A donor-acceptor cruciform π-system: High contrast mechanochromic properties and multicolour electrochromic behavior

Article abstract of DOI:10.1039/c4tc00516c

A donor-acceptor (D-A) cruciform conjugated luminophore DMCS-TPA was designed and synthesized. The DMCS-TPA solid shows both aggregation induced emission (AIE) effect and high contrast mechanochromic (MC) behavior with a remarkable spectral shift of 87 nm. The obvious fluorescence switching from yellowish green to orange can be realized by pressing at only 10 MPa or simply grinding. The photophysical properties, theory calculation and XPS results demonstrate that the extension of the conjugation length and subsequent enhancement of intramolecular charge transfer (ICT) transition are responsible for the improved MC performance. In addition, DMCS-TPA is readily deposited on the ITO electrode surface by the electrochemical method to form an electrochromic (EC) film with multiple colours showing (light green at 0 V, red at 1 V, grey at 1.1 V and blue at 1.45 V) and a high optical contrast of 65% at 769 nm. The results suggest that incorporation of electroactive moieties into luminophores to constitute D-A cruciform conjugated structures is a promising design strategy for preparing dual functional materials combining MC and EC properties. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4tc00516c

Journal of
Materials Chemistry C
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A donor–acceptor cruciform p-system: high
contrast mechanochromic properties and
Cite this: J. Mater. Chem. C, 2014, 2,
multicolour electrochromic behavior†
5365
Jingwei Sun, Xiaojing Lv, Pingjing Wang, Yujian Zhang, Yuyu Dai, Qichao Wu,
*
*
Mi Ouyang and Cheng Zhang
A donor–acceptor (D–A) cruciform conjugated luminophore DMCS-TPA was designed and synthesized.
The DMCS-TPA solid shows both aggregation induced emission (AIE) effect and high contrast
mechanochromic (MC) behavior with a remarkable spectral shift of 87 nm. The obvious fluorescence
switching from yellowish green to orange can be realized by pressing at only 10 MPa or simply grinding.
The photophysical properties, theory calculation and XPS results demonstrate that the extension of the
conjugation length and subsequent enhancement of intramolecular charge transfer (ICT) transition are
responsible for the improved MC performance. In addition, DMCS-TPA is readily deposited on the ITO
electrode surface by the electrochemical method to form an electrochromic (EC) film with multiple
colours showing (light green at 0 V, red at 1 V, grey at 1.1 V and blue at 1.45 V) and a high optical
contrast of 65% at 769 nm. The results suggest that incorporation of electroactive moieties into
luminophores to constitute D–A cruciform conjugated structures is a promising design strategy for
preparing dual functional materials combining MC and EC properties.
Received 15th March 2014
Accepted 26th April 2014
DOI: 10.1039/c4tc00516c
www.rsc.org/MaterialsC
pressing, one of the recent goals for practical applications is
improving the contrast ratio in emission intensity or wave-
Introduction
length. Several uorescent on–off switching materials with high
contrast have been reported.7 However examples with a broad
colour change are rather scarce at the current stage8 due to the
complicated requirements of both remarkable shi of PL
wavelength and high solid-state emission efficiency. Tian's
group obtained divinylanthracene derivatives showing more
than 100 nm red-shi under high pressure, for example, above
one GPa,9 but relatively low pressure is preferred for applica-
tions in our daily life. Therefore, development of new AIE-active
luminogens with large emission wavelength change under
moderate pressure is strikingly desirable. As for electro-
chromism, that the colour can be reversibly modulated by
applying electrochemical potential, the construction of mono-
mers having multiple redox states with different absorptions is
fairly important for preparation of multicolour electrochromic
materials.10 Besides, to achieve dual response characteristic
(such as MC and EC), the key design concept is incorporating
corresponding functional units in a single molecule, while
along with it is the ambiguous intramolecular and intermolec-
ular interference inuencing the band-gap and excitonic
coupling and thus the photophysical performance of the
material. As such, outlining the molecular design principles is a
great challenge for preparing efficient mechano-electrochromic
materials.
