Synthesis, Thermal, and Optical Properties of Tris(5-aryl-1,3,4-oxadiazol-2-yl)-1,3,5-triazines, New Star-Shaped Fluorescent Discotic Liquid Crystals

Article abstract of DOI:10.1002/chem.201902975

The synthesis of tris(aryloxadiazolyl)triazines (TOTs), C₃-symmetrical star-shaped mesogenes with a 1,3,5-triazine center, 5-phenyl-1,3,4-oxadiazole arms, and various peripheral alkoxy side chains is reported. Threefold Huisgen reaction on a ce

Full text of DOI:10.1002/chem.201902975

A Journal of
Accepted Article
Title: Synthesis, Thermal, and Optical Properties of Tris(5-aryl-1,3,4-
oxadiazol-2-yl)-1,3,5-triazines, New Star-shaped Fluorescent
Discotic Liquid Crystals
Authors: Natalie Tober, Thorsten Rieth, Matthias Lehmann, and Heiner
Detert
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201902975
Link to VoR: http://dx.doi.org/10.1002/chem.201902975
Supported by

10.1002/chem.201902975
Chemistry - A European Journal
FULL PAPER
Synthesis, Thermal, and Optical Properties of Tris(5-aryl-1,3,4-
oxadiazol-2-yl)-1,3,5-triazines, New Star-shaped Fluorescent
Discotic Liquid Crystals
N. Tober,[a] T. Rieth,[a] M. Lehmann*[b] and H. Detert*[a]
Dedicated to Prof. Dr. Herbert Meier, Mainz, on the occasion of his 80th birthday
Abstract: The synthesis of `TOTs´, C3-symmetrical star-shaped
mesogenes with a 1,3,5-triazine centre, 5-phenyl-1,3,4-oxadiazole
arms and various peripheral alkoxy side chains is reported.
Threefold Huisgen reaction on a central triazine tricarboxylic acid
and suitable aryltetrazoles yields the title compounds. Selected
analogues with a benzene centre are included in this study and allow
an evaluation of the impact of the central unit on physical properties.
Thermal (DSC, POM), optical (UV-Vis, fluorescence), electric (TOF)
and structural (single crystal, WAXS) properties of these compounds
are investigated. The modification of alkoxy chain length and
substitution pattern allows a tuning of physical properties. TOTs emit
blue to yellow light, depending on conjugation length, donor-acceptor
substitution and solvent polarity, whereas concentration quenches,
aggregation enhances the emission. The width of the mesophases is
typically around ΔT = 100 - 150 K but can even exceed 220 K.
Polarization optical microscopy and X-ray diffraction on oriented
filaments reveal that TOTs are highly ordered LCs with long range
hexagonal columnar structure.
(DLC) is only in its beginning.[10,11] Further interesting features of
DLCs are self-assembly, mostly to formation of columnar
mesophases, self-healing, and aggregation-induced emission
enhancement.[12] The columnar arrangement provides the ability
of an one dimensional charge transfer[4,10] by overlapping of the
aromatic π-orbitals (“π-stacking”).[13] The majority of DLCs
consists of an electron-rich aromatic core, for example
triphenylene, (triaza)truxene, or thiophene, often with electron-
rich arms like alkoxybenzene or thiophene.[9,14,15] In contrast,
electron-deficient heterocycles like pyrimidines, triazines or
oxadiazoles are less common as components of the π-
conjugated core.[13, 16-18]
1,3,5-Tris-(5-phenyl-1,3,4-oxadiazol-2-yl)benzene (TOB), one of
the first reported discotic oxadiazole compounds[19] melts at
335°C without any liquid crystalline phase, but a few molecules
of this structure with flexible side chains attached are reported to
form broad mesophases with the characteristic textures of a
columnar arrangement, as observed by polarisation optical
microscopy (POM).[20,21]
The exchange of benzene with 1,3,5-triazine leads to a new core
for discotic liquid crystals: tris(aryloxadiazolyl)triazine (TOT, N1 -
N15, scheme 1, fig. 1), a fluorescent scaffold with excellent
tendency towards columnar arrangement in the LC phase and
broad mesophases. The synthesis, thermal, optical and
luminescent properties of these compounds and some benzene
analogues (TOBs C2 - C11) and the comparison of their
properties are subject of this report.
Introduction
The development of new materials for electronic and opto-
electronic devices, e.g (NLO)-absorbers, emitters, and semi-
conductors for the application in solar cells, LEDs, FETs and
quantum computers is a highly active research field with an
extraordinary commercial potential.[1–4]
Especially organic compounds are of great interest, they are
required to replace rare, toxic and expensive inorganic
materials.[3,5] Organic opto-electronic devices were developed
already, like organic photovoltaics (OVPs)[6], organic light
emitting diodes (OLEDs)[7] and organic field effect transistors
(OFETs)[8]. Whereas calamitic liquid crystals are the key
compound in LCDs[2,8,9], the technology of discotic liquid crystals
Synthesis and Investigations
Synthesis
[a]
Natalie Tober, Dr. Thorsten Rieth, Prof. Dr. Heiner Detert,
Institute of Organic Chemistry
University of Mainz
Duesbergweg 10 - 14
55128 Mainz, Germany
Scheme 1. Huisgen reaction: (13 –72%)
E-mail: detert@uni-mainz.de
The common route to 1,3,4-oxadiazoles is the stepwise
formation of diacylhydrazine followed by dehydration/cyclization
with POCl3.[21-23] This method has been successfully applied for
the synthesis of star-shaped molecules with a benzene center.
An alternative way to construct oxadiazoles is opened by the
Huisgen reaction of tetrazoles and acid chlorides in presence of
pyridine bases.[20,24,25] This method is particularly rewarding for
[b]
Prof. Dr. Matthias Lehmann,
Institute of Organic Chemistry
University of Würzburg
Am Hubland
97074 Würzburg, Germany
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/chem.201902975
Chemistry - A European Journal
FULL PAPER
the preparation of sensitive products.[26] Hence, we followed this
strategy to build discotic LCs with a tris-1,3,4-oxadiazolyl-1,3,5-
triazine nucleus N1 - N15 (scheme 1).
purity of all materials is demonstrated by standard analytical
methods, such as 1H-, 13C-NMR, TLC and HR-MS.
For the synthesis of the carbon-analogues C2 – C9, trimesic
acid trichloride 2b in the presence of 2,4,6-collidine was a
successful protocol, the pure TOBs were obtained in yields up to
61% after chromatography.
