Tristriazolotriazines with Azobenzene Arms - Acidochromic Dyes and Discotic Liquid Crystals

Article abstract of DOI:10.1002/ejoc.201900665

Tristriazolotriazines with azobenzene substitution and peripheral alkoxy- or alkylamino chains were prepared from the corresponding aryltetrazoles and cyanuric chloride. These star-shaped dyes are highly acidochromic. Alkoxy-substitution allows reversible trans-cis photoswitching. Compounds with a 3,4-dialkoxy substitution are discotic liquid crystals that form broad and stable thermotropic mesophases. The thermal behavior was studied by DSC and polarizing optical microscopy.

Full text of DOI:10.1002/ejoc.201900665

A Journal of
Accepted Article
Title: Tristriazolotriazines with Azobenzene Arms - Acidochromic Dyes
and Discotic Liquid Crystals
Authors: Marcel Sperner, Natalie Tober, and Heiner Detert
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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
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201900665
Link to VoR: http://dx.doi.org/10.1002/ejoc.201900665
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10.1002/ejoc.201900665
European Journal of Organic Chemistry
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Tristriazolotriazines with Azobenzene Arms - Acidochromic Dyes
and Discotic Liquid Crystals
Marcel Sperner, Natalie Tober and Heiner Detert*
Dedicated to Helmut Ringsdorf on the occasion of his 90th birthday
Abstract: Tristriazolotriazines with azobenzene substitution and
peripheral alkoxy- or alkylamino chains were prepared from the
corresponding aryltetrazoles and cyanuric chloride. These star-
shaped dyes are highly acidochromic. Alkoxy-substitution allows
reversible trans-cis photoswitching. Compounds with a 3,4-dialkoxy
substitution are discotic liquid crystals that form broad and stable
thermotropic mesophases. The thermal behaviour was studied by
DSC and polarizing optical microscopy.
the azobenzene carries electronically neutral or donating substi-
tuents. Tristriazolotriazines (TTTs), tetracyclic discs with a C3-
symmetry, are heterocyclic but electron deficient analogues of
triphenylene.[20] Star-shaped molecules[21] with this core can be
mesomorphous, the LC phases are usually very broad and
display hexagonal-columnar arrangements. [22, 23]
The focus of this study is on tristriazolotriazines with azoben-
zene arms. These molecules combine mesomorphism and
photoswitching. Contrary to the usually alkyl(oxy)-substituted
azobenzenes in LC materials, the TTT core and the alkoxy/
amino periphery provoke an electronic donor-acceptor
substitution of the azobenzene. This scarcely investigated
combination[24] adds photoswitching and non-linear optical
properties[25] to mesomorphism.
Introduction
Liquid crystals (LCs) are a unique category of soft matter, which
retains molecular order even in the molten state. Thus represen-
ting an intermediate state between the isotropic fluid and that of
a crystal.[1] Rod-like liquid crystals are the most important group
of LCs, especially because of their application as active com-
pounds in LCD technology.[2] Disc-shaped molecules constitute
another class of liquid crystals (DLCs),[3] possible applications
are in optoelectronics or as sensors. Azobenzene is the working
horse for research in photoactive materials, polymers,[4] hybrid
materials,[5] and soft matter.[6] Already Vorländer[7] reported liquid
crystalline azobenzenes.[8] The combination of mesomorphism
and photoswitching of azobenzene LCs, molecular,[9] as units in
the main chain or as side chain in polymers, is a highly active
field in materials science.[10] Possible applications are holo-
graphic displays, [11] data storage [12] and actuators.[13]
Photochemical trans-cis-isomerization disorganizes the liquid-
crystalline surrounding of the molecule. This may lead to a
transformation of the LC-phase to an isotropic fluid.[14] Smectic,
columnar, and even nematic phases have been found for azo-
benzene-triphenylene conjugates. Uchida reported a stunning
phenomenon: the photochemical switch between calamitic and
discotic mesomorphism.[15] Furthermore, isothermal phase
transitions between isotropic, smectic, and columnar phases
could be controlled by the intensity of the incident light. trans-cis
Isomerization do not only provoke changes of the optical and
The synthesis of discotic liquid crystals composed of a TTT core
with three donor-acceptor substituted azobenzene arms, their
spectroscopic and thermal properties as well as photochemical
switching experiments are reported.