Stimuli-responsive materials are receiving increasing attention
in terms of academic importance and practical application,
especially organic chromophores whose emission or colour can
be tuned by various external stimuli.1 Nowadays compounds
with mechano-thermo-vapochromic,2 mechano-photochromic,3
photo-electrochromic,4 electro-acidochromic5 or mechano-
acidochromic6 properties are being developed. However,
mechano-electrochromic materials, which synchronously
possess force and electric dependent optical properties, have
rarely been reported due to the lack of molecular design prin-
ciples. As electrical power is indispensable to the modern world,
and mechanical stimulation can be carried out simply with
hands, the mechano-electrochromic chromophores can nd
signicant and captivating potential applications in touch
screens, biosensors and optoelectronic devices, especially the
displays whose input information can be supplied as both a
sophisticated electrical signal and an in situ manual drawing.
As for mechanochromic (MC) properties, meaning that the
emission can be reversibly transformed through altering of
molecular packing structures upon grinding, shearing or
State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, College
of Chemical Engineering and Materials Science, Zhejiang University of Technology,
HangZhou, P. R. China. E-mail: czhang@zjut.edu.cn; ouyang@zjut.edu.cn
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4tc00516c
The donor–acceptor cruciform p-system, which is charac-
terized by rigid X-shaped geometry with donors and acceptors
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respectively on two crossed axes, has been explored widely in electrode surface by the electrochemical method to form an
chemical sensors, non-linear optical devices, OLEDs, OFETs electrochromic lm with multiple colours showing (light green,
and molecular electronics owing to its unique electronic and red, grey and blue). A systematic study of the photophysical
optical properties as well as aggregate structures.11 Herein, for properties, structure characteristics and theoretical calculations
the design of organic chromophores that respond to both has been carried out to examine the reasonable molecular
mechanic and electric stimuli, we present the electron D–A design strategy.
cruciform conjugation strategy via adopting triphenylamine
(TPA) donors suspended on both sides of the central phenyl of
the dicyanodistyrylbenzene (DCS) moiety. This approach has
the following advantages. First, the cruciform structure can
Results and discussion
Photophysical properties
successfully incorporate units with different functions into each
branch, for instance, one bar provides the electroactive species
(TPA) while the other serves as the luminogen (DCS). Second,
the crowding in the central part forces the surrounding
substituents to distort from the ring plane, resulting in effective
depression of close packing and enhancement of emission
quantum yields in the solid state.12 Finally, it has been
demonstrated that a large bathochromic shi of uorescence
can be expected from mechanochromic dyes with push–pull
features owing to their strong dipole–dipole interactions.13 In
particular, the D–A cruciform conjugations generally show
spatially separated frontier molecular orbitals (FMOs) with a
vanishingly small overlap in the central core between the
HOMO and LUMO.11e–g The extraordinary HOMO and LUMO
located on crossed directions respectively might induce
intriguing optical and electronic properties.
In this work, we designed and synthesised an interesting
novel model compound DMCS-TPA (Scheme 1). For compar-
ison, the linear molecule BMBCP without TPA donors was
prepared and characterized. DMCS-TPA exhibits MC properties
with a remarkable emission peak shi of 87 nm and uorescent
efficiencies of 48.59% and 34.53% before and aer grinding,
much higher than those of BMBCP. The obvious uorescence
(colour) transition from yellowish green (yellow) to orange
(orange) can be realized by simply grinding or pressing at only
10 MPa. In addition, DMCS-TPA is readily deposited on the ITO
The optical properties of DMCS-TPA in solvents of varying
polarities were investigated by UV-vis absorption and PL spec-
troscopy. For comparison, the absorption and emission spectra
of BMBCP in dilute solution are shown in Fig. 1. DMCS-TPA
exhibits two prominent emission bands: one with a vibrational
structure that remains located at around 430 nm and the other
signicantly shis from 513 nm to 595 nm with the solvent
changing from hexane to chloroform. The blue region emis-
sions of DMCS-TPA, which are similar in different solvents,
might originate from the DCS moiety because of their analo-
gous spectra with those of BMBCP in the monomer state. The
hypochromatic peaks of about 21 nm relative to those of
BMBCP are attributed to the twisted molecular conformation
and decreased conjugation induced by the steric hindrances.
