A Novel Strategy to Design and Construct AIE-active Mechanofluorochromic Materials via Regulation of Molecular Structure

Article abstract of DOI:10.1002/chem.202102578

In this work, we first designed and synthesized tetraphenylene-fused aryl-imidazole derivatives TM-1–4 via regulation of molecular structure, which were consisted of 1H-imidazo[4,5-f][1,10]phenanthroline, 1H-phenanthro[9,10-d]imidazole, 4,5-diphenyl-1H-im

Full text of DOI:10.1002/chem.202102578

Accepted Article
Accepted Article
Title: A Novel Strategy to Design and Construct AIE-active
Mechanofluorochromic Materials via Regulation of Molecular
Structure
Authors: Kaibo Zheng, Hui Chen, Yufeng Xiao, Xiang Liu, Jiaying Yan,
and Nuonuo Zhang
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To be cited as: Chem. Eur. J. 10.1002/chem.202102578
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A
Novel Strategy to
Design
and
Construct
AIE-active
Mechanofluorochromic Materials via Regulation of Molecular
Structure
Kaibo Zheng,*a Hui Chen,a Yufeng Xiao,a Xiang Liu,*a Jiaying Yan,a and Nuonuo Zhang*a
[a]
Prof. K Zheng, H Chen, Y Xiao, X Liu, J Yan, N Zhang
College of Materials and Chemical Engineering, Key laboratory of inorganic nonmetallic crystalline and energy conversion materials
China Three Gorges University
Yichang 443002, P. R. China
E-mail: zhengkbo@126.com(K Zheng); nnzhang2015@ctgu.edu.cn(N Zhang); xiang.liu@ctgu.edu.cn(X. Liu)
Supporting information for this article is given via a link at the end of the document.((Please delete this text if not appropriate))
aggregated state, which seriously limits the effective applications
of the mechanofluorochromic materials. Interestingly, Tang et
al.[8] and Park et al.[9] first discovered two unusual phenomena
Abstract: In this work, we first designed and synthesized
tetraphenylene-fused aryl-imidazole derivatives TM-1~4 via
regulation of molecular structure, which were consisted of 1H-
imidazo[4,5-f][1,10]phenanthroline, 1H-phenanthro[9,10-d]imidazole,
Aggregation
Induced/Enhanced
Emission
(AIE/AIEE),
respectively. Therefore, the AIE/AIEE characteristics are
contributed to the acquisition of new emissive solid-state
4,5-diphenyl-1H-imidazole,
3,3'-(1H-imidazole-4,5-diyl)dipyridine
moieties and AIE-active tetraphenylethene units, respectively. The
results illustrated that TM-1~4 exhibited obvious AIE characteristics.
Meanwhile, TM-2 and TM-3 show excellent solid emission properties
(ΦTM-2=13.73% and ΦTM-3=36.21%), whereas TM-1 and TM-4 exhibit
the opposite properties (ΦTM-1=1.48% and ΦTM-4=4.83%). The
multiple rotors (pyridine and benzene ring) causes twisted
conformations of the molecule that prevents π-π stacking and
fluorophores, and provides
a new strategy for designing
mechanofluorochromic materials.
The fluorescence emission properties of organic
fluorophores, mainly depending on molecular planarity, π-
conjugate structure, substituted heteroatoms, and so on.
Such as the position and number of the nitrogen atoms in
the aromatic frameworks exert influence on fluorescence
emission properties, the multiple rotors causes twisted
conformations of the molecule, prevents π-π stacking and
enhances solid emission. TPE, as one representative of
AIE fluorophore has been widely utilized for the
construction of AIE-active mechanofluorochromic materials
owing to its nonplanar π-conjugated structure, and it is a
beneficial core for solid-state materials.[6,10] The structural
modulation of TPE moiety by the introduction of novel
chemical bonds or substitution of heterocyclic rings would
lead to the acquisition of emissive solid-state materials. In
this work, we first designed and synthesized
tetraphenylene-fused aryl-imidazole derivatives TM-1~4 via
regulation of molecular structure, which were consisted of
1H-imidazo[4,5-f][1,10]phenanthroline, 1H-phenanthro[9,10-
d]imidazole, 4,5-diphenyl-1H-imidazole and 3,3'-(1H-
imidazole-4,5-diyl)dipyridine moieties and AIE-active
tetraphenylethene units, respectively (Scheme 1).