Initial results were disappointing, upon addition of
tris(chlorocarbonyl)triazine 2a to the tetrazole/collidine mixture, a
brown precipitate was formed and tetrazoles were converted to
nitriles (mass spectrometry). Since the acid chloride 2a
decomposed in the presence of bases and no oxadiazole was
formed, the reaction has to be performed in the absence of
bases in spite of some side reactions due to HCl. Good yields of
heterocyclic stars N1 - N15 were obtained, accompanied by
small amounts of 1,2,4-triazoles as byproducts (NMR, MS).
The required triazine acid chloride 2a was prepared in three
steps by acid catalysed trimerization of ethyl cyanoformate,
saponification, and chlorination of the tripotassium salt 1 with
POCl3 to obtain pure 2a in 71 % yield after distillation (method A).
Similar results in the Huisgen reaction were obtained when 1
was converted to 2a with thionyl chloride and excess
chlorinating agent was evaporated (method B).[28] It appeared to
be essential that 2a was prepared immediately before the
Huisgen reaction.
Figure 1. Synthesized compounds and analogues from literature.
Table 1. Tris(aryl-1,3,4-oxadiazolyl)triazines and -benzenes, substitution
pattern, chain length, yield and references.(Yields over 2 steps)
R
Y
R
Y
N1
N2
C2
N3
C3
N4
C4
N5
N6
N7
R1 = R3 = H, R2 = 47%
n-propyloxy [A]
N8
N9
C9
R1 = R2 = R3 =
n-hexyloxy
31%
[B]
R1 = H, R2 = R3 = 48%
n-octyloxy [A]
R1 = R2 = R3 =
n-octyloxy
34%
[A]
R1 = H, R2 = R3 = 61%
n-octyloxy
R1 = R2 = R3 =
n-octyloxy
13%
28%[21]
Scheme 2. Synthesis of tetrazoles.
R1 = H, R2 = R3 = 38%
N10 R1 = R2 = R3 =
45%
[A]
n-decyloxy
[A]
n-decyloxy
The tetrazoles (scheme 2) were synthesized in multistep
reactions starting with protocatechuic nitrile 3 or methyl gallate
6.[29,30] 3,4-(Dialkoxyphenyl)-tetrazoles 5a,b are accessible via
alkylation of 3 and 1,3-dipolar cycloaddition of azide.[29] The
3,4,5-analogues 9a-c were synthesized from methyl gallate 6 via
alkylation, saponification, chlorination/ammonolysis (SI) followed
by dehydration/ azide transfer with triazidochlorosilane.[31]
Biphenyl tetrazole 10 is accessible via Suzuki cross-coupling
reaction of iodophenyl tetrazole and di(decyloxy)phenyl boronic
acid.[32] 5,6-Di(decyloxy)naphth-2-yl-tetrazole 11 was prepared
by oxidation of 6-bromo-2-naphthol to the o-quinone, reduction,
alkylation and Rosenmund-von-Braun cyanation followed by
azide addition similar to a literature procedure.
R1 = H, R2 = R3 = 59%
C10 R1 = R2 = R3 =
D[23]
n-decyloxy
D[23]
n-decyloxy
R1 = H, R2 = R3 = 47%
n-dodecyloxy [A]
C11 R1 = R2 = R3 =
D[27]
n-dodecyloxy
R1 = H, R2 = R3 = 33%
N12 R1 = R2 = R3 =
55%
[B]
n-dodecyloxy
87%[25]
2-ethylhexyloxy
R1 = H, R2 = R3 = 70%
N13 R1 = R2 = R3 = 3,7-
72%
[B]
n-tetradecyloxy
[B]
dimethyloctyloxy
R1 = H, R2 = R3 = 52%
4-ethyloctyloxy [B]
N14 R4 = n-decyloxy
46%
[B]
With
these
tetrazoles
in
hand,
14
and
different
four
R1 = H, R2 = R3 = 29%
N15 R5 = n-decyloxy
49%
[B]
trisaryloxadiazolyltriazines
(TOT, N1-N15)
3,7-
[B]
dimethyloctyloxy
trisoxadiazolylbenzenes (TOB, C2 – C4, C9) were synthesized
in yields ranging from 13% up to 72% (figure 1, table 1).
Triazoles are formed as by-products, their chromatographic
behavior is generally very similar to the tris(oxadiazolyl) stars.
Therefore, excessive chromatography is occasionally required -
and responsible for reduced yields. Residual triazole in the
yellow fluorescent TOT can easily be distinguished by its blue
fluorescence on solvent-loaded TLC plates. The identity and
[A] Method A: C3N3(COOK)3, POCl3. [B] Method B: C3N3(COOK)3, SOCl2, [C]
trimesic acid chloride; [D] Yield not given in literature. Compounds C3, C4
and C9 have been reported in the literature and were newly synthesized for
this study.
This article is protected by copyright. All rights reserved.

10.1002/chem.201902975
Chemistry - A European Journal
FULL PAPER
Thermal properties: DSC and POM
consequently the mesophase ranges are 20 - 64K larger (figure
4). Transition temperatures of 3,4-dialkoxy TOTs N2-N5 are
weakly affected by elongation of alkyl chains (octyl - tetradecyl);
maximum Tc is reached with decyl and dodecyl chains. Tc is
more influenced by chain length then Tm. The sensitivity of
transition points to chain length is more pronounced in the 3,4,5-
trialkoxy series N8-N10. Compared to the 3,4-dialkoxy
derivatives, their LC phases are much broader (up to 220 K!)
and appear at significantly lower temperatures.
Polarized optical microscopy revealed birefringend mesophases
for 18 out of 20 star-shaped molecules (including 2 mesogenes
from literature[23,27]) under investigation. The LC-phases show
textures, typical for hexagonal-columnar arrangements (Fig. 2,
a,b). A standard discotic liquid crystal shows usually two
transitions in a DSC heating scan - melting and clearing. TOTs
and TOBs are highly viscous liquid crystals in the high
temperature range as evidenced by shearing experiments. Upon
cooling, the structure and texture of the mesophase is
maintained, even after complete congealing. Therefore,
determination of the melting point is hard to observe by POM. In
highly viscous mesophases (TOTs and TOBs), crystallization
can be slow, resulting in partial or complete preservation of the
mesophase structure. As a consequence, measured melting
enthalpies in the cooling scan are lower than those of the first
heating cycle. Thus data in table 2 are values for not completely
relaxed materials. These phenomena have been observed for
several TOTs and TOBs (N2 - N8, N14, C2, C3). The partial
recrystallization can give rise to a cold crystallization just below
the melting point during the subsequent heating scan (N5, N7,
N14). Glass transitions were detected for N12 and also
transitions between crystal phases (N15, C3, C9) which occur
only in the first heating curve or after prolonged storage.
TOTs N6 and N8 are strongly inhibited in crystallization, a
second measurement of the same DSC-sample after 2 months
did not exhibit any CrM transitions, only after two years a DSC
experiment revealed a signal attributed to such a transition.
