From Tetraphenylfurans to Ring-Opened (Z)-1,4-Enediones: ACQ Fluorophores versus AIEgens with Distinct Responses to Mechanical Force and Light

Article abstract of DOI:10.1002/chem.201801507

Two aryl-substituted tetraphenylfurans (TPF-1 and TPF-2) and the corresponding ring-opened (Z)-1,4-enedione derivatives (TPBD-1 and TPBD-2) have been successfully synthesized. Although all the molecules adopt propeller-like configurations, experimental re

Full text of DOI:10.1002/chem.201801507

A Journal of
Accepted Article
Title: From Tetraphenylfurans to Ring-Opening (Z)-1,4-Enediones:
ACQ Fluorophores versus AIEgens with Distinct Responses to
Mechanical Force and Light
Authors: Xia Liu, Mengwei Li, Meifang Liu, Qiuhua Yang, and Yulan
Chen
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To be cited as: Chem. Eur. J. 10.1002/chem.201801507
Link to VoR: http://dx.doi.org/10.1002/chem.201801507
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From Tetraphenylfurans to Ring-Opening (Z)-1,4-Enediones: ACQ
Fluorophores versus AIEgens with Distinct Responses to
Mechanical Force and Light
Xia Liu,a Mengwei Li,a Meifang Liu,b Qiuhua Yang*a and Yulan Chen*a
Abstract: Two aromatic substituted tetraphenylfuran TPFs (TPF-1
and TPF-2) and the corresponding ring-opening (Z)-1,4-enedione
derivatives TPBDs (TPBD-1 and TPBD-2) have been successfully
synthesized. Although all the molecules adopted propeller-like
configurations, experimental results revealed that TPFs were
aggregation-caused quenching (ACQ) fluorophores whereas TPBDs
were aggregation-induced emission (AIE) active. Additionally, TPFs
fluorochromic materials are attracting increasing research
attention.3
Mechanochromic fluorescent (MCF) materials show
photoluminescence and color change when mechanical force
(such as grinding, crushing, rubbing, or extrusion) is applied.4 It
is a unique family of smart materials which are able to present
visualized signalling accompanied with force induced transition
of molecular structure or aggregate morphology, and thus are
greatly promising in the applications of mechanosensors,
security papers, and optical storage.5 AIEgens generally
possess twisted conformations and hence afford a more loosely
packing pattern rather than a planar structure. This facilitates
their transformation between different morphologies by external
stimuli, such as heating, solvent fuming, mechanical deformation,
and so forth. Therefore, recently, AIEgens with MCF
performance are delicately developed. However, until now,
those with advanced performances in high emission contrast
and turn-on emission are scarce. Moreover, the coexistence of
diverse properties in a single molecular platform, though highly
desirable, is rare.
and
TPBDs
exhibited
prominently
opposite
“turn-on”
mechanochromic behaviours, with unusual blue shift of
mechanochromic fluorescence for TPFs and remarkable red shift
mechanochromism for TPBDs. Both of these solid state optical
properties are proved highly dependent on molecular packing mode
and substituents effect. In particular, besides the aggregation and
mechanical force controllable fluorescent properties, the ground
TPF-1 is found efficiently sensitive to light. On the basis of these
findings, we constructed a smart film with ground TPF-1 and
demonstrated its utility in data encryption and decryption well
controlled by UV light. Therefore, this work not only provides an
insight into the mechanism of AIE as well as mechanochromic
effects, but also paves the way towards developing multi-functional
stimuli-responsive materials and devices.
As pioneered by Tang and coworkers, the (hetero)
cyclopentadiene derivatives, for instance, 1-methyl-1,2,3,4,5-
pentaphenylsilole,6
1,2,3,4-tetraphenyl-1,3-cyclopentadiene
(TPC),7 1,1-dimethyl-2,3,4,5-tetraphenylsilole (TPS),8 1,2,3,4,5-
pentaphenylpyrrole (PPP)9 were identified as a modular type of
AIEgens. They all have propeller-shaped structures and exhibit
AIE properties due to the well-established restriction of
intramolecular motion (RIM) mechanism. However, when the
hetero atom of cyclopentadiene was replaced with O, the
resultant compound, tetraphenylfuran (TPF) displayed
unpredicted ACQ effect.10 In contrast, the (Z)-tetraphenylbut-2-
ene-1,4-dione (TPBD), which can be regarded as the ring
opening derivative of tetraphenylfuran, was found AIE active
recently by our group.11 These unexpected and sharply different
optical properties of the two propeller like analogues inspired us
to take a deep insight into their mechanistic understanding.
Furthermore, although all these pristine tetraphenyl modified
compounds are silent toward external perturbation including
mechanical force and light, to expand the advanced utilities of
TPF based luminophores, we are now intending to find out a
modular approach for the cost-effective fabrication of multi-
responsive and -functional molecular optical materials.
