Photoresponsive ionic liquid crystals based on azobenzene guanidinium salts

Article abstract of DOI:10.1039/c4cp04783d

The use of non-ionic LC phases as anisotropic matrices for E/Z-isomerization of azo-guest molecules is often restricted due to limited solubilities and demixing effects. In this study we therefore employed an ionic liquid crystal (ILC) matrix to follow the photo-induced E/Z-isomerization of ionic mesogenic azobenzene guanidinium guests. The latter were prepared from 4-hydroxy-4′-(octyloxy)azobenzene, which was first treated with N-(bromoalkyl)phthalimides to introduce the spacer with varying chain length. Removal of phthalimide and final reaction with a formamidinium salt linked the ionic head group to the photoisomerizable azobenzene unit. Investigation of the mesomorphic behaviour revealed for all azobenzene ILCs smectic A mesophases with high translational order parameters and partial bilayers, as could be stated by layer spacing d. Similar packing behaviour was found for the solid state by X-ray crystal structure analysis. E/Z-isomerization of azobenzene ILCs which were completely miscible with the ionic LC phase of C₁₂MIM-Br as anisotropic host was induced by irradiation with UV light and the reisomerization observed by time-resolved UV-Vis spectroscopy. For comparison, water was used as isotropic host. Z/E-reisomerization activation energies exhibited similar values of 97-100 kJ mol^-1 irrespective of spacer lengths and the type of host. The results demonstrate that a proper match of steric requirements of host and guest as well as layer spacings are needed for a decreased activation energy. This journal is

Full text of DOI:10.1039/c4cp04783d

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Photoresponsive ionic liquid crystals based on
azobenzene guanidinium salts†
Cite this:DOI: 10.1039/c4cp04783d
a
b
b
b
Eugen Wuckert,‡ Marc D. Harjung,‡ Nadia Kapernaum, Carsten Mueller,
a
a
b
a
Wolfgang Frey, Angelika Baro, Frank Giesselmann* and Sabine Laschat*
The use of non-ionic LC phases as anisotropic matrices for E/Z-isomerization of azo-guest molecules is
often restricted due to limited solubilities and demixing effects. In this study we therefore employed an
ionic liquid crystal (ILC) matrix to follow the photo-induced E/Z-isomerization of ionic mesogenic azobenzene
0
guanidinium guests. The latter were prepared from 4-hydroxy-4 -(octyloxy)azobenzene, which was first
treated with N-(bromoalkyl)phthalimides to introduce the spacer with varying chain length. Removal of
phthalimide and final reaction with a formamidinium salt linked the ionic head group to the photoisomerizable
azobenzene unit. Investigation of the mesomorphic behaviour revealed for all azobenzene ILCs smectic A
mesophases with high translational order parameters and partial bilayers, as could be stated by layer spacing d.
Similar packing behaviour was found for the solid state by X-ray crystal structure analysis. E/Z-isomerization
of azobenzene ILCs which were completely miscible with the ionic LC phase of C12MIM-Br as anisotropic
host was induced by irradiation with UV light and the reisomerization observed by time-resolved UV-Vis
spectroscopy. For comparison, water was used as isotropic host. Z/E-reisomerization activation energies
Received 20th October 2014,
Accepted 17th December 2014
ꢀ1
exhibited similar values of 97–100 kJ mol irrespective of spacer lengths and the type of host. The results
demonstrate that a proper match of steric requirements of host and guest as well as layer spacings are
needed for a decreased activation energy.
DOI: 10.1039/c4cp04783d
www.rsc.org/pccp
7
Chen prepared vinylimidazolium ILCs with p-nitroazobenzene and
symmetric azobenzenes with two imidazolium ions. Kaszynski
1
Introduction
8
1
2
ꢀ
In the late seventies Pelzl and Nelson independently reported studied ILCs based on [closo-1-CB
9
H
10
]
clusters, where the
9
that the mesomorphic properties of azobenzenes and stilbenes closo-monocarborate is part of an ‘‘azo-heterobenzene’’ unit.
can be changed by E/Z-photoisomerization. Later work by Ikeda More recently, Deng reported the photo-induced isothermal
showed that photochromic azobenzene guests in a nematic 5CB phase transition of N-dodecyl-N-methyl-imidazolium tetrafluoro-
0
0
(
4 -pentyl-cyanobiphenyl) host can induce photochemical iso- borate doped with small amounts of 4-methoxy-4 -methylazo-
3
10
thermal phase transitions of the guest–host mixture. These benzene. In such ILCs nanosegregation of charged head groups
seminal contributions stimulated numerous research activities and lipophilic side chains and/or aromatic mesogenic subunits in
on the photoisomerization of thermotropic low molecular weight combination with steric constraints is the major driving force for
4
5
11
liquid crystals as well as liquid crystalline polymers. In con- the formation of mesophases, resulting in novel materials with
trast, only a few examples of ionic liquid crystals (ILCs) bearing fluid-like viscosity, long-range orientational order and anisotropic
6
mesogenic azobenzene units have been described up to now.
physical properties. Thus, ILCs may be considered as anisotropi-
cally ordered fluids.
Non-ionic liquid crystalline phases were used as anisotropic
a
Institut f u¨ r Organische Chemie, Universit a¨ t Stuttgart, Pfaffenwaldring 55,
matrices in which the kinetics of the E/Z-isomerization of azo-
D-70569 Stuttgart, Germany. E-mail: sabine.laschat@oc.uni-stuttgart.de;
12,13
guest molecules was investigated.
Upon irradiation with UV
Fax: +49 711 685 64285; Tel: +49 711 685 64565
b
light the equilibrium between the two states is shifted towards
Institut f u¨ r Physikalische Chemie, Universit a¨ t Stuttgart, Pfaffenwaldring 55,
the Z-state while in a thermal reisomerization process the
D-70569 Stuttgart, Germany
†
Electronic supplementary information (ESI) available: Anion exchange in molecular shape changes from the bend Z-isomer back to the
chloride 6dꢁCl and DSC measurement of the resulting azobenzene guanidinium
salts 6dꢁX, photoisomerization of ILC 6cꢁCl in the anisotropic C12MIM-Br matrix,
X-ray crystal structure of 6aꢁCl as well as data of all guanidinium salts 6. CCDC
rod-like E-isomer, which is favoured by the rod-like environ-
ment in the LC-matrix. Thus, the activation energy for the
thermal Z/E-reisomerization in the LC host is clearly lower than
1
030119 and 1030120. For ESI and crystallographic data in CIF or other electronic
1
2
that in an isotropic host phase as reported by Zentel and
format see DOI: 10.1039/c4cp04783d
Both coauthors contributed equally to this work.
1
3
‡
Finkelmann. As common azobenzene dyes are often polar or
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even ionic their miscibility with non-ionic LCs is rather limited,
leading to a demixing of the LC and the azobenzene especially
1
4
after the photoisomerization to the Z-isomer. Ionic liquid
crystals (ILCs) are so-called designer solvents, whose properties
can easily be tuned by a systematic selection of cations and
anions. Thus, to overcome the solubility problem we developed
a new approach where an ionic liquid crystal (ILC) matrix is
used to investigate the kinetics of the Z/E-reisomerization of
ionic azobenzene molecules. This method may be of particular
interest as it would lead to tunable reaction media. For this
purpose we synthesized novel guanidinium ILCs which are
tethered via flexible spacer to the mesogenic azobenzene unit
and studied their thermotropic mesomorphic behaviour as well
as E/Z-photoisomerization in an anisotropic and in an isotropic
host medium. The results are reported below.
2
Results and discussion
2.1 Synthesis of guanidinium azobenzene ILCs
The synthesis of guanidinium azobenzene ILCs 6 commenced
with p-nitrophenol (1), which was submitted to Williamson
etherification with octylbromide followed by Pd-catalyzed hydro-
genation to provide 4-octyloxyaniline (2) in 91% (Scheme 1).
