Layered dinitrostilbene-based molecular solids with tunable micro/nanostructures and the reversible fluorescent response to explosives

Article abstract of DOI:10.1021/cg400979d

The ability to modulate and control the fluorescence properties of molecular solids at the micro/nanoscale is important to develop high-performance optoelectronic materials and sensors. Here we report the tunable one-photon and two-photon fluorescence as well as micro/nanostructures of dinitrostilbene- based (DNS) chromophore by the formation of layered multicomponent crystals with guanidinium cation (GD) through hydrogen-bonding assembly. The as-prepared GD₂DNS bulk crystal shows a red-shift emission as well as enhanced photoluminescence quantum yield and fluorescence lifetime compared with those of the Na₂DNS sample, which is related to the structural transfer of DNS from staggered arrangement to parallel fashion within the crystal. Periodic density functional theoretical calculations further show that the introduction of different cationic units can modify the frontier orbital distribution and electronic structure of DNS anions within the multicomponent crystals. Moreover, one-dimensional GD₂DNS nanobelts with well-aligned orientation can be further obtained by a combined ultrasound and coprecipitation method. The GD₂DNS nanobelts undergo a blue-shift fluorescence compared with its bulk crystal, and exhibit alternated photoresponse (such as emission wavelength and intensity) upon interaction with different nitroaromatic explosives (trinitrotoluene, picric acid and m-dinitrobenzen). Therefore, this work gives a facile bottom-up self-assembly rout to prepare organic multicomponent materials with tunable fluorescence properties and micro/nanostructures, which can be potentially used as luminescence detector for nitroaromatic explosives.

Full text of DOI:10.1021/cg400979d

Article
pubs.acs.org/crystal
Layered Dinitrostilbene-Based Molecular Solids with Tunable Micro/
Nanostructures and the Reversible Fluorescent Response to
Explosives
Dongpeng Yan,* Yanjun Lin, Qingyun Meng, Minjun Zhao, and Min Wei
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, P. R. China
S
* Supporting Information
ABSTRACT: The ability to modulate and control the fluorescence properties of
molecular solids at the micro/nanoscale is important to develop high-performance
optoelectronic materials and sensors. Here we report the tunable one-photon and
two-photon fluorescence as well as micro/nanostructures of dinitrostilbene-based
(DNS) chromophore by the formation of layered multicomponent crystals with
guanidinium cation (GD) through hydrogen-bonding assembly. The as-prepared
GD2DNS bulk crystal shows a red-shift emission as well as enhanced photo-
luminescence quantum yield and fluorescence lifetime compared with those of the
Na2DNS sample, which is related to the structural transfer of DNS from staggered
arrangement to parallel fashion within the crystal. Periodic density functional
theoretical calculations further show that the introduction of different cationic units
can modify the frontier orbital distribution and electronic structure of DNS anions
within the multicomponent crystals. Moreover, one-dimensional GD2DNS nanobelts with well-aligned orientation can be further
obtained by a combined ultrasound and coprecipitation method. The GD2DNS nanobelts undergo a blue-shift fluorescence
compared with its bulk crystal, and exhibit alternated photoresponse (such as emission wavelength and intensity) upon
interaction with different nitroaromatic explosives (trinitrotoluene, picric acid and m-dinitrobenzen). Therefore, this work gives a
facile bottom-up self-assembly rout to prepare organic multicomponent materials with tunable fluorescence properties and
micro/nanostructures, which can be potentially used as luminescence detector for nitroaromatic explosives.
nanomaterials can present alternated photophysical properties
compared with those of the bulk, due to the size-dependent
effect.16 Moreover, low-dimensional organic micro/nanostruc-
tures also endowed great opportunities to develop miniaturized
optoelectronic devices, such as the optical waveguide and fiber
materials.17 However, the investigation on the optical proper-
ties of organic multicomponent micro/nanomaterials is still in
an early stage, and examples are rather few.18 Such self-
assembled systems organized from two or more organic units
can result in unique photophysical behaviors,19 which also
supply an effective way to tune the compositions within the
micro/nanostructures and thus extends the design and
assembly scope of organic solid materials.