The longer wavelength emissions can be assigned to the intra-
molecular charge transfer (ICT) effect due to the large sol-
vatochromism with increasing solvent polarity. In addition, the
quantum yields (fF) of DMCS-TPA in solution decrease from
6.9% (toluene) to 5.0% (chloroform) and less than 0.01%
(DMF). The excitation spectra monitored at both emission
maxima are shown in Fig. S1.† Particularly, when monitored at
430 nm, DMCS-TPA molecules exhibit excitation proles almost
mirror symmetric with the emission spectra. For BMBCP, no
obvious ICT emission was observed in solutions. The results
imply that an obvious charge transfer from the TPA axis to the
DCS axis takes place in excited DMCS-TPA. Unlike the case of
emission, the absorption spectra of DMCS-TPA are almost
identical irrespective of the kinds of solvents, showing the main
band at 349 nm together with a much weaker shoulder at
around 438 nm. The shoulder peak, which is apparently absent
Scheme 1 Synthesis route to DMCS-TPA and BMBCP. (a) (4-(Diphe-
nylamino) phenyl)boronic acid, Pd(PPh3)4, Na2CO3 (aq), toluene/THF, Fig. 1 Normalized absorption and photoluminescence (PL) spectra of
reflux; (b) 2-(3-methoxyphenyl)acetonitrile, NaOCH3, chromato- DMCS-TPA in (a) hexane, (b) toluene, (c) chloroform and (d) BMBCP in
graphic grade ethanol, r.t.
toluene.
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Table 1 Optical properties of DMCS-TPA and BMBCP in the solid state
in BMBCP, is ascribed to the ICT transition. On one hand, the
congested central part where bulky substituents suspend
surround the benzene core leads to largely twisted molecular
conformation with shortened conjugation, which might result
in a blue-shi tendency; on the other hand, the electron-rich
TPA units together with the electron-withdrawing –CN induce
the ICT effect in the excited state and give rise to red-shied
emission depending on the solvent polarity. The joint effect
between the conjugation and ICT degree denes the emission of
DMCS-TPA.
Samples
lem (nm) fF (%) s1 (ns) (%)
s2 (ns) (%)
2.138 (56.08) 5.920 (43.92)
2.147 (48.67) 10.040 (51.33)
s (ns)
3.80
6.20
9.83
DMCS-TPA 512
powder
DMCS-TPA 599
ground
BMBCP
powder
BMBCP
ground
48.59
34.53
42.35
22.48
500
555
6.785 (33.75) 19.316 (66.25) 15.09
The dual emission observed for DMCS-TPA in solution is
unusual and intriguing. Further studies on excitation wave-
length dependent emission have been conducted. Fig. 2 shows
the PL spectra of DMCS-TPA in hexane with excitation wave-
length increasing from 310 nm to 390 nm. Different from linear
D–A molecules,14a the higher energy emission keeps intensi-
fying, while the ICT emission enhances with excitation wave-
length changing from 310 nm to 350 nm, then gradually
weakens and even vanishes when excitation increases to 390
nm. A similar phenomenon was observed for DMCS-TPA in
toluene and chloroform solutions (Fig. S2 and S3†). These
results are consistent with the excitation proles in Fig. S1.†
The special wavelength dependent emission, together with the
dual emission feature, implies a large gap between the local
excited (LE) and ICT energy level and a very slow internal
conversion between the two states, which leads the LE to
dominate the luminescence when excited at the lower energy
region.
To elucidate the inuence of the geometric and electronic
structure of DMCS-TPA on photophysical properties, we con-
ducted theoretical calculations. The DFT calculations were
performed via Gaussian 09 at the B3LYP/6-31 G (d) level. As
shown in Fig. 3, compared with BMBCP, DMCS-TPA shows a
specially twisted conformation. The dihedral angles between
two side benzene rings and the central core are 44.4ꢀ and 47.9ꢀ,
respectively. And the dihedral angles between two vinyl planes
and the central benzene are 28.7ꢀ and 28.8ꢀ respectively, much
larger than those in BMBCP (5.5ꢀ and 5.2ꢀ). Such high torsional
angles in DMCS-TPA would inhibit close packing and p–p
interactions in the condensed state, leading to an emissive
organic solid. In addition, it is intriguing to note that the
HOMO for DMCS-TPA is concentrated predominantly on the
TPA units and the central phenyl, while the LUMO rearranges
along the –CN containing axis. The strong charge transfer from
one TPA to the crossed axis further reveals its typical ICT nature.
The bandgap of 2.58 eV is consistent with that estimated from
the onset wavelength of absorption.
The AIE effect of DMCS-TPA was examined in THF–water
mixtures via UV-vis absorption and PL spectra (Fig. S4 and S5†).