Subsequent diazotation and azo coupling with phenol following
1
5
0
a sequence by Shi yielded 4-hydroxy-4 -(octyloxy)azobenzene (3).
Its treatment with the known N-phthalimido-protected spacer units
4
16
a–f under Williamson conditions afforded the N-phthalimido
derivatives 5a–f. Hydrazinolysis and subsequent reaction with
commercially available chloroformamidinium chloride following
17
our previously established method yielded the corresponding
guanidinium chlorides 6(a–f)ꢁCl. Chloride 6d with hexyl spacer
18
was also converted via salt metathesis to guanidinium ILCs 6dꢁX
4 6
with different anions (X = Br, I, OTf, SCN, BF , PF ) (see ESI†).
2
ILCs
.2 Mesomorphic properties of guanidinium azobenzene
Scheme 1 Synthesis of azobenzene guanidinium chlorides 6ꢁCl. Num-
bering for assignment of individual NMR signals.
The mesomorphic properties of guanidinium azobenzenes 6ꢁCl
were determined by differential scanning calorimetry (DSC),
polarizing optical microscopy (POM) and X-ray diffraction (wide homologues 6(a–f)ꢁCl melting and clearing points increased
angle (WAXS) and small angle X-ray scattering (SAXS)).
from 6aꢁCl to a maximum for 6bꢁCl and 6cꢁCl and then
Under the POM on plain glass plates all compounds 6ꢁCl dis- decreased continuously for spacer lengths of n = 6–8 (Fig. 3).
played homeotropic textures indicating the presence of SmA phases, The mesophase widths, however, remained similar. A compar-
as shown in Fig. 1a for guanidinium chloride 6fꢁCl as example.
ison of the transition temperatures during heating and cooling
By filling the samples into polyimide coated LC-cells planar also revealed supercooling, thus the phase widths are usually
fan-shaped textures could be observed in the SmA phase. In broader in the cooling cycle.
order to suppress photo-induced isomerization, phase transi-
tions were studied under POM using monochromatic light at mesophase geometry, the guanidinium chlorides 6ꢁCl were
56 nm, which made the textures appear red (Fig. 1b). A typical further characterized by X-ray measurements. The temperature-
In order to obtain more information about the smectic A
6
DSC curve with a hysteresis between heating and cooling cycle dependent layer spacings d of the SmA phases of 6(a–f)ꢁCl were
indicating some degree of supercooling is exemplarily given for obtained by small angle X-ray scattering (SAXS) upon cooling
chloride 6fꢁCl with octyl spacer (Fig. 2).
(Fig. 4a). All azobenzene ILCs 6ꢁCl showed a linear increase of
The results of the DSC experiments upon third heating and the layer spacings with decreasing temperature being typical for
cooling are summarized in Table 1 and illustrated in Fig. 3. All SmA phases. By comparing the phase transition temperatures
guanidinium azobenzene chlorides 6ꢁCl displayed enantiotropic received from X-ray measurements with the POM observations
mesomorphism irrespective of the spacer lengths. Within the a broader phase range of the SmA phase due to supercooling
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ꢀ1
Table 1 Phase transition temperatures [1C] (and enthalpies [kJ mol ]) of
a,b
guanidinium azobenzene ILCs 6ꢁCl upon third heating and cooling cycle
Compd Spacer length n Cr
SmA
I
Cycle
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
6aꢁCl
6bꢁCl
6cꢁCl
6dꢁCl
6eꢁCl
6
fꢁCl
3
3
4
4
5
5
6
6
7
7
8
8
118 (18.9)
—
139 (1.2)
153
Heating
Cooling
Heating
Cooling
Heating
Cooling
Heating
Cooling
Heating
Cooling
Heating
Cooling
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
c
c
125 (27.9)
109 (24.9)
125 (30.7)
105 (29.3)
117 (33.1)
95 (6.2)
111 (19.2)
97 (7.7)
100 (28.1)
100 (2.5)
151 (1.0)
153 (1.0)
150 (1.5)
151 (1.6)
137 (1.9)
137 (2.0)
129 (0.4)
134 (0.2)
125 (3.5)
132 (3.5)
a
Phase transitions were determined by DSC (heating/cooling rate
ꢀ1
b
1
0 K min ). The following phases were observed: crystalline (Cr),
c
smectic A (SmA), isotropic (I). The phase transitions could not be
determined by DSC; the given temperature was obtained by POM. Strong
supercooling, however, led to unreproducible data for the SmA - Cr
transition. By POM the transition values Cr 130.3 1C SmA 153.5 1C I were
observed upon heating.
Fig. 1 (a) Homeotropic texture of 6fꢁCl typical for SmA phases at 129 1C
as seen between crossed polarizers upon cooling from the isotropic liquid
(
magnification ꢂ200) and (b) in a LC-cell with polyimide coated glassplates
at 133.3 1C and a wavelength filter at 656 nm; left: fan-shaped texture of
Fig. 3 Mesophase widths of guanidinium azobenzene ILCs 6(a–f)ꢁCl
depending on the spacer lengths n upon third heating/cooling obtained
the planar oriented SmA phase, right: homeotropic orientation.
ꢀ1
by DSC (heating/cooling rate 10 K min ).
transition is plotted against the theoretical values of the
molecular lengths that were received from molecular modelling
using an energy minimization by a semi empirical force field
based on the MM2 basis set (ChemDraw 3D). The relation of
the layer spacing d and the calculated molecular length lopt
showed a quite linear behaviour (Fig. 4b). The layer spacing was
found to be about 1.4 times the molecular length indicating the
formation of partial bilayers with interdigitated molecules.
SAXS measurements also allow the calculation of the transla-
tional order parameter S of the SmA phase providing a measure for
the quality of the translational periodicity of the smectic layers. S
was calculated in the SmA phase by extrapolation of the integrated
temperature-dependent scattering intensity of the layer peak to
Fig. 2 DSC curves of guanidinium azobenzene ILC 6fꢁCl upon 3 heating and
19
ꢀ1
cooling (heating/cooling rate 10 K min ). Cr = crystalline, Sm = smectic, absolute zero by using our previously developed method. The
I = isotropic liquid.
determined smectic order parameters for 6cꢁCl, 6eꢁCl, and 6fꢁCl
show quite high values of up to 0.9 (Fig. 5) compared to
effects could be found especially for 6aꢁCl and 6cꢁCl. In Fig. 4b conventional thermotropic liquid crystals which usually ranged
2
0
the smectic layer spacing at the isotropic to SmA phase around 0.7. The high value of the translational order in the
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Fig. 4 (a) Smectic layer spacing d in the SmA phase vs. the temperature
difference to the isotropic phase T–Tiso. (b) Smectic layer spacing d at the
isotropic to SmA phase transition plotted against the modelled molecular
length (lopt) of chlorides 6(a–f)ꢁCl by using ChemDraw 3D.
Fig. 6 Orientational order parameters S2 in the smectic A phase of
mesogens 6bꢁCl, 6cꢁCl and 6eꢁCl in dependence on the temperature
difference to the isotropic phase transition T–Tiso
.
mesogens 6ꢁCl implies that the molecules are only little dis-
located out of the partial double layers. This might be due to a
strong segregation tendency of the ionic head group from the
non-ionic part of the mesogens which try to avoid each other.
The influence of the spacer length on the parallel orienta-
tion of the molecules was investigated by determining the
orientational order parameters S
ILCs 6bꢁCl, 6cꢁCl and 6eꢁCl. These parameters S
the diffuse wide angle X-ray scattering arcs using the method by
2
in the mesophase of azobenzene
2
were derived from
21
Davidson and Levelut.
The measurements were performed at a smectic monodomain
in the sample (uniform orientation of the layer normal and
director). The samples of mesogens 6bꢁCl, 6cꢁCl and 6eꢁCl exhibit
orientational order parameters S in the range of 0.5 (Fig. 6), thus
2
no dependence on the spacer length could be observed.
