Solvatochromism, Reversible Chromism and Self-Assembly Effects of Heteroatom-Assisted Aggregation-Induced Enhanced Emission (AIEE) Compounds

Article abstract of DOI:10.1002/chem.201501902

Two compounds, 9,10-bis[2-(quinolyl)vinyl]anthracene (BQVA) and 9,10-bis[2-(naphthalen-2-yl)vinyl]anthracene (BNVA), have been synthesised and investigated. Both of them have aggregation-induced enhanced emission (AIEE) properties. Heteroatom-assisted BQVA shows solvatochromism, reversible chromism properties and self-assembly effects. When increasing the solvent polarities, the green solution of BQVA turns to orange with a redshift of the fluorescence emission wavelengths from λ=527 to 565 nm. Notably, BQVA exhibits reversible chromism properties, including mechano- and thermochromism. The as-prepared BQVA powders show green fluorescence (λ_em=525 nm) and the colour can turn into orange (λ_em=573 nm) after grinding. Interestingly, the orange colour can return at high temperature. Based on these reversible chromism properties, a simple and convenient erasable board has been designed. Different from BQVA, non-heteroatom-assisted BNVA has no clear chromic processes. The results obtained from XRD, differential scanning calorimetry, single-crystal analysis and theoretical calculations indicate that the chromic processes depend on the heteroatoms in BQVA. Additionally, BQVA also exhibits excellent self-assembly effects in different solvents. Homogeneous nanospheres are formed in mixtures of tetrahydrofuran and water, which are then doped into silica nanoparticles and treated with 3-aminopropyltriethoxysilane to give amino-functionalised nanoparticles (BQVA-AFNPs). The BQVA-AFNPs could be used to stain protein markers in polyacrylamide gel electrophoresis.

Full text of DOI:10.1002/chem.201501902

DOI: 10.1002/chem.201501902
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&
Synthesis Design |Hot Paper|
Solvatochromism, Reversible Chromism and Self-Assembly Effects
of Heteroatom-Assisted Aggregation-Induced Enhanced Emission
(AIEE) Compounds
Caixia Niu,[a] Ying You,[a] Liu Zhao,[a] Dacheng He,[b] Na Na,[a] and Jin Ouyang*[a]
Abstract: Two compounds, 9,10-bis[2-(quinolyl)vinyl]anthra-
cene (BQVA) and 9,10-bis[2-(naphthalen-2-yl)vinyl]anthracene
(BNVA), have been synthesised and investigated. Both of
them have aggregation-induced enhanced emission (AIEE)
properties. Heteroatom-assisted BQVA shows solvatochrom-
ism, reversible chromism properties and self-assembly ef-
fects. When increasing the solvent polarities, the green solu-
tion of BQVA turns to orange with a redshift of the fluores-
cence emission wavelengths from l=527 to 565 nm. Nota-
bly, BQVA exhibits reversible chromism properties, including
mechano- and thermochromism. The as-prepared BQVA
powders show green fluorescence (lem =525 nm) and the
colour can turn into orange (lem =573 nm) after grinding.
Interestingly, the orange colour can return at high tempera-
ture. Based on these reversible chromism properties,
a simple and convenient erasable board has been designed.
Different from BQVA, non-heteroatom-assisted BNVA has no
clear chromic processes. The results obtained from XRD,
differential scanning calorimetry, single-crystal analysis and
theoretical calculations indicate that the chromic processes
depend on the heteroatoms in BQVA. Additionally, BQVA
also exhibits excellent self-assembly effects in different sol-
vents. Homogeneous nanospheres are formed in mixtures of
tetrahydrofuran and water, which are then doped into silica
nanoparticles and treated with 3-aminopropyltriethoxysilane
to give amino-functionalised nanoparticles (BQVAÀAFNPs).
The BQVAÀAFNPs could be used to stain protein markers in
polyacrylamide gel electrophoresis.
