Ionization and Anion-π+ Interaction: A New Strategy for Structural Design of Aggregation-Induced Emission Luminogens

Article abstract of DOI:10.1021/jacs.7b10150

Recent years have witnessed the significant role of anion-π⁺ interactions in many areas, which potentially brings the opportunity for the development of aggregation-induced emission (AIE) systems. Here, a new strategy that utilized anion-π

Full text of DOI:10.1021/jacs.7b10150

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Article
Ionization and Anion-#+ Interaction: A New Strategy for
Structural Design of Aggregation-Induced Emission Luminogens
Jianguo Wang, Xinggui Gu, Pengfei Zhang, Xiaobo Huang, Xiaoyan Zheng, Ming
Chen, Haitao Feng, Ryan T. K. Kwok, Jacky W. Y. Lam, and Ben Zhong Tang
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b10150 • Publication Date (Web): 30 Oct 2017
Downloaded from http://pubs.acs.org on October 30, 2017
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Ionization and Anionꢀπ+ Interaction: A New Strategy for Structural
Design of AggregationꢀInduced Emission Luminogens
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Jianguo Wang,†,⊥,ǁ Xinggui Gu,†,ǁ Pengfei Zhang,† Xiaobo Huang,‡ Xiaoyan Zheng,† Ming Chen,†
Haitao Feng,† Ryan T. K. Kwok,† Jacky W. Y. Lam† and Ben Zhong Tang*,†,ǂ,§
†Department of Chemistry, Hong Kong Branch of Chinese National Engineering, Research Center for Tissue Restoration and
Reconstruction, Institute of Molecular Functional Materials, State Key Laboratory of Molecular Nanoscience, Division of
Life Science and Biomedical Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowꢀ
loon, Hong Kong, China
‡College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035, China
ǂ
State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640,
China
§Guangdong Provincial Key Laboratory of Brain Science, Disease and Drug Development, HKUST Shenzhen Research Inꢀ
stitute, Shenzhen 518057, China
⊥Key Laboratory of OrganoꢀPharmaceutical Chemistry, Gannan Normal University, Ganzhou 341000, China
ABSTRACT: Recent years have witnessed the significant role of anionꢀπ+ interactions in many areas, which potentially brings the
opportunity for the development of aggregationꢀinduced emission (AIE) systems. Here, a new strategy that utilized anionꢀπ+ interꢀ
actions to block detrimental πꢀπ stacking was first proposed to develop inherentꢀcharged AIE systems. Two AIEꢀactive luminogens,
namely 1,2,3,4ꢀtetraphenyloxazolium (TPOꢀP) and 2,3,5ꢀtriphenyloxazolium (TriPOꢀPN) were successfully synthesized.
Comprehensive techniques such as singleꢀcrystal analysis, theoretical calculation and conductivity measurement were used to illusꢀ
trate the effects of anionꢀπ+ interactions on the AIE feature. Their analogues tetraphenylfuran (TPF) and 2,4,5ꢀtriphenyloxazole
(TriPOꢀC) without anionꢀπ+ interactions suffered from the aggregationꢀcaused emission quenching in the aggregate state, demonꢀ
strating the important role of anionꢀπ+ interactions in suppressing πꢀπ stacking. TriPOꢀPN was biocompatible and could specifically
target lysosome in fluorescence turnꢀon and washꢀfree manners. This suggested that it was a promising contrast agent for bioimagꢀ
ing.
