Aggregation-induced emission in fluorophores containing a hydrazone structure and a central sulfone: Restricted molecular rotation

Article abstract of DOI:10.1039/c6ra02209j

Four D-π-A-π-D structured 4,4′-di(E)-2-(4-4-alkoxyaniline)hydrazinyldiphenyl sulfones were synthesized and their structures were characterized using NMR, IR, and element analysis. These compounds displayed weak fluorescence emission in THF while their flu

Full text of DOI:10.1039/c6ra02209j

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Aggregationꢀinduced emission in fluorophores containing
hydrazone structure and sulfone central: restricted molecular rotation
Received 00th January 20xx,
Accepted 00th January 20xx
Jing Lia, Wen Yanga, WeiqunZhoua*, Chunchun Li a, Zhongqing Chengb, Mengying Li b,
Liqun Xiec , Youyong Li d
DOI: 10.1039/x0xx00000x
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Four 4, 4’-Di((E)-2-(4-4-alkoxyaniline)hydrazinyldiphenyl sulfones of D-π-A-π-D were synthesized and their structures were
characterized by NMR, IR, and element analysis. These compounds displayed weak fluorescence emission in THF while
fluorescence enhancement in THF/water mixture solvent. Fluorescent microscope imaging showed the formation of the
aggressive state. The mechanism of aggregation-induced emission (AIE) was supported by molecular dynamic calculations.
The intermolercular hydrogen bonds between adjacent molecules inhibited the intramolecular rotations, preventing π-π
stacking and causing AIE enhancement. Living cell imaging experiments opened up a new way to cell fluorescence staining.
24]
.
In 2003, Tang et al. had synthesized TTPEPy [25] with high
1. Introduction:
fluorescent efficiency and high AIE effect which overcame ACQ
The main organic photoimaging materials are of great
importance in photochemical and applied chemical field [1-5]
effect. The appearance of AIE made it possible to apply the
organic photoimaging materials in the real-world applications.
It is realized that rational restricted intramolecular rotation
(RIR) closed the possible non-radiative decay channels and
activated radiative decay channels, which led to the strong
fluorescence [26,27,28]. Some typical examples of the AIE systems
have been developed such as hexaphenylsilole (HPS) [29] with a
propeller-shaped non-planar molecule, butterfly-shaped pyran
derivatives [30], cyano-substituted biphenyl ethylene with J-
aggregation typed spatial structure [31], and BODIPY dyes with
V-shaped structure [32]. V-shaped compounds have the twisted
nonplanar structures to prevent π-π stacking and induce the
.
Significant developments have taken place in the past few
years leading to practical organic photoimaging materials.
Outstanding fluorescent materials are often designed with
large conjugated systems [6-10], so the conventional structural
design strategy of organic fluorophores enlarged the extent of
π-conjugation by melding more and more aromatic rings
together. Although the bigger conjugate structure can produce
high fluorescence in the dilute solutions, the fluorescence can
be usually quenched in concentrated solutions and solid state.
This phenomenon is usually called aggregation-caused
fluorescence quenching (ACQ) because of π-π stacking and
other non-radiative pathways [11]. The ACQ effect has restricted
the real-world applications of fluorescent materials [12,13]. For
example, as common organic materials are insoluble in water,
the materials of the ACQ effect cannot be used as sensors to
detect biological molecules in physiological buffers and
monitor ions in river water [14,15]. Since the luminescent
materials as the light-emitting devices must be fabricated in a
solid film form, the ACQ effect materials cannot be used to the
fabrication of efficient organic light-emitting diodes (OLEDs) [16-
fluorescence enhancement in the aggregated states. For
[32]
instance, V-shaped BODIPY
is able to reduce the close
intermolecular interactions and correspondingly improve solid
state emission of the BODIPY dyes. V-shaped pyridinium salts
[33]
DMDPN
has also exhibited a typical aggregation-induced
emission behavior.