As we expected, The TM-1~4 still exhibited obvious AIE
characteristics. Meanwhile, TM-2 and TM-3 showed
enhances
solid
emission(ΦTM-2<ΦTM-3,
ΦTM-1<ΦTM-4).
Significantly, TM-2 and TM-3 also exhibited reversible
mechanochromic behavior (Emission red shifts: ΔλTM-2=43 nm and
ΔλTM-3=41 nm) with color changes between blue and green
emissions. The powder X-ray diffraction (PXRD) suggested the
disordered state of ground sample could be readily returned to an
ordered crystalline. Therefore, the mechanochromisms of TM-2 and
TM-3 are ascribable to the phase transformation between crystal
and amorphous structure. The single crystal X-ray analysis of TM-2
reveals a twisted conformation for TPE moiety and the absence of
π-π intermolecular stacking. These excellent optical properties of
TM-2 and TM-3 make them potentially applications in
mechanochromic materials and imaging agents.
Introduction
In recent several years, organic fluorophores have sparked
tremendous interest on account of their promising use in
mechanofluorochromic materials,[1] semiconductor,[2] bioimaging
and sensor,[3] etc. Among them, mechanofluorochromic, as a
functional materials with solid-state emission, is altered on
applying mechanical stimuli such as grinding, crushing and
pressing.[4] So far, a large number of mechanofluorochromic
materials have been reported and applied in anti-counterfeiting,
data storage, mechanosensors and light sources, such as
borate complexes,[5] tetraphenylethylene (TPE) derivatives,[6]
and so on.[7] However, there are still lack of a clear design
guideline for mechanofluorochromic materials owing to the
complicated nature of mechanoresponsive process. Therefore,
the search for new organic fluorophores with mechanical
discoloration is still a challenge.
Unfortunately, most conventional organic fluorophores
subjected to notorious aggregation-caused quenching (ACQ)
effect due to extensive π-π stacking interaction in the
Scheme 1. The molecular structure of TM-1~4
1
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excellent solid emission properties, whereas TM-1 and TM-
and pyridine ring). We further investigated the effect of
acids on their fluorescence emission. As shown in Figure
S15, with the addition of acid (HCl: 0 to 10 µM) it leads to a
gradual decrease of emission intensity. The results showed
that the acid can quench the fluorescence of the TM-1 and
4
exhibited the opposite properties. Significantly, TM-2 and
TM-3 also exhibited reversible mechanochromic behavior
with color changes from blue to green. The powder X-ray
diffraction (PXRD) suggested that the disordered state of
ground sample can be readily returned to an ordered
crystalline. The single crystal X-ray analysis of TM-2 further
confirmed a twisted conformation for moiety and the
absence of π-π intermolecular stacking. In particular, the
fluorophores could be applied in living cells.
TM-4
.
Results and Discussion
The synthetic routes towards the fluorophores TM-1,
TM-2, TM-3 and TM-4 are shown in Scheme 2. The TM-1,
TM-2, TM-3 and TM-4 were synthesized by a classical
“one-pot” reaction of the compound
1 with ammonium
acetate and 1,2-diaryl ethylenedione in good yields. The
TM-1, TM-2, TM-3 and TM-4 were characterized with 1H
NMR and 13C NMR spectroscopy, HRMS (Figures S1-S13).
TM-2 were further characterized by X-ray single crystal
structural analysis.
Figure 1. Fluorescence emission spectra of 5 μM TM-1(a), TM-2(c), TM-3(e)
and TM-4(g) in water/THF mixtures solvents with different fw (0-95%). Plots of
the fluorescence emission intensity with different fw (0-95%) (TM-1 (b), TM-2
(d), TM-3 (f) and TM-4 (h). λex=350 nm, dex=5.0 nm, dem=10 nm.
