Pyrene-based aggregation-induced emission luminogens (AIEgens) with less colour migration for anti-counterfeiting applications

Article abstract of DOI:10.1039/d1tc03022a

Traditional luminescent materials are subject to aggregation-caused quenching, which limits their use for high-technological applications in the solid state. In an attempt to address such issues when using luminescent materials in fluorescent inks, by taking advantage of the aggregation-induced emission (AIE) behaviour, this article presents a set of pyrene-based AIEgens which possess high thermal stability, excellent fluorescence properties, and good biocompatibility. These AIEgens can be utilized as fluorescent inks for anti-counterfeiting applications at ultralow/low concentration (0.004-0.5 wt%) (weight_AIEgens?:?weight_binder= 5?:?125?000-5?:?1000) with slight colour migration (<27 nm) for different printing substrates. The use of such a fluorescent ink containing pyrene-based AIEgens has extended the scope of application over the range from ultralow to high concentration thereby avoiding the aggregation-caused quenching (ACQ) effect. Additionally, this system would lower the product cost, and be beneficial for the environment. The high-quality fluorescence pattern was found to exhibit good printability on different types of paper by old printing technology (screen printing technology). This work highlights that pyrene-based AIEgens are excellent candidates for use in anti-counterfeiting, and these results have the potential to enrich the practical applications of AIEgens in both academic and industrial fields.

Full text of DOI:10.1039/d1tc03022a

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Materials Chemistry C
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Pyrene-based aggregation-induced emission
luminogens (AIEgens) with less colour migration
Cite this: DOI: 10.1039/d1tc03022a
for anti-counterfeiting applications†
a
a
Xiaohui Wang,
Lirong Wang,b Xiaoyu Mao,a Qingsong Wang,a Zhongfei Mu,
Li An,c Wan Zhang,c Xing Feng, *a Carl Redshaw,
Changyong Cao,e
d
Anjun Qin *b and Ben Zhong Tang
*
bfg
Traditional luminescent materials are subject to aggregation-caused quenching, which limits their use
for high-technological applications in the solid state. In an attempt to address such issues when using
luminescent materials in fluorescent inks, by taking advantage of the aggregation-induced emission (AIE)
behaviour, this article presents a set of pyrene-based AIEgens which possess high thermal stability,
excellent fluorescence properties, and good biocompatibility. These AIEgens can be utilized as
fluorescent inks for anti-counterfeiting applications at ultralow/low concentration (0.004–0.5 wt%)
(weightAIEgens : weightbinder = 5 : 125 000–5 : 1000) with slight colour migration (o27 nm) for different
printing substrates. The use of such a fluorescent ink containing pyrene-based AIEgens has extended
the scope of application over the range from ultralow to high concentration thereby avoiding the
aggregation-caused quenching (ACQ) effect. Additionally, this system would lower the product cost, and
be beneficial for the environment. The high-quality fluorescence pattern was found to exhibit good
printability on different types of paper by old printing technology (screen printing technology). This work
highlights that pyrene-based AIEgens are excellent candidates for use in anti-counterfeiting, and these
results have the potential to enrich the practical applications of AIEgens in both academic and industrial
fields.
Received 29th June 2021,
Accepted 4th August 2021
DOI: 10.1039/d1tc03022a
rsc.li/materials-c
Introduction
Counterfeiting is a challenging global problem that causes huge
economic losses and potential risk to individuals and social
security.1,2 Various advanced anti-counterfeiting technologies
have been developed for fighting the fast-growing counterfeit
markets.3,4 Among them, the use of fluorescent labels/tags as
a School of Material and Energy, Guangdong University of Technology,
Guangzhou 510006, P. R. China. E-mail: hyxhn@sina.com
b NSFC Center for Luminescence from Molecular Aggregates, SCUT-HKUST Joint
Research Laboratory, State Key Laboratory of Luminescent Materials and Devices,
South China University of Technology, Guangzhou 510640, P. R. China.
E-mail: msqinaj@scut.edu.cn
a
preferred anti-counterfeiting technology has attracted
great attention for practical application in banknotes, brands,
and documents, because of their extraordinary superiority
with regard to a fast response, visualization, extra security
c Beijing Institute of Graphic Communication, Beijing 102600, P. R. China
d Department of Chemistry, University of Hull, Cottingham Road, Hull,
Yorkshire HU6, UK
features, etc.4–7 Thus,
a large quantity of luminescent
e Laboratory for Soft Machines & Electronics, Michigan State University,
materials with high fluorescence intensity/efficiency, including
rare-earth-doped nanostructures,8–10 carbon dots,11–13 organic–
inorganic complexes,14–16 upconversion nanoparticles17,18 and
perovskites,19,20 as well as organic dyes,21–23 have been widely
utilized as fluorescent labels/tags for printing technology.
Generally, the luminescent materials are used in the solid
state for anti-counterfeiting applications, but the emission of
traditional luminescent materials is subject to fluorescence
quenching at high concentration or in the solid state, resulting
in aggregation-caused quenching (ACQ).24 The nature of
East Lansing 48824, MI, USA
f Department of Chemistry and Hong Kong Branch of Chinese National Engineering
Research Center for Tissue Restoration and Reconstruction, The Hong Kong
University of Science & Technology, Kowloon, Hong Kong 999077, P. R. China.
E-mail: tangbenz@ust.hk
g Shenzhen Institute of Molecular Aggregate Science and Engineering,
School of Science and Engineering, The Chinese University of Hong Kong,
Shenzhen 518172, China
† Electronic supplementary information (ESI) available. CCDC 2059788 and
2059789. For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/d1tc03022a
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conventional fluorescent dyes and their ACQ effect limit their the pyrene-based AIEgens as functional fluorescent pigments
practical application for anti-counterfeiting. For example, a low to prepare fluorescent inks for anti-counterfeiting by screen-
concentration of luminescent materials could achieve a weak printing technology, which resulted in high-quality anti-
anti-counterfeiting pattern, whilst a higher concentration not counterfeiting at ultralow/low concentrations (0.004–0.5 wt%,
only lowers the emission intensity, but also adds to the production weightAIEgens : weightbinder = 5 : 125000–5 : 5 : 1000) with relatively
costs, as well as probably adding risks to the ecosystem. small colour migration (o27 nm) in butter paper and tissue
A significant milestone occurred in 2001 when Tang and paper substrates. Thus, this example opens up new avenues
coworkers found that a propeller-shaped molecule (such as for the industrial application of pyrene-based AIEgens as anti-
tetraphenylethene, siloles, etc.) exhibited aggregation-induced counterfeiting inks.
