Fluorination of supramolecular liquid crystals-tuning tool and analytical probe

Article abstract of DOI:10.1039/c6tc05472b

A study on the impact of fluorination on the properties of photo-responsive hydrogen-bonded liquid crystals is reported. The chosen modular approach allows for efficient screening of a variety of hydrogen-bonded assemblies. Tremendous effects on the mesophase stabilization and morphology are described. In addition, the fluorine substituents are used as analytical probes for ¹⁹F solid-state NMR studies, providing insight into the molecular alignment of the assemblies.

Full text of DOI:10.1039/c6tc05472b

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Materials Chemistry C
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Fluorination of supramolecular liquid
crystals – tuning tool and analytical probe†
Cite this:DOI: 10.1039/c6tc05472b
a
b
b
a
Matthias Spengler, Ronald Y. Dong, Carl A. Michal, Michael Pfletscher and
Michael Giese*
a
Received 19th December 2016,
Accepted 30th January 2017
DOI: 10.1039/c6tc05472b
rsc.li/materials-c
A study on the impact of fluorination on the properties of photo- Likewise, the properties of hydrogen-bonded materials are
responsive hydrogen-bonded liquid crystals is reported. The chosen significantly influenced by fluorination. For example, the work
1
5,16
17
modular approach allows for efficient screening of a variety of of Percec
and Manners on fluorinated dendrons and
hydrogen-bonded assemblies. Tremendous effects on the mesophase perfluorinated LC block copolymers, respectively, shows that
stabilization and morphology are described. In addition, the fluorine employing fluorinated alkyl chains is a promising tool to
19
substituents are used as analytical probes for F solid-state NMR control the self-assembly behaviour of the building blocks.
studies, providing insight into the molecular alignment of the However, fluorination of the arene units in hydrogen-bonded
18
assemblies.
materials is less common and systematic studies on the impact
on hydrogen-bonded LCs are lacking.
Molecular self-assembly has attracted much attention as a
bottom-up approach for new functional materials. The supra- based on phloroglucinol and azopyridyl (Ap) derivatives showing
Recently, we reported on a series of hydrogen-bonded LCs
1
c
molecular approach is especially attractive, since it facilitates fast and reversible phase transition (nematic N - isotropic I, T )
1
9
synthetic routes and yields dynamic functional aggregates upon irradiation with purple light (l = 405 nm). The supra-
combining the properties of the individual building units with the molecular modular concept allows the systematic study of structure–
2,3
properties induced by the formation of a supramolecular entity.
property relationships by screening a broad variety of molecular
In respect of supramolecular liquid crystals (LCs) in particular, building blocks. Our initial approach has proven the use of this
4
,5
two intermolecular forces have been employed, hydrogen- and methodology by identifying promising combinations of hydrogen-
6
–8
halogen-bonding.
In this context, Kato, Fr ´e chet and their bond donors and acceptors towards photo-switchable functional
co-workers introduced an elegant approach to hydrogen-bonded materials. Employing these aggregates as molecular guests in
LCs by employing the interaction between pyridyl- and benzoic mesoporous silica films with thermochromic behaviour results
9
–12
acid derivatives.
More recently, Bruce and co-workers utilized in materials interesting for applications in thermo-responsive
2
0
this concept and reported the first examples of halogen-bonded optical filters and sensors.
6,7,13,14
LCs.
The properties of such materials are the result of the
Given that the impact of fluorination on hydrogen-bonded
interplay of intermolecular forces causing tremendous effects on LCs remains so far obscure, the present work employs the
the behaviour of the self-assembled systems. Slightly altering the mentioned approach to systematically investigate the structure–
structure thus allows selective manipulation towards tailor-made property relationships and the associated influence of different
materials.
arene fluorination patterns on the LC materials. Therefore,
For conventional LCs, the introduction of fluorine substituents phloroglucinol (PHG) and its mono-fluorinated derivative (F-PHG)
is a common method to tweak the mesomorphic behaviour. The have been employed as hydrogen bond donors (core units) and were
strength and high polarity of the CF-bond has a remarkable combined with a series of Aps with different fluorination patterns
effect on melting point, mesophase morphology, transition (Scheme 1).
1
19
13
temperatures and dielectric properties as well as optical anisotropy.