Scheme 2. Synthetic routes of TM-1~4
Firstly, the photophysical properties and fluorescence
quantum yields (ΦF) of TM-1, TM-2, TM-3 and TM-4 in the solid
state were measured. The absorption peaks of TM-1, TM-2, TM-
3 and TM-4 showed at 403, 411, 406 and 386 nm, respectively
(Fig. S16 in the Supporting Information and Table 1). The
corresponding fluorescence emission peaks are 583, 454, 448
and 449 nm (Figure 2a) with Φ of 1.48%, 13.73%, 36.21% and
4.83%, respectively. It is noteworthy that TM-2 and TM-3
showed bright blue fluorescence emission, while TM-1 and TM-4
exhibted very weak fluorescence emission in solid state under
UV lamp (365 nm) (Figure 2c). The fluorescence emission color
and intensity showed good agreement with Φ and emission
bands. In solid states, the free rotation of the phenyl groups in
TPE moiety were suppressed for TM-1 and TM-4, and thus
decreased the corresponding nonradioactive decay. However,
the fluorescence emission intensity of TM-1 and TM-4 was still
weak (ΦTM-1=1.48%, ΦTM-4=4.83%). The phenomenons are
probably attributed to the presence of phenanthroline and
pyridine rings in the molecular scaffolds, which could produce
other non-radiative decay process via increasing the intersystem
crossing (ISC) efficiency (S1→T1), and leading to a decrease in
the fluorescence quantum yield.[6c,11] Meanwhile, TM-2 and TM-3
Firstly, the UV-vis absorption spectra of TM-1, TM-2,
TM-3 and TM-4 in water/THF mixtures solvents (water
fraction, fw=0-95%) were investigated, respectively. The
TM-1, TM-2, and TM-3 exhibit two major absorption
wavelength range of about 270 nm-315 nm and 315 nm-
400 nm, in solvent mixtures with fw≥80%, the absorption
peaks decreases and slight sways (Figures S14a-c in the
Supporting Information). The absorption peaks of TM-4 at
330 nm, when fw reaches 80%, and the absorption peak red
shifts (Figures S14d in the Supporting Information). The
absorption bands can be assigned to the π-π* transition
and the charge transfer (CT) transition. Subsequently, their
emission spectra were tested in water/THF mixtures (water
fraction, fw=0-95%)) for investigating the AIE properties.
The TM-1, TM-2, TM-3 and TM-4 were nearly non-emissive
in pure THF solution, but they became strong emissive in
higher water contents (>70%), which reveals that they still
retain AIE active because of the twisted conformation for
TPE moiety (Figures 1a-h). The molecular structures of TM-
1
and TM-4 contain nitrogen heterocycles (phenanthroline
2
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show excellent solid emission properties (ΦTM-2=13.73% and
ΦTM-3=36.21%). Obviously, the results further indicated that π-
expanded nitrogen heterocyclic (phenanthroline and pyridine
rings) of such kinds of organic fluorophores quench the solid
fluorescence emission. Meanwhile, the multiple rotors (TM-3 and
TM-4) causes twisted conformations of the molecule that
prevents π-π stacking and enhances solid emission(ΦTM-2<ΦTM-3,
ΦTM-1<ΦTM-4). The TM-1, TM-2, TM-3 and TM-4 showed
moderate fluorescence lifetimes (4.14 ns, 1.30ns, 1.56 ns and
1.29 ns), respectively (Figure 2b).
packing from the crystal state and amorphous state is a key
factor of mechanochromism.
Figure 3. fluorescence emission spectra of TM-2 (a) and TM-3 (c), as
synthesized, grinded and soaked solids, Inset) photographs TM-2 (a) and TM-
3 (c), as synthesized, grinded and soaked solids under 365 nm UV light.
Powder X-ray diffractograms changes of TM-2 (b) and TM-3 (d), as
synthesized, grinded and soaked solids.
Figure 2. (a) Normalized fluorescent spectra of TM-1, TM-2, TM-3 and TM-4
in solid state. λex,TM-1=400 nm, λex,TM-2~4=350 nm, dex=3.0 nm, dem=3 nm. (b)
Excerpts of lifetime-decays spectra of TM-1, TM-2, TM-3 and TM-4 in solid
state. (c) The picture of colors from the powders of TM-1, TM-2, TM-3 and TM-
4 under ambient light (top) and 365 nm UV light (bottom).
The slow evaporation of EtOH/ acetonitrile solvent mixtures
was used to grow single crystals for TM-2 (CCDC: 2082247) at
room temperature, and then analyzed by single crystal X-ray
diffraction. CCDC-2082247 (TM-2) contains the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/structures. TM-2 single crystal
is belonged to monoclinic crystal system and P21/c space group.
