A Λ-shaped cyanostilbene derivative: Multi-stimuli responsive fluorescence sensors, rewritable information storage and colour converter for w-LEDs

Article abstract of DOI:10.1039/c8tc02973c

A new Λ-shaped α-cyanostilbene derivative (TSA) containing an active amino group with fluorescence emission both in solution and the solid state was designed, synthesized and characterized. Its colour and fluorescence emission can be switched by external stimuli including acid/base, trinitrophenol (picric acid, PA) and grinding. The ¹H NMR spectra of TSA were recorded before and after alternately adding trifluoroacetic acid (TFA) and triethylamine (TEA), which confirmed that acidichromism originated in the transformation of protonation/deprotonation between TSA and TSA-H⁺. Powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) revealed the crystalline-amorphous state transformation between the original and ground compounds, and this transformation could reasonably account for the mechanochromic (MFC) luminescence properties. The results revealed that TSA can be used as a fluorescence sensor for acid/base and PA, and as a rewritable information storage material. Moreover, it can also be applied in white light-emitting diodes (w-LEDs) based on its desirable fluorescence emission in the solid state.

Full text of DOI:10.1039/c8tc02973c

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PAPER
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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
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ARTICLE
A Λ-shaped cyanostilbene derivative: multi-stimuli
Cite this: DOI: 10.1039/x0xx00000x
responsive
fluorescence
sensors,
rewritable
information storage and colour converter for w-LED
Received 00th January 2012,
Accepted 00th January 2012
Wenyan Fanga,b, Wang Zhaob, Pan Peib, Rui Liub, Yuyang Zhanga, Lin Konga,
Jiaxiang Yanga,c*
DOI: 10.1039/x0xx00000x
www.rsc.org/
A new Λ-shaped α-cyanostilbene derivative (TSA) containing active amino-group with
fluorescence emission both in solution and solid state was designed, synthesized and
characterized. Its colour and fluorescence emission can be switched by external stimuli
1
including acid/base, trinitrophenol (picric acid, PA) and grinding. The H NMR spectra of
TSA were measured before and after alternately adding trifluoroacetic acid (TFA) and
triethylamine (TEA), which confirmed that the acidichromism originated in the
transformation of protonation/deprotonation between TSA and TSA-H+. Powder X-ray
diffraction (PXRD), differential scanning calorimetry (DSC) and scanning electron
microscopy (SEM) revealed the crystalline-amorphous state transformation between the
original and ground compounds, and this transformation could reasonably account for the
mechanochromic (MFC) luminescent properties. The results revealed that TSA can be used
as fluorescence sensors for acid/base and PA, and as rewritable information storage material.
Moreover, it can also be applied in white light-emitting diode (w-LED) based on its
desirable fluorescence emission in solid state.
and can be used to suitable and versatile option for the
development of functional materials.28 It is well known that a
1. Introduction
Stimuli-responsive organic fluorescent materials have attracted great number of α-cyanostilbene derivatives have the
considerable interest due to their potential applications, such as advantages of relatively simple synthetic procedures and
fluorescent sensors,1-2 bioimaging,3-5 memory chips,6-7 logic AIE/AIEE-activity due to the steric and electronic effect of
operation,8-10 optical encoding,11-12 optical switch,13-14 data cyano group.29-33 Although many stimuli-responsive properties
storage,15-21 security paper or security ink,21-27 and so on. of α-cyanostilbene derivatives have been reported, multi-stimuli
Generally, most organic fluorescent materials suffer from an responsive of them have been relatively less reported so far.
