Tuning the Magnetic Properties of Columnar Benzo[e][1,2,4]triazin-4-yls with the Molecular Shape

Article abstract of DOI:10.1002/cphc.201800965

A homologous series of disc-like 1,3,6-trisubstituted benzo[e][1,2,4]triazin-4-yls 1[n] was synthesized and their structural, thermal, optical, magnetic, and electric properties were investigated. The results demonstrate that all members of the series dis

Full text of DOI:10.1002/cphc.201800965

DOI: 10.1002/cphc.201800965
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Tuning the Magnetic Properties of Columnar Benzo[e]
[1,2,4]triazin-4-yls with the Molecular Shape
Marcin Jasiński,[a] Katarzyna Szymańska,[a] Anita Gardias,[b] Damian Pociecha,[c]
Hirosato Monobe,[d] Jacek Szczytko,[b] and Piotr Kaszyński[a, e, f]
Dedicated to Professor Janusz Zakrzewski of University of Łódź on the occasion of his 70th birthday.
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A homologous series of disc-like 1,3,6-trisubstituted benzo[e]
[1,2,4]triazin-4-yls 1[n] was synthesized and their structural,
thermal, optical, magnetic, and electric properties were inves-
tigated. The results demonstrate that all members of the series
display a Colh phase with clearing temperatures depending on
the length of the alkoxy chains at the N(1) position, hence the
shape of the disc. Powder XRD and magnetic data indicate a
gradual change in the column diameter and magnetic behavior
in the series in transition from half-disc in 1[0] (antiferromag-
netic interactions) to full-disc geometry in the 1[12] homologue
(ferromagnetic interactions with J/kB = +7.5 K). Studies of
binary systems revealed that a 1:1 mixture of 1[0] and 1[12]
exhibits modest stabilization of the Colh phase with an
expanded range, and magnetic behavior typical for 1[0] in the
rigid phase obtained from the melt. Electric measurements
demonstrated hole mobility of ~10À 3 cm2 VÀ 1 sÀ 1 and dark
conductivity of ~10À 11 ScmÀ 1 in the mixture and individual
compounds. The latter is enhanced up to
simultaneous illumination with UV light.
4 times by
1. Introduction
channels and many columnar discotic phases exhibit semi-
conductive properties and high charge mobility.[6] The highest
mobility is observed in aligned columnar liquid crystalline
phases with either homeotropic (face-on) orientation of
columns (attractive for e.g. photovoltaic cells) or planar (edge-
on) orientation desired in field-effect transistors.
There is an increasing interest in organic spin-containing
molecules as potential materials for information processing and
bottom up fabrication of organic spintronic devices,[1] such as
spin valves and spin filters.[2] The advantage of organic
compounds over inorganic materials lies in weak spin-orbit
coupling and hyperfine interactions,[1b] and consequently rela-
tively long spin lifetime and spin diffusion lengths.[3] One
approach to such devices involves a hierarchical self-assembly
of nano-sized structures, e.g. paramagnetic microtubes and
vesicles,[4] that exhibit charge and spin transport properties.
Another attractive way to organize organic paramagnetic
materials is to use self-assembly properties of liquid crystals.[5]
For instance, disc-like molecules self-organize in unidimensional
Recently, we reported[7] discotic materials derived from the
exceptionally stable benzo[e][1,2,4]triazin-4-yl[8] in which the
electron spin is delocalized in the π-system of the rigid core.
Preliminary experiments indicated that the contact of the π
faces and hence the type of spin-spin interactions is controlled
by the peripheral substituents. Thus, compound 1[0] with a
small substituent at the N(1) position (Figure 1) exhibits strong
[a] Dr. M. Jasiński, K. Szymańska, Prof. P. Kaszyński
Faculty of Chemistry, University of Łódź
Tamka 12, 91-403 Łódź, Poland
[b] A. Gardias, Dr. J. Szczytko
Institute of Experimental Physics, Faculty of Physics University of Warsaw,
Pasteura 5, 02-093 Warsaw, Poland
[c] Dr. D. Pociecha
Figure 1. The structure of members of homologous series 1[n].
Faculty of Chemistry, University of Warsaw, Żwirki i Wigury 101, 02-089
Warsaw, Poland
[d] Dr. H. Monobe
National Institute of Advanced Industrial Science and Technology (AIST),
Kansai Centre, Ikeda, Osaka 563-8577, Japan
[e] Prof. P. Kaszyński
antiferromagnetic interactions, while 1[12] derivative shows
weak ferromagnetic spin-spin exchange interactions. In addi-
tion, both derivatives exhibit photoinduced charge carrier (hole)
mobility (μh) of about 1.4×10À 3 cm2 VÀ 1 sÀ 1 in partially aligned
samples. For further development of this type of molecular
materials for molecular electronics and spintronic applications it
is important to understand the origin of the observed structure-
dependent magnetic behavior through systematic investigation
of the homologous series.