Introduction
In the last decade, many researchers committed to the
development of solid state luminescent materials for their
widespread applications in organic light-emitting diodes (OLEDs),
photoacoustic imaging and bioimaging, etc.1 In practical, these
fluorophores are usually used in their film state, so the
properties of the aggregates dominate devices’ performance
eventually. However, many traditional luminogens were usually
highly emissive in dilute solution but weak in aggregate state,
which was known as the aggregation-caused quenching (ACQ)
effect.2 In contrast, the so called aggregation-induced emission
(AIE) discovered by Tang and co-workers is excited, since the
non-emissive luminogens can become productive in emitting
upon aggregation. Therefore, AIE luminogens (AIEgens) are
ideal building blocks to construct emissive materials, devices
and AIE based probes. Currently, beyond the above-mentioned
applications,
AIEgens
as
versatile
stimuli-responsive
To this end, in this contribution, we designed and synthesized
two aryl substituted tetraphenylfurans and their 1,4-enediones
derivatives by oxidative ring opening of the furan ring (Scheme
1). Their crystal structures, photophysical properties both in
solution and solid states were systematically characterized,
through which the TPF derivatives are demonstrated as ACQ
luminophores while the TPBD ones are AIE active. Notably, all
the aryl substituted derivatives are mechanochromic fluorescent,
among which, the triphenylamine substitution was found
efficiently to promote the mechanical sensitivity, leading to high
[a]
[b]
X. Liu, M. Li, M. Liu, Prof. Dr. Q. Yang and Prof. Dr. Y. Chen
Tianjin Key Laboratory of Molecular Optoelectronic Science,
Department of Chemistry, Tianjin University, Tianjin, 300354, P. R.
China
E-mail: yulan.chen@tju.edu.cn; qiuhuay@tju.edu.cn
Dr .M. Liu,
Department of Chemistry, Weifang University, Weifang, 261061, P.
R. China
Supporting information for this article is given via a link at the end of
the document.
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substituted furans TPF-1, TPF-2, and their ring-opening
derivatives, the aryl-substituted (Z)-tetraphenylbut-2-ene-1,4-
diones TPBD-1 and TPBD-2 are showed in Figure 1. Their
synthetic routes are depicted in Scheme 1. The dibromo-
substituted intermediate 5 was synthesized according to the
reported procedures.12 Seteroselective oxidization of 5 with
potassium nitrate afforded cis-but-2-ene-1,4-dione 6 in the yield
of 90%. Subsequently, Suzuki cross-coupling of 5 or 6 with
pinacol(4-(N,N-diphenylamino)phenyl)boronate 7 or thiophene-
2-bronic ester 9 furnished the target compounds TPF-1, TPF-2,
TPBD-1 and TPBD-2 with good yields (80-88%). Their
1
structures were unambiguously characterized with H NMR and
13C NMR spectra and matrix assisted laser desorption ionization
time-of-flight mass spectroscopy (MALDI-TOF).
Theoretical calculation. In order to shed more light on the
structure-property relationship at molecular level, we obtained
the optimized structures and orbital distributions of HOMO and
LUMO energy levels of the four molecules by density functional
theory (DFT) calculations at the level of B3LYP/6-31G*. As
revealed in Figure 2, the π electrons of the HOMO molecular
orbitals of TPF-1 and TPF-2 are mainly localized on the central
heterocyclic rings with HOMO energy levels of –4.90 eV and –
5.19 eV, respectively, indicating that TPF-1 shows better
conjugation than TPF-2.10 The LUMO of TPF-1 is mainly
localized on the furan ring and the four peripheral phenyl rings
with LUMO energy level of –1.17 eV, whereas it is distributed
evenly on the whole molecule with LUMO energy level of –1.31
eV for TPF-2. In contrast, as for TPBDs, distinct intramolecular
charge transfer (ICT) process between triphenylamine or thienyl
groups as electron donating units and 1,4-enedione as electron
withdrawing part were illustrated, regarding the more twisted
structures and severely uneven distribution of the electrons
(Figure 2). Indeed, the HOMOs are primarily localized around
the peripheral aromatic moieties, whereas the LUMOs remain
localizing around the carbonyl groups and the phenyl groups.
The calculated energy gap of TPBD-1 (2.93 eV) was lower than
Figure 1. Chemical structures of TPFs and TPBDs in this work.
color contrast and turn-on emission. Intriguingly, besides the
aggregation and mechanical force controllable solid state optical
properties, the ground TPF-1 is found efficiently sensitive to light.
We then successfully fabricated a TPF-1 based smart film
switchable by light and mechanical force. As a result, light
directed reversible luminescent patterning was realized,
manifesting its promising applications in photo erasing and anti-
counterfeiting related areas.