Synthesis
The synthesis of TTTs 1 - 4 follows Huisgens original proce-
dure,[26] threefold reaction of cyanuric chloride with tetrazoles
and thermal ring transformation to form the tetracyclic
tristriazolotriazine (scheme 1). Since twelve reactions are
required to form the TTT, a careful control of the reaction
conditions is necessary; substituents on the tetrazole can have
decisive influence on reactivity, formation of by-products, and
stability of the product.[27] The Huisgen protocol generates TTTs
with a tangential orientation of the substituents, thus giving the
molecule the shape of a paddle-wheel. The required tetrazoles
with azo-groups were prepared from p-aminobenzoic acid as
starting material (scheme 1). Diazotation to 5 (R4 = H) and azo-
coupling to N,N-didecylaniline (7, R1 = N(C10H21)2, R2 = R3 = H)
in acetic acid[28] gave anilino-azo benzoic acid 11 (63 %). Due to
the coupling conditions, diazotized ethyl p-amino-benzoate 6 (R4
= CH2CH3) was the preferred starting material for the prepara-
tion of the 2´,4´-didecyloxy-derivative (18, R1 = R3 = OC10H21, R2
= H, 76 %) via a sequence involving azo-coupling with resorcinol
8 (R1 = R3 = OH, R2 = H), O-alkylation, and alkaline hydroly-
sis.[29] During the O-alkylation a side-reaction, additional C-alky-
lation on the resorcinol ring (R2 = C10H21) occurred, which forced
to extensive chromatographic purification and loss of material.
The analogous coupling of 6 with catechol 9 (R1 = R2 = OH, R3 =
H) failed completely, even after broad variation of pH. But a
detour, using 2-ethoxyphenol 10 (34 %) as coupling partner,[30]
removal of the protecting group (76 %) and alkylation (70 %), led
thermal properties, photomodulation of thin films and surfaces
[17]
[16] and nonlinear optical properties
hot topics in material science.
of azobenzene LCs are
Disc-shaped liquid crystals with azobenzene subunits are
typically based on benzene[18] or triphenylene as core,[15, 19] and
Dr. M. Sperner, MSc N. Tober, Prof. Dr. H. Detert
Institute for Organic Chemistry
Johannes Gutenberg-University Mainz
Duesbergweg, 10 – 14, D-55099 Mainz, Germany
E-mail: detert@uni-mainz.de
Homepage: https://www.blogs.uni-mainz.de/fb09ak-detert/
to the desired 3´,4´-didecyloxyazobenzene 19 (R1 = R2
=
Supporting information for this article is given via a link at the end of
the document.
OC10H21, R3 = H) and the 3´,4´-didodecyl derivative 20 (R1 = R2
= OC12H25, R3 = H). Transformation of the carboxylic acid into
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10.1002/ejoc.201900665
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tetrazole was performed by reaction with thionyl chloride,
ammonolysis of the acid chloride, and a combined dehydra-
tion/azidination with in situ generated triazidochlorosilane.[31]
Tetrazoles 25 - 28 were obtained in 28 - 65 % yield.
only weak ( < 5 nm), the efficient dialkylamino donor in amino-
TTT
1 provokes a strong and positive solvatochromism
(cyclohexane – ethanol:  = 69 nm,  = 3068 cm-1), indicating
a polarity-enhanced charge transfer from the amino group to the
acceptor azophenyltriazole. This screening shows the largest
change of dipole moment from ground to excited state in 1.
