Stability of a columnar liquid crystalline phase in isomeric derivatives of the 1,4-dihydrobenzo[e][1,2,4]triazin-4-yl: Conformational effects in the core

Article abstract of DOI:10.1016/j.molliq.2019.01.014

Fluid phase behaviour of three isomeric 1,3,6-trisubstituted benzo[e][1,2,4]triazin-4-yl derivatives with the half-disc molecular architecture was examined in the pure form and in binary mixtures. Results indicate that the position of substitution with two wedge-shaped 3,4,5-tridodecyloxyphenyl groups and one Ph group has dramatic impact on the Col_h phase stability, which ranges from 73 °C to presumably below ?60 °C. Analysis of electronic and steric factors suggests that the intermolecular interactions of the wedge-shaped substituents are dominant and through their conformational behaviour they affect packing of the column's core and hence phase stability.

Full text of DOI:10.1016/j.molliq.2019.01.014

Accepted Manuscript
Stability of a columnar liquid crystalline phase in isomeric
derivatives of the 1,4-dihydrobenzo[e][1,2,4]triazin-4-yl:
Conformational effects in the core
Marcin Jasiński, Szymon Kapuściński, Piotr Kaszyński
PII:
S0167-7322(18)35081-5
DOI:
https://doi.org/10.1016/j.molliq.2019.01.014
MOLLIQ 10245
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
3 October 2018
18 November 2018
2 January 2019
Please cite this article as: Marcin Jasiński, Szymon Kapuściński, Piotr Kaszyński ,
Stability of a columnar liquid crystalline phase in isomeric derivatives of the
1
,4-dihydrobenzo[e][1,2,4]triazin-4-yl: Conformational effects in the core. Molliq (2019),
https://doi.org/10.1016/j.molliq.2019.01.014
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ACCEPTED MANUSCRIPT
J. Mol. Liq. October 3, 2018
Revised: November 16, 2018
Stability of a columnar liquid crystalline phase in isomeric derivatives of the 1,4-
dihydrobenzo[e][1,2,4]triazin-4-yl: conformational effects in the core
Dedicated to Professor Janusz Zakrzewski of University of Łódź on the occasion of his 70th
birthday
a
a
a,b,c
Marcin Jasiński, Szymon Kapuściński, and Piotr Kaszyński
a
Faculty of Chemistry, University of Łódź, 91403 Łódź, Poland
b
Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, 90363 Łódź,
Poland
c
Department of Chemistry, Middle Tennessee State University, Murfreesboro, 37132 TN, USA
Abstract:
Fluid phase behaviour of three isomeric 1,3,6-trisubstituted benzo[e][1,2,4]triazin-4-yl
derivatives with the half-disc molecular architecture was examined in the pure form and in
binary mixtures. Results indicate that the position of substitution with two wedge-shaped 3,4,5-
tridodecyloxyphenyl groups and one Ph group has dramatic impact on the Col phase stability,
h
o
o
which ranges from 73 C to presumably below –60 C. Analysis of electronic and steric factors
suggests that the intermolecular interactions of the wedge-shaped substituents are dominant and
through their conformational behaviour they affect packing of the column’s core and hence
phase stability.
Keywords: Liquid crystals, columnar phase, stability, conformations, stable radical
Graphical abstract
1

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1
. Introduction
Self-organization of molecules in a liquid and formation of liquid crystalline phases [1]
mesophases) [2] is a reasonably well understood process involving nanosegregation of
(
incompatible parts of anisometric molecules.[3] The mesophase stability critically depends on
the molecular anisometry, and this relationship has been extensively investigated mainly in rod-
like mesogens [4] and to a much smaller extent in bent-core and discotic derivatives.[5] Besides
the steric bulk affecting static molecular anisometry, also conformational effects influence the
packing fraction,[6] which, in turn, impacts phase stability.[7] Such empirical structure –
mesophase behaviour relationships in liquid crystals are of fundamental importance in the design
of practical materials with desired properties for e.g. display applications.[8]
Steric effects on discotic phase stability have been examined to a much smaller extent. It
has been demonstrated, however, that an increase of steric bulk in the rigid core of a discotic
liquid crystal leads to a decrease of phase stability, and the effect is stronger when the substituent
is closer to the molecular center.[9-12] While the static bulk of large substituents on mesophase
is well documented in the literature, dynamic steric effects related to conformation of the biaryl
junction are much less examined.
Recently, we have focused on the 1,4-dihydrobenzo[e][1,2,4]triazin-4-yl [13] which
serves as a structural element of a new class of paramagnetic liquid crystals with conductive and
magnetic properties.[14-16] The design of discotic materials derived from this spin-containing
heterocycle involves substitution positions N(1), C(3) and C(6) with Ar groups (Fig. 1). In
contrast to most core elements used in discotic liquid crystals, [17] the 1,4-
dihydrobenzo[e][1,2,4]triazin-4-yl lacks higher symmetry (C point group symmetry) and all
s
substitution positions, especially N(1), C(3) and C(6), are chemically and conformationally
nonequivalent. Consequently, when the three substituents are not identical, such as in series 1
(Fig. 1), the question arises whether the substitution site affects self-organization of the liquid
and stability of the mesophase and, if so, which way and to what extent. Answers to these
questions are important in the context of development of other functional materials containing
two or more benzo[e][1,2,4]triazin-4-yl units connected through a central unit such as a benzene
ring for molecular electronics and spintronic applications.
2