Results and Discussion
Synthesis and characterization. The structures of aryl-
Scheme 1. Synthetic routes to TPFs and TPBDs.
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that of TPBD-2 (3.38 eV), since the triphenylamine is more
electron rich than thienyl group. Additionally, comparing to TPF-
1 (3.73 eV) and TPF-2 (3.88 eV), both TPBD-1 and TPBD-2
exhibited narrower energy gaps, owing to the stronger ICT effect
mainly derived from the 1,4-enediones part.
when large amounts of water was added into the THF solution
(Figure 3c,d). When the water fraction reached to 95%, the
corresponding fluorescence quantum yield of TPBD-1 and
TPBD-2 increased to 11.16% and 8.9%, respectively, which was
more than 11 and 9 times higher than that in diluted solution.
Additionally, TPBD-1 showed a larger stokes shift value than
that of TPBD-2 in solution state (Figure S6), indicating the
greater rigidity of TPBD-1 than TPBD-2.10 The spectra of TPBDs
in the film state were almost identical to those in THF/H2O (v/v =
5/95). But for the crystalline state of TPBD-1 and TPBD-2, the
emission bands remarkably blue-shifted (Figure S5c,d), which
was ascribed to the more orderly molecular packing in crystal
state. The corresponding ΦF value of TPBD-1 and TPBD-2 in
crystal were 12.3% and 7.6% with fluorescence lifetimes of 1.38
and 0.45 ns, respectively (Figure S7). The above results
unveiled that TPBD-1 and TPBD-2 were AIEgens.8 All the
photophysical data were collected in Table S1.
Figure 2. Molecular-orbital amplitude plots and energy levels of the HOMOs
and LUMOs for TPF-1, TPF-2, TPBD-1 and TPBD-2 in the gas phase, as
calculated at the level of B3LYP/6-31G*.
(a)
(b)
Photophysical properties. All the four molecules were soluble
in common organic solvents such as toluene, tetrahydrofuran
(THF), dichloromethane (DCM) etc. The furan cored molecules
TPFs and the 1,4-enedione cored TPBDs exhibited prominently
different optical properties. First, their UV/vis absorption spectra
in dilute THF were studied. As can be seen in Figure S1a, TPF-
1 and TPF-2 exhibited a maximum absorption at 332 and 302
nm, respectively, which should be ascribed to the π-π* transition
band. And the main peaks of TPBD-1 and TPBD-2 were located
at 300 and 259 nm, with shoulder peaks appearing at ca. 349
nm (Figure S1b). The shoulder peak could be assigned to the
ICT transition due to the inherent D-A feature of TPBDs, as is
also evidenced by their solvent polarity dependent ground state
electronic structures. With the polarity of solvents increased from
nonpolar solvent (hexane) to highly polarized DMSO, the
absorption maximum of TPBD-1 and TPBD-2 red-shifted by
about 4 and 10 nm, respectively (Figure S2). Both the
triphenlyamine substituted molecules exhibited redder maximum
absorption than the thiophene modified molecules, which
demonstrates that the formed ones possess better conjugation
than the later ones, with good agreement with the calculated
results.
The fluorescence emission properties of TPFs were depicted
in Figure 3a,b. In THF, both TPF-1 and TPF-2 are emissive with
fluorescence peak at 417 and 407 nm, respectively. In THF/H2O
mixture, their ACQ effect was determined. They showed lower
quantum yields in the aggregate state (TPF-1: ΦPL 0.14, TPF-2:
ФPL 0.09) than those in THF (TPF-1: ФPL 0.99, TPF-2: ФPL 0.45),
with more than 7-fold or 5-fold decrement. Figure S3 showed
the dependency of the emission-intensity ratio (I/I0) of TPFs and
TPBDs on solvent compositions with THF/H2O mixture system.
For instance, the I/I0 values of TPF-1 significantly decreased to
0.17 when the water content reached over 60 vol%. And
resemble quenching effect was detected in their solid powder
state and film state, upon the formation of J-aggregates (Figure
S4, S5a,b). TPBDs behaved differently, when molecularly
dissolved in THF, they are almost non-emissive with a faint
fluorescence quantum yield of 0.97% and 0.96%, respectively
(Figure S6). Simutaneously, they emitted intense green light
(c)
(d)
Figure 3. Fluorescence spectra of (a) TPF-1, (b) TPF-2, (c) TPBD-1, (d)
TPBD-2 in THF/water mixtures with different water fractions (concentration:
2×105 M; excitation wavelength for TPF-1: 332 nm; for TPF-2: 303 nm; for
TPBD-1: 430 nm; for TPBD-2: 370 nm); Inset: Images of the corresponding
molecules in THF and THF/water mixtures under illumination with 365 nm UV
light.