by multiple noncovalent interactions such as hydrogen
bonding and CHꢀπ interactions between molecules.21
INTRODUCTION
Noncovalent interactions, such as hydrogen bonding, πꢀπ
stacking, CHꢀπ and anionꢀπ+/cationꢀπꢀ interactions, play
significant roles in broad areas such as supramolecular
chemistry, structural biology and material science.1ꢀ7 They are
crucial to maintain the structures of lifeꢀrelated
biomacromolecules like proteins and DNA/RNA and also
show an determinate effect on the structures and properties of
materials.8ꢀ11 In particular, noncovalent interactions exert great
influence on the emission behaviors of luminescent
materials.12ꢀ18 For example, traditional luminogens often
suffered from notorious aggregationꢀcaused quenching (ACQ)
effect in the aggregate state, mainly due to the πꢀπ stacking of
their molecules.19,20 Recently, some luminogens have been
found to exhibit a phenomenon of aggregationꢀinduced
emission (AIE) characteristic that is exact opposite of the
ACQ effect. These molecules are weakly emissive in solution
but show efficient light emission in the aggregate state. Such
property makes them find wide applications in optoelectronics
and biomedical field.21ꢀ29 The efficient emission of AIE
luminogens (AIEgens) in the solid state is ascribed to their
twisted conformations, which hamper the detrimental πꢀπ
stacking, and also the restriction of the intramolecular motion
Anionꢀπ interactions are a class of important noncovalent
interactions and their existence was first proved
experimentally in 1993.30 Since then, they have received
growing attention for their prominent contribution in the areas
of supramolecular chemistry and molecular recognition.30ꢀ38
When the aromatic π systems inherently bear positive charges,
the positive charges are often found to be participated in
anionꢀπ bonding to strengthen the binding ability. Such kind of
electrostaticꢀdominating interactions was defined as anionꢀπ+
interactions.39 Because of the special position of the anions
close to the aromatic π systems, the anionꢀπ+ interactions
could be endowed with the ability to tune the emission of
luminogens by interfering the intermolecular stacking,
especially as barriers to impede the πꢀπ stacking in AIE
systems (Chart 1). To our best knowledge, no paper on the
role of anionꢀπ+ interactions on the AIE feature has been
reported. On the other hand, charge interactions are ubiquitous
in biological systems and are widely studied in biomacromoleꢀ
cules such as DNA, RNA and proteins and intracellular orgaꢀ
nelles. Thus, AIEgens carrying charges have greatly extended
their applications in biosensors and bioimaging because their
charge interactions with biomacromolecules are anticipated to
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improve the biocompatibility and subcellular targeting abilꢀ
(Figure 1E). The fluorescence quantum yield (Φsolid) of TPOꢀP
ity.40ꢀ43 However, the introduction of charges to AIEgens curꢀ
rently suffers from tedious synthesis, laborious purification
and high cost. Thus, it is of great interest to develop inherentꢀ
charged AIEgens with anionꢀπ+ interactions and systematically
investigate the dependence of their light emissions on these
noncovalent interactions.
solid powder was measured to be 18.58%, which was about
16ꢀfold higher than that in solution. The radiative decay rate
(kr) increased from 1×107 sꢀ1 in solution to 1.9×108 sꢀ1 in the
solid powder, while the nonradiative decay rate (knr) decreased
from 11.5×108 sꢀ1 to 8.1×108 sꢀ1 (Table 1). Clearly, TPOꢀP is
AIEꢀactive. However, according to the reported paper,45 its
analogue tetraphenylfuran (TPF) exhibited ACQ effect (Figure
1A). This motivates us to study the origin of strong emission
of TPOꢀP in the solid state.
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In this work, we intent to develop inherentꢀcharged AIE
systems by taking the advantage of anionꢀπ+ interactions to not
only restrict the intramolecular motions but also block πꢀπ
interactions (Chart 1). We utilized oxazole, a wellꢀknown
subunit of natural products,44 as a building block to construct
AIEꢀactive 1,2,3,4ꢀtetraphenyloxazolium (TPOꢀP) with
inherent positive charge. Single crystal analysis, theoretical
calculation and conductivity experiments have been carried
out to elucidate the structureꢀproperty relationship. Further
reducing the number of peripherical phenyl rotors at different
positions of TPOꢀP produced positiveꢀcharged 2,3,5ꢀ
triphenyloxazolium (TriPOꢀPN) and nonꢀionic 2,4,5ꢀ
triphenyloxazole (TriPOꢀC) displaying AIE and ACQ
phenomena, respectively. This verifies the crucial role of
anionꢀπ+ interactions on the AIE feature. In addition, TriPOꢀ
PN was also developed to function as visualizing agent for
specific imaging of lysosome with the merits of good
biocompatability, fast response and washꢀfree procedure.