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Fig. 1. Structure of three isomers 1a–1c.
Herein, we examine three isomeric derivatives 1a–1c, which differ in the position of
attachment of two wedge-shaped groups and a small Ph substituent. We investigate their thermal
and optical behaviour in the pure state and in binary mixtures, and optical spectroscopic studies
augmented with DFT calculations.
2
. Results and Discussion
2
.1. Synthesis
Radicals 1 were obtained following a general method,[18] which involves azaphilic
addition of aryllithium reagents to the appropriate benzo[e][1,2,4]triazine 2, followed by aerobic
oxidation of the initially formed anion, as shown in Scheme 1. Thus, compounds 1b and 1c were
prepared in 75% and 84% yield, respectively, by treatment of the corresponding triazines 2b and
2
c with excess freshly prepared 3,4,5-tridodecyloxyphenyllithium, in dry THF. Synthesis and
properties of 1a was described previously.[14]
Ar1
i)
N
N
N
N
N
N
Ar3
Ar2
Ar3
Ar2
2
1
1
Scheme 1. Synthesis of radicals 1a–1c. Reagents and conditions: i) 1. Ar -Li (ca. 2.0–2.5
equiv.), 0 °C to rt, 40 min; 2. air, 30-50 min; 1b – 75% yield, 1c – 84% yield.
Synthesis of the requisite triazine 2b was accomplished in three steps starting with
benzhydrazide (3), which was N’-arylated with 4-bromo-1-fluoro-2-nitrobenzene to afford
3

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hydrazide 4 (Scheme 2). Its subsequent cyclization under reductive conditions gave 6-
bromobenzo[e][1,2,4]triazine 5, which upon Suzuki-Miyaura cross-coupling with 3,4,5-
tridodecyloxyphenylboronic acid [14] provided the required triazine 2b isolated in an overall
yield of 30%. Arylation of the known 6-bromobenzo[e][1,2,4]triazine 6 [14] with phenylboronic
acid under analogous Pd-catalyzed reaction conditions provided benzo[e][1,2,4]triazine 2c in
9
0% yield (Scheme 3).
O
N
N
5
CONHNH2
H
N
N
i)
ii)
N
H
Br
Br
NO2
3
4
N
N
N
iii)
C12H25
C12H25
O
O
OC12H25
2b
Scheme 2. Synthesis of benzo[e][1,2,4]triazine 2b. Reagents and conditions: i) 4-bromo-1-
fluoro-2-nitrobenzene (1.0 equiv.), DMSO, 85 °C, 6 hrs, 61% yield; ii) Sn powder (5.9 equiv.),
AcOH, rt, 1.5 hrs, then reflux 25 min, 59% yield; iii) 3,4,5-tridodecyloxyphenylboronic acid (ca.
1
.25 equiv.), Pd(PPh ) , K CO , THF/H O, reflux, 24 hrs, 84% yield.
3 4 2 3 2
N
N
N
N
N
N
OC12H25
OC12H25
i)
OC12H25
OC12H25
Br
6
2c
OC12H25
OC12H25
Scheme 3. Synthesis of key benzo[e][1,2,4]triazine 2c. Reagents and conditions: i) PhB(OH)2
(
1.25 equiv.), Pd(PPh ) , K CO , THF/H O, reflux, 24 hrs, 90% yield.
3 4 2 3 2
2
.2. Liquid crystalline properties
Thermal behaviour of compounds in series 1 was investigated by differential scanning
calorimetry (DSC) and polarized optical microscopy (POM). The results are shown in Table 1
and Fig. 2 and 3.
Among the three isomers only 1a and 1c exhibit a birefringent fluid phase (Table 1). The
mesophase in the later derivatives is destabilized relative to that in 1a by 35 K and appears as
monotropic (Fig. 2). The structure of the mesophase in 1a was established by powder XRD to be
4

