An Organic Crystal with High Elasticity at an Ultra-Low Temperature (77 K) and Shapeability at High Temperatures

Article abstract of DOI:10.1002/anie.201912236

Organic single crystals with elastic bending capability and potential applications in flexible devices and sensors have been elucidated. Exploring the temperature compatibility of elasticity is essential for defining application boundaries of elastic mate

Full text of DOI:10.1002/anie.201912236

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Accepted Article
Title: An Organic Crystal with High Elasticity at an Ultra-Low
Temperature (77 K) and Shapeability at High Temperatures
Authors: Hongyu Zhang, Huapeng Liu, Kaiqi Ye, and Zuolun Zhang
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201912236
Angew. Chem. 10.1002/ange.201912236
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10.1002/anie.201912236
Angewandte Chemie International Edition
An Organic Crystal with High Elasticity at an Ultra-Low
Temperature (77 K) and Shapeability at High Temperatures
Huapeng Liu, Kaiqi Ye, Zuolun Zhang*, and Hongyu Zhang*
Abstract: Organic single crystals with the elastic bending capability
have been known recently, and potential applications of this type of
unusual crystals in flexible devices and sensors have been
elucidated. Exploring the temperature compatibility of elasticity is
essential for defining application boundaries of elastic materials.
However, related studies have rarely been reported for elastic
organic crystals. Here, we show an organic crystal which displays
elasticity even in liquid nitrogen (77 K). The elasticity can be
maintained below ca. 150 °C. At higher temperatures, the heat
setting property enables us to make various shapes of crystalline
fibres based on this single kind of crystal. Through detailed
crystallographic analyses and contrast experiments, the
mechanisms behind the unusual low-temperature elasticity and high-
temperature heat setting are disclosed.
elasticity is usually examined at room temperature (r.t.). To the
best of our knowledge, only one organic crystal has been
observed to maintain elasticity at –100 °C and lose elasticity at
60 °C (due to the loss of co-crystallized solvents).[15] In-depth
investigations of the elastic properties of EOSCs at low and high
temperatures is a step forward for applications.
In line with our studies on EOSCs and their applications,[31–35]
we have developed a new EOSC based on a π-conjugated
molecule,
(Z)-2-(4-(((E)-2-hydroxy-5-
methylbenzylidene)amino)phenyl)-3-phenylacrylonitrile
(HMBPPA) (Figure 1a). The crystal was found to show elasticity
not only at r.t. but also even in liquid nitrogen (LN2). We note
that some low-density and porous aerogels/foams based on
inorganic boron nitride[36] or carbon materials[30,37‒39]
, e.g.
graphene, carbon nanotubes, have recently been reported to
show elasticity in LN2. However, purely organic materials
(including polymers) that display elasticity at such extreme
circumstances are not known. It is amazing for the high-density
materials formed with organic small molecules, especially those
in the highly crystalline state, to show elasticity at ultra-low
temperatures. Properties of the crystal at high temperatures
have also been tested. The elasticity was maintained before
150 °C. Higher temperatures result in the interesting heat-setting
property induced by phase transition, which enables us to make
different shapes of inelastic crystalline fibers with this single kind
of elastic crystal. This property provides a potential method for
the free shaping of crystalline materials.
Introduction
Organic single crystals have attracted a great deal of research
interest as functional materials, including the active materials for
optoelectronic applications (e.g. organic light-emitting diodes,[1,2]
field-effect transistors[3,4] and optical waveguides[5,6]), as well as
the
responsive
materials
for
light,[7,8]
heat,[9,10]
Recently,
pressure/grounding[11,12]and solvent vapors[13,14]
.