Collectively, this work thus demonstrates a promising strategy
of anionꢀπ+ interactions to guide the design of potential
AIEgens with inherent charges for biological applications.
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Chart 1. Design rationale of inherentꢀcharged AIE system
based on anionꢀπ+ interactions.
Figure 1. (A) Chemical structures of TPOꢀP, TPF, TriPOꢀPN
and TriPOꢀC. PL spectra of (B) TPOꢀP and (C) TriPOꢀPN in
THF/hexane mixtures with different hexane fractions (fH). (D)
PL spectra of TriPOꢀC in THF/water mixtures with different
water fractions (fW). Inset: fluorescent photographs of TPOꢀP
and TriPOꢀPN and TriPOꢀC in mixed solvents with different
fH or fW taken under 365 nm UV irradiation. (E) Plot of
relative PL intensity (I/I0) versus the composition of the
THF/hexane mixtures of TPOꢀP and TriPOꢀPN and
THF/water mixtures of TriPOꢀC, where hexane and water
served as poor solvents and I0 was the PL intensity in pure
THF. Concentration: 10 ꢁM. Excitation wavelength (nm): 347
for TPOꢀP and TriPOꢀPN and 320 for TriPOꢀC.
RESULTS AND DISCUSSION
TPOꢀP was readily obtained in three steps with high yield
according to the synthetic route shown in Scheme S1 in the
Electronic Supporting Information. All the intermediates and
desirable products were characterized by standard
spectroscopies methods with satisfactory results (Figures
S1−S9). Its single crystal was obtained from methanol and
characterized crystallographically (Table S1). It inherently
bears a positive charge during the fiveꢀmembered ring
formation (Figure 1A). Its UV/vis spectrum was measured in
THF solution with the absorption maximum at 314 nm (Figure
S10 and Table 1). Upon photoexcitation, weak photoluminesꢀ
cence (PL) at 442 nm was detected with negligible fluoresꢀ
cence quantum yield (Φsoln = 1.18%) (Figure 1B). The emisꢀ
sion of TPOꢀP affected little by the solvent polarity, as veriꢀ
fied by large similarity of its PL spectra measured in different
solvents (Figure S11). Addition of hexane with a volume fracꢀ
tion of below 60% into the THF solution showed no obvious
fluorescence enhancement. Afterward, the PL intensity was
abruptly enhanced, accompanying with a blue shift in the
emission maximum by 23 nm due to the aggregate formation
The single crystal structure of TPOꢀP was shown in Figure
2A. The torsion angles between phenyl rings at 2ꢀ and 5ꢀ
positions and oxazole core were 28.19º(θ2) and 21.11º(θ5),
respectively. However, they became remarkably large for
those at 3ꢀ and 4ꢀpositions with values of 58.61º(θ3) and 80.77
º(θ4), respectively. The ionization of the oxazole core may
lead to poor conjugation between the two units. Coupled with
the synergetic steric hindrance of the phenyl rings at 3ꢀ and 5ꢀ
positions, that explain why the phenyl ring at 4ꢀposition was
nearly perpendicular to the oxazole core. The highest occupied
molecular orbital (HOMO) and lowest unoccupied molecular
orbital (LUMO) of TPOꢀP were calculated based on its single
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crystal structure by singleꢀpoint calculations using the oxazole core. As a result of large torsion angles of the periphꢀ
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B3LYP/6ꢀ31G(d,p) method. As shown in Figure 3, the elecꢀ
tron density of HOMO was mainly localized on the oxazole
core and the 2ꢀ and 5ꢀphenyl rings, while the LUMO was conꢀ
tributed by the orbitals from the oxazole core and the 2ꢀphenyl
ring. Neither orbitals from 3ꢀphenyl ring nor those from 4ꢀ
phenyl ring contributed to the HOMO and LUMO because
these phenyl rings were not electronically conjugated with the
eral phenyl rings, TPOꢀP adopted a twisted conformation in
crystal state which was immobilized by CHꢀπ interactions with
distance of 2.838 Å and hydrogen bonding between the
fluorine atoms of hexafluorophosphate anion and phenyl
hydrogens atoms with distances of 2.352 Å and 2.596 Å
(Figure 4A and S12).