Introduction
The fall-known aggregation-induced emission (AIE) or aggre-
gation-induced enhanced emission (AIEE) phenomena reported
by Tang and co-workers in 2001 effectively overcome the inter-
ference of ACQ, and have become popular topics in many ma-
terials fields.[9] To date, abundant AIE/AIEE materials have been
reported,[10] such as hexaphenylsilole (HPS),[11] tetraphenyl-
ethene (TPE),[12] distyrylanthracene (DSA)[13,14] and their deriva-
tives. The AIE/AIEE materials possess amazing properties, for
instance, high quantum yields, controlled self-assembly effects
and photostabilities,[15–17] which result in potential applications
in organic light-emitting diodes (OLEDs) materials,[18] label-free
bioprobes,[19,20] bioimaging[21] and so on. Interestingly, many
AIE/AIEE materials can respond to external stimuli, including
pressure, temperature and solvent vapours. It is worth men-
tioning that many reported TPE and HPS derivatives possess
multi-chromism properties.[22–26] In addition, DSA derivatives
that possess piezo- and thermochromism have been report-
ed,[27] although the solvatochromism of DSA derivatives is still
restricted. General mechanisms of chromism are considered to
be associated with changes in the molecular packing modes
and crystallinities in external environments.[28,29] However, the
design and synthesis of AIE/AIEE molecules, the molecular
packing modes of which are easily and reversibly changed by
external stimuli, is still a challenge. Hence, it is essential to
introduce new synthetic methods for AIE/AIEE chromic
luminescent materials.
Organic chromic luminescent materials, including thermochro-
mic, pizeochromic and other “smart” materials, have attracted
increasing attention by virtue of their extensive applications in
anti-counterfeiting of brands, temperature/pressure sensor
films and so forth.[1–3] Although changing the chemical struc-
tures is the most effective way to control the chromic process-
es, both low reaction efficiency and irreversibility in the solid
state mean that this way is not suitable for exploitation and
applications.[4] Notably, controlling the physical state of aggre-
gations is easier to achieve colour changes in the materials by
using external forces.[5–7] However, most chromic luminescent
materials suffer from aggregation-caused quenching (ACQ) ef-
fects in the solid state, which ultimately limit the development
of chromic materials.[8]
[a] C. Niu, Y. You, L. Zhao, N. Na, Prof. J. Ouyang
Key Laboratory of Theoretical and Computational Photochemistry
Ministry of Education, College of Chemistry
Beijing Normal University, Beijing, 100875 (P.R. China)
E-mail: jinoyang@bnu.edu.cn
[b] Prof. D. He
Key Laboratory of Cell Proliferation and Regulation Biology
Ministry of Education, Beijing Normal University
Beijing, 100875 (P. R. China)
Abundant AIE/AIEE materials possess self-assembly
effects.[18,30] It is important to expand the biological application
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201501902.
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ranges of self-assembly effects, although there
a few
Results and Discussion
biocompatible AIE/AIEE materials have been reported; these
expand the biological applications.[31–33] The idea of combining
AIE/AIEE materials and polymers to obtain organic fluorescent
nanoparticles (OFNs) with enhanced water solubilities and bio-
compatibilities would greatly broaden the applications of AIE/
AIEE materials in biofields.[34] However, these OFNs rely on spe-
cial chemical reactions between appropriate AIE/AIEE com-
pounds and polymers.[35] Thus, reports on AIE-based OFNs are
rare. Another way of preparing OFNs is to use silica because
silica is known to be biocompatible and easy to modify.[36,37]
AIE/AIEE materials are able to self-assemble into regular aggre-
gates in mixed solvents. Therefore, coating these aggregates
with silica layers provides a new approach to prepare more
biocompatible OFNs and greatly broadens their bio-
applications.
We synthesised BQVA and BNVA through the Witting–Horner
reaction. The general synthetic route is shown in Scheme S1 in
the Supporting Information. The compounds were character-
ised by 1H NMR spectroscopy, MALDI-TOF MS and elemental
analysis. The optimised molecular structures were calculated
by DFT calculations (B3LYP/6-31G). Figure 1 shows the chemical
and optimised molecular structures. The results suggest that
both optimised molecular structures of BQVA and BNVA are
highly twisted, which makes it possible for them to possess
AIEE properties.