Furthermore some TOTs show exothermic transitions in their
second heating cycles (e.g. N5, figure 3) caused by thermally
induced crystallization.[33] This is followed by two endothermic
transitions, melting (T = 88.5 °C, ΔH = 46.0 kJ·mol-1) and
clearing (T = 184.3 °C, ΔH = 3.9 kJ·mol-1).
Figure 4. Overview of phase width of tris(aryloxadiazolyl)arene stars
Table 2. Phase transition temperatures (°C) and corresponding enthalpies
(kJ·mol-1)
Compound
Compound
N1
N2
Cr 276 I
N8
Cr 55 [24.8]c M 220 [1.2]c I
Cr 97 [3.7]b Colh 192 [3.4]b I N9
Cr -10 [Tg]b Colh 210 [4.5]b I
Cr 106 [67.1] Colh 181 [4,8]
I
Cr 1 [8.0] Cr 34 [20.9] Colh
190 [4.9] I
C2
C9
N3
Cr 84 [3.9]b M 203 [4.3]b I
N10
Cr 33 [21.9]a M 179 [4.0]b I
C10[23] Cr 46 [86.2] M 169 [15.5] I
C11[27] Cr ca.20 [e] M ca.145 [e] I
Cr 51 [92.7] Cr 83 [189.6]
Cr 107 [26.7] M 176 [18.4] I
C3[23]
Figure 2. a) POM: fan texture of (N8) at 200°C (0.5 K/min) upon cooling b)
POM: focal conic fan texture of (N2) at 195°C (10 K/min) upon cooling
N4
Cr 87 [3.4]b M [4.9]b 202 I
Cr 103 [54.4] M 184 [3.9] I
C4[25]
N5
N12
I
Cr 89 [46.0]b M 184 [3.9]b I N13
Cr -19 [Tg]c M 72 [0.9]b I
Cr 121 [1.9]b M 210 [3.0]b I
Cr 93 [4.1]b Cr 165 [26.9]b I
N6
Cr 56 [2.9]c M 156 [2.3]c I
Cr 95 [0.6]a M 170 [2.1]b I
N14
N15
N7
Figure 3. DSC: second heating curve of (N5)
a) onset of the signal in first heating cycle b) onset of the signal in second
heating cycle c) onset of the signal in heating cycle of the second
measurement d) absence of mobility (POM), [e] not given in literature
The results of POM and DSC investigations on TOTs and TOBs
are collected in figure 4 and table 2. TOTs and TOBs show
broad mesophases with phase widths of 69-220 K. Generally,
the triazine based compounds possess lower melting and higher
clearing temperatures than their carbon analogous and
Branching in the alkyl chains of the triazine stars (N6, N7, N12,
N13) reduces transition temperatures and width of the LC phase.
This article is protected by copyright. All rights reserved.

10.1002/chem.201902975
Chemistry - A European Journal
FULL PAPER
This effect is more pronounced in the 3,4,5-trialkoxy series, even
a complete loss of mesomorphism has been found (N12). This
can be due to two reasons: diastereomeric mixtures and steric
crowding especially for the 3,4,5-trialkoxy series.
Extending the aromatic system of TOTs, from peripheral phenyl
(N3) to peripheral naphthalene N14, results in an increase of the
melting point by 37 K and of the clearing point by 7 K. The even
longer biphenyl derivative N15 reveals only a crystalline phase
at much lower temperature, which may be attributed to the non-
planar structure of this building block and therefore reduced
mobility in a column. The thermal behavior (Cr 25(6) Colh 114 (4)
iso) of a thiophene analogue to N9 and a higher homologue
of alternating oriented molecules along a diagonal through the
unit cell. Each two molecules have a center of inversion and the
central triazines are off-diagonal, bringing oxadiazoles and
alkoxyphenyl in close proximity. These features correspond to
the results of simulation of the mesophase structure (vide infra).
2D-Scattering on oriented fibres
Two-dimensional wide-angle X-ray scattering (WAXS)
experiments on macroscopically aligned extruded fibers were
carried out to determine the intra- and intercolumnar
organization of the TOTs and TOBs in their liquid crystal phases.
reveals
a strong stabilization of the mesophase by the
oxadiazole, probably due to CT interactions between electron
deficient oxadiazoles and alkoxyphenyl rings.[34] Similarly, 1,2,3-
triazoles stabilize the mesophase, phase widths are in the range
of 160 K.[17]
X-Ray scattering.
Single crystals of p-propyloxy-TOT N1 were obtained via slow
evaporation of a solution in toluene.[35] N1 crystallizes in triclinic
space group P-1 (a = 8.62 Å, α = 89.91°, b = 13.59 Å, β = 85.75°,
c = 15.79 Å, γ = 76.78°) and contains two molecules per unit cell
(fig. 5). Crystallographic data exhibit a non-planar molecular
structure. In contrast to the expected C3-symmetry (Fig. 5), N1
adopts a “Y”-shaped form since one phenyloxadiazole arm is
flipped around the triazine-oxadiazole bond. These rings show a
dihedral angle of 16° whereas all other biaryl units are
essentially planar ( 1°). The dihedral angle between the
benzenes and oxadiazoles are about 10-14°. Furthermore two
propyloxy-unit are disordered.
Figure 6: Diffraction pattern of N2 at 176°C (A) and C9 at 125 °C (B). (C) and
(D) show the integrated intensity of the equator and the meridian at various
temperatures.
Filaments were obtained by extrusion of N2, N9 in their LC-
phase (175°C, 10 min annealing) and of C2, C9 (140°C, 5 min
annealing). Table 3 and figure 6 summarise the results. The
patterns in Figure 6 (A, B) reveal characteristic features of well-
aligned columnar LC samples: (i) reflections centred at the
equator attributed to a hexagonal 2D lattice of columns, (ii) a
halo corresponding to the liquid-like chains with an average
distance between 4.0-4.6 Å (see table 3) and (iii) a rather broad
signal at wider angles reminiscent of the average aromatic
distances (π-π stacking). The corresponding integration of the
patterns along the equator and the meridian (Figure 6 C and D)
reveal general trends. First, the reflections with larger and mixed
indices are obviously more intense for the carbon derivatives
than for the nitrogen derivatives. For N2 the 11 and 20
reflections appear only at lower temperature. This points to a
higher two-dimensional order of columns for the derivatives C2
and C9 when compared to N2 and N9. The cell parameters of
the hexagonal unit cells decrease with increasing temperature
(see also table 3), while simultaneously the distances along the
columns increase. However, this effect is surprisingly small
since a changes only by 0.7 Å, when heating N2 from 25 °C to
176 °C. These observations are the same for the nitrogen and
Figure 5. Single crystal structure of N1 A) asymmetric molecular Y-
conformation, B) nearly perfect planarity C) unit cell with alternating arranged
molecules.