Mechanochromic properties. Besides the aggregation
dependent optical variations, TPFs and TPBDs are also
sensitive towards mechanical stimuli. Upon grinding, TPF-1 and
TPF-2 exhibit unusual MCF effect with emission blue-shifting by
91 nm and 25 nm, respectively (Figure 4a,b). Whereas the
emission peaks of TPBD-1 and TPBD-2 red-shifted by 100 nm
and 32 nm, respectively (Figure 4c,e). The most prominent
optical transition was achieved in the triphenylamine attached
compounds. And relative to TPFs, the TPBDs showed a more
considerable optical transition. In detail, TPBD-1 switched from
yellow green (λem = 498 nm, ФF = 12.3%) to orange red (λem
598 nm, ФF = 14.2%) luminescence upon grinding. As for TPF-1,
it’s emission light changed from green (λem = 508 nm, ФF
9.6%) to blue-purple (λem = 417 nm, ФF = 15.9%). The high color
contrast and turn-on emission upon mechanical activation
highlighted their great advances in sensitive mechanical sensors.
After fuming with CH2Cl2 vapor, the color and fluorescence of
TPBDs ground samples can be converted into the original state,
and the switching of fluorescence between mechanical force and
=
=
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vapor stimuli could be repeated many times with almost no
fatigue (Figure 4d,f). All the optical changes of TPFs and
TPBDs before and after grinding were summarized in Table S1
and S2.
dihedral angles from 42.99o to 58.61o (Figure S10a,b), indicative
of a weak π-conjugation in the 2,5-diphenylfuran skeleton. The
stacking diagram of TPFs displayed that the molecules packed
in an antiparallel style with large side-slipping, driven by multiple
intermolecular interactions, such as C–H…π interaction (in TPF-
1) and C–H…S hydrogen bonds (in TPF-2), with distances in the
range of 2.7–2.9 Å (Figure S11a,b). Additionally, for TPF-1, the
distance of the two adjacent oxygen atoms was 4.495 Å,
whereas it was 6.128 Å and 6.210 Å in TPF-2 (Figure 5).
Similarly to that of tetraphenylfuran reported by Tang and
coworkers, these values are in accordance with distinctive
intermolecular n-π* interactions in TPFs aggregates to prompt
the nonradiative channel, and efficiently quench the emission in
their aggregate state.10 While compared with tetraphenylfuran,
the introduction of triphenylamine and thiophene groups
extended the distance of the two adjacent oxygen atoms, thus
the relatively weakened n-π* interactions led to the weakened
ACQ effect of the two TPFs in contrast to tetraphenylfuran.
Meanwhile, the distance between the mean planes of the planar
tera-aryl skeletons is longer than those of typical π-stacked
structures, indicating that the π-skeletons are arranged slightly
apart from each other. Compared with that of TPBDs, structural
analysis also suggests that the furan cored molecules TPFs
form a relatively dense packing structure in the crystalline state
because of the smaller steric hindrance (Table S3-6). The close-
packing structure in the crystalline state can induce
comparatively high planarity and strong intermolecular
interactions between the conjugated skeleton, in contrast with
those in the amorphous state. As a result, the emission band
could be shifted to the shorter wavelength region after a
transformation to an amorphous state in which the molecules
are randomly distributed.13 Moreover, at the molecule level, the
triphenylamine substituents are more steric hindered with more
rotatable bonds, than that of the thiophene groups, which would
be more susceptible to external perturbation to endow a
sensitive chromic response. This is consistent with the fact that
TPF-1 showed more prominent optical transition than that of
TPF-2 under force stimuli.
Generally, intramolecular conformation and packing modes
have a great influence on the mechanochromic properties of
solid state material. We thereby carried out the powder X-ray
diffraction (PXRD) measurements. It was found that all the four
pristine samples of TPFs and TPBDs showed intense and sharp
diffraction peaks, indicating the crystalline state of the solids.
Upon grinding, profiles of the ground samples all exhibited
relatively weak diffraction peaks (Figure S8), corresponding to
the partially destroyed ordered structures by grinding.
Additionally, a cold-crystallization transition peak before melting
point emerged in DSC curves of the ground samples of TPFs
and TPBDs (Figure S9), indicating that the ground powders
presented in a metastable phase and converted to a stable
crystalline phase via an exothermal recrystallization process.4d
(a)
(b)
(c)
(e)
(d)
(f)
(a)
(b)
Figure 4. Normalized fluorescence spectra of (a) TPF-1, (b) TPF-2, (c) TPBD-
1, and (e) TPBD-2 in different states (excited at 370 nm for TPF-1 and TPF-2,
410 nm for TPBD-1 and 420 nm for TPBD-2). Reversible switching of
emission of (d) TPBD-1 and (f) TPBD-2 by repeated grinding/fuming cycles.
Inset: Images of the corresponding powders in different solid states under 365
nm UV illumination.