S
2
values of 0.5 are quite low for a smectic mesophase.
Usually values around 0.7 are found in thermotropic liquid
2
2
crystals. The low orientational together with the high transla-
tional order in the mesophases of ILCs 6ꢁCl indicate that the
layer formation due to nanosegregation is much more important
than the parallel orientation of the molecules. For conventional
2
3
thermotropic materials the opposite was found.
2
.3 Solid state properties of guanidinium azobenzene ILCs
Fig. 5 Translational order parameters S in the SmA phase of ILCs 6cꢁCl,
We were able to obtain single crystals of 6bꢁBr, which were
6
eꢁCl, and 6fꢁCl in dependence on the temperature difference to the
isotropic phase transition T–Tiso
.
suitable for X-ray crystal structure analysis (Fig. 7). In the solid
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Fig. 7 (a) X-ray structure of 6bꢁBr in the solid state (atomic numbering system used only for X-ray diffraction studies). The H1W1–Br1 distance is 2.55(3) Å
with an angle O1W–H1W1–Br1 of 175(3)1. The H2W1–N2 distance is 2.28(4) Å with an angle O1W–H2W1–N2 of 165(3)1. The relevant distance H3–Br1 is
2
.47 Å and the angle N3–H3–Br1 is 1651. (b) Packing diagram for 6bꢁBr. The interdigitation situation of 6bꢁBr (only cation) is given in (c) side-view and
(d) top-view (hydrogens omitted for clarity).
12
state 6bꢁBr crystallized in the space group P1% with one ion pair Z-isomer to the rod-like E-isomer was already reported. Therefore,
and one water solvent molecule in the asymmetric unit (Fig. 7a). we were interested to investigate the influence of an ionic liquid
The water builds up intermolecular hydrogen interactions to crystalline (ILC) host phase on the E/Z-photoisomerization of the
the bromide ion and to N2 of the azo function. Additionally, the series of homologues 6(a–f)ꢁCl. For this purpose the anisotropic
N3–H3 function of the guanidinium head group acts as hydro- ionic smectic A phase of 1-dodecyl-3-methylimidazolium bromide
gen bond donor to the bromide anion as acceptor. In the bc-view (C12MIM-Br) was used as host and water as isotropic host phase for
of the packing diagram (Fig. 7b) a layer-type stacking of the comparison. Diluted solutions of the azobenzene chlorides 6(a–f)ꢁCl
guanidinium cations is evident with an alternate antiparallel in the two host phases were prepared without any miscibility
interdigitated orientation (Fig. 7b–d).
problems. The reisomerization of all samples was studied by using
The total length of the guanidinium cation is 30.93 Å. In time-resolved UV-Vis spectroscopy in the temperature range of
consideration of the interdigitated layer the length is increased 50–75 1C in either UV-Vis quartz glass cuvettes (d = 1 cm) for
to 42.95 Å. The resulting factor of 1.39 (Fig. 7c and d) agreed aqueous solutions or in commercial polyimide coated liquid crystal
well with the packing in the liquid crystalline phase. A nearly cells (thickness 1.6 mm) for ILC–C MIM-Br mixtures. The mixtures
12
coplanar orientation of the terminal octyloxy group, both of ILCs 6ꢁCl and the host phases were first irradiated with strong
phenyl moieties and the butyl spacer (C6–C9) supports the UV-light for 20 seconds with a commercially available 75 W
capability of the cation to interdigitate. The average distance UV-lamp to achieve a sufficient shift of the E/Z-equilibrium towards
of the nearest atoms between the interdigitated layers is 3.79 Å. the Z-isomer. UV-Vis spectra were then recorded in specific time
In contrast, the C1, N3, N4, N5 guanidinium core shows an intervals to observe the reisomerization to the thermodynamically
interplanar angle of 49.5(1)1 to the directly attached butyloxy more stable E-isomer. Fig. 8a shows exemplarily the absorption
chain. The packing is stabilized by a number of weak inter- spectra of 6cꢁCl at T = 73.6 1C in water. The increase of the p–p*
molecular electrostatic interactions. Another layer-type orienta- absorption band of the E-isomer with time at 360 nm is clearly
tion is evident with a stacking vector along the c-axis building visible. The time-dependent behaviour of the absorption at this
up alternate by the guanidinium head groups and the alkoxy- wavelength was recorded for mesogens 6(a–f)ꢁCl at different tem-
azobenzene chains (Fig. 7b). It should be noted that the X-ray peratures in both host phases and was found to follow a first-order
crystal structure analysis of 6bꢁCl which crystallized with one kinetics in all samples. The rate constants were therefore obtained
ion pair and two chloroform solvent molecules in the unit cell from monoexponential fits of the respective curves at different
gave comparable packing results (see ESI†).
temperatures, as shown for azobenzene 6cꢁCl in water (Fig. 8b).
The activation energies (E ) of derivatives 6(a–f)ꢁCl in the two
A
2.4 Isomerization of guanidinium azobenzene ILCs in
different host phases were calculated from the temperature-
dependent rate constants by using an Arrhenius plot. The activation
different matrices
A positive influence of a calamitic liquid crystalline (LC) host phase energies for 6(a–f)ꢁCl obtained in the anisotropic ILC and in water
on the reisomerization of a liquid crystalline polymer containing an as isotropic solution were compared in Fig. 8c (for measurements
azobenzene derivative as covalently linked side group from the bend of 6ꢁCl in the ILC host see the ESI†).
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Fig. 9 Schematic drawing of an ionic liquid crystalline host phase doped
with azo guest molecules. (a) The length of the guest molecules is shorter
than the layer spacing of the matrix. Therefore, the E-isomer of the azo
compounds can be easily accommodated in the host without any steric
hindrance. (b) The guest molecules are longer than the layer spacing of the
matrix, consequently they need to be kinked to fit into the smectic layers
of the host.
than the bulkier ionic molecules of C12MIM-Br which are
furthermore locked in the nanosegregated layers. In addition
the differences in size between guest and host molecules might
A
inhibit the reduction of E in the ordered SmA phase compared
to the isotropic medium water. The C12MIM-Br molecules show
a layer spacing of their bilayers of 27.5–29 Å, the azobenzene
guest molecules 6ꢁCl, however, possess molecular lengths of
already 31–37 Å for a single molecule and layer spacings in their
bilayers are in between 45 and 65 Å. Therefore, the guest
molecules might just simply be too long to fit into the layers
of the host matrix and thus, stabilization of the rod-like E-isomer
in the SmA matrix cannot occur. The two cases that might occur
by adding an ionic guest molecule into an ionic matrix are
depicted in Fig. 9.
When the guest molecules are shorter than the layer spacing of
the matrix they fit well into the layers and the E-isomer is stabilized
by the rod-like anisotropic environment of the matrix (Fig. 9a). In
this case, the activation energy of the Z/E-reisomerization should be
reduced compared to an isotropic matrix. In Fig. 9b the guest
molecules are longer than the layer spacing of the matrix. Due to
nanosegregation an ionic sheet is formed between two double
layers. This ionic layer might act as a barrier preventing the guest
Fig. 8 Photoisomerization experiments of ILCs 6ꢁCl. (a) Wavelength-
dependent absorption spectra of 6cꢁCl in aqueous solution during the
E/Z-reisomerization at T = 73.6 1C. (b) UV-Vis absorption at 360 nm vs. molecules from compensating their long length by out-of-layer
time curves for 6cꢁCl in water (symbols) as well as the mono exponential fluctuations like it is known from non-ionic bidisperse thermo-
fit curves (black solid lines) for different temperatures and the obtained
24
tropic liquid crystals. Therefore the guest molecules are kinked to
A
rate constants. (c) Activation energies E for the Z/E-reisomerization of
fit into the layers. This kinked form of the azo-mesogens is
assumed to be responsible for the loss of positive influence of
the rod-like matrix on the stabilisation of the rod-like E-isomer.
mesogens 6(a–f)ꢁCl in the two different host phases.