With the developments of both the multicomponent
materials and micro/nanostructures in mind, in this work, we
have designed and developed the new type of organic solid-
state materials by the assembly of 4,4′-dinitrostilbene-2,2′-
disulfonate (DNS, Scheme 1A) anion with the guanidinium
cation (GD, Scheme 1B). DNS is generally used as a
fluorescent brightener in the chemical industry; moreover, the
phenylenevinylene or stilbene unit in DNS has also attracted
much interest because of its excellent optical and electronic
1. INTRODUCTION
Organic photoactive materials have received considerable
attention due to their potential applications in fields of dye
lasers,1 light-emitting diodes,2 and fluorescent sensors.3 From
the perspectives of both fundamental research and practical
applications, the regulation of the solid-state luminescent
properties of an organic material is important to realize
multicolor displays and tunable light-emitting device.4 To date,
the key strategy to tune the fluorescence of a compound is to
alter its molecular arrangement and packing mode.5 In this case,
intermolecular interactions within the organic solid can be
further modified.6 Specifically for small organic chromophores,
the formation of polymorphisms7 and multicomponent
crystals8 can result in the changeable luminescence. Compared
with the polymorphisms, the multicomponent crystals (such as
cocrystals9 and salts10) present more predictability, which can
be designed by appropriate selection and design of building
blocks and the interaction types (such as hydrogen-11 and
halogen-bonding12) within the crystal based on the supra-
molecular assembly principle.13 Several studies have shown that
the construction of multicomponent crystals can result in the
fine-tuning of supramolecular structures and thus further tailor
the photo-related properties of organic solid state materials.14
Recently, a great deal of effort has been paid to the synthesis
of pure organic chromophores with variable morphologies at
the micro/nanometer level.15 The as-obtained organic micro/
Received: June 29, 2013
Revised: August 8, 2013
Published: August 12, 2013
© 2013 American Chemical Society
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shows that the Na2DNS crystal features P21/c symmetry. Figure
1a shows the typical side view of the Na2DNS structure in the
(100) direction, in which the adjacent NDS anions exhibit a
staggered-type arrangement with the center distance of ca. 0.55
nm. The fluorescence spectra for the Na2DNS sample were
shown in Figure 1b. The excitation and emission positions are
located at 441 and 485 nm, respectively. Moreover, the power-
dependent emission spectrum of an individual crystal was
measured for comparison with that of the bulk. Upon excitation
by a laser at 405 nm, the Na2DNS microcrystal showed
enhanced fluorescent brightness with increasing excitation
intensity, as shown in Figure 1c. Their emission intensities
correlate nearly linearly with the excitation power (inset plot),
illustrating that a one-phonon emission process is involved. The
main emission peak of Na2DNS appears at approximately 485
nm with the CIE 1931 color coordinates of (0.283, 0.458),
illustrating that no obvious shift in the emission maximum of
the individual crystal was observed compared to the Na2DNS
ensemble. The microcrystalline compositions with well-defined
bluish green emission can be visible easily by the naked eye, as
shown in the inset of Figure 1c.
B. GD2DNS Single Crystal. By mixing an aqueous solution
of Na2DNS (0.005 mol) and an aqueous solution of GD (0.01
mol), the single crystal of GD2DNS can readily be formed upon
evaporation of the solvent. The crystal structure exhibited a
layered structure with P21/n symmetry, and the unit cell
contains one crystalline water molecule. The DNS anions
within the same layer present a parallel arrangement with the
average distance between the neighboring DNS of 0.68 nm and
the relative orientation of ca. 32.8°. Such arrangement fashion is
favorable to the formation of the J-type aggregation within the
crystals, and the presence of a layered stacking structure with a
periodicity of 1.61 nm is related to the strong H-bonding
assembly within the GD2DNS. Different from the common
GD-based assembled systems,21 H-bonding modes in GD2DNS
consist of N−H···OS and N−H···ON between the GD
and DNS units as well as N−H...O−H and SO...H−O
between the GD/DNS units and H2O (Figure 2a). Figure 2b
shows the excitation and emission spectra with the positions at
450 and 517 nm, respectively.