(c)
(d)
Single crystal analysis. The single crystals of TPF-1 (CCDC:
1825911), TPF-2 (CCDC: 1825912), TPBD-1 (CCDC: 1825909)
and TPBD-2 (CCDC: 1825908) were successfully obtained,
which enabled us to directly investigate the effect of molecular
packing on their underlying photophysical properties as well as
MCF mechanisms. In the crystal structures of TPFs, the two
phenyl rings at 2- and 5-positions showed relatively small
dihedral angles in the range from 14.85o to 37.46o, whereas the
other two phenyls adopted twisted conformations with large
Figure 5. Packing arrangements in crystals of (a) TPF-1, (b) TPF-2, (c) TPBD-
1 and (d) TPBD-2. The distances are in the unit of Å.
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In contrast to TPFs, TPBDs exhibited a highly twisted
propeller-like geometry with large twisting angles in the range
from 28.2o to 69.1o (Figure S10c,d). Thus the peripheral rotors
could rotate freely in solution state which consumed the excited
state energy, resulting in the emission quenching. In aggregates,
such rotations are suppressed partially due to the physical
constraint. The radiation-less pathway is thus blocked, while the
radiative channel is opened. As the steric effect of thiophene
was weaker than that of triphenylamine, more energy was
consumed by vibration in the lattice resulting in the lower
fluorescence quantum efficiency of TPBD-2 than TPBD-1.
Moreover, the intermolecular π-π* interactions could be inhibited
due to the sufficient steric effect. The weak intermolecular
interactions such as C–H…π, S–H…π as well as C=O…H–C,
C–H…S hydrogen bonds with distances in the range of 2.3–3.2
Å (Figure S11c-f), connected the adjacent twisted molecules
together, contributing to the stability of the crystalline state.
Based on the above results, we can get a conclusion of the
stimuli-responsive behaviours of TPBDs. In comparing to the
TPFs, the larger steric hindrance of TPBDs results in the
formation of intrinsically loose packing even in crystalline state.
Thus, the crystalline state of these luminogens may adopt a
more twisted conformation, thus partially excited energy was
consumed by non-radiative transitions. Upon grinding, the
molecular structure slightly turned planar and the effective
intramolecular conjugation was increased, which further blocked
the non-radiative deactivation pathways.14 Also, the
neighbouring molecules did not get close to one another due to
steric effect of substituents, which weakened the intermolecular
interactions. As a result, the fluorescence quantum efficiency of
ground powders increased slightly with the red shift of their
maximum emission wavelength.
(Figure S13). The patterning process could be reversibly
switching between UV irradiation and grinding, highlighting its
great promising applications in data recording, security
protection and anti-counterfeiting. Notably, the fast response
time and high contrast emission variation under UV light offer
exciting opportunities for smart optical devices with excellent
temporal and spatial resolution. We also envisioned that, if well
controlled, UV light could be used for micropatterning and have
potential for microdevice fabrication.
Figure 6. Left: schematic of solid-state sensor for patterning (film made of
TPF-1 powders by grinding) before and after the irradiation by UV light (365
nm). Right: luminescent “fish” patterning before and after UV irradiation (365
nm) for 1 minute with a mask in front of the paper, which can be reversibly
recovered upon grinding.
Fabrication of photo-erasable film. Intriguingly, the ground
powders of TPF-1 showed remarkable response to UV light
irradiation (365 nm). Time dependent fluorescence spectroscopy
of the ground powder under 365 nm illumination were measured.
We can see that the emission peak at 417 nm gradually
decreased with the extension of irradiation time within few
seconds, with distinctive fluorescence color changing from blue
to green (Figure S12). The above observations demonstrated
that amorphous state of TPF-1 produced by force stimuli is a
metastable state, and upon UV excitation, the molecules were
readily moving to a more stable packing status in the excited
state, thus achieving lower energy state with green fluorescence
emission,15
Considering the unique light responsive feature of ground
TPF-1, its applications in photo erasing device were exploited. In
detail, the ground powders of TPF-1 were prepared as a film on
a piece of weighing paper. It exhibited blue emission under UV
light excitation (λex = 365 nm). Upon UV irradiation (365 nm) for
one minute with a fish-shaped mask in front of the paper, a
bright blue “fish” emerged on the paper after the mask was
removed, because the area outside the “fish” was irradiated and
turned completely to the pristine state (green fluorescence)
(Figure 6). Additionally, after removing the mask, the blue
fluorescence pattern of “fish” produced by light irradiation could
fade after continuing exposure to UV lamp. Jointly with several
control experiments, its light responsive character was
confirmed. For instance, neither the day light nor heating could
make the blue fluorescence convert into the green emission
Conclusions
In summary, aryl-substituted furans (TPF-1, TPF-2) and their
ring-opening 1,4-enedione derivatives (TPBD-1 and TPBD-2)
were designed and synthesized. Their optical properties in both
solution and aggregation states were investigated systematically.