The activation energies were similar irrespective of the spacer This might explain why no decrease of the activation energies of
lengths n and of the host phase, thus, both the alkyl chain and the the E/Z-reisomerization of azobenzene ILCs 6ꢁCl could be found in
host seem to have only little influence on the E/Z-isomerization. For the (C MIM-Br) matrix compared to the isotropic medium water.
12
the aqueous solution a slightly lower activation energy by average
A second possibility may arise from the very low orientational
can be found than for the anisotropic SmA phase of C12MIM-Br. order in the hydrophilic alkyl sublayer of the smectic A phase of
This could be due to the fact that the small polar water molecules the host C12MIM-Br. The two sharp Bragg peaks (Fig. 10) in the
may stabilize the transition state of the E/Z-isomerization better small angle regime indicate a nearly perfect alignment of the
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anisotropic host. This result is in contrast to previous findings
1
3
by Finkelmann which revealed that a flexible anisotropic
environment of a nematic phase reduced the activation energy
1
2
of the Z/E-reisomerization. On the other hand Zentel was able
to demonstrate this effect also for the relatively rigid aniso-
tropic environment of a LC polymer with azo compound as part
of the polymer network. Presumably, in our case a steric misfit
of the ILC host and the azo ILC guest as well as the very low
orientational order of the hydrophobic alkyl sublayer of the ILC
host might counteract rapid Z/E-reisomerization. In order to
clarify this, future work utilizing combinations of azo ILC guests
and ILC hosts of similar size must be carried out. Furthermore,
ILCs with a mesogenic core exhibiting higher orientational order
parameters than ILCs without mesogenic cores, should be used
as hosts to investigate the influence of the orientational order on
the E/Z-reisomerization. On the other hand, Z/E-isomerization
kinetics of azo ILC guests in ILC hosts with an even larger
mismatch of the molecular length as compared to ours might
further increase the activation barrier and thus result in the
kinetic stabilization of the Z-isomer. This would be relevant for
Fig. 10 2D WAXS diffractogram of an aligned sample of C12MIM-Br in the future applications of ILCs as reaction media.
SmA phase at 100 1C. While the smectic layer peaks in the small angle
regime exhibits two sharp maxima in dependence on the azimuthal angle,
no angular-dependence could be found for the broad reflex in the wide
angle regime. Explanations see text.
4 Experimental section
4.1 Materials and instrumentation
1
13
smectic layers with an almost uniform direction of the layer
H and C NMR spectra were recorded on a Bruker Avance DPX
normal. The orientational order of the alkyl chains is reflected 250, Avance 300 and Avance 500 (tetramethylsilane as internal
1
3
by the azimuthal distribution of the diffuse wide angle scattering, standard). C multiplicities were assigned by DEPT experi-
that, however, does not show any significant azimuthal modula- ments. Variable temperature NMR spectra were acquired on a
tion, similar to the scattering of an isotropic fluid. The 2D X-ray Bruker Avance 50. IR spectra were recorded on a Bruker Vector
pattern confirms the absence of significant orientational order of 22 FT-IR spectrometer with ATR technique. Mass spectrometry
the alkyl tails in the hydrophobic SmA sublayer of C12MIM-Br and was performed on a Varian MAT 711 mass spectrometer with EI
E/Z-reisomerization therefore takes place in a mainly isotropic ionization (70 eV), a Finnigan MAT 95 with CI ionization using
environment leading to only marginal differences in the activation methane as reactant gas and a Bruker micrOTOF_Q with electro-
energy in comparison to water. A similar finding of highly spray ionization. Elemental analyses were performed on a Carlo
disordered alkyl chains in the smectic phase of a viologen-based Erba Strumentazione Elemental Analyzer Model 1106. Column
25
ILC was recently reported by Saielli.
chromatography was performed using silica gel 60 (Fluka, mesh
0–63 mm). Single-crystal X-ray structure analyses were performed
on a Bruker kappa APEX II Duo diffractometer (l = 0.71073 Å) at
00 K. Differential scanning calorimetry was performed using a
Mettler Toledo DSC822. Optical polarizing microscopy was per-
4
1
3
Conclusions
A series of novel guanidinium azobenzene ILCs 6ꢁCl was prepared formed using an Olympus BX 50 polarizing microscope combined
and both the solid state behaviour and the liquid crystalline with a Linkam LTS 350 hot stage and a Olympus BH2 polarizing
properties studied. WAXS and SAXS data revealed a SmA phase microscope equipped with a Linkam LTS 350 hot stage and a
with interdigitated bilayers, that was in good agreement with Scope Tek DCM 500 digital camera.
single-crystal X-ray structure analysis of two derivatives.
The reaction kinetics of the azo Z/E-reisomerization of ILCs using standard Schlenk techniques. All chemicals used were
O and C12MIM-Br was investi- commercially available and used without further purification,
All air sensitive reactions were carried out under nitrogen
6
ꢁCl in the different hosts H
2
gated. A good miscibility of the ionic azobenzene molecules in unless otherwise noted. Reactions under microwave irradiation
both host phases was observed. In aqueous isotropic solution were carried out in a CEM Explorer in closed vials under
the ionic mesogens 6(a–f)ꢁCl showed similar activation energies isothermal conditions. 1-Dodecyl-3-methylimidazolium bro-
ꢀ
1
26
in the range of 97 kJ mol independent of their spacer lengths. mide was prepared according to known procedures and
The same result was found for mixtures with the anisotropic host showed the expected physical and spectral properties.
ꢀ1
medium C12MIM-Br, in which the average E
A
was 100 kJ mol
.
X-ray diffraction. Wide angle X-ray measurements on aligned
Thus, no activation energy decrease was realized by using the samples (magnetic field B 1 T) at variable temperatures were
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PCCP
performed with a Bruker AXS Nanostar C (Ni filtered CuK
a
,
General procedure for the preparation of 2-[x-{(4-(E)-[4-
l = 1.5418 Å, with crossed G o¨ bel-mirrors as monochromator). (octyloxy)phenyl]diazenyl}phenoxy)alkyl]-1H-isoindole-1,3(2H)-
The diffraction patterns were recorded on a real-time 2D-detector diones 5. To a suspension of 3 (0.60 g, 1.80 mmol) and K CO3
2
(HI-STAR, Bruker). The samples were filled into Mark capillary (1.40 g, 10.0 mmol) in acetonitrile (20 mL) was added the respective
tubes (0.7 mm outside diameter) from Fa. Hildenberg GmbH and N-(o-bromoalkyl)phthalimide 4 (2.00 mmol) and the resulting
tempered in a temperature-controlled sample holder (Eurotherm, mixture was refluxed for 18 h. After removal of the solvent in vacuo,
with a control from mri, Physikalische Ger ¨a te GmbH). A Kratky the crude product was dissolved in CH
compact camera and a SAXSess-System from Anton Paar were concentrated in vacuo and recrystallized from acetonitrile.
used to perform small-angle X-ray scattering (Ni-filtered CuK 2-[3-{(4-(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)propyl]-1H-
radiation with wavelength l = 1.5418 Å) The unaligned samples isoindole-1,3(2H)-dione (5a). Yellow crystalline solid (120 mg,
2 2
Cl (50 mL), filtered,
a
ꢀ
1
were filled into Mark capillary tubes of 0.7 mm diameter and put 0.34 mmol, 76%), mp 129 1C. FT-IR (ATR) n~ /cm 2921s, 2852m,
into a temperature controlled sample holder (Anton Paar). The 1768m, 1712vs, 1592s, 1499m, 1465m, 1391s, 1372m, 1328w,
SAXSess is equipped with a CCD detector, the Kratky compact 1254vs, 1186w, 1145vs, 1109w, 1169m, 970w, 942m, 903w, 870w,
camera uses a one-dimensional electronic detector by M. Braun. 841vs, 815w, 787w, 720vs, 641w, 622w, 577w, 550s, 535m, 507m.