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Col .[14] The meta-stable nature of the mesophase in 1c precludes such an analysis, but the
h
structural similarity of the two isomers, formation of typical textures (Fig. 3), and miscibility
with 1a (vide infra) strongly indicate the presence of the Colh.
1
1
1
b
c
a
Cr
I
I
I
Colh
Cr
Cr
Colh
60
0
20
40
80
100
o
temperature / C
-1
Fig. 2. DSC traces of 1a–1c. Heating and cooling rates are 5 K min .
Fig. 3. Optical texture of a Col phase obtained for 1c on cooling from the isotropic phase.
h
5

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Table 1.
Mesogenic behaviour of series 1.
a
b
phase behaviour
virtual Col →I transition
h
o
o
compound
T / C
[T] / C
in 1a
–
in 7
c
1
a
Cr 46 Col
h
73 I
[68±1]
[50±3]
[65±2]
1
b
Cr 73 I
[-13±3]
[9±2]
d
1
c
Cr 69 (Col 38) I
h
a
Cr = crystal, Col = columnar hexagonal, I = isotropic; peak transition temperatures of freshly
h
-1
b
prepared samples recorded on heating. Heating/cooling rates 5 K min . Virtual transition
temperatures established from binary mixtures in the indicated host. For details see the text and
SI. Ref.[14] Monotropic transition on cooling.
c
d
Compound 1b does not form a mesophase even upon supercooling of the isotropic liquid
o
by over 75 K to –5 C. To make a comparison of mesogenic properties of the three isomers and
to get more insight into factors affecting their liquid crystalline behaviour, the isomers were
investigated as low concentration (5–15 mol%) additives to two discotic benzo[e][1,2,4]triazinyl
hosts, isomer 1a and derivative 7 (Fig. 4), both exhibiting a Col phase.[14] The former host is a
h
member of the isomeric series of “half-discs” 1, while 7 is their “full-disc” analogue.
Fig. 4. The structure of discotic mesogen 7; Cr 67 Col 75 I, ref.[14].
h
Analysis of data for binary mixtures with host 1a demonstrated full miscibility with
additive 1c in the investigated range of concentrations, while the Col phase of 15 mol% mixture
h
with additive 1b was inhomogeneous. Both compounds destabilize the Col phase of the host
h
with the non-mesogenic 1b having stronger effect than 1c, and the approximately linear
6

ACCEPTED MANUSCRIPT
dependence of the Col –I transition temperature on concentration is show in Fig. 5. Extrapolation
h
of transition temperatures to pure components gave their virtual transition temperatures [TColh-I],
which together with the TColh-I for 1a are in order consistent with behaviour of pure substances:
1
a > 1c > 1b (Table 1). To compare virtual transition temperature for all three derivatives,
similar analysis was conducted for binary mixtures of 1 with “full-disc” host 7 (Fig. 4). Results
demonstrate that all three isomers 1 destabilize the Col phase of the host, although to a much
h
smaller extent than observed in host 1a. The order of extrapolated [TColh-I] is identical as in
previous experiments and follows: 1a > 1c > 1b. The smaller effect in host 7 than in 1a results
presumably from a better accommodation of the “half discs” of the additive by the “full discs” of
the host. To explain the observed significantly different phase stability in the three isomers we
focused on conformational properties of the Ph–core junction in series 1.
Fig. 5. Peak temperatures for enantiotropic Col I transitions in binary mixtures of isomers 1 in
h
“full disc” 7 and in “half-disc” 1a hosts.
DFT analysis of three methoxy analogues of series 1, derivatives 8a–8c, demonstrates
that the dihedral angle  vary significantly between different positions (Table 2). The highest
o
torsion angle of about 46 is observed for the N(1)–Ar junction in all three derivatives and the
o
smallest of about 4 for the C(3)–Ar connection. Small variations in the value of  are due to the
different electronic nature of the Ph vs 3,4,5-trialkoxyphenyl substituents:  and  are slightly
1
2
smaller for the Ph than for the latter substituent.
7

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Table 2.
a
DFT calculated torsion angles  for Ph–core junction in 8.
b
Torsion angle
compound
1
/