Usually, D-π-A-π-D type fluorescent materials have become
an efficient way for designing brilliant fluorescence materials
for they emit stronger intramolecular charge transfer (ICT)
fluorescence. For example, V-shaped D-π-A-π-D compound
[34]
BCPPM exhibited strong ICT fluorescence in the solid state
.
In this article, we synthesized four V-shaped compounds of D-
π-A-π-D, 4, 4’-Di((E)-2-(4-4-alkoxyaniline)hydrazinyldiphenyl
sulfone (BAHDS1-4), where the sulfone unit served as the
central acceptor core, two hydrazinyldiphenyl conjugated
chains served as the π-bridge to extend the conjugation
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length, and methoxy, n-butoxy, tert-butoxy and 4-phenoxy The ground and excited states of molecules were optimized
[35-37]
was introduced as donor units. The larger substituent group with the Becke-3-Lee-Yang-Parr (B3LYP)
by density
such as n-butoxy, tert-butoxy and phenoxy were introduced to functional theory (DFT) and time-dependent DFT (TD-DFT)
restrict the intramolecular rotation and enhance fluorescence calculations at the level of 6-311G(d) with Gaussian 09
emission. Four compounds emitted weak fluorescence in THF, program [38]. TD combining with a SCRF method
[39]
(CPCM, by
but the fluorescence gradually enhanced with the addition of THF as solvent) at the same level were applied to indicate the
the non-soluble water in THF and presented AIE effect.
energies of HOMO and LUMO. The vibrational frequencies
calculations were also performed to ensure the stability of the
calculation result and to avoid virtual frequency.
2. Experimental section
The MD(molecular dynamic) simulations were performed by
Discover module within Materials Studio 7.0 with the
2.1 Materials and instruments
COMPASS force field for the studied molecular with the
[40]
Bis(4-chlorophenyl)sulphone, hydrazine hydrate(85%), 4-
methoxybenzaldehyde, 4-n-butoxy benzaldehyde, 4-t-butoxy
benzaldehyde, 4-methoxybenzaldehyde, THF, DMSO, acetone,
acetonitrile and DMSO-D6 were purchased from J&K (CHINA).
Melting points were measured on a Kofler melting point
apparatus and uncorrected. IR spectra were obtained in KBr
discs using a Nicolet 170SX FT-IR spectrometer. Elemental
analyses were performed on a Yannaco CHNSO Corder MT-3
analyzer. 1H NMR and 13C NMR has been recorded respectively
on INOVA 400 at 400 and 100MHz, with TMS as internal
standard, DMSO-D6 as deuterated solvents and chemical shifts
reported as ppm. Mass spectra were recorded on a Finnigan
MAT95 mass spectrometer. The absorption and fluorescence
amorphous cell
. It was carried out with constant
temperature and constant volume ensemble (NVT). The
temperature was set at 300K and kept constant using a nose
thermostat [41]. Pressure was set at 1 atm. Electrostatic
energies were calculated by the vdW & Coulomb method with
a 9.5-Å non-bonded cutoff. the total simulation time was
10.0ps and each step took 1.0fs.
3. Result and Discussion
3.1 Synthesis
spectra were
spectrophotometer
recorded
and
on
an
a
FLS920
CARY50
UV-VIS
fluorescence
The synthetic route was shown in Scheme 1.
3.1.1 4, 4’-Dihydraziondiphenyl sulfone
spectrophotometer. The Quantum Yield (QY) of the as-
synthesized BAHDS derivatives was calculated based on the
Two to three drops of triethylamine were added to a
suspension of 4,4’-dichlorodiphenyl sulfone (5.74g, 0.02mol)
and 50mL hydrazine hydrate(85%) in the round flask (250mL).
Then the mixture was reflux for 24 hours until the solid
completely dissolved. The resulting solution was cooled and
diluted with ice water; the precipitate was removed by
filtration, washed to neutrality with water, and dried over KOH.
The yield was 5.0g (90.0%). Found: M+, 278; calculation, 278.
ꢂ
ꢄ
ꢈ
ꢃꢄꢅꢆꢇ
following equation: Φꢀ
=
Φꢁ
∙
∙
.
Φf is the
ꢂ
ꢄ
ꢃꢄꢅꢆꢇ
ꢈ
fluorescence quantum yield,
I
is the intensity of the
fluorescent spectra, and A is the optical density at excitation
wavelength. QY was measured by taking anthracene as a
standard for BAHDS. R referred to the standard anthracene
with known quantum yield. Film samples for the
measurements of UV-vis and fluorescence spectroscopy were
prepared by drop casting and the subsequent spin-coating
(2000 rpm, 30 s) from THF solutions (100 mL) on quartz cell
(12.5 ×12.5×45 mm). The fluorescence microscope imaging of
the aggregations was obtained by Leica DM2500M. The cell
images were gathered with the inverted fluorescence
microscope (Olympus, IX71) and processed with Nikon AY
software. The scanning electron microscope (SEM) images of
the aggregations were obtained by Hitachi S4800. All the
experiments were carried out at room temperature.
3.1.2 Bis 4,4’-((E)-2-(4-4-alkoxyaniline
sulfone(BAHDS)
)
hydrazinyldiphenyl
The mixtures of 4-alkoxybenzaldehyde (0.0045 mol) and 4, 4’-
dihydraziondiphenyl sulfone (0.002 mol) dissolved in 10 ml of
dioxane. After stirred at 60°C for 2 h, the reaction mixtures
were cooled to room temperature. The solvents were removed
by evaporation. The obtained product was washed with water
for three times, and dried over anhydrous MgSO4 to yield the
product. Those structures were analysed by elemental
analysis, 1H NMR, 13C NMR and IR.
2.2 Cell culture and fluorescence imaging
A549 cells (human lung adenocarcinoma cell) were purchased from
the Shanghai Institute of Cell Biology. The cells were cultured in
Roswell Park Memorial Institute culture medium (RPMI-1640),
supplemented with 6% calf serum, penicillin (100 U∙mL-1),
streptomycin (100×10-6 g∙mL-1) and 2.5×10-4mol∙L-1 L-glutamine at
37°C in a 5% CO2 incubator. The cells were cultured in a 15 mm
diameter cell culture dish for 2 days. A549 cells were incubated
with the aggregations at a final concentration of 50 μg∙mL-1 for 30
min, and washed with PBS buffer to remove extra cellular material.
Then the dish placed to get a long-term imaging under an inverted
fluorescence microscope (Olympus, IX71) at 450 nm (λ = 380 nm).
2.3 Computational methods
BAHDS-1: White powder. Yield: 78%. m.p.: 259.6°C. Anal. calc.
formula: C28H26N4O3S. (%): C, 65.35; N, 10.89; H, 5.09. Found (%):C,
1
65.38; N, 10.72; H, 5.12. H-NMR (400 MHz, DMSO-D6) δ 10.79 (s,
2H), 7.94 (s, 2H), 7.68 (dd, J=9.2Hz, 8.8Hz, 8H), 7.16 (d, J = 8.8 Hz,
4H), 7.01 (d, J = 8.8 Hz, 4H), 3.61(s, 6H). 13C-NMR (100 MHz, DMSO-
D6) δ 50.22(CH3) 111.46(Ph) 114.23(Ph) 127.64(Ph-C) 128.73(Ph)
130.65(Ph-S) 139.86(C=N) 148.77(Ph-N) 159.89(Ph-O). FT-IR (ν, cm-
1): 3304 (νN-H) 2930, 2837 (νC-H) 1598 (νC=N)1279, 1105 (νSO2), 1030
(νC-O).
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BAHDS-2: White powder; Yield: 74%. m.p.: 225.5°C. Anal. calc. 3.2 Photo-physical properties
formula: C34H38N4O3S. (%): C, 68.20; N, 9.36; H, 6.40. Found (%):C,
Fig.1(a) showed UV absorption and fluorescence emission of
BAHDS derivatives in THF. Four BAHDS derivatives have similar
absorption and emission curves because of similar molecular
structure. The maximum absorption wavelength was located
at 355-365nm. The very weak fluorescent emissions were
displayed under a 365nm UV lamp, and the fluorescence
quantum yield was lower than 1% (Table1). The UV-vis spectra
and fluorescent spectra of BAHDS-1 in different solvents were
recorded in Fig.1 (b). The slightly red-shift with the polarity
increase of the solvents were observed in UV spectra. Stocks
shift (Δλ) was between 55 and 60 nm. Both of the moderate
Stocks shift (Δλ =55~60 nm) and the characteristics of
wavelength red-shift indicated the π-π* transition of the
absorption.
68.32; N, 9.41; H, 6.38. 1H-NMR (400 MHz, DMSO-D6) δ 10.78
(s,2H), 7.93 (s, 2H), 7.67 (dd, J=9.2Hz, 8.8Hz, 8H), 7.15 (d, J = 8.8 Hz,
4H), 6.99 (d, J = 8.8 Hz, 4H), 4.02(t, J = 6.4Hz, 4H), 1.72(m, 4H),
1.46(m, 4H), 0.96(t, J = 7.2Hz, 6H) 13C-NMR (100 MHz, DMSO-D6) δ
13.70(CH3) 18.72(C-C) 30.71(C-C) 67.24(C-O) 111.44(Ph) 114.69(Ph)
127.52(Ph-C) 128.72(Ph) 130.62(Ph-S) 139.89(C=N) 148.77(Ph-N)
159.35(Ph-O) FTIR (ν, cm-1): 3328 (νN-H), 3092, 2962, 2879 (νC-H),
1593 (νC=N), 1273, 1098 (νSO2), 1022 (νC-O
)
BAHDS-3: White powder; Yield: 73%. m.p.: 195.1°C. Anal.
calc.formula: C34H38N4O3S. (%): C, 68.20; N, 9.36; H, 6.40. Found
1
(%):C, 68. 27; N, 9.41; H, 6.38. H-NMR (400 MHz, DMSO-D6) δ
10.85 (s,2H), 7.95 (s, 2H), 7.67 (dd, J=9.2Hz, 8.4Hz, 8H), 7.16 (d, J =
8.8 Hz, 4H), 7.03 (d, J = 8.4 Hz, 4H), 1.35(s, 18H) 13C-NMR (100 MHz,
DMSO-D6)
δ
28.56(CH3) 78.47(C-C) 111.53(Ph) 123.53(Ph)
Optimized molecular structures at B3LYP/6-311G(d) level
and molecular orbital amplitude plots of HOMO and LUMO for
BAHDS derivatives were depicted in Fig.2. Because of their
similar structures, BAHDS 1-4 have similar HOMO, LUMO. Take
BAHDS-1 as an example: the hydrazine moiety of two sides
conjugated to the adjacent two benzene rings consisting of a π
conjugated plane separately. Two side π conjugated planes
intersected at sulfone and formed V-shaped D-π-A-π-D
molecular structures (the sulfone as the central acceptor core,
two hydrazinyldiphenyl conjugated chains as the π-bridge to
extend the conjugation length, and methoxy, n-butoxy, tert-
butoxy and 4-phenoxy as donor separately). The charges of
HOMO were focused on the hydrazone moiety and its nearby
phenyl ring, while charges of LUMO were centred on sulfone
moiety, which indicated the intramolecular charge transition
127.00(Ph-C) 128.76(Ph) 129.84(Ph) 130.79(Ph-S) 139.64(C=N)
148.70(Ph-N) 155.90(Ph-O) FTIR (ν, cm-1): 3290 (νN-H)，3115, 2978
(νC-H), 1593 (νC=N), 1273, 1098 (νSO2), 1022 (νC-O).
BAHDS-4: Yellow powder; Yield: 68%. m.p.: 178.4°C. Anal.
calc.formula: C38H30N4O3S. (%): C, 73.29; N, 9.00; H, 4.86. Found
(%):C, 72.98; N, 9.11; H, 4.56. 1H-NMR (400 MHz, DMSO-D6) δ 10.89
(s,2H), 7.98 (s, 2H), 7.73 (d, J= 9.2Hz, 7.2Hz, 8H), 7.45 (t, J= 8.0 Hz,
4H), 7.19 (m, 6H), 7.08 (t, J = 8.8 Hz, 8H). 13C-NMR (100 MHz,
DMSO-D6)
δ 111.46(Ph) 118.93(Ph) 123.81(Ph) 127.91(Ph-C)
128.77(Ph) 130.33(Ph) 130.90(Ph-S) 139.86(C=N) 148.77(Ph-N)
159.89(Ph-O). FTIR (ν, cm-1): 329 (δN-H) ，3067, 3042 (δC-H), 1591
(δC=N), 1273, 1105 (δSO2), 1061 (δC-O).
(ICT)
of
HOMO
to
LUMO.
Scheme 1 The synthetic route of BAHDS
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Fig. 1(a) UV-Vis absorption and fluorescence emission of BAHDS derivatives in THF (1×10-5mol∙L-1). (b) UV-vis and fluorescent spectra of BAHDS-1 in
different solvents (1×10-5mol∙L-1)
Table 1 the maximum absorption wavelength (λab, nm), emission wavelength, (λem, nm) and fluorescence quantum yield ( Φf , %) of BAHDS derivatives in THF and
THF/water
THF
λab(nm)
365
THF-water
λem(nm)
433
film
*
λem(nm)
408
Φf(%)
0.04
0.03
0.03
0.16
Φf(%)
2.7
water(%)
I/I0
λem(nm)
432
93
93
70
90
66.6
BAHDS-1
BAHDS-2
BAHDS-3
BAHDS-4
364
423
433
6.9
228.4
190.4
140.0
433
365
423
423
5.7
423
363
413
438
22.4
437
*I/I0:the proportion of Φf in THF to Φf in THFꢀwater
Time-dependent density functional theory calculation (TD- LUMO were close to the corresponding UV absorption
DFT) were applied to indicate the energies of HOMO and energies with a difference value of 0.15eV, 0.18eV, 0,19eV,
LUMO. Table 2 showed the energy gaps between the HOMO 0.22eV for BAHDS1-4 respectively. The distinction between the
and LUMO orbitals of DFT predicted and UV absorption. From calculations and experiments was in the acceptable ranges to
Table 2, the calculated energy gaps between the HOMO and indicate the significance of DFT calculations.
Fig.2 HOMO(top) and LUMO(bottom) orbitals of BAHDSꢀ1 BAHDSꢀ2 BAHDSꢀ3 and BAHDSꢀ4 computed by the B3LYP/6ꢀ311G(d) level of the theory from left to
right.
Table 2 Energy gaps of UV and TD-DFT (B3LYP/6-311G(d)/SCRF)
3(a)). With an increase in fw (water volume fraction) from 0% to
Experimental(eV)
Calculated(eV)
LUMO(eV)
HOMO
ꢀ5.40
ꢀ5.40
ꢀ5.36
ꢀ5.48
（eV）
80%, the absorption peaks basically remained at the same
positions. However, when the fw increased to 90%, the shoulder
absorption peak at about 300 nm rose. Meanwhile, the leveled-off
tails appeared in the visible region when fw equal to 90%, indicating
that aggregates were probably at nanoscale sizes. When fw≤80%,
no leveled-off spectral tails in the long-wavelength region
confirmed that the molecules dissolved as isolated species in the
solvent mixture. A very weak fluorescence emission was observed
in pure THF with Φf = 0.04% (Table 1). Similar to the UV spectra, the
fluorescence spectra exhibited no obvious changes as the content
of water increased from 0% to 80%. A dramatic fluorescence
enhancement was observed when fw equal to 90%. When fw equal
to 93%, the fluorescence increased to a maximum value, the
intensity was 66.6 times (Table 1) higher than that in pure THF, and
the fluorescence quantum yield increased to 2.7% (Table 1). In
addition, the maximum emission wavelength showed a red shift of
24 nm, which indicated that aggregates were probably at nanoscale
BAHDS-1
BAHDS-2
BAHDS-3
BAHDS-4
3.40 (365nm)
3.41 (364nm)
3.40 (365nm)
3.42 (363nm)
3.25
3.23
3.21
3.20
ꢀ1.68
ꢀ1.70
ꢀ1.69
ꢀ1.81
3.3 Aggregation-Induced Properties
A poor-solvent photoluminescence (PL) test, commonly used for
studying the AIE phenomenon [42-44], was performed to explore the
luminescent behaviour of the prepared BAHDS derivatives. As water
was a poor solvent of BAHDS 1-4, the molecules would aggregate in
THF/water mixtures with high water contents. Thus, the
luminescence from such systems primarily attributed to molecule
aggregation, not the solute molecules. AIE effect (I/I0) of BAHDS
derivatives was shown in Fig.3 and Table 1. In Fig.3, the changes of
UV in THF/water mixtures with varying water volume fractions
could confirm the formation of aggregate in BAHDS. BAHDS-1
exhibited an absorption peaks at 365 nm in pure THF solution (Fig
sizes [45]
.
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Fig.3 UV-vis and emission spectra of BAHDS-1 (a), BAHDS-2 (b), BAHDS-3 (c) and BAHDS-4 (d) in THF-water mixtures (5×10-5 mol∙L-1 ),
Our strategy toward increasing the steric hindrance of substituted Table 1, the fluorescence quantum yield of BAHDS-4 was 0.16% in
group was introducing the larger alkoxy, n-butoxyl, tert-butoxyl and THF. The further investigated aggregation fluorescence in
phenoxyl into the phenyl cycle of the molecules, which could THF/water solutions showed BAHDS-4 exhibited the large
prevent π-π stacking and was beneficial to AIE effects of BAHDS fluorescence enhancement for fw to 80 % in Fig.3 (d). When the
derivatives. In Fig.3 (b), Fig.3(c) and Fig.3(d) as fw increased to 70%, water fractions increased to 90 %, the intensity reached to the
the shoulder absorption peak appeared and the leveled-off tails maximum, the emission enhanced 140 times (fw= 90%) compared
appeared in the visible region, indicating the formation of with BAHDS-4 in THF(Table1), and the Φf increased to 22.4%, the
aggregates states for all of BAHDS-2,3,4. It can be found that both largest in BAHDS 1-4. Additionally, the emitted wavelength red
BAHDS-2 and BAHDS-3 exhibited outstanding fluorescence shifted from 422 nm of BAHDS-1 to 438 nm of BAHDS-4.
enhancement for fw> 70% in the THF/water solutions. The
maximum emission enhancements of 228.4-fold(fw = 93%), 190.4-
fold (fw =70%) (Table 1) for BAHDS-2 and BAHDS-3 respectively are
larger than that of BAHDS-1 in THF/water (66.6-fold), and their
fluorescence quantum yields were measured to be 6.9% and 5.7%.
Moreover, the maxima emission wavelengths shifted red 10-20nm.
As shown in MD calculations ( Fig. 4), an intramolecular hydrogen
bond interaction was found in BAHDS-4. It affected the vibration of
BAHDS-4 and increasing of the rigidity of molecule, which benefited
to the fluorescence enhancement in THF solution. As shown in
Fig.4 molecular dynamic calculation of BAHDS-4 in THF solution
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As we can envisage, the steric hindrance relevant to phenyl rings characteristics, which will be also beneficial for the novel molecular
was gradually enhanced with increasing substituted groups. The design.
steric hindrance of the substituted groups, n-butoxy, tert-butoxy
Fig. 5(a) displayed SEM image of BAHDS derivatives. In the image
and phenoxy were larger than methoxyl in BAHDS system, and the of SEM, the diameter of nanoscale size of BAHDS derivatives in
motion or vibration of the phenyl rings were suppressed in THF/water was about 500nm. BAHDS-1 and BAHDS-4 were sphere
aggregation states, which led to the enhanced fluorescence. In shaped nanostructure, and BAHDS-2 and BAHDS-3 were needle like
comparison with BAHDS-2 and BAHDS-3, because of the p-π nanoscale structures .Fluorescence microscope image of BAHDS
conjugation between oxygen and phenyl, the rigidity of BAHDS-4 derivatives under UV irradiation was showed in Fig.5(b). The
molecule probably improved as well, on account of the steric nanoscale particles of BAHDS1-4 emitted strongest bright blue
repulsion of the large groups, giving rising to fluorescence quantum fluorescence under illumination with a 365nm UV lamp. The
yields boosting from 0.01 (BAHDS-1) to 0.16 (BAHDS -4) in THF formation of aggregation state could also be proved by the level-off
solution (Table 1). Namely, by internal control through the tail stretching into the longer wavelength region in film state in
introduction of alkoxylgroups, the PL properties of the BAHDS Fig.5(c). Calculations of full-width half maximum (fwhm) revealed
derivatives can be modulated. This indicated that steric congestion that the emission spectra of the BAHDS in the solid state were
of the relevant substituted can fix the molecules and significantly comparable and narrower as compared to the emission spectra
inhibit the non-radiance annihilation process, leading to the high obtained in THF/water. Formation of higher order aggregates in
luminescence of BAHDS-4 even in dilute solution. Based on steric water or solution resulted in such narrower and higher intensity
hindrance, by the introduction of para- alkoxylin the BAHDS unit, emission bands because of reduced intermolecular interactions.
the triggered RIR as the fundamental mechanism of the intriguing The packing efficiency and intermolecular interactions also
AIE phenomenon was directly verified through simple chemical contribute to enhanced luminescence.
modifications. Probably, the investigations on AIE phenomenon can
give us a definite understanding of the mechanism of AIE
Fig. 5(a) SEM image of BAHDS-1 (1), BAHDS-2 (2), BAHDS-3 (3), BAHDS-4 (4) under UV irradiation. (b) Fluorescence microscope image of BAHDS-1 (1), BAHDS-2 (2),
BAHDS-3 (3), BAHDS-4 (4). (c) Normalised PL spectra of BAHDS derivatives in film state.
Fluorescence spectral measurement was determined every six of BAHDS derivatives could remain stable for a long time. Also, Fig.
hours until forty-eight hours. It was shown in Fig. 6(a) that with the 6(b) indicated the excellent stability of BAHDS derivatives in a large
increasing standing time of BAHDS derivatives, few change could be range of pH from 3 to 8.
observed. It showed that strong aggregation induced fluorescence
Fig.6 Normalized PL spectra of BAHDS 1-4 (10μM in THF/Water solvent) at different standing time (a) and different pH (b).
3.4 Mechanism of the AIE of BAHDS
To find the links between AIE and the packing mode in the solid calculation of the packing of BAHDS-1. In Fig.7, the main
state, molecular dynamic calculation of BAHDS-1, BAHDS-2 and intermolecular interactions existed in O…H, and the distance
BAHDS-4 were performed. Fig.7(a) showed the molecular dynamic between O and H were 2.774Å and 2.467Å respectively (Fig.7(a)).
6 | J. Name., 2012, 00, 1-3
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The intermolecular interaction forced tortuosity of the molecules, Both two reasons above increased AIE effect(I/I0 = 228.4 times
which prevented the face-to-face packing mode, and caused AIE (Table 1)). Because of similar structures, we did not calculate the
enhancement: I/I0 was 66.6 times (Table 1). Fig.7(b) showed the packing mode of BAHDS-3. We held that the mechanism of AIE
molecular dynamic calculation of BAHDS-2. Different from BAHDS- enhancement was similar to that of BAHDS-2 (I/I0 = 190.4). In the
1, the intermolecular hydrogen bonds were found in BAHDS-2 (Fig. packing mode of BAHDS-4, the intermolecular hydrogen bonding
7(b)). The distance between O and H were 1.858Å and 1.818Å. The
intermolecular hydrogen bonding interaction inhibited the
intramolecular rotation[46-48], which benefited to AIE enhancement.