emission (AIE) characteristics.25 AIE is an impressive photo-
physical phenomenon, given that luminescent materials
exhibit non or weak emission in solution but enhanced
Results and discussion
fluorescence intensity in the aggregation (solid) state, due to
Synthesis and characterization
the restricted intramolecular motion (RIM) mechanism. More
The four pyrene-based cyanostyrene derivatives are presented
in Fig. 1, and all target compounds were obtained via two
reaction steps (a Suzuki–Miyaura coupling reaction and a
Knoevenagel reaction) in good yield. The detailed synthetic
routes are illustrated in Scheme S1 (ESI†). The molecular
structures of the compounds were fully characterized by
1H/13C NMR spectroscopy, high resolution mass spectrometry
(HRMS) and single crystal X-ray diffraction. The relationship
between the length of the p-conjugation (Py-2Ph-Cz and Py-Ph-
Cz), the different substituents (Py-Ph-Cz and Py-1-TPE) or the
substituent position (Py-1-TPE and Py-2-TPE) and the thermal
properties, and the electronic spectra were systematically
investigated by thermogravimetric analysis (TGA), UV-vis and
fluorescence spectra, as well as by DFT calculations.
All compounds possess considerable solubility in common
organic solvents, such as dichloromethane (DCM), tetrahydrofuran
(THF) or toluene. Moreover, the twisted 3D molecular geometries of
Py-1-TPE and Py-2-TPE exhibit better solubility than Py-2Ph-Cz
and Py-Ph-Cz, which may be ascribed to the twist molecular
structure of the bulky tetraphenylethylene unit hindering intra-
molecular interactions. As shown in Fig. S23 (ESI†), the TGA
results indicated that compounds Py-1-TPE and Py-2-TPE
displayed a slight weight loss (o5%) over the range 25–220 1C,
attributed to the water molecules in the lattice (the theoretical
weight loss of H2O is 2.64% for Py-1-TPE and 2.01% for Py-2-
TPE). It is noted that the endothermic band at around 233 1C
with a weight loss of ca. 43% corresponds to the fragment of
phenylcarbazole in the molecular scaffold Py-2Ph-Cz being
lost (the theoretical weight loss of phenylcarbazole in the
compounds is 42.6%). The decomposition temperatures
importantly, the development of AIE luminogens (AIEgens) led to
significant advantages in emission efficiency, biocompatibility,
and light stability.24–28
As an excellent fluorophore, pyrene exhibits high fluorescence
intensity and quantum yield, has a long fluorescence lifetime
and is extremely responsive to its micro-environment. These
attributes mean that it is widely used to construct various
organic luminescent materials for potential application in
organic electronic devices,29 chemosensors,30 cell imaging,31
etc. On the other hand, pyrene derivatives can also be used to
prepare fluorescent inks for the preparation of fluorescent
labels by writing and printing.32–35 Much effort has been
devoted to the functionalization of pyrene in order to improve
the fluorescence properties.36 Most of the efficient strategies
involve transforming pyrene-based ACQ luminogens to AIE
luminogens through the adjustment of the twist conformation
of the substituents.37–40 For example, the integration of
pyrene and tetraphenylethene results in high-performance
pyrene-based AIE luminogens with blue emission and high
quantum yield suitable for organic light emitting diode (OLED)
fabrication.41,42 Also, the cyanostyrene-type molecules are a
well-known class of AIE/AIEE fluorophores, which have been
widely applied in diverse areas, such as mitochondrial
imaging,43 mechanochromism,44–46 and OLEDs.47
Generally, commercial inorganic fluorescent materials
(inks) are composed of one or more metal elements, such as
rare-earths48,49 or heavy metals,50,51 which increases the cost of
the products, as well as increasing the risk of environmental
pollution. On the other hand, to realize the anti-counterfeiting
application, the content of inorganic luminescent materials in
fluorescent inks needs to be in the range of 0.1 wt% to 25 wt%
according to previous reports,52,53 whilst a higher content
fraction of the fluorescent material would cause the fluorescence
intensity to decrease due to the ACQ effect.54 More importantly,
the micro-environment of the content of the fluorescent ink
plays a significant role in affecting the chemical/physical
properties of fluorescent pigments (such as chemical stability,
colour migration, etc.), resulting in low quality printing
products/patterns. Thus, in this article, a set of new pyrene-
based cyanostyrenes have been synthesized by introducing
twisted bulky units, which exhibited clear AIE characteristic
sky-blue or cyan emission. Subsequently, we attempted to use
Fig. 1 The synthesized target pyrene-based cyanostyrenes.
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Fig. 3 UV-vis spectra of the four pyrene-based cyanostyrene derivatives
in THF solution (10ꢁ5 M).
extension of the p conjugation of the molecular skeletons.
Compared to the 4-position substituted pyrene-based cyanostyrene
(lmax abs = 327 nm),39 the absorption spectra of Py-Ph-Cz still exhibit
a red-shifted absorption band at 358 nm, which may be due to the
substituent effect at the 1-position of pyrene.55 Theoretically, the
substituents at the 1-position of pyrene exhibit strong electronic
communication, whilst weak electronic communication occurs at
the 2-position, which is because the nodal plane of pyrene passes
through the C2 and C7 atoms,55 and the difference in the electronic
structure of pyrene would result in distinguishable electronic
transitions. In this case, Py-2-TPE exhibits a pyrene-like absorption
band at around 320–340 nm with a broad absorption peak at
377 nm, whilst for Py-1-TPE, with the substituent at the 1-position
of pyrene, the absorption peak at the long wavelength (377 nm) is
the same as that for Py-2-TPE; however the molar absorption
coefficient of Py-1-TPE (48 425 Mꢁ1 cmꢁ1) is higher than that of
Py-2-TPE (31 392 Mꢁ1 cmꢁ1) (Table 1), which indicates that the
1-substituted pyrene strengthens the S1 ’ S0 transitions, but
weakens the S2 ’ S0 transitions. In contrast, the 2-substituted
pyrene exerts a large influence on the S2 ’ S0 transitions, which is
in good agreement with Marder’s report.55 In addition, compound
Py-Ph-Cz exhibited a relatively large molar absorption coefficient
compared to Py-2Ph-Cz in the range 275–300 nm, which is
consistent with the S3 ’ S0 transitions. Thus, the results of this
experience of molecular design can aid the construction of novel
high-performance pyrene-based luminescent materials.
Fig. 2 Single crystal structures of (A) Py-1-TPE and (B) Py-2-TPE, as
ORTEP drawings with thermal ellipsoids at 30% probability. (C) The packing
structure of Py-1-TPE showing the C–Hꢀ ꢀ ꢀp interactions.