/

/
2
o
3
o
o
2
3
1
8
8
8
a: R = R = OCH , R = H
44.6
46.5
47.3
4.2
3.9
4.7
36.7
36.4
36.9
3
1
3
2
b: R = R = OCH , R = H
3
1
2
3
c: R = R = OCH , R = H
3
a
b
B3LYP/6-31G(2d,p) level of theory, tight convergence. Defined as  : C –C –N(1)–N(2);
1
Ph
Ph
2
: C –C –C(3)–N(4);  : C –C –C(6)–C(7).
Ph
Ph
3
Ph
Ph
Fig. 6. A plot of virtual transition temperatures [TColh-I] in host 7 vs values of torsion angles  for
the Ph group (blue) and the sum of two torsion angles for the wedge-shaped 3,4,5-
trialkoxyphenyl substituents (black) attached to the core.
Analysis of data in Tables 1 and 2 indicates that the increasing phase stability in series 1
coincides with increasing torsion angle of the Ph substituent and decreasing sum of the torsion
angle values for the wedge-shaped 3,4,5-trialkoxyphenyl substituents (Fig. 6). Thus, the most
o
stable mesophase exhibits compound 1a in which the Ph–core angle is the highest (44.6 ) and the
o
sum of the torsion angles for the 3,4,5-trialkoxyphenyl substituents is the smallest (40.9 ) in the
series. It is not clear which steric factor, maximum co-planarity of the wedge-shaped substituent
or the Ph group, is dominant in phase stability. Interestingly, if the geometry–mesophase stability
8

ACCEPTED MANUSCRIPT
relationship holds for pure compounds then the expected Col I transitions for the non-
h
o
o
mesogenic 1b is no higher than –60 C or about –130 C using two data points for [TColh-I]
obtained in host 7 and TColh-I for the pure derivatives 1a and 1c. This prediction is consistent with
the lack of mesophase appearance in the deeply supercooled sample of 1b.
According to a model indicated for 1a by powder XRD results,[14] the “half-discs”
overlap antiparallel in columns of the Col phase, as shown in Fig. 7 and evident from a
h
comparable column size for 1a (a = 30.0 Å) and for 7 (a = 32.5 Å). The nearly “radial”
distribution of alkyl chains observed in the model for antiparallel two molecules of 1a and
favorable for column formation is also found in analogous models of 1b and 1c (see the SI). The
model implies a high degree of co-planarity (low torsion angle) of the Ph group with the
heterocycle to achieve the most efficient packing of the column core. Therefore, it is surprising
that the most stable mesophase is observed for 1a with the least co-planar Ph group (Table 2). A
more plausible explanation for highest thermal stability of 1a is the highest co-planarity of the
wedge-shaped substituents, which through intermolecular interactions at the periphery of the
column defines the overall separation between the molecules and hence packing of the column
core.
OC12H25
OC12H25
OC12H25
C12H25O
N
N
C12H25
O
OC12H25
N
N
N
N
C12H25O
C12H25O
OC12H25
OC12H25
OC12H25
OC12H25
Fig. 7. A proposed antiparallel arrangement of molecules 1a in a column of the Col phase.
h
An alterative explanation of the phase stability may involve dipolar interactions of the
molecular cores. DFT calculations show that the 1,4-dihydrobenzo[e][1,2,4]triazin-4-yl is
…
moderately polar with the net dipole of 3.08 D oriented approximately along the C(3) C(8a) line
(Fig. 8). Inspection of the molecular models suggests favorable dipolar interactions in all
derivatives 1a–1c with antiparallel molecular arrangements such as for 1a in Fig 7. Thus, the
9

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polarity should not significantly affect the molecular organization into columns and hence phase
stability in the three isomeric derivatives.
Fig. 8. Electric dipole components  and  in the parent 1,4-dihydrobenzo[e][1,2,4]triazin-4-yl
x
y
(the B3LYP/6-31G(2d,p) level of theory).
2
.4. Electronic Absorption Spectroscopy
The availability of the three isomers 1a – 1c permits to investigate the impact of the
substitution pattern on absorption spectra.
4
5
4
3
2
1
x 10
x 10
x 10
x 10
x 10
412 nm
4
4
4
4
e
-
1
-1
414 nm
428 nm
L mol cm
3
80
400
420
440
1a
1
1
b
c
0
300
400
500
wavelength /nm
600
700
Figure 9. UV-vis spectra for derivatives 1a-1c.
All three isomers 1a – 1c exhibit typical for the Blatter radical [19] derivatives patterns in
the UV-vis spectra: an intense absorption band at about 300 nm (log  ≈ 4.6), medium intensity
absorptions at about 400 nm (log  ≈ 4.0) and a broad, low intensity absorption in the visible
range up to about 600 nm (Fig. 9). Consequently, all three compounds appear as dark brown in
1
0