The absorption spectra of DMCS-TPA are slightly affected with
water fractions below 40%. When the water content increased to
50%, the maximum absorption dropped abruptly with a rise in
the shoulder around 430 nm and the long tail region, indicating
the formation of DMCS-TPA nano-aggregates. Meanwhile, the
maximum absorption wavelength shows a minor red shi from
347 nm to around 355 nm, which might arise from the extended
p-conjugation in aggregates. Correspondingly, the uorescence
strengthened dramatically above 50% of water addition. The PL
intensity continuously enhanced with increasing water content
to 80%, leading to resultant intensity more than 10 fold larger
than that of pure THF solution. The fF of DMCS-TPA in THF was
estimated to be 5.3% using 9,10-diphenylanthracene (DPA) in
ethanol (fF ¼ 95%) as the standard.16 While the DMCS-TPA
powder shows bright yellowish green uorescence with a fF of
48.59% (Table 1), indicating its efficient emission in the solid
state. The phenomenon demonstrates the AIE nature of DMCS-
TPA, which could be attributed to the restricted internal rota-
tions and decreased solvent polarity effect14 when molecules
precipitate. The comparatively larger fF value of DMCS-TPA
powder than that of BMBCP (42.35%) implies that the cruciform
structure of DMCS-TPA effectively depresses strong p–p inter-
actions between the DCS axis thus diminishing emission
quenching.
Mechanochromic properties
The uorescence responses of DMCS-TPA towards mechanical,
thermal and solvent-fuming processes are illustrated in Fig. 4.
The as-prepared powder switch from yellowish green (lem ¼ 512
nm, fF ¼ 48.59%) to orange (lem ¼ 599 nm, fF ¼ 34.53%)
luminescence was accompanied by the colour change from
yellow to orange upon grinding. As shown in Fig. 5a, the PL
spectra of the initial powder are signicantly red-shied by 87
nm with the peak width (FWHM) broadened from 69 nm to 116
nm aer grinding. The remarkable conversion of the maximum
PL wavelength is among the best results reported currently,8,9,17
Fig. 2 Dependence of emission spectra as a function of excitation
wavelength for DMCS-TPA in hexane solution.
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32 nm accompanied by an increase of more than 12% of fF aer
grinding for DMCS-TPA relative to BMBCP. In addition, for
BMBCP, both original powder and ground samples yield much
longer uorescence lifetime, implying the strong p–p interac-
tions and excimer formation between BMBCP molecules.
To understand the mechanism of mechanochromic behav-
iour, powder XRD patterns of DMCS-TPA before and aer
grinding were investigated. As revealed in Fig. S6,† the pristine
powder shows several sharp and intense reections accompa-
nied by a broad and diffuse peak around 22ꢀ, indicating a mixed
crystal and amorphous phase. The ground solid does not give
any noticeable diffraction in the XRD prole, reecting its
amorphous feature. In most cases, the MC phenomenon is
mainly attributed to the change of intermolecular interactions
and molecular arrangement in the condensed state,1a however
the unusual large shi of chromism in this case seems to reside
mostly in the D–A cruciform module for its lower degree of
crystallinity. A proposed explanation for the enhanced MC
properties is that the distorted molecules, especially the TPA
donors with large torsion angles, are subjected to conforma-
tional change and rotate to a position more parallel to the co-
planar under external pressure,7f leading to extended conjuga-
tion18 and subsequent planar intramolecular charge transfer
(PICT).7d The ICT delocalization in DMCS-TPA molecules will be
greatly strengthened, resulting in remarkable red-shi of
emission and decrease of uorescent intensity. This proposal is
evidenced by the UV-vis absorption13c and XPS spectra of orig-
inal and ground DMCS-TPA.
Fig. 3 Optimized conformation of DMCS-TPA and BMBCP (above)
and calculated spatial electron distributions of HOMO and LUMO
(below) of DMCA-TPA.
Absorption spectra of DMCS-TPA in the two forms are pre-
sented in Fig. 6a. It is obvious that the shoulder peak at 430 nm
red shis to about 460 nm, indicating the extension of p-
conjugation aer grinding. As shown in Fig. 6(b), the high
resolution core level carbon C(1s) spectra of DMCS-TPA exhibit
two features both before and aer grinding: the main peak at
around 284.8 eV which can be deconvoluted into four distinct
peaks (Fig. S7 and S8†), and a much smaller satellite peak at the
higher energy side originated from p electrons delocalized over
the aromatic system. Table S1† summarizes the BE positions
and percentage contributions from each of the resolved XPS
peaks, which are in fair agreement with the characteristic
banding features19 and the ideal stoichiometry. Aer grinding, a
gentle increase in the intensity of the signal at 284.8 eV and a
narrowing on the high binding energy side of the C(1s) peak
were clearly observed. Meanwhile, the shake-up satellite, seen
Fig. 4 Photographs of DMCS-TPA under 365 nm UV light upon
different treatments.
which is enough clear to be readily visualized by the naked eye.