The broken symmetry has also been observed for a tris-1,2,3-
triazolyl-1,3,5-triazine,[36] but a star similar to N1 with thiophene
replacing oxadiazole[34,37, 38] shows nearly perfect C3-symmetry.
This was explained by attractive S-N interactions. The high
planarity, dihedral angles between the heterocycles of 1 - 11°,
was found to improve charge transport properties. While these
molecules are rotationally displaced with respect to adjacent
molecules, the packing of Y-shaped N1 corresponds to columns
This article is protected by copyright. All rights reserved.

10.1002/chem.201902975
Chemistry - A European Journal
FULL PAPER
bases of XRS and density data. Figure 7 highlights the results
for compound N2. Various starting set-ups with non-C3-
symmetric and C3-symmetric conformers could be geometry
optimised to obtain large attractive non-covalent interaction
energies after several minimization and annealing procedures.
In general, the van der Waals energy was large and negative (-
1670 to -1768 kcal/mol, values are given for a set of four unit
cells, with 24 molecules), while the electrostatic energy was
always positive but decreased slightly when compared with the
single molecule (850-898 kcal/mol in the LC phases versus 973
kcal/mol for the single molecule, see SI).
the carbon series. The distinct difference in both series is the
intensity of the π-π signal corresponding to distances between
3.2-3.5 Å, which is much more intense for the compounds C2
and C9 and very small or almost absent for N2 and N9. The
correlation length calculated by the Scherrer formula[39] amounts
to 6-7 repeating units for C2, C9 and only about 4 repeating
units for N2 and N9.In order to gain more insight in the packing
of these star-shaped, shape persistent mesogens the density
has been measured at 23.5 °C and extrapolated to the
temperatures of the LC phases (table 4, for details see SI).
Table 4. Experimental, extrapolated densities, and number of molecules in a
columnar repeating unit h.
A
C
푉퐷
휌퐸
푉푚퐵표푙
푉퐶
휌퐴
퐼퐴푟
퐴푟
columnar
repeat h /Å
ZF
푒푥푝
/ Å3
#
(crystal)
(at T / °C)
/ gcm-3
/ Å3
/ Å3
/ gcm-3
N2 1.065
N9 1.012
C2 1.029
C9 1.022
2000
2736
2065
2704
698
783
763
751
609
625
616
632
1.02 (100)
0.96 (100)
0.97 (125)
0.95 (125)
3
2
3
2
7.50
6.84
7.68
7.08
B
D
A: experimental density at 23.5 °C (buoyancy method) B: molecular volume at
23.5 °C. C: aromatic volume at 23.5 °C D: incremental aromatic volume E:
estimated densities at different temperatures (calculation see SI). F: Number of
molecules Z in the columnar repeat.
Figure 7: Packing of N2 in the columnar assembly. Molecules are displaced
from the centre of the column and occupy spaces from different columnar
slices to fill efficiently the space.
From the density data the molecular volume can be calculated
and subsequently the aromatic volumes are available when the
known volumes of the aliphatic chains are subtracted.[40] Here it
is evident that all aromatic volumes are larger when compared
with the volumes occupied in a crystal, which were calculated by
an increment method.[41] The volumes are 15-25 % higher in the
mesophases. This is certainly a consequence of the less dense
packing in the soft crystalline and liquid crystalline matter but the
large values points also to the fact that the intrinsic free space
between the shape-persistent branches cannot be completely
filled. There is obviously much less free space in the aromatic
part for the derivative N2 with six chains, which has the highest
density. The integer number of molecules filling the columnar
repeating h unit (twice the π-π distance) can be calculated to be
three molecules for the six chains derivatives and two molecules
for the columnar stratum of the nine chain mesogens. For all
systems the number of aliphatic chains is identical, the a-
parameter is almost identical, too, and therefore the value h
must increase for N2 and C2 owing to the larger number of
aromatic units in the core area of the column. However, this
increase amounts only to 0.6-0.7 A and assuming coplanar
stacked mesogens N2 and C2 would be only 2.5-2.6 Å apart
while for N9 and C9 the intramolecular distances are in
agreement with π-stacks (3.4-3.5 Å). Since the distances
between the six chain derivatives are smaller than van der
Waals distances, modelling of the LC phases has been
performed in order to unravel packing details. Thus, the
columnar phases of N2, N9 and C9 have been constructed with
the program Materials Studio (Forcite, COMPASS II) on the
The best results were obtained for the “Y”-shaped conformer
similar to the one found in the single crystal. It can be observed,
that the core position deviates from the centre of the column
(figure 7 C) and that the aromatic units contribute to the space
filling of different columnar slices (figure 7 D). The chains
densely occupy the peripheral space. As a consequence of this
dense packing, the intracolumnar order reduces and almost no
π-stacking is visible in the experimental pattern. However, note
that C2, with the same number of mesogens per columnar
stratum must pack in as similar way but nevertheless, exhibit a π
stacking signal. Consequently, also the electrostatic repulsion
discussed in detail below must be important for the LC self-
assembly. When comparing N9 and C9 it was apparent that the
columnar stratum of height h consists of two molecules with 18
chains and the intracolumnar spacing was calculated to be 3.4 Å
(N9) and 3.5 Å (C9). This can be also confirmed by modelling
(see SI). While C9 shows a clear π-stacking of the mesogens
N9 lacks this signal. The missing π-stacking for N9 may be
explained by the increase in the electrostatic interactions for N9
compared to single molecules, while for C9 the electrostatic
interactions do not change (see SI).[42] Thus mesogens N9 avoid
evidently the cofacial stacking.
Electrical conductivity of N2, C2 and N9
This article is protected by copyright. All rights reserved.

10.1002/chem.201902975
Chemistry - A European Journal
FULL PAPER
Conductivity was studied using the Time-of-Flight method to get
information of their charge transfer ability (SI). For the 3,4-
substituted derivative N2, charge carrier mobilities of μ = 10-
3cm2V-1s-1 in the crystalline (25°C) and mesophase (120°C) ) are
significantly higher as those of its carbon analogue C2 and the
3,4,5-substituted N9, which are in the range of μ = 10-5cm2V-1s-1
at 120°C. The latter can be rationalised by the much denser
packing of the aromatic scaffold in the centre of the columns
when considering N2 and N9. The lower charge carrier mobility
of C2 is not yet well understood, since the aromatic units pack
as compact as N2, and moreover, show in contrast to N2 a clear
signal for a higher intracolumnar order.
depicted in figure 6, all other spectra of TOTs and TOBs are
given in the supporting information. Like excitation, the emission
maxima for TOBs appear at significantly lower wavelengths
퐹푙
compared to TOTs (C3: 휆푚푎푥 = 326 nm, 휆
= 396 nm, N2:
푚푎푥
퐹푙
휆푚푎푥 = 382 nm, 휆
= 500 nm) and the Stokes shifts are
푚푎푥
smaller for TOBs (Δ휈̃푡표푙푢푒푛푒 (C3) = 5422 cm-1 ˂ Δ휈̃푡표푙푢푒푛푒 (N2) =
6178 cm-1). The significant shift of excitation and emission
maxima to lower energy of 1,3,5-triazine derivatives relative to
the benzene analogues is due to the higher acceptor effect of
the central electron-deficient triazine. Again, the polarized
intramolecular charge distribution causes higher local dipole
moments which are more stabilized in polar solvents.