aggregation-caused quenching (ACQ) effect in the aggregate or
Currently, white light-emitting diodes (w-LEDs) have been
solid state, which restricted the scope of their practical investigated widely due to their extraordinary advantages, such
applications. On the contrary, aggregation-induced emission as energy saving, environmental friendliness, high luminous
(AIE) or aggregation-induced enhanced emission (AIEE) efficiency, compact size, fast response time (10-20 ns) and long
contributes to the strong fluorescent emission in the solid-state lifetime.34-40 However, many commercial phosphor-converted
but weak or even no emission in solution. Although some w-LEDs employing inorganic phosphors still suffer some
fluorescent materials could emit efficiently both in solution and weaknesses, such as utilizing expensive rare-earth starting
solid state, they is only achieving in one system for multi- materials, the rigorous synthetic procedures (typically prepared
stimuli responsive applications. Therefore, developing multi- under 1800 °C, 0.5 MPa N2 pressure) and serious photon
stimuli responsive fluorescent materials both in solution and in reabsorption phenomenon, and so on.41-46 Hence, it is essential
solid state for their applications in dual system remains a great to synthesize organic small molecules luminescence materials
challenge.
applied in w-LEDs by using low-cost raw materials with simple
Recently, it is worth highlighting the significant interest in and easily controlled synthesis procedures.
the α-cyanostilbene derivatives, because they have exhibited
Based on the above considerations, in this work, a novel Λ-
remarkable optical features and interesting electrical properties, shaped α-cyanostilbene derivative (TSA) containing active
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amino-group was designed and synthesized by introducing the The synthesis route is shown in Scheme 1
α-cyanostilbene unit and active amino-group into structure of
.
molecule. It is well known that the lone-pair electrons on N
atoms which tend to accept protons and make it easier
responsive for acid.47-48 The synthesis process of the TSA is
1
relatively simple. The TSA was characterized by FT-IR, H
NMR, 13C NMR and mass spectroscopy, respectively. The
luminescence properties and multi-stimuli responsive
fluorescent for acid/base, PA and grinding of the TSA were
studied. The results demonstrated that the TSA had
fluorescence emission both in solution and solid state. The
color and fluorescence emission of the TSA can be tuned by
external stimuli including acid/base, PA and grinding. The
results display that it can be used as indicator for acid/base and
Scheme 1. Synthetic route of TSA
.
PA sensor and as information data storage material. Moreover,
it can also be applied in white light-emitting diode (w-LED) on
the basis of its desirable fluorescence emission in solid state.
2.2.1. Synthesis of compound TS
The POCl3 (93.2 mL, 1 mol) was added by dropwise to dry
DMF (77.4 mL, 1 mol), the mixture was stirred at ice-salt-bath
until solidified. Then N,N-dimethylaniline (12.6 mL, 0.1 mol)
was added to the mixture. The resultant mixture system was
heated at 60 °C until they reacted completely monitoring by
TLC. Subsequently the mixture was poured into ice water (300
mL) under stirring, and was neutralized with NaOH solution.
Finally the mixture was extracted by dichloromethane (DCM).
The combined organic layers were dried with MgSO4 and the
solvent was removed under vacuum. The crude product was
purified by column chromatograph of silica gel with petroleum
2. Experimental
2.1. Materials and measurements
All chemicals with analytical grade were commercially
available and were used without further purification. FT-IR
spectra were obtained in KBr discs on a Nicolet 380 FT-IR
spectrometer in the 4000-400 cm-1 region. H and 13C NMR
1
spectra were recorded on a 400 MHz Bruker Avance
spectrometer by using CDCl3 or CD3CN as solvent and
tetramethylsilane (TMS) as an internal standard. Mass spectrum
was obtained using an LC-MS (LTQ Orbitrap XL/LTQ
Orbitrap XL). Thermogravimetric analysis (TGA) was
performed on a Perkin Elmer Pyris 1 TGA Thermogravimetric
Analyzer. Differential scanning calorimetry (DSC) curves were
performed on DSC Q2000 in the temperature range from 25 to
300 °C at a heating rate of 10 °C min-1 under N2 atmosphere.
UV-vis absorption spectra of samples were recorded on an
Ultraviolet, Visible, Near-Infrared spectrophotometer (U-4100).