Attractively, it can be restored to its original uorescence
through either thermal annealing at 80 ꢀC for 5 min or solvent
fuming with DCM. The pressure dependent emission of DMCS-
TPA was further examined. A progressive change of the shape
and position of uorescence spectra with increased pressure
from 2 MPa to 10 MPa was observed. As shown in Fig. 5b,
application of 2 MPa induces a slight widening on the tail with
little change of maximum PL wavelength. The powder pressed
at 5 MPa exhibits a red shied uorescence at 544 nm. Adoption
of 10 MPa causes a noticeable emission change by 74 nm from
yellowish green to orange. The wide coverage of emissive
spectra under a small load of pressure reveals the sensitive
feature of DMCS-TPA towards mechanical stimuli. Whereas the
sample subjected to 10 MPa is not stable at room temperature,
showing a partial recovery within seconds. The mechano-
chromism can be recycled many times with almost no deterio-
ration, indicating its reversibility and durability.
In comparison, BMBCP shows PL spectra switching from 500
nm to 555 nm with the fF dropping from 42.35% to 22.48%
upon grinding (Table 1). It is worth noting that the change of
emission maximum before and aer grinding is increased by
Fig. 5 Luminescence spectra of the DMCS-TPA solid upon different
treatments.
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from the magnied spectra, intensied and shied from
291.5 eV to 292.8 eV compared with the pristine sample. The
differences imply a large electronic rearrangement in the
ground sample. As the electron donating ability of arylamine
enhances with the increasing conjugation degree,15 the direc-
tion of charge rearrangement is supposed to be from the N (in
TPA) to adjacent C atoms, resulting in electron-rich character-
istic of C and downward BE positions. The intensied shake-up
satellite is attributed to the enhanced delocalization of the p
electron associated with the stronger charge transfer transition
aer grinding.
Electrochromic properties
As TPA is electroactive, we investigated the electrochemical
characteristics of DMCS-TPA, and observed the intriguing
electrochromic behaviour from its homopolymer. DMCS-TPA
can be successfully polymerized via electro-synthesis, which is
an effective approach for preparing cross-linked lms directly
onto a conducting substrate. Fig. 7(a) shows the cycle voltam-
metry polymerization spectra of DMCS-TPA on the ITO elec-
trode. The CV traces show two oxidation peaks at 0.96 and 1.32
V and corresponding reduction peaks at 0.86 V and 1.04 V,
respectively. Under repeated scanning, the oxidation currents at
0.96 V gradually raised, suggesting the growth of the conducting
polymer lm. The slight increase in the peak potential is
attributed to the increase of resistance as the lm thickening.
The surface morphology of the lm prepared through constant
potential polymerization is depicted in the inset of Fig. 7(a).
The polymerized lm displays four typical colours as
increasing applied voltage. Those are light green at 0 V, red at 1
V, grey at 1.1 V and blue at 1.45 V. To understand the electro-
chromic properties, electrode potential correlated UV-vis
absorption spectra of the lm polymerized at 1.35 V were
recorded. As shown in Fig. 7(b), in the neutral state from 0 V to
0.8 V, the lm exhibits a strong absorption band centred at 350
nm, which can be assigned to the p–p* transition of the poly-
mer backbone. Upon increasing the voltage gradually to 1.45 V,
the peak at 350 nm continuously weakened. When the voltage
reached 0.9 V, a shoulder peak at 484 nm appeared and
strengthened to the maximum at 1.0 V. Then the intensity of the
shoulder peak decreased and nally vanished at potentials from
1.1 V to 1.45 V. Simultaneously a new absorption band at
around 769 nm emerged and enhanced along with the increase
of the applied potential. The formation of new peaks at 484 and
Fig. 7 Spectroelectrochemical spectra of the P (DMCS-TPA) film at
constant voltages from 0 V to 1.45 V in ACN solution containing 0.1 M
TBAP.
769 nm could be ascribed to the evolution of polaron and
bipolaron bands (Fig. 7).
The EC switching behaviour of the electro-polymerized
DMCS-TPA lms was monitored at the maximum absorption
(350 and 769 nm) in order to characterize their optical
contrasts. Fig. S9† exhibits the optical contrasts of the lm,
which were carried out between 0 and 1.45 V with a residence
time of 3 s. A particularly high optical contrast of 65% was
observed at wavelength of 769 nm, and 21% at 350 nm. While
aer multiple cycles of potential change, the lm showed
gradually weakened optical contrast, indicating that its stability
was not good. Work aimed at improving the stability and
durability of the electrochromic lm is underway in our lab.