Scheme 1. Chemical Structures of (A) 4,4′-Dinitrostilbene-
2,2′-disulfonate (DNS) Anion and (B) Guanidinium Cation
(GD)
properties.20 The selection of the guanidinium cation is based
on the fact that it has been successfully served as a hydrogen-
bonding coassembled motif with sulfonate-bearing anions for
engineering bulk crystal topologies.21 However, few guanidi-
nium sulfonate systems have been observed in nanostructured
crystals, and their exact properties at the micro/nanometer
scale are still unknown. Compared with the pure sodium salt of
DNS (Na2DNS), the as-prepared GD2DNS crystal at the
micrometer size undergoes a red-shift emission as well as an
enhanced fluorescence lifetime and photoluminescence quan-
tum yield (PLQY). Periodic density functional theoretical
(DFT) calculations further show that the difference in the
cationic units can influence the frontier orbital distribution and
electronic structure of DNS anions within the multicomponent
crystals. Moreover, one-dimensional (1D) GD2DNS nanobelts
with high orientation can also be fabricated by a coprecipitation
method under an ultrasound condition. The GD2DNS
nanobelts exhibit different photoresponse (emission wave-
length and intensity) upon interaction with different nitro-
aromatic explosives. With a combination of experimental
methodology and theoretical study on the micro/nanostruc-
tures, this work not only provides a feasible way to construct
highly ordered micro/nanosized multicomponent organic
solids but also gives a detailed understanding of the energy
levels of the DNS-based materials. It is also expected that the
GD2DNS nanobelt system can potentially be applied in the
field of luminescence sensors for explosives.
Figure 3 (panels a and b) show the microcrystalline
GD2DNS sample under optical and fluorescence microscopy,
and the needlelike compositions can be visualized easily by the
naked eye. A typical scanning electron microscopy (SEM)
image of the GD2DNS crystal ensemble is shown in Figure 3c.
Further magnification shows that the crystal has a relatively
smooth surface, and several defects can also be detected. The
width of the crystals can be estimated to be ca. 10 μm, as shown
2. RESULTS AND DISCUSSION
A. Sodium Salt of DNS. The single crystal of Na2DNS can
be obtained by a single-step neutralization of H2DNS and
NaOH with a 1:2 ratio. The single crystal structure analysis
Figure 1. (a) Crystal structure [viewed from the (100) direction], (b) fluorescence spectra, and (c) power-dependent emission (inset shows the
selected crystals under a fluorescence microscope) of Na2DNS.
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Figure 2. (a) Crystal structure [viewed from (100) direction] of GD2DNS (the blue dash line is the H-bonding interaction) and (b) its fluorescence
spectra.
Figure 4. Power-dependent emission (inset shows the selected crystals
under a fluorescence microscope) of Na2DNS.
power of 80 mW is visible to the naked eye, as shown in the
inset of Figure 4.
C. Comparison of Photophysical Properties of
GD2DNS and Na2DNS. Compared with the microcrystalline
Na2DNS, the GD2DNS single crystal undergoes a red-shift
emission of ca. 32 nm. Moreover, the photoluminescence
quantum yield (PLQY) enhanced from 0.37% (Na2DNS) to
1.65% (GD2DNS). In our opinion, the red shift can mainly be
attributed to the fact that the arrangement fashion of the DNS
anions transfer from the staggered form to the parallel stacking,
as illustrated by the crystal structure analysis. As a result, the
overlap of the electronic density of the DNS chromophore
Figure 3. (a and b): GD2DNS samples under optical and fluorescence
microscopes; (c and d): SEM profiles for the GD2DNS crystal at
occurs. To further study the excited-state properties of the
DNS-based crystal, the fluorescence lifetime of the samples was
further recorded. The typical fluorescence decay curves of
Na2DNS and GD2DNS are shown in Figure 5 and their
corresponding fluorescence lifetimes were 0.34 and 0.70 ns,
respectively. The enhancement of the fluorescence lifetimes is
also in agreement with the latter structure favoring the
formation of molecular excimers and J-type aggregations of
DNS.
It was noted that the stilbene compound can be a two-
photon emissive chromophore, and thus, two-photon excited
fluorescence measurements were further made. Upon excitation
by 800 nm of laser light, both the Na2DNS (Figure 6a) and
GD2DNS (Figure 6b) crystals exhibit well-defined green-light
photoemission with the position at 492 and 527 nm,
respectively; the emission intensity shows a nearly quadratic
increase as a function of the incident energy, confirming the
two-photon absorption/emission mechanism of the DNS-based
organic solids. Therefore, it can be concluded that the two-
photon fluorescence can also be tuned by regulating the
different magnifications; (e) TEM and (f) HRTEM images of a single
GD2DNS crystal.
in both SEM (Figure 3d) and transmission electron microscopy
(TEM, Figure 3e) images. Figure 3f shows a typical high-
resolution TEM (HRTEM) image of the edge of the crystal, in
which the crystal plane is not well-solved, probably due to high
thickness of the selected sample.