BQVA and BNVA are soluble in common organic solvents,
such as acetone, THF and dichloromethane (DCM). To further
confirm their AIEE characterisation, we chose acetone and THF
as the good solvents and water as the poor solvent. Figure S1
in the Supporting Information shows the absorption spectra of
BQVA in mixtures of acetone and water; the concentrations of
the suspension are 100 mm. The absorption maximum (labs) of
a solution of BQVA in acetone is lꢀ423 nm. When the water
fraction, fw, is 30%, labs remains at the same wavelength,
whereas the intensity is stronger than that in solution. When fw
reaches 50%, the absorption intensity at l=423 nm is reduced
greatly. In the suspension with more water (fw =70%), the in-
tensity at l=423 nm disappears, while a weak band appears
at lꢀ460 nm. When fw is as high as 90%, a remarkable ab-
sorption band at l=460 nm represents the formation of BQVA
aggregates in suspensions. The absorption spectra of BQVA are
in accordance with the FL spectra, as shown in Figure 2A and
B.
Herein, inspired by acceptor–p–A (A-p-A) structures, we
have synthesised and investigated the heteroatom-assisted
AIEE compound 9,10-bis[2-(quinolyl)vinyl]anthracene (BQVA). It
shows excellent solvatochromism, reversible chromism and
self-assembly effects at the same time. With increasing water
fractions, the fluorescence (FL) intensity of suspensions is en-
hanced 10-fold and the emission colours change from green
to orange. Owing to the A-p-A structure of BQVA, it possesses
remarkable solvatochromism characteristics, along with en-
hancement of the solvent polarities, and the emission bands
redshift from l=527 to 565 nm. The as-prepared powders
show a green emission under UV light and after mechanical
grinding the solids show an orange emission. This colour
change can be recovered by thermal stimulation. We also syn-
thesised non-heteroatom-assisted 9,10-bis[2-(naphthalen-2-yl)-
vinyl]anthracene (BNVA) for comparison. The results show that
BNVA only has AIEE properties and no chromism properties.
The XRD, differential scanning calorimetry (DSC), crystal struc-
ture and theoretical calculations results confirm that heteroa-
toms in BQVA play an important role in multi-chromism. Firstly,
the heteroatoms in BQVA lead to the A-p-A structure, which in-
duces solvatochromism. Secondly, the nitrogen atoms make it
possible for intermolecular CÀH···N bonds to exist and stabilise
the molecular sheets in the BQVA packing structures. These
molecular sheets will slip under external stimulus, such as pres-
sure or temperature, which results in reversible multi-chrom-
ism. The results confirm the significance of heteroatoms in the
multi-chromism AIEE materials, they also provide new ideas for
the design and exploration of more materials with these prop-
erties. In addition, we also used the self-assembled nanoparti-
cles (NPs) of BQVA in mixtures of THF/water to prepare silica-
coated OFNs, and amination modification to give amino-func-
tionalised nanoparticles (BQVAÀAFNPs). Finally, we used them
to stain protein markers in the gel after 1D polyacrylamide gel
electrophoresis (PAGE). The preparation of BQVAÀAFNPs pro-
vides a new method to prepare more biocompatible AIEE-
OFNs and broadens the bioapplications of self-assembly
effects.