ACCEPTED MANUSCRIPT
solutions. The spectra for the three isomers differ in the middle range. Thus, exchanging the
N(1)–Ph group in 1a with the 3,4,5-trialkoxyphenyl shifts the maximum of absorption at 428 nm
to higher energies by about 13 nm in isomers 1b and 1c (Fig. 9 inset).
3
. Summary and Conclusions
Analysis of a series of isomeric “half-disc” derivatives 1 in the pure form and in binary
mixtures suggests that the conformations and steric properties of the wedge-shaped substituents
forming the periphery of the columns is the dominant factor affecting Col phase stability in this
h
series. This tendency apparently overrides the conformational effects of the Ph substituent in the
column’s core. Thus, self-organization of molecules in the fluid phase of 1 prefers co-planar
arrangements of the wedge-shaped substituents around the core, which presumably results in
tighter packing of the cores, despite high torsion angle of the N(1) substituent in the core.
These findings provide an important insight into the design of other discotic mesogens
derived form the benzo[e][1,2,4]triazinyl system.
4
. Computational Details
Quantum-mechanical calculations were carried out using the Gaussian 09 suite of programs.[20]
Geometry optimizations were undertaken at the B3LYP/6-31G(2d,p) level of theory using tight
convergence limits.
5
. Experimental Section
5
.1. General procedures
Reagents and solvents were used as received without further purification.
Tetrahydrofuran was dried over sodium metal in the presence of benzophenone and distilled just
before usage. Products were purified by flash chromatography on silica gel (230–400 mesh,
Merck or Fluka). Reported yields refer to analytically pure samples. NMR spectra were recorded
with a Bruker AVIII 600 instrument. Chemical shifts are reported relative to solvent residual
1
13
peaks ( H NMR:  7.26 ppm [CDCl ];  2.50 ppm [DMSO-d ]; C NMR:  77.0 ppm [CDCl ];
3
6
3
13

39.52 ppm [DMSO-d ]). All C-NMR spectra are proton-decoupled. For detailed peak
6
assignments 2D spectra were measured (COSY, HMQC, HMBC): unmarked signals below 100
pm are triplets, while above 100 ppm are doublets. IR spectra were measured with a FTIR
1
1

ACCEPTED MANUSCRIPT
NEXUS spectrometer (as KBr pellets). MS spectra were performed with a Finnigan MAT-95
(EI-) or with a Varian 500-MS LC Ion Trap (ESI-) instruments. Positive ion MALDI mass
spectra were recorded on the Voyager-Elite instrument in reflector mode. A 10 mg/mL solution
of -cyano-4-hydoxycinnaminic acid (CHCA) in THF was used as the matrix. Melting points
were determined in capillaries (MEL-TEMP II apparatus) and are uncorrected. UV-vis spectra
were recorded with Perkin Elmer Lambda 45 Spectrometer in spectroscopic grade cyclohexane
–
6
at concentrations of 2–20  10 and fitted to the Beer–Lambert law. Synthesis of 1 was carried
out under argon in a flame-dried flask with addition of the reactants via a syringe; subsequent
manipulations were conducted in air.
5
.2. Synthesis of 1,4-dihydrobenzo[e][1,2,4]triazinyl radical 1. A general procedure.
To a solution of 1-bromo-3,4,5-tridodecyloxybenzene [21] (710 mg, 1.00 mmol) in dry THF (18
mL), a solution of tert-BuLi (1.7M in pentane, 1.29 mL, 2.20 mmol) was added dropwise at –25
°
C. The resulting mixture was stirred at this temperature until the starting bromide was fully
consumed (20 min, TLC monitoring of samples quenched with acetone; SiO , petroleum
2
ether/CH Cl 3:1, visualization with the p-anisaldehyde stain), and the cooling bath was removed
2
2
to allow the mixture slowly warm up. After the yellow color of the solution faded indicating
decomposition of excess tert-BuLi, the mixture was cooled to 40 °C, and immediately used for
subsequent step.
An excess solution of freshly prepared 3,4,5-tridodecyloxyphenyllithium (ca. 0.40-0.50
mmol) in dry THF was added dropwise at 0 °C to a vigorously stirred solution of appropriate
benzo[e][1,2,4]triazine 2 (167 mg, 0.20 mmol) in dry THF (1.5 mL) under Ar atmosphere. The
mixture was kept at rt for 30 min, then it was opened to air, diluted with petroleum ether (ca. 25
mL), and the stirring was continued for 1.5 h. After solvents were removed under reduced
pressure, the resulting mixture was flash chromatographed on silica gel (SiO deactivated with
2
2
% Et N in petroleum ether before usage; petroleum ether/Et O 5:1). Crude product was washed
3 2
with hot MeCN (3  100 mL) to remove 3,4,5-(C H O) C H byproduct (TLC monitoring), and
1
2
25
3
6
3
purified by column chromatography (deactivated SiO , petroleum ether/Et O 8:1; visualization
2
2
with p-anisaldehyde stain) to yield pure 1, which was recrystallized 6 times from a
MeCN/EtOAc mixture.
1
2