The unit cell parameters are as follows: a=19.7046(18) Å,
b=10.2384(7) Å, c=17.9682(16) Å, α=90°, β=114.755(11)° and
γ=90° (Table 2). As shown in Figure 4, the crystal structure of
TM-2 shows twisted conformation of TPE moiety, and adopt a
head-to-tail slipped stacking arrangement. The molecular
stacking structure provided large amounts of cavities, making it
susceptible to destruction of the lattice by external forces, and
leaded to excellent mechanochromic properties.6e Whereas, no
π-π stackings between aromatic rings are formed. The twisted
conformation promotes intramolecular rotations in solution
leading to weak
Table 1 Photophysical properties of TM-1, TM-2, TM-3 and TM-4 in solid
state.
λabs (nm)
403
λem (nm)
583
Φ
τ/ns
4.14
1.30
1.56
1.29
TM-1
TM-2
TM-3
TM-4
1.48%
13.73%
36.21%
4.83 %
411
454
406
448
386
449
In view of the good solid-state fluorescence emission
properties of TM-2 and TM-3, we have further studied their
mechanochromic properties. After grinding, the bright blue
emitting of TM-2 and TM-3 can to bright green emitting and the
emission peaks are remarkable red-shifted to a range from 454
to 497 nm(Δλ = 43 nm) and 448 to 489 nm (Δλ = 41 nm) (Figure
3a and 3c), respectively. The emission peak position and
fluorescence color after soaking (EtOH) treatment are close to
those before grinding. It is worthy noting that their
mechanochromic effect are reversible. To explore insight into
the the mechanisms of emission color changes, powder X-ray
diffraction (PXRD) measurements were used to investigate the
structures of molecular aggregation before and after grinding.
Many diffraction sharp curves of the untreated sample, indicating
that the TM-2 and TM-3 are ordered arrangement forms of
crystals. However, after grinding, The diffraction peaks
weakened or vanished, which indicated an amorphous structure.
Furthermore, when soaked with EtOH, the sharp diffraction
peaks, similar to those of the as-prepared sample, could be
reappeared (Figure 3b, 3d). The results suggesting the
amorphous state of ground sample can be readily recovered to
crystalline. Therefore, the mechanochromism of TM-2 and TM-3
should be attributed to the phase interconversion between
crystal and amorphous. The red-shift in emission spectra is
ascribable to the change from the twisted crystalline to the
planar amorphous state reflecting enhanced conjugation.[12] The
PXRD study reveals that the destruction of solid state molecular
Figure 4. Crystal structure and packing arrangements of TM-2
.
3
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Reflections collected
Independent reflections
Data/restraints/parametrs
Goodness-of-fit on F2
Final R indexes [I>=2σ (I)]
Final R indexes [all data]
Largest diff. peak/hole / e Å-3
12879
6435 [Rint = 0.0714, Rsigma = 0.1068]
6435/0/392
fluorescence. In the packing diagram of TM-2, the intermolecular
C-H···π (2.690 Å and 2.644 Å) weak interactions lead to a loose
packing motif (Figure 4). So it exhibts a high fluorescence
quantum yield in solid state. Therefore, The order of ΦTM-2<ΦTM-3
and ΦTM-1<ΦTM-4 are attributed to twisted conformations of
benzene and pyridine ring, hindering π-π stacking in solid state.
To sum up, the π-π stacking patterns play an important role for
0.974
R1 = 0.0666, wR2 = 0.1551
R1 = 0.1131, wR2 = 0.1802
0.45/-0.34
improving solid emission.
To illuminate the electronic and geometry structure of such
kinds of fluorophore, the theoretical calculations were performed
according to the density functional theory (DFT) with the
Gaussian 16 programs.[13] The optimised geometries structures
for TM-1, TM-2, TM-3 and TM-4 show twisted conformation, and
effectively block π-π stacking. The lowest unoccupied molecular
orbitals (LUMOs) energy level in TM-1, TM-2, TM-3 and TM-4
are mostly located on the TPE unit and imidazole, whereas the
highest occupied molecular orbitals (HOMOs) energy levels of
TM-1, TM-2, TM-3 and TM-4 are locate in the entire molecules.
The theoretical band gap for TM-1, TM-2, TM-3 and TM-4 are
3.62 eV, 3.54 eV, 3.58 eV and 3.64 eV respectively (Figure 5).