(Td, 5% weight loss) of the four compounds are 189 1C, 430 1C,
466 1C and 459 1C, respectively.
We attempted to cultivate suitable single crystals of the four
pyrene-based cyanostyrene derivatives for X-ray crystallographic
analysis, but only two suitable plate-like crystals, namely Py-1-
TPE and Py-2-TPE, were achieved via slow evaporation of a
mixture of hexane and dichloromethane (VHexane : VDCM = 1 : 1) at
room temperature. The key crystallographic data and refinement
parameters are presented in Table S1 (ESI†).
The crystal lattices of both Py-1-TPE and Py-2-TPE are
centrosymmetric with the monoclinic space group C12/c1. As
shown in Fig. 2, the pyrene and tetraphenylethylene units are
separated by a cyanostyrene unit in the two crystals, which
possess a unique non-planar geometry between the pyrene unit
and the adjacent phenyl ring (at the 1- or 2-position of pyrene)
with a dihedral angle of 52.921 for Py-1-TPE and 34.661 for Py-2-
TPE. Although there are substituents at different positions
of pyrene (the 1- or 2-position), it is noteworthy that both
compounds adopted almost identical molecular packing (head-
to-tail manner) via several C–Hꢀ ꢀ ꢀp interactions (Fig. 2(C) and
Fig. S25–S27, ESI†) in the crystalline state. Moreover, both
crystals have trapped disordered water molecules in the void
channels. No significant pꢀ ꢀ ꢀp interactions are observed in the
AIE characteristics
packing of either structure because of the bulky 3D steric effect Previously, our group reported that the 4-substituted cyanostyrene
of the tetraphenylethylene unit.
pyrene derivatives were AIE-active materials.39 In order to further
explore the AIE properties of the four pyrene-based cyanostyrenes,
the emission spectra (10ꢁ5 M) were measured in THF (good
Photophysical properties
The UV-vis spectra of the four pyrene-based cyanostyrene solvent) and THF/water (poor solvent) mixtures. Taking Py-2Ph-
derivatives in THF solution (10ꢁ5 M) are illustrated in Fig. 3. Cz as an example (Fig. 4A and D), the emission maximum of
Compounds Py-2Ph-Cz and Py-Ph-Cz display two strong absorption Py-2Ph-Cz was located at 488 nm in pure THF solution, and as the
bands in the range 275–300 nm and 320–425 nm, and the water fraction ( fw) increased from 0% to 60%, the emission red-
maximum absorption peak of Py-2Ph-Cz is red-shifted by 26 nm shifted to 498 nm with a weak blue fluorescence. Subsequently,
compared to that of Py-Ph-Cz. This may be ascribed to the emission intensity rapidly increased with a larger red-shifted
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Table 1 The photophysical properties of the four pyrene-based cyanostyrene derivatives
a
e (lmax abs
)
Ff solnsa/ t (ns) solnsa/
kr (ꢂ108 sꢁ1 d
)
solnsa/
c
Compd
(Mꢁ1 cmꢁ1
)
lmaxPL (nm) solnsa/filmsb filmsb
filmsb
aAIE filmsb
knr (ꢂ108
49.50/3.69
5.69/2.43
s
ꢁ1)e solnsa/filmsb
Py-2Ph-Cz 2.98 ꢂ 104 (384) 488/547
0.01/0.08 0.20/2.49
0.30/0.36 1.23/2.63
0.01/0.45 1.29/1.97
0.01/0.39 1.16/2.34
8
0.50/0.32
Py-Ph-Cz
Py-1-TPE
Py-2-TPE
2.41 ꢂ 104 (358) 497/514
4.84 ꢂ 104 (377) 498/514
3.14 ꢂ 104 (377) 438, 496/498
1.2 2.44/1.37
45
39
0.08/2.28 (0.17/2.68) f 7.67/2.79 (4.19/1.43) f
0.08/1.67 (0.01/2.77) f 8.5/2.6 (657.21/0.02) f
a
b
c
d
Maximum absorption wavelength measured in THF solution at room temperature. Measured in thin neat films. a = Fsolid/Fsoln
.
kr =
e
f
radiative decay rate (F/t). knr = nonradiative decay rate (1/t ꢁ kr). Calculated by BDF package.
Fig. 4 PL spectra of (A) Py-2Ph-Cz, (B) Py-Ph-Cz and (C) Py-1-TPE in THF/water mixtures with different water fractions (fw). Plot of relative PL intensity
(I/I0) versus the composition of a THF/water mixture of (D) Py-2Ph-Cz, (E) Py-Ph-Cz and (F) Py-1-TPE and Py-2-TPE, respectively. Inset: Fluorescent
photographs of Py-2Ph-Cz in THF/water mixtures (fw = 0% and 80%), Py-Ph-Cz in THF/water mixtures (fw = 0%, 60% and 80%) and Py-1-TPE in THF/
water mixtures (fw = 0% and 99%) taken under UV irradiation (lex = 365 nm), where I0 is the PL intensity in pure THF solution. The blue squares are for the
effect on I/I0, while the red circles are for the wavelength.
emission at 548 nm when fw increased to 90%, due to molecular to 0.08 and 0.36 in the film (Table 1), respectively, indicating that
aggregation. Furthermore, the formation of molecular aggregation Py-2Ph-Cz is AIE-active and Py-Ph-Cz is AIEE-active.
at fw = 99% would slightly quench the fluorescence intensity of the
When the phenylcarbazole group was replaced by a tetra-
maximum emission peak at 545 nm.