organic crystals with elasticity, which break the traditional
thinking that organic crystals are hard and brittle, have been
known, and more and more elastic organic single crystals
(EOSCs) have been reported.[15–22] Besides the interesting
elastic phenomenon itself, potential applications of EOSCs in
flexible devices and sensors were the driving force for related
studies.[23–29]
Results and Discussion
Regarding the application of an elastic material, the influence
of temperature on elasticity is nonnegligible. Take rubbers
(natural and synthetic) as an example, they only show elasticity
and are applicable at the temperatures between the brittle (Tb)
and the viscous flow (Tf) temperatures, and such applicable
temperatures are typically within –60 to 300 °C for the most
commonly used rubbers.[30] Expanding the applicable
temperature range of elastic materials is essential for extending
application boundaries. Specially, good elasticity at low
temperatures is fairly important as there are a number of low-
temperature circumstances to meet, but the elastic materials
tend to get harder and display significantly reduced elasticity at
HMBPPA was synthesized in a good yield by three steps of
reactions (Supporting Information, Scheme S1). Needle-shaped
crystals of the compound were easily obtained by diffusing
hexane to the saturated CH2Cl2 solution. The crystals are
orange in color and emit orange light under UV irradiation.
Under microscope, the crystal body shows two pairs of parallel
faces, with one pair being much wider (Figure 1b). The lengths
of the crystals are in centimeters scale, and widths/thicknesses
are tens to hundreds of micrometers. At r.t., the wider pair of
faces can be bent to the thickness direction under external
forces applied at the ends of the crystal and recover immediately
its straight shape after the release of external forces (Supporting
Information, Movie 1). Thus, the crystal is elastically bendable.
The good elasticity is indicated by the feasibility to form a loop
(Figure 1c) and the integrity of the crystal after multiple bending-
relaxation processes. Amazingly, even in LN2 (77 K), the
bending-relaxation process can still be performed and repeated
(Figure 1d and Supporting Information, Movie 2). The well-
maintained elasticity in LN2 conflicts with the common sense
that elastic materials tend to get hard and lose elasticity at a too
low temperature. An intuitive comparison is the irreversible
deformation of an elastic isobutylene isoprene rubber bar in LN2
(Figure 1e). Considering that the crystal is composed of highly
low
temperatures
due
to
the
deactivated
atom
bonding/molecular motion of elastic materials.[30] Although the
EOSCs are a potential class of useful elastic materials, their
[*]
H. Liu, Prof. Dr. K. Ye, Dr. Z. Zhang, Prof. Dr. H. Zhang
State Key Laboratory of Supramolecular Structure and Materials
College of Chemistry, Jilin University
Qianjin Street, Changchun (P. R. China)
E-mail: zuolunzhang@jlu.edu.cn
hongyuzhang@jlu.edu.cn
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201912236
Angewandte Chemie International Edition
ordered organic small molecules, having not even the factors
contributing to the elasticity of rubbers, e.g. low crystallinity,
compressible and stretchable polymer segments, and various
additives, the high elasticity at 77 K is fantastic.
with neighboring chain dimers through C–H⋅⋅⋅O hydrogen bonds
to form a layered structure (Figure 2e and f). There are no
obvious intermolecular interactions between molecular layers.
Notably, each molecule in a molecular chain is linked with two
molecules in the adjacent chain of the same chain dimer, as well
as two molecules in a neighboring chain dimer (Figure 2e). This
feature makes all the molecules in a layered structure included
in a hydrogen-bond network.
Figure 1. Elastic bending of the needle-shaped HMBPPA crystal at r.t. and 77
K. a) chemical structure of HMBPPA. b) microscopic image of the crystal body
showing the wider and narrower faces. c) a crystal bent to form a knot shape
at r.t. d) bending experiments of a crystal in LN2: the edges of two pieces of
cover glass were stuck together through Scotch tapes, and one end of a
crystal was stuck on one of the cover glass through glue, while the other end
was free; thus, when folding the two pieces of cover glass, the crystal was
bent. e) the loss of elasticity of the isobutylene isoprene rubber after frozen in
LN2 for comparison.