Ri
R1
R2
+
N2
COOR4
Table 1: Photophysical data of TTTs 1 - 3
5, 6
7 - 10
N
R3
i
i, ii
iii
i, vi,
ii, iii
N
TTT 1
/ nm
TTT 2
max / nm
TTT 3
max / nm

N
N
(/103M-1cm-1)
(/ 103 M-1cm-1)
(/103M-1cm-1)
N
N
Ri
N
N
COOH
R1
N
N
cyclohexane
toluene
441 (106)
450 (110)
474 (106)
495 (76)
387 (78)
390 (83)
392 (90)
389 (66)
386 (57)
387 (78)
-67 cm-1
382 (61)
387 (67)
385 (79)
387 (53)
386 (52)
382 (61)
338 cm-1
N
N
N
N
11, 18 - 20
R2
N
N
R3
a) SOCl2
b) NH3
c) SiCl(N3)3
dichloromethane
acetonitrile
ethanol
1 - 4
N
510 (85)
R3
R2
cyclohexane
solvatochromic
shift#
441 (106)
3068 cm-1
N
C3N3Cl3
collidine
NH
Ri
N
N
N
N
25 - 28
R1
neat film
464
393
388
Scheme 1. Synthesis of tristriazolotriazines with azobenzene arms i) azo
coupling; ii) alkyl-Br, K2CO3; iii) KOH; HCl; vi) AlCl3, pyridine. 1: R1 =
film with PS
film with CA
film CA + TFA
10-6 M TFA /
DCM
458
393
388
N(C10H21)
2, R2 = R3 = H (55%); 2: R1 = R3 = OC10H21, R2 = H (44%); 3: R1 = R2
470
393
388
= OC10H21, R3 = H (32%); 4: R1 = R2 = OC12H25, R3 = H (34%).
532, 574
477 (107)
393, 500 sh
392 (99)
388, 542 sh
385 (77)
10-5 M TFA /
DCM
477 (111)
477 (114)
479 (106)
392 (93)
385 (75)
385 (71)
n.d.
The convergent and most critical step for building the TTT had to
be controlled carefully. Starting with an excess of tetrazole, the
mixture was stirred at 25 °C and additional cyanuric chloride was
added in small portions over four days. The TTTs were isolated
10-4 M TFA /
DCM
393 (106)
10-3 M TFA /
DCM
393 (87), 470 sh
(30)
1
as orange to red solids in 32-55 % yield. According to H-NMR
spectra, chromatographically purified TTTs 1 - 4 are composed
of solely one compound (SI). Upon storage at ambient
conditions, some cis isomer is formed. 1H NMR reveals 4 % cis
configured azobenzene for 2 and 8 % cis for 3; the amount of
cis-1 is below the detection limit. UV-irradiation (366 nm, CDCl3,
28°C, ca. 12 min) enhances the percentage of cis in 2 to 12 %
in 3 to 13%, slowly decreasing (18h, 27 °C) to 9% and 12%
respectively .
5 ˟ 10-3 M TFA /
DCM
488 (92) 562
sh (45)
405 (64),
487 (85)
385 (95)
10-2 M TFA /
DCM
10-1 M TFA /
DCM
565 (164)
492 (136), 405
sh (52)
385 (71), 517
(49)
563 (205)
487 (179)
397 (48), 541
(109)
1 M TFA / DCM
acidochromic
shift§
557 (224)
3351 cm-1
484 (183)
4890 cm-1
538 (191)
7356 cm-1
#: cyclohexane - ethanol; § dichloromethane - 0.1 M TFA; sh: shoulder
Optical Spectroscopy
films of 1:
1,0
TTTs 1-4 are orange to dark red compounds, in the solid state
and in solution. The length of alkyl chains has no effect on
optical properties (3: decyl vs. 4: dodecyl). The solution spectra
are dominated by an intense band with maximum in the violet (1)
to near UV range (2-4). Spectroscopic data are collected in
Table 1, the spectra are depicted in the supporting information.
The stronger donor-effect of the 2,4-dialkoxy substitution in 2
compared to the 3,4-substituted congeners 3, 4 shifts the
absorption maximum to longer wavelengths; the 4´-amino group
neat
neat, Irrad.
1 in PS
1 in CA
1 in PVA
1 in PS + TFA
1 in CA + TFA
0,5
1 in PVA + TFA
in
1 provokes the largest redshift and hyperchromism.