Such density changes of the electron clouds indicated that the
four molecules had an ordinary intramolecular charge transfer
process. The optimised geometries structure of TM-3 and TM-4
confirmed that the dihedral angles between imidazole ring and
phenyl or pyridine rings were 38.68° and 44.21°, the change of
fluorescence quantum yield of solid-state emission was
attributed to twisted conformations of the molecule.
Table 2 Crystal data and structure refinement for TM-2
Identification code
TM-2
Empirical formula
Formula weight
Temperature/K
Crystal system
C41H28N2
548.65
99.98(10)
monoclinic
P21/c
19.7046(18)
10.2384(7)
17.9682(16)
Space group
a/Å
b/Å
c/Å
α/°
β/°
γ/°
90
114.755(11)
90
3291.9(5)
Volume/Å3
Z
ρcalcg/cm3
μ/mm-1
F(000)
Crystal size/mm3
Radiation
4
1.107
0.492
1152.0
0.12 × 0.11 × 0.08
Cu Kα (λ = 1.54184)
9.854 to 146.99
-19 ≤ h ≤ 23, -7 ≤ k ≤ 12, -22 ≤ l ≤ 21
2Θ range for data collection/°
Index ranges
Figure 5. Optimised geometries and spatial distribution of the HOMO, LUMO of TM-1, TM-2, TM-3 and TM-4.
In order to explore the application of the TM-1
and TM-4 as fluorescent agents in celluler imaging.
confocal fluorescent microscopy was used to study the
application of the TM-1 TM-2 TM-3 and TM-4 for staining
of the live cells. B-16 cells were incubated with 5 μM TM-1
TM-2 TM-3 and TM-4 for 20 mins at 37 °C, respectively.
, TM-2, TM-
3
,
,
,
,
The cells incubated with the fluorophores displayed
significantly fluorescence signs (Figure 6b, e, h, and k).
These results demonstrated that TM-1, TM-2, TM-3 and
TM-4 were cell membrane permeable and capable of
fluorescence imaging in living cells. These fluorophores
4
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have potential applications in the biomedical fields.
Figure 7. Proposed mechanism of fluorescence regulation.
Conclusion
In summary,
a
series of microstructural change
tetraphenylene-fused imidazole derivatives (TM-1, TM-2,
TM-3 and TM-4) have been first designed and synthesized
by a classical “one-pot” reaction. The chemical structures of
these fluorophores were fully confirmed by 1H NMR, 13C
Figure 6. Fluorescence images of B-16 cells incubated with 5 μM TM-1
TM-2 TM-3 and TM-4 for 20 min at 37 , (b, e, h, k) fluorescence
imaging of TM-1 TM-2 TM-3 and TM-4; (a, d, g, i) bright-field image; (c,
,
NMR, and HRMS. The TM-1
, TM-2, TM-3 and TM-4
,
℃
manifest obvious AIE characteristics. It is noteworthy that
TM-2 and TM-3 showed wonderful solid-state emission
(ΦTM-2=13.73% and ΦTM-3=36.21%). The results could
further indicated that π-expanded nitrogen heterocyclic
(phenanthroline and pyridine rings) of such kinds of organic
fluorophores quench the solid fluorescence emission (ΦTM-
1=1.48%, ΦTM-4=4.83%). Meanwhile, the multiple rotors
,
,
f, i, l) overlay of parts a and b, d and e, g and h, j and k, respectively.
Scale bar=20 μm. λEX=405 nm, λem =470±40 nm.
Considering the wide range of applications of
mechanofluorochromic materials in chemical engineering
and materials science, it is crucial to reveal the structure-
property relationships through chemical modification. In
other words, it is crucial to understand the mechanism of
fluorescence regulation. As showed in Figure 7, it is clear
that the introduction of different nitrogen heterocyclic
scaffolds and multiple rotors on the same TPE montys is a
facile strategy to change solid-state emission the properties.