Conclusions
In summary, a novel D–A cruciform p-system DMCS-TPA with
electroactive TPA substituted on both sides of the DCS moiety
was designed and synthesized. The photophysical properties
and theory calculation imply that DMCS-TPA possesses a highly
twisted conformation with ICT character. Owing to the special
cross-conjugated structure, DMCS-TPA shows both AIE effect
and high contrast mechanochromic behavior with a remarkable
spectral shi of 87 nm. The solid emission can be changed from
yellowish green to orange upon simply grinding or pressing at
only 10 MPa. From the results of absorption and XP spectra, the
conjugation extension and ICT enhancement are believed to be
responsible for the improved MC performance compared with
BMBCP. In addition, DMCS-TPA can be electrochemically
Fig. 6 (a) The absorption and (b) XPS spectra of DMCS-TPA before and
after grinding, the inset shows the magnified image.
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deposited directly on ITO and exhibit electrochromic properties toluene (50 mL)/THF (30 mL) was stirred at 90 ꢀC for 24 h. Aer
with multicolours showing (light green at 0 V, red at 1 V, grey at it was cooled to room temperature, 100 mL of CHCl3 was added
1.1 V and blue at 1.45 V) and a high optical contrast of 65% at to the mixture. The organic portion was separated and washed
769 nm. As far as we know, this is the rst report on functional with brine before drying over anhydrous MgSO4. The solvent
materials with combined MC and EC properties. The results was evaporated off, and the solid residues were puried by
suggest that incorporation of electroactive moieties into lumi- column chromatography to afford 0.87 g of 1 with a yield of
nophores to constitute D–A cruciform conjugated structures 70.1%. 1H NMR (500 MHz, CDCl3): d (ppm) 10.18(s, 2H); 8.11(s,
might be a promising molecular design strategy for preparing 2H); 7.33(t, J ¼ 7.5 Hz, 8H); 7.29(d, J ¼ 8.5 Hz, 4H); 7.20 (d, J ¼
efficient mechano-electrochromic materials.
7.5 Hz, 8H); 7.18(d, J ¼ 9.0 Hz, 4H); 7.11 (t, J ¼ 7.5 Hz, 4H). 13
C
NMR (125 MHz, CDCl3): d (ppm) 192.15; 148.82; 147.30; 143.87;
136.75; 130.95; 130.15; 129.52; 125.11; 123.74; 122.46.
Experimental section
Chemicals and instruments
Synthesis of DMCS-TPA. 2-(3-Methoxyphenyl) acetonitrile
(0.23 g, 1.55 mmol) and 1 (0.80 g, 1.29 mmol) were dissolved in
anhydrous ethanol (20 mL) in the presence of sodium meth-
oxide (0.80 g, 1.50 mmol). The mixture was stirred at room
temperature for 6 hours. The resulting precipitate was ltered
and washed with methyl alcohol several times to afford 0.94 g of
DMCS-TPA with a yield of 82.9%. 1H NMR (500 MHz, CDCl3): d
(ppm) 8.26 (s, 2H); 7.66 (s, 2H); 7.37 (d, J ¼ 8.5 Hz, 4H); 7.34 (s,
2H); 7.31 (t, J ¼ 7.5 Hz, 8H); 7.21 (d, J ¼ 7.0 Hz, 4H); 7.19 (d, J ¼
8.0 Hz, 8H); 7.17 (d, J ¼ 8.5 Hz, 4H); 7.09 (t, J ¼ 7.5 Hz, 4H); 6.95
(dd, J ¼ 8.5 Hz, 2H); 3.86 (s, 6H). 13C NMR (125 MHz, CDCl3): d
(ppm) 206.89, 160.14, 148.08, 147.34, 141.95, 140.88, 135.43,
131.15, 130.95, 130.25, 129.44, 125.04, 123.55, 122.44, 118.61,
114.96, 113.29, 111.69, 55.44, 53.43, 30.93. MS m/z: 878.4 (M+).