Centre of Molecular and Macromolecular Studies
Polish Academy of Sciences
Sienkiewicza 112, 90-363 Łódź, Poland
E-mail: piotrk@cbmm.lodz.pl
[f] Prof. P. Kaszyński
Department of Chemistry, Middle Tennessee State University, Murfreesboro,
TN 37132, USA
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/cphc.201800965.
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Herein, we report the behavior of a homologous series 1[n]
containing even members of the series. We report thermal,
magnetic and electric behavior in the series and for binary
mixtures of two terminal homologues.
Analysis of data in Table 1 demonstrates that all compounds
exhibit a columnar hexagonal phase (Colh) with characteristic
textures as shown for 1[8] in Figure 2. Upon substitution of the
N(1)À Ph ring in 1[0] with three OMe groups, the mesophase is
stabilized by 20 K. Extension of the alkyl chain leads to a
decrease of the mesophase stability, which for 1[4] and 1[6]
homologues is monotropic (Table 1, and Figure 3) with the
lowest in the series ColhÀ I transition temperatures. Further
increase of the chain length gradually brings the clearing
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2. Results
2.1. Synthesis
°
temperature up to above 70 C. The variation of transition
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Radicals in series 1[n] were obtained in typical yields of 70–90%
using our recently reported protocol[7,9] involving addition of
ArLi to benzo[e][1,2,4]triazine 2 followed by aerial oxidation of
the intermediate anion (Scheme 1). The ArLi reagents were
generated from the corresponding ArBr 3[n] and t-BuLi. The
benzo[e][1,2,4]triazine 2 was prepared as shown in Scheme 1.
temperatures in the homologous series is shown graphically in
Figure 4.
Table 1. Transition temperatures [ C] and enthalpies (kJmolÀ 1, in italics)
°
for 1[n].[a]
n
Ar
Phase behavior
0
1
2
4
6
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12
Ph[b]
Cr 46 (49.2) Colh 73 (6.0) I
Cr 64 (86.9) Colh 93 (5.9) I
Cr 69 (72.9) Colh 76 (4.9) I
Cr 60 (72.1) [Colh 50 (6.6)][c]
Cr 61 (69.4) [Colh 52 (6.8)][c]
Cr 57 (51.9) Colh 64 (11.0) I
Cr 64 (83.5) Colh 72 (13.9) I
Cr 67 (85.7) Colh 75 (15.2) I
C6H2-3,4,5-(OCH3)3
C6H2-3,4,5-(OC2H5)3
C6H2-3,4,5-(OC4H9)3
C6H2-3,4,5-(OC6H13)3
C6H2-3,4,5-(OC8H17)3
C6H2-3,4,5-(OC10H21)3
C6H2-3,4,5-(OC12H25)3
I
I
[b]
[a]
Peak temperatures obtained on first heating: Cr=crystal, Colh =
columnar hexagonal, I=isotropic; enthalpy of transition in parentheses.
[b]
[c]
Ref. [7] Monotropic transition temperature obtained on heating.
Scheme 1. Synthesis of benzo[e][1,2,4]triazinyl derivatives 1[n]. Reagents and
conditions: i) 1) Sn, AcOH, rt 2 hrs, reflux 25 min 2) NaIO4, MeOH/CH2Cl2; ii)
3,4,5-(C12H25O)3C6H2B(OH)2, Pd(PPh3)4, K2CO3, THF/H2O, reflux 24 hr; iii) 1) ArLi,
THF, 2) air.
Figure 2. Left: optical texture of a Colh phase obtained for 1[8] upon cooling
from the isotropic phase. Right: the same phase after sheering.
Scheme 2. Synthesis of 3,4,5-trialkoxybromobenzenes (3[n]). Reagents and
°
conditions: i) BBr3, CH2Cl2, À 78 C to rt, 16 h; ii) alkyl bromide (3.3–4.0 equiv.),
°
K2CO3, DMF, 80 C, 24 hrs.
The requisite 3,4,5-trialkoxybromobenzenes (3[n]) were
obtained by alkylation of 3,4,5-trihydroxybromobenzene (4,
Scheme 2)[10] according to a general literature procedure.[11]
2.2. Thermal and Optical Characterization
Thermal behavior of compounds in series 1[n] was investigated
by differential scanning calorimetry (DSC) and polarized optical
microscopy (POM). The results are shown in Table 1 and
Figures 2–4.
Figure 3. DSC trace of 1[4]. The heating and cooling rates are 5 KminÀ 1
.