Furthermore, the optical spectra of these TTTs are influenced by
the environment. Solvatochromism is connected with changes in
dipole moments, a necessary prerequisite for non-linear optical
phenomena.[32] A selection of different solvents from non-polar
to polar-protic was used for 1 - 3. Whereas solvent-induced
spectroscopic shifts of alkoxy substituted azo-TTTs (2 - 4) are
0,0
400
450
500
550
600
650
700
750
wavelength / nm
Figure 1 UV-vis spectra of 1 in neat and polymer supported films normalized
to identical absorption
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In thin spin-coated films, the absorption spectra of the neat com-
pounds peak at slightly higher wavelengths compared to solution
in cyclohexane, this holds for pristine and annealed films. In
films composed of 1 - 3 and a polymer matrix, only amino-TTT 1
shows an impact of the matrix on the excitation (Figure 1). With
polystyrene, cellulose acetate and polyvinyl alcohol, three
polymers of very different polarity were chosen, their impact on
the absorption of 1 combines polarity of the matrix and its ability
to act as host for 1 in competition with self organization of 1.
Whereas max nmin polystyrene is red-shifted compared
to toluene solution (nm), the spectrum of 1 in polyvinyl
alcohol peaks at 488 nm – about  = 22 nm at higher
energies relative to ethanol solution. These shifts indicate a
significant aggregation of 1 as in the neat film (nm).
back to the trans form. This process is much faster, new
photostationary equilibria are established within 1 min – the
extinctions at max indicate significant amount of cis isomers (2:
I/I0 = 0.78; 3: max = 388 nm, ; I/I0 = 0.67). The thermal way back
is also possible but with t1/2  1h at 300 K.
The isosbestic points and the reversibility of the
photoisomerization prove homogeneous reactions and that the
molecules 2, 3 are composed of three identical and independent
triazolyl-azobenzene subunits.
Despite considerable interest in the photoisomerization of
azobenzenes, there is only scant information concerning the
interconversion of derivatives having both electron-donor and
electron-acceptor substituents in a conjugative relationship.[33]
.
This substitution reduces the bond order of the azo group and
thus enhances the cis-trans isomerization rate. The half-lifes of
the cis isomers of several 4-amino-4´-nitro-azobenzenes at
293 °C were determined as 1 s or less.[34] Whereas TTT 1
belongs to this group, only one electron pair donating alkoxy
group in 3 is in direct conjugation with the triazole acceptor and
the half-life greatly increases. In the solid film, azobenzene units
are buried in the viscous bulk, the photo-responsiveness is
usually remarkably weakened[35] or even completely suppressed,
e.g. due to severe H-aggregation.[16a]
Like methyl red or similar indicator dyes, the optical spectra of
azo-TTTs are sensitive towards protonation. Addition of trifluoro-
acetic acid (TFA) to solutions of TTTs in dichloromethane
changes the absorption spectra significantly (Figure 3 and SI).
Common features are that the absorption band around 400 nm
vanishes and a new band in the green-yellow region appears.
The spectra of the transition from neutral to protonated form
show isosbestic points, indication of a simultaneous protonation
of all three azobenzene units. Amino-TTT 1 has a transition
point at 5 x 10-4 M TFA in dichloromethane, the 2,4- and the 3,4-
didecyloxy derivatives 2 and 3, 4 are about 1 or 2 pK units less
basic. Noteworthy, the red shifts of the absorption maxima
increase in this series ( = 3351 (1); 4980 (2); 7356 (3) cm-1)
and extinction coefficients of the protonated forms are about
twice as high as of the neutral molecules.
3,0
3 in CH2Cl2
30 s 366 nm
90 s 366 nm
2,5
360 s 366 nm
810 s 366 nm
30 s 400 nm
60 s 400 nm
2,0
1,5
1,0
0,5
0,0
350
400
450
500
wavelength  nm
Figure 2 Reversible photoswitching of 3 upon irradiation with  = 366 nm and
 = 400 nm.
Monochromatic irradiation ( = 545 nm) into the long-wavelength
tail of the absorption band of neat 1 (film) results in a successive
reduction of the main absorption band and a small increase of
the absorption around  = 370 nm. Two isosbestic points ( =
335 nm, 397 nm) indicate a homogeneous reaction (SI). The
same experiments performed with 2 and 3 and irradiation at  =
445 nm resulted only in weak (2) or nearly negligible (3)
reduction of the max extinction. Upon irradiation into the high-
energy flank of the main absorption band of 1 (nm2 3
(nm, 3 shows photoswitching in contrast to 1, 2. The
photochemical equilibrium is reached in less than 10 min;
thermal relaxation at 300 K occurs with t1/2  90 min.