Fluorescence quantum yields were determined using quinine
sulfate as reference.[43] The quantum yields of TOTs in highly
diluted cyclohexane solution (ca. 0.15 μM) are moderate to high:
N1 (19%), N2 (64%), N9 (40%), N15 (18%), N14 (27%) and
TOBs have even higher quantum yields: C3 (80%) and C9
(81%).
푆푡
푆푡
Optical Spectroscopy
Solid tris(oxadiazolyl)triazines are yellow (e.g. branched alkoxy
chains) to red (3,4,5-n-alkoxy substituted TOTs) compounds
whereas the TOBs are colorless. In solution, the latter absorb
only in the UV (λmax  325 nm, λ0.1  360 nm) whereas the
absorption bands of TOTs extend into the blue region (λmax
=
360 - 400 nm, λ0.1  406 - 478 nm. A comparison with analogous
stars with thiophene[34,37] or 1,2,3-triazole[17,18] replacing the
oxadiazole in TOTs reveals a similarity between oxadiazole and
thiophene stars, the latter absorb at slightly longer wavelengths
(λ  8 nm). On the other hand, UV-spectra of 1,2,3-triazole
derivatives peak about λ  -75 nm at shorter wavelengths.[34]
The excitation maxima of triazine-centered stars (N1, N2, N9,
N14) in cyclohexane are nearly independent from the analytes’
polarity and peak between 380 nm and 385 nm. Only the
Table 4. Optical Spectroscopy
푆푡
Solve
nt
logε
휆
0.1/nm
휆퐹푚푎푥/nm
∆휈̃
/
휆푚푎푥/nm
푐푚−1
CH
Tol
DCM
380
364
371
356
3.39
4.83
4.75
nd
407
450
478
-
1746
5250
6034
406
420
406
N1
N2
AN
CH
Tol
DCM
382
382
390
4.55
4.60
4.57
440
439
453
446
500
-
3756
6178
-
absorption maximum of biphenyl N15 is at higher energy (λmax
=
365 nm). Change of solvent has nearly no effect on the
absorption spectra, except N14, N15 with the extended π-
N3
N6
Film
Film
382
382
581
555
solv
systems; here, solvatochromic displacements reach 휈̃
=
1851 cm-1 (cyclohexane-dichloromethane). Additionally, reduced
solubility of some compounds in cyclohexane and acetonitrile
provokes turbidity even at 10 μM concentration.
CH
Tol
DCM
AN
Film
324
326
325
337
326
4.81
4.84
4.83
4.58
360
364
364
nd
375
396
428
464
409
4389
5422
7500
7792
C3
CH
Tol
DCM
Film
380
379
383
380
4.60
4.60
4.56
438
437
451
494
524
501
565
6073
7301
6150
N9
C9
CH
Tol
DCM
Film
321
323
320
-
4.78
4.80
4.81
361
360
359
390
419
462
450
5772
7093
9466
CH
Tol
DCM
AN
385
394
401
371
4.45
4.50
4.48
4.36
nd
452
478
nd
463
503
-
4376
5500
-
N14
N15
559
8065
CH
Tol
DCM
AN
362
383
388
377
4.54
4.72
4.65
4.72
nd
441
464
nd
465
519
-
6119
6842
-
Figure 8. Emission spectra of TOTs with increasing donor substitution (N1, N2,
N9) and increasing size of conjugated system (N2, N14, N15) (cyclohexane).
559
8795
Furthermore, all studied compounds are fluorescent in highly
diluted solution in non-polar solvents. The normalized emission
spectra of N1, N2, N9, N15, and N14 in cyclohexane are
This article is protected by copyright. All rights reserved.

10.1002/chem.201902975
Chemistry - A European Journal
FULL PAPER
higher energies (휈̃254 cm-1) compared to dichloromethane
solution. Furthermore, the emission of films of TOTs and TOBs is
temperature-dependent.(SI) Pristine TOT films emit with 휆푚퐹푎푥= 581
nm (N3); 555 nm (N6), 570 nm (N9). Heating into the
mesophase (150 °C) provokes significant blue-shifts ( 휆푚퐹푎푥= 536
nm (N3); 538 nm (N6), 531 nm (N9)). Upon cooling to 25 °C,
these maxima loose intensity (N3: 15%, N6: 15%, N6: 23%),
whereas the intensity in the long-wavelength shoulder (N3: 휆 =
569 nm, N6: 휆 = 565 nm, N6: 휆 = 570 nm) is not affected. The
impact of temperature on the emission of TOTs with linear side
chains N3 (휈̃= 1941 cm-1), N9 (휈̃= 1288 cm-1) is higher than
Solvents: CH: cyclohexane; Tol: toluene, DCM: dichloromethane, AN:
acetonitrile, λ0.1 = absorption edge at 10% of λmax nd: not determined due to
turbidity
An increasing number of alkoxy substituent (N1 < N2 < N9)
enhances the donor-acceptor character that results in
bathochromic shifts of emission maxima. According to the
extended π-system of N15 (biphenyl), and N14 (naphthyl), their
emission peaks appear at slightly lower energies than recorded
for the shorter dialkoxyphenyl star N2.
Comparison of the emission of TOTs with similar 1,2,3-triazole
derivatives reveals that the latter emit at much higher energies
of N6 ( 휈̃ = 569 cm-1) with branched chains.
A slow
퐹푙
(휆
= 415 - 471 nm, THF), whereas the thiophene congener of
푚푎푥
reorganization process (N6 > N9 > N3) shifts the fluorescence
back to longer wavelengths.
N9 fluoresces with 휆퐹푚푙푎푥 = 528 nm (CH2Cl2).[17,18,34]
With an increasing solvent polarity, the emission maxima are
shifted to lower energies, solvatochromic shifts (cyclohexane-
= 3650 cm-1 (N1) have been
푆표푙푣
dichloromethane) up to Δ휈̃
recorded. The moderate positive solvatochromism of the
emission is accompanied by an efficient fluorescence quenching
in polar solvents, e.g. in acetonitrile and even dichloromethane.