The fluorescence spectra of samples were measured with F-
ether/ethyl acetate mixture (3/1, v/v) as the eluent to give
1
(13.51 g, off-whit filamentous solid) with the 76% yield. FT-IR
(KBr, cm-1): 2830 (w), 2746 (w), 2739 (w), 1662 (s), 1608 (s),
1527 (m), 1394 (m), 1259 (m), 1206 (m), 1180 (m), 1116 (m),
1
962 (m), 817 (m), 709 (m). H NMR (CDCl3, 400 MHz) δ:
10.04 (s, 1H), 9.85 (s, 1H), 8.19 (d, J = 2.1 Hz, 1H), 7.92 (dd,
J1 = 8.8 Hz, J2 = 2.1 Hz, 1H), 7.02 (d, J = 8.8 Hz, 1H), 3.12 (s,
6H).
4500
fluorescence
spectrophotometer.
The
absolute
2.2.2 Synthesis and characterization of compound TSX
photoluminescence quantum yields (ΦF) of TSA in THF
solution (1 × 10−5 M) and the solid state were determined using
a Fluoromax-4 spectrophotometer with an integrating sphere.
Powder X-ray diffraction (PXRD) patterns were measured
using a Smart Lab X-ray diffractometer with Cu Kα radiation (λ
= 1.54050 Å), operating in the 2θ range from 10° to 80°.The
field emission scanning electron microscopy (FE-SEM) images
4-Nitrophenylacetonitrile (4.05 g, 0.025 mmol) was added to a
solution of compound TS (1.77 g, 0.01 mol) in 100 mL of
absolute ethanol. Then two drops of piperidine were added and
the mixture was refluxed under stirring for a night. After
cooling to room temperature, the precipitate was filtered and
washed with ethanol for several times, then dried under vacuum
giving rose red solid TSX 4.09 g (with a yield of 88%). FT-IR
(KBr, cm-1): 3076 (w), 2923 (w), 2210 (s), 1600 (w), 1565 (vs),
were
observed
on
a
Jeol
JSM-4800
scanning
electronmicroscopy. Fluorescence lifetime test was carried out
using an HORIBA FluoroMax-4P fluorescence spectrometer
1
1511 (vs), 1430 (s), 1336 (vs), 1209 (s), 1108 (s), 854 (vs). H
equipped with
a time-correlated single-photon counting
NMR (CDCl3, 400 MHz) δ: 8.34 (d, 2H, J = 8.8 Hz), 8.30 (m,
4H), 7.90 (d, 2H, J = 8.8 Hz), 7.85 (m, 3H), 7.65 (s, 1H), 7.18
(d, 1H, J = 8.4 Hz), 2.96 (s, 6H).
(TCSPC) card. The photoelectric parameters of the fabricated
w-LED were measured using an Everfine HAAS-2000
spectroradiometer equipped with a barium sulfate coated
integrating sphere and a CCD detector.