Irradiation of solutions of 1-3 with UV-light completely changes
the behavior. Variation of the exciting light in seven steps from 
= 366 to 445 nm amino-TTT 1 gives the identical UV-vis spectra.
On the other hand, the alkoxy-TTTs 2, 3 are highly reactive upon
UV irradiation (Figure 2, SI). Within less than 10 min, the
photostationary cis-trans equilibrium (2: max = 393 nm; I/I0
=
0.56; 3: max = 388 nm, I/I0 = 0.43) was reached, with isosbestic
points for 2 at  = 322 nm and for 3 at  = 318 and 468 nm.
Irradiation of these solutions with  = 400 nm induces the way
Figure 3. Absorption spectra of TTT 2 in dichloromethane with increasing
TFA concentration.
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Irradiation of protonated azo-TTTs 1 ( = 445 nm) and 2, 3 ( =
400 nm) does not change the electronic spectra but 1+H+
exhibits a very weak fluorescence with max = 610 nm. Proton-
induced spectral changes are also possible in polymer-
supported films (Figure 1 and SI). Cellulose acetate provided the
best combination of film stability and dye sensitivity.
It should be noted that the elongation of the alkyl chain about an
ethylene unit raises the clearing point about 30 °C!
Conclusions
A series of threefold azobenzene substituted tristriazolotriazines
has been prepared via Huisgen reaction. These star-shaped
dyes are solvatochromic and acidochromic, UV and visible light
allow photochemical switching between cis- and trans-alkoxy
TTTs. A 3,4-dialkoxy substitution results in discotic LCs that
form broad enantiotropic mesophases, though the viscosity of
the LC phase strongly hampers crystallization. The LC phases
are stable under illumination with sunlight. Increasing length of
the side chains to dodecyl enhances the width of the LC phase.
Thermal Properties
The thermal behavior of azo-TTTs 1-4 was investigated by
polarized optical microscopy (POM) and differential scanning
calorimetry (DSC). Whereas TTTs with didecylamino group (1)
or 2,4-didecyloxy substitution (2) are not mesomorphous (1:
m.p.: 132 °C, 2: m.p.: 134 °C), the 3,4-dialkoxy substitution
leads to liquid crystalline behaviour. POM reveals pseudo-focal
conical textures of the mesophases (figure 4). The schlieren
texture after shearing, and the restoration of the pseudo-focal
conical texture are strong indicators of mesomorphism. The
observed pseudo focal conical textures are characteristic for
discotic liquid crystals with columnar arrangement in the
mesophase.[36] These textures are stable even under prolonged
Experimental Section
Experimental Details.
1H and 13C NMR spectra: Bruker AC 300 (300 MHz), Bruker AV 400 (400
MHz), and Bruker ARX 400 (400 MHz), solvents were CDCl3, C6D6,
DMSO-d6. Chemical shifts are expressed as δ values in ppm, coupling
constants are given in Hz. Calibration on the residual 1H signal of the
solvent, in CDCl3/DMSO mixtures calibration on DMSO. Assignments of
1H and 13C signals on the basis of HSQC and HMBC experiments.
Abbreviations used for assignment of spectra: ph: phenyl, tet: tetrazole,
tria: triazole, TTT: tristriazolotriazine. Melting points: Büchi HWS SG 200,
Stuart Scientific SMP3. DSC: Perkin Elmer, DSC 7, Perkin Elmer Pyris
Software (4.01). IR: JASCO 4100 FT-IR (ATR), FD-MS: Mat 95
(Finnigan); HR-ESI: Q-TOF-ULTIMA 3, Lock Spray device (Waters-
Micromass), NaICsI as reference. UV-vis: Perkin-Elmer Lambda 16.