All building blocks were characterized by H, F, C NMR,
and IR spectroscopy as well as by mass spectrometry. The Aps
were also characterized by UV-Vis-spectroscopy. The mesomorphic
behaviour of the obtained hydrogen-bonded aggregates was
investigated by means of polarized optical microscopy (POM)
and dynamic scanning calorimetry (DSC). The introduction of
a
Institute of Organic Chemistry, University of Duisburg Essen, Universit a¨ tsstraße 7,
D-45117 Essen, Germany. E-mail: michael.giese@uni-due.de
b
Department of Physics and Astronomy, University of British Columbia,
6
224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/c6tc05472b fluorine into the assemblies is also interesting, since it opens
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Fig. 1 POM images of the HBAs upon cooling under crossed polarizers:
Scheme 1 Modular concept for the investigation of the impact of fluorination
on the properties of hydrogen-bonded LCs.
0
0 0
(
A) PHG(Ap3 F-8)
3 3
@73 1C, (B) F-PHG(Ap-8) @95 1C, (C) F-PHG(Ap3 5 F-
0
0
8
)
3
@70 1C and (D) PHG(Ap3 5 F-8) @67 1C.
3
1
9
the opportunity for variable temperature solid state F NMR
spectroscopy studies providing insights into the molecular
order of the assemblies in their mesophase.
assemblies show monotropic phase transitions, only the meso-
morphic behaviour upon cooling will be discussed in the following.
3
The PHG(Ap-N) system serves as a reference, however in order to
19
The hydrogen-bonded assemblies (HBAs) were obtained by
separately dissolving the building blocks (core unit and Ap side
chain) in acetone and subsequently mixing the solutions. After
removal of the solvent, the aggregates were dried under vacuum
and showed a 1 : 3 stoichiometry (core : sidechain) as proven by
elemental analysis. The formation of the HBAs was confirmed
by IR-spectroscopy and POM. As reported earlier, the broad vibration
yield comparable results, the DSC measurements were reproduced
with our current setup (Fig. 2A). The phloroglucinol based
assemblies showed mesomorphic behaviour starting with
PHG(Ap-6)3 (DT = 8.9 1C). The mesophase range broadened
gradually to DT = 21.0 1C for PHG(Ap-9) . Further elongation
3
of the alkyl chain, however, led to a decrease of the mesophase
ranges. The transition temperatures showed a slight even–odd
effect, whereby T remained almost constant, while the N - Cr
c
transition temperatures (TN-Cr) alternated with the number of
carbon atoms of the alkyl chain. As shown by the POM studies,
ꢀ
1
band of the OH-group of the phloroglucinol (B3200 cm ) shifts
ꢀ
1
to lower wavenumbers (B3050 cm ) when complexed by the
hydrogen bond acceptor with an additional signal at 2630 cm
ꢀ
1 19
.
Similar behaviour was found for the formed HBAs based on the
the F-PHG(Ap-N) aggregates show the same morphology as the
3
fluorinated core unit (F-PHG). The IR signals of F-PHG at
PHG(Ap-N) aggregates. However, the transition temperatures
are affected by the fluorination of the core unit (Fig. 2B). While
T remains almost unaffected, TN-Cr is significantly lowered
c
3
ꢀ1
ꢀ1
ꢀ1
B3400 cm and B3140 cm shifted to B3000 cm and
ꢀ1
B2600 cm upon combination with the Ap units, confirming
the formation of the HBAs. Similar results were found for all
investigated HBAs (Fig. S1–S7, ESI†).
leading to slightly broader mesophase ranges. The broadening
of the mesophase is attributed to the stabilization of the HBAs
by non-classical hydrogen bonds between the core unit and the
To investigate the LC behaviour of the HBAs and its dependence
on the fluorination degree and pattern, we initially studied the
samples by POM in the temperature range of 25–110 1C upon
heating and cooling (Fig. S8–S14, ESI†). It should be noted that
none of the individual building blocks showed LC properties. In
contrast, most of the investigated HBAs showed a mesophase upon
2
1
Ap side chains (C–Fꢁ ꢁ ꢁH–C).
As mentioned, the system based on Ap3F-N did not reveal a
liquid crystalline behaviour, neither with PHG nor F-PHG.
3
cooling. The mesomorphic behaviour of the PHG(Ap-N) series was
reported earlier and serves as a reference system in this study.