ACCEPTED MANUSCRIPT
5
.2.1. 3,6-Bis(3,4,5-tridodecyloxyphenyl)-1-phenyl-1,4-dihydrobenzo[1,2,4]triazinyl (1a).[14]
UV (cyclohexane), max (log ) 296 (4.70), 375 (3.85), 428 (3.91), 620 (2.78) nm.
.2.2. 1,6-Bis(3,4,5-tridodecyloxyphenyl)-3-phenyl-1,4-dihydrobenzo[1,2,4]triazinyl (1b).
Off-white solid; yield: 220 mg (75%); UV (cyclohexane), max (log ) 293 (4.54), 350 (3.90),
5
-1
4
12 (4.10), 519 (3.17) nm; IR (KBr) v 1584, 1469, 1237, 1119 cm ; MALDI-MS, m/z 1466.4
+
(
100, [M] ). Anal. Calcd for C H N O : C, 79.45; H, 11.14; N, 2.87. Found: C, 79.56; H,
97
162
3
6
1
1.23; N, 2.78.
.2.3. 1,3-Bis(3,4,5-tridodecyloxyphenyl)-6-phenyl-1,4-dihydrobenzo[1,2,4]triazinyl (1c). Green
5
solid; 84% yield; UV (cyclohexane), max (log ) 299 (4.66), 354 (3.97), 414 (3.91), 586 (2.94),
-1
6
17 (2.85) nm; IR (KBr) v 1593, 1501, 1468, 1442, 1380, 1230, 1122 cm ; MALDI-MS, m/z
+
1
466.4 (100, [M] ). Anal. Calcd for C H N O : C, 79.45; H, 11.14; N, 2.87. Found: C, 79.33;
9
7
162
3
6
H, 11.29; N, 2.73.
5
.3. Synthesis of 3,6-diarylbenzo[e][1,2,4]triazine 2. A general procedure.
A solution of 6-bromobenzo[e][1,2,4]triazine derivative 5 or 6 (1.00 mmol), K CO (516 mg,
2
3
3
.73 mmol), and appropriate arylboronic acid (1.25 mmol; for the preparation of 3,4,5-
tridodecyloxyphenylboronic acid, see ref [14]) in THF/H O (5:2 mixture, 25 mL) was degassed
2
by a repeated procedure of freeze-pump-thaw and Pd(PPh ) (144 mg, 10 mol% with respect to
3
4
the boronic acid) was added. The mixture was refluxed for 24 hrs, poured into water (70 mL) and
extracted with CH Cl (3  50 mL). Combined organic layers were dried over Na SO , and the
2
2
2
4
solvents were removed under reduced pressure. Crude product was flash chromatographed (SiO2,
gradient petroleum ether/CH Cl 1:1 to pure CH Cl ) and recrystallized from EtOH/EtOAc
2
2
2
2
mixture to give 3,6-diaryl benzo[e][1,2,4]triazine 2.
5
.3.1 6-(3,4,5-Tridodecyloxyphenyl)-3-phenyl-benzo[e][1,2,4]triazine (2b).
1
Yellow solid; 84% yield; mp 95-96 °C; H NMR (CDCl , 600 MHz)  0.88 (t, J = 7.0 Hz, 6H),
3
0
.89 (t, J = 7.0 Hz, 3H), 1.23-1.41 (m, 48H), 1.49-1.54 (m, 6H), 1.80 (quint, J = 6.6 Hz, 2H),
.87 (quint, J = 6.6 Hz, 4H), 4.06 (t, J = 6.6 Hz, 2H), 4.10 (t, J = 6.6 Hz, 4H), 6.97 (s, 2H), 7.57-
.62 (m, 3H), 8.07 (dd, J = 8.8 Hz, J = 1.9 Hz, 1H), 8.21 (d, J = 1.9 Hz, 1H), 8.55 (d, J = 8.8
1
7
1
2
1
3