Fluorescence: Perkin-Elmer LS 50B; Photochemistry: LOT Xe-arc lamp,
300 W, equipped with IR-filter and color filters. Polarized microscopy:
Olympus BX51, ColorView Olympus camera, heattable Linkam LTS
350 for temperature regulation. DSC: Perkin Elmer DSC7, heating rate:
10 Kmin-1. Details for synthesis of intermediates are collected in the SI.
illumination with unfiltered visible light.
A resistance of
mesomorphism towards azo-cis-trans isomerization has recently
reported for related stars with a trimesic triamide core.[37]
Figure 4. POM textures of TTTs 3 (140 °C), 4 (120 °C) in the mesophase
under crossed polarizers.
General procedure for the synthesis of azo-tristriazolotriazines
A solution of the tetrazole (ca. 400 mg, 1 eq.) in dry toluene (30 mL) and
2,4,6-collidine (1 eq.) was stirred for 1 h at ambient temperature before
cyanuric chloride (0.25 eq.) in toluene (2 mL) was added. The mixture
was stirred for 1 day, additional cyanuric chloride (0.03 eq.) was added in
4 daily portions. The mixture was washed with hydrochloric acid (2M), the
organic layer was dried over MgSO4, concentrated, and the residue
purified by chromatography on a silica column with a head of basic
alumina using toluene/ethyl acetate (70/1) as an eluent.
Since POM revealed that the 3,4-dialkoxy substituted azo-TTTs
3 and 4 form birefringent and liquid phases at elevated tempera-
tures, we used DSC to get further information about the thermal
behavior. TTT 3 melts at 56 °C and the mesophase is stable up
to 143 °C (ΔH = 1.2 kJ mol-1). Upon cooling, the material
becomes mesomorphous, but a crystallization of these star-
shaped molecules from the viscous mesophase was not
observed. Accordingly, the second heating scan revealed only
the clearing transition, but a third heating scan of this sample,
performed after a several months, revealed both transitions
again (SI). Similarly, DSC of freshly prepared TTT 4 showed no
melting transition but a clearing point at 171 °C (ΔH = 2.5 kJ mol-
1). A third heating experiment on the thermally equilibrated
sample revealed three transitions: 61 °C (ΔH = 8.5 kJ mol-1),
111 °C (ΔH = 6.3 kJ mol-1) and the clearing point at 171 °C. The
first transition corresponds to CrCr and the second to CrM.
Upon cooling, the viscous LC phase solidified to a plastic phase.
3,7,11-Tris{4-(4-N,N-didecylaminophenylazo)phenyl}tris([1,2,4]tri-
azolo)[4,3-a:4',3'-c:4'',3''-e][1,3,5]triazine 1
According to the general procedure, 213 mg (391 μmol) 5-[4-(4-N,N-
didecylaminophenylazo)phenyl]tetrazole (25) gave 116 mg (213 μmol,
55 %) of a dark red solid with m.p.: 132 °C. 1H-NMR (300 MHz, CDCl3): δ
/ ppm = 8.35 (d, 3J = 8.6 Hz, 2H, 2-H, 6-H (Ph)), 8.01 (d, 3J = 8.2 Hz, 2H,
3-H, 5-H (Ph)), 7.87 (d, 3J = 8.1 Hz, 2H, 2-H, 6-H (Ph')), 6.67 (d, 3J = 8.5
3
Hz, 2H, 3-H, 5-H (Ph')), 3.35 (t, J = 7.2 Hz, 4H, NCH2), 1.66 – 1.61 (m,
4H, NCH2CH2), 1.32 – 1.28 (m, 28H, Alkyl), 1.16 – 0.55 (m, 6H, CH3).