2.2.3. Synthesis and characterization of compound TSA
2.2. Synthesis of the target molecule
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A mixture of (3.72 g, 8 mmol) TSX and SnCl2·H2O (18.05 g, The optical properties of TSA in THF and solid state were
80 mmol) in 100 mL of ethanol was heated to reflux monitoring tested, respectively. The UV-vis absorption and fluorescence
by TLC. After the reaction finished and the mixture cooled to spectra are displayed in Fig. 1. As showed in Fig. 1a, TSA in
room temperature, the mixture pH was tuned to 8-9 with the THF exhibited relatively broad band and the maximum
saturated K2CO3 solution adding slowly under stirring. The absorption wavelength appeared at 387 nm. The extinction
resultant solution was extracted with ethyl acetate. The organic coefficient value (k) was higher with 104 L·cm-1·mol-1
(Table
phase was dried with anhydrous Na2SO4 and concentrated in ). The value suggested that the transform of electron of TSA
1
vacuum. The crude product was purified by column was permitted. To gain an insight into the absorbing behavior
chromatography using DCM eluent and then recrystallized with of TSA, the theoretical characterization with density functional
ethanol to give the pale yellow solid TSA (2.63 g, yield 81%). theory (DFT) was used. Geometry optimization of TSA was
FT-IR (KBr, cm-1): 3452 (s), 3357 (s), 2920 (s), 2212 (s), 1622 performed using the B3LYP/6-31G (d) basis set, while the
(s), 1515 (vs), 1492 (w), 1452 (w), 1301 (w), 1186 (s), 831 (s). electronic excitations corresponding to the absorption spectra
1H NMR (400 MHz, CDCl3) δ: 8.17 (d, J = 2.0 Hz, 1H), 8.01 were calculated using time-dependent-DFT (TD-DFT) by
(dd, J1 = 8.8 Hz, J2 = 2.4 Hz, 1H), 7.56(s, 1H), 7.50 (d, J = 8.8 Gaussian 09.51 The calculated value and experimental results of
Hz, 2H), 7.49 (s, 1H), 7.47 (d, J = 8.8 Hz, 2H), 7.18 (d, J = 8.4 the absorption wavelength, oscillator strength, the main orbital
Hz, 1H), 6.75 (d, J = 8.0 Hz, 2H), 6.73 (d, J = 8.4 Hz, 2H), 4.54 contribution and energy gap are listed in Table S1, and the
(s, H), 4.50 (s, 2H), 2.86 (s, 6H). 13C NMR (CDCl3, 100 MHz), electron density distributions of the frontier molecular orbital
δ: 154.28, 147.55, 147.27, 137.93, 136.61, 131.82, 129.31, are shown in Fig. S6. The theoretic absorption peak of TSA is
127.45, 127.18, 127.09, 127.00, 124.81, 118.78, 118.25, located 401 nm, which is close to the experimental datum (387
117.86, 115.14, 111.45, 109.48, 44.43. LC-MS (APCI): m/z = nm) obtained from absorption spectra. By investigating the
406.2014, calcd for (C26H24N5)+= 406.1953 ([M+H]+).
frontier molecular orbital (FMO) energy levels of TSA, the
absorption band at 401 nm predicted that it had a sum of two
main electronic transition modes H-1→L (56%) and H→L + 1
(26%), which could be ascribed to the combination of π-π* and
intramolecular charge transfer (ICT) transition. In addition, by
comparison with the absorption spectrum of TSA in THF, the
3. Results and discussion
3.1 Synthesis and characterization of the samples
The synthetic routes of TS, TSX and TSA are illustrated in broader absorption band with obvious bathochromic shift of
Scheme TS was synthesized with Vilsmeier-Haack TSA in the solid state was observed (Fig. 1a). This could be
1
.
formylation reaction by using DMF and POCl3. TSX was attributed to the increasing of π-conjugation length in its solid
fabricated utilizing a typical Knoevenagel reaction of TS with state due to the molecular stacking.52 As showed in Fig. 1b,
4-nitrophenylacetonitrile in the presence of piperidine as the TSA has fluorescence emission both in solution and in solid
catalyst. TSA was obtained via a reduction reaction by using state. The maximum emission peaks are located at 520 nm and
compound TSX and SnCl2·2H2O in ethanol solution. TSA and 529 nm, respectively. In addition, the quantum efficiencies of
1
its intermediates were characterized by FT-IR, H NMR, 13C TSA in THF solution and solid state were 4% and 28%,
NMR and mass spectroscopy, respectively. TSA could be respectively.
dissolved easily in most organic solvents, such as benzene,
DCM, tetrahydrofuran (THF), N,N-dimethylformamide (DMF) Table 1 The linear optical physical parameters of TSA in
and dimethylsulfoxide (DMSO), but was insoluble in water.