1
UV-Vis spectroscopy. Solutions of azobenzene ILCs 6ꢁCl in
H-NMR (500 MHz, CDCl
), 1.44–1.51 (m, 2H, CH
), 2.20–2.25 (m, 2H, OCH CH CH N), 3.93 (t, J =
on a Perkin-Elmer Lambda25 spectrometer equipped with a PTP-1 6.8 Hz, 2H, 1 -H), 4.02 (t, J = 6.4, 2H, OCH
3
): d = 0.89 (t, J = 6.9 Hz, 3H, CH
3
),
H
2
O (ca. 0.0018 wt% ILC) and in C12MIM-Br (1.5–3.5 wt% ILC) 1.24–1.39 (m, 8H, CH
were prepared. UV-Vis spectra in aqueous solution were recorded (m, 2H, CH
2
2
), 1.79–1.84
2
0
2
2
2
0
2
), 4.11 (t, J = 6.0, 2H,
0
Peltier system (Perkin-Elmer) for heating and cooling. The sam- NCH ), 6.88 (d, J = 6.9 Hz, 2H, 3-H), 6.98 (d, J = 6.9 Hz, 2H, 3 -H),
ples were filled into quartz glass cuvettes with 1 cm thickness 7.71–7.73 (m, 2H, 2-H), 7.80–7.83 (m, 2H, 2 -H), 7.84–7.86
Hellma).The UV-Vis spectra in the ILC host were recorded on a (m, 4H, 3 -H, 4 -H) ppm. C-NMR (125 MHz, CDCl ): d = 14.1
2
0
0
0
00
13
(
3
Perkin-Elmer Lambda2 spectrometer equipped with a homemade (CH
temperature control. The samples were filled into commercially 66.0 (C-1 ), 68.3 (C-CH
available liquid crystal cells from AWAT PPW, Poland. The thick- 124.3 (C-2 ), 124.3 (C-2), 132.2 (C-2 ), 134.0 (C-4 ), 146.9 (C-1 ),
ness of the cells was 1.6 mm. The samples were irradiated with a 147.1 (C-1), 160.6 (C-4 ), 161.2 (C-4), 168.4 (CQO) ppm. MS
3
), 22.7, 26.0, 28.3, 29.2, 29.2, 29.4, 31.8 (CH
2
2
), 35.5 (N-CH ),
0
0
0
00
2
O), 114.6 (C-3 ), 114.6 (C-3), 123.3 (C-3 ),
0
00
00
0
0
+
+
75 W UV-lamp (Q LUX pro V from Rolence Enterprise Co. Ltd).
(ESI): m/z 393.30, 514.27 [M] , 536.25 [M + Na] . HRMS (ESI):
+
+
4-Octyloxyaniline (2). To a solution of 1 (34.0 g, 134 mmol) in calcd for [C H N O + Na] 536.2520, found 536.2505 [M + Na] .
3
1
35 3 4
acetonitrile (0.7 L) were added KOH (8.20 g, 147 mmol) and Found: C, 72.49; H, 6.84; N, 8.18. Calcd for C H N O : C, 72.49;
3
1
35 3 4
then 1-bromooctane (27.4 g, 141 mmol) and the reaction mixture H, 6.87; N, 8.18%.
was heated at 85 1C for 45 h. The solvent was evaporated in vacuo 2-[4-{(4-(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)butyl]-1H-
and the residue was suspended in H O (100 mL) and extracted isoindole-1,3(2H)-dione (5b). Yellow crystalline solid (0.14 g,
with CH Cl
(3 ꢂ 100 mL). The combined extracts were dried 0.27 mmol, 84%), mp 154 1C. FT-IR (ATR) n~ /cm 2925s, 2854m,
MgSO ) and the solvent was evaporated in vacuo. The residue 1771w, 1697vs, 1700s, 1578s, 1494m, 1474m, 1465w, 1435w,
2
ꢀ
1
2
2
(
4
was purified by destillation (b.p. 130 1C/0.02 mbar), followed by 1397s, 1360m, 1316m, 1297w, 1241vs, 1188w, 1144vs, 1106m,
recrystallization from MeOH to give 4-octyloxynitrobenzene as a 1070w, 1041s, 999m, 966w, 948w, 892w, 868w, 844vs, 777w,
1
pale yellow solid (32.8 g, 93%).
760w, 714vs, 640w, 608w, 553s, 530s. H-NMR (250 MHz, CDCl ):
3
To a solution of 4-octyloxynitrobenzene (10.2 g, 41 mmol) in d = 0.89 (t, J = 6.9 Hz, 3H, CH ), 1.29–1.47 (m, 10H, CH ), 1.76–
3
2
0
0
MeOH/DMF (1 : 1) was added under inert atmosphere Pd on 1.91 (m, 6H, CH
carbon (0.28 g, 260 mmol, 10% Pd) and hydrogen was bubbled OCH , NCH
2
), 3.79 (t, J = 6.5 Hz, 2H, 1 -H), 4.02–4.09 (m, 4H,
0
2
2
), 6.95–7.00 (m, 4H, 3-H, 3 -H), 7.69–7.74 (m, 2H,
0
00
00
13
through the mixture under vigorous stirring at r.t. for 18 h. The 2-H), 7.82–7.87 (m, 6H, 2 -H, 3 -H, 4 -H) ppm. C-NMR
mixture was filtered over celite and the solvent was removed to (125 MHz, CDCl ): d=14.1 (CH ), 22.7, 25.3, 26.0, 26.6, 28.3,
give 2 as a brown crystalline solid (8.42 g, 38 mmol, 91%). Spectro- 29.2, 29.4, 31.8 (CH ), 37.6 (N-CH
3
3
0
0
2
2
), 67.4 (C-1 ), 68.3 (C-CH
2
O),
27
0
00
0
00
scopic data are in accordance with those in the literature.
114.7 (C-3 , 3), 123.2 (C-3 ), 124.3 (C-2 , C-2), 132.1 (C-2 ), 134.0
0
0
0
0
0
4
-Hydroxy-4 -(octyloxy)azobenzene (3). A solution of 2 (25.2 g, (C-4 ), 146.9 (C-1 ), 147.1 (C-1), 160.6 (C-4 ), 161.2 (C-4), 168.4
+
+
1
14 mmol) in 2 M HCl (140 mL) was cooled to ꢀ3 1C. Then 2 M (CQO) ppm. MS (ESI): m/z 528.29, 514.27 [M] , 550.27 [M + Na] .
+
NaNO
2 37 3 4
(60 mL, 116 mmol) was added dropwise at 0 1C. After HRMS (ESI): calcd for [C32H N O + Na] 550.2676, found
+
stirring for 30 min, urea (87 mg, 1.4 mmol) was added and the 550.2688 [M + Na] . Found: C, 72.86; H, 7.03; N, 7.90. Calcd for
resulting mixture was dropwise added to a cooled solution of
phenol (11.3 g, 114 mmol) in 2 M NaOH (114 mL, 228 mmol) and
C
32
H
37
N
3
O
4
: C, 72.84; H, 7.07; N, 7.96%.
2-[5-{(4-(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)pentyl]-1H-
stirring was continued for 1 h. The resulting brown precipitate isoindole-1,3(2H)-dione (5c). Yellow crystalline solid (0.60 g,
ꢀ
1
was collected on a fritted funnel, suspended in hot acetic acid 1.12 mmol, 67%), mp 119 1C. FT-IR (ATR): n~ /cm 2922s, 2855m,
and filtered. Upon storage of the filtrate overnight at 0 1C a brown 1782w, 1770w, 1709vs, 1598s, 1579s, 1496m, 1466m, 1401s, 1332w,
solid precipitated from the solution, which was isolated and washed 1315w, 1297w, 1242vs, 1146s, 1107m, 1064m, 1046m, 1024m,
with n-hexane to yield 3 as a brown powder (24.2 g, 74 mmol, 58%). 1007m, 962m, 901w, 880w, 842vs, 776w, 720s, 705s, 640w, 625w,
2
8
1
Mp 103 1C (103–103.5 1C ). Spectroscopic data are in accordance 552s, 531s. H-NMR (250 MHz, CDCl
3
): d = 0.89 (t, J = 6.9 Hz,
2
7
with those in the literature.