Interestingly, both TPFs and TPBDs exhibited mechanochromic
properties, whereas they showed opposite optical properties as
ACQ and AIEgens, respectively. Analyses from single crystal X-
ray diffractions and theoretical calculations reveal their strong
dependence of the fluorescence emission on molecular packing
mode and substituents effect. More interestingly, the ground
TPF-1 is found highly sensitive to light. We then successfully
fabricated a TPF-1 based smart film switchable by light and
mechanical force, implying its practical applications in memory
devices, data encryption, etc, with excellent temporal and spatial
resolution. It is anticipated that further modification of their
molecular structures by molecular engineering endeavor will
lead to new AIE-active materials with multi-response beyond
mechanical force suitable for a wide range of optical applications.
Additionally, our current study concerning the different behaviors
between TPFs and TPBDs would accelerate and enrich the
chemistry of the mechanochromism.
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reaction mixture. TLC confirmed that the reaction was completed (3 h),
solvent was removed under vacuum. The reaction mixture was diluted
with ethyl acetate (5 mL) and then washed with water (5 mL × 2).
Subsequently, the aqueous solution was extracted with ethyl acetate (10
mL × 3). The combined organic layer was washed with brine (5 mL × 2)
and then dried over anhydrous sodium sulfate. The solvent was removed
and the crude product purified by column chromatography using hexane
as eluent, yielded the product as yellow solid (130 mg, 49%). 1H NMR
(400 MHz, DMSO): δ: 7.54 (m, 4H, ArH), 7.45 (m, 4H, ArH), 7.37 (m, 4H,
ArH), 7.30 – 7.14 (m, 6H, ArH).
Experimental Section
General. Unless noted otherwise, all chemicals were purchased from
Aldrich, Acros or Adamas and used without further purification.
Dichloromethane (CH2Cl2) was distilled over CaH2. Tetrahydrofuran
(THF) was distilled over sodium and benzophenone. Other solvents were
dried with standard procedures. If not specified, all reactions were
performed under an atmosphere of nitrogen and monitored by TLC with
silica gel 60 F254. Column chromatography was carried out on silica gel
(200-300 mesh). The catalyst precursor Pd(PPh3)4 was prepared
according to the literature,16 and stored in a Schlenk tube under nitrogen.
Compound 6. In a two-necked flask, 5 (0.94 mmol), potassium nitrate
(47.52 mg, 0.47 mmol) were suspended in 3 mL aqueous acetic acid
under N2, and then heated the mixture to reflux under O2. When all of the
starting material had been consumed. The reaction mixture was cooled,
diluted with cold water, and filtered. The crude product was purified by
recrystallization from methanol to afford 6 as a faint yellow solid (463 mg,
90%). 1H NMR (400 MHz, CDCl3): δ 7.80 (d, J = 7.4 Hz, 4H, ArH), 7.46 (t,
J = 7.4 Hz, 2H, ArH), 7.36 – 7.32 (m, 8H, ArH), 7.03 (d, J = 8.5 Hz, 4H,
ArH). 13C NMR (100 MHz, CDCl3) δ 196.24, 143.84, 135.94, 133.83,
133.37, 132.20, 131.26, 130.00, 128.47, 123.11. MALDI-TOF (m/z):
calculated for C28H18Br2O2 [M + H]+, 544.9746; found, 545.2192.
Measurements. 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra
were recorded on a 400 MHz Bruker AV 400 spectrometer. The UV-Vis
absorption spectra were obtained on
spectrophotometer. Fluorescence spectra and quantum yields of solid
powders were recorded on Hitachi F-7000 fluorescence
a PerkinElmer Lambda 750
a
spectrophotometer. The transient fluorescence decay curves were
measured on an Edinburgh FLS 920 fluorescence spectrometer. Matrix
assisted laser desorption ionization time-of-flight mass spectroscopy
(MALDITOF) was performed on a miorOTOF-QII mass spectrometer
(Bruker Daltonics) using α-cyano-4-hydroxycinnamic acid as the matrix.
Thermogravimetric analyses (TGA) were carried out using
a TA
General Procedure for the Synthesis of TPFs and TPBDs. A mixture
of the precursor (5, 6) (7, 9), NaHCO3, THF and H2O was carefully
degassed before and after Pd(PPh3)4 was added. The mixture was
heated to reflux and stirred under nitrogen overnight. CH2Cl2 and brine
was added, and the organic layer was separated and dried over
anhydrous Mg2SO4. After the removal of the solvent, the residue was
purified by chromatography on a silica gel column to afford the desired
product (TPF-1, TPF-2).