13C-NMR (75 MHz, CDCl3): δ / ppm = 155.16 (C-4 (Ph)), 151.25 (C-4
(Ph')), 150.79 (C-5 (tria)), 143.03 (C-1 (Ph')), 140.71 (C-3 (tria)), 131.20
(C-2, C-6 (Ph)), 125.87 (C-2, C-6 (Ph')), 123.96 (C-1 (Ph)), 122.27(C-3,
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C-5 (Ph)), 111.28 (C-3, C-5 (Ph')), 51.47 (NCH2), 32.03, 29.79, 29.71,
29.62, 29.56, 29.47, 27.47, 27.25, 22.83 (CH2), 14.27 (CH3). FD-MS: m/z
(%) = 813.6 (1), 814.2 (87), 814.8 (6), 815.6 (4) [M]2+, 1085.5 (4), 1086.5
(2) [M3]2+, 1627.6 (68), 1628.5 (100), 1629.3 (23), 1630.6 (16), 1631.6 (2)
[M]+. IR (ATR): ὕ / cm-1 = 2921 s, 2852 m, 1592 ss, 1512 m, 1467 w,
1391 m, 1362 m, 1255 m, 1130 ss, 845 m, 822 m. HRMS-ES(+): [M+H]+
calcd.: 1628.2369, found: 1628.2408.
(Ph)), 152.99 (C-4 (Ph')), 150.64 (C-5 (tria)), 149.72 (C-3 (Ph')), 146.83
(C-1 (Ph')), 140.74 (C-3 (tria)), 131.34 (C-2, C-6 (Ph)), 125.05 (C-1 (Ph)),
122.75 (C-3, C-5 (Ph)), 122.01 (C-6 (Ph')), 112.06 (C-5 (Ph')), 103.83 (C-
2 (Ph')), 69.36 (OCH2), 69.27 (OCH2), 32.08, 29.87, 29.82, 29.79, 29.61,
29.57, 29.53, 29.28, 29.24, 26.21, 26.14, 22.85 (CH2), 14.28 (CH3). IR
(ATR): ὕ / cm-1 = 2923 s, 2853 m, 1590 s, 1504 m, 1468 m, 1258 ss,
1113 m, 1016 w, 907 s, 848 w, 729 ss. FD-MS: m/z (%) = 923.3 (23),
923.7 (65), 924.6 (47), 925.2 (3) [M]2+, 1844.4 (3), 1845.5 (1), 1846.5
(16), 1847.0 (100), 1847.7 (76), 1848.6 (27), 1849. 3 (6), 1849.8 (3),
1850.6 (3), 1852.1 (1) [M]+. EA: C114H171N15O6 (1847.67) calcd.: 74.11%
C, 9.33% H, 11.37% N, found.: 73.75% C, 8.77% H, 11.24% N.
3,7,11-Tris{4-(2,4-didecyloxyphenylazo)phenyl}tris([1,2,4]tria-
zolo)[4,3-a:4',3'-c:4'',3''-e][1,3,5]triazin 2
According to the general procedure, 200 mg (355 μmol, 1 eq.) 5-[4-(2,4-
didecyloxyphenylazo)phenyl]tetrazole (26) gave 87 mg (155 μmol, 44
%) of an orange-red solid with m.p.: 111 °C.
3
1H-NMR (300 MHz, CDCl3): δ / ppm = 8.35 (d, J = 8.3 Hz, 2H, 2-H, 6-H
Acknowledgments
(Ph)), 8.06 (d, 3J = 8.3 Hz, 2H, 3-H, 5-H (Ph)), 7.79 (d, 3J = 8.9 Hz, 1H, 6-
H (Ph')), 6.57 (d, 4J = 2.4 Hz, 1H, 3-H (Ph')), 6.53 (dd, 3J = 9.0, 4J = 2.5
Hz, 1H, 5-H (Ph')), 4.17 (t, 3J = 6.7 Hz, 2H, OCH2), 4.02 (t, 3J = 6.5 Hz,
2H, OCH2), 2.09 – 1.87 (m, 2H, OCH2CH2), 1.87 – 1.72 (m, 2H,
OCH2CH2), 1.70 – 1.06 (m, 28H, Alkyl), 1.08 – 0.68 (m, 6H, CH3). 13C-
NMR (101 MHz, CDCl3): δ / ppm = 164.19, 159.35 (C-4, C-2 (Ph')),
155.06 (C-4 (Ph)), 150.76 (C-5 (tria)), 140.79 (C3 (tria)), 137.12 (C-1
(Ph')), 131.23 (C-2, C-6 (Ph)), 124.73 (C-1 (Ph)), 122.85 (C-3, C-5 (Ph)),
118.27 (C-6 (Ph')), 106.77 (C-5 (Ph')), 100.93(C-3 (Ph')), 70.05 (OCH2),
68.62 (OCH2), 32.05, 29.77, 29.72, 29.66, 29.54, 29.48, 29.45, 29.34,
26.16, 22.82, 22.78 (CH2), 14.27 (CH3). IR (ATR): ὕ / cm-1 = 2923 s,
2853 m, 1591 ss, 1465 m, 1286 s, 1247 s, 1181 s, 1109 m, 1018 m, 753
s. FD-MS: m/z (%) = 839.1 (5), 839.7 (10), 840.5 (2) [M]2+, 1678.3 (46),
1679.0 (100), 1679.7 (14), 1680.1 (7), 1681.3 (7), 1682.3 (2) [M]+.