Table 1. Photophysical properties of TPOꢀP, TriPOꢀPN and TriPOꢀC.
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c
E (kcal/mol)f
λabs
(nm (nm)
314 419
λem
τ (ns)a
Ф (%)b
kr (×108 sꢀ1)d
knr (×108 sꢀ1)e
αAIE
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soln solid
0.86 1.02
2.42 1.32
1.13 0.89
soln
1.18
2.56
solid
soln
0.1
solid
1.9
soln
11.5
4.0
solid
TPOꢀP
18.58 15.75
17.70 6.91
8.1 ꢀ63.95, ꢀ71.97
6.2 ꢀ65.08, ꢀ64.02
TriPOꢀPN 314 431
TriPOꢀC 308 373
0.1
1.4
54.32 22.20 0.41
4.8
2.5
4.1
8.8
/
aτ: average fluorescence lifetime calculated by τ = ΣA τ 2/ΣA τ , where A is the preꢀexponential for lifetime τ . bФ = fluorescence quantum yield measured by using an integrating sphere. cα
= Ф
solꢀ
. dk = radiative decay rate (Φ/τ). ek = nonradiative decay rate (1/τ ꢀ k ). fE = interaction energies between π+ and anion calculated based on their single crystal structures by singleꢀpoint calculations
nr
i i
i i
i
i
AIE
/Ф
id soln
r
r
using the M062X/6ꢀ31+G(d,p) method.
block the detrimental πꢀπ stacking, and restrict further the
intramolecular motions. The ACQ effect was thus largely
diminished, making TPOꢀP a strong emitter in the solid state.
Figure 4. Intermolecular stacking of (A) TPOꢀP, (B) TriPOꢀ
PN and (C) TriPOꢀC.
To further demonstrate the critical role of positive charge
and anionꢀπ+ interactions on the AIE characteristic, TriPOꢀPN
and TriPOꢀC were designed and synthesized by removing the
phenyl ring at different positions of TPOꢀP (Figure 1A,
Scheme S2 and Figures S13−S21). TriPOꢀPN possessed the
inherent positive charge. It showed weak emission in THF but
its emission was turned on by aggregate formation (Figure 1C
and 1E). Clearly, similar to TPOꢀP, TriPOꢀPN was AIEꢀactive.
The Φsoln of TriPOꢀPN was only 2.56%, while Φsolid was much
higher (17.70%) (Table 1). The Φsoln of TriPOꢀPN was nearly
two times larger than that of TPOꢀP, which might be attributed
to the lesser consumption of the excited energy by the
intramolecular motions of smaller number of phenyl rings.[5a]
The nonꢀcharged TriPOꢀC emitted strongly in THF solution
(Φsoln = 54.32%) but its emission was partially quenched upon
aggregation (Φsolid = 22.20%), displaying the ACQ behavior
(Figure 1D, 1E and Table 1). The AIE and ACQ
characteristics of TriPOꢀPN and TriPOꢀC were also supported
by comparing their kr and knr values in the solution and solid
states. As summarized in Table 1, the kr of TriPOꢀPN
increased from 1×107 sꢀ1 in solution to 1.4×108 sꢀ1 in the solid
state. However, the kr of TriPOꢀC decreased from 4.8×108 sꢀ1
to 2.5×108 sꢀ1 upon aggregation. Evidently, ionization of the
oxazole core played an indispensable effect on the AIE feature
of TPOꢀP and TriPOꢀPN.
