis(triphenylphosphine)palladium(II) dichloride (PdCl (PPh ) ) and copper(I) iodide (CuI) in
2
3 2
anhydrous triethylamine (TEA) solvent offered final discotic liquid crystal compounds (14a–
4f). From UV absorption spectra, it is clearly indicated that the appearance of new red shifted
1
peak at 487 nm is obtained from the π-extension of triphenylene ring.
5

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Scheme 1. (i) p-TOSCl, pyridine, r.t, 24 h; (ii) Br , NaOAc, acetic acid, 110 ºC, 3 h; (iii) Con.
2
H
2
SO
methyl-3-butyn-2-ol, PdCl
FeCl , CH Cl , r.t, 30 min; (viii) catechol boron bromide, CH
4
, 110 ºC, 15 min; (iv) alkyl halide, anhydrous K
(PPh , CuI, TEA, reflux, 12 h; (vi) NaOH, toluene, reflux, 3 h; (vii)
Cl , r.t, 24 h; (ix) CAN, CH CN,
2 3
CO , dry DMF, reflux, 12 h; (v) 2-
2
3 2
)
3
2
2
2
2
3
r.t, 30 min; (x) acetic acid: toluene (7:3), reflux, 6 h; (xi) 4-alkyl-phenylacetylene or 4-alkoxy
phenylacetylene, PdCl (PPh ) , CuI, TEA, reflux, 24 h.
2
3 2
6

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2
.2. Mesomorphic properties
The thermotropic liquid crystalline behaviour of all the synthesised compounds (14a–14f) was
first viewed using optical microscopy with crossed polarisers which display characteristic defect
texture of columnar phase. The exact phase transition temperature (peak temperature in ºC) and
−
1
associated enthalpy values (∆H in kJ mol ) were investigated with the help of DSC
−1
measurement on both heating and subsequent cooling scans with a scan rate of 10 ºC min and
recorded under nitrogen atmosphere. The phase transition temperature of all mesogens agrees
very well with POM observations, as summarized in Table 1.
Table 1. Phase behaviour of discotic mesogens (14a–14f).
Cr = crystalline phase; Col = hexagonal columnar phase; I = isotropic phase.
h
Phase transition
–
1
Compound peak temperature (ºC); (∆H, [kJ mol ])
Second heating scan Second cooling scan
1
1
1
1
1
1
4a
4b
4c
4d
4e
4f
Cr 37.2 [44.0] Col
Cr 64.8 [50.0] Col
Cr 49.9 [42.9] Col
Cr 49.0 [39.5] Col
Cr 69.5 [79.1] Col
Cr 40.9 [45.3] Col
h
h
h
h
h
h
217 [3.2] I
I 209.3 [-3.1] Col
h
h
h
h
h
h
12.2 [-38.3] Cr
27.3 [-39.5] Cr
21.2 [-41.1] Cr
23.3 [-42.7] Cr
37.1 [-71.6] Cr
19.6 [-41.9] Cr
231.7 [2.1] I I 224.4 [-2.2] Col
228.5 [4.0] I I 221.7 [-2.5] Col
163.6 [2.3] I I 162.2 [-2.2] Col
139.4 [0.6] I I 135.1 [-0.7] Col
200.3 [2.7] I I 196.9 [-2.6] Col
7