phenylethylene unit, both compounds Py-1-TPE and Py-2-TPE
On the other hand, the solvatochromic effect results exhibited typical AIE characteristics. As shown in Fig. 4C and F,
indicated that Py-2Ph-Cz exhibited a large red-shifted emission both compounds showed fluorescence signals in THF solution,
with the maximum emission peak shifting from 488 nm to as following the enhancement of fw from 10% to 50%, the
500 nm as the solvent polarity was increased from cyclohexane fluorescence intensity slightly increased. On sequentially
(Cy) to DMSO (Fig. S28, ESI†), and this can be attributed to the increasing fw to 90%, the emission intensity increased drama-
ICT effect.56–58 Thus, we speculate that the maximum emission tically by ca. 35-fold compared with that in pure THF solution,
peak at 545 nm for Py-2Ph-Cz at fw = 99% is originating from the with the maximum emission wavelength at 515 nm for Py-1-TPE
synergistic effect of the excimer emission plus the ICT process. and 514 nm for Py-2-TPE. The PL quantum yield increased from
In the case of Py-Ph-Cz, as fw increased from 0% to 60%, the 0.01 in THF solution to 0.45 for Py-1-TPE and 0.39 for Py-2-TPE
emission intensity gradually decreased with a red-shifted emission in films. Thus, both Py-1-TPE and Py-2-TPE are AIE-active
from 497 nm to 539 nm compared to that observed in pure THF materials. In addition, the emission of both Py-1-TPE and
solution. Then, when fw increased to 80%, the emission intensity Py-2-TPE in thin film exhibited a slightly red-shifted (o16 nm)
increased again (Fig. 4B and E). However, the fluorescence intensity emission compared with that in THF solution. This may be due
decreased with an accompanied blue-shifted emission band at to the presence of TPE units, which play a crucial role in
around 514 nm, which can be ascribed to the formation of inhibiting the p–p stacking in the aggregation state. Generally,
molecular aggregates at fw = 99%, resulting in H-aggregation. TPE-based molecules are known to follow the RIM mechanism,
As expected, the absolute PL quantum yield (Ff) of Py-2Ph-Cz and and major changes between the solution and solid state are
Py-Ph-Cz was measured at 0.01 and 0.30 in THF solution compared mainly related to knr which is strongly decreased by forced
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rigidification of the structure (and restriction of rotation/vibra-
In fact, the pyrene unit is an interesting chromophore,
tions and mostly isomerization processes) while kr is marginally which can act as either an electron-donor or electron-acceptor
increased. For the case of Py-1-TPE and Py-2-TPE, kr increased depending on the micro-environment of the bulk structure.61
from 106 sꢁ1 in solution to 108 sꢁ1 in the film, while knr Thus, according to DFT calculations, the pyrene may act as an
decreased by ca. 3-fold in the film compared to that in solution electron-donating (D) or electron-withdrawing (A) group
(Table 1 and Fig. S39, ESI†). This may be attributed to the depending on the electronic properties of the peripheral
presence of cyanostyrene and TPE moieties, the synergistic effect substituent groups present. The carbazole and cyanostyrene
of the RIM and the lone pairs participating in the light emission fragments are regarded as the electron-donating and electron-
processes.59
withdrawing group (A) respectively. Thus, the four pyrene-based
Furthermore, density functional theory (DFT) calculations cyanostyrene derivatives can be regarded as D–A type molecules.
(B3LYP/6-311G(d,p)) on Py-2Ph-Cz, Py-Ph-Cz, Py-1-TPE and Py-1- Indeed, the fluorescence spectra of the four compounds
TPE were performed to understand the effect of the electron displayed a significant bathochromic shift as the solvent polarity
delocalization on the optical behaviour. The highest occupied increased from cyclohexane to dimethyl sulfoxide (DMSO)
molecular orbital (HOMO) and the lowest unoccupied molecular (Fig. S28–S31, ESI†). Notably, large Stokes shifts of over 50 nm
orbital (LUMO) energy levels are presented in Fig. 5. The HOMO were observed, which further confirmed that the pyrene-based
of Py-Ph-Cz is almost completely delocalized over the entire cyanostyrene with a D–A molecular structure can undergo a
molecule, whilst the HOMO of Py-2Ph-Cz is primarily distributed typical ICT transition, where the highly polar excited state is
in the carbazole unit, and the HOMO of Py-1-TPE is localized on stabilized by polar solvents.56 This result is consistent with their
the pyrene unit and a portion of the cyanostyrene unit. Given optical behaviour.
that the nodal plane of pyrene passes through the carbon atoms
at the 2- and 7-positions in the HOMO and LUMO, the sub-
Mechanochromic properties
stituents at the 2-position will interact weakly with the pyrene Generally, the cyanostyrene derivatives with AIE characteristics
core. On the other hand, when the substituents are at the prefer to exhibit mechanoluminescence/mechanochromism
1-position, the electronic communication ability between pyrene (ML/MC) properties under mechanical stimuli, which mainly
and the substituents would be increased. In our case, according originates from the molecular packing patterns or changing
to DFT calculations, pyrene mainly acts as an electron donor in molecular configuration.62 To test the MC properties of the
compounds Py-Ph-Cz and Py-1-TPE, and in Py-2Ph-Cz, where twisted pyrene-based cyanostyrenes, the solid-state emission
the pyrene unit is directly connected with the cyanostyrene behaviour was investigated before and after grinding.
fragment, it may act as a weak electron-withdrawing group. Compound Py-Ph-Cz exhibited an intense green emission
On the other hand, although the 2-position of pyrene was (518 nm) in the crystalline state, and after grinding, the crystal-
functionalized, this position has a limited effect on the electronic line structure easily crashed and the powder emitted a maximum
structure of the whole molecule.55,60 The molecular orbital density emission peak at 512 nm, i.e. a slight hypsochromic shift in
in the HOMO of Py-2-TPE is localized on the tetraphenylethylene the fluorescence spectra (Fig. 6A and B). For Py-2Ph-Cz, the
unit and the fragment of cyanostyrene. Contrastingly, the LUMO maximum emission wavelength changed slightly from 546 nm
level of Py-Ph-Cz, Py-1-TPE and Py-2-TPE is distributed over the to 550 nm upon grinding (Fig. S38A, ESI†). It is noteworthy that
cyanostyrene fragment and partially on the tetraphenylethylene the maximum emission peak of both crystals Py-1-TPE and Py-2-
(phenylcarbazole) unit. For Py-2Ph-Cz, the LUMO is mainly TPE exhibited a red-shift from 494 nm to 512 nm after grinding
spread on the pyrene ring and the cyanostyrene units. The (Fig. 7 and Fig. S38B, ESI†). Clearly, the TPE-containing pyrene-
separated HOMO and LUMO levels indicated that the pyrene- based cyanostyrenes Py-1-TPE and Py-2-TPE revealed an obvious
based cyanostyrene derivatives can undergo a twisted intra- contrast of emission before and after grinding compared to
molecular charge transfer process in polar solvents, leading to Py-Ph-Cz and Py-2Ph-Cz. This can be attributed to the former
an obvious red-shifted emission, as well as a decreased energy TPE-containing compounds with the larger twist conformation
band gap.
becoming more planar.39
Furthermore, powder X-ray diffraction (PXRD) was utilized
to determine the molecular pattern before and after grinding
(Fig. 6C, D and Fig. S40, ESI†). The powdered samples of
compounds Py-2Ph-Cz, Py-Ph-Cz and Py-1-TPE displayed a
sharp and intense diffraction pattern before grinding, where
the PXRD peak in the region 2y = 201–301 is tentatively assigned
to p–p stacking interactions in the range 3.1–4.40 Å.39,63
However, after grinding, the PXRD pattern of Py-2Ph-Cz and
Py-Ph-Cz is the same as their crystalline PXRD pattern with a
decreased reflection intensity and broadened FWHM, which
indicates that the crystal unit cell remains unchanged after
grinding. For Py-1-TPE, the diffraction peaks at 2y = 22.01
disappeared with a new peak appearing at 2y = 38.21, which
Fig. 5 Molecular orbital plots of pyrene-based cyanostyrene AIEgens
(from left to right: Py-2Ph-Cz, Py-Ph-Cz, Py-1-TPE and Py-2-TPE)
calculated at the RB3LYP/6-311G(d,p) level.