different solvents
Solvent
K
104)[c]
Δν [d]
3.2 The thermal property of TSA
Sample
(
s

380
378
387
382
387
375
394
4.09
4.15
4.39
4.27
4.24
3.91
4.11
benzene
DCM
THF
EA
ethanol
AN
514
527
520
524
540
536
540
6860
7480
6609
7094
7321
8010
6862
To investigate the thermal stability of TSA
,
the
thermogravimetric analysis (TGA) was carried out at a heating
rate of 10 °C/min under nitrogen atmosphere. The result is
shown in Fig. S5. As shown in Fig. S5, an obvious weight loss
of TSA was located in the temperature range from 349 °C to
TSA
in solution
421 °C, the quickest decomposition temperature (Tdecomp
)
DMF
occurred at 382 °C, the Td value was 351 °C (Td represents the
temperature with 5% weight loss, and it is often used to
estimate the thermal stability of a material49-50). The above data
indicate that TSA is thermal stable below 340 °C and thus
suitable for application of optical devices.
TSA
in solid
state
425
529
10.12
4554
[a] Peak position of the maximum absorption band. [b] Peak
position of fluorescence emission, excited at the absorption
maximum, [c] Molar absorptivity (L·cm-1·mol-1). [d] Stokes’
shift in cm-1.
3.3 The photophysical properties of TSA
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different solvents under irradiation at 365 nm. Abbreviations:
Δν-Stokes’ shifts, Δf -orientation, polarizability - (ε - 1)/(2ε +
1)-(n2 - 1)/(2n2 + 1), where ε - dielectric constant and n -
refractive index.
3.5 Multi-stimuli responsive fluorescence
3.5.1 Stimuli-responsive fluorescence for acid/base
In consideration of the basicity of the nitrogen atom in the
Fig. 1 The UV-vis (a) and PL (b) spectra of TSA (1.0 × 10-5 M) structure of TSA, the molecule should be protonated and
in THF solution and in solid state, Insert: photographs of deprotonated in the presence of acid and base.53-55 Therefore,
fluorescence emission of TSA in solution and in solid state.
the acid/base stimuli-responsive fluorescence was investigated
not only in solutions such as benzene, DCM, trichloromethane,
ethyl acetate (EA), ethanol, acetonitrile (ACN), DMF and
DMSO but also in solid state. It is found that TSA possessed
3.4 The solvent effect
The solvent polarity dependence of the fluorophores is more remarkable acidochromic behavior stimulating by TFA,
important in fluorescent field. Thus the solvatochromic hydrochloric acid and/or their vapors.
behaviors of TSA were also studied in various solvents with
increasing polarity. The results are displayed in Fig. 2. From
Fig.
2
(a), UV-vis absorption spectra showed slight
bathochromic (from 380 nm to 394 nm) by increasing the
solvent polarity. As can be seen in Fig. 2 (b), with increasing of
the solvent polarity, the emission bands exhibited an obvious
bathochromic (from 514 nm to 540 nm). The fluorescent photos
of TSA in different polar solvents (Fig. 2 d) also demonstrated
the same red-shifted fluorescence emissive phenomenon. The
Lippert-Mataga plot (Fig. 2 c) of Stokes’ shift against the
orientation polarizability of the solvent gave an upward straight
line with a small slope (slope = 2227). The results indicate that
the dipole moment of the TSA molecule in excited state is
larger than that in ground state. The main reason is attributed to
an ICT between the electron-donating and the accepting group
in the molecular structure.
Fig. 3 (a) Photos of TSA in ACN were taken under daylight
and UV lamp (365 nm). (b) Change in the emission intensity of
TSA in ACN by repeated treated with TFA or TEA. (c) Change
in the PL spectra of TSA between ‘off’ and ‘on’ by reversibly
treated with TFA-TEA.
As showed in Fig. 3, as TFA was added to the solution of
TSA in ACN, the obvious naked-eye color changing could be
observed from yellow-green to light, moreover the emission
spectra were slightly red-shifted accompanied by strong
quenching of luminescence. Furthermore, with addition of
excess TEA into the above solution, the fluorescence emission
could be recovered to the original one. The fluorescence
emission could be switched between ‘on’ and ‘off’ by
alternately treating with TEA-TFA solvents without attenuation
for many times. The results verify that TSA can be used as an
indicator for acid/base in solution state.