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All the mesogens exhibit wide range of enantiotropic hexagonal columnar mesophase with two
types of endothermic phase transition from crystal to Col at lower temperature and Col phase to
h
h
isotropic phase at higher temperature and they retain columnar phase up to room temperature
upon cooling from the isotropic liquid. The first compound in the series 14a, with mixed alkyl
–
1
and alkoxy chains, melts at 37.2 ºC with phase transition enthalpy 44 kJ mol to Col phase and
h
–
1
h
transition from Col phase to isotropic phase at 217 ºC (∆H = 3.2 kJ mol ). Upon slow cooling
from the isotropic liquid under POM, the texture with rectilinear defects of Col phase was
h
observed as shown in Fig. 1a. As a representative example of DSC thermogram of compound
1
4a is shown in Fig. 2. The compound 14b with alkoxy chains melts to Col at 64.8 ºC (∆H = 50
h
–
1
kJ mol ) and Col to isotropic liquid at 231.7 ºC with corresponding heat transition (∆H = 2.1 kJ
h
–
1
mol ) (ESI, Fig. S2). Columnar textures were observed upon cooling from the isotropic liquid at
2
24.4 ºC (ESI, Fig. S1). On the other hand, compounds 14c and 14d exhibit phase transition
–
1
from crystalline phase to columnar phase at 49.9 ºC (∆H = 42.9 kJ mol ) and 49 ºC (∆H = 39.5
–
1
–1
kJ mol ) respectively, and the peak temperatures at 228.5 ºC (∆H = 4.0 kJ mol ) and 163.6 ºC
–
1
(
h
∆H = 2.3 kJ mol ) were attributed to Col to isotropic phase transition (ESI, Fig. S1 & S2).
Under POM, the compound 14c exhibit mesophase texture at 221.7 ºC (on cooling) as shown in
Fig. 1b. The compounds 14d exhibit similar mesophase texture observed under POM upon
cooling from isotropic liquid (ESI, Fig. S1). Similarly, compound 14e transformed to Col phase
h
–
1
at 69.5 ºC (∆H = 79.1 kJ mol ) at lower temperature and Col
h
to isotropic phase at 139.4 ºC (∆H
–
1
=
0.6 kJ mol ) at higher temperature (Fig. S2). The compound 14f with branched alkoxy chain
–
1
show similar behaviour, peak temperature at 40.9 ºC, with enthalpy change at 45.3 kJ mol
–
1
characteristic for Cr to Col
h
phase and Col
h
to isotropic liquid at 200.3 ºC (∆H = 2.7 kJ mol ).
8

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(
Fig. S2). Upon cooling under POM, the mesophase texture appeared at 135.1 ºC (14e) and 196.9
ºC (14f) respectively (ESI, Fig. S1).
Fig. 1. Polarised optical microscopy textures for compound 14a, (a) early growing rectilinear
defect texture of Col phase at 202 ºC, viewed at 100× magnification; for compound 14c (b)
h
hexagonal columnar texture recorded at 114 ºC, viewed at 200× magnification. Both POM
images were recorded on slow cooling from the isotropic liquid.
Fig. 2. DSC thermogram of compound 14a showing phase transitions on heating and cooling
−1
cycles at a scan rate of 10 °C min . Vertical arrows indicate phase transition points.
9

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Thermal stability of all the discotic mesogens (14a−14f) was measured using thermogravimetric
−1
analysis (TGA). All the compounds were subjected to heat scan of 10 ºC min under a nitrogen
atmosphere. All the compounds were found stable up to 365−375 ºC depending on the alkyl
chain length as shown in Fig. S3. All the compounds initiated weight loss at 385 ºC−400 ºC and
decomposed at 480 ºC. The decomposition temperature of the mesogens was much higher than
the isotropic temperature. It inferred that all the compounds possess good thermal stability over
broad temperature.
3
. X-ray diffraction measurements
In order to understand the mesophase structure of all the novel mesogens, X-ray diffraction
experiments were carried out using LC samples filled in Lindemann capillaries. X-ray diffraction
patterns are recorded for all the mesogens (14a
both heating and subsequent cooling scans as shown in Table 2 and a representative example is
shown in Fig. 3. All the mesogenic compounds 14a 14f showed increasing order of diffraction
angle. The -spacing of the first reflection in the small angle region to the second one is in the
ratio of 1:1/
3:1/2:1/ 7. These values corresponding to those obtained from two-dimensional
‒14f) in the hexagonal columnar mesophase on
‒
d
√
√
hexagonal lattice and relatively broad peaks in the wide angle regime corresponding to the liquid
like packing of the molten aliphatic chains and core-core separation. The intercolumnar distance,
a
, calculated by using the relation a = d10/(cos30º), where d10 is the spacing corresponding to the
strongest peak in the small angle region (Table 2). As a representative and typical XRD pattern
obtained for compound 14a (on heating scan) and 14d (on cooling scan) are shown in Fig. 3. The
XRD pattern of compound 14a at 100 ºC on heating in the columnar phase is shown in Fig. 3a
and respective lattice parameters were tabulated in Table 2. In the small angle region four peaks
being observed, one very strong and other three weak peaks of d- spacing d1 = 28.26 Å, d2 =
1
0