Figure 2. Molecular structures and torsion angles of (A) TPOꢀ
P, (B) TriPOꢀPN and (C) TriPOꢀC. Anionꢀπ+ distances of (D)
TPOꢀP and (E) TriPOꢀPN.
Figure 3. B3LYP/6ꢀ31G(d,p) calculated molecular orbital
amplitude plots of HOMOs and LUMOs of TPOꢀP, TriPOꢀPN
and TriPOꢀC based on their single crystal structures.
Notably, two hexafluorophosphate anions were found on
both sides of the positiveꢀcharged oxazole core with distances
of 2.881 Å and 3.017 Å (Figure 2D). Evidently, this indicated
the existance of anionꢀπ+ interactions, which was first
observed in AIE systems according to our best knowledge.
The energy of such interactions was calculated to be ꢀ63.95
and ꢀ71.97 kcalꢁmolꢀ1 (Table 1),31,39,46 implying that the anionꢀ
π+ interactions were strong and could serve as good tool to
Next, the molecular conformations and interactions of
TriPOꢀPN and TriPOꢀC were investigated (Figure 2B and 2C).
Similar to TPOꢀP, TriPOꢀPN showed a twisted conformation
with a large torsion angle of 79.14º between the 3ꢀphenyl ring
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and the oxazole core due to the ionization of the oxazole core. confine the free movement of ions. The conductivity of TPOꢀP,
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The orbitals of 3ꢀphenyl ring contributed neither to the HOMO
nor the LUMO of TriPOꢀPN (Figure 3). In sharp contrast,
TriPOꢀC exhibited a more planar structure and its HOMO and
LUMO were contributed by orbitals from the whole molecule.
Further investigation of the single crystal structure of TriPOꢀ
PN found that anionꢀπ+ interactions with distances of 3.385 Å
and 3.416 Å and energies of ꢀ65.08 and ꢀ64.02 kcalꢁmolꢀ1 were
TriPOꢀPN and TriPOꢀC in THF/hexane mixtures was not afꢀ
fected by salts or surfactants, such as NaCl, sodium 1ꢀ
hexadecylsulfonate (SHDS) and hexadecyl trimethyl ammoniꢀ
um bromide (CTAB) (Figure S26). However, when methanol,
a highly polar solvent was added to the THF solutions of TPOꢀ
P, TriPOꢀPN and TriPOꢀC, their conductivity increased linearꢀ
ly with its fraction owing to its high conductivity (Figure S27).
Collectively, the XRD diffractograms, TEM and SEM images
and conductivity results are consistent with the PL behaviors
and further verified the formation of anionꢀπ+ interactions
during aggregation and their significant role to the AIE
phenomenon.
observed
between
the
two
fluorine
atoms
of
hexafluorophosphate anions and the positiveꢀcharged oxazole
core (Figure 2E and Table 1). Such strong anionꢀπ+
interactions efficiently impeded the πꢀπ stacking to avoid
emission quneching. In addition, CHꢀπ interactions with a
distance of 2.922 Å, hydrogen bonds such as FꢀH interactions
with distances of 2.586 Å and 2.536 Å, and πꢀπ interactions
with a distance of 3.396 Å were also found in the crystal
lattice to restrict the intramolecular motions (Figure 4B and
S22). Without the interference from the 4ꢀphenyl ring, πꢀπ
interaction may occur in the flat portion of TriPOꢀPN
involving the 2,5ꢀphenyl rings and the oxazole core. However,
πꢀπ stacking was hampered by anionꢀπ+ interactions. On the
other hand, π–π stacking served as dominant interactions in
crystals of TriPOꢀC without positive charge and anionꢀπ+
interactions (Figure 4C), resulting in severe emission
quenching in the solid state. Clearly, ionization and anionꢀπ+
interactions contributed significantly in the AIE characteristics
of TPOꢀP and TriPOꢀPN.