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Figure 6. Temperature dependence of the lattice parameter a in the
homologous series 1[n].
Figure 4. Phase diagram for homologous series 1[n].
2.3. Phase Structure
also visible in a comparison of lattice parameter values a for all
homologues 1[n], measured at 10 K below the ColhÀ I transition
(Figure 7). Thus, for n�4 the column diameter is essentially
X-ray diffraction (XRD) method was used to confirm the phase
identification made on the basis of optical textures. All
homologues 1[n] gave qualitatively the same diffraction
patterns, with a series of sharp, Bragg-type reflections at low
angle and two broad signals at high angle range (Figure 5). Low
Figure 7. Lattice parameter a in the homologous series 1[n] obtained at TColh
À 10 K.
independent on the length of terminal chains attached to N
(1)À Ph ring, while it linearly increases for longer homologues.
Two broad diffraction signals detected in the high angle
range (Figure 5) indicate short-range (liquid-like) positional
correlations of molecules along the columns, which are
characteristic of disordered-type LC columnar phases. Their
positions reflect the mean distance between aliphatic chains
and the mesogenic cores, and they are practically temperature
independent for each compound. It should be noted that the
former signal is essentially independent on the homologue and
is typically 4.4–4.5 Å, while the latter slightly increases with
increasing n, from 3.4 Å for 1[0] to 3.7 Å for 1[12]. The growing
separation between the discs along the columns is presumably
due to the increasing steric demands of the elongated alkoxy
chains. Analysis of the shape of this signal in 1[2] (Figure 5)
indicates a slight increase of the correlation length of positional
Figure 5. X-ray diffractogram for 1[2] obtained by integration of the 2D
°
pattern at 50 C (inset): Colh, a=29.8 Å, diffused 4.4 Å and 3.6 Å.
pffiffiffi
angle peaks, which positions in q-space are in a ratio 1: 3:2,
point to a long-range positional order of columns that are
arranged in a two-dimensional hexagonal lattice, with a lattice
parameter a (column diameter) corresponding roughly to the
dimension of a single molecule. Interestingly, the lattice
parameter a exhibits different dependence on temperature for
short- and long-tail homologues: the thermal expansion
coefficient is positive for 1[0], 1[1] and 1[2], while it is negative
for 1[4] and higher homologues (Figure 6). This cross-over is
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order of molecules along the column from 15 Å to 17 Å upon
liquid moves in the capsule, which results in changing
geometry and difficulties in centering of the magnetic signal. In
addition, all homologues 1[n] exhibit significant diamagnetic
anisotropy, which makes isotropic and general Pascal constants
unreliable to calculate the diamagnetic contribution. Therefore,
the diamagnetic correction χdia, which accounts for the sample
and the sample holder, was established by assuming para-
magnetic saturation in the isotropic phase, which implies the
horizontal χp ·T(T) plot. This analysis was performed separately
for data obtained in heating and cooling cycles for each
homologue. Details are provided in the ESI.
Cooling of 1[6] from the isotropic phase results in a steady
increase of the antiferromagnetic interactions with a slight
decrease of magnetization at the I!Colh transition (Figure 8).
Upon crystallization at 292 K the number of free spins increases
by 8%. Finally, below 10 K the χp ·T curve shows an upturn
indicative of ferromagnetic interactions. Similar analysis was
performed for other members of the homologous series and
their χp ·T(T) plots for the cooling cycle are shown in Figure 9.
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°
°
cooling from 80 C to 30 C.
2.4. Magnetic Characterization
Magnetic susceptibility measurements in series 1[n] revealed
significant and diverse intermolecular spin-spin interactions,
which are dependent on the alkyl chain length and thermal
history of the sample.
Analysis of pristine crystalline samples of 1[n] demonstrated
weak ferromagnetic interactions in the solid state for homo-
logues n�6. This is evident from the upturn of the χp ·T(T)
curve, as shown for 1[6] in Figure 8. Assuming close π-stacked
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Figure 8. χp ·T versus temperature plot for 1[6] obtained on heating of a
pristine sample (red) and subsequent cooling (blue). Temperature change
rate 0.8 KminÀ 1, field 0.1 T.
arrangements of molecules in the solid phase (similar to those
in the Colh) and hence 1-D Heisenberg ferromagnetic chain
model, the magnitude of these interactions was estimated with
Baker’s high temperature series expansion[12] (eq 1) at J/kB =
2.20(1) K.
Figure 9. χp ·T versus temperature plots for 1[n] obtained on cooling
(0.8 KminÀ 1) at 0.1 T. Red: lower members (n=0–4); black: higher members
(n=6–12).