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1
6.24 Å, d = 14.07 Å and d = 10.64 Å respectively, values are in agreement with the hexagonal
3
4
columnar lattice. The broad peak at wide angle region d = 4.65 Å corresponds to liquid like
packing of molten aliphatic chains and the intercolumnar distance is found to be 32.63 Å
respectively (Fig. 3a). Similarly, X-ray diffraction pattern obtained for compound 14d in the
columnar phase at 70 ºC on cooling from the isotropic liquid is shown in Fig. 3b. The compound
1
1 2
4d shows similar reflections in the small angle regime with d-spacing d = 30.04 Å, d = 17.24
Å and d = 14.95 Å. The broad peak in wide angle regime at 4.66 Å corresponds to a flexible
3
alkyl chain length and the core-core gap is 3.54 Å. It is evident that with an increase in the
number of alkyl chain length, the width of the columns obtained discotic molecules also
increases. Similar X-ray diffraction patterns were obtained for all other compounds as shown in
Fig. S4. The above results further confirmed that all the mesogenic derivatives are self-
assembled in the hexagonal columnar fashion in their liquid crystal phase as shown in graphical
model Fig. 4.
Fig. 3. The intensity profile of the X-ray pattern: (a) 14a at 100 ºC (heating scan) and (b) 14d at
7
0 ºC (cooling scan) respectively.
1
1

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Fig. 4. Schematic representation of self-assembly of hexagonal columnar phase obtained for the
representative compound 14e.
Table 2. XRD data of all the discotic mesogens (14a-14f)
Comp Tempe 2θ
ound rature (degr Spacin Paramete indice chain
d-
gs
Colh
Miller Alkyl-
Core-
Core
separati distance
Intercolu
mnar
(
ºC)
00
ees)
r
s
length
(Å)
(Å)
on
(a)
(Å)
(Å)
14a
3.12
5.43
28.26
16.24
1
100
110
200
210
100
110
200
100
110
200
100
110
200
100
110
200
100
110
200
210
1
1/√3
1/2
1/√7
1
1/√3
1/2
1
1/√3
1/2
1
1/√3
1/2
1
1/√3
1/2
1
1/√3
1/2
1/√7
4
.65
3.51
32.63
28.67
31.40
34.68
34.97
6.273 14.07
8.29
10.64
24.73
14.25
12.36
27.12
15.71
13.51
30.04
17.24
14.95
30.23
17.51
15.24
28.28
16.25
14.13
10.65
14b
14c
14d
14e
14f
122
70
3.56
6
7
.19
.14
4.50
4.49
4.66
4.62
3.61
3.52
3.54
3.55
3.25
5.61
6.50
70
2.93
5
5
.11
.90
2.91
5.03
8
5
5
5.80
3.12
5.43
6
4.60
3.48
32.65
6
8
.24
.26
1
2

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4
. Photophysical properties
The photophysical properties of all the novel discotic mesogens were investigated by a Perkin-
Elmer UV-Vis lambda 35 double-beam spectrometer and photoluminescence (PL) spectra using
spectrofluorometer (Flurolog-3, Horiba Jobin Yvon). The UV-absorption properties of all the
−5
liquid crystalline compounds (14a–14f) were studied in anhydrous chloroform solvent (10 M)
recorded at room temperature to determine absorption maxima as presented in Fig. 5 (a) and the
respective absorption values are summarized in Table 3. Compound 14a having 4-alkyl
phenylacetylene chains show maximum absorption (λmax) bands at 482 nm and 368 nm which
corresponds to n−
phenylacetylene fused phenazine derivative. The less intense peaks at 313 nm, 217nm may be
because of * transitions of aromatic benzene rings. The alkoxy chain compounds 14b– 14f
exhibit similar kind of absorption behaviour with λmax corresponds to n− * transitions at
85−487 nm and * transition at 374 nm along with negligible shoulder peak around 360 nm.
Compounds 14d, 14e and 14f with longer alkyl chain length show λmax corresponds to n−
transitions at 485−487 nm and * transition at 370–374 nm along with negligible shoulder
peak around 360 nm. The less intense peaks at around 297 nm and 270 nm correspond to
transitions of benzene ring. The high delocalized electronic system and high molar absorption
π* and π−π* transitions of triphenylene ring containing extended 4-alkyl-
π−π
π
4
π−π
π*
π−π
π−π*
6
−1
−1
coefficients (
mesogens. In general, the maximum light absorption depends on the molecules that absorb light
of a given wavelength. It is also known that extended delocalised –electron conjugation present
in these discotic mesogens causes bathochromic shift (longer wavelength).
ε = 4.6−5.8 ×10 L mol cm ) attribute to the maximum absorption in this novel
π
1
3

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Fig. 5. (a) UV-Visible absorption spectra and (b) fluorescence emission spectra of all the
discotic mesogens (14a−14f).
Photoluminescence spectra of all the mesogens (14a−14f) were recorded in anhydrous
chloroform solvent. The emission spectra were recorded using a slit size of 2 nm in dilute
anhydrous chloroform solution at room temperature and all the compounds were excited at λmax
=
490 nm. All the mesogens exhibit strong emission band at 657−663 nm. A stokes shift in the
range of 286−295 nm was observed for all the mesogens (Table 3).
Table 3. Photophysical properties of discotic mesogens recorded using anhydrous chloroform
−
5
(
10 M).
6
−
1
−1
Compound Absorption λ /nm (ε/10 L mol cm )
Emission/ nm
abs
1
1
1
1
1
4a
4b
4c
4d
4e
277, 313, 368, 482 (5.3)
270, 300, 370, 485 (4.6)
270, 296, 371, 486 (5.7)
270, 297, 360, 374, 486 (5.8)
270, 297, 360, 374, 487 (5.7)
663
661
657
663
660
1
4

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1
4f
271, 297, 359, 374, 485 (5.3)
660
5
. Nonlinear optical studies
Nonlinear optical studies of all the discotic mesogens (14a–14f) are carried out by utilizing the
open aperture Z-scan technique using a frequency doubled Nd:YAG laser (Minilite I,
Continuum) providing linearly polarized Gaussian of 5 ns pulse width at 532 nm wavelength.
The experimental setup consists of the laser source, focusing lens, a 1 mm quartz cuvette
containing sample (which is fixed on a stepper motor controlled translation stage) and a pyro-
electric detector (Fig. S5).
The laser light is focused using a lens of focal length 9.5 cm along the z axis. All the discotic
mesogens (14a–14f) were dissolved in anhydrous chloroform solvent, which is kept between the
focusing lens and the detector and moved along the z axis, in order to change the laser fluence.
The transmitted energy is then measured using the pyroelectric detector (Laser probe, RJP-735).
The open aperture Z-scans obtained are shown in Fig.6.
The fluence of the laser beam, which is a function of position with respect to the focal point, is
given by
ꢈ
ꢉ
ꢍ
ꢉ
ꢀꢁꢂ
ꢃꢄꢅ = 4ꢃꢆꢇ2ꢅ
ꢊꢋ /ꢌ
ꢁꢂ
ꢎꢃꢄꢅꢏ…………………………………….(1)
ꢏꢊ
ꢈ
ꢉ
ꢒ
Where Ein is input energy (3 µJ) and ωꢃzꢅ =ꢊω ꢃ1 + ꢑ ꢔ ꢅ
, ꢎ ꢊis the radius of the laser beam
ꢐ
ꢐ
ꢒ
ꢓ
ꢏ
at the focus, and z is the Rayleigh length given by ꢄ =ꢊꢌꢎ ⁄ꢕ
.
0
ꢐ
ꢐ
The normalized transmittance (Tnorm) vs. position graph is plotted to obtain the Z-scan curve. The
pulse propagation equation is given by
1
5