3H, CH
3
), 1.29–1.60 (m, 12H, CH
2
), 1.72–1.90 (m, 6H, CH ), 3.73
2
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0
0
00
0
(
6
7
t, J = 7.1 Hz, 2H, 1 -H), 3.99–4.05 (m, 4H, OCH
2
, NCH
2
), 1.62–1.84 (m, 6H, CH
, NCH
2
), 3.68 (t, J = 7.2 Hz, 2H, 1 -H), 3.98–4.05
0
.94–7.00 (m, 4H, 3-H, 3 -H), 7.69–7.74 (m, 2H, 2-H), 7.82– (m, 4H, OCH
.87 (m, 6H, 2 -H, 3 -H, 4 -H) ppm. C-NMR (63 MHz, CDCl3): (m, 2H, 2-H), 7.80–7.87 (m, 6H, 2 -H, 3 -H, 4 -H) ppm. C-NMR
2
2
), 6.96–7.00 (m, 4H, 3-H, 3 -H), 7.68–7.73
0
00
00
13
0
00
00
13
d = 14.1 (CH ), 22.7, 23.4, 26.0, 28.3, 28.8, 29.2, 29.4, 31.8 (CH ), (63 MHz, CDCl ): d = 14.1 (CH ), 22.7, 25.9, 26.0, 26.8, 28.6,
3
2
3
3
00 0 00
7.8 (N-CH ), 67.9 (C-1 ), 68.3 (C-CH O), 114.6 (C-3 ), 114.6 29.1, 29.2, 29.2, 29.4, 31.8 (CH ), 38.0 (N-CH ), 68.2 (C-1 ), 68.3
2 2 2 2
3
(
00 0 00 00 0 00 0
C-3), 123.2 (C-3 ), 124.3 (C-2 , C-2), 132.1 (C-2 ), 133.9 (C-4 ), (C-CH O), 114.6 (C-3 , 3), 123.2 (C-3 ), 124.3 (C-2 , C-2), 132.2
2
0 0 00 00 0 0
46.9 (C-1 ), 147.0 (C-1), 161.0 (C-4 ), 161.2 (C-4), 168.5 (CQO) (C-2 ), 133.8 (C-4 ), 146.9 (C-1 , C-1), 161.1 (C-4 ), 161.2 (C-4),
1
+
+
+
ppm. MS (ESI): m/z 542.30 [M] , 564.28 [M + Na] . HRMS (ESI): 168.5 (CQO) ppm. MS (ESI): m/z 427.16, 584.35 [M] , 606.33
+
+
+
+
39 3 4 45 3 4
calcd for [C33H N O + Na] 564.2833, found 564.2833 [M + Na] . [M + Na] . HRMS (ESI): calcd for [C36H N O + Na] 606.3302,
+
Found: C, 73.11; H, 7.30; N, 7.65. Calcd for C33
H N O
39 3 4
: C, 73.17; found 606.3320 [M + Na] . Found: C, 73.90; H, 7.71; N, 7.29.
Calcd for C H N O : C, 74.07; H, 7.77; N, 7.20.
H, 7.26; N, 7.76%.
3
6
45 3 4
2
-[6-{(4-(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)hexyl]-1H-
General procedure for the preparation of N-[x-(4-{(E)-[4-
isoindole-1,3(2H)-dione (5d). Yellow crystalline solid (0.14 g, (octyloxy)phenyl]diazenyl}phenoxy)alkyl]tetramethylguanidinium
ꢀ
1
0
2
1
1
.25 mmol, 88%), mp 115 1C. FT-IR (ATR): n~ /cm
850m, 1770m, 1711vs, 1597s, 1578s, 1498m, 1466m, 1433w, (5 mL) was treated with hydrazine hydrate (200 mL, 4.10 mmol,
394s, 1366m, 1329w, 1311w, 1298w, 1238vs, 1146s, 1106w, 100%) at 120 1C under microwave irradiation for 1 h. The resulting
015w, 986w, 960w, 926w, 896w, 872w, 840vs, 799w, 777w, 719vs, yellow precipitate was collected via a fritted funnel, washed with
2925s, chlorides 6(a–f)ꢁCl. A solution of respective 5 (0.41 mmol) in EtOH
1
6
40w, 620w, 550s, 530s. H-NMR (250 MHz, CDCl
3
): d = 0.89 (t, J = EtOH and the amine used without further purification.
To a suspension of the amine (1.00 mmol) in CH Cl (1 mL)
6
.9 Hz, 3H, CH ), 1.29–1.57 (m, 14H, CH ), 1.70–1.87 (m, 6H, CH ),
3
2
2
2
2
00
.71 (t, J = 7.2 Hz, 2H, 1 -H), 3.99–4.05 (m, 4H, OCH , NCH ), 6.94– tetramethylchloroformamidinium chloride (12.5 mL, 1.25 mmol,
2 2
3
0
.00 (m, 4H, 3-H, 3 -H), 7.68–7.73 (m, 2H, 2-H), 7.81–7.88 (m, 6H, 0.1 M in CH Cl ) was added dropwise, followed by dropwise
2 2
7
2
0
00
00
13
-H, 3 -H, 4 -H) ppm. C-NMR (63 MHz, CDCl
3
): d = 14.1 (CH
3 3
), addition of NEt (0.2 mL, 1.4 mmol) at 50 1C and the resulting
2
2.7, 25.7, 26.0, 26.6, 28.5, 29.0, 29.2, 29.4, 31.8 (CH
2
), 37.9 (N-CH
2
), mixture was stirred for 2 h. After cooling to r.t., the mixture was
00
0
00
0
68.1 (C-1 ), 68.3 (C-CH
2
O), 114.6 (C-3 , 3), 123.2 (C-3 ), 124.3 (C-2 , concentrated in vacuo and the residue was dissolved in CH
Cl
2 2
00
00
0
0
C-2), 132.1 (C-2 ), 133.9 (C-4 ), 146.9 (C-1 , C-1), 161.1 (C-4 ), and extracted with 2 M HCl. The organic layer was separated,
+
161.2 (C-4), 168.5 (CQO) ppm. MS (ESI): m/z 556.32 [M] , 578.30 dried (MgSO
4
) and concentrated in vacuo. The crude product was
+
+
[M + Na] . HRMS (ESI): calcd for [C H N O + Na] 578.2989, purified by chromatography on SiO with CH Cl , then EtOAc,
34
41
3
4
2
2
2
+
found 578.2982 [M + Na] . Found: C, 73.38; H, 7.38; N, 7.50. Calcd then CH Cl /MeOH (10 : 1) to give the product as a yellow solid.
2
2
for C H N O : C, 73.49; H, 7.44; N, 7.56%.