Figure 2. Molecular and packing features of the needle-shaped HMBPPA
crystal at r.t. a) schematic presentation of the crystal showing the face indexes.
b) molecular conformation with high planarity. c) one-dimensional molecular
chains formed along the crystallographic
b axis through π⋅⋅⋅π stacking
(double-headed arrows). d) overlapping area and vertical distance of the π⋅⋅⋅π
interaction (view perpendicular and along the mean plane of the non-hydrogen
atoms of a molecule). e) hydrogen-bond network connecting the molecules:
blue and green dashed lines represent two types of C–H⋅⋅⋅N hydrogen bonds
within a chain dimer; red and gray dashed lines represent two types of C–
H⋅⋅⋅O hydrogen bonds between chain dimers. f) the crosswise packed chain
dimers in molecular layers (the units labelled with red and yellow represent
respectively a chain dimer), and the expansion and contraction directions of
outer and inner arcs formed in the bending process, respectively.
For EOSCs, elasticity is basically determined by molecular
arrangements and intermolecular interactions.[16,19] Thus, single-
crystal X-ray diffraction (SCXRD) was performed at r.t. to resolve
the crystal structure and get insight into the factors related to
elasticity. By face indexing, the wider and bendable crystal faces
were confirmed to coincide with the crystallographic (100) plane
(Figure 2a). The length direction of the crystal corresponds to
the crystallographic b axis, and the thickness direction is along
the crystallographic a axis. There is one molecule in the
asymmetric unit of the crystal. The molecular skeleton shows
high planarity. The phenolyl group and the central benzene ring
are almost coplanar, and the terminal phenyl group is only
slightly twisted out of the plane defined by the central benzene
ring with an angle of 12.12° (Figure 2b). Along the crystal-length
direction (b axis), molecules are packed to form a chain
structure through intermolecular π⋅⋅⋅π interactions (Figure 2c).
The π-stacked molecules are perfectly parallel and exhibit a
quite large overlapping area and a short interaction distance (ca.
3.37 Å). Thus, strong π⋅⋅⋅π interactions can be concluded
(Figure 2d). As-formed molecular chains are dimerized along the
Various intermolecular non-covalent interactions, including
hydrogen bonding,[21] halogen-halogen,[16] π⋅⋅⋅π[23] and van der
Waals[32] interactions, have been proposed to contribute to the
elasticity of EOSCs. These interactions are generally weak and
adjustable so that, in the bending process, they cannot only
enhance the linkage between molecules to enhance the
resistance of a crystal towards external forces, but also allow the
crystal deformation through slight self-changes. Among these
interactions, the π⋅⋅⋅π interactions are quite often detected in
EOSCs,[15,16,20] and some of the EOSCs,[23,26] including the
present one, are designed based on relevant considerations. In
this crystal, the π-stacked molecules can turn intermolecular
horizontal distance to fit the length requirement of
a
compressed/shortened inner arc and a stretched/elongated
outer arc formed in the bending process (Figure 2f).[15] A slight
relative slippage between adjacently stacked π-systems along
crystallographic
c axis (width direction) through C–H⋅⋅⋅N
interactions (Figure 2e). Each chain dimer is crosswise packed
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10.1002/anie.201912236
Angewandte Chemie International Edition
Table 1. Crystallographic information of the HMBPPA and DPIN crystals at r.t. and 100 K.
Crystals
a
b
c
α
β
γ
V
HMBPPA (r.t.)
HMBPPA (100 K)
14.7884(12)
14.7445(18)
(0.296%)[a]
5.1980(3)
5.2089(3)
(-0.210%)[a]
4.6170(4)
4.5978(5)
(0.416%)[a]
9.9584(6)
9.8280(6)
(1.309%)[a]
25.987(2)
25.854(3)
(0.511%)[a]
29.0475(17)
28.5562(16)
(1.691%)[a]
90.0
90.0
100.057(3)
99.538(6)
(0.519%)[a]
93.243(2)
92.709(2)
(0.573%)[a]
90.0
90.0
1747.1(2)
1728.5(3)
(1.060%)[a]
1501.20(15)
1460.25(15)
(2.728%)[a]
DPIN (r.t.)