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ꢖꢗ
ꢚꢓ
=
ꢊ− ꢙꢛꢜ + ꢠꢡꢢ ꢡ ……………………….. (2)
ꢝ
ꢖꢘ
ꢞꢟ
With
α
(I) being the net nonlinear absorption coefficient,
ꢚꢓ
ꢞ
ꢣꢃꢡꢅ =ꢊꢛꢜ + ꢠꢡ………………………….. (3)
ꢞꢟ
where ꢡꢤ is the saturation intensity (in ꢥ⁄ꢦꢏ) and
β
is the reverse saturable absorption
coefficient (in ꢦ⁄ꢥ). These parameters can be obtained by numerically fitting the measured
nonlinear transmission data to equation 2.
s
The calculated values of I and β are given in Table 1. While doing the numerical calculations,
we noticed that though RSA [66,67] dominates the nonlinearity, SA [68], which is not very
obvious from the measured Z-scan curves, is also present in the system and should be accounted
by including, I in the calculation for getting good fits. The high NLO response of discotic
s
mesogens arises due extended conjugation. The donor ability of symmetrical
phenylacetylene groups through alkyne spacer and heteroaromatic phenazine acceptor ring
enhance the intramolecular delocalization of –electrons, which are responsible for high
π–extended
π
nonlinear properties in these materials. These high NLO materials are subject of numerous
investigations of photonic applications like optical switches and optical limiters etc. [69]
Table 4:
β and I values calculated for the samples
s
Compounds Linear
β
Is
transmittance × 10ꢧꢛꢛ m/W × 10ꢛꢛ W/m2
1
4a
0.57
96
25
1
6

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1
1
1
1
1
4b
4c
4d
4e
4f
0.69
0.57
0.69
0.62
0.69
36
72
41
61
34
50
32
28
55
45
Fig. 6. (a) Open aperture Z-scan measurements done at the laser pulse energy of 3 micro Joules,
b) Normalized transmission as a function of input laser fluence, calculated from the Z-scan data.
(
6
. Experimental section
6.1.General procedure for the synthesis of final compounds
The compounds 4,5-dibromobenzene-1,2-diamine 4 [55], 1-ethynyl-4-alkoxybenzene 8 [56],
,6,7,10,11-pentakis(alkyloxy)triphenylene-1,2-diones 8 [54], and 13,14-dibromo-2,3,6,7,10-
3
pentapropoxyphenanthro[9,10-a]phenazine [52] were synthesized as reported and confirmed by
spectral and elemental analysis.
1
7

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Synthesis of 13,14-bis(2-(4-decylphenyl)ethynyl)-2,3,6,7,10-pentakis(dodecyloxy) phenanthro
[
9,10-a]phenazine
(
14a)
and
13,14-bis(2-(4-alkoxyphenyl)ethynyl)-2,3,6,7,10-
14f).
penta(alkoxy)phenanthro[9,10-a]phenazine (14b
−
To a stirring solution of compound 13 (0.5 g, 1 eq.) in triethylamine (40 mL) solvent was added
PdCl (PPh ) (0.06 eq.) and CuI (0.07 eq.) under argon atmosphere. The resulting reaction
2
3 2
mixture was allowed to stirred for 10 mines under argon at room temperature. To this, 1-decyl-4-
ethynylbenzene or 1-ethynyl-4-alkoxybenzene (2.6 eq.) was added under argon flow. The
resulting reaction mixture was heated to 72 ºC for 24 h. After completion of reaction, the
reaction mixture was allowed to cool to room temperature and diluted with diethyl ether,
followed by filtered through celite pad. The filtrate was washed with excess of water and
2 4
extracted with diethyl ether (3 × 40 mL). The combined extracts were dried over Na SO and
solvent was evaporated under vacuum. The residue was purified by column chromatography
using silica gel (n-hexane/dichloromethane 9:1). Recrystallisation of the pure product with
absolute ethanol affords dark red color solid (14a–14f) in about 65–70% yield.
-1
1
4a: IR (film) υmax = 2951, 2922, 2852, 2216, 1624, 1516, 1456, 1375, 1261, 1163, 1080 cm ;
1
H NMR (500 MHz, CDCl
.57 (d, J = 5 Hz, 4H), 7.21 (d, J = 6.5 Hz, 4H), 4.46 (m, 4H), 4.30−4.27 (m, 6H), 2.65 (t, J = 7
Hz, 4H), 2.16–2.10 (m, 4H), 2.0–1.96 (m, 6H), 1.69 (m, 8H),1.66–1.63 (m, 4H), 1.49–1.20 (m,
3
): δ = 10.72 (s, 1H), 8.53 (s, 1H), 8.33 (s, 1H), 7.94−7.88 (m, 4H),
7
1
3
1
1
1
6
2
3
08 H), 0.88–0.83 ppm (m, 21H); C NMR (125 MHz, CDCl ): δ = 149.83, 148.24, 147.63,
46.94, 143.89, 143.07, 142.98, 138.89, 138.11, 136.49, 131.58, 130.91, 129.40, 127.52, 125.69,
23.88, 123.33, 121.44, 119.27, 111.43, 106.86, 104.99, 104.40, 95.21, 86.64, 68.72, 68.54,
8.34, 68.08, 67.91, 35.04, 30.94, 30.30, 28.78, 28.73, 28.68, 28.65, 28.55, 28.41, 28.35, 28.12,
5.31, 25.27, 25.17, 21.69, 13.10 ppm; elemental analysis: C H N O ; calculated (%): C
1
20 182
2
5
1
8