With increasing fw, the FL intensities are enhanced 10-fold
and the emission wavelengths are redshifted. In mixtures of
acetone/water with a low water content (ꢁ30%), the FL sig-
nals are weak at l=565 nm. The FL intensity of the suspension
(fw =50%) increases dramatically; the emission wavelength is
l=510 nm with a green colour under a UV lamp. With fw in-
creasing to 70%, the suspension shows a yellow emission at l
ꢀ556 nm. In the suspensions with the highest water contents
(fw =90%), the emission wavelength continuously redshifts to
l=562 nm with a strong orange emission. The results indicate
that BQVA has AIEE and colour-tuning characteristics. Similar
AIEE behaviour can be observed under the same conditions as
those used for BQVA. Figure S2 in the Supporting Information
shows the absorption spectra of BNVA in mixtures of acetone/
water with different water fractions. Due to its poor solubility
in acetone, the absorption intensity is weaker than that of
BQVA. In acetone, BNVA shows an absorbance band at
l=408 nm, which is blueshifted by 15 nm relative to BQVA.
This blueshift implies that naphthyl has a weaker electron-
withdrawing ability than quinolyl. When water is added,
suspensions of BNVA show no absorbance band. The disapp-
earance of the absorption also proves the generation of BNVA
aggregates in mixtures of acetone/water. The FL intensity of
the suspension (fw =50%) is 1.5 times stronger than that of the
solution (fw =0%). Different from BQVA, the emission wave-
length is redshifted by only 5 nm (from l=539 to 544 nm),
and the emission colour remains yellow–green with various fw.
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Figure 1. A) Chemical, and B) optimised molecular structures of BQVA. C) Chemical, and D) optimised molecular structures of BNVA.
than that in acetone. With high
water fractions, the absorption
bands of BQVA and BNVA red-
shift remarkably, which repre-
sents the formation of aggre-
gates. The FL spectra (Figure 3)
further confirm the AIEE proper-
ties.
Quinolyl possesses a stronger
electron-withdrawing
ability
than naphthyl. Quinolyl groups
make it possible for BQVA to
have A-p-A structures. In gener-
al, molecules with donor–accept-
or (D-A) structures exhibit solva-
tochromism when they are excit-
ed in solvents. We examined the
absorption and FL spectra of
BQVA in six solvents with differ-
ent polarities. The results are
shown in Table S1 in the Sup-
porting Information. Along with
the growing solvent polarities,
labs of BQVA redshifts from l=
420 to 425 nm. The slight
changes in labs of BQVA suggest
that the polarities of the solvents
have little effect on the ground-
Figure 2. A) FL spectra, and B) corresponding FL intensity of BQVA in mixtures of acetone/water with different fw
excited at l=365 nm. C) FL spectra, and D) corresponding FL intensity of BNVA under the same conditions. The
insets show the corresponding emission colours under UV illumination. Suspension concentrations: 100 mm.
The absorption results for BQVA and BNVA in mixtures of THF/
water with different fractions (0, 30, 50, 70 and 90%) are also
determined (Figures S3 and S4 in the Supporting Information).
The results indicate that the solubility of BNVA in THF is better
state electron distribution. In contrast, the FL spectra (Figure 4)
show a remarkable redshift (l=527 to 565 nm): with solvents
varying from hexane to acetone, the emission colours also vary
from green to yellow to orange. We also determined the pho-
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between emission wavelengths
and empirical parameters; this
gave a slope of 98.1 (Figure S6
in the Supporting Information).
According to the good results
from the two methods, we con-
firmed that BQVA had remark-
able solvatochromic properties.
Organic chromic luminescent
materials have attracted much
attention because of their exten-
sive applications. In addition of
solvatochromism, we investigat-
ed the mechano- and thermo-
chromism properties of BQVA
and BNVA. The results are shown
in Figure 5.
Figure 5A shows photographs
of initial and ground powders of
BQVA taken under RL and UV.
The initial powders of BQVA are
yellow with green emission
under UV illumination. After
being mechanically ground, the
yellow powders changed into
orange powders, with emission
colours varying from green to
Figure 3. A) FL spectra, and B) corresponding FL intensity of BQVA in mixtures of THF/water with different fw
excited at l=365 nm. C) FL spectra, and D) corresponding FL intensity of BNVA under the same conditions. The
insets show the corresponding emission colours under UV illumination. Suspension concentrations: 100 mm.
orange under UV illumination. Figure 5B exhibits the corre-
sponding FL spectra; the emission wavelengths of as-prepared
and ground powders are l=525 and 573 nm, respectively.