The power-dependent emission spectrum of a single
GD2DNS crystal was further measured and compared with
that of the bulk. Upon laser excitation at 405 nm, the single
crystal showed increasing fluorescence intensity with increasing
excitation intensity, as shown in Figure 4. The main emission
peak of the selected single crystal appeared at ca. 520 nm with
the CIE 1931 color coordinates of (0.279, 0.653), and no
obvious shift in the emission maximum of the individual crystal
was observed compared to the ensemble. In addition, the
typical dark-field image of the selected sample excited with laser
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Figure 5. The fluorescence decay curves of the GD2DNS and
Na2DNS.
arrangement fashion of DNS, and no obvious red- or blue shift
of the two-photon fluorescence can be observed compared with
those excited at 360 nm UV light, illustrating that the same
emission process from one-photon and two-photon excited
states to the ground state are involved.
Figure 7. (A and C) HOMOs and (C and D) LUMOs profiles for
Na2DNS and GD2DNS.
D. Theoretical Calculations on the Na2DNS and
GD2DNS. To better understand the energy level and electronic
structure of the DNS-based multicomponent systems, periodic
density functional theoretical (PDFT) calculations were
performed on the Na2DNS and GD2DNS crystal models. For
the Na2DNS system, total electronic densities of states
(TDOS) and partial electronic densities of states (PDOS)
analyses (Figures S1 and S2 of the Supporting Information)
show that the highest occupied molecular orbitals (HOMOs)
are mainly populated on stilbene units and −SO3 group in DNS
as well as the Na atom, while the lowest unoccupied molecular
orbitals (LUMOs) are solely located on 2p orbitals of the C
atoms in DNS anions. This can be visualized by observing the
frontier orbital profiles of Na2DNS, as shown in Figure 7
(panels A and B), and such a result further indicates that the
energy or electron transfer occurs between DNS and Na atom
during the fluorescence process. For the GD2DNS system,
around the Fermi level, the TDOS mainly consisted of the 2p
electrons of the C atoms in the DNS; both the HOMOs and
LUMOs are contributed from the stilbene units and −NO2
group (Figures S3 and S4 of the Supporting Information),
suggesting that no obvious intramolecular and intermolecular
energy transfer appears during the photoexcitation/emission
process. These results show that the introduction of different
cationic units can influence the frontier orbital distribution and
electronic structure of DNS anions within the multicomponent
crystals, which may further influence the luminescent properties
of the organic solids, as shown in Experimental Section above.
E. Fabrication of GD2DNS Nanobelt. The GD and DNS
with a 2:1 ratio were separately dissolved to obtain an aqueous
solution and then simultaneously injected into a chloroform
solution under ultrasound condition; the slurry sample was
filtered or extended on a glass substrate. The powder XRD
pattern of the obtained sample (Figure 8) is consistent well
with the simulated XRD result from the GD2DNS single
crystals, further confirming that the multicomponent GD2DNS
sample can be obtained by the combined ultrasound and
coprecipitation method. The synthesis of the GD2DNS has
taken advantage of the strong H-bonding recognition between
the compositions. In addition, the strong (020) reflection
Figure 6. Two-photon fluorescence spectra of the (a) Na2DNS and (b) GD2DNS excited by an 800 nm laser under different pump intensities. Insets
show the changes in intensity at 492 and 527 nm with increasing pump intensity.
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9d. Figure 9e shows a typical TEM image of a single nanobelt,
in which well-defined crystal planes with a lattice distance of
∼1.6 nm can be further resolved along the long-axis direction of
the nanobelt, as shown in the HRTEM image (Figure 9f),
suggesting a high degree of molecular arrangement within the
nanocrystal. Moreover, such observation is also in agreement
with the preferred orientation in the (010) direction, as shown
in the XRD pattern.
The photophysical properties of the as-prepared GD2DNS
nanobelts were further detected to obtain the insight into the
size-dependent effect of the multicomponent GD2DNS system.