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revealed that the external forces can strengthen the inter-
molecular interactions, such as C–Hꢀ ꢀ ꢀp interactions.
Preparation of pyrene-based AIEgens fluorescent ink for
patterning
Before utilizing these systems for printing ink, the cytoto-
xicity was evaluated using a 3-(4,5-dimethyl-2-thiazolyl)-2,5-
diphenyltetrazolium bromide (MTT) assay. As shown in
Fig. S41 (ESI†), the NCTC clone 929 [L cell, L-929] cell viability
remained close to 100% as the concentration of the four
compounds increased from 0 to 50 mM after 24 h of incubation.
This indicated that the pyrene-based AIEgens exhibited low
toxicity to normal live cells. Thus, the results of cell survival
experiments indicated that the pyrene-based AIEgens would be
suitable luminescent materials to be used as fluorescent inks
for industrial applications.
Thus, based on the high thermal stability, excellent fluores-
cence properties, and good biocompatibility, a new fluorescent
ink was fabricated using the pyrene-based AIEgens as the
luminescent material.64 The selected AIEgens powders (Py-
2Ph-Cz, Py-Ph-Cz and Py-1-TPE; Py-2-TPE was not tested due
to its similar photophysical features to Py-1-TPE) were dissolved
in epoxy resin (100 g) to achieve a colourless or pale yellow
fluorescent (depending on the concentration of pyrene-based
AIEgens) ink under sunlight. The schematic of the anti-
counterfeiting ink and the screen-printing process is illustrated
in Fig. 7A. The three fluorescent inks exhibited bright blue or
sky-blue emission in both resins’ (epoxy resin and polypropylene)
solution. Moreover, the ink was stable even after prolonged
standing (4 months) at room temperature.
Fig. 6 The PL spectrum of (A) Py-Ph-Cz and (B) Py-1-TPE before and
after grinding. Inset: The images of compounds in the crystalline state and
after grinding taken under 365 nm UV light. Wide angle XRD diffractograms
of (C) Py-Ph-Cz and (D) Py-1-TPE in different states.
Before printing, for the epoxy resin system, the curing agent
(593 curing agent, 25 g) was added into the ink in order to
solidify the epoxy resin. Then, as shown in Fig. 7B and Fig. S42–
S43 (ESI†), the letters ‘‘AIE’’ were printed upon filter paper,
butter paper and tissue paper via screen printing technology
using the pyrene-based AIEgens inks. As the content of
the fluorescent powder increased from 1 mg to 5 mg, the
high quality fluorescence patterns (such as high contrast,
distinguishable outlines) became clearer with good printability
on the three types of papers. When the weight ratio of the
pyrene-based AIEgens : (epoxy resin + curing agent) reached ca.
5 : 125 000 (0.004 wt%), the emission intensity increased by ca.
1–4 fold and with clear ‘‘AIE’’ images observed (Fig. S51–S54,
ESI†).
Thus, under the above-mentioned printing conditions, the
QR codes were printed by screen-printing technology on the
tissue paper, butter paper and filter paper using Py-2Ph-Cz,
Py-Ph-Cz and Py-1-TPE as fluorescent inks, respectively (Fig. 7 and
Fig. S44–S45, ESI†). For comparison, the common commercial
black ink (fluorescent material free), commercial inorganic
Fig. 7 (A) The schematic of the anti-counterfeiting ink and the screen-
printing process. (B) Digital photographs of letter ‘‘AIE’’ pattern printing on
filter paper, butter paper and tissue paper using pyrene-based AIEgens
Py-1-TPE as fluorescent ink with different concentrations (weightAIEgens
:
weightEpoxylite+curing agent = 1 : 125 000, 3 : 125 000 and 5 : 125 000) under phosphor (BaMgAl11O19 Ce3+Tb3+, Ff = 0.90), RhodamineB (RhB)
sunlight (left) and UV irradiation (lex = 365 nm) (right). (C) Digital photo-
and fluorescein (the last two are selected as commercial red/
yellow fluorescent dyes with ACQ feature) were also selected.
As shown in Fig. 7C and Fig. S44 and S45 (ESI†), the fluorescent
inks show an almost invisible profile on butter paper and tissue
paper, but a shallow imprinting on filter paper in sunlight.
graphs of QR code pattern printing on tissue paper using pyrene-based
AIEgens fluorescent ink or commercial ink (weightAIEgens or inorganic phosphor
:
weightEpoxylite+curing agent = 5 : 125 000) under sunlight (left) and under UV
irradiation (lex = 365 nm) (right) (under UV irradiation: aperture: f/1.8,
exposure time: 1/40 s, ISO speed: ISO-400).
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Upon irradiation (lex = 365 nm), the clear figures of QR code
for the pyrene-based AIEgens appeared, while the commercial
inorganic phosphor did not exhibit a visible pattern, because of its
ultralow concentration in the fluorescent ink. Only when the
weight ratio was increased to 5 : 32, did the commercial inorganic
phosphor display a visible image (Fig. S46, ESI†) under lex
=
256 nm irradiation. Also, the letters ‘‘AIE’’ were printed on the
wall with bright emission under UV irradiation in the dark
(Movies S1, ESI†).
On the other hand, one of the greatest challenges when
employing organic fluorescent ink is how to avoid or minimize
colour migration of the fluorescence pattern, which is related to
the quality of the printing products. As shown in Fig. S42, S43,
S47 and Table S5 (ESI†), the fluorescent ink containing pyrene-
based AIEgens (0.004 wt%) has a relatively small colour
migration (o27 nm) in butter paper and tissue paper
substrates compared to AIEgens powders in the solid state.
In contrast, the fluorescent ink containing RhB or fluorescein
also showed a clear fluorescence pattern with a maximum blue
shifted emission of 140 nm at ultralow concentration in the
three print substrates compared to the pure compound in the
solid state (Fig. S48 and S49, ESI†). The large blue-shift may be
ascribed to the fluorescent dyes with an ACQ feature reacting
with the curing agent.