ACCEPTED MANUSCRIPT
13
Hz, 1H), 8.76-8.79 (m, 2H) ppm; C NMR (CDCl , 151 MHz)  14.1(q), 22.68, 22.70, 26.14,
3
2
6
1
1
6.15, 29.36, 29.40, 29.43, 29.5, 29.62, 29.65*, 29.66*, 29.71*, 29.75, 29.76, 30.4, 31.93, 31.95,
9.5, 73.7, 106.6*, 125.4, 128.8*, 129.0*, 129.7, 130.2, 131.4, 133.8(s), 135.8(s), 139.8(s),
41.5(s), 145.8(s), 148.4(s), 153.8(s)*, 160.2(s) ppm (*higher intensity); IR (KBr)  1581, 1467,
-1
+
+
439, 1331, 1135 cm ; EI-MS, m/z 835.7 (28, [M] ), 807.6 (100, [M-N ] ). Anal. Calcd for
2
C H N O : C, 78.99; H, 10.24; N, 5.02. Found: C, 78.79; H, 10.31; N, 5.01.
55
85
3
3
5
.3.2. 3-(3,4,5-Tridodecyloxyphenyl)-6-phenyl-benzo[e][1,2,4]triazine (2c).
1
Yellow solid; 90% yield; mp 65-66 °C; H NMR (CDCl , 600 MHz)  0.880 (t, J = 7.0 Hz, 6H),
3
0
.883 (t, J = 7.0 Hz, 3H), 1.24-1.42 (m, 48H), 1.50-1.56 (m, 6H), 1.80 (quint, J = 6.5 Hz, 2H),
.89 (quint, J = 6.5 Hz, 4H), 4.10 (t, J = 6.5 Hz, 2H), 4.18 (t, J = 6.5 Hz, 4H), 7.48-7.52 (m, 2H),
.54-7.58 (m, 2H), 7.79-7.82 (m, 2H), 8.05 (s, 2H), 8.07 (dd, J = 8.7 Hz, J = 1.8 Hz, 1H), 8.27
1
7
1
2
1
3
(
d, J = 1.8 Hz, 1H), 8.55 (d, J = 8.7 Hz, 1H) ppm; C NMR (CDCl , 151 MHz)  14.1(q), 22.69,
3
2
3
1
2.70, 26.14, 26.18, 29.37, 29.40, 29.5*, 29.63, 29.67*, 29.68*, 29.71, 29.72, 29.75, 29.77, 30.4,
1.93, 31.95, 69.3, 73.6, 107.2*, 126.0, 127.7*, 129.21, 129.25*, 129.8, 129.9, 130.4(s),
38.9(s), 141.5(s), 141.6(s), 145.5(s), 148.1(s), 153.6(s)*, 160.0(s) ppm (*higher intensity); IR
-1
(
KBr)  1616, 1584, 1489, 1467, 1451, 1432, 1347, 1122, 755, 720 cm ; ESI-MS, m/z 859 (88,
+
+
[
M+Na] ), 837 (100, [M+H] ). Anal. Calcd for C H N O : C, 78.99; H, 10.24; N, 5.02. Found:
55 85 3 3
C, 78.86; H, 10.31; N, 5.09.
5
.4. Synthesis of N’-(4-bromo-2-nitrophenyl)benzhydrazide (4).
A mixture of 4-bromo-1-fluoro-2-nitrobenzene (4.40 g, 20.00 mmol, 2.43 mL) and
benzhydrazide (3, 2.72 g, 20.00 mmol) in dry DMSO (15 mL) was stirred at 85 °C for 6 hrs. The
mixture was allowed to reach room temperature, diluted with EtOAc (150 mL) and extracted
with H O (3  50 mL). The separated organic layer was dried over Na SO , filtered, and the
2
2
4
solvents were removed in vacuo. The crude product was purified by recrystallization from hot
EtOH (two times) to provide 4.10 g (61% yield) of benzhydrazide 4 as an orange crystals: mp
1
1
2
2
99-201 °C; H NMR (DMSO-d , 600 MHz)  7.15 (d, J = 9.1 Hz, 1H), 7.54 (brt, J ≈ 7.6 Hz,
6
H), 7.62 (brt, J ≈ 7.4 Hz, 1H), 7.72 (dd, J = 9.1 Hz, J = 2.3 Hz, 1H), 7.95 (brd, J ≈ 7.9 Hz,
1
2
1
3
H), 8.23 (d, J = 2.3 Hz, 1H), 9.52 (brs, 1H), 10.82 (brs, 1H) ppm; C NMR (DMSO-d , 151
6
1
4