Similar to that in BAHDS-1, face-to-face stacking was not found.
interaction were also found and the distance of O…H were 1.879Å,
1.955Å, 1.875Å and 1.826Å respectively. Strong hydrogen bonds in
BAHDS-4 held the structure of BAHDS-4 more securely, thus the
bond vibration decreased and AIE increased (I/I0 = 140.0).
(c)
(a)
(b)
Fig.7 Packing mode of BAHDS-1(a), BAHDS-2(b) and BAHDS-4(c) computed by MD method
3.5 living cell imaging
Fig.8 Fluorescence images of A549 treated with 50 μg.mL-1 BAHDS-1 under visible light (left) and UV irradiation (right).
Living cell imaging of A549 was obtained at 450 nm (λ = 380 nm) by cell membrane permeable and can also be used for the imaging of
inverted fluorescence microscope. The cells displayed a bright blue cells. [49-51]
fluorescence image. The fluorescence images were depicted in
Fig.8. The fluorescence and bright-field images revealed a high cell probe should be taken into consideration. The MTT assay was
membrane permeability of BAHDS-1. performed to evaluate the toxicity of BAHDS-1 by A549 cells. 8-16-
As for intracellular imaging applications, the cytotoxicity of the
To confirm the formation of aggregation inside the cells, small 24 h incubation was taken at the same condition. The experimental
amount of BAHDS-1 was added to the cell culture fluid to simulate data were expressed in Table 3. BAHDS-1 exhibited little
the cell environment, and dynamic light scattering (DLS) cytotoxicity for cells, and at the concentration of 20 µM, the cell
measurement was conducted. As it was shown in Fig.9, the average viability was still more than 85%. This result demonstrates that
diameter of the particle was 391.5nm, which indicated the BAHDS-1 had a good biocompatibility.
formation of aggregation inside the cells. BAHDS-1 could probably
permeate the cell membrane in the solution state, and aggregate
inside the cell. These results demonstrated that the BAHDS-1 was
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Journal Name
3
4
5
6
7
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Concentration
of BAHDS-
Cell survival
16h
8h
24h
1(×10-5 mol·L-1
)
0
99%
98%
97%
95%
93%
98%
98%
95%
92%
89%
98%
96%
94%
90%
85%
0.5
1
1.5
2
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Wang, Y. C. Wu, C. C. Lo, A. Lien, J. B. Peng, Y. Cao and S. J.
Su, J. Mater. Chem. C, 2015, 3, 6986-6996.
Table 3 Cell survival with 0, 0.5, 1, 1.5, 2 mol∙L-1 BAHDS-1 after 8, 16, 24h.
8
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Fig.9 DLS data of BAHDS-1 in the cell culture fluid.
Conclusions
BAHDS derivatives were designed and synthesized, and their
structures were characterized by NMR, IR, and element analysis.
The investigation of photo-physical properties displayed the strong
AIE effect of BAHDS in THF/water mixture solvent. The maximum
enhancement was 228.4 times of that in pure THF. Fluorescent
microscope imagines showed blue fluorescence in THF/water
mixture solvent, which attributed to the formation of the aggressive
state. The mechanism of aggregation induced emission (AIE) was
supported by molecular dynamic calculations. The results depicted
that the packing mode and intermolecular hydrogen bond inhibited
the intramolecular rotation and prevented π-π stacking, which
caused AIE effect. Living cell imaging considered that BAHDS
derivatives had good cell permeability and distinct blue
fluorescence in A549 living cells. It was successfully applied to living
cells staining, which demonstrated its value for practical
applications in physiological systems.
25 B. Z. Tang, Chem Mater, 2003;15:1535-1546.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (No. 51079094) and the Natural Science
Foundation of Jiangsu Province (No. BK2010215). The Project
was funded by the Priority Academic Program Development of
Jiangsu Higher Education Institutions.
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The SEM and fluorescence microscope image of BAHDS derivatives showed its nanoscale size and the strong
fluorescence in solid state.