Fig. 8 Digital photographs of letter ‘‘AIE’’ pattern printing on filter paper,
butter paper and tissue paper using pyrene-based AIEgens Py-2Ph-Cz
(A) and Py-1-TPE (B) as fluorescent ink at different concentrations
(weightAIEgens : weightpp = 5 : 100 000, 5 : 10 000 and 5 : 1000, respectively)
under sunlight and UV irradiation of 365 nm: aperture: f/1.8, exposure
time: 1/40 s, ISO speed: ISO-400), (C and D) CIE 1931 chromaticity
diagram and the colour coordinates for the corresponding concentration.
Furthermore, we used polypropylene (PP) as a binder for
preparing the fluorescent ink which easily solidified by
evaporation at room temperature. The effect of concentration
on the colour migration was investigated using Py-2Ph-Cz,
Py-1-TPE, RhB and fluorescein as fluorescent dyes in the poly-
propylene system. For example, the fluorescent ink containing
(such as RhB, fluorescein, etc.) and prefer to undergo an
uncontrollable colour migration, leading to a concentration-
dependent emission colour in the fluorescent ink, and the
inorganic fluorescent ink has a large content of inorganic
phosphor. More importantly, both inorganic fluorescent materials
and commercial organic dyes would cause the fluorescence
intensity to decrease due to the ACQ effect at high concentration.
However, the AIE materials are molecularly dispersed in a matrix
and the RIM mechanism still works. The fluorescent inks
containing a low concentration of pyrene-based AIEgens show
some advantages, namely (I) a wide scope of application over the
range from ultralow to low concentration (0.005–0.5 wt%) to avoid
the ACQ effect, (II) good biocompatibility with impressive anti-
counterfeiting features, and (III) slight colour migration,
which not only offers an example of the use of AIEgens as anti-
counterfeiting inks with ultralow consumption for commercial
application, but also enriches the practical applications of AIEgens.
Py-2Ph-Cz revealed
a clear security pattern with similar
emission colour from weightAIEgens : weightpp = 5 : 100 000 to
5 : 10 000 (0.005 wt% to 0.05 wt%) with small colour migration
(9 nm) in the three printing substrates, and this was almost
imperceptible by naked-eye detection. When the concentration
increased to 0.5 wt%, the maximum emission band was red-
shifted to ca. 530 nm, which corresponded to its emission peak
(547 nm) in the aggregate state (Fig. 8A and Fig. S57, ESI†).
In the case of Py-1-TPE, the fluorescent ink exhibited similar
emission behaviour (lmax em: 472–492 nm) with slight colour
migration (17 nm) in the three substrates as the concentration
increased ca. 100-fold from weightAIEgens : weightpp = 5 : 100 000
to 5 : 1000 (0.005 to 0.5 wt%). More importantly, the higher the
concentration of the content of AIEgens in the PP resin, the
brighter the emission observed (Fig. 8B and Fig. S57, S58, ESI†).
However, in the fluorescein and RhB systems, as the concen-
tration increased from 0.005 to 0.5 wt%, both fluorescent inks
exhibited dual emissive fluorescence behaviour with tunable-
colour emission from a blue to yellow-green colour for
fluorescein, and a white to orange-red colour for RhB.
Moreover, the emission intensity suffered somewhat from
fluorescence quenching at high concentration of fluorescein
(0.5 wt%) compared to 0.05 wt% concentration (Fig. S50, S51,
S59 and S60, ESI†).
Experimental
Materials
Unless otherwise stated, all reagents used were purchased from
commercial sources and were used without further purification.
Tetrahydrofuran was distilled prior to use.
Characterization
Based on our previous knowledge and the experimental 1H and 13C NMR spectra (400 MHz or 600 MHz) were recorded
results, traditional fluorescent inks contain organic dyes on a Bruker AV 400M or AVANCE III 600M spectrometer using
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chloroform-d as the solvent and tetramethylsilane as the inter- (1.56, 3.13, 6.25, 12.5, 25, and 50 mg mLꢁ1) of pyrene-based
nal reference. J-Values are given in Hz. High-resolution mass AIEgens, and cells were incubated for another 24 h. After
spectra (HRMS) were recorded on a LC/MS/MS, which consisted incubation, the culture media were removed and each well
of a HPLC system (Ultimate 3000 RSLC, Thermo Scientific, USA) was filled with 100 mL of new culture media containing MTT
and a Q Exactive Orbitrap mass spectrometer. UV-vis absorption (0.5 mg mLꢁ1) and incubated for an additional 4 h. Then the
spectra and photoluminescence (PL) spectra were recorded on a media were discarded and each well was filled with another
Shimadzu UV-2600 and a Hitachi F-4700 spectrofluorometer. PL 100 mL of DMSO. The OD490 value (Abs.) of each well was
quantum yields were measured using absolute methods using a immediately measured using a microplate reader. Cell viability
Hamamatsu C11347-11 Quantaurus-QY Analyzer. The lifetime was calculated by the ratio of OD490 values of the cells incubated
was recorded on an Edinburgh FLS 980 instrument and with Py-2Ph-Cz, Py-Ph-Cz, Py-1-TPE, Py-2-TPE or pyrene suspension
measured using
a time-correlated single-photon counting to that of the cells incubated with culture medium only.
method. Thermogravimetric analysis was carried out on a
Mettler ToledoTGA/DSC3+ under dry nitrogen at a heating rate
The screen-printing procedure
of 10 1C minꢁ1. The quantum chemistry calculation was For the epoxy resin system fluorescent ink: An amount of
performed on the Gaussian 09 (B3LYP/6-311G(d,p) basis set) fluorescent powder (Py-2Ph-Cz, Py-Ph-Cz, Py-1-TPE, RhB or
software package. The solid environment was simulated using a commercial phosphor BaMgAl11O19 Ce3+Tb3+) (1 mg, 3 mg
two-layer ONIOM model with the QM/MM method, and the and 5 mg) was added into epoxy resin (100 g) and stirred for
simulated rates of radiative/nonradiative decay were calculated 1 h to ensure uniform fluorescence dispersion. Before printing,
with the Molecular Material Property Prediction Package the curing agent (25 g) was added into the fluorescent ink
(MOMAP).
system for controlling the curing time. Then the anti-
counterfeiting images were fabricated using the common
screen-printing technology.