ACCEPTED MANUSCRIPT
1
13
8
3.18, H 10.59, N 1.62; found: C 83.26, H 10.64, N 1.68. H NMR and C NMR spectra are
shown in the ESI Fig. S6.
-1
1
4b: IR (film) υmax = 2924, 2893, 2852, 2208, 1606, 1510, 1454, 1377, 1249, 1163, 1078 cm ;
1
H NMR (500 MHz, CDCl3):
δ
= 10.70 (s, 1H), 8.47 (s, 1H), 8.24 (s, 1H), 7.86–7.83 (m, 4H),
.58 (br, 4H), 6.90 (d, J = 8 Hz, 4H), 4.43 (m, 4H), 4.30–4.24 (m, 6H), 4.01 (t, J = 6.5 Hz, 4H),
.16–2.11 (m, 4H), 2.09–1.97 (br, 6H), 1.82–1.79 (m, 4H), 1.69–1.21 (m, 94H), 1.01 (t, J = 7
7
2
1
3
Hz, 6H), 0.88 ppm (br, 15H); C NMR (125 MHz, CDCl
3
) = 159.78, 159.71, 151.64, 150.91,
1
1
9
2
49.40, 148.76, 148.07, 144.97, 140.10, 139.31, 137.61, 133.48, 133.45, 132.32, 131.57, 130.54,
27.24, 126.80, 126.68, 125, 124.47, 122.65, 118.08, 114.64, 112.62, 108.62, 105.69, 96.36,
6.21, 87.07, 69.85, 69.67, 69.49, 69.21, 69.02, 67.83, 31.96, 31.29, 29.82, 29.79, 29.75, 29.73,
9.66, 29.62, 29.57, 29.54, 29.42, 29.21, 26.31, 26.27, 26.20, 22.71, 19.26, 14.12, 13.87 ppm;
elemental analysis: C H N O ; calculated (%): C 81.25, H 9.98, N 1.75; found: C 81.34, H
1
08 158
2
7
1
13
1
0.05, N 1.84. H NMR and C NMR spectra are shown in the ESI, Fig. S7.
-1
1
4c: IR (film) υmax = 2956, 2924, 2852, 2206, 1606, 1510, 1454, 1377, 1249, 1163, 1078 cm ;
1
H NMR (500 MHz, CDCl3):
.58 (br, 4H), 6.90 (d, J = 8 Hz, 4H), 4.41 (br, 4H), 4.28–4.23 (m, 6H), 3.99 (t, J = 6Hz, 4H),
.16–2.10 (m, 4H), 1.97 (br, 6H), 1.82 (t, J = 6.5 Hz, 4H), 1.68–1.58 (m, 12H), 1.49–1.21 (m,
δ = 10.68 (s, 1H), 8.44 (s, 1H), 8.20 (s, 1H), 7.84–7.81 (m, 4H),
7
2
9
1
1
6
2
1
3
8H), 0.90–0.84 ppm (m, 21H); C NMR (125 MHz, CDCl ) = 158.65, 158.58, 150.16, 149.56,
3
48.03, 147.39, 146.66, 143.62, 138.57, 137.82, 136.09, 132.46, 132.41, 131.03, 130.47, 129.15,
25.67, 125.41, 125.20, 123.80, 123.69, 123.06, 121.26, 94.95, 94.88, 68.49, 68.36, 68.06, 67.92,
7.77, 67.10, 30.97, 30.84, 28.97, 28.84, 28.77, 28.68, 28.64, 28.44, 28.42, 28.30, 28.27, 28.16,
5.37, 25.34, 25.30, 25.15, 25.09, 25.07, 21.71, 21.67, 13.11 ppm; elemental analysis:
1
9