ACCEPTED MANUSCRIPT
MHz)  107.8(s), 117.3, 127.51*, 127.55, 128.5*, 132.07, 132.13(s), 132.14(s), 138.7, 144.6(s),
1
66.1(s) ppm (*higher intensity); IR (KBr)  3326 (N-H), 3237 (N-H), 1654 (C=O), 1527, 1511,
-1
1
473, 1328, 1258, 1217, 1135, 685, 660 cm . Anal. Calcd for C H BrN O : C, 46.45; H, 3.00;
13 10 3 3
N, 12.50. Found: C, 46.37; H, 2.95; N, 12.65.
5
.5. Synthesis of 6-bromo-3-phenylbenzo[e][1,2,4]triazine (5).
To a suspension of benzhydrazide 4 (2.60 g, 7.74 mmol) in glacial acetic acid (50 mL), Sn
powder (5.39 g, 45.40 mmol) was added, and the mixture was vigorously stirred at ambient
temperature for 1.5 h. The resulting mixture was heated by immersing the reaction flask into a
preheated oil bath at 130 °C for 25 min. After cooling, the mixture was extracted with EtOAc
(
300 mL) and H O (150 mL), and the layers were separated. The organic layer was washed with
2
H O (4  100 mL), then with sat. NaHCO (3  50 mL), and dried over Na SO . The resulting
2
3
2
4
mixture was dissolved in a MeOH/CH Cl mixure (1:1, 50 mL), solid NaIO (2.47 g, 11.55
2
2
4
mmol) was added, and the mixture was stirred at room temperature until the oxidation of the
respective dihydro-derivative was completed (TLC monitoring, CH Cl ). The mixture was
2
2
filtered, the filtrate was evaporated, and the resulting dark-red residue was purified by column
chromatography (SiO , CH Cl ). The product was recrystallized from hot EtOH to afford 1.31 g
2
2
2
1
(
59% yield) of bromobenzo[e][1,2,4]triazine 5 as an orange solid: mp 141-142 °C; H NMR
(
CDCl , 600 MHz)  7.58–7.61 (m, 3H), 7.89 (dd, J = 8.9 Hz, J = 2.0 Hz, 1H), 8.30 (d, J = 2.0
3
1
2
1
3
Hz, 1H), 8.39 (d, J = 8.9 Hz, 1H), 8.73–8.75 (m, 2H) ppm; C NMR (CDCl , 151 MHz) 
3
1
28.9*, 129.0*, 130.6(s), 130.8, 131.4, 131.8, 134.0, 135.2(s), 141.6(s), 145.2(s), 160.2(s) ppm
-1
(
*higher intensity); IR (KBr)  1594, 1508, 1448, 1325, 1011, 902, 774, 701 cm . Anal. Calcd
for C H BrN : C, 54.57; H, 2.82; N, 14.69. Found: C, 54.55; H, 2.77; N, 14.81.
1
3
8
3
5
.6. Preparation of binary mixtures
A mixture of known amounts of additive 1 (~1 mol) and the host (1a or 7, ~10 mol) was
placed in a small vial and 1,2-dichloroethane (0.1 mL) was added. The mixture was heated
and stirred with a spatula at 50 °C (hot stage) to give a homogenous solution. The solvent
was removed under stirring at about 80 °C and the resulting mixture was analyzed by POM
to confirm homogeneity. Typically, each mixture was analyzed by DSC in 3 heating-cooling
1
5

ACCEPTED MANUSCRIPT
cycles and reproducible results (within 0.5 K) were averaged. The resulting transition peak
temperatures TColh-I were used to obtain virtual transition temperatures [TColh-I] for the
additive by linear extrapolation to x = 1 with the intercept value set at the T
for the pure
Colh-I
i
o
o
host (73 C for 1a and 75 C for 7).[14]
Acknowledgements
Support for this project was provided by the National Science Center (2017/25/N/ST5/01805 and
014/13/B/ST5/04525).
2
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3444.
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Highlights of the paper



Isomeric disc-like derivatives of a stable radical with diverse mesophase behavior
Columnar phase binary mixture investigation
Correlation of DFT-derived structural parameters with mesophase behavior
1
8