This effect correlates with increasing donor-acceptor character.
In addition to polarity, concentration has a detrimental effect on
the emissivity. THF solutions with triazine star concentrations of
ca. 5 ˟ 10-4 M are essentially not emissive. Dilution to 5 ˟ 10-5 M in
THF allows a weak emission which increases dramatically upon
further dilution to 5 ˟ 10-7 M. Compared to the `concentrated´ (10-
4 M) solutions, the fluorescence efficiencies increase by a factor
of 1.4 104 (N2) and 2.9 104 (N9) upon dilution to 10-7 M.
˟
˟
Though benzene-centered stars are less sensitive to self-
quenching, dilution from 5 10-4 M to 5 10-5 M enhances the
˟
˟
fluorescence efficiency by a factor of 45 (C3) or 28 (C9) but the
emission maximum of TOBs is independent from the
concentration. However, a diluted solution of N2 emits with 휆푚퐹푎푥
= 562 nm, 37 nm more on the red side than a concentrated
solution whereas 휆푚퐹푎푥 of N9 shifts to the blue, from 휆푚퐹푎푥 = 440
nm to 422 nm. For investigation of optical properties in the solid
state, N3, C3, N6, N9, and C9 with a 3,4- and 3,4,5-substitution
pattern and central triazine or benzene ring were studied as
representative examples. While films of TOBs and TOTs show
absorption maxima very similar to the dyes in solution, the long-
wavelength tail of triazine stars brings a yellow (N6) or orange-
red color (N3, N9). The impact of the environment on the
emission is more pronounced. TOBs emit blue light while the
emission of TOTs is yellow (N9: 휆퐹푚푙푎푥 = 567 nm, 휆퐹0.푙1 = 642 nm;
N3: 휆퐹푚푙푎푥 = 580 nm, 휆퐹0.푙1 = 651 nm).
A comparison of solution and film spectra reveals that the
interaction of the -systems of TOTs strongly affects the
emission. While the emission maxima of solid TOBs are blue-
shifted compared to dichloromethane solution (C3: 휈̃ = -1025
cm-1, C9: 휈̃ = -676 cm-1), the - interaction in solid TOTs gives
rise to large bathochromic shifts. These exceed the effect of the
polar dichloromethane by 휈̃2260 cm-1 (N9, 휆퐹푚푙푎푥= 565 nmor
even휈̃= 3027 cm-1 (N2/N3, 휆퐹푚푙푎푥= 580 nm). Branching in the
Figure 9. Emission spectra of N3 with at 150 °C and at 25 °C with different
thermal history.
Contrary to the TOTs, only variation of the fluorescence
intensity, but no significant spectral changes occurred upon
changing the temperature of films of TOBs. A film of C3 on glass
looses about 24% of its emissivity upon cooling from 150 °C to
25 °C. Surprisingly, the same experiment with C9 gives an initial
fluorescence enhancement (24%) upon cooling from 150 °C,
followed by reduction of the fluorescence to 87% (at 25 °C) of
the initial intensity (150 °C). Here again, in addition to the
particular electronic structure, the specific molecular order in the
columns controls the electronic properties.
Adding water or heptane as poor solvents to solutions of TOTs
(N2, N9) and TOBs (C3, C9) in THF results in the formation of
aggregates (concentration of stars in all solutions: 0.3 – 0.5
mM). Besides turbidity, the effect on absorption is very
individual.
Heptane (up to 90% in THF) has no significant effect on the
absorption spectra of C3, C9, N9, but generates a long-
wavelength shoulder of N2 at 470 nm. Water, a highly polar non-
solvent (50 - 90%), shifts 휆푚푎푥 to the red ( 50 nm). The more
impressive part is the change of emission behaviour: Whereas
the solutions in THF (0.3 - 0.5mM) are essentially not emissive,
the suspensions of aggregates in the mixed solvents are! N2
( 휆푚퐹푎푥 = 507 nm) and N9 ( 휆푚퐹푎푥 = 517 nm) in THF-heptane
mixtures emit at lower energies than in THF-water mixtures
(N2: 휆푚퐹푎푥= 470 nm; N9: 휆푚퐹푎푥= 468 nm), but the opposite is true
side chains (N6, 4-ethyloctyloxy) requires more space and
퐹푙
deranges the - interaction, the yellow film emits with 휆
=
푚푎푥
퐹푙
554 nm (휆 = 633 nm). The strong intermolecular electronic
0.1
interaction of excited N9 in the solid state is in sharp contrast to
the behaviour of the thiophene analogue,[34] which emits at
This article is protected by copyright. All rights reserved.

10.1002/chem.201902975
Chemistry - A European Journal
FULL PAPER
for the benzene analogues (C2: 휆푚퐹푎푥= 390 (heptane), 휆푚퐹푎푥
=
Experimental Section
413 nm (water); C9: 휆푚퐹푎푥 = 412 (heptane), 휆푚퐹푎푥 = 475 nm
(water)). A comparison of the emission from aggregates and
from films reveals that the aggregates of TOTs emit at
significantly higher energies than TOTs in solution cast films
( 휆푚퐹푎푥 = 564 - 580 nm) whereas 휆푚퐹푎푥 of TOBs in THF/water
peak at lower energies.
Synthetic procedures, analyses, spectra, and equipment are
collected in the Supporting Information
Acknowledgements
Obviously, the electronic spectra of these stars, especially those
with a triazine center, are strongly controlled by intermolecular
interactions. Surprisingly, a concentration quenching of the
fluorescence in solution is opposed by aggregation-induced
emission. This and the different optical properties of aggregates
and films imply a plethora of molecular arrangements of triazine-
centered stars.
The authors gratefully acknowledge Dr. Johannes Liermann
(NMR), Prof. Dr. F. Laquai (ToF), M. Müller (DSC) and Dr. C.
Kampf (MS), Dr. D. Schollmeyer (Single Crystal X-Ray
Scattering), the Deutsche Forschungsgemeinschaft (DE 515/9-
1) for partial funding and the Carl-Zeiss Stiftung for a generous
fellowship (N. Tober).
Keywords: discotic liquid crystal • fluorescence • heterocycle •
mesophase • star-shaped compound • conjugated Oligomers •
solvatochromism • X-ray scattering • aggregation induced
emission
Conclusions
Two series of discotic molecules composed of three alkoxyaryl-
1,3,4-oxadiazolyl arms attached to a benzene center or electron
deficient triazine core were synthesized via threefold Huisgen
reaction of tetrazoles with trimesic acid trichloride and 2,4,6-
tris(chlorocarbonyl)-1,3,5-triazine as central rings. The latter is
much more sensitive and requires a modified procedure. Almost
all di- and tri-alkoxy substituted TOTs and TOBs exhibited
thermotropic mesophases with the characteristic textures of
hexagonal columnar arrangements. A variation of chain number
and length allows control of the width of mesophase. In general
triazine derivatives have broader mesophases (ΔT  220°C) than
[1] B. Roy, N. De, K. C. Majumdar, Chem. Europ. J. 2012, 18(46),
14560–14588.