These results demonstrate that BQVA possesses mechano-
chromism properties. In addition, BQVA has thermochromatic
abilities. As shown in Figure 5A, the colours of ground pow-
ders return to the initial colours after being heated at 1308C.
To further study the chromic effects of BQVA, we determined
the recyclability between two emission powders (Figure 5C).
BQVA demonstrates excellent recyclability after five grinding
and heating cycles. In contrast to BQVA, BNVA shows incon-
spicuous mechano- and thermochromatic properties. The ini-
tial and ground powders are orange under RL and yellow
under UV. The FL spectra (Figure 5E) show that after grinding
the emission wavelength redshifts by only 10 nm (from l=546
to 556 nm). Although BNVA displays good repeatability be-
tween grinding and heating (Figure 5F), considering its un-
changed colours, we conclude that BNVA molecules are not
mechano- and thermochromism materials. Based on the good
chromism properties of BQVA, we applied it in a simple and
convenient erasable board (Figure 6).
Figure 4. Absorption (dashed lines) and FL (excited at l=365 nm, solid
lines) spectra of BQVA in different solvents. The inset shows the correspond-
ing emission properties under illumination with a UV lamp.
tophysics of BNVA in same solvents and observe opposite phe-
nomena. Figure S5 in the Supporting Information shows that
the absorption spectra, FL spectra and emission colours of
BNVA in various solvents are slightly altered. Thus, the polari-
ties of the solvents have a slight effect on both the ground-
and excited-state electron distributions of BNVA. This is possi-
ble due to the absence of D-A structures in BNVA.
To further determine the solvent effects on BQVA, we investi-
gated the linear correlation between the Stokes shift (Dv) and
solvent polarity parameter (Df) calculated by using the Lip-
pert–Mataga equation. Figure S6 in the Supporting Information
shows that the slope of the fitting line gives a value of 2885.5,
which suggests satisfactory solvatochromism. Additionally, we
used the Reichardt equation to investigate the relationships
On the other hand, BQVA and BNVA possess high thermal
decomposition temperatures (Td, corresponding to 5% weight
loss) of 366.02 and 398.138C (Figures S8 and S9 in the Support-
ing Information). The good Td results give them potential to be
luminogens for OLEDs. For BQVA, in particular, its multi-
chromism and high Td make it possible for BQVA to be used as
an effective material in many fields.
To explain the chromatic mechanisms of BQVA, we used
powder X-ray diffraction (PXRD) to determine the patterns of
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tern changes for BQVA were also
studied by DSC. The results in
Figure S10 in the Supporting In-
formation indicate that there is
an endothermic peak at around
2408C in the DSC curve of the
initial powder. A new exothermic
peak appears in the DSC curve
of the ground powder. This new
peak indicates the metastable
amorphous state of the ground
powder.[39]
According to previous reports,
molecules are often more twist-
ed in the crystalline state than in
the amorphous state.[28] We used
crystal and electronic structures
to further study chromic pro-
cesses. The solvent diffusion
method was used to prepare the
crystals. A clubbed and green-
emitting crystal suitable for X-ray
analysis was obtained from satu-
rated solutions in THF placed in
petroleum ether (Figure S11 in
the Supporting Information).
This crystal belongs to the mon-
oclinic system. The crystal struc-
tures, intermolecular forces and
packing structures are shown in
Figure 8. The results reveal that
the green-emitting BQVA mole-
Figure 5. A) Photographs of initial and ground powders of BQVA taken in room light (RL) and under UV light (UV).
B) FL spectra of initial and ground powders of BQVA, excited at l=365 nm. C) Reversible switching of emission
wavelengths of BQVA after repeated grinding and heating cycle. D) Photographs of initial and ground powders of
BNVA taken under RL and UV. E) FL spectra of initial and ground powders of BNVA, excited at l=365 nm. F) Re-
versible switching of emission wavelengths of BNVA after repeated grinding and heating cycles. The heating
temperature was 1308C.