N-[3-(4-{(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)propyl]tetra-
3
4 41 3 4
2
-[7-{(4-(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)heptyl]-1H- methylguanidinium chloride (6aꢁCl). Yellow solid (39 mg, 75 mmol,
ꢀ1
isoindole-1,3(2H)-dione (5e). Yellow crystalline solid (0.65 g, 34%). FT-IR (ATR): n~ /cm
.14 mmol, 71%), mp 110 1C. FT-IR (ATR): n~ /cm 2939m, 1578vs, 1500s, 1469m, 1403m, 1294w, 1236vs, 1169w, 1146s,
921s, 2853m, 1768m, 1707vs, 1598m, 1577s, 1498m, 1466s, 1105m, 1123m, 946w, 926w, 907w, 840s, 802m, 726s, 640w,
438w, 1394m, 1372m, 1294w, 1140s, 1106m, 1152m, 1123m, 549m. H-NMR (500 MHz, CDCl
99w, 933m, 923w, 869w, 842s, 839s, 810w, 778m, 718s, 707m, CH ), 1.25–1.38 (m, 8H, CH ), 1.45–1.49 (m, 2H, CH ), 1.78–1.85
39w, 619m, 558m, 548s, 530s. H-NMR (250 MHz, CDCl ): d = (m, 2H, CH ), 2.35–2.40 (m, 2H, OCH CH CH N), 2.92 (br s, 6H,
.89 (t, J = 6.9 Hz, 3H, CH ), 1.29–1.48 (m, 16H, CH ), 1.65–1.84 N[CH ] ), 3.08 (br s, 6H, N[CH ] ), 3.47–3.50 (m, 2H, NCH ),
m, 6H, CH
2920s, 2851s, 1693m, 1597vs,
ꢀ1
1
2
1
9
6
0
1
3
): d = 0.89 (t, J = 6.9 Hz, 3H,
3
2
2
1
3
2
2
2
2
3
2
3 2
3 2
2
0
0
0
00
(
2
), 3.69 (t, J = 7.2 Hz, 2H, 1 -H), 3.99–4.05 (m, 4H, 4.03 (t, J = 6.3, 2H, OCH
2
), 4.16 (t, J = 5.7, 2H, 1 -H), 6.95–7.00
0
0
OCH
2
, NCH
2
), 6.95–7.00 (m, 4H, 3-H, 3 -H), 7.68–7.73 (m, 2H, (m, 4H, 3,3 -H), 7.85–7.87 (m, 4H, 2,2 -H), 9.76 (br t, 1H, N–H) ppm.
0
00
00
13
13
2
-H), 7.82–7.87 (m, 6H, 2 -H, 3 -H, 4 -H) ppm. C-NMR (63 MHz,
CDCl ): d = 14.1 (CH ), 22.7, 25.9, 26.0, 26.8, 28.5, 28.9, 29.1, 29.2, 29.2, 29.4, 31.8 (CH
9.4, 31.8 (CH ), 38.0 (N-CH
C-NMR (125 MHz, CDCl
), 40.0 (N[CH
00
2 2
), 68.2 (C-1 ), 68.3 (C-CH O), 114.6 (C-3 , 65.0 (C-1 ), 68.4 (C–O), 114.5 (C-3 ), 114.7 (C-3), 124.4 (C-2 ),
3
): d = 14.1 (CH
3
), 22.7, 26.0, 28.9, 29.2,
3
3
2
3
]
2
0
), 40.5 (N[CH
3 2
]
), 42.4 (C–N),
0
00
0
2
3
(
2
00 0 00 00 0 0
), 123.2 (C-3 ), 124.3 (C-2 , C-2), 132.2 (C-2 ), 133.9 (C-4 ), 146.9 124.4 (C-2), 146.8 (C-1 ), 147.3 (C-1), 160.4 (CQN), 161.4 (C-4 ),
0
0
+
C-1 , C-1), 161.1 (C-4 ), 161.2 (C-4), 168.5 (CQO) ppm. MS (ESI): 161.8 (C-4) ppm. MS (ESI): m/z 482.35 [M] . HRMS (ESI): calcd for
+
+
+
+
m/z 570.33 [M] , 592.31 [M + Na] ; HRMS (ESI): calcd for [C H N O ] 482.3490, found 482.3490 [M] .
28 44 5 2
+
+
[C
35
H
43
N
3
O
4
+ Na] 592.3146, found 592.3139 [M + Na] . Found:
N-[4-(4-{(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)butyl]tetra-
C, 73.77; H, 7.66; N, 7.08. Calcd for C35
H, 7.61; N, 7.38%.
43 3 4
H N O
: C, 73.78; methylguanidinium chloride (6bꢁCl). Yellow solid (204 mg,
ꢀ1
380 mmol, 65%). FT-IR (ATR): n~ /cm
2921s, 2852s, 1599s,
2
-[8-{(4-(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)octyl]-1H- 1578vs, 1500m, 1472m, 1401m, 1316m, 1241vs, 1171w, 1146s,
isoindole-1,3(2H)-dione (5f). Yellow crystalline solid (0.96 g, 1105w, 1065w, 1025m, 1002m, 895w, 841s, 776w, 759w, 728w,
ꢀ1
1
1
.60 mmol, 91%), mp 107 1C. FT-IR (ATR): n~ /cm
2925s, 641w, 551s. H-NMR (250 MHz, CDCl ): d = 0.89 (t, J = 6.8 Hz,
3
2
854m, 1773m, 1713vs, 1599s, 1579s, 1498m, 1464m, 1434w, 3H, CH ), 1.30–1.50 (m, 10H, CH ), 1.76–2.05 (m, 6H, CH ),
3
2
2
1
1
395s, 1364m, 1334w, 1316w, 1298w, 1240vs, 1187w, 1146s, 2.94 (br s, 6H, N[CH ] ), 3.10 (br s, 6H, N[CH ] ), 3.27–3.35
3 2 3 2
0
0
105m, 1088w, 1055m, 1041m, 1021m, 953w, 878w, 841vs, (m, 2H, NCH
2
), 4.00–4.10 (m, 4H, 1 -H, OCH
2
), 6.94–7.00 (m,
1
0
0
801w, 778w, 720vs, 641w, 625w, 551s, 531s. H-NMR (250 MHz, 4H, 3,3 -H), 7.84–7.87 (m, 4H, 2,2 -H), 9.69 (br t, 1H, N–H) ppm.
1
3
CDCl
3
): d = 0.89 (t, J = 6.9 Hz, 3H, CH
3
), 1.29–1.47 (m, 18H, CH
2
),
3 3
C-NMR (125 MHz, CDCl ): d = 14.1 (CH ), 22.7, 26.0, 26.5, 26.6,
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9.2, 29.2, 29.4, 31.8 (CH
PCCP
ꢀ
1
2
2
), 40.0 (N[CH
3
]
2
), 40.6 (N[CH
]
3 2
), 45.2 FT-IR (ATR): n~ /cm 2920s, 2852s, 1600vs, 1579vs, 1497m, 1472m,
00
0
0
(
1
1
C–N), 67.6 (C-1 ), 68.3 (C–O), 114.6 (C-3 ), 114.7 (C-3), 124.3 (C-2 ), 1403m, 1316m, 1296w, 1242vs, 1179w, 1147s, 1107m, 1167w,
24.3 (C-2), 146.8 (C-1 ), 147.0 (C-1), 160.7 (CQN), 161.3 (C-4 ), 1123m, 1001m, 943w, 898w, 843vs, 776w, 727w, 640w, 554s.
0
0
+
1
61.4 (C-4) ppm. MS (ESI): m/z 496.36 [M] . HRMS (ESI): calcd for
H-NMR (250 MHz, CDCl ): d = 0.89 (t, J = 6.8 Hz, 3H, CH ),
3 3
1.30–1.47 (m, 18H, CH ), 1.78–1.84 (m, 6H, CH ), 2.92 (br s, 6H,
+
+
[
C H N O ] 496.3646, found 496.3631 [M] .