ACCEPTED MANUSCRIPT
1
C
116 174 2 7
H N O ; calculated (%): C 81.54, H 10.26, N 1.64; found: C 81.74, H 10.41, N 1.79. H
1
3
NMR and C NMR spectra are shown in the ESI, Fig. S8.
-1
1
4d: IR (film) υmax = 2956, 2906, 2895, 2210, 1606, 1529, 1454, 1377, 1249, 1161, 1078 cm ;
1
H NMR (500 MHz, CDCl3):
.57 (br, 4H), 6.90 (d, J = 8 Hz, 4H), 4.50–4.46 (m, 4H), 4.32–4.26 (m, 6H), 4.0 (t, J = 6.5 Hz, 4
H), 2.18-2.10 (m, 4H), 2.0–1.96 (m 6H), 1.81 (t, J = 6.5 Hz, 4H), 1.71–1.20 (m, 110H), 0.88–
δ = 10.76 (s, 1H), 8.52 (s, 1H), 8.34 (s, 1H), 7.97–7.90 (m, 4H),
7
1
3
0
1
1
1
8
2
2
3
.85 ppm (m, 21H); C NMR (125 MHz, CDCl ) = 158.66, 158.59, 151.22, 150.17,
49.59,148.06, 147.42, 146.68, 143.63, 138.59, 138.21, 137.82, 136.10, 135.06, 132.46, 132.41,
31.01, 130.47, 129.69, 129.17, 127.81, 125.70, 125.44, 125.24, 123.82, 123.69, 123.09, 121.28,
16.54, 114.11, 113.54, 113.52, 113.04, 111.32, 106.51, 104.65, 104.14, 103.94, 94.99, 94.92,
6.17, 68.51, 68.39, 68.09, 67.94, 67.79, 67.11, 35.12, 33.30, 32.81, 30.97, 30.93, 29.29, 28.86,
8.84, 28.77, 28.71, 28.68, 28.67, 28.65, 28.52, 28.48, 28.46, 28.44, 28.37, 28.35, 28.32, 28.29,
8.23, 28.13, 25.37, 25.34, 25.30, 25.15, 25.10, 25.08, 21.71, 21.69, 13.11 ppm; elemental
198 2 7
analysis: C128H N O ; calculated (%): C 81.91, H 10.63, N 1.49; found: C 82.29, H 10.74, N
1
13
1
.83. H NMR and C NMR spectra are shown in the ESI, Fig. S9.
-1
1
4e: IR (film) υmax = 2955, 2918, 2850, 2210, 1606, 1514, 1454, 1377, 1259, 1161, 1074 cm ;
1
H NMR (500 MHz, CDCl3):
.57 (br, 4H), 6.90 (d, J = 7.5 Hz, 4H), 4.44 (br, 4H), 4.30–4.25 (m, 6H), 3.99 (t, J = 6 Hz, 4H),
.17–2.09 (m, 4H), 1.98 (br, 6H), 1.83–1.80 (m, 4H), 1.69–1.58 (m, 14H), 1.48–1.21 (m, 136 H),
δ =10.71 (s, 1H), 8.47 (s, 1H), 8.25 (s, 1H), 7.88–7.84 (m, 4H),
7
2
0
1
1
8
1
3
3
.88–0.84 ppm (m, 21H); C NMR (125 MHz, CDCl ) = 159.72, 151.66, 150.93, 149.41,
48.78, 148.10, 144.99, 140.12, 139.33, 137.63, 133.48, 133.45, 132.32, 131.57, 130.56, 127.27,
26.82, 126.71, 125.01, 124.49, 122.67, 118.11, 114.98, 114.65, 108.10, 105.73, 105.57, 96.39,
7.10, 69.86, 69.69, 69.52, 69.23, 69.04, 68.18, 31.96, 29.79, 29.73, 29.68, 29.66, 29.63, 29.57,
2
0