NAg2m2B
4kBT
Analysis of results for the homologous series demonstrates
that antiferromagnetic interactions are becoming weaker with
increasing length of the alkyl chain (increasing n). This is
evident from the increasing paramagnetic character of the
isotropic liquid, for which the χp ·T value changes from about
0.19 Kcm3 molÀ 1 for 1[1] to 0.43 Kcm3 molÀ 1 for 1[12] (Figure 9).
A similar change is observed for the Colh!Cr transition. While
magnetization slightly decreases upon crystallization for 1[0],
1[1] and 1[4], it clearly increases starting with homologue 1[6]
up to 13% for 1[12]. On the other hand, at the I!Colh transition
the magnetic moment slightly decreases for all members of the
series with the largest decrease for 1[0] (12%) and smallest for
1[4] and 1[6]. Thus, organization of molecules in columns
results in small increase of antiferromagnetic interactions, while
crystallization of the columnar phase results in an onset of
ferromagnetic interaction for higher homologues. An estimate
of the magnitude of these ferromagnetic interactions with
Baker’s function (eq 1) demonstrates again increasing ferromag-
netic character of the intermolecular interactions in the
ð1Þ
cp ¼
� A
in which
�
1 þ 5:797991x þ 16:902653x2 þ 29:376885x3þ
A ¼
1 þ 2:7979916x þ 7:008678x2þ
2
�
þ29:832959x4 þ 14:036918x5
3
þ8:6538644x3 þ 4:5743114x4
and
J
x ¼
2kBT
Upon heating above 300 K homologues melt and form fluid
phases. As shown for 1[6] in Figure 8, the abrupt increasing of
the paramagnetic character of the sample at 334 K coincides
with melting to an isotropic liquid. The resulting paramagnetic
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Figure 12. Nona-methoxy derivative 4. Left: antiparallel alignment of two
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molecules. Right: total spin density map.
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containing central heterocyclic rings governed by steric require-
ments of the molecules undergoing nanosegregation of the
rigid and flexible parts (column formation) during the phase
transition. Thus, nanosegregation results in co-facial π–π
interactions most likely with antiparallel molecular orientation,
as shown for 4 in Figure 12, an all-methoxy analogue of 1[1].
The length of the alkyl chains of the N(1)À Ar substituent affects
the relative position of the π systems, hence the overlap of
positive and negative spin densities (Figure 12) and resulting
from it magnetic interactions, according to the McConnell’s
model.[17] Thus, for homologues 1[0], 1[1], 1[2] and 1[4] with
short alkyl chains, column self-assembly allows for relatively
little restricted π–π contacts with favourable aniferromagnetic
spin-spin interactions, as evident from essentially constant
column size of about 30 Å (Figure 7). For molecules with longer
alkyl substituents, nanosegregation of aliphatic and aromatic
segments apparently overrides the preference for low spin
system. To accommodate the increasing steric demand of the
longer alkyl chains, the relative positions of the π faces are
shifted, which changes the type of overlap between the
heterocycles and gives rise to weak ferromagnetic exchange
interactions. The effect of this steric demand on column
geometry is evident from increasing column size (Figure 7) and
inter-core separation.
Figure 10. Exchange interaction values J/kB obtained for 1[n] on heating of
pristine samples (red) and on cooling from the isotropic liquid (blue) at a
rate 0.8 KminÀ 1 at 0.1 T.
crystalline phase of series 1[n] (Figure 10). Analysis of the results
shows that stronger exchange interactions are observed in
pristine crystalline samples than in solid samples obtained by
crystallization of the liquid. This difference might be due to
partial glassification of the columnar phase and incomplete
crystallization, previously observed for 1[12].[7]
Further analysis of 1[12], with a full disc molecular shape
and the largest in the series ferromagnetic exchange inter-
actions (Figure 10), was performed at a constant temperature
and variable magnetic field, B. Thus, magnetization data, Mp(B),
for 1[12] obtained at 2 K confirmed the variable temperature
measurements and demonstrated good fit to the Bruillouin
function for S=5/2 or 3 (Figure 11).
2.5. Binary Mixtures
Binary mixtures of two extreme members of the homologous
series, 1[0] and 1[12], exhibiting the most diverse magnetic and
steric properties were prepared in ratios 1:3, 1:1 and 3:1 and
the partial phase diagram is shown in Figure 13.
The graph in Figure 13 shows that despite mixing of
molecules with two different shapes, the ColhÀ I transition is not
depressed, as it might be expected. On the contrary, the 1:1
mixture exhibits a small stabilization of the Colh relative to the
pure components. Interestingly, the 1:1 mixture could be
considered as a mimic of homologue 1[6], for which the ColhÀ I
Figure 11. Paramagnetic component of molar magnetization (Mp) as a
function of applied field measured for 1[0] and 1[12] at 2 K. The solid lines
represent Brillouin functions for spin state S=1/2, S=1, S=3/2, S=2, S=5/
2 and S=3.