Fig. 2 (a) The UV-vis and (b) PL spectra, (c) Lippert-Mataga
plotof TSA in solvents with different polarities. Concentration:
10 μM, excitation wavelength with the maximum absorption. (d)
Insert: the photograph of fluorescent change of TSA in
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(bottom) and TEA (up) vapors. TSA spots on the filter paper
(a), the quartz glass slide (b) and the TLC plate(c). The photos
were taken under daylight (left) and UV lamp (right, 365 nm)
respectively.
Additionally, the stimuli-responsive fluorescence of TSA in
solid state for acid/base was also investigated. The results are
shown in Fig. 5. In these experiments, the sample was
deposited on the filter paper (a), the quartz glass slide (b) and
the TLC plate (c) by TSA in DCM, respectively. After being
dried and fumed with TFA vapor in turn, the dye spots were
immediately turned from brilliant yellow to orange (b) or/and
obscure (a, c), and the fluorescence intensity changed to weak.
The above phenomenon could be quickly converted back to
their original forms as they were treated with TEA vapor. This
reversible change could repeat many times in spite of slight
attenuation of the fluorescent intensity via alternately fuming
with TFA and TEA vapors. The results indicate that TSA has
the potential in application as a solid-state fluorescence
switching material.
3.5.2 Mechanical grinding responsive fluorescence
It is well known that MFC behavior can be achieved by the
transformation of the molecular conformation, packing mode,
1
Fig. 4 The H NMR spectra of (a) TSA (10 μM), (b) TSA (10 etc.56-61 Thus, the feature of stimuli-responsive luminescence
μM) + 4 equiv. TFA and (c) TSA (10 μM) + 4 equiv. TFA + switching was performed by grinding in a mortar with a pestle.
excess TEA in CD3CN. is the peak of H+ of TEA.
As showed in Fig. 6, the as-synthesized TSA was a yellow
crystalline powder with bright fluorescence (λem = 529 nm).
To prove the reversible transformation of protonation and After grinding, an orange powder with weak orange-yellow
1
deprotonation, the H NMR spectra were investigated (Fig. 4). fluorescence (λem = 549 nm) was detected. The grinding
When 4.0 equiv. of TFA was added to the TSA solution in treatment could cause a spectral red-shift of ca. 20 nm before
1
CDCl3, the protons of TSA shift downfield in the H NMR and after grinding. Interestingly, when DCM was dropped in
spectra because of the transformation of TSA into an electron- mortar, the color and fluorescence emission of the ground
deficient form TSA-H+. After adding excess TEA into the powder were recovered immediately (the inset photos in Fig.
1
above solution, the H NMR spectrum was recovered fully to
6). To investigate the reversibility of the MFC effect, the drying
the original one, suggesting that the transformation between powder was ground again after DCM being evaporated at room
TSA and TSA-H+ was completely reversible and essentially temperature. The ground sample changed back to orange
non-destructive in nature.
powder. This reversible cycle of fluorescence switching by
mechanical grinding could repeat many times, suggesting the
good stability of TSA
.
To further obtain the fluorescence excited-state decay
information of TSA in solid state before and after grinding, the
time-resolved emission-decay behaviors were measured. The
fluorescence decay curves and the lifetime data are illustrated
in Fig. S7. For initial sample, the fluorescence lifetime is
estimated to be 0.6 ns, while the value is 1.22 ns of its ground
sample. We speculated that the difference of molecular
conformation and arrangements in their aggregation state
resulted in the change of fluorescence lifetime. The result
indicates that the fluorescence lifetime of TSA solid can also be
adjusted by grinding.
Fig. 5 Recycling of the fluorescence emission and color
switching of TSA in solid state upon fuming with TFA
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morphology of TSA. In contrast, the ground state of TSA
revealed an additional exothermic recrystallization peak at 104
°C, which predicted that the TSA crystal was partially
destroyed and converted to an amorphous state and ground
sample was partially in a metastable amorphous state by the
grinding. The DSC result demonstrates that grinding can
convert thermodynamically stable crystals into metastable
state.62-63
Fig. 8 SEM images of polymorphsTSA (Magnification =
1800). (a) presents the initial sample, (b) presents ground
Fig. 6 The normalized emission spectra of the corresponding sample and (c) presents sample recrystallized with ethanol.
samples, inset: photographic images of the corresponding
samples under irradiation of daylight and UV light lamp: (1)
The morphological changes of polymorphs TSA from the
pristine sample, (2) ground sample, (3) ground sample upon crystalline state to the amorphous state were collected by SEM,
addition of DCM.
and the results are shown in Fig. 8. As showed in Fig. 8, the
initial sample presented rod-like morphology, but the ground
sample presented amorphous state. However, after
To study the mechanism of the MFC phenomenon of TSA
,
the PXRD and DSC tests were carried out. The results are recrystallization of the ground sample with ethanol, it recovered
shown in Fig. 7a. From Fig. 7a, the diffraction pattern of the essentially into the original pattern of the rod-like morphology.
initial powder showed sharp and intense reflections, indicating All the above results authenticate that TSA is a very promising
that the aggregate was ordered well in the crystalline powders. MFC material.
After grinding, the original sharp and intense diffraction peaks
attenuated or even disappeared, which revealed that the initial 4. Application of TSA
orderly arrangement was destroyed. After recrystallization in
ethanol, the diffraction patterns of the powders were essentially 4.1 Fluorescence sensor for acid/base and PA
same with that of pristine powder. The result reveals that the
microcrystalline structure of powders has been recovered The investigation of stimuli-responsive fluorescence for
basically. The above PXRD results confirm that the reversible acid/base (in 3.5.1 section) indicates that TSA can be used as
transition between the ordered and disordered molecular fluorescence sensor for acid/base. It prompts us to explore the
aggregation is crucial for the MFC behaviors.
potential application of TSA as a sensory material for the
detection of PA.
Based on the fluorescence quenching effect for acidic
materials, the recognition behavior of TSA towards the selected
acidic explosive aromatic nitro compounds (NACs) was
investigated in ethanol/water mixture (fw = 5%). As shown in
Fig. S8, approximately 60% quenching of the fluorescence
intensity occurred when 4 equivalents of PA were titrated.
However, other NACs did not exceed 20% when keeping the
same equivalents, it indicated that TSA exhibited selectivity
toward PA. The main reason for this is that PA exhibits acidity
in an aqueous system, and can combine with the amino group.
And other NACs only exhibit weak acidity or neutral behavior,
and cannot bond with TSA. The results suggested that
compound TSA can be used as a chemosensor for PA.
Fig. 7 (a) PXRD patterns of initial, ground and recrystallized
with ethanol sample of TSA. (b) DSC curves of TSA before
and after grind.
As can be seen in Fig. 7b, the differential scanning
calorimetry (DSC) curve for the heating pristine sample of TSA
had a clear melting endothermic peak at 188 °C and no
exothermic peak was found, which manifested the crystalline
To investigate the property of the TSA recognizing PA, the
titration experiments were carried out in ethanol/water mixture
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(fw = 5%) by adding aliquots of PA. As showed in Fig. 9, by TSA is a very promising candidate for application in data
adding PA amount from 0 to 4 equiv. to the solution of TSA storage.
(10 μM), it was observed the increasing of the absorption
intensity with slight blue-shift and the quenching of the
fluorescence emission. The detection limit (DL) for PA was
about 300 ppb calculating according to the DL = 3δ/S (δ is the
standard deviation of the blank solution and S is the slope of the
calibration plot). The results indicate that TSA can act as the
fluorescence sensor for PA, even in the ppb concentration level.
This can be rationalized as follows. As a strong acid, the PA
has an obvious tendency to transfer proton of hydroxyl groups
to the basic of amino or N,N-dimethylamino group which Fig. 10 Photographs of the writing/erasing cycle under daylight
makes an electrostatic complex between TSA and PA. This and UV light lamp.
strong complexation between the TSA and PA facilitates the
photoinduced electron transferring, so as to shift the electron to 4.3 White light-emitting diode (w-LED)
a nonradiating decay path and quench fluorescence emission.
Owing to the preferable fluorescence emission in solid state of
TSA, the w-LED was fabricated. The detailed LED packaging
process contains the following main steps: Firstly, the as-
synthesized TSA (20 mg) was mixed thoroughly with silicone
encapsulant (5 g, 1׃1 weight ratios of silicone A to silicone B)
in a small beaker. Then, the obtained TSA–silicone mixture
was degassed using vacuum, and then coated on the surface of a
commercial InGaN blue-emitting chip. Finally, the
encapsulation was solidified at 150 ºC for 1 h. The chromaticity
feature and optical performance of the prototype device were
measured. The results are displayed in Fig. 11. From Fig. 11
,
Fig. 9 The changes of absorption (a) and fluorescence (b)
spectra of compound TSA (10 μM) with increasing the
concentrations of PA in ethanol/water mixture (fw = 5%), Inset:
linear equation plots of I0-I versus [PA] in ethanol/water
mixture (fw = 5 %); I0 is the peak intensity of TSA, and I is the
peak intensity of TSA after addition of PA (0-4 equiv.).
the w-LED exhibited a correlated color temperature (CCT,
7544 K), a color rendering index (CRI, Ra = 70.2) and a
luminous efficacy (LE, 25.41 lm/W) under a 150 mA current.
The calculated chromaticity coordinate (x, y) in CIE 1931
chromaticity space was (0.2912, 0.3418), which is in the cold
white region. The results demonstrate that the TSA has the
potential ability to apply to w-LED.
4.2 Rewritable data storage
Information processing including recording, storage and
security technologies of data has become an integral part of the
human life. Based on the above reversible mechanical-
responsive luminescence switching features (in 3.5.3 section),
the technology of rewritable information storage was designed.
The results are displayed in Fig. 10. In Fig. 10, the mechanical
friction, the solvent and vapor of DCM were utilized to realize
the rewritable data storage. TSA was coated on typing paper
using the suspension of DCM and dried at room temperature.
The letters ‘An Da’ with orange light and weak fluorescence
resulting from the amorphous structure were written on the
TSA with a glass rod. Then the letters were easily erased by
grinding on the bright background. In the next picture, the
“Huai Shi” with yellow (under daylight) and strong kelly
fluorescence (under UV lamp) revealed clearly by using a
cotton swab and DCM solvent as pen and ink, respectively.
Following the weak emission background can quickly be erased
after using fuming treatment with DCM vapor. By repeating the
steps above, the reversible writing and erasing of different
fluorescent letters were performed. The results indicate that
Fig. 11 (a) CIE chromaticity diagram of the fabricated w-LED.
(b) Electroluminescent spectra of the fabricated w-LED, insets
show the photographs of the fabricated w-LED driven without
(I) and with (II) a 150 mA current.
5. Conclusions
A novel Λ-shaped α-cyanostilbene derivative (TSA) was
designed and synthesized successfully. The photophysical and
multi-stimuli-responsive properties of TSA were investigated
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Journal Name
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both in solution and solid state. The color and fluorescence Chem. Int. Ed., 2004, 43, 6346-6350.
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Moreover, the TSA had desirable potential application in w-
LED by sealing TSA on blue chips.
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This work was supported by the National Natural Science
Foundation of China (51673001, 51432001) and the
Educational Commission of Anhui Province of China
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