[2] S. Laschat, A. Baro, N. Steinke, F. Giesselmann, C. Hägele, G.
Scalia, R. Judele, E. Kapatsina, S. Sauer, A. Schreivogel, M. Tosoni,
Angew. Chem. Int. Ed. 2007, 46(26), 4832–4887.
[3] V. Balzani, G. Bergamini, P. Ceroni, Angew. Chem. Int.Ed. 2015,
54(39), 11320–11337.
[4] S. Kumar, Chemistry of discotic liquid crystals: From monomers to
polymers; CRC Press, Boca Raton, FL, 2011.
[5] V. Balzani, G. Bergamini, P. Ceroni, Angew. Chem. 2015, 127(39),
11474–11492.
benzene analogues (ΔT
 170°C). The mesophases are
[6] a) L. Schmidt-Mende, Science 2001, 293, 1119–1122; b) C. W. Tang,
Appl. Phys. Lett. 1986, 48, 183; c) I. Seguy, P. Jolinat, P. Destruel,
J. Farenc, R. Mamy, H. Bock, J. Ip, T. P. Nguyen, J. Appl. Phys.
2001, 89, 5442;
[7] a) W. Pisula, A. Menon, M. Stepputat, I. Lieberwirth, U. Kolb, A.
Tracz, H. Sirringhaus, T. Pakula, K. Müllen, Adv. Mater. 2005, 17,
684–689; b) T. Hassheider, S. A. Benning, M. W. Lauhof, R.
Oesterhaus, S. Alibert-Fouet, H. Bock, J. W. Goodby, M. D. Watson,
K. Muellen, H.-S. Kitzerow in Liquid Crystal Materials, Devices, and
Applications IX; (Ed. L.-C. Chien), Proc. SPIE 2003, 5003, 167-174.
[8] D. Adam, P. Schuhmacher, J. Simmerer, L. Häußling, W. Paulus, K.
Siemensmeyer, K.-H. Etzbach, H. Ringsdorf, D. Haarer, Adv. Mater.
1995, 7, 276–280.
[9] B. R. Kaafarani, Chem. Mater. 2011, 23, 378–396.
[10] M. Bäker, Funktionswerkstoffe; Springer Fachmedien Wiesbaden,
Wiesbaden, 2014.
[11] a) D. Demus, J. W. Goodby, G. W. Gray, H. W. Spiess, V. Vill,
Handbook of Liquid Crystals; Wiley, Weinheim, 2011; b) T. Wöhrle, I.
Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J. Litterscheidt, J.
C. Haenle, P. Staffeld, A. Baro, F. Giesselmann, S. Laschat, Chem.
Rev. 2016, 116, 1139–1241.
enantiotropic though several TOTs are crystallization inhibited.
X-Ray diffraction and density measurements on oriented fibres
proved the dense packing of all derivatives in high temperature
hexagonal columnar phases. The 3,4,5-substituted derivatives
(C9, N9) stack with average π - π distances of 3.4-3.5 Å and
with 18 alkyl chains in a columnar stratum of approximately 7 Å
height, i.e. with two molecules. While the carbon analogue C9
show a strong π stacking signal, this is reduced for the triazine
derivative N9, presumably, because of electrostatic repulsion. In
contrast the two chain derivatives C2 and N2 contain three
molecules in a columnar repeat between 7.5-7.7 Å. Again, the
number of chains sum up to 18, but three aromatic cores fill now
the centre of the columns, where a coplanar stacking is not
anymore possible. For all derivatives a denser packing can be
achieved with a Y-shaped conformer of the star, minimising the
intrinsic free space.[44]
[12] a) S.-H. Wu, H.-H. Chen, Tetrahedron 2019, 75, 220–229; b) N.
Röder, T. Marszalek, D. Limbach, W. Pisula, H. Detert,
ChemPhysChem 2019, 20, 463–469; c) C. Cuerva, J. A. Campo, P.
Ovejero, M. R. Torres, E. Oliveira, S. M. Santos, C. Lodeiro, M.
Cano, J. Mater. Chem. C 2014, 2, 9167–9181.
The charge carrier mobilities of TOBs and TOTs (μ = 10-3 - 10-
5cm2V-1s-1) are in the medium range of discotic liquid crystals.
TOBs are colourless and TOTs are yellow to red coloured
substances, their emission behaviour is largely controlled by
intermolecular interactions. Efficient emission in highly diluted
solution, concentration quenching, aggregation induced
emission (enhancement) and sensitivity of the emission
spectrum to solvents, temperature, and aggregation are optical
phenomena that complement the thermal mesomorphism.
[13] a) S. Kumar, Chemical Soc.Rev. 2006, 35, 83–109; b) H. Detert, M.
Lehmann, H. Meier, Materials 2010, 3, 3218–3330.
[14] a) M. Talarico, R. Termine, E. M. García-Frutos, A. Omenat, J. L.
Serrano, B. Gómez-Lor, A. Golemme, Chem. Mater. 2008, 20,
6589–6591; b) M. Vadivel, I. S. Kumar, K. Swamynathan, V. A.
Raghunathan, S. Kumar, ChemistrySelect 2018, 3, 8763–8769; g) A.
Gowda, L. Jacob, D. P. Singh, R. Douali, S. Kumar,
ChemistrySelect 2018, 3, 6551–6560.
[15] a) J. Luo, B. Zhao, J. Shao, K. A. Lim, H. S. On Chan, C. Chi, J.
Mater. Chem. 2009, 19, 8327; b) H. Taing, J. G. Rothera, J. F.
This article is protected by copyright. All rights reserved.

10.1002/chem.201902975
Chemistry - A European Journal
FULL PAPER
Binder, C. L. B. Macdonald, S. H. Eichhorn, Liq. Cryst. 2018, 45,
1147–1154; c) K.-C. Zhao, J.-Q. Du, H.-F. Wang, K.-Q. Zhao, P. Hu,
B.-Q. Wang, H. Monobe, B. Heinrich, B. Donnio, Chem. Asian J.
2019, 14, 462–470; d) D. Tian, Y. Zhou, Z. Li, S. Liu, J. Shao, X.
Yang, J. Shao, W. Huang, B. Zhao, ChemistrySelect 2017, 2, 8137–
8145; e) L. Zhang, D. L. Hughes, A. N. Cammidge, J.Org. Chem.
2012, 77, 4288–4297.