°
transition at 52 C (Table 1) is 27 K lower than for the 1[0]–1[12]
mixture.
The observed intermolecular spin-spin interactions in 1[n]
are significantly stronger than those found in mesogenic
derivatives of 6-oxoverdazyl,[13] triphenylmethyl,[14] nitroxyl,[15]
and bent-core benzo[e][1,2,4]triazinyl,[16] in which spins are
largely isolated. The diverse nature of these spin-spin inter-
actions is presumably due to different overlap of the spin-
While the ColhÀ I transition is little affected by the composi-
°
tion of the mixture and remains at about 75 C, melting is
suppressed by over 25 K and two mixtures, 1:3 and 1:1, melt
below 20 C (Figure 13). This greatly expands the range of the
columnar phase, which is attractive in the context of applica-
°
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Powder XRD analysis of the 1:1 mixture 1[0]–1[12] con-
firmed the formation of a columnar hexagonal phase, Colh, and
revealed that the value of the lattice parameter a is close to
that of pure 1[12], while its very weak temperature dependence
is reminiscent of that of 1[0] (Figure 14). One possible
interpretation of this result is that the two homologues form
mixed stacks and that the less voluminous N(1)À Ph group in
1[0] derivative provides the necessary space for the more
sterically demanding dodecyloxy chains of the N(1) substituent
in 1[12]. Consequently, the alkoxy chains undergo little
conformational change and the column diameter remains
approximately constant in the temperature range.
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TOF transient photocurrent measurements revealed that the
positive charge mobility, μh, in an unaligned multidomain
sample of 1:1 mixture 1[0]–1[12] is slightly higher than that in
the pure components[7] and about 1.7×10À 3 cm2 VÀ 1 sÀ 1 in the
Figure 13. Partial phase diagram for a binary system of 1[0] and 1[12]
CrÀ Colh transition: diamonds, ColhÀ I transition: full circles. The dashed line
connects the ColhÀ I transition for pure components.
°
entire range 30–70 C (Figure 15). It should be noted, that while
°
for pure 1[12] the Colh phase is metastable at 30 C, in the
mixture thermodynamic stability of the mesophase extends to
°
20 C. The observed hole mobility is typical for columnar phases
formed by polycyclic aromatic derivatives[6,18] and its weak
temperature dependence suggests a hopping mechanism for
charge transport. Also the same order of magnitude for charge
mobility observed in all three materials, 1[0], 1[12] and the
mixture 1[0]–1[12], indicates that there are no fundamental
differences in the bulk structure and no additional deep level
traps in electronic conduction.
Further measurements of 1[0], 1[12] and the 1[0]–1[12]
mixture in the same electro-optical cells demonstrated dark
conductivity in the unaligned Colh mesophase on the order of
10À 11 ScmÀ 1 for 1[0] and the mixture, while for 1[12] an order of
magnitude smaller (Figure 15 bottom). The current increased 2–
4 times during irradiation of the samples with UV light. For
Figure 14. Temperature dependence of the lattice parameter a in pure
derivatives 1[0] and 1[12] (black dots) and their 1:1 binary mixture (red
diamonds).
°
instance, at 50 C the dark current was 4.8, 0.9 and 8.1×
10À 11 ScmÀ 1 for 1[0], 1[12] and the 1[0]–1[12] mixture,
respectively, while during illumination with a 365 nm UV-LED
lamp it increased to 7.8, 3.5 and 13.3×10À 11 ScmÀ 1, respectively
at 1 Hz.
Magnetization studies revealed ferromagnetic interactions
in the fresh solid sample similar to those found in pure 1[12]
(Figure 16), but with a smaller ferromagnetic exchange inter-
action (J/kB =1.96(3) K vs 7.48(4) K). On the other hand, the
binary mixture cooled from the isotropic phase shows magnetic
behavior similar to lower members of series 1[n], in which only
antiferromagnetic interactions are observed at lower temper-
atures. This is presumably due to large degree of glassification
of the Colh phase, as evident from a small decrease in χp ·T
values at 287 K.
Figure 15. Top: temperature dependence of positive carrier mobility μh
obtained by the TOF method for 1[0], 1[12] and 1:1 binary mixture 1[0]–
1[12] at 337 nm. Electric field strength 50 or 60 kVcmÀ 1. Bottom: dark
conductivity for 1[0], 1[12] and 1:1 binary mixture 1[0]–1[12].