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The positiveꢀcharged character of TPOꢀP and TriPOꢀPN
should enable them to well dispersed in aqueous solution.
These solutions are presumably to be nonꢀemissive as the fast
movements of all dye cations and anions prevent the formation
of anionꢀπ+ interactions. When TPOꢀP and TriPOꢀPN enter the
cell and are docked at organelles, intramolecular motions and
movements of TPOꢀP and TriPOꢀPN were restricted to turnꢀon
their light emission. If this holds true, TPOꢀP and TriPOꢀPN
can function as fluorescence contrast agents for live cell imagꢀ
ing in a washꢀfree manner, involving no tendious and timeꢀ
consuming washing procedures as required in traditional
fluorescent probes.48ꢀ50 We then explored the potential applicaꢀ
tions of TPOꢀP and TriPOꢀPN in live HeLa cells imaging.
Before exploring such possibility, the cytotoxicity of TriPOꢀ
PN was first evaluated by CCKꢀ8 assay. As shown in Figure
S28, no significant change in the cell viability was observed
when the HeLa cells were incubated with TriPOꢀPN at a conꢀ
centration of up to 100 ꢂM, revealing the low cytotoxicity of
the dye molecule to living cells. Then, the HeLa cells were
incubated with TriPOꢀPN and after 15 min, the lysosomes of
the HeLa cells were lighted up with blue color (Figure 5A). To
verify the specific staining of lysosome by TriPOꢀPN, a cosꢀ
taining experiment was carried out with Lysotracker® Green
DNDꢀ26 (LTG), a commercial available lysosome targeting
probe. The good overlapping clearly demonstrated that only
the lysosomes were targeted (Figure 5A). When continuously
observed the staining process in 6 min under a confocal
microscopy (Figure 5B), it was found that TriPOꢀPN could
quickly stain the living HeLa cells as fluorescence was
observed in lysosomes within 96 s with a negligible
background emission. In sharp contrast, the fluorescence of
HeLa cells stained with LTG was always on and the
backgound emission was still very strong even after staining
for 312 s. This indicated that TriPOꢀPN was a good washꢀfree
lysosomeꢀspecific probe, which endowed it with a great
potential for monitoring biological processes in real time. We
also replaced TriPOꢀPN by TPOꢀP but the dye could not enter
the cells, presumably due to its large molecular size.
In order to disclose whether anionꢀπ+ interactions form
during aggregation, TPOꢀP was chosen as a representative and
the structures of its microcrystals and aggregates were anaꢀ
lyzed by powder XRD diffraction. The microcrystals of TPOꢀ
P were grown by slow evaporation of its methanol solution,
and were found to show anionꢀπ+ interactions by singleꢀcrystal
Xꢀray crystallography. The aggregates of TPOꢀP were obꢀ
tained by filtration of its suspension in THF/hexane mixture
with a hexane fraction of 90%. As shown in Figure S23, the
XRD diffractogram of the aggregates largely resembles to the
microcrystals, indicating that they possess similar packing
arrangements. The TEM and SEM images of the aggregates
display wellꢀaligned and highlyꢀordered architectures (Figure
S24). All these results suggest the high crystallinity of the
aggregates and the existence of anionꢀπ+ interactions in their
structures.