(
TM-3 and TM-4) causes twisted conformations of the
molecule, prevents π-π stacking and enhances solid
emission (ΦTM-2 ΦTM-3 ΦTM-1 ΦTM-4 The optimised
<
,
<
).
geometries structure of TM-3 and TM-4 confirmed that the
dihedral angles between imidazole ring and phenyl or
pyridine rings were 38.68° and 44.21°, the increasing
Introduction
of
nitrogen
heterocyclic
scaffolds
fluorescence quantum yield (ΦTM-2<ΦTM-3, ΦTM-1<ΦTM-4) of
(phenanthroline and pyridine rings) could produce other
non-radiative decay process via increasing the ISC
efficiency (S1→T1),[6c,11] and leading to a decrease in the
fluorescence quantum yield (ΦTM-1(phenanthroline)<ΦTM-
solid-state emission was attributed to twisted conformations
of the molecule. Significantly, TM-2 and TM-3 also exhibited
reversible mechanochromic behavior (blue to green). The
powder X-ray diffraction (PXRD) suggested the disordered
state of ground sample can be readily returned to an
ordered crystalline. Therefore, the mechanochromisms of
TM-2 and TM-3 are ascribable to the phase transformation
between crystal and amorphous structure. The single
4(pyridine)<ΦTM-2(phenanthrene)<ΦTM-3(benzene)).
DFT
calculations showed that the conformation of nonplanar
molecules (multiple rotors: benzene and pyridine rings)
improved the fluorescence quantum efficiency because of
preventing π-π stacking (ΦTM-2<ΦTM-3 and ΦTM-1<ΦTM-4). The
crystal X-ray analysis of TM-2 reveals
a
twisted
results showed that the fluorescence properties were
closely related to the molecular planarity, π-conjugate
structure and substituted heteroatoms. The microchemical
structure modification based on TPE core maybe provide a
good strategy for the synthesis of mechanofluorochromic
materials.
conformation for TPE moiety and the absence of π-π
intermolecular stacking. In particular, these fluorophores
have been successfully applied in living cells. These
excellent optical properties of TM-2 and TM-3 make them
potentially applications in mechanofluorochromic materials
and imaging agents. Fruther, we really hope TMs will be
applied
in
anti-counterfeiting,
data
storage,
mechanosensors and light sources with high functional
performance.
Experimental Section
5
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Compound
1
was prepared according to the literature.[14] 1
H
130.90, 130.71, 130.68, 130.63, 127.97, 127.87, 127.79,
126.65, 126.56, 125.16, 123.68, 122.41, 122.12. HRMS:
NMR (400 MHz, CD2Cl2) δ 9.88 (s, 1H), 7.61-7.59(m, 2H),
7.20(d, J=8.2 Hz, 2H), 7.14-7.12(m, 9H), 7.05-7.01(m, 6H).
+
calcd for C39H29N4 [M+H]+: calcd for 553.2387. found m/z
TM-1/TM-2
mmol), ammonium acetate (0.75 mmol) and 1,10-
phenanthroline-5,6-diketone or Phenanthrenequinone
:
4-(1,2,2-triphenylvinyl)benzaldehyde (0.15
553.2409.
(0.18mmol) in 5 mL acetic acid were stirred and refluxed for
3.5 h. And then cooled to room temperature, the mixtures
were poured into 20 mL water. The precipitate was filtered
and washed with water, EtOH, respectively, dried to give
Acknowledgements
This work was supported by financial support from National
Natural Science Foundation of China (Nos. 21805166 and
21606145), the 111 Project (D20015), the Engineering
Research Center of Eco-environment in Three Gorges
Reservoir Region, Ministry of Education, China Three
Gorges University (KF2019-05), the outstanding young and
middle-aged science and technology innovation teams,
Ministry of Education, Hubei province, China (T2020004)
and Foundation of Science and Technology Bureau of
Yichang City (A21-3-012).
TM-1 and TM-2
.
1
TM-1: Yield: 58.9%, H NMR (400 MHz, DMSO-d6) δ 13.69
(s, 1H), 9.03 (d, J=2.9 Hz, 2H), 8.91 (d, J=8.1 Hz, 2H), 8.02
(d, J=8.2 Hz, 2H), 7.84 (dd, J=7.8, 4.3 Hz, 2H), 7.24-7.12
(m, 11H), 7.05 (d, J=7.1 Hz, 4H), 7.00 (d, J=6.3 Hz, 2H). 13
C
NMR (100 MHz, DMSO-d6) δ 150.37, 147.59, 143.03,
142.95, 142.73, 141.39, 139.93, 131.31, 130.72, 130.68,
130.59, 129.96, 127.93, 127.83, 126.76, 126.66, 125.73,
+
123.43. HRMS: calcd for C39H27N4 [M+H]+: calcd for
551.2230, found m/z 551.2227.