3. Summary and Conclusions
Series 1[n] represents
a rare, self-organizing, multi-phase
system, in which magnetic properties are substituent-depen-
dent in all three phases: isotropic liquid, columnar and
crystalline with abrupt changes between them. Magnetization
at the ColhÀ Cr transition decreases for low homologues
tions. For this reason, the phase structure, magnetic and
conducive properties of the 1:1 binary mixture 1[0]–1[12] were
briefly investigated.
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Experimental Section
1
2
General. Reagents and solvents were purchased (Sigma-Aldrich,
Acros) and used as received without further purification. Tetrahy-
drofuran 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 of non-radical intermediates were measured with a
Bruker AVIII 600 instrument. Chemical shifts are reported relative to
solvent peaks (1H NMR: δ=7.26 ppm [CDCl3]; δ=2.50 ppm [DMSO-
d6]; 13C NMR: δ=77.0 ppm [CDCl3]). For peak assignment in 13C NMR
2D spectra were obtained (COSY, HMQC, HMBC). IR spectra were
measured with a FTIR spectrometer as KBr pellets or thin films. ESI-
MS spectra were performed with a Varian 500-MS LC Ion Trap.
Positive ion MALDI mass spectra were recorded on the Voyager-
Elite instrument in reflector mode. A 10 mg/mL solution of α-
cyano-4-hydroxycinnaminic acid (CHA) in THF was used as the
matrix. The synthesis of radicals 1[n] was carried out under argon in
a flame-dried flask with addition of the reactants by a syringe;
subsequent manipulations were conducted in air.
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Figure 16. χp ·T vs temperature plot for a 1:1 mixture of 1[0] and 1[12]
obtained on first heating (red) and subsequent cooling (blue). Temperature
change rate 0.8 KminÀ 1, field 0.1 T. The horizontal line marks the
0.375 Kcm3 molÀ 1 value. Vertical dashed lines mark phase transitions. The
diamagnetic correction obtained on heating was used for analysis of both
curves. The discontinuity at about 75 and 125 K is due to magnetization
crossing zero.
Preparation of 1,4-Dihydrobenzo[e][1,2,4]triazin-4-yl Radicals
1[n]: A General Procedure: An excess solution of appropriate
aryllithium (ca. 0.40-0.50 mmol) in dry THF was added dropwise at
°
0 C to a magnetically stirred solution of benzo[e][1,2,4]triazine 2
(antiferromagnetic interactions in half discs) and increases in
high homologues (ferromagnetic interactions in full discs).
Results suggest that nanosegregation of the molecules and
column formation drive the co-facial alignment of the spin-
containing cores, while the size of the N(1)À Ar substituent
affects the intermolecular contact and the strength of anti-
ferromagnetic interactions. As evident from powder XRD
studies, the increasing size of the N(1)À Ar substituent and
consequently change of the molecular shape causes a gradual
modification of molecular packing in the columns. This, in turn,
results in increasing concentration of uncompensated spins in
all three phases and increasing strength of ferromagnetic
interactions in the crystalline phase. The strength of these
interactions also depends on thermal history of the sample. The
strongest ferromagnetic exchange interactions were found in
the fully crystalline sample of 1[12] (J/kB =7.48(5) K), which can
be ascribed to local interactions of average 5–6 spins in a 1D
chain.
Electric measurements revealed hole mobility and dark
electric conduction typical for unaligned discotic materials (~
10À 3 cm2 VÀ 1 sÀ 1 and ~10À 11 ScmÀ 1, respectively). The latter
increases upon illumination with UV light due to generated
additional charge carriers. Data indicates that increasing size
of the N(1)À Ar substituent results in slight decrease in hole
mobility and conductivity with simultaneous increase of
ferromagnetic interactions in the homologous series due to
the expanded distance between the cores.
(278 mg, 0.2 mmol) in dry THF (2.5 mL) under Ar atmosphere. The
mixture was kept at rt for 30 min, then it was opened to air, then
diluted with dry petroleum ether (ca. 20 mL), and the stirring was
continued for 1.5 h. Resulting mixture was filtered through short
plug of Celite, the solvents were removed under reduced pressure,
and the crude product was washed with hot MeCN (3×60 mL) to
remove byproducts, mainly the 3,4,5-trialkoxybenzene. Purification
by column chromatography on silica gel (SiO2 deactivated with 2%
Et3N in petroleum ether before use; petroleum ether/Et2O 5:1;
visualization with the p-anisaldehyde stain) provided 1[n], which
was recrystallized 4–6 times from a MeCN/EtOAc mixture.
Preparation of Aryllithium Reagents: A General Procedure: To a
solution of the corresponding 1-bromo-3,4,5-trialkoxybenzene
(3[n], 0.6 mmol, for details see the SI) in dry THF (10 mL), a solution
of tert-BuLi (1.7 M in pentane, 0.78 mL, 1.32 mmol) was added
°
dropwise at À 40 C (due to limited solubility of bromides 3[10] and
3[12] in THF at low temperatures, the addition of tert-BuLi was
°
performed at À 25 C). The resulting mixture was stirred at this
temperature until the starting bromide was fully consumed
(typically ca. 20–30 min, TLC monitoring of samples quenched with
acetone; SiO2, petroleum ether/dichloromethane 3:1, visualization
with p-anisaldehyde stain), and the cooling bath was removed to
allow the mixture to slowly warm up. After the yellow color of the
solution faded indicating decomposition of excess tert-BuLi, the
°
mixture was cooled to À 40 C, and immediately used for subse-
quent step.
1-Phenyl-3,6-bis(3,4,5-tridodecyloxyphenyl)-1,4-dihydrobenzo[e]
[1,2,4]triazin-4-yl (1[0]):[7] Commercially available PhLi (1.9 M
solution in Bu2O) was used for the reaction with benzo[e][1,2,4]
triazine 2; olive solid, yield 214 mg (73%).
Formation of mixtures expands the range of the columnar
mesophase without significantly affecting the charge transport
properties, but it modulates magnetic behavior of the materials.
This opens a possibility for controlling material’s properties by
structure, composition, and thermal history in the context of
transporting spin information.
3,6-Bis(3,4,5-tridodecyloxyphenyl)-1-(3,4,5-trimethoxyphenyl)-
1,4-dihydrobenzo[e][1,2,4]triazin-4-yl (1[1]): Brown solid, yield
283 mg (91%); IR (KBr) v 2920, 2851, 1594, 1501, 1468, 1231,
1126 cmÀ 1; MALDI-MS (m/z) 1556.6 (100, [M]+). Anal. Calcd for
C
100H168N3O9: C, 77.17; H, 10.88; N, 2.70. Found: C, 77.14; H, 10.85; N,
2.68.
3,6-Bis(3,4,5-tridodecyloxyphenyl)-1-(3,4,5-triethoxyphenyl)-1,4-
dihydrobenzo[e][1,2,4]triazin-4-yl (1[2]): Brown solid, yield 284 mg
(89%); IR (KBr) v 2921, 2851, 1588, 1469, 1387, 1120 cmÀ 1; MALDI-
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MS (m/z) 1598.6 (100, [M]+). Anal. Calcd for C103H174N3O9: C, 77.39; H,
10.97; N, 2.63. Found: C, 77.23; H, 10.85; N, 2.42.
Charge Mobility and Dark Conductivity Measurements: Electric
measurements of a binary mixture of 1[0]–1[12] were conducted in
a thin electro-optical cell. Charge mobility was obtained using the
TOF (time-of-flight) method and a nitrogen gas laser at λ=337 nm.
The conductivity for 1[0], 1[12] and a 1:1 binary mixture 1[0]–1[12]
was measured by the parallel plate capacitor method using a LCR
meter in a frequency range of 0.1 Hz to 1 MHz at 0.1 V. Details and
data analysis are provided in the SI.
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1-(3,4,5-Tributoxyphenyl)-3,6-bis(3,4,5-tridodecyloxyphenyl)-1,4-
dihydrobenzo[e][1,2,4]triazin-4-yl (1[4]): Brown solid, yield: 239 mg
(71%); IR (KBr) v 2920, 2851, 1592, 1468, 1432, 1231, 1115 cmÀ 1
;
MALDI-MS (m/z) 1682.5 (100, [M]+). Anal. Calcd for C109H186N3O9: C,
77.80; H, 11.14; N, 2.50. Found: C, 77.89; H, 11.04; N, 2.46.
3,6-Bis(3,4,5-tridodecyloxyphenyl)-1-(3,4,5-trihexyloxyphenyl)-
1,4-dihydrobenzo[e][1,2,4]triazin-4-yl (1[6]): Brown-green solid;
yield 279 mg (79%); IR (KBr) v 2922, 2851, 1590, 1468, 1114 cmÀ 1
;
Supplementary information
MALDI-MS (m/z) 1766.7 (100, [M]+). Anal. Calcd for C115H198N3O9: C,
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78.18; H, 11.30; N, 2.38. Found: C, 78.21; H, 11.32; N, 2.24.
It contains further information on full details of synthesis and
characterization of series 3[n], NMR spectra, additional DSC,
XRD, magnetization, and conductivity details.