The POM images reveal tremendous differences between the
0
investigated samples. While the complexes of Ap-N and Ap3 F-N
with PHG as well as with F-PHG showed the characteristic
‘‘Schlieren’’ texture of a N mesophase (Fig. 1A and B), the HBAs
of Ap3F-N with PHG or F-PHG crystallized directly from the
isotropic phase without undergoing a phase transition to the
mesophase. The same behaviour was observed for the aggregates
0
0
0 0
of Ap3 5 -N with F-PHG (Fig. 1C). HBAs of Ap3 5 -N with PHG,
however, yielded liquid crystalline HBAs with the typical conic
texture of a smectic phase (Fig. 1D). These results demonstrate the
crucial impact of the fluorination pattern on the mesomorphic
behaviour of the investigated HBAs.
Fig. 2 Graphical representation of the thermal behaviour of PHG(Ap-N)
3
To quantify the effect, detailed DSC studies were performed
0
0
(
A), F-PHG(Ap-N)
3
(B), PHG(Ap3 F-N)
3
(C), and F-PHG(Ap3 F-N)
3
(D) upon
(
Fig. S15–S20 and Tables S1–S6, ESI†). Since most of the cooling from 110 1C to 30 1C.
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However, the melting points are shifted to lower temperatures by this method, we compare our results to the H NMR studies
2
0
with respect to the corresponding non-fluorinated Aps. These of a related system. A representative set of variable temperature
1
9
0
findings can be attributed to repulsive interactions between the
F spectra during cooling is shown for F-PHG(Ap3 F-8)3
fluoro substituent and the electronic environment of the diazo (Fig. S26, ESI†). The effects of different fluoro substitutions on
bond, decreasing the coplanarity of the Ap system and thereby the orientational order parameter S of the molecular core in the
zz
2
2
0
the stability of the mesophase. N phase are examined. The fluorinated Ap side chain (Ap3 F-8)
In contrast to Ap3F-N, aggregates with Ap3 F-N yielded provides two NMR observables, the H–F dipolar splitting (Dn)
liquid crystals with both PHG and F-PHG as the core moiety between the fluorine and the adjacent proton and the
0
1
9
F
0
(
(
Fig. 2C and D). While for PHG(Ap3 F-N)
DTmeso) gradually increases with increasing alkyl chain length
3
the mesophase range chemical shift (dobs) in the mesophase, while F-PHG gives only
d
obs. Both Dn and dobs should give the same order parameter
from DTmeso = 8.1 1C (N = 6) to DTmeso = 13.3 1C (N = 12), the when all Ap3 F-8 side chains are oriented the same way with
mesophase range for the PHG(Ap-N)3 (Fig. 2A) aggregates respect to the core. This is borne out in the present study,
0
increases up to a chain length of N = 9 and then gradually suggesting an N phase as previously found in [trans-4-butoxy-
col
0
0
20
decreases again. The T
is significantly lowered when compared to the PHG(Ap-N)
which is a well-known effect for lateral fluoro substitution of LCs.
Also, since the TN-Cr is reduced, however, to a smaller extent, the The F line will be shifted and split in the Ncol phase. The
c
of the PHG(Ap3 F-N)
3
aggregates (Fig. 2C) 4 -stilbazole/PG]3 : 1
system, Here, the director n, the preferred orientation of the
PHG(Ap-8) symmetry z axis, is perpendicular to the B field.
.
3
23
3
1
9
DTmeso of these systems is narrower (max. DTmeso = 13.3 1C for doublet splitting is given by Dn = (3/4)ꢁP
2
ꢁ(cos y)ꢁDꢁSzz, where
0
19
1
PHG(Ap3 F-N) with N = 12 vs. DT
= 21.0 1C for PHG(Ap-N)3 D is the dipolar coupling between the F and adjacent H. The
3
meso
0
25
with N = 9). For the related F-PHG(Ap3 F-N) aggregates (Fig. 2D), distance r = 2.535 Å yields D = 13.86 kHz and the angle y, the
3
the T and T
mesophase ranges as observed for the PHG(Ap3 F-N)
are reduced even further, leading to similar angle between the para axis and the symmetry z axis is 191
c
N-Cr
0
19
3
systems.