Anal. calcd (%) for C62H46N4O2: C, 84.71; H, 5.27; N, 6.37; O,
3.64. Found: C, 85.15; H, 5.14; N, 6.21; O, 3.49.
1,4-Dibromo-2,5-dimethylbenzene, terephthalaldehyde, (4-(diphe-
nylamino)phenyl)boronic acid and 2-(3-methoxyphenyl) acetoni-
trile were purchased from commercial sources and used without
further purication. 2,5-Dibromoterephthalaldehyde was synthe-
sized according to the literature procedure.20 All solvents and
reagents (analytical grade) were used as received, unless otherwise
claimed.
The 1H and 13C NMR spectra were recorded on a Bruker
AVANCE III 500 MHz instrument (Bruker, Switzerland) using
chloroform-d (CDCl3) as the solvent. Mass spectroscopy was
carried out with a Thermo LCQ Fleet MS spectrometer.
Elemental analyses were performed using the Thermo-Finnigan
Flash EA-1112 (CE, Italy) instrument. The UV-vis absorption
spectrum was recorded on a Perkin Elmer Lambda 35 spectro-
photometer. Fluorescent measurements were recorded on a
Perkin-Elmer LS-55 luminescence spectrophotometer. The
uorescence quantum yield fF was determined using a cali-
brated integrating sphere. Fluorescence lifetime experiments
were performed by using the time-correlated single-photon
counting (PicoHarp 300 TCSPC) system with right-angle sample
geometry. A picosecond diode laser (PDL 800-B) was used to
excite the samples. The minimum pulse width is 50 ps. The
detection system uses a photomultiplier tube from Picoquant
(R3809U-50) with an instrument response time less than 250 ps.
Powder X-ray diffraction (XRD) was performed on a X0 Pert PRO,
PANalytical, with Cu-Ka radiation operating at 40 kV and 40 mA.
X-ray photoelectron spectroscopy data were obtained with an
ESCALab220i-XL electron spectrometer from VG Scientic using
300 W AlKa radiation. The base pressure was about 3 ꢁ 10ꢂ9
mbar. The binding energies were referenced to the C1s line at
284.6 eV from adventitious carbon. Field-emission scanning
electron microscopy (SEM) measurements were performed by
using a Hitachi S-4800 scanning electron microscope (Hitachi,
Japan). The electrochemical property measurement was per-
formed in a three-compartment system on a CHI660C electro-
chemical analyser (CH Instruments, China).
Synthesis of BMBCP. The procedure is similar to that
1
described for the synthesis of DMCS-TPA. H NMR (500 MHz,
CDCl3): d (ppm) 8.01 (s, 4H); 7.57 (s, 2H); 7.40 (t, J ¼ 8.0 Hz, 2H);
7.31 (d, J ¼ 7.5 Hz 2H); 7.23 (s, 2H); 6.98 (dd, J ¼ 8.5 Hz, 2H);
3.90 (s, 6H). 13C NMR (125 MHz, CDCl3): d (ppm) 160.19, 140.88,
135.62, 135.46, 130.21, 129.82, 118.56, 117.57, 115.24, 112.96,
111.78, 55.49. MS m/z: 392.3 (M+). Anal. calcd (%) for
C
26H20N2O2: C, 79.57; H, 5.14; N, 7.14; O, 8.15. Found: C, 79.65;
H, 5.17; N, 7.01; O, 8.17.
Quantum chemical calculations
Single molecule calculations including optimized geometry,
FMOs and dipolar moment in the ground state were performed
at the density functional theory (DFT) level with B3LYP func-
tional and 6-31G* basis set using the Gaussian 09 soware.
Electrochemistry
Electrochemical polymerization and measurements were per-
formed in a conventional three-electrode cell with an ITO-
coated glass as the working electrode which was sequently
washed with deionized water, ethanol and acetone under
ultrasonication before use, a platinum (Pt) sheet and a double-
junction Ag/AgCl electrode (silver wire coated with AgCl in
saturated KCl solution) were applied as the counter electrode
Synthesis
Synthesis of 4,400-bis(diphenylamino)-[1,10:40,100-terphenyl]- and the reference electrode, respectively. The lms used for
20,50-dicarbaldehyde (1). Under a nitrogen atmosphere, a characterization were prepared via the constant potential poly-
mixture of (4-(diphenylamino)phenyl)boronic acid (1.74 g, 6 merization of 1.5 mM DMCS-TPA and 0.1 M TBAP in CH2Cl2
mmol), 2,5-dibromoterephthalaldehyde (0.58 g,
2 mmol), solutions at 1.35 V, and then measured in ACN solution con-
Pd(PPh3)4 (0.065 g, 0.06 mmol), Na2CO3 (2.0 M, 3.0 mL), and taining 0.1 M TBAP as a supporting electrolyte from 0 V to 1.45
5370 | J. Mater. Chem. C, 2014, 2, 5365–5371
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Paper
Journal of Materials Chemistry C
V. All the electrochemistry experiments were carried out at 25 ꢀC 10 (a) T. Komatsu, K. Ohta, T. Fujimoto and I. Yamamoto, J.
under a N2 atmosphere.