Figure 6. Photographs of writing and erasing on an erasable board with
BQVA coated on filter paper.
different powders. Figure 7A demonstrates that the initial and
heated samples of BQVA show sharp and intense reflection
peaks, whereas ground powders exhibit weak and broad
peaks. The changes to the peaks are in accordance with colour
variations. This indicates different packing of the molecules
after grinding and heating.[38] No clear differences can be
found in the PXRD spectra of BNVA. In other words, grinding
and heating have little effect on the packing of BNVA
molecules. Thus, we infer that colour changes under different
conditions are induced by the packing of molecules. After
grinding, the molecules change from the crystalline state to an
amorphous state, along with redshifts of the emission. The pat-
Figure 7. XRD patterns of initial powders, ground powders and heated
powders for: A) BQVA, and B) BNVA.
cule is highly twisted; the dihedral angle between the anthra-
cene and quinoline planes is nearly 908. The twisted structure
is stabilised by 16 intermolecular forces of the type CÀH···p
(d=2.846 Š, 2.834 Š), CÀH···N (d=2.665 Š) and p–p (d=
3.315 Š). All forces are shown in Figure S12 in the Supporting
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Figure 9. Electron cloud distribution of frontier molecular orbitals of BQVA
(crystal structure), BQVA (optimised structure) and BNVA (optimised
structure).
conformation of the optimised structure is more planar than
that of the crystal structure; better co-planarity of BQVA after
grinding will also lead to the redshifted emission.[28] The
energy gaps of BQVA and BNVA in the optimised structures are
same (0.107 eV), so it can be inferred that BQVA in its
optimised structures shows a yellow emission.
Because AIE or AIEE molecules usually show interesting self-
assembly characteristics,[30] we used the method of evapora-
tion-induced self-organisation (EISO) to prepare self-assembled
structures. The results were characterised by SEM and FL mi-
croscopy, and all suspensions were 100 mm. Figure 10 shows
that the self-assembled structures are induced by solvents. The
morphologies of BQVA in mixtures of THF/water with fw =90%
are nanospheres with diameters of approximately 200 nm.
When the solvent was a mixture of THF/petroleum ether (fp =
90%), BQVA molecules self-assembled into structured micro-
rods. Figure 10D shows that the emission colour of the micro-
rods is green. When BQVA molecules are dissolved in THF, they
organise into flower-like structures (Figure 10C). The results
provide a new way to control the self-assembly of AIEE mole-
cules. On the other hand, the structured morphologies also
prove the regular conformations of BQVA. We acquired crystals
of BQVA from microcrystalline structures in mixtures of
THF/petroleum ether, whereas the preparation of BNVA
crystals failed.
Figure 8. A) Single-crystal structure and intermolecular forces of BQVA.
B) Packing mode of BQVA in the single crystal.
Information. The forces prevent rotation and strong p–p inter-
actions in the BQVA molecule, reduce non-radiative decay and
result in the strong green emission.
Figure 8B shows the packing mode of BQVA in the single
crystal. Molecular sheets are formed in the packing structures.
The sheets are stabilised by intermolecular CÀH···N bonds (Fig-
ure S13 in the Supporting Information). These molecular sheets
are able to slip under external stimuli, such as pressure or tem-
perature.[40] When stimulated by pressure, the packing struc-
tures are destroyed and the transformation of the molecules
from the crystalline state to an amorphous state results in the
redshift of the emission. After heating, both the packing struc-
tures and emission colour are restored. These results are in
agreement with the PXRD results. Because no CÀH···N bonds
exist in BNVA molecules, we infer that there is no easy slippage
of the molecular sheets and BNVA cannot possess multiple
chromism properties.
The fabrication of NPs for bioapplications is very important.