Instruments Q-50 with a heating rate of 10 °C/min. Differential scanning
calorimetry (DSC) measurements were conducted using the TA
Instruments Q-20 with a scan rate of 10 °C/min. The powder XRD
patterns were obtained with
a Rigaku SmartLab (9 kW) X-ray
diffractometer. The single crystal X-ray diffraction was recorded on a
Rigaku SCX-mini diffractometer with graphite monochromatic Mo Kα
radiation (λ = 0.7173 Å) by ω scan mode. Density functional theory (DFT)
calculations were performed in Gaussian 09 software at the B3LYP
functional with the 6-31G* basis set level.
Compound 8. 5 (50 mg, 0.09 mmol), 7 (87.53 mg, 0.24 mmol), NaHCO3
(403 mg, 4.79 mmol), THF (3.60 mL), H2O (1.20 mL) and Pd(PPh3)4
(5.43 mg, 0.005 mmol) were used, and ether/CH2Cl2 (v/v, 5:1) was used
as the eluent to afford TPF-1 as a white solid (71.06 mg, 88%). 1H NMR
(400 MHz, CDCl3) δ 7.58 (d, J = 7.2 Hz 4H, ArH), 7.50 (t, J = 3.8 8H,
ArH), 7.26–7.24 (m, 16H, ArH), 7.12 (m, 12H, ArH), 7.02 (t, J = 3.8 4H,
ArH). 13C NMR (100 MHz, CDCl3) δ 147.88, 147.67, 147.25, 138.99,
134.47, 131.69, 130.92, 130.81, 129.28, 128.40, 127.52, 127.38, 126.45,
125.97, 124.73, 124.35, 124.10, 122.91. MALDI-TOF (m/z): calculated
for C36H24O2S2 [M•]+, 859.3683; found, 858.3697.
Preparation of Aggregates.17 Stock solutions (2 mM) of ACQ effect and
AIE-active molecules in THF were prepared. An aliquot (0.04 mL) of the
stock solution was diluted with an appropriate amount of THF in a
volumetric flask (5 mL), and then water was added dropwise under
vigorous stirring. A series of THF/water solutions were obtained with
different water fractions (fw) ranging from 0 to 95 vol%.
Compound 2. 4-Bromobenzaldehyde (9.25 g, 0.05 mol), acetophenone
(6.00 g, 0.05 mol) and potassium hydroxide (0.08 g, 1.5 mmol) were
dissolved in ethanol/H2O (85/15 v/v, 100 mL) and stirred at rt for 24 h.
During the course of the reaction, the product precipitated from the
reaction mixture. Filtration of the reaction mixture and recrystallization
from ethanol yielded the product as a yellow solid (14 g, 98%). 1H NMR
(400 MHz, CDCl3) δ: 8.02 (d, J = 7.7 Hz, 2H, ArH + CH), 7.75 (d, J = 15.7
Hz, 1H, CH), 7.63 – 7.48 (m, 8H, ArH).
Compound 10. 5 (50 mg, 0.09 mmol), 9 (48.32 mg, 0.23 mmol),
NaHCO3 (403 mg, 4.79 mmol), THF (3.60 mL), H2O (1.20 mL) and
Pd(PPh3)4 (5.43 mg, 0.005 mmol) were used, and ether/CH2Cl2 (v/v, 5:1)
was used as the eluent to afford TPF-2 as a white solid (38.64 mg, 80%).
1H NMR (400 MHz, DMSO) δ 7.63 (d, J = 8.2 Hz, 4H, ArH), 7.55 (d, J =
4.3 Hz, 4H, ArH), 7.51 (d, J = 7.6 Hz, 4H, ArH), 7.37 (t, J = 7.6 Hz, 4H,
ArH), 7.31 (d, J = 7.3 Hz, 2H, ArH), 7.26 (d, J = 8.2 Hz, 4H, ArH), 7.15 –
7.10 (m, 2H, ArH). 13C NMR (100 MHz, DMSO) δ 147.80, 143.17, 133.36,
132.00, 131.31, 130.45, 129.25, 129.04, 128.37, 126.39, 125.91, 125.89,
124.94, 124.47. MALDI-TOF (m/z): calculated for C36H24O2S2 [M•]+,
553.1290; found, 536.1246.