DPIN (100 K)
90.0
90.0
90.0
90.0
[a] Values in parentheses are the contraction ratios from r.t. to 100 K.
the length direction of the π-skeleton, accompanied by the
formation of a small angle between the parallel π-systems, can
also occur to fit the curvature of the bent faces in the bending
process.[20] These factors ensure a prerequisite for elastic
bending. The hydrogen-bond network in a molecular layer
makes intra-layer π-systems become an integer and prefer
synergic movements, which should reduce the cracking risk of
the crystal in the bending process because higher uniformity and
less defects of the crystal body can be expected. Moreover, the
hydrogen-bond network, together with the strong π⋅⋅⋅π
interactions, should enhance the tolerance of the molecular
chains to tensile forces/pressure. These factors contribute to the
good elasticity of the crystal.
accompanied by the slight shortening of not only the horizontal
distance but also the vertical (0.594%) distance between parallel
π-skeletons. Overall, slightly stronger π⋅⋅⋅π interactions were
observed. A slight rotation of the π-skeleton towards a smaller
dihedral angle (0.318% less) relative to the (100) plane (i.e.
bending faces) was also observed, which is likely the response
to the contraction of the a axis (Supporting Information, Figure
S3). As for the DPIN crystal, the cell volume was contracted
more seriously (2.728%) at 100 K, which was accompanied by
the large contraction of the b (1.309%) and c (1.691%) axes and,
interestingly, the expansion of the a axis (0.210%) along which
the π-skeletons are stacked one-dimensionally (Table 1). The
expansion of the a axis at 100 K was accompanied by the
lengthening of the horizontal distance between π-skeletons, as
To further understand the elasticity at 77 K, a known room-
temperature elastic crystal (DPIN crystal) reported by us has
also been subjected to low-temperature experiments because
this crystal is a good example with the elasticity closely related
to π⋅⋅⋅π interactions.[31] Actually, the π-skeletons in DPIN crystal
are also one-dimensionally stacked along the length direction of
the crystal, similar to the case in the needle-shaped crystal of
HMBPPA (see ref. 31 and Supporting Information, Figure S1).
However, molecules of DPIN are more twisted, and the π-
skeletons possess a reduced overlapping degree and a longer
vertical distance. In addition, there are no obvious intermolecular
interactions in the width direction of the crystal to link molecules,
unlike the well-linked network observed in the crystal of
HMBPPA. The DPIN crystal was found to break immediately
when bent in LN2 regardless of thicknesses and lengths
(Supporting Information, Movie 3), although the crystal still
possessed smooth surfaces after it was put into LN2 in the
straight shape (Supporting Information, Figure S2). This result
indicates that the one-dimensional π⋅⋅⋅π stacking, the common
feature of the two crystals, is not simply the reason for elasticity
at 77 K. To analyse the factors potentially leading to the distinct
low-temperature properties, the cell parameters and molecular
and packing structures of the crystals measured at 100 K were
compared with corresponding results obtained at r.t. To get a
reliable comparison, the diffraction experiments at these
well as
a more twisted molecular conformation that was
indicated by the increases of 2.67 and 7.98° for two of the key
torsion angles within the molecular skeleton (Supporting
Information, Figure S4). The more twisted conformation made
the π⋅⋅⋅π interactions become poorer at 100 K. Based on above
results, the distinct low-temperature properties of the two
crystals can be understood. For the HMBPPA crystal, the cold
contraction is weaker and relatively isotropic, and thus the
molecular conformation and packing features are well
maintained. Therefore, the ease of bending at ultra-low
temperatures is similar to that at r.t. Moreover, the slightly
strengthened π⋅⋅⋅π interactions at low temperatures further
enhance the tolerance of the molecular chains to tensile
forces/pressure. These two factors contribute to the good
elasticity of the HMBPPA crystal at low temperatures. The
difficulty in the changes of molecular conformations and packing
structures at low temperatures benefit from the hydrogen-bond
network, because it makes the change/movement of a molecule
restricted seriously by a number of other molecules. In particular,
the crosswise arrangement of chain dimers in the hydrogen-
bond network strongly restricts the crystal contraction along the
a axis (thickness direction), because the contraction prefers the
rotation of π-skeletons towards a smaller dihedral angle relative
to the (100) plane but such rotation is harder due to the mutual
restriction of crosswise packed chain dimers through hydrogen
bonds. As for the DPIN crystal, the severer and anisotropic
response to cooling makes the molecular conformation and
packing structure changed to a larger extent, and thus the
bending property under external forces is significantly changed.
The nature of the loss of elasticity could be related to the
increased difficulty in the relative slippage of neighboring π-
skeletons as they are more twisted, as well as the weaker ability
of molecular chains to confront with tensile forces as the π⋅⋅⋅π
interactions are poorer. In addition, the larger change of
temperatures were performed using
a single sample of
HMBPPA/DPIN crystal settled in the diffractometer. Only the
temperatures were changed in the experiments. The three axes
of the HMBPPA crystal were contracted by 0.296–0.511% from
r.t. to 100 K, and the cell volume was contracted by 1.060%
(Table 1). The molecules of HMBPPA at 100 K maintained
basically the geometry observed at r.t., with the key
intramolecular torsion angles changed within 1.16° (Supporting
Information, Figure S3). The contraction of the b axis was
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10.1002/anie.201912236
Angewandte Chemie International Edition
molecular conformation and packing structure may lead to large
internal stresses after cooling, which may increase the cracking
risk of the crystal.
can be insured for the HMBPPA crystal (ca. 1–1.5% determined
by experiments), although the strain is still smaller than
corresponding value of the DPIN crystal (ca. 2–3%) (Figure 3).
The tolerance of the molecular packing structure to large forces
for compression is also reasonably expected.
The outstanding bending properties of the HMBPPA crystal at
low temperatures inspired us to test the high-temperature
properties. At the temperatures below 150 °C, the elasticity of
the crystal was well maintained. Interestingly, the crystal was
found to lose elasticity and become brittle at higher
temperatures, and the disappearance of elasticity was
accompanied by the changes of crystal color and emitting light
(Figure 4a). When the crystal was cooled to r.t., the changes
were not reversed. The changing process is caused by an
endothermic crystalline-phase transition as confirmed by the
differential scanning calorimetry (DSC) analyses (Figure 4a).
Interestingly, based on such a property of the HMBPPA crystal,
heat setting of the crystal enables us to prepare various shapes
of crystals. The preparation process includes: 1) bending the
crystal at r.t. to form a desired shape; 2) heating the crystal to
the temperature of ca. 170 °C; and 3) cooling the crystal to r.t.
As an example, a long crystal with a helical shape was prepared
(Figure 4b). Our results provide a new thinking for shaping
crystalline materials, which is the construction and utilization of
EOSCs with the phase transition property.
Figure 3. Stress-strain curves of the HMBPPA (a) and DPIN (b) crystals, as
well as the elastic modulus (EM) and fracture strength (FS) values, obtained
from the tensile tests of three samples of each crystal.
To explore the influence of molecular packing structures on
their stretchability that is closely related to the extension of the
outer arc in the bending process, the tensile test of the HMBPPA
crystal was performed at r.t. through the tension at the two ends
of the crystal. Contrast experiments were also performed on the
DPIN crystal. For both crystals, only the elastic deformation
occurred before breaking as indicated by the linear correlation
between tensile stresses and strains. The elastic modulus (EM,
slopes of the stress-strain curves) of the HMBPPA crystal is
large (4000–4900 MPa), being much higher than that of the
DPIN crystal (560–730 MPa) (Figure 3). This result indicates
that, under the same external force, a HMBPPA crystal can be
stretched to a much less degree compared with a DPIN crystal
with the same transversal area. However, the HMBPPA crystal
can endure much larger stress at a unit transversal area as
indicated by its much larger fracture strength (FS: 47–65 MPa
for the HMBPPA crystal vs. 11–19 MPa for the DPIN crystal).
The larger fracture strength clearly indicates the advantage of
strong π⋅⋅⋅π interactions and molecular synergic movement for
the tolerance to external forces for stretch. It means that larger
maximum external forces can be applied for stretching the
HMBPPA crystal to overcome the difficulty in stretch caused by
a larger elastic modulus, so that an appreciable maximum strain
Figure 4. Heat-setting property of the needle-shaped HMBPPA crystal. a) the
DSC curve of the HMBPPA crystal showing the phase transition process
leading to the heat setting (insets show the changes of crystal color in the
process). b) the preparation of an inelastic helical-shaped crystal through
using the heat-setting property (the crystal was initially screwed on a glass
tube to form a helical shape, and the two ends of the crystal were stuck on the
tube with glues).
To get insight into the molecular packing features of the new
crystalline form generated after phase transition, SCXRD was
performed. However, the diffraction data of the new form was
poor for resolving detailed structures. The poor data is likely due
to the formation of many defects in the crystal, which is implied
by the loss of transparency of the crystal after phase transition.
After various attempts, crystals with a crystalline phase same as
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10.1002/anie.201912236
Angewandte Chemie International Edition
Single-crystal growth. Saturated dichloromethane solution of HMBPPA
was added in test tubes, and then triple volume of cyclohexane was
added along the tube-wall without destroying the previous solution
surface. The test tubes were sealed with a cover. After standing at r.t. for
3–7 days, the needle-shaped crystals of HMBPPA were obtained. Block-
shaped crystals of HMBPPA were grown by vacuum sublimation.
HMBPPA solid was heated at 180 °C under vacuum (ca. 3 Pa) in a
sublimator and the crystals were generated at the deposition area with a
setting temperature of 100 °C. The crystals of DPIN were regrown
through the method described in our previous paper.[31]
that obtained after phase transition (determined by X-ray powder
diffraction and DSC) have finally been achieved by vacuum
sublimation (Supporting Information, Figure S5). These crystals
are block-shaped without the possibility of being bent.
Compared with the molecules in the needle-shaped crystals
obtained from solvent diffusion, the molecules in the block-
shaped crystals are much more twisted as indicated by the
larger torsion angles formed within the molecular skeleton
(Figure 5a). In the block-shaped crystals, molecules also form
molecular chains through π⋅⋅⋅π interactions (Figure 5b).
However, the π⋅⋅⋅π interactions between the twisted molecules
X-ray diffraction analyses. Single-crystal X-ray diffraction data were
collected on a Bruker D8 Venture diffractometer using the ω-scan mode
with graphite-monochromator Mo•Kα radiation. The structures were
solved with direct methods using the Olex2 programs and refined with
full-matrix least-squares on F2. Non-hydrogen atoms were refined
anisotropically. The positions of hydrogen atoms were calculated and
refined isotropically. The crystallographic information has been deposited
at the Cambridge Crystallographic Data Centre (CCDC). CCDC
numbers: 1917965, 1917964, 1917953, 1917952 and 1917951 for the
needle-shaped crystal of HMBPPA measured at r.t. and 100 K, block-
shaped crystal of HMBPPA, and the crystal of DPIN measured at r.t and
100 K, respectively.
are weak, as indicated by
a crosswise and nonparallel
arrangement of neighboring molecules and the resulting limited
overlapping degree, as well as a large interaction distance
(Figure 5c). The poor π-stacking and the defects in the crystal,
caused by the phase transition process, could be the reason for
the loss of elasticity.
Tensile tests. Tensile stress was measured using an Instron 5944
Universal Testing System. The static load cell is Instron 2530 load cell
with capacities of 10 N. The sample was fixed on one surface of the
mechanical grip by 502 glue to avoid slippage during testing. Raw data
were obtained in displacement controlled mode at a rate of 1 mm/min.
During the mechanical testing, load and displacement were recorded in
real time. The stress, strain and elastic modulus were calculated by the
equations below.[20]
ꢌꢄꢍꢎꢃꢃ
ꢀꢁꢂꢃꢄꢅꢆ ꢇꢈꢉꢊꢁꢊꢃ ꢋ
ꢌꢄꢍꢂꢅꢏ
Figure 5. Molecular and packing features of the block-shaped HMBPPA
crystal. a) molecular conformation with the key torsion angles being shown. b)
one-dimensional molecular chains formed through π⋅⋅⋅π stacking (double-
headed arrows). c) overlapping area and vertical distance of the π⋅⋅⋅π
interactions (view perpendicular and along the plane defined by the central
ꢔ
ꢕꢖꢁꢁꢅꢎꢉ ꢗꢈꢍꢆꢎ
ꢌꢄꢍꢎꢃꢃ ꢐꢑꢒꢂꢓ ꢋ
ꢋ
ꢕ
ꢘꢍꢈꢃꢃ ꢙ ꢃꢎꢆꢄꢅꢈꢏ ꢂꢍꢎꢂ
ꢚꢛ ꢘꢜꢂꢏꢝ ꢅꢏ ꢁꢎꢏꢝꢄꢜ
ꢌꢄꢍꢂꢅꢏ ꢋ
ꢋ
ꢛ
ꢞꢏꢅꢄꢂꢁ ꢁꢎꢏꢝꢄꢜ
benzene ring)
.
The elastic modulus of a sample was determined from the slope of the
stress-strain curve. The fracture strength corresponds to the maximum
stress value of the stress-strain curve.
Conclusion
In summary, the elasticity in liquid nitrogen, an unusual property
for elastic materials, has been discovered for an organic single
crystal. The strong π⋅⋅⋅π interactions, a hydrogen-bond network
connecting the π-systems, as well as crosswise packed
molecular chains, are crucial for the elasticity at ultra-low
temperatures. Another unusual and interesting property, i.e. heat
setting caused by phase transition, has also been found for the
same crystal. This study provides a method for achieving
elasticity at ultra-low temperatures based on materials with
organic components, which is the highly crystalline and rational
packing of organic small molecules rather than the mobility
enhancement of polymer fragments. It may give birth to new
organic materials applicable in extreme circumstances, such as
the outer space. Although more and more factionalized single
crystals have been developed, the free shaping of crystals is
challenging. The heat-setting strategy of elastic crystals shown
in this paper is a potentially useful shaping method for achieving
functional crystals with various shapes for diverse applications.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (51622304, 51773077, 51603082 and
51773079).
Conflict of interest
The authors declare no conflict of interest.
Keywords: organic crystal • elastic bending • 77 K • low-
temperature crystal structure • heat setting
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This article is protected by copyright. All rights reserved.

10.1002/anie.201912236
Angewandte Chemie International Edition
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RESEARCH ARTICLE
Here, we report an organic crystal
which displays elasticity even in liquid
nitrogen (77 K). It may give birth to
new organic materials applicable in
extreme circumstances, such as the
outer space. Another unusual and
interesting property, i.e. heat setting
caused by phase transition, has also
been found for the same crystal. At
higher temperatures, the heat setting
property enables us to make various
shapes of crystalline fibres based on
this single kind of crystal.
H. Liu, K. Ye, Z. Zhang*, and H. Zhang*
Page No. – Page No.
An Organic Crystal with High
Elasticity at an Ultra-Low
Temperature (77 K) and Shapeability
at High Temperatures
This article is protected by copyright. All rights reserved.