ACCEPTED MANUSCRIPT
2
9.54, 29.48, 29.46, 29.42, 29.38, 29.28, 29.27, 26.31, 26.28, 26.21, 26.08, 22.71, 14.12 ppm;
elemental analysis: C H N O ; calculated (%): C 82.12, H 10.84, N 1.41; found: C 82.19, H
1
36 214
2
7
1
13
1
0.91, N 1.52. H NMR and C NMR spectra are shown in the ESI, Fig. S10.
-
1 1
1
4f: IR (film) υmax = 2949, 2924, 2852, 2210, 1606, 1512, 1454, 1377, 1261, 1161, 1080 cm ; H
= 10.75 (s, 1H), 8.52 (s, 1H), 8.20 (s, 1H), 7.92 (m, 4H), 7.59–7.57
m, 4H), 6.91 (d, J = 8.5 Hz, 4H), 4.48 (br, 4H), 4.32–4.27 (m, 6H), 4.03 (t, J = 6.5 Hz, 4H),
.16–2.0 (m, 4H), 1.99–96 (m, 6H), 1.71–1.67 (m, 2H), 1.65–1.17 (m, 102H), 0.97 (d, J = 6.5Hz,
NMR (500 MHz, CDCl3):
δ
(
2
6
1
1
1
6
2
2
1
3
H), 0.89–0.83 ppm (m, 33H); C NMR (125 MHz, CDCl ) = 159.76, 159.69, 151.58, 150.88,
3
49.35, 148.73, 148.04, 144.94, 140.06, 139.25, 137.54, 133.48, 133.45, 132.28, 131.58, 130.51,
27.19, 126.77, 126.65, 124.97, 124.44, 124.03, 123.49, 122.61, 118.02, 115.95, 115, 114.91,
14.65, 114.07, 112.57, 108, 106.19, 105.63, 105.45, 96.34, 96.20, 87.09, 69.82, 69.64, 69.45,
9.19, 69, 66.49, 39.27, 37.36, 37.34, 36.18, 31.96, 31.63, 29.92, 29.91, 29.83, 29.80, 29.78,
9.74, 29.71, 29.68, 29.64, 29.58, 29.55, 29.43, 29.13, 28.01, 26.32, 26.28, 26.20, 24.69, 22.72,
2.63, 19.68 ppm; elemental analysis: C120
H
182
N O
2 7
; calculated (%): C 81.67, H 10.40, N 1.59;
1
13
found: C 82.05, H 10.72, N 1.81. H NMR and C NMR spectra are shown in the ESI, Fig. S11.
7
. Conclusions
A new class of triphenylene based discotic liquid crystals were synthesised using Sonogashira
coupling reaction between alkoxy phenylene acetylene or alkyl phenylacetylene with
intermediate dibrominated phenazine fused triphenylene. All the extended mesogens were self-
assembled into hexagonal columnar mesophase over wide temperature range and retains liquid
crystalline properties upto room temperature upon cooling from isotropic liquid. The liquid
crystalline properties were investigated using polarised optical microscopy, differential scanning
2
1

ACCEPTED MANUSCRIPT
calorimetry. The mesophase structure of all the mesogens were investigated using X-ray
diffraction studies. All the extended discotic compounds exhibit strong photoluminescence
properties in the anhydrous chloroform solvent. The π- extended heteroaromatic triphenylene
discotic mesogens enhance nonlinear optical properties and are suitable for materials for electro-
optical applications
Acknowledgments
The authors thank Dr. Vijayaragavan for recording NMR spectra, Dr. Srinivas HT and Ms.
Vasuda for their technical support.
Supplementary information
The general methods, POM textures, DSC thermograms, TGA, XRD, NLO setup and spectral
data have been given in supplementary information.
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