29
46
5
2
2
2
N-[5-(4-{(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)pentyl]tetra- N[CH
3
]
2
), 3.10 (br s, 6H, N[CH
3
]
2
), 3.15–3.23 (m, 2H, NCH
2
), 4.00–
00
0
methylguanidinium chloride (6cꢁCl). Yellow solid (50 mg, 4.05 (m, 4H, 1 -H, OCH
2
), 6.96–7.00 (m, 4H, 3,3 -H), 7.84–7.87
ꢀ
1
0
13
9
1
1
7
(
(
3
6
1
2
4
1
1
2 mmol, 21%). FT-IR (ATR): n~ /cm
598s, 1578vs, 1498s, 1469s, 1406m, 1317w, 1238vs, 1167w, CDCl
142s, 1105w, 1072w, 1044w, 1000m, 924w, 898w, 835s, 809w, 29.4, 29.8, 31.8 (CH
2925s, 2851s, 1621s, (m, 4H, 2,2 -H), 9.76 (br t, 1H, N–H) ppm. C-NMR (125 MHz,
): d = 14.1 (CH ), 22.7, 25.9, 26.0, 26.9, 29.1, 29.1, 29.2, 29.2,
3
3
2
), 39.9 (N[CH
3
0
]
2
), 40.6 (N[CH
3
]
2
), 45.5 (C–N),
1
00
0
0
76w, 725m, 640w, 547s. H-NMR (250 MHz, CDCl ): d = 0.89 68.2 (C-1 ), 68.3 (C–O), 114.7 (C-3 ,3), 124.3 (C-2 ,2), 146.9 (C-1 ),
3
0
t, J = 6.8 Hz, 3H, CH ), 1.29–1.60 (m, 12H, CH ), 1.76–1.94 146.9 (C-1), 161.1 (CQN), 161.2 (C-4 ), 161.5 (C-4) ppm. MS (ESI):
3
2
+
+
m, 6H, CH ), 2.92 (br s, 6H, N[CH ] ), 3.11 (br s, 6H, N[CH ] ), m/z 552.43 [M] . HRMS (ESI): calcd for [C H N O ] 552.4272,
2
3 2
3 2
33 54 5 2
0
0
+
.19–3.28 (m, 2H, NCH
2
), 4.00–4.06 (m, 4H, 1 -H, OCH
2
), found 552.4260 [M] .
Crystal structure determination of guanidinium bromide
0
0
.95–7.00 (m, 4H, 3,3 -H), 7.84–7.87 (m, 4H, 2,2 -H), 9.77 (br t,
1
3
H, N–H) ppm. C-NMR (125 MHz, CDCl
3
): d = 14.1 (CH
3
), 22.7, 6bꢁBr (CCDC 1030119).
3.5, 26.0, 28.7, 29.2, 29.2, 29.4, 29.4, 31.8 (CH
2
), 39.9 (N[CH
]
3 2
),
5 3
Crystal data. C29H48BrN O , M = 594.63, triclinic, a = 8.0979(1),
0
0
0
3
0.6 (N[CH
]
3 2
), 45.4 (C–N), 67.8 (C-1 ), 68.3 (C–O), 114.6 (C-3 ), b = 10.1206(6), c = 20.3102(12) Å, V = 1526.23(15) Å , T = 100 K,
14.7 (C-3), 124.3 (C-2,2 ), 146.9 (C-1 ), 147.0 (C-1), 160.9 (CQN), space group P1%, Z = 2, 26 683 reflections measured, 7547 unique
61.2 (C-4 ), 161.4 (C-4) ppm. MS (ESI): m/z 510.38 [M] . HRMS (Rint = 0.0443) which were used in all calculations. The final
ESI): calcd for [C H N O ] 510.3803, found 510.3767 [M] .
0
0
0
+
+
+
(
wR(F ) was 0.0911 (all data).
3
0
48
5
2
2
N-[6-(4-{(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)hexyl]tetra-
methylguanidinium chloride (6dꢁCl). Yellow solid (396 mg,
ꢀ
1
Acknowledgements
2931s, 2853s, 1620s,
7
1
1
8
(
(
3
(
(
10 mmol, 68%). FT-IR (ATR): n~ /cm
599vs, 1578vs, 1495m, 1469m, 1405w, 1316m, 1296w, 1238vs,
185w, 1147s, 1106w, 1071w, 1044w, 1023w, 995w, 944w, 899w,
47s, 835s, 814w, 779w, 762w, 731w, 639w, 553s. H-NMR
Financial support by the Deutsche Forschungsgemeinschaft
(
grant # La 907/17-1, Gi 243/8-1), the Bundesministerium f u¨ r
Bildung und Forschung (shared instrumentation grant # 01 RI
5177), the Ministerium f u¨ r Wissenschaft, Forschung und Kunst
des Landes Baden-W u¨ rttemberg, the Forschungsfonds der Univer-
sit ¨a t Stuttgart and the Fonds der Chemischen Industrie is gratefully
acknowledged.
1
250 MHz, CDCl ): d = 0.89 (t, J = 6.8 Hz, 3H, CH ), 1.30–1.59
3
3
0
m, 12H, CH ), 1.77–1.94 (m, 8H, CH ), 2.93 (br s, 6H, N[CH ] ),
2
2
3 2
.10 (br s, 6H, N[CH
]
3 2
), 3.17–3.25 (m, 2H, NCH
), 6.95–7.00 (m, 4H, 3,3 -H), 7.84–7.87
m, 4H, 2,2 -H), 9.80 (br t, 1H, N–H) ppm. C-NMR (125 MHz,
2
), 4.00–4.05
00
0
m, 4H, 1 -H, OCH
2
0
13
3 3
CDCl ): d = 14.1 (CH ), 22.7, 25.6, 26.0, 26.6, 29.0, 29.2, 29.2,
2
9.4 29.7, 31.8 (CH
2
), 39.9 (N[CH
3
]
2
), 40.6 (N[CH
3
]
2
), 45.4 (C–N),
References
00
0
0
68.0 (C-1 ), 68.3 (C–O), 114.6 (C-3 ), 114.7 (C-3), 124.3 (C-2 ,2), 146.8
0
0
(C-1 ), 146.9 (C-1), 161.0 (CQN), 161.2 (C-4 ), 161.4 (C-4) ppm. MS
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+
+
(ESI): m/z 524.40 [M] . HRMS (ESI): calcd for [C H N O ]
31 50 5 2
+
524.3959, found 524.3967 [M] .
N-[7-(4-{(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)heptyl]tetra-
methylguanidinium chloride (6eꢁCl). Yellow solid (149 mg,
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ꢀ
1
2
1
1
6
60 mmol, 72%). FT-IR (ATR): n~ /cm
2932s, 2853s, 1599vs,
579vs, 1497m, 1471m, 1402m, 1316m, 1296w, 1244vs, 1446s,
105w, 1069w, 1026m, 946w, 898w, 842s, 777w, 727w, 640w,
1
04w, 552s. H-NMR (250 MHz, CDCl ): d = 0.89 (t, J = 6.8 Hz, 3H,
3
CH ), 1.29–1.47 (m, 16H, CH ), 1.72–1.87 (m, 6H, CH ), 2.93 (br s,
3
2
2
6
4
7
H, N[CH
.00–4.05 (m, 4H, 1 -H, OCH
.87 (m, 4H, 2,2 -H), 9.38 (br t, 1H, N–H) ppm. C-NMR (125
3
]
2
), 3.10 (br s, 6H, N[CH
3
]
2
), 3.16–3.24 (m, 2H, NCH
2
),
00
0
2
), 6.96–7.00 (m, 4H, 3,3 -H), 7.84–
0
13
MHz, CDCl
3
): d = 14.1 (CH
3
), 22.7, 25.9, 26.0, 26.9, 28.9, 29.0,
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4
1
9.2, 29.2, 29.4, 29.7, 31.8 (CH
2
), 39.9 (N[CH
3
]
2
), 40.6 (N[CH
3
0
2
] ),
00
0
5.5 (C–N), 68.1 (C-1 ), 68.3 (C–O), 114.7 (C-3 ,3), 124.3 (C-2 ,2),
0
0
46.9 (C-1 ), 146.9 (C-1), 161.1 (CQN), 161.2 (C-4 ), 161.5 (C-4)
+
ppm. MS (ESI): m/z 538.41 [M] . HRMS (ESI): calcd for
+
+
[C
32
H
52
N
5
O
2
] 538.4116, found 538.4109 [M] .
N-[8-(4-{(E)-[4-(Octyloxy)phenyl]diazenyl}phenoxy)octyl]tetra-
methylguanidinium chloride (6fꢁCl). Yellow solid (0.40 g, 68%).
Phys. Chem. Chem. Phys.
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Phys. Chem. Chem. Phys.