(assuming +COH of 1091). For the azobenzene F, the aniso-
Interestingly, the HBAs based on the difluorinated Aps tropic chemical shift daniso (=dobs ꢀ diso) is given by (2/3)ꢁDdꢁP
2
ꢁ
0
0
(
Ap3 5 F-N) show a remarkably different mesomorphic behaviour (cos y)ꢁSzzꢁP
2
ꢁ(cos g), where Dd = dzz ꢀ (dxx + dyy)/2, angle g is
19
than any of the previously described systems (Fig. S21, ESI†). The between the principal z axis of the F chemical shielding
0
0
first difference between PHG(Ap3 5 F-N)
3
and the other HBAs tensor (CST) and the para axis, and (Sxx ꢀ Syy) = 0 is due to
became apparent during POM investigations of the samples, the rapid ring flip. For the F-PHG ring, S ꢀ S is taken to be
xx
yy
2
0
showing the formation of a different mesophase morphology. While zero, giving daniso = (2/3)ꢁDdꢁS ꢁP ꢁ(cos 901). To find S = S , the
zz
2
zz
0
0
all other systems tend to create nematic phases, PHG(Ap3 5 F-N)
CST elements and orientation must first be determined. Here,
3
2
5
forms the characteristic texture of a smectic phase. The following we make use of a sideband analysis of the MAS spectra taken
discussion focuses on the C8 assemblies as representative examples. at room temperature for the two fluorinated sites of powder
0
The two fluoro substituents in the lateral position of the aggregates samples F-PHG(Ap-8)
3
(Fig. S28, ESI†) and PHG(Ap3 F-8)
3
(Fig.
0
19
significantly reduce the T
c
(91.0 1C (Ap-8), 76.4 1C (Ap3 F-8), 76.4 1C S29, ESI†). For F-PHG, the PAS z axis of the F CST lies on the
Ap3 5 F-8)) as well as the Tmeso-Cr (71.4 1C (Ap-8), 67.8 1C (Ap3 F-8), PG ring plane, while the g angle can only be determined by
0
0
0
(
0
0
0
5
5.8 1C (Ap3 5 F-8)) leading to DT
of 20.6 1C. In contrast to our equating S from Dn with Ddaniso of the Ap3 F-8 chains. It is
meso
expectations, the exchange of the PHG unit by F-PHG led to an found that g = 32.71. This value is consistent with the values of
1
9
absence of liquid crystallinity (Fig. S26, ESI†), which is in
contradiction to the stabilizing effect observed for the HBAs of different chemical environments (Table S8, ESI†).
the non-fluorinated side chains (Ap-N). These results prove the and daniso vs. T (Fig. S27, ESI†) are used to determine the S values.
significant impact of fluorination on the properties of the Since the Ncol ranges are quite different, Fig. 3 shows the
investigated liquid crystalline HBAs. While the combination of order parameter S plotted against the reduced temperature
the non-fluorinated side-chains with F-PHG led to a stabilization (Tred = T/T ) for direct comparison. Interestingly, fluorine sub-
F CST determined by DFT calculations in LC compounds of
26,27
Plots of Dn
c
of the mesophase, most likely due to non-classical CFꢁ ꢁ ꢁHC stitution on the PHG alone (i.e. F-PHG(Ap-8) ) yields S values
3
2
0
hydrogen bridges and p-stacking of the fluorinated and non- close to those of the reference system (Fig. 3), despite the
fluorinated aromatic units, the mesophase ranges of the lateral different side chains. Moreover, although the N ranges are smaller
col
0
0
0
0
0
fluorinated systems (Ap3 F-N, Ap3 5 F-N) are significantly for PHG(Ap3 F-8)
reduced, which we attribute to a disruption of the intermolecular ordering at the same Tred seems to be enhanced, more so for
3 3 3
and F-PHG(Ap3 F-8) than for F-PHG(Ap-8) , the
18,21
0
attraction and molecular packing.
To get an insight into the supramolecular structure of determination of the S values from each side chain with a
the HBAs in their mesophase, solid-state F NMR studies of fluorine substituent. When both PHG and Ap side chains
representative fluorinated HBAs (F-PHG(Ap-8) , PHG(Ap3 F-8)
and F-PHG(Ap3 F-8) ) were performed as a function of temperature. apparently shows a slight variation from the one of F-PHG at
PHG(Ap3 F-8) . More importantly, there are two samples for
3
1
9
0
contain fluorine substituents, the S from the side chains
3
3
0
3
1
9
F NMR is a powerful tool to investigate the structural and low temperatures. This could arise from experimental errors,
molecular ordering of LCs and has recently demonstrated its the assumed geometry (e.g. +COH) and/or the CFꢁ ꢁ ꢁHC bonding.