Additionally, conductivity measurements of TPOꢀP, TriPOꢀ
PN and TriPOꢀC were also carried out in THF/hexane
mixtures with different fH and different concentrations. Since
conductivity depends mainly on the diffusion coefficients of
counterion, the smallꢀsized hexafluorophosphate anion should
carry most of the ionic current. Once it participated in anionꢀπ+
interaction after aggregation, its movement will be largely
confined to result in dramatic decrease in conductivity.47 As
shown in Figure S25, with an increase of fH in THF/hexane
mixture, the conductivity of TPOꢀP and TriPOꢀPN became
lower. At fH of 60% or above, the conductivity reached to a
value similar to that of blank. Thickening the solution
concentration just affected the value at fH of below 60% but
not the later ones. In contrast, the conductivity of TriPOꢀC in
different THF/hexane mixtures was almost the same as that of
blank due to the absence of charge. In solution, TPOꢀP and
TriPOꢀPN form no anionꢀπ+ interactions, due to the fast
movements of the ions. Once aggregates formed, the
conductivity of TPOꢀP and TriPOꢀPN started to decrease
owing to the gradual formation of anionꢀπ+ interactions to
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ACKNOWLEDGMENT
This work was partially supported by the National Basic Research
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Program of China (973 Program, 2013CB834701 and
2013CB834702), the University Grants Committee of Hong Kong
(AoE/Pꢀ03/08), the Innovation and Technology Commission
(ITCꢀCNERC14SC01 and ITCRD/17ꢀ9), the Research Grants
Council of Hong Kong (16308016, 16305015, C2014ꢀ15G,
N_HKUST604/14 and AꢀHKUST605/16), the Guangdong
Innovative Research Team Program (201101C0105067115), the
Science
and
Technology
Plan
of
Shenzhen
9
(JCYJ20160229205601482), the National Natural Science
Foundation of China Grant (81271476), Guangzhou Science and
Technology Research Grant (201300000154), the 111 Project
Grant (B13037) and the Shenzhen Peacock Plan.
10
11
12
13
Figure 5. (A) Confocal images of HeLa cells costained with
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TriPOꢀPN (1 ꢁM) and LTG (1 ꢁM). (B) Realꢀtime
fluorescence images of the HeLa cells stained with TriPOꢀPN
(1 ꢁM) or LTG (1 ꢁM) without undergoing the washing
process at different incubation times.
CONCLUSIONS
In this work, we proposed a novel strategy for developing
inherentꢀcharged AIEgens by introducing anionꢀπ+ interactions
to block the detrimental πꢀπ stacking. AIEꢀactive TPOꢀP and
TriPOꢀPN with inherent positive charges and nonꢀcharged
TriPOꢀC with ACQ effect were wellꢀdesigned and synthesized
based on the oxazole core. The negligible emission of TPOꢀP
and TriPOꢀPN in solutions was stemmed from the ionization
of the oxazole core, which lead to poor conjugation between
the core and the rotors to result in free rotation of the 3ꢀ and 4ꢀ
phenyl rings. The strong emission of TPOꢀP and TriPOꢀPN in
the solid state was dominantly attributed to anionꢀπ+
interactions that prevented the formation of πꢀπ stacking.
Single crystal analysis, theoretical calculation and
conductivity study had been carried out to illustrate the effect
of anionꢀπ+ interactions on the AIE characteristic. Their nonꢀ
ionic analogue TriPOꢀC suffered from the ACQ effect, further
revealing the significant role of anionꢀπ+ interactions to AIE.
TriPOꢀPN exhibited good cell permeability functioned as a
contrast agent for specific targeting of lysosomes in a
fluorescence turnꢀon fashion. Compared to commercial LTG,
no washing was required for TriPOꢀPN after incubation,
demonstrating its promising application in bioimaging in real
time. Thus, this work will open a new view to develop
inherentꢀcharged AIEgens for various biological applications.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website.
Materials and methods, synthetic procedures, characterization,
crystallographic data and computational details, including Figures
S1− S28 and Tables S1. (PDF)
AUTHOR INFORMATION
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B.; Tian, W.; Gao, H.; Angew. Chem. Int. Ed. 2016, 55, 155.
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izza, E.; Striccoli, M.; Gu, X.; Leung, N. L. C.; Tang, B. Z.; Pucci, A.
Mater. Chem. Front. 2017, 1, 1406.
Corresponding Author
*tangbenz@ust.hk
Author Contributions
ǁThese authors contributed equally.
Notes
(28) Gu, X.; Kwok, R. T. K.; Lam, J. W. Y.; Tang, B. Z. Bioꢀ
materials 2017, 146, 115.
The authors declare no competing financial interest.
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