The typical fluorescence spectra are shown in Figure 10a, and
the excitation and emission position appear at 452 and 496 nm,
respectively. Compared with the GD2DNS crystal at the
micrometer level, a blue-shift of ca. 24 nm occurs for the
nanobelt samples; such behavior may be related to the fact that
the decrease of the size results in lattice softening and weaker
interaction energies, and thus the band gap was further
increased.16 The analysis of the fluorescence decays (Figure
10b) reveals that the fluorescence lifetime of the nanobelt
samples is prolonged to 0.85 ns, as compared to the
microdimensional crystals (0.70 ns). This increase may be
attributed to the deaggregation of the crystals, which decrease
the excited-state nonradioactive relaxation from excitonic
coupling between the crystal particles. To the best of our
knowledge, although the size-dependent optical properties have
largely been reported in both inorganic and pure organic
nanomaterial systems,22 very few studies have focused on such
multicomponent organic nanobelts. In addition, power-depend-
ent excitation on the GD2DNS nanobelts under 405 and 800
nm laser was further measured; it can be observed that the
nanobelt sample exhibits both one-photon (Figure 11a) and
two-photon (Figure 11b) emission with the emission peak of
ca. 500 nm, which is close to that of the nanobelt ensemble.
F. Reversible Photoresponse of GD2DNS Nanobelt to
Nitroaromatic Explosive Compounds. Recently, the
organic fluorescence-based sensor for the detection of
explosives has drawn much attention due to the high
sensitivity.23 In this work, it was noted that the GD2DNS
nanobelt features a highly exposed surface, which can contact
with the analytes effectively. Herein, the ability of the GD2DNS
nanobelt to detect nitroaromatic explosives [trinitrotoluene
(TNT), picric acid (PA) and m-dinitrobenzen (mDNB)] was
studied by adding small amount of explosives in methanol
solution with 1, 5, 10, and 20 ppm into the GD2DNS nanobelt
samples. Figure 12A shows the typical emission spectra of the
GD2DNS nanobelt responding to the TNT sample. It can be
observed that the fluorescent position undergoes a red shift
toward 536 nm upon interaction with TNT, and the
photoemission intensity of the GD2DNS nanobelt decreases
systematically upon increasing the TNT concentration. Similar
behavior can also be observed when detecting the PA and
mDNB explosives, in which the emissive wavelengths of the
GD2DNS nanobelt moved to 520 and 511 nm, respectively
(Figure 12B and 12C). Moreover, the recovery and
reproducibility of the fluorescence for the GD2DNS nanobelt
were further investigated. After the nanobelt was eluted with
methanol and then heated for full removal of the explosives, the
fluorescence wavelength and intensity can nearly recover to
their initial state. Figure 13 shows the typical examples of the
variation of the luminescence dependent on the alternate
treated with 1 ppm TNT and methanol over four continuous
cycles, which shows that the wavelength and the intensity ratio
Figure 8. Experimental and simulated XRD results of the GD2DNS
sample.
accompanied by the absences of (002) and (004) reflections in
the XRD profile can be observed, suggesting extremely good b
axis oriented assembly of the as-prepared GD2DNS sample.
Figure 9a and 9b show the obtained sample under optical and
Figure 9. (a and b) GD2DNS nanobelts under optical and
fluorescence microscopes. (c and d) SEM profiles for the GD2DNS
sample on a glass substrate at different magnifications. (e) TEM and
(f) HRTEM images of a single GD2DNS nanobelt.
fluorescence microscopes, from which it can be observed that
the GD2DNS exhibits one-dimensional (1D) beltlike morphol-
ogy, which may be related to the 1D anisotropy of the DNS
anions in the long-axis direction. The well-oriented nanostruc-
tures with high dispersion on the substrate can be obtained by
diluting the as-prepared sample, as shown in Figure 9c. On the
basis of the SEM observation, the products can be regarded as
1D nanobelts, and each individual nanostructure has a smooth
surface and a uniform width of ca. 600 nm, as shown in Figure
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Figure 10. (a) Fluorescence spectra and (b) fluorescence decay profile of the GD2DNS nanobelts and microcrystal.
Figure 11. Power-dependent emission (inset shows the selected crystals under a fluorescence microscope) of the GD2DNS nanobelt excited at (a)
405 and (b) 800 nm.
between two states can readily be cycled, confirming the
recovered nanobelt could also be reused immediately.