X-Ray crystallography
Crystallographic data for the compounds were collected on a
For the polypropylene (PP) system fluorescent ink: 5 mg of
Bruker APEX 2 CCD diffractometer with graphite monochro- fluorescence powder (Py-2Ph-Cz, Py-Ph-Cz, Py-1-TPE, RhB or
mated Mo Ka radiation (l = 0.71073 Å) in the o scan mode.65,66 fluorescein) was added to polypropylene (100 g) and stirred for
The structures were solved by charge flipping or direct methods 1 h to ensure uniform fluorescence dispersion. Then the anti-
algorithms and refined by full-matrix least-squares methods on counterfeiting images were fabricated using the common
F2.67 All esds (except the esd in the dihedral angle between two screen-printing technology.
l.s. planes) were estimated using the full covariance matrix. The
cell esds were considered individually in the estimation of esds
Synthetic procedures
in distances, angles and torsion angles. Correlations between The starting compound 2-Bpin-pyrene (1c)60 or intermediates 2-(40-
esds in cell parameters were only used when they were defined (8a,9a-dihydro-9H-carbazol-9-yl)-[1,10-biphenyl]-4-yl)acetonitrile (2a),69
by crystal symmetry. An approximate (isotropic) treatment of 1-(4-formylphenyl)pyrene (2b),70 2-(4-(pyren-1-yl)phenyl)acetonitrile
cell esds was used for estimating esds involving l.s. planes. The (2c), 2-(4-(pyren-2-yl)phenyl)acetonitrile (2d) and (Z)-2-(4-
final cell constants were determined through global refinement bromophenyl)-3-(4-(pyren-1-yl)phenyl)acrylonitrile (3a) were
of the xyz centroids of the reflections harvested from the entire synthesized and are listed in Scheme S1 (ESI†).
data set. Structure solution and refinements were carried out
General procedure for the synthesis of (Z)-2-(40-(9H-carbazol-
using the SHELXTL-PLUS software package.67 The partially 9-yl)-[1,10-biphenyl]-4-yl)-3-(pyren-1-yl)acrylonitrile (Py-2Ph-Cz).
occupied water molecule of crystallization was modelled by Into a 100 mL two-necked flask was added 2-(40-(9H-carbazol-
the Platon Squeeze procedure.68 Data (excluding structure 9-yl)-[1,10-biphenyl]-4-yl)acetonitrile (150 mg, 0.41 mmol, 1 eq.),
factors) on the structures reported here have been deposited 1-(4-formylphenyl) pyrene (113 mg, 0.50 mmol, 1.22 eq.), KOtBu
with the Cambridge Crystallographic Data Centre. CCDC (150 mg, 1.34 mmol, 3.27 eq.) and dry ethanol (10 mL). The
2059788 and 2059789 contain the supplementary crystallo- reaction mixture was degassed with nitrogen for 5 min, and the
graphic data for this paper.†
mixture was refluxed overnight at 90 1C. After cooling to room
temperature, the reaction mixture was filtered and washed with
cold ethanol three times, and then the residue was further
Cell viability
L929 mouse fibroblasts were cultured in Dulbecco’s modified crystallized from a solution mixture of hexane and dichloro-
Eagle’s medium (DMEM) containing 10% fetal bovine serum at methane to afford (Z)-2-(40-(9H-carbazol-9-yl)-[1,10-biphenyl]-4-
37 1C in a humidified environment containing 5% CO2. The yl)-3-(pyren-1-yl) acrylonitrile (Py-2Ph-Cz) as a yellow solid
cytotoxicity of compounds Py-2Ph-Cz, Py-Ph-Cz, Py-1-TPE, Py-2- (320 mg, 74%) (in addition, compound Py-2Ph-Cz can slowly
TPE and pyrene was assessed by the 3-(4,5-dimethylthiazol-2- transform from the trans-configuration to cis-configuration in
1
y1)-2,5-diphenyltetrazolium bromide (MTT) method. L929 the solvent slowly). H NMR (400 MHz, CDCl3): d 8.71 (d, J =
mouse fibroblasts were firstly seeded into a 96-well plate at a 8.2 Hz, 1H), 8.69 (s, 1H), 8.35–8.04 (m, 10H), 8.00 (d, J = 8.5 Hz,
density of 8000 cells per well in DMEM, and incubated for 24 h. 2H), 7.94–7.89 (m, 2H), 7.87 (d, J = 8.6 Hz, 2H), 7.77–7.68
Then the media were replaced by different concentrations (m, 2H), 7.52 (d, J = 8.2 Hz, 2H), 7.49–7.43 (m, 2H), 7.38–7.29
(0, 0.78, 1.56, 3.12, 6.25, 12.5, and 25 mg mLꢁ1) of pyrene and (m, 2H) ppm. 13C NMR (101 MHz, CDCl3) d 141.3, 140.8, 140.2,
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139.0, 137.5, 133.9, 133.0, 131.3, 130.7, 123.0, 128.9, 128.5, Under a nitrogen atmosphere, a mixture of 2d (80 mg,
127.9, 127.8, 127.5, 126.8, 126.4, 126.3, 126.2, 126.1, 126.0, 0.252 mmol, eq.), 4-(1,2,2-triphenylethenyl)benzaldehyde
1
125.1, 124.8, 124.6, 123.5, 122.6, 120.4, 120.1, 118.2, 114.3, (100 mg, 0.277 mmol, 1.1 eq.) and KOtBu (80 mg, 0.71 mmol,
109.8 ppm. HRMS (FTMS ꢁ p APCI) m/z: found, 570.2116[M]+; 2.8 eq.) in dry ethanol (8 mL) was refluxed overnight at 90 1C.
calcd for C43H26N2 requires [M]+ 570.2096.
After cooling to room temperature, the reaction mixture was
General procedure for the synthesis of (Z)-2-(4-(9H- filtered and washed with cold ethanol three times, and then the
carbazole-9-yl)phenyl-3-(4-(pyren-1-yl)phenyl)acrylonitrile (Py- residue was further crystallized from a mixture solution of
Ph-Cz). Under a nitrogen atmosphere, a mixture of (Z)-2-(4- hexane and dichloromethane to give a yellow-green powder
bromophenyl)-3-(4-(pyren-1-yl)phenyl)acrylonitrile (220 mg, Py-2-TPE (58 mg, 35%). 1H NMR (400 MHz, CDCl3) d 8.41 (s,
0.45 mmol, 1.0 eq.), carbazole (91 mg, 0.54 mmol, 1.2 eq.) 2H), 8.21 (d, J = 7.6 Hz, 2H), 8.17–8.09 (m, 4H), 8.06–7.99 (m, 2H),
and K2CO3 (300 mg, 2.18 mmol, 4.84 eq.) were dissolved in a 7.96 (d, J = 8.4 Hz, 2H), 7.96 (d, J = 8.4 Hz, 2H), 7.82 (d, J = 8.4 Hz,
mixture of P(tBu)3 (1 mL)/toluene (8 mL). After degassing with 2H), 7.72 (d, J = 8.4 Hz, 2H), 7.52 (d, J = 3.2 Hz, 2H), 7.10 (m, 17H)
nitrogen for 5 min, Pd(OAc)2 (50 mg, 0.22 mmol, 0.48 eq.) was ppm, 13C NMR (151 MHz, CDCl3) d 146.6, 143.4, 143.3, 143.2,
added, and the mixture was refluxed for 2 days at 110 1C. After 142.4, 142.2, 141.7, 140.1, 137.6, 133.8, 132.0, 131.7, 131.4, 131.4,
cooling to room temperature, the mixture was poured into H2O 131.3, 131.2, 128.9, 128.6, 128.0, 127.9, 127.9, 127.7, 127.5, 126.9,
(100 mL) and extracted with CH2Cl2 (3 ꢂ 50 mL). The combined 126.8, 126.5, 126.1, 125.3, 124.5, 124.2, 123.5, 118.2, 110.2 ppm.