The authors are grateful to Maria Müller for measuring DSC
thermograms, the DFG for generous funding (De 515/9-1), and
to the reviewers for important advice.
Keywords: star-shaped compounds • discotic liquid crystals •
azobenzene • differential scanning calorimetry • polarizing
optical microscopy
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1H-NMR (300 MHz, CDCl3): δ / ppm = 8.37 (d, J = 8.3 Hz, 2H, 2-H, 6-H
(Ph)), 8.02 (d, 3J = 8.3 Hz, 2H, 3-H, 5-H (Ph)), 7.55 (dd, 3J = 8.3, 4J = 2.1
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Hz, 1H, 5-H (Ph')), 4.04 (m, 4H, OCH2), 1.94 – 1.70 (m, 4H, OCH2CH2),
1.55 – 1.13 (m, 28H, Alkyl), 0.98 – 0.78 (m, 6H, CH3). 13C-NMR (101
MHz, CDCl3): δ / ppm = 154.51 (C-4 (Ph)), 152.74 (C-4 (Ph')), 150.53 (C-
5 (tria)), 149.63 (C-3 (Ph')), 146.85 (C-1 (Ph')), 140.63 (C-3 (tria)), 131.25
(C-2, C-6 (Ph)), 125.04 (C-1 (Ph)), 122.69 (C-3, C-5 (Ph)), 121.58 (C-6
(Ph')), 111.94 (C-5 (Ph')), 103.66 (C-2 (Ph')), 69.30 (OCH2), 69.21
(OCH2), 32.07, 29.80, 29.80, 29.78, 29.75, 29.66, 29.60, 29.58, 29.51,
29.27, 29.24, 26.19, 26.13, 22.84, 22.83, 22.82 (CH2), 14.27 (CH3). IR
(ATR): ὕ / cm-1 = 2923 s, 2853 m, 1589 s, 1503 m, 1465 m, 1258 ss,
1112 s, 1012 m, 908 m, 851 m, 807 w, 730 ss. FD-MS: m/z (%) = 838.3
(1), 839.4 (49), 840.1 (10), 840.7 (3) [M]2+, 1676.7 (1). 1678.5 (94),
1679.2 (100), 1679.8 (4), 1680.3 (31), 1681.6 (8) 1682.2 (1) [M]+. EA:
C102H147N15O6 (1679.36) calcd.: 72.95% C, 8.82% H, 12.51% N, found:
72.13% C, 8.58% H, 12.41% N.
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1H-NMR (300 MHz, CDCl3): δ / ppm = 8.37 (d, J = 8.2 Hz, 2H, 2-H, 6-H
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European Journal of Organic Chemistry
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FULL PAPER
Layout 1:
FULL PAPER
Tristriazozotriazines with three
azobenzene arms and alkylamino or
alkoxy side chains are prepared via
Huisgen reaction. These stars are
solvatochromic and acidochromic
dyes, protonation of all arms occurs
simultaneously. Alkoxy-Azo-TTTs are
efficient photoswitches. Peripheral
3,4-dialkoxy substitution leads to
mesomorphism, the LC phase is
stable in daylight.
Star-Shaped π-Systems
Marcel Sperner, Natalie Tober and
Heiner Detert
Page No. – Page No.
Tristriazolotriazines with Azobenzene
Arms - Acidochromic Dyes and
Discotic Liquid Crystals
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