2
4
0
use in the analysis of self-assembly in confined spaces. Since In summary, by comparing the S values of Ap3 F-8 and the F-PHG
this is the first investigation of fluorinated supramolecular LCs ring, the former appears to reflect higher molecular ordering.
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In summary, we report the first systematic study on the
impact of fluorination on the LC properties of hydrogen-bonded
aggregates. The different fluorination patterns in the LC assemblies
revealed significant differences in the mesomorphic behaviour.
While the fluorinated core unit (F-PHG) tends to stabilise the
mesophase, mono side chain fluorination generally causes a
decrease of the mesophase stability. Introducing a second lateral
0
0
fluoro substituent (Ap3 5 -N), however, results in the formation of a
mesophase with a smectic morphology which proves the impact of
fluorination on the properties of supramolecular LCs. Reversible
photo-switching experiments evidence a decrease in the response
0
Fig. 3 Order parameter S as a function of Tred (T/T
c
) of [trans-4-butoxy-4 - depending on the fluorination degree and mesophase morphology.
2
stilbazole/PG]3:1 (ꢂ) as determined previously by H-NMR, F-PHG(Ap-8)
3
(
),
19
In addition, we presented the first solid state F-NMR study of these
0
19
3 3
0
PHG(Ap3 F-8) from F Dn (D) and daniso (,), and F-PHG(Ap3 F-8) from Dn (} )
and ). See separately plotted data for the HBAs in Fig. S30 (ESI†).
kinds of materials, supporting the change in the molecular ordering
by the introduction of the fluorine substituent.
and daniso
(
M. S. and M. G. are thankful for the generous support by
Although not a focus of the current study, the photo- Professor Werdelmann Stiftung and the Fonds der chemischen
initiated phase transition of the HBAs was studied and is briefly Industrie. C. M. is supported by a Discovery grant from the
discussed here. The photo-isomerisation of the pristine Ap Natural Sciences and Engineering Research Council (NSERC) of
1
19
derivatives has been investigated via H/ F-NMR spectroscopy, Canada. We would like to thank the MacLachlan group for
proving reversible trans - cis transformation upon irradiation hosting MS during his research stay at the UBC.
or heating, respectively (Fig. S22, ESI†). The UV-Vis spectra of thin
films of the HBAs have been recorded showing no significant
changes in the absorption bands for the different fluorination
Notes and references
patterns (Fig. S23, ESI†). The photo-initiated phase transition for
all HBAs from the meso- to the isotropic phase was observed via
POM upon irradiation with a laser pointer (405 nm, 5 mA).
The photo-induced trans - cis isomerization of the Ap moiety
upon irradiation, causing a phase transition to the I phase and
erasure of the LC texture, is attributed to the destabilizing effect
1 K. Liu, Y. Kang, Z. Wang and X. Zhang, Adv. Mater., 2013, 25,
5530–5548.
2 X. Yan, F. Wang, B. Zheng and F. Huang, Chem. Soc. Rev.,
2012, 41, 6042–6065.
3 Z.-T. Li and L.-Z. Wu, Hydrogen Bonded Supramolecular Materials,
Springer, Heidelberg, 2015.
4 T. Kato, T. Yasuda, Y. Kamikawa and M. Yoshio, Chem.
Commun., 2009, 729–739.
28
of the bent shape structure of the cis-isomer. Once the irradiation is
stopped, the mesophase reappears within a few seconds. According
to POM assisted photo switching experiments, the photo-response
seems to depend on the morphology of the formed mesophase.
5 B. Fering ´a n, P. Romero, J. L. Serrano, R. Gim ´e nez and T. Sierra,
Chem. – Eur. J., 2015, 21, 8859–8866.
0
While the N - I switching of PHG(Ap3 F-8) occurs almost instan-
6 C. Prasang, H. L. Nguyen, P. N. Horton, A. C. Whitwood and
D. W. Bruce, Chem. Commun., 2008, 6164–6166.
7 D. W. Bruce, P. Metrangolo, F. Meyer, T. Pilati, C. Pr ¨a sang,
G. Resnati, G. Terraneo, S. G. Wainwright and A. C. Whitwood,
Chem. – Eur. J., 2010, 16, 9511–9524.
3
taneously (1–2 s) (Fig. 4A) and returns to its initial state in around
B8 s after the laser has been turned off, it takes significantly longer
0 0
(
B3–5 s) for PHG(Ap3 5 F-8) (Fig. 4B) to transfer from the meso- to
3
the isotropic phase and back again (B12 s). The notable longer
response of the difluorinated compound could be attributed to the
higher molecular order of the smectic phase.
8 Y. Chen, H. Yu, L. Zhang, H. Yang and Y. Lu, Chem. Commun.,
2014, 50, 9647–9649.
9
T. Kato and J. M. J. Frechet, J. Am. Chem. Soc., 1989, 111,
533–8534.
0 U. Kumar, T. Kato and J. M. J. Frechet, J. Am. Chem. Soc.,
992, 114, 6630–6639.
8
1
1
1
1
1
1
1 T. Kato, T. Uryu, F. Kaneuchi, C. Jin and J. M. J. Fr ´e chet, Liq.
Cryst., 1993, 14, 1311–1317.
2 T. Kato, H. Kihara, U. Kumar, T. Uryu and J. M. J. Fr ´e chet,
Angew. Chem., Int. Ed., 1994, 33, 1644–1645.
3 H. L. Nguyen, P. N. Horton, M. B. Hursthouse, A. C. Legon
and D. W. Bruce, J. Am. Chem. Soc., 2004, 126, 16–17.
4 P. Metrangolo, C. Prasang, G. Resnati, R. Liantonio, A. C.
Whitwood and D. W. Bruce, Chem. Commun., 2006, 3290–3292.
0
Fig. 4 Reversible photo-induced phase transition at 75 1C of PHG(Ap3 F-8)
3
0
0
15 V. Percec, M. Glodde, G. Johansson, V. S. K. Balagurusamy
and P. A. Heiney, Angew. Chem., Int. Ed., 2003, 42,
4338–4342.
(
A) and PHG(Ap3 5 F-8)
3
(B) from the mesophase (1) to the I state (2) upon
irradiation with laser light (405 nm, 5 mA). The efficiency differs significantly
depending on the mesophase morphology exhibited by the HBAs.
J. Mater. Chem. C
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View Article Online
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Communication
1
6 V. Percec, M. Glodde, M. Peterca, A. Rapp, I. Schnell, 22 G. W. Gray, C. Hogg and D. Lacey, Mol. Cryst. Liq. Cryst.,
H. W. Spiess, T. K. Bera, Y. Miura, V. S. K. Balagurusamy, 1981, 67, 1–23.
E. Aqad and P. A. Heiney, Chem. – Eur. J., 2006, 12, 23 K. M. Fergusson and M. Hird, J. Mater. Chem., 2010, 20,
298–6314. 3069–3078.
7 X. Li, B. Jin, Y. Gao, D. W. Hayward, M. A. Winnik, Y. Luo 24 K. P. Nartowski, D. Malhotra, L. E. Hawarden, J. Sibik,
6
1
and I. Manners, Angew. Chem., Int. Ed., 2016, 55, 11392–11396.
8 M. Hird, Chem. Soc. Rev., 2007, 36, 2070–2095.
D. Iuga, J. A. Zeitler, L. F ´a bi ´a n and Y. Z. Khimyak, Angew.
Chem., Int. Ed., 2016, 55, 8904–8908.
9 M. Pfletscher, C. Wolper, J. S. Gutmann, M. Mezger and 25 J. Herzfeld and A. E. Berger, J. Chem. Phys., 1980, 73, 6021–6030.
1
1
M. Giese, Chem. Commun., 2016, 52, 8549–8552.
0 M. Giese, T. Krappitz, R. Y. Dong, C. A. Michal, W. Y. Hamad,
B. O. Patrick and M. J. MacLachlan, J. Mater. Chem. C, 2015, 3,
26 S. Borsacchi, L. Calucci, J. Czub, R. Dabrowski, M. Geppi,
W. Kuczy n´ ski, A. Marini, B. Mennucci and S. Urban, J. Phys.
Chem. B, 2009, 113, 15783–15794.
2
2
1
537–1545.
27 M. Geppi, A. Marini, B. Mennucci, P. Kula, A. Spadło,
W. Kuczy n´ ski and S. Urban, Mol. Cryst. Liq. Cryst., 2011, 541, 104.
28 H. Yu, J. Mater. Chem. C, 2014, 2, 3047–3054.
1 J. P. W. Wong, A. C. Whitwood and D. W. Bruce, Chem. –
Eur. J., 2012, 18, 16073–16089.
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