1
TM-2: Yield: 78.4%, H NMR (400 MHz, DMSO-d6) δ13.37
Conflicts of interest
(s, 1H), 8.85 (dd, J=14.0, 8.4 Hz, 2H), 8.54 (dd, J=17.2, 7.8
Hz, 2H), 8.06 (d, J=8.2 Hz, 2H), 7.79-7.68 (m, 2H), 7.66-
7.59 (m, 2H), 7.23-7.10 (m, 11H), 7.05 (d, J=6.6 Hz, 4H),
7.00 (d, J=6.3 Hz, 2H).13C NMR (100 MHz, DMSO-d6) δ
148.80, 144.09, 143.09, 143.02, 142.81, 141.22, 140.03,
137.03, 131.22, 130.74, 130.68, 130.61, 128.38, 127.90,
127.82, 127.65, 127.50, 127.11, 127.03, 126.92, 126.72,
126.61, 125.59, 125.31, 125.11, 124.05, 123.69, 122.35,
121.93, 121.84. HRMS: calcd for C41H28N2Na+ [M+Na]+:
calcd for 571.2145. found m/z 571.2114.
TM-3: 4-(1,2,2-triphenylvinyl)benzaldehyde ( 0.2 mmol),
NH4OAc (1 mmol) and 1,2-diphenylethane-1,2-dione
(0.3mmol) in 5 mL acetic acid were stirred and refluxed for
3.5 h. And then cooled to room temperature, the mixtures
poured into 20 mL water. The precipitate was filtered and
There are no conflicts to declare.
Keywords: Dyes • Mechanofluorochromic materials• AIE-active
• Organic fluorophores • Tetraphenylethylene
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washed with water, EtOH, respectively, dried to give TM-3
.
Yield: 50.5%, 1H NMR (400 MHz, DMSO-d6) δ12.60 (s, 1H),
7.84 (d, J=8.2 Hz, 2H), 7.50 (dd, J=18.2, 7.4 Hz, 4H), 7.43
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2H), 7.19-7.11 (m, 10H), 7.07-6.99(m, 8H). 13C NMR (100
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124.57. HRMS: calcd for C41H31N2 [M+H]+: calcd for
551.2482. found m/z 551.2474.
TM-4
: 4-(1,2,2-triphenylvinyl)benzaldehyde ( 0.15mmol),
NH4OAc (0.76 mmol) and 1,2-di(pyridin-2-yl)ethane-1,2-
dione (0.23mmol) in 5 mL acetic acid were refluxed for 3.5
h. And then cooled to room temperature, the mixture was
added to the dilute solution of NaOH, brought pH to about
7.0, and extracted with CH2Cl2; then the organic phase was
dried by anhydrous Na2SO4, filtered and evaporated in
vacuo. The residue was subjected to column
chromatography eluting with ethyl acetate/petroleum ether
(1:4) to give TM-4. Yield: 22.2%, 1H NMR (400 MHz,
DMSO-d6)δ 12.92 (s, 1H), 8.66 (s, 1H), 8.51 (s, 1H), 8.17 (d,
J=7.7 Hz, 1H), 7.99 (d, J = 8.0 Hz, 2H), 7.86-7.75 (m, 2H),
7.31 (s, 2H), 7.19-7.10 (m, 10H), 7.05-6.98 (m, 8H). 13C
NMR (100 MHz, DMSO-d6) δ154.07, 148.66, 145.64,
143.45, 143.10, 142.93, 141.01, 140.14, 136.56, 136.01,
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In this work, we first designed and synthesized tetraphenylene-fused aryl-imidazole derivatives TM-1~4 via regulation of molecular
structure. The results illustrated that TM-1~4 exhibited obvious AIE characteristics. Meanwhile, TM-2 and TM-3 show excellent solid
emission properties (ΦTM-2=13.73% and ΦTM-3=36.21%), whereas TM-1 and TM-4 exhibit the opposite properties (ΦTM-1=1.48% and
ΦTM-4=4.83%). The multiple rotors (pyridine and benzene ring) causes twisted conformations of the molecule that prevents π-π
stacking and enhances solid emission(ΦTM-2<ΦTM-3, ΦTM-1<ΦTM-4). Significantly, TM-2 and TM-3 also exhibited reversible
mechanochromic behavior (Emission red shifts: ΔλTM-2= 43 nm and ΔλTM-3= 41 nm) with color changes between blue and green
emissions.
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