Considering that nanospheres formed in mixtures of THF/
water, we doped these nanospheres into silica NPs to prepare
fluorescent nanoparticles (FNPs). Figure 11 A shows the related
schematic illustration. To enhance the hydrophilicity, we used
3-aminopropyltriethoxysilane (APTES) to give BQVAÀAFNPs. To
demonstrate that BQVAÀAFNPs can supply accurate detection
of proteins, we applied BQVAÀAFNPs to stain protein markers
in the gel after 1D PAGE, and used the conventional protein
detection method of CBB-R250 staining as a reference.[41] The
protein markers include thyroglobulin, ferritin, catalase, lactate
dehydrogenase and albumin. From the results in Figure 11 C,
we can see that both methods, traditional CBB-R250 staining
and new BQVAÀAFNPs FL imaging, can detect the five protein
makers with different molecular masses. We conclude that the
new method of BQVAÀAFNPs FL imaging has potential
applications in protein detection in gels after PAGE.
We also used DFT calculations at the B3LYP/6-31G level to
calculate the distributions of the HOMO and LUMO energies of
BQVA (crystal structure), BQVA (optimised structure) and BNVA
(optimised structure). Figure S14 in the Supporting Information
reveals that the crystal structure of BQVA has a higher degree
of twisting and lower degree of conjugation than those of the
optimised structure. This implies that the crystal structure has
stronger torsional stress than that of the optimised structure.
Figure 9 shows the corresponding electron cloud distributions.
The calculated orbital energy gaps of crystal and optimised
structures are 0.119 and 0.107 eV. The higher energy of the
crystal structure confirms its instability, which contributes to its
multiple chromism characteristics. In addition, the molecular
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vironment, these molecular sheets slipped easily and induced
reversible chromism. Additionally, we used the self-assembly
effects of BQVA to prepare BQVAÀAFNPs, and applied them in
the staining of protein markers in a gel after PAGE. The prepa-
ration of BQVAÀAFNPs broadens the bioapplications of self-as-
sembly effects. Overall, we not only prepared new chromic
AIEE “smart” materials, but also shed some light on introducing
heteroatoms into AIE/AIEE molecules to prepare multi-chromic
AIE/AIEE luminogens.
Experimental Section
Synthesis of 9,10-bis(dichloromethyl)anthracene
Figure 10. SEM micrographs of the self-assembled structures of BQVA
generated by mixtures of: A) THF/water (fw =90%); inset scale bar: 100 nm,
B) THF/petroleum ether (fp =90%); inset scale bar: 100 nm; and C) THF;
D) FL microscopy images of BQVA generated in mixtures of THF/petroleum
ether (fp =90%).
A two-necked, round-bottomed flask (500 mL) was oven-dried and
cooled under a nitrogen atmosphere. Anthracene (9 g, 0.05 mol)
and paraformaldehyde (7.6 g) were dissolved in 1,4-dioxane
(72 mL) and hydrochloric acid (12 mL). The mixture was stirred for
2 h at 110 8C under the HCl atmosphere. After removal of the HCl
gas, the reaction was stirred for 5 h at 110 8C. After being cooled to
room temperature, the resulting precipitate was filtered and
1
washed with 1,4-dioxane to give a yellow product (38%). H NMR
(400 MHz, CDCl3,): d=8.40–8.38 (m, 4H), 7.67–7.65 (m, 4H),
5.61 ppm (s, 4H).
Synthesis of tetraethylanthracene-9,10-diylbis(methylene)-
diphosphonate
9,10-Bis(dichloromethyl)anthracene (7.5 g, 25 mmol) was dissolved
in triethylphosphate (50 mL) and added to an oven-dried, one-
necked, round-bottomed flask (250 mL). The mixture was stirred
for 24 h at 1508C under a nitrogen atmosphere. The reaction mix-
ture was cooled to room temperature, then the resulting precipi-
tate was filtered and washed with petroleum ether to give the
1
light-yellow product (70%). H NMR (400 MHz, CDCl3): d=8.39–8.37
(m, 4H), 7.58–7.56 (m, 4H), 4.29–4.21 (d, 4H), 3.93–3.77 (m, 8H),
1.08–1.05 ppm (m, 12H).