organic layer was washed with water and brine (50 mL), and HRMS (FTMS + p APCI) m/z: found, 660.2690 [M + H]+; calcd for
then the solution was dried over MgSO4 and evaporated. The C51H33N requires [M]+ 659.2613.
crude product was further purified by column chromatography
using hexane/dichloromethane (Vhexane : VCH2Cl2 = 1 : 1) as the
eluent which eventually afforded the yellow solid Py-Ph-Cz
Conclusions
(105 mg, 40%) (in addition, compound Py-Ph-Cz can transform
In summary, a series of pyrene-based AIEgens were synthesized
by a Knoevenagel reaction and a Pd-catalyzed coupling reaction
in high yield. Owing to their high thermal stability, excellent
fluorescence properties, good biocompatibility, and light stability,
the pyrene-based AIEgens were employed in the preparation
of fluorescent inks for anti-counterfeiting by screen-printing
technology. More importantly, the fluorescent ink containing
compound Py-1-TPE with the TPE unit exhibited a much better
from the trans-configuration to cis-configuration in the solvent
1
within 60 min (Fig. S12, ESI†)). H NMR (400 MHz, CDCl3) d
8.31–7.97 (m, 15H), 7.82 (s, 3H), 7.79 (d, J = 4.7 Hz, 2H), 7.73 (d,
J = 8.4 Hz, 2H), 7.54–7.42 (m, 4H), 7.34 (t, J = 7.3 Hz, 2H) ppm.
13C NMR (151 MHz, CDCl3) d 144.4, 144.0, 143.3, 142.2, 140.6,
140.4, 138.8, 138.7, 136.4, 136.2, 133.4, 132.5, 132.3, 131.6,
131.5, 131.3, 131.1, 131.0, 130.98, 131.0, 130.6, 123.0, 129.5,
128.5, 128.3, 128.0, 127.8, 127.6, 127.5, 127.4, 126.2, 126.2,
125.5, 125.1, 125.1, 125.0, 124.9, 124.8, 124.8, 124.8, 124.7
ultralow/low concentration (weightAIEgens :weightbinder = 0.005–
123.7, 120.5, 120.4, 120.4, 120.1, 118.1, 113.5, 110.8, 109.8,
printability on different substrates with small colour migration at
0.5 wt%). Thus, such a fluorescent ink containing the pyrene-
based AIEgens is a promising candidate for anti-counterfeiting
applications and has the potential to significantly lower the costs
with limited colour migration involved in this industry. Ongoing
work is focused on more colour-tunable pyrene-based AIEgens for
the preparation of blue to red fluorescent inks.
109.7, 77.3, 77.0, 76.8 ppm. HRMS (FTMS + p APCI) m/z: found,
571.2163[M + H]+; calcd for C43H26N2 requires [M]+ 570.2096.
General procedure for the synthesis of (Z)-2-(4-(pyren-1-yl)
phenyl)-3-(4-(1,2,2-triphenylvinyl)phenyl)acrylonitrile (Py-1-TPE).
Under a nitrogen atmosphere, a mixture of 2c (100 mg,
0.315 mmol,
1 eq.), 4-(1,2,2-triphenylethenyl)benzaldehyde
(124 mg, 0.35 mmol, 1.1 eq.) and KOtBu (100 mg, 0.89 mmol,
2.83 eq.) in dry ethanol (6 mL) was refluxed overnight at 90 1C.
After cooling to room temperature, the reaction mixture was
filtered and washed with cold ethanol three times, and then the
residue was further crystallized from a mixture solution of
hexane and dichloromethane to give a yellow-green powder
Py-1-TPE (103 mg, 50%). 1H NMR (400 MHz, CDCl3) d 8.29–
8.14 (m, 4H), 8.12 (s, 2H), 8.09–7.95 (m, 3H), 7.84 (d, J = 8.3 Hz,
2H), 7.72 (dd, J = 8.3, 6.5 Hz, 4H), 7.55 (s, 1H), 7.22–6.99 (m, 17H)
ppm. 13C NMR (151 MHz, CDCl3) d 146.6, 143.4, 143.3, 143.2,
142.4, 142.1, 141.9, 140.0, 136.5, 133.7, 132.0, 131.7, 131.5, 131.4,
131.4, 131.3, 131.3 130.9, 130.9, 128.9, 128.5, 127.9, 127.9, 127.8,
127.7, 127.4, 127.4, 126.9, 126.8, 126.7, 126.1, 125.9, 125.3, 125.0,
125.0, 124.9, 124.9, 124.7, 118.2, 110.3 ppm. HRMS (FTMS + p
APCI) m/z: found, 660.2687 [M + H]+; calcd for C51H33N requires
[M]+ 659.2613.
Author contributions
X. Wang, L. Wang, X. Mao, Q. Wang and Xing Feng contribution
in designing and performing the whole project and writing the
paper; Z. Mu, L. An, W. Zhang, C. Cao and C. Redshaw
contribution in revising the manuscript and giving scientific
advice; X. Feng, A. Qin and B. Z. Tang contribution in designing
and supervising the whole project.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
General procedure for the synthesis of (Z)-2-(4-(pyren-2-yl) This work was supported by the National Natural
phenyl)-3-(4-(1,2,2-triphenylvinyl)phenyl)acrylonitrile (Py-2-TPE). Science Foundation of China (21975054 and 21905028),
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Natural Science Foundation of Guangdong Province of China
(2019A1515010925), Guangdong Provincial Key Laboratory of
Information Photonics Technology (2020B121201011), ‘‘One
Hundred Talents Program’’ of the Guangdong University
of Technology (GDUT) (1108-220413205), and Guangdong
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