PLQY and fluorescence lifetime compared with the Na2DNS
sample, suggesting that the alternation of the fluorescence
properties can be achieved by modulating the arrangement
fashion of the DNS anions within the crystal. Furthermore, the
GD2DNS nanobelt with well-aligned orientation can be further
obtained by a combined ultrasound and coprecipitation
method. The fluorescence of the GD2DNS nanobelt undergoes
a blue shift compared with its bulk crystal, suggesting the
luminescent properties of the multicomponent system can also
be modified by adjusting the micro/nanometer size. Moreover,
the GD2DNS nanobelts exhibit a reversible photoresponse
(such as wavelength and intensity) upon treatment with
different nitroaromatic explosives, indicating that the as-
prepared nanobelt can be potentially used as a luminescence
detector for explosives. It is expected that the strategy to form
micro/nanocrystal with tunable components and morphologies
can be extended to other chromophore systems for developing
new types of organic luminescent materials and sensors.
Further work is still underway with the research on the gas
phase detection of nitroaromatic compounds.
To date, most reported fluorescent sensors24 for detecting
explosives are based on the fluorescence quenching mechanism
as a result of interaction between chromophore materials and
analytes; their fluorescence emissive position has nearly no
change, and such intensity-based detection may be largely
influenced by the stability of the excitation light source. For this
GD2DNS nanobelt system, it can be observed that the
fluorescence wavelength can vary dependent on three different
nitroaromatic explosives, which facilitates the detection for the
analytes. From a molecular recognition perspective, the
electron-withdrawing unit (−NO2 group) in nitroaromatic
compounds can potentially form a hydrogen-bond interaction
with the GD cation in the GD2DNS nanobelt, which may
further influence the electronic structure of the DNS anions
within the GD2DNS nanobelt and thus alter the emission
behaviors of the nanobelt. The remarkable change in the
luminescence and the reversibility guarantee that the as-
prepared nanobelt can potentially be used as an explosive-
induced luminescence sensor.
4. EXPERIMENTAL SECTION
3. CONCLUSION
4.1. Reagents. 4,4′-Dinitrostilbene-2,2′-disulphonic acid (H2DNS)
and guanidinium chloride (GD), NaOH, and chloroform were
purchased from Sigma Chemical Company Ltd. and used without
further purification.
4.2. Synthesis of Sodium Salt of DNS and Microsized
GD2DNS. A 100 mL aqueous solution containing H2DNS (0.01 mol)
and NaOH (0.02 mol) was slowly evaporated, and the single crystal of
In summary, well-organized dinitrostilbene-based multicompo-
nent organic crystals with tunable micro/nanostructures have
been fabricated. The as-prepared GD2DNS bulk crystal exhibits
a 2D pillared structure with the chromophores parallel with
each other and shows a red-shift emission as well as enhanced
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Figure 12. GD2DNS nanobelts (a) before and (b) after treatment with different concentrations (1, 5, 10, and 20 ppm) of (A) TNT, (B) PA, and
(C) mDNB.
Figure 13. The fluorescent spectra of the GD2DNS nanobelt after alternate treatment by TNT (1 ppm) and methanol over four continuous
reversible cycles [the insets show the fluorescent wavelength and the intensity ratio between the maximum wavelengths (495 and 536 nm) of two
states].
Na2DNS was formed within two weeks. Single crystals of GD2DNS
were obtained by mixing a 50 mL aqueous solution of Na2DNS (0.005
mol) and a 50 mL aqueous solution of GD (0.01 mol) and were
allowed to evaporate within one day. Thermogravimetry analysis
(TGA, Figure S5 of the Supporting Information) shows that the
dehydration occurs for both the samples before 150 °C and the
amount of water in the samples can be estimated as 18.6% and 6.4%,
which is close to the results based on single crystal analysis (19.4% and
6.2%). Elemental analysis gave C, 28.8%; H, 3.5%; N, 4.8%; S, 11.0%
and C, 33.1%; H, 4.1%; N, 19.2%; S, 10.9% for the Na2DNS and
GD2DNS samples, respectively. Therefore, the chemical compositions
of two samples can be determined as C14H8N2S2O10Na2(6H2O) and
(CN3H6)1.96(C14H8N2O10S2)(2H2O).
4.3. Fabrication of GD2DNS Nanobelts. The nanobelts were
obtained by a combined ultrasound and coprecipitation method. In a
typical process, 100 mL of an aqueous solution containing 0.002 mol
of GD and 100 mL of an aqueous solution containing 0.001 mol of
DNS were simultaneously added to 50 mL of a chloroform solution
under low-intensity ultrasonic radiation (using an ultrasonic cleaning
bath with a frequency of 25 kHz) and mixed for 3 min. The resulting
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slurry was extended on a glass or quartz substrate and allowed to dry
naturally under ambient conditions.