Synthesis of BQVA
Tetraethylanthracene-9,10-diylbis(methylene)diphosphonate (1 g,
2.08 mmol) and tBuOK (1 g, 9 mmol) were dissolved in dry THF
(40 mL) under a nitrogen atmosphere. 2-Quinolinecarbaldehyde
(1 g, 6.34 mmol) in dry THF (40 mL) was added dropwise to this
mixture at room temperature and stirred for 12 h. The resulting
precipitate was filtered and washed with methanol to give the
bright-yellow product (30%). 1H NMR (400 MHz, CDCl3): d=8.68–
8.64 (d, J=16.3 Hz, 2H), 8.50–8.47 (m, 4H), 8.24–8.22 (d, J=8.5 Hz,
2H), 8.18–8.16 (d, J=8.4 Hz, 2H), 7.86–7.84 (d, J=8.1 Hz, 2H),
7.81–7.79 (d, J=8.5 Hz, 2H), 7.78–7.74 (m, 2H), 7.57–7.50 (m, 6H),
7.31–7.27 ppm (d, J=16.4 Hz, 2H); 13C NMR (100 MHz, CDCl3): d=
155.5, 148.4, 137.7, 136.6, 132.5, 131.3, 129.8, 129.53, 129.47,
127.61, 127.57, 126.5, 126.4, 125.6, 119.8 ppm; MALDI-TOF MS: m/
z: 485.5 [M+H]+; elemental analysis calcd (%) for C36H24N2: C 89.26,
H 4.96, N 5.78; found: C 90.11, H 4.71, N 5.18.
Figure 11. A) Schematic illustration of the synthesis of BQVA-AFNPs and their
application for protein visualisation after PAGE. CTAB=cetyltrimethylammo-
nium bromide, TEOS=tetraethyl orthosilicate. B) TEM imaging of BQVA-
AFNPs dispersed in water (scale bar: 200 nm). C) Detection of standard
proteins after 1D PAGE with BQVA-AFNPs (left) and CBB-R250 (right).
Conclusion
We synthesised and investigated the AIEE compound BQVA,
which possessed solvatochromism, reversible chromism and
self-assembly effects at the same time. To confirm the critical
role of heteroatoms in the chromism process, we used BNVA,
in which non-heteroatoms exist, for comparison with BQVA.
Results from XRD, single-crystal analysis and theoretical
calculations revealed that nitrogen atoms in BQVA played an
important role. BQVA had typical A-p-A structures, which
contributed to the solvatochromism characteristics. In addition,
intermolecular CÀH···N bonds stabilised molecular sheets in the
BQVA packing structures. When stimulated by the external en-
Synthesis of BNVA
Tetraethylanthracene-9,10-diylbis(methylene)diphosphonate (1 g,
2.08 mmol) and tBuOK (1 g, 9 mmol) were dissolved in dry THF
(40 mL) under
a nitrogen atmosphere. 2-Naphthaldehyde(1 g,
6.40 mmol) in dry THF (40 mL) was added dropwise to this mixture
at room temperature and stirred for 12 h. The resulting precipitate
Chem. Eur. J. 2015, 21, 13983 – 13990
www.chemeurj.org
13989
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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was filtered and washed with methanol to give the orange–yellow
product (39%). 1H NMR (400 MHz, CDCl3): d=8.48–8.46 (m, 4H),
8.07–8.01 (d, J=24.2 Hz, 2H), 7.99–7.94 (m, 6H), 7.91–7.88 (d, J=
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Acknowledgements
We gratefully acknowledge support from the National Nature
Science Foundation of China (21175014, 21475011, 21422503,
91027034), the National Grant of Basic Research Program of
China (no. 2011CB915504) and the Fundamental Research
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Keywords: aggregation · nanoparticles · reversible chromism ·
self-assembly · solvatochromism
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Received: May 14, 2015
Published online on August 13, 2015
Chem. Eur. J. 2015, 21, 13983 – 13990
www.chemeurj.org
13990
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim