Chemical reaction method for growing photomechanical organic microcrystals

Article abstract of DOI:10.1039/c4ce02387k

(E)-3-(Anthracen-9-yl)acrylic acid (9-AYAA) exhibits a strong photomechanical response in bulk crystals but is challenging to grow in microcrystalline form. High quality microcrystals of this molecule could not be grown using techniques like sublimation, reprecipitation, and the floating drop method. If the tertbutyl ester of 9-AYAA is used as a starting material, however, high quality, size-uniform microwires could be grown via acid catalyzed hydrolysis. 9-AYAA microwires with uniform length and thickness were produced after a suspension of (E)-tert-butyl 3-(anthracen-9-yl)acrylate ester microparticles was tumble-mixed in a mixture of phosphoric acid and sodium dodecyl sulfate at 35°C. The dependence of the results on temperature, surfactant and precursor concentration, and mixing mode was investigated. This chemical reaction-growth method was extended to grow microplates of 9-anthraldehyde using the corresponding acylal as the starting material. Under 475 nm irradiation, the 9-AYAA microwires undergo a photoinduced coiling-uncoiling transition, while the 9-anthraldehyde microplates undergo a folding-unfolding transition.

Full text of DOI:10.1039/c4ce02387k

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Chemical reaction method for growing
photomechanical organic microcrystals†
Cite this: DOI: 10.1039/c4ce02387k
a
b
a
c
Rabih O. Al-Kaysi,* Lingyan Zhu, Maram Al-Haidar, Muhannah K. Al-Muhannah,
a
a
b
Kheireddine El-Boubbou, Tarafah M. Hamdan and Christopher J. Bardeen*
IJE)-3-IJAnthracen-9-yl)acrylic acid IJ9-AYAA) exhibits a strong photomechanical response in bulk crystals
but is challenging to grow in microcrystalline form. High quality microcrystals of this molecule could not
be grown using techniques like sublimation, reprecipitation, and the floating drop method. If the tertbutyl
ester of 9-AYAA is used as a starting material, however, high quality, size-uniform microwires could be
grown via acid catalyzed hydrolysis. 9-AYAA microwires with uniform length and thickness were produced
after a suspension of (E)-tert-butyl 3-IJanthracen-9-yl)acrylate ester microparticles was tumble-mixed in a
mixture of phosphoric acid and sodium dodecyl sulfate at 35 °C. The dependence of the results on tem-
perature, surfactant and precursor concentration, and mixing mode was investigated. This chemical
reaction-growth method was extended to grow microplates of 9-anthraldehyde using the corresponding
acylal as the starting material. Under 475 nm irradiation, the 9-AYAA microwires undergo a photoinduced
coiling–uncoiling transition, while the 9-anthraldehyde microplates undergo a folding–unfolding transition.
Received 2nd December 2014,
Accepted 7th January 2015
DOI: 10.1039/c4ce02387k
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problem is that large molecular crystals can prevent the
photoreaction from going to completion because photoprod-
Introduction
In the past decade there has been increased interest in molec-
ular crystals that can deform or actuate when exposed to UV
uct absorption on the surface blocks incident radiation from
1
9
reaching the rest of the reactant inside the crystal. The prac-
tical application of photoreactive molecules requires the capa-
bility to grow them as well-defined micron-sized crystals.
In recent years we have developed a general method for
fabricating highly crystalline and uniformly shaped molecular
crystal nanorods by using solvent annealing inside anodic
1
–3
or visible light.
In the majority of cases, this deformation
is driven by a crystal-to-crystal photochemical reaction where
the simultaneous presence of two different crystal phases
(
reactant and product) leads to internal strain that drives
4
–9
10,11
12
bending , twisting
or jumping. The nature of the
2
0
deformation depends not only on the chemical reaction and
crystal packing, but also on the overall shape of the crystal
aluminum oxide (AAO) templates. Unfortunately, the lim-
ited pore sizes and lengths of these AAO templates limits the
types of crystal shapes that can be formed. This template
method requires the liberation of the annealed wires by
polishing and dissolution of the AAO in an acid or base.
Surface templating methods have been used to grow arrays
1
0,13,14
itself.
To make molecular crystal actuators with well-
defined properties, it is vital to control their shape and
dimensions. Photoreactive molecular crystals with large
dimensions tend to either shatter or disintegrate when irradi-
ated due to buildup of internal stress between the photoprod-
of organic crystals, but size and shape control remain
1
5
21–23
uct and reactant phases. This problem can often be solved
challenging.
It is also likely that the ability of surface-
1
6–18
by shrinking the crystal to micron dimensions.
A separate
bound crystals to respond to light will be diminished. Free-
floating microcrystals can be grown without the use of tem-
plates, but at the expense of size and shape control. There
are reports in which aqueous self-assembly can yield crystals
a
College of Science and Health Professions-3124, King Saud bin Abdulaziz
University for Health Sciences, and King Abdullah International Medical Research
Center, Ministry of National Guard Health Affairs, Riyadh 11426,
24–29
with uniform or variable shapes,
but these cases tend to
be molecule-specific and have not involved photochemically
reactive species. We have grown molecular crystal micro-
ribbons and micro-needles of various 9-anthracene carbox-
Kingdom of Saudi Arabia. E-mail: rabihalkaysi@gmail.com, kaysir@ksau-hs.edu
b
Department of Chemistry University of California, Riverside 501 Big Springs
Road, Riverside, CA 92521, USA. E-mail: christopher.bardeen@uc.edu
c
Materials Science Research Institute, National Nanotechnology Center,
10,30,31
13
ylic acid derivatives,
9
4-chloro-cinnamic acid
-methylanthracene using the floating drop method, in
which evaporation of a good solvent leaves ribbon or needle-
and
King Abdulaziz City for Science and Technology (KACST), Riyadh 11442,
Kingdom of Saudi Arabia
1
4
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
3
2
c4ce02387k
shaped crystals on the surface of ultrapure water. But this
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method often yields a wide range of sizes and the crystals
can aggregate as well. For many molecules, it is difficult or
impossible to grow well-defined microcrystals using either
method.
yl)acrylic acid IJ9-AYAA) (Scheme 1a) under acidic conditions.
Crystals of the tert-butyl ester are photostable and have no
photomechanical response. On the other hand, 9-AYAA molec-
ular crystals are photomechanically responsive when excited
3
3
Controlling the rate of crystal growth is vital to obtain a
uniform sample of micron-sized crystals with useful proper-
ties. Often this control is achieved by varying monomer
concentration and growth conditions (temperature, growth
medium, rate of solvent evaporation). In this paper we
describe a new approach based on the chemical reaction of a
precursor molecule, followed by a controlled reprecipitation
of the photoreactive product molecule. Acid catalyzed hydro-
lysis of randomly shaped reactant crystals with acid sensitive
functional groups, like tert-butyl esters or acylals, combined
with gentle agitation in a surfactant solution, can yield
significant control over crystal size and shape for molecules
with COOH or CHO functionalities. In the current paper,
we apply this chemical reaction-growth sequence to make
photomechanically active microcrystals of two anthracene
derivatives, IJE)-3-IJanthracen-9-yl)acrylic acid IJ9-AYAA) and
with UV (365 nm) or visible light (475 nm).
Previously, we grew large (millimeter dimension) crystals
of 9-AYAA by solvent evaporation and sublimation and deter-
3
3
mined its crystal structure. We found that these crystals
could bend after prolonged UV or visible light illumination.
Attempts to grow smaller crystals that might show more
dramatic photomechanical behavior were unsuccessful.
Reprecipitation of a 9-AYAA–THF solution into an aqueous
solution of phosphoric acid/sodium dodecyl sulfate (SDS)
yielded both randomly shaped microcrystals and micro-tubes.
Using the floating drop method over pure water or a phos-
phoric acid–SDS solution yielded branched or randomly
shaped crystals with no apparent control over size and mor-
phology. Sublimation of 9-AYAA also yielded a broad distribu-
tion of macro crystal sizes and variable shapes. Representa-
tive SEM and optical microscope images of these results are
shown in Fig. 1.
9
-anthraldehyde IJ9-AA). New crystal shapes lead to qualita-
tively new types of photomechanical responses for both micro-
wires of 9-AYAA and microplates of 9-AA. Our results demon-
strate that efforts to grow novel crystal shapes can be rewarded
by the observation of novel photomechanical behaviors.
It appeared that 9-AYAA crystallized rapidly and without
a preferred growth axis under standard conditions. In order
to grow more regularly shaped crystals, we wanted to slow
down the nucleation and growth processes. We decided to
use an in situ chemical reaction to gradually release the mole-
cule of interest into the solution. Since 9-AYAA is a carboxylic
acid, we chose a tert-butyl ester as our precursor molecule.
Acid sensitive functional groups such as tert-butyl esters or
acylals can be cleaved at low pH to yield the corresponding
Results and discussion
In the following, we will focus on growing crystals of (E)-tert-
butyl 3-IJanthracen-9-yl)acrylate to form IJE)-3-IJanthracen-9-
Scheme 1 a) Acid catalyzed hydrolysis of a tert-butyl ester leads to the formation of a carboxylic acid IJ9-AYAA) and 2-methylpropene gas. b) Acid
catalyzed hydrolysis of an acylal yields an aldehyde and water-soluble acetic acid.
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Fig. 1 a) SEM image of reprecipitated 9-AYAA in 3.6 M H
3
PO
4
/0.1% SDS at room temperature without mixing. b) Optical microscope image of
9
-AYAA crystals prepared by the floating drop method. c) Optical microscope image of 9-AYAA prepared by sublimation. Panels b) and c) are with
the same scale, scale bar = 100 μm.
3
4
35
carboxylic acid or aldehyde respectively (Scheme 1a and b).
For high yield product formation, the reactant has to be in a
homogenous phase with the aqueous acid. Since the organic
molecule precursors in this paper are not water soluble, we
used the amphiphilic SDS as a pseudo phase transfer catalyst
to enable the hydrolysis.
growth at the expense of uniformity and final length, as illus-
trated in Fig. 3. Starting with the same initial conditions,
growth at 45 °C yielded nanowires that were on average 35%
shorter than microwires grown at 30 °C. But it took only
30 hours for these wires to reach their maximum length, as
compared to several days at 30 °C. The microwires grown
at higher temperatures were on average wider than those
grown at lower temperatures, with many incidents of
fused crystals with a star-shaped morphology. We found
the optimum temperature to be around 35 °C with 0.1% SDS,
which provided a good compromise between crystal quality
and growth time.
When a suspension of randomly shaped tert-butyl-9-AYAA
ester microcrystals in a 3.6 M H PO /0.1% SDS was tumble-
3
4
mixed at 35 °C, the tert-butyl ester was slowly hydrolyzed to
generate microwires of 9-AYAA. The microwires had strikingly
uniform lengths and thicknesses as shown in Fig. 2. The length
of the microwires grew steadily over a period of several
days until all the reactant was consumed. A plot of microwire
length versus time (Fig. 3) shows that the growth was initially
fast then gradually tapered off to reach a final length with a
narrow distribution. Optical microscopy images showed
that the microwire width remained constant throughout the
growth process, with an average width of 990 nm and an aver-
age standard deviation of 12%. During the growth process,
microwire growth could be halted by simply cooling the sam-
ple to <0 °C or washing away the acid–SDS solution. To opti-
mize the growth of the 9-AYAA microcrystals, we examined the
effects of several different parameters, as described below.
3 4
2) Surfactant and H PO concentration
When the tert-butyl ester precursor was stirred at 35 °C in 3.6
molar aqueous phosphoric acid (pH ~1) or dilute HCl, there
was no observed cleavage of the acid sensitive functional
group. Even after several days of mixing at high temperatures
no product crystals were observed. This was expected since
the reactant has negligible solubility in the acid solution.
3 4
After adding SDS to make a 0.1% IJw/v) solution in H PO ,
the acid catalyzed hydrolysis occurs over a period of several
days at room temperature or several hours at 45 °C. The con-
centration of SDS plays a crucial role in the uniformity of the
obtained microwires. In general for SDS concentrations
>0.6% we obtained randomly shaped and fused crystals of
1
) Temperature
The rate of microwire growth and maximum length depends
on temperature. Higher temperatures lead to faster nanowire
Fig. 2 a) Optical microscope image of 9-AYAA microwires, scale bar = 500 μm. b) SEM image of 9-AYAA microwires. In both images the
microwires were grown with 3.6 M H PO /0.1% SDS at 35 °C with gentle rotation-mixing. Inset: Zoomed image of a 9-AYAA microwire tip.
3
4
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4) Precursor concentration
The initial amount of the ester precursor affected the unifor-
mity and length of the microwires. The optimum ester con-
−
1
centration was 0.1 mg mL yielding uniform microwires with
a narrow size distribution and a final length of 200 micro-
meters on average. Increasing the initial ester concentration
resulted in poorer uniformity with no increase in length. In
order to grow longer 9-AYAA microwires, we had to add a
−
1
fresh tert-butyl ester suspension in SDS/H PO (0.1 mg mL )
3
4
to a suspension of previously grown microwires. This sequen-
tial addition led to microwires whose average length doubled
to ~400 microns (ESI,† Fig. S4). Adding additional aliquots
of precursor solution resulted in even longer microwires,
although these tended to snap or become entangled with
each other.
To demonstrate that the chemical reaction-crystal growth
method could be extended to acyclal derivatives (Scheme 1b),
we used similar conditions to generate microcrystals of
Fig. 3 Plot of the length versus time of 9-AYAA microwires grown
at various temperatures. The error bars reflect standard deviation in
length.
9-anthraldehyde IJ9-AA). The crystal structures of both this
molecule and its photodimer have been determined previ-
3
6,37
−1
ously. When 0.1 mg mL of the acylal was added to 3.6 M
4
PO /0.1% SDS and tumble mixed at 35 °C, 9-AA grew as
9
-AYAA (ESI,† Fig. S1). Thus the optimum SDS concentration
H
3
was between 0.1% and 0.3% to generate microwires with the
most uniform dimensions. When the concentration of SDS
dropped to 0.05%, microwire formation slowed down dra-
matically and we again observed a high proportion of non-
uniform crystals. The use of a cationic surfactant, centrim-
onium bromide (CTAB), did not yield well-defined crystals.
We found the optimum concentration of phosphoric acid
was between 1 and 3.5 M to give uniform microwires. For
higher concentrations (>7.5 M) the crystals precipitated out
as a tangled mass of very long microwires with variable
thicknesses, rather than as separated microwires (ESI,† Fig. S2).
When a dilute HCl/0.1% SDS solution with similar pH
was used instead of phosphoric acid, randomly shaped clus-
ters of 9-AYAA crystals were liberated. It may be that the
presence of undissociated phosphoric acid helps slow the
reaction-growth process by increasing the viscosity of the
solution. It is possible that a more extensive investigation
of different surfactants and acids could improve on our
results, but that is beyond the scope of this paper.
rectangular microplates with rounded edges, with dimen-
sions of about 100 μm by 150 μm (Fig. 4). The dimensions of
these rectangular crystals were uniform to within ~10%, and
the microplates were the only morphology seen in the sam-
ple. Note that we did not do a systematic investigation of the
growth parameters as we did for 9-AYAA. We were able to
extend this method to include other 9-AA derivatives. For
example starting with the propylal derivative of 9-AA, the
reaction-growth yielded similarly shaped microplates but
with slightly different morphology.
38
The success of the chemical reaction method for crystal
growth deserves some comment. The production of uniform
crystals suggests that the initial nucleation events are followed
3
) Mixing
We noticed that mixing the sample was required for the for-
mation of uniform micro-structures. When we allowed a sam-
ple to sit at 35 °C undisturbed for several days, we obtained
microcrystals and microwires with a much broader distribu-
tion of lengths and widths (ESI,† Fig. S3). The mode of
mixing also affected the uniformity of the crystals. Stirring
the mixture with a magnetic stirrer resulted in much shorter
microwires with variable lengths. We suspect that the micro-
wires tend to break when struck by the magnetic stirring rod.
The best mode of mixing utilized a 90° tumble rotator mixer
set at speeds ranging from 8 to 24 rpm. Higher rotation
speeds caused the microwires to stick to the edge to the vial
and the formation of undesirable SDS foam.
Fig. 4 Optical microscope image of microplates of 9-AA. Scale bar =
250 μm.
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by a slower growth phase, corresponding to a two-step
process that starts in the labile region of an Ostwald-Miers
crystal types, the photodeformation is maximized at an inter-
mediate point in the photoreaction, after which the fully
reacted crystals return to close to their original shapes.
These observations are consistent with our previous results
showing that 9-methylanthracene microribbons and micro-
needles also maximize their bend or twist when roughly
equal amounts of reactant and product are present in the
crystal, then return to their original shape as they become
3
9
diagram and then moves into the metastable region. It
is possible that the nucleation rate of crystals is limited by
the fact that crystallizing molecules are only produced in the
presence of SDS, which solubilizes them until they can be
added to an already formed crystal. In this scenario, the chemi-
cal reaction serves as a way to control both the concentration
of the crystallizing molecules, and also their local environ-
ment. Simply adding molecules to a surfactant solution cannot
afford this level of controlled release over the course of hours.
The dynamics of the 9-AYAA and 9-AA microcrystals
under illumination were investigated to demonstrate that the
reaction-crystal growth technique can produce photomechan-
ically responsive structures. When a 9-AYAA microwire was
illuminated with 475 nm light, the wire started to bend,
eventually forming a circular loop. A unique feature of these
microwires was their ability to form a closed loop when par-
tially photoreacted, then open back up as the photoreaction
goes to completion. A typical coiling–uncoiling sequence for
a 9-AYAA microwire is shown in Fig. 5. By halting the reac-
tion at specific times (Fig. 3) we can obtain microwires with
predetermined lengths that affects how many times the wire
can coil upon illumination, with longer wires forming more
coils (ESI,† Videos 1–3). When crystalline microplates of 9-AA
were illuminated with visible light (475 nm) on their domi-
nant face (corresponding to the (002) Miller plane, ESI†
Fig. S7), they folded and then unfolded exclusively along the
long crystal axis, as shown in Fig. 6 (ESI,† Video 4). In both
1
4
predominantly the product phase.
The structural changes that underlie the photomechanical
deformations appear to be different for 9-AYAA and 9-AA.
Although it is well-positioned to undergo a [4 + 4] photo-
3
3
dimerization in its crystal form, 9-AYAA appears to prefer-
entially undergo a trans–cis photoisomerization. Analysis of
the solid-state reaction by high-pressure liquid chromatogra-
phy shows that a complicated mixture of products is formed,
possibly including oligomers produced by sequential asym-
metric [2 + 4] dimerization reactions enabled by the trans–cis
1
isomerization (ESI,† Fig. S5). H-NMR of the product revealed
the presence of overlapping multiplets in the aromatic
region, also suggesting the presence of multiple photo-
products (ESI,† Fig. S6). This complicated photoproduct
mixture drives a crystal-to-amorphous transition, as inferred
from the loss of structure in the powder X-ray diffraction
(PXRD) pattern (Fig. 7). The coiling of the microwire is remi-
niscent of the photoinduced coiling of nanowires composed
of an anthracene-9-IJ1,3-butadiene) derivative, dimethyl-
2IJ3-IJanthracen-9-yl)allylidene)malonate, which also involved a
4
0
crystal-to-amorphous transition. The difference here is that
Fig. 5 Optical microcopy images of 9-AYAA microwire (~60 μm long) coiling and uncoiling when exposed to 475 nm light: a) before light
exposure; b) during light exposure; c) after light exposure. Scale bar = 30 μm for panels a), b) and c).
Fig. 6 Optical Microscopy images of 9-AA microplate folding and unfolding when exposed to 475 nm light: a) before light exposure; b) during
light exposure; c) after light exposure. Scale bar = 50 μm for panels a), b) and c).
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microcrystals with controlled shapes and/or sizes. The moti-
vation for growing such crystals is that they can exhibit
useful types of photomechanical shape changes, like the
coiling and folding motions demonstrated in this work.
Experimental
Synthesis of precursor molecules
All starting materials used were purchased from TCI America
and used without further purification. Synthesis of the
tert-butyl esters and acylals was accomplished following pro-
3
3,43
cedures previously established in the literature
respectively.
Fig. 7 Powder X-ray diffraction patterns of trans-9-AYAA microcrys-
tals a) before irradiation, showing well-resolved peaks; b) after irradia-
tion, showing loss of structure indicative of amorphous product.
9
-AYAA microcrystal growth
A 3.6 molar solution of H PO
by diluting the appropriate volume of 15 M phosphoric acid
85% in water) then adding enough SDS to make a 0.1% IJw/v)
solution in the phosphoric acid. To the acid solution, a mea-
3
4
in distilled water was prepare
(
the 9-AYAA wires partially uncoil, rather than undergoing a
complete collapse in their amorphous product phase. 9-AA,
on the other hand, is known to undergo a [4 + 4] photo-
−
1
sured quantity of the tert-butyl ester to make a 0.1 mg ml
concentration was added directly and briefly sonicated for
minutes to disperse the crystals. In a typical experiment
we added 1 mg ester to 10 ml of 3.6 M H PO /0.1% SDS in a
0 ml glass vial with a PTFE lined screw cap. In general the
4
1,42
dimerization in the solid-state.
The reaction of the
2
cofacial 9-AA molecules leads to a crystal-to-crystal transition,
and we have confirmed that the photoproduct PXRD pattern
has the peaks predicted from the structure of the dimer crys-
3
4
5
mole ratio of SDS to reactant was 10 : 1. The vial was tightly
capped and mounted on a tumble rotator (Labquake tube rota-
tor from Thermo Scientific) set at 8 rpm. The rotator was placed
inside an oven set at 35 °C. The reaction was allowed to mix for
a couple of days depending on the desired length of the
microwires.
3
7
tal (ESI,† Fig. 7). Thus the physical basis of the photoin-
duced motion is different for the two molecules. Both start
as crystalline solids, but the 9-AYAA coiling is driven pre-
dominantly by a unimolecular isomerization that leads to
a crystal-to-amorphous transition, while the 9-AA folding is
driven by [4 + 4] photodimerization of the 9-AA molecules
leading to a crystal-to-crystal transition. We note that more
detailed mechanistic information about the photomechanical
response could be obtained by determining the relation
between specific crystal axes and the coiling or folding. But
measuring the absolute orientations of individual microcrys-
tals before and after irradiation is somewhat complicated
and beyond the scope of the current paper. The main point
is that these types of solid-state photoreactions can lead to
interesting shape changes, provided the crystal has the
appropriate shape.
9-AA microcrystal growth
Microplates of 9-anthraldehyde were grown using similar
−
1
conditions to 9-AYAA. 0.1 mg mL of the acylal precursor
was added to 3.6 M H PO /0.1% SDS and tumble mixed at
5 °C. Characterization of the microplates using an SEM
3
4
3
was unsuccessful because the 9-AA sublimed under the high
vacuum conditions of the SEM.
Characterization
The crystallinity of the microcrystals was confirmed by
observing them using a cross polarized filter in a microscope.
All of the microcrysals exhibited a uniform birefringence,
indicating that they were composed of a single crystal domain.
9-AYAA microwire length measurements were performed by
placing a 20 microliter sample of the microwire suspension
to a microscope glass slide and measuring the length of
approximately 100 microwires. Several samples were collected
and averaged. SEM measurements were performed using
JEOL JSM-6510LV scanning electron microscope. Samples
were sputter coated with Pt prior to scanning. Powder X-ray
diffraction data were collected on a PANalytical Empyrean
X-ray powder diffractometer (CuK radiation, λ = 1.540598 Å,
45 KV/40 mA power) at 296 K.
Conclusion
As mentioned above, we think that the size and shape control
achieved using the chemical reaction-crystal growth method
originates in the slow release of product molecules generated
by an in situ hydrolysis reaction. This growth strategy is sensi-
tive to precursor and surfactant concentrations, temperature,
and agitation speed. It is likely that the ideal set of condi-
tions will depend on the molecule to be crystallized. While
the acid hydrolysis method is only suited to growing crystals
of carboxylic acids and aldehydes, we think that the general
concept may be applicable to the crystallization of other types
of molecules as long as a suitable precursor reaction can be
found. The use of an in situ chemical reaction to control crys-
tal growth provides a new approach to the preparation of
Photomechanical studies were performed using Nikon
Eclipse 80 fluorescence microscope equipped with a 2 MP
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digital camera. The samples were illuminated with 475 nm
light, passing through a band pass filter, from a 100 W
medium pressure Hg lamp.
acid on crystal shape and size, CrystEngComm, 2012, 14,
7792–7799.
14 T. Kim, L. Zhu, L. J. Mueller and C. J. Bardeen, Mechanism
of photo-induced bending and twisting in crystalline micro-
needles and microribbons composed of 9-methylanthracene,
J. Am. Chem. Soc., 2014, 136, 6617–6625.
Acknowledgements
This research was supported by the National Science Founda-
tion grant DMR-1207063 (CJB) and King Abdulaziz City for
Science and Technology (KACST) through Grant AT-30-435
15 A. E. Keating and M. A. Garcia-Garibay, Photochemical solid-
to-solid reactions, in Organic and Inorganic Photochemistry,
ed. V. Ramamurthy and K. S. Schanze, Dekker, New York,
1st edn, 1998, vol. 2, pp. 195–248.
(ROK).
1
6 R. O. Al-Kaysi, A. M. Muller and C. J. Bardeen,
Photochemically driven shape changes of crystalline organic
nanorods, J. Am. Chem. Soc., 2006, 128, 15938–15939.
References
1
M. A. Garcia-Garibay, Molecular crystals on the move: From
single-crystal-to-single-crystal photoreactions to molecular
machinery, Angew. Chem., Int. Ed., 2007, 46, 8945–8947.
N. K. Nath, M. K. Panda, S. C. Sahoo and P. Naumov,
Thermally induced and photoinduced mechanical effects
in molecular single crystals-a revival, CrystEngComm, 2014,
17 D. K. Bucar and L. R. MacGillivray, Preparation and
reactivity of nanocrystalline cocrystals formed via
sonocrystallization, J. Am. Chem. Soc., 2007, 129, 32–33.
18 S. Takahashi, H. Miura, H. Kasai, S. Okada, H. Oikawa and
H. Nakanishi, Single-crystal-to-single-crystal transformation
of diolefin derivatives in nanocrystals, J. Am. Chem. Soc.,
2002, 124, 10944–10945.
2
1
6, 1850–1858.
3
4
5
6
T. Kim, L. Zhu, R. O. Al-Kaysi and C. J. Bardeen, Organic
Photomechanical Materials, ChemPhysChem, 2014, 15,
19 M. J. E. Resendiz, J. Taing and M. A. Garcia-Garibay,
Photodecarbonylations of 1,3-Dithiophenyl Propanone:
Using Nanocrystals to Overcome the Filtering Effect of
Highly Absorbing Trace Impurities, Org. Lett., 2007, 9,
4351–4354.
20 R. O. Al-Kaysi and C. J. Bardeen, General method for the
synthesis of crystalline organic nanorods using porous
alumina templates, Chem. Commun., 2006, 1224–1226.
21 T. W. Odom, V. R. Thalladi, C. J. Love and G. M. Whitesides,
Generation of 30–50 nm structures using easily fabricated,
composite PDMS masks, J. Am. Chem. Soc., 2002, 124,
12112–12113.
22 A. L. Briseno, S. C. B. Mannsfeld, M. M. Ling, S. Liu,
R. J. Tseng, C. Reese, M. E. Roberts, Y. Yang, F. Wudl and
Z. Bao, Patterning organic single-crystal transistor arrays,
Nature, 2006, 444, 913–917.
23 H. Minemawari, T. Yamada, H. Matsui, J. Tsutsumi, S. Haas,
R. Chiba, R. Kumai and T. Hasegawa, Inkjet printing of
single-crystal films, Nature, 2011, 475, 364–367.
4
00–414.
S. Kobatake, S. Takami, H. Muto, T. Ishikawa and M. Irie,
Rapid and reversible shape changes of molecular crystals on
photoirradiation, Nature, 2007, 446, 778–781.
J. T. Good, J. J. Burdett and C. J. Bardeen, Using two-photon
excitation to control bending motions in molecular-crystal
nanorods, Small, 2009, 5, 2902–2909.
P. Naumov, J. Kowalik, K. M. Solntsev, A. Baldridge,
J.-S. Moon, C. Kranz and L. M. Tolbert, Topochemistry and
photomechanical effects in crystals of green fluorescent
protein-like chromophores: effects of hydrogen bonding and
crystal packing, J. Am. Chem. Soc., 2010, 132, 5845–5857.
F. Terao, M. Morimoto and M. Irie, Light-driven molecular-
crystal actuators: rapid and reversible bending of rodlike
mixed crystals of diarylethene derivatives, Angew. Chem., Int.
Ed., 2012, 51, 901–904.
7
8
9
H. Koshima, H. Nakaya, H. Uchimoto and N. Ojima,
Photomechanical motion of furylfulgide crystals, Chem. Lett.,
24 R. O. Al-Kaysi, A. M. Muller, T. S. Ahn, S. Lee and
C. J. Bardeen, Effects of sonication on the size and
crystallinity of stable zwitterionic organic nanoparticles
formed by reprecipitation in water, Langmuir, 2005, 21,
7990–7994.
2
012, 41, 107–109.
H. Koshima, K. Takechi, H. Uchimoto, M. Shiro and
D. Hashizume, Photmechanical bending of salicylideneaniline
crystals, Chem. Commun., 2011, 47, 11423–11425.
1
1
1
0 L. Zhu, R. O. Al-Kaysi and C. J. Bardeen, Reversible
photoinduced twisting of molecular crystal microribbons,
J. Am. Chem. Soc., 2011, 133, 12569–12575.
1 D. Kitagawa, H. Nishi and S. Kobatake, Photoinduced
twisting of a photochromic diarylethene crystal, Angew.
Chem., Int. Ed., 2013, 52, 9320–9322.
2 P. Naumov, S. C. Sahoo, B. Z. Zakharov and E. V. Boldyreva,
Dynamic single crystals: kinematic analysis of photoinduced
crystal jumping (the photosalient effect), Angew. Chem., Int.
Ed., 2013, 52, 9990–9995.
3 T. Kim, L. Zhu, L. J. Mueller and C. J. Bardeen, Dependence of
the solid-state photomechanical response of 4-chlorocinnamic
25 X. Zhang, X. Zhang, W. Shi, X. Meng, C. Lee and S. Lee,
Morphology-Controllable Synthesis of Pyrene Nanostructures
and Its Morphology Dependence of Optical Properties,
J. Phys. Chem. B, 2005, 109, 18777–18780.
26 X. Zhang and X. Zhang, Single-Crystal Nanoribbons,
Nanotubes, and Nanowires from Intramolecular Charge-
Transfer Organic Molecules, J. Am. Chem. Soc., 2007, 129,
3527–3532.
27 X. Zhang, X. Zhang, B. Wang, C. Zhang, J. C. Chang,
C. S. Lee and S.-T. Lee, One- or Semi-Two-Dimensional
Organic Nanocrystals Induced by Directional Supramolecular
Interactions, J. Phys. Chem. C, 2008, 112, 16264–16268.
1
This journal is © The Royal Society of Chemistry 2015
CrystEngComm

View Article Online
Paper
CrystEngComm
2
8 X. Zhang, C. Dong, J. A. Zapien, S. Ismathullakhan, Z. Kang,
J. Jie, X. Zhang, J. C. Chang, C.-S. Lee and S.-T. Lee,
Polyhedral Organic Microcrystals: From Cubes to Rhombic
Dodecahedra, Angew. Chem., Int. Ed., 2009, 48, 9121–9123.
9 Z.-Q. Lin, P.-J. Sun, Y.-Y. Tay, J. Liang, Y. Liu, N.-E. Shi,
L.-H. Xie, M.-D. Yi, Y. Qian, Q.-L. Fan, H. Zhang, H. H. Hng,
J. Ma, Q. Zhang and W. Huang, Kinetically Controlled
as a Mild Reagent for Deprotection of tert-Butyl Carbamates,
Esters, and Ethers, J. Org. Chem., 2006, 71, 9045–9050.
35 R. A. McClelland, Mechanisms of Acylal Hydrolysis in
Sufuric Acid Solutions, Can. J. Chem., 1975, 53, 2763–2771.
36 J. Trotter, The crystal structures of some anthracene
derivatives. VI. 9-Anthraldehyde, Acta Crystallogr., 1959, 12,
922–928.
2
Assembly of
Polyhedral Micro/Nanocrystals, ACS Nano, 2012, 6,
309–5319.
a
Spirocyclic Aromatic Hydrocarbon into
37 M. Ehrenberg, The Crystal Structure of the Dimer of 9-Anthr-
aldehyde, Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst.
Chem., 1968, 24, 1123–1125.
5
3
3
0 R. O. Al-Kaysi and C. J. Bardeen, Reversible photoinduced
38 V. Kavala and B. K. Patel, Reinvestigation of the Mechanism
of gem-Diacylation: Chemoselective Conversions of
Aldehydes to Various gem-Diacylates and Their Cleavage
under Acidic and Basic Conditions, Eur. J. Org. Chem., 2005,
441–451.
shape changes of crystalline organic nanorods, Adv. Mater.,
2
007, 19, 1276–1280.
1 L. Zhu, F. Tong, C. Salinas, M. K. Al-Muhanna, F. S. Tham,
D. Kisailus, R. O. Al-Kaysi and C. J. Bardeen, Improved
Solid-State Photomechanical Materials by Fluorine Substitu-
tion of 9-Anthracene Carboxylic Acid, Chem. Mater., 2014,
39 K. W. Benz and W. Neumann, Introduction to Crystal Growth
and Characterization, Wiley, New York, 2014.
2
6, 6007–6015.
40 T. Kim, M. K. Al-Muhanna, S. D. Al-Suwaidan, R. O. Al-Kaysi
and C. J. Bardeen, Photo-induced Curling of Organic Molecular
Crystal Nanowires, Angew. Chem., Int. Ed., 2013, 52, 6889–6893.
41 D. P. Craig and P. Sarti-Fantoni, Photochemical Dimerisation
in Crystalline Anthracenes, Chem. Commun., 1966, 742–743.
42 S. Ates and A. Yildiz, Determination of the Absolute
Quantum Efficiency of the Luminescence of Crsytalline
Anthracene and of Meso-Dimeso Derivatives Using Photo-
acoustic Spectroscopy, J. Chem. Soc., Faraday Trans. 1, 1983,
79, 2853–2861.
3
3
3
2 M. Campione, R. Ruggerone, S. Tavazzi and M. Moret,
Growth and characterization of centimetre-sized single
crystals of molecular organic materials, J. Mater. Chem.,
2
005, 15, 2437–2443.
3 L. Zhu, R. O. Al-Kaysi, R. J. Dillon, F. S. Tham and
C. J. Bardeen, Crystal structures and photophysical properties
of 9-anthracene carboxylic acid derivatives for photomechanical
applications, Cryst. Growth Des., 2011, 11, 4975–4983.
4 B. Li, M. Berliner, R. Buzon, C. K. F. Chiu, S. T. Colgan,
T. Kaneko, N. Keene, W. Kissel, T. Le, K. R. Leeman,
B. Marquez, R. Morris, L. Newell, S. Wunderwald, M. Witt,
J. Weaver, Z. Zhang and Z. Zhang, Aqueous Phosphoric Acid
43 H. V. Huynh and R. Jothibasu, Syntheses and Catalytic
Activities of Pd(II) Dicarbene and Hetero-Dicarbene Com-
plexes, J. Organomet. Chem., 2011, 696, 3369–3375.
CrystEngComm
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