Compound 4. HTIB (3.92 g, 0.01 mol) was added to a solution of
chalcone 2 (1.44 g, 0.005 mol) in CH2Cl2 (40 mL). The resulting mixture
was allowed to stir at 40–42 °C. HTIB was highly insoluble in CH2Cl2, but
gradually disappeared as the reaction proceeded. The stirring was
allowed to continue for about 16–18 h. The solvent was evaporated in
vacuo. And then EtOH (10 mL) as well as KOH (0.06 g, 0.01 mol) were
added to the reaction bottle. The mixture was heated under reflux for 2–3
h. The progress of the reaction was monitored by TLC. When all of the
starting material had been consumed, the reaction mixture was poured
over crushed ice, extracted with CH2Cl2 and the crude product 4 was
purified by column chromatography using EtOAc-PE as eluent, yielded
the product as a white solid (0.468g, 34%). 1H NMR (400 MHz, CDCl3): δ:
8.00 (d, J = 7.5 Hz, 2H, ArH), 7.58 (t, J = 7.2 Hz, 1H, ArH), 7.47 (t, J =
8.7 Hz, 4H, ArH), 7.14 (d, J = 7.7 Hz, 2H), 4.25 (s, 2H, CH2).
Compound 11. 6 (50 mg, 0.09 mmol), 7 (87.53 mg, 0.24 mmol),
NaHCO3 (393 mg, 4.68 mmol), THF (3.60 mL), H2O (1.20 mL) and
Pd(PPh3)4 (5.43 mg, 0.005 mmol) were used, and ether/CH2Cl2 (v/v, 5:1)
was used as the eluent to afford TPBD-1 as a orange solid (64.41mg,
80%). 1H NMR (400 MHz, DMSO) δ 7.83 (d, J = 7.4 Hz, 4H, ArH), 7.53 (t,
J = 8.8 Hz, 10H,ArH), 7.41 (t, J = 7.6 Hz, 4H, ArH), 7.30 (t, J = 7.8 Hz, 8H,
ArH), 7.20 (d, J = 8.2 Hz, 4H, ArH), 7.04 (dd, J1,2 = 20.4, J1,3 = 7.5 Hz,
12H, ArH), 6.95 (d, J = 8.6 Hz, 4H, ArH). 13C NMR (100 MHz, DMSO) δ
196.64, 147.56, 147.34, 144.26, 139.75, 136.54, 134.05, 133.80, 132.83,
130.62, 130.07, 129.05, 127.95, 126.68, 125.41, 124.75, 123.87, 123.33.
MALDI-TOF (m/z): calculated for C36H24O2S2 [M•]+, 874.3632; found,
874.1293.
Compound 5. A mixture of benzyl ketones derivatives 4 (275 mg, 1.0
mmol) and AgF (12.8 mg, 0.1 mmol) in xylene (3 mL) was stirred at
140 °C under air. When the starting material was consumed completely
(8 h), p-toluenesulfonic acid (258 mg, 1.5 mmol) was added to the
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10.1002/chem.201801507
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Compound 12. 6 (50 mg, 0.09 mmol), 9 (79.00 mg, 0.38 mmol),
NaHCO3 (393 mg, 4.68 mmol), THF (3.60 mL), H2O (1.20 mL) and
Pd(PPh3)4 (5.43 mg, 0.005 mmol) were used, and ether/CH2Cl2 (v/v, 5:1)
was used as the eluent to afford TPBD-2 as a white solid (40 mg, 80%).
1H NMR (400 MHz, DMSO) δ 7.82 (d, J = 7.2 Hz, 4H, ArH), 7.54 (m, 10H,
ArH), 7.42 (t, J = 7.6 Hz, 4H, ArH), 7.20 (d, J = 8.4 Hz, 4H, ArH), 7.11 (dd,
J1,2 = 5.0, J1,3 = 3.7 Hz, 2H, ArH). 13C NMR (100 MHz, DMSO) δ 196.53,
144.31, 142.71, 136.45, 134.49, 134.22, 133.86, 130.83, 130.05, 129.11,
129.08, 126.92, 126.04, 124.96. MALDI-TOF (m/z): calculated for
C36H24O2S2 [M + H]+, 553.1290; found, 553.1360.
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Acknowledgements
Financial support by the National Natural Science Foundation of
China (Grants 21522405, 51503142 and 21734006), the
National Key Research and Development Program of China
(Grants 2017YFA0204503 and 2017YFA0207800), the
Thousand Youth Talents Plan and the Natural Science
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10.1002/chem.201801507
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Entry for the Table of Contents (Please choose one layout)
Layout 1:
FULL PAPER
Multi-functional fluorophores:
Aromatic substituted tetraphenylfuran
TPFs and their ring-opening (Z)-1,4
enedione derivatives TPBDs were
synthesized, exhibiting prominently
opposite optical properties and “turn-
on” mechanochromic behaviours. A
smart film with photo-responsive
ground TPF was constructed and
reversible patterning was facilely
realized under the control of UV light,
demonstrating its utility in data
Xia Liu, Mengwei Li, Meifang Liu,
Qiuhua Yang* and Yulan Chen*
Page 1. – Page 7.
From Tetraphenylfurans to Ring-
Opening (Z)-1,4-Enediones: ACQ
Fluorophores versus AIEgens with
Distinct Responses to Mechanical
Force and Light
encryption and decryption.
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