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Material Studio.26 The single crystal structures of Na2DNS and
GD2DNS were selected as the initial models, which were optimized by
the Perdew−Wang (PW91)27 generalized gradient approximation
(GGA) method with the double numerical basis sets plus the
polarization function (DNP). The SCF convergence criterion was
within 1.0 × 10−5 hartree/atom, and the convergence criterion of
structure optimization was 1.0 × 10−3 hartree/bohr. The Brillouin
zone (BZ) was sampled by 1 × 1 × 1 k points, and test calculations
revealed that an increased number of k points does not influence the
results.
4.5. Characterization. The powder X-ray diffraction patterns were
recorded on a X-Pert PRO MPD powder X-ray diffractometer, using
Cu Kα radiation (0.154184 nm) at 30 kV, 40 mA with a scanning rate
of 10°/min, and a 2θ angle ranging from 3 to 50°. Single crystal X-ray
diffraction data were collected on a Nonius KappaCCD diffractometer
equipped with a graphite monochromator and an Oxford cryostream,
using Mo Kα radiation. Thermogravimetry was measured on a PCT-
1A thermal analysis system under ambient atmosphere with a heating
rate of 10 °C/min. Carbon, hydrogen, nitrogen, and sulfur analyses
were carried out using a Perkin-Elmer Elementarvario elemental
analysis instrument. The solid-state fluorescence spectra were recorded
on a RF-5301PC fluorospectrophotometer with 360 nm excitation
light. The width of both the excitation and emission slit was 3 nm.
PLQY and 1931 CIE color coordinates were measured using an
HORIBA Jobin Yvon FluoroMax-4 spectrofluorometer, equipped with
an F-3018 integrating sphere. Two-photon fluorescence of the samples
was excited by a 800 nm laser on a Tsunami-Spitfire-OPA-800C
ultrafast optical parameter amplifier (Spectra-Physics). The fluores-
cence images were obtained on an Olympus U-RFLT50 fluorescence
microscope. The morphology of samples was investigated using a
scanning electron microscope (SEM Hitachi S-3500) equipped with
an energy-dispersive X-ray analysis (EDX) attachment, and the
accelerating voltage applied was 20 kV.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Total and partial electronic density of states (e.g., TDOS and
PDOS) profiles for Na2DNS (Figure S1); TDOS and PDOS
profiles for different atoms in Na2DNS (Figure S2); TDOS and
PDOS profiles for GD2DNS (Figure S3); TDOS and PDOS
profiles for different atoms in GD2DNS (Figure S4);
Thermogravimetry analysis of the (a) Na2DNS and (b)
GD2DNS samples (Figure S5). This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: yandongpeng001@163.com and yandp@mail.buct.
edu.cn. Fax: +86-10-64425385. Tel: +86-10-64412131.
(10) (a) Anthony, S. P.; Varughese, S.; Draper, S. M. Chem. Commun.
2009, 7500. (b) Yan, D.; Delori, A.; Lloyd, G. O.; Patel, B.; Frisc
̌ ̌ ́
ic, T.;
Day, G. M.; Bucar, D.-K; Jones, W.; Lu, J.; Wei, M.; Evans, D. G.;
̌
Duan, X. CrystEngComm 2012, 14, 5121. (c) Yan, D.; Patel, B.; Delori,
A.; Jones, W.; Duan, X. Cryst. Growth Des. 2013, 13, 333.
Notes
The authors declare no competing financial interest.
(11) (a) Yan, D.; Delori, A.; Lloyd, G. O.; Frisc
Jones, W.; Lu, J.; Wei, M.; Evans, D. G.; Duan, X. Angew. Chem., Int.
Ed. 2011, 50, 12483. (b) Yan, D.; Bucar, D. K.; Delori, A.; Patel, B.;
̌ ̌ ́
ic, T.; Day, G. M.;
ACKNOWLEDGMENTS
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Lloyd, G. O.; Jones, W.; Duan, X. Chem.Eur. J. 2013, 19, 8213.
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This work was supported by the National Basic Research
Program of China (Grant 2014CB932103), the National
Natural Science Foundation of China, and the 111 Project
(Grant B07004), Central University Research Funds, and
Program for Changjiang Scholars, and the Innovative Research
Team in University (PCSIRT: IRT1205).
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