[28] G. Xu, L. Zheng, S. Wang, Q. Dang, X. Bai, Synth. Commun.2010,
40, 361–369.
[29] R. Cristiano, Santos, D. M. Pereira de Oliveira, H. Gallardo, Liq.
Cryst. 2005, 32, 7–14.
[30] T. Rieth, S. Glang, D. Borchmann, H. Detert, Mol. Cryst.Liq. Cryst.
2015, 610, 89–99.
[31] A.-A. S. El-Ahl, S. S. Elmorsy, A. H. Elbeheery, F. A. Amer,
Tetrahedron Lett. 1997, 38, 1257–1260.
[32] T. Rieth, T. Marszalek, W. Pisula, H. Detert, Chem. Europ. J. 2014,
20, 5000–5006.
[33] R. Cristiano, H. Gallardo, A. J. Bortoluzzi, I. H. Bechtold, C. E. M.
Campos, R. L. Longo, Chem. Commun. 2008, 5134–5136.
[34] T. Yasuda, T. Shimizu, F. Liu, G. Ungar, T. Kato, J. Am. Chem. Soc.
2011, 133, 13437–13444.
[35] CCDC 1894806 (N1) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/ datarequest/cif.
[36] A. R. Katritzky, S. K. Singh, N. K. Meher, J. Doskocz,, K. Suzuki, R.
Jiang, G. L. Sommen, D. A. Ciaramitaro, P. J. Steel, Arkivoc 2005,
2006, 43-62.
[16] a) J. Han, J. Mater. Chem. C 2013, 1, 7779; b) E. Beltrán, J. L.
Serrano, T. Sierra, R. Giménez, Org. Lett. 2010, 12, 1404–1407.
[17] a) E. Beltrán, J. L. Serrano, T. Sierra, R. Giménez, J. Mater. Chem.
2012, 22, 7797-7805; b) . B. Feringán, P. Romero, J. L. Serrano, R.
Giménez, T. Sierra, Chem. Europ. J. 2015, 21, 8859–8866.
[18] a) H. Meier, M. Lehmann, H. C. Holst, D. Schwoeppe, Tetrahedron
2004, 60, 6881-6888; b) A. Navarro, M. P. Fernández-Liencres, G.
García, J. M. Granadino-Roldán, M. Fernández-Gómez, Phys.
Chem. Chem. Phys.2015, 17, 605–618.
[19] K. Naito, A. Miura, J. Phys. Chem. 1993, 97, 6240–6248.
[20] S. Varghese, N. S. S. Kumar, A. Krishna, D. S. S. Rao, S. K.
Prasad, S. Das, Adv. Funct. Mater. 2009, 19, 2064–2073.
[21] Y.-D. Zhang, K. G. Jespersen, M. Kempe, J. A. Kornfield, S. Barlow,
B. Kippelen, S. R. Marder, Langmuir 2003, 19, 6534–6536.
[22] a) T. Curtius, F. H. Dellschaft, J. Prakt. Chem. 1901, 64, 419–438;
b) R. Stollé, H. P. Stevens, J. Prakt. Chem. 1904, 69, 366–381; c) B.
Pradhan, S. K. Pathak, R. K. Gupta, M. Gupta, S. K. Pal, A. S.
Achalkumar, J. Mater. Chem. C 2016, 4, 6117–6130; d) K. Kotwica,
A. S. Kostyuchenko, P. Data, T. Marszalek, L. Skorka, T. Jaroch, S.
Kacka, M. Zagorska, R. Nowakowski, A. P. Monkman, A. S. Fisyuk,
W. Pisula, A. Pron, Chem. Europ. J. 2016, 22, 11795–11806.
[23] S. K. Pathak, R. K. Gupta, S. Nath, D. S. S. Rao, S. K. Prasad, A. S.
Achalkumar, J. Mater. Chem. C 2015, 3, 2940–2952.
[37] K. Navamani, K. Senthilkumar, J. Phys. Chem. C 2014, 118,
27754–27762.
[38] H. Muraoka, M. Mori, S. Ogawa, Phosphorus, Sulfur, and Silicon
and the Related Elements 2015, 190, 1382–1391.
[39] P. Scherrer, Nachrichten von der Gesellschaft der Wissenschaften
zu Göttingen 1918, 98–100.
[40] B. Donnio, B. Heinrich, H. Allouchi, J. Kain, S. Diele, D. Guillon, D.
W. Bruce, J. Am. Chem. Soc. 2004, 126, 15258–15268.
[41] A. Immirzi, B. Perini, Acta Cryst A 1977, 33, 216–218.
[42] V. Lemaur, D. A. da Silva Filho, V. Coropceanu, M. Lehmann, Y.
Geerts, J. Piris, M. G. Debije, A. M. van de Craats, K. Senthilkumar,
L. D. A. Siebbeles, J. M. Warman, J.-L. Brédas, J. Cornil, J. Am.
Chem. Soc. 2004, 126, 3271–3279.
[24] a) R. Huisgen, J. Sauer, H. J. Sturm, J. H. Markgraf, Chem. Ber.
1960, 93, 2106–2124; b) D. D. Prabhu, N. S. S. Kumar, A. P.
Sivadas, S. Varghese, S. Das, J. Phys. Chem. B 2012, 116, 13071–
13080.
[25] E. Girotto, J. Eccher, A. A. Vieira, I. H. Bechtold, H. Gallardo,
Tetrahedron 2014, 70, 3355–3360.
[43] J. R. Lakowicz, Principles of fluorescence spectroscopy; Springer,
New York, NY, 2010.
[26] a) H. Detert, E. Sugiono, G. Kruse, J. Phys. Org. Chem. 2002, 15,
638–641; b) H. Detert, Synthesis 1999, 999–1004.
[44] M. Lehmann, M. Dechant, M. Lambov, T. Ghosh, Acc.Chem.Res.
2019, 52, 1653-1664.
[27] S. H. Gihm, B. G. Kim, S. Kim, J. Seo, S. Y. Park, C. R. Park, J.
Mol. Struct. 2010, 984), 371–375.
This article is protected by copyright. All rights reserved.

10.1002/chem.201902975
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents
COMMUNICATION
Natalie Tober, Thorsten Rieth,
Matthias Lehmann* and Heiner Detert*
Page No. – Page No.
Synthesis, Thermal, and Optical
Properties of Tris(5-aryl-1,3,4-
oxadiazolyl)-1,3,5-triazines, New Star-
shaped Fluorescent Discotic Liquid
Crystals
A series of C3-symmetrical stars is prepared via Huisgen reaction of alkoxyaryl-
tetrazoles and a central tricarboxylic acid. These π-conjugated discotic molecules
are solvatochromic fluorophores, a rim of six to nine alkoxy chains provokes broad
mesophases.
This article is protected by copyright. All rights reserved.