3,6-Bis(3,4,5-tridodecyloxyphenyl)-1-(3,4,5-trioctyloxyphenyl)-1,4-
dihydrobenzo[e][1,2,4]triazin-4-yl (1[8]): Olive solid; yield 252 mg
(68%); IR (KBr) v 2923, 2852, 1591, 1468, 1226, 1115 cmÀ 1; MALDI-
MS (m/z) 1850.4 (100, [M]+). Anal. Calcd for C121H210N3O9: C, 78.52; H,
11.44; N, 2.27. Found: C, 78.77; H, 11.39; N, 2.21.
Acknowledgements
1-(3,4,5-Tridecyloxyphenyl)-3,6-bis(3,4,5-tridodecyloxyphenyl)-
1,4-dihydrobenzo[e][1,2,4]triazin-4-yl (1[10]): Olive solid; yield
321 mg (83%); IR (KBr) v 2956, 2920, 2851, 1589, 1468, 1408,
1115 cmÀ 1; MALDI-MS (m/z) 1934.9 (100, [M]+). Anal. Calcd for
C127H222N3O9: C, 78.82; H, 11.56; N, 2.17. Found: C, 78.78; H, 11.60; N,
2.09.
Financial support was provided by the FNP (TEAM-3/2016-3/24),
National Science Center of Poland (2013/09/B/ST5/01230, 2013/
11/B/ST3/04193, 2014/13/B/ST5/04525) grants.
1,3,6-Tris(3,4,5-tridodecyloxyphenyl)-1,4-dihydrobenzo[e][1,2,4]
triazin-4-yl (1[12]).[7] Yield: 321 mg (80%).
Conflict of Interest
Preparation of 1-Bromo-3,4,5-trialkoxybenzene (3[n]): A General
Procedure: A mixture of freshly prepared 1-bromo-3,4,5-trihydroxy-
benzene[10] (1.02 g, 5.0 mmol) and K2CO3 (4.15 g, 30.0 mmol) in dry
DMF (40 mL) was stirred at room temperature for 30 min. Then,
appropriate alkyl bromide (20.0 mmol) was added, and the mixture
The authors declare no conflict of interest.
Keywords: columnar phase
· liquid crystals · magnetic
properties · stable radicals · synthesis
°
was heated under inert atmosphere overnight at 75 C. After
cooling, the resulting mixture was diluted with water (150 mL) and
organic products extracted with hexanes (3×30 mL). Combined
organic layers were dried (Na2SO4), solvents were removed in vacuo,
and the residue was purified by column chromatography (SiO2, pet.
ether/CH2Cl2 3:1). The products were dried under vacuum to afford
pure 3[n] in about 90% yield as colourless low melting solids or oils
(3[6] and 3[8]). Full analytical data is provided in the SI.
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Preparation of Binary Mixtures: A mixture of known amounts of
radicals 1[0] (0.5–1.5 mmol) and 1[12] (0.5–1.5 mmol) 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 to give a
homogenous solution. Then, the solvent was removed under
°
stirring at about 80 C, the resulting mixture was vacuum dried and
analysed by POM to confirm homogeneity. Each mixture was
analysed by DSC in 3 heating/cooling cycles at a rate of 5 KminÀ 1
.
Powder XRD Measurements: X-ray diffraction experiments in broad
angle range were performed using a Bruker D8 GADDS system
(parallel Cu Kα beam formed by Göbel mirror and 0.5 mm point
collimator, area detector Vantec 2000) equipped with a modified
Linkam heating stage. For precise determination of lattice parame-
ters, temperature evolution a Bruker D8 Discover system was used
(parallel Cu Kα radiation, Göbel mirror monochromator, Anton Paar
DCS350 heating stage, scintillation counter). Samples were pre-
pared in a form of droplet or thin film on flat heated surface.
Magnetization Measurements: Magnetic susceptibility measure-
ments for 1[n] were conducted using a SQUID magnetometer
(Quantum Design MPMS-XL-7T) in heating (2 K !400 K) and
cooling (400 K!2 K) cycles at a rate 0.8 KminÀ 1 in a magnetic field
of 0.1 T. Details and data analysis are provided in the SI.
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[10] For details see the Supporting Information.
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Manuscript received: October 16, 2018
Revised manuscript received: December 19, 2018
Version of record online: ■■■, ■■■■
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ARTICLES
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Dr. M. Jasiński, K. Szymańska, A.
Gardias, Dr. D. Pociecha, Dr. H.
Monobe, Dr. J. Szczytko, Prof. P.
Kaszyński
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1 – 10
Tuning the Magnetic Properties of
Columnar Benzo[e][1,2,4]triazin-4-
yls with the Molecular Shape
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The magnitude of the ferromagnetic
exchange interaction J in series 1[n] is
tuned by the size of the Ar substituent
at the N(1) position (shape of the
molecular disc) and by the formation
of binary mixtures.