Mater. Chem., 1994, 4, 533; (b) D. R. Rosseinsky and
D. M. S. Monk, J. Appl. Electrochem., 1994, 24, 1213; (c)
S. Koyuncu, O. Usluer, M. Can, S. Demic, S. Icli and
N. S. Saricici, J. Mater. Chem., 2011, 21, 2684.
Acknowledgements
The authors gratefully thank the support of the National
Natural Science Foundation of China (51203138 and 51273179),
the International S&T Cooperation Program, China
(2012DFA51210) and the National Basic Research Program of
China (2011CBA00700).
11 (a) A. J. Zucchero, P. L. Mcgrier and U. H. F. Bunz, Acc.
Chem. Res., 2010, 43, 397; (b) K. Osowska and O. Miljanic,
Chem. Commun., 2010, 46, 4276; (c) J. Sun, H. Zhong,
E. Xu, D. Zeng, J. Zhang, H. Xu, W. Zhu and Q. Fang, Org.
Electron., 2010, 11, 74; (d) Y. Li, F. Li, H. Zhang, Z. Xie,
W. Xie, H. Xu, B. Li, F. Shen, L. Ye, M. Hanif, D. Ma and
Y. Ma, Chem. Commun., 2007, 231; (e) J. N. Wilson and
U. H. F. Bunz, J. Am. Chem. Soc., 2005, 127, 4124; (f)
V. Martinez-Martinez, J. Lim, J. Banuelos, I. Lopez-
Arbeloa and O. S. Miljanic, Phys. Chem. Chem. Phys., 2013,
15, 18023; (g) P. L. McGrier, K. M. Solntsev,
J. Schonhaber, L. M. Tolbert and U. H. F. Bunz, Chem.
Commun., 2007, 2127.
12 (a) M. Shimizu, Y. Asai, Y. Takeda, A. Yamatani and
T. Hiyama, Tetrahedron Lett., 2011, 52, 4084; (b) C. Zhao,
Y. Zhao, H. Pan and G. Fu, Chem. Commun., 2011, 47,
5518; (c) J. E. Klare, G. S. Tulevski, K. Sugo, A. Picciotto,
K. A. White and C. Nuckolls, J. Am. Chem. Soc., 2003, 125,
6030; (d) F. He, L. Tian, Y. Wang, W. Xie, M. Hanif, J. Xia,
F. Shen, B. Yang, F. Li, Y. Ma, Y. Yang and J. Shen, Adv.
Funct. Mater., 2007, 17, 1551; (e) G. Fu and C. Zhao,
Tetrahedron, 2013, 69, 1700.
13 (a) Y. Ooyama and Y. Harima, J. Mater. Chem., 2011, 21, 8372;
(b) Y. Ooyama, N. Yamaguchi, S. Inoue, T. Nagano,
E. Miyazaki, H. Fukuoka, I. Imae, K. Komaguchi,
J. Ohshita and Y. Harima, Tetrahedron, 2012, 68, 529; (c)
F. Chen, J. Zhang and X. Wan, Chem.–Eur. J., 2012, 18, 4558.
14 (a) Y. J. Zhang, J. W. Sun, G. F. Bian, Y. Y. Chen, M. Ouyang,
B. Hu and C. Zhang, Photochem. Photobiol. Sci., 2012, 11,
1414; (b) M. P. Aldred, Z. Guo-Feng, L. Chong, C. Gui,
C. Tao and M. Zhu, J. Mater. Chem. C, 2013, 1, 6709.
15 C. Wang, S. Chen, K. Wang, S. Zhao, J. Zhang and Y. Wang, J.
Phys. Chem. C, 2012, 116, 17796.
Notes and references
1 (a) Y. Sagara and T. Kato, Nat. Chem., 2009, 1, 605; (b)
X. Wang, O. S. Woleis and R. J. Meier, Chem. Soc. Rev.,
2013, 42, 7834; (c) P. M. Beaujuge and J. R. Reynolds,
Chem. Rev., 2010, 110, 268; (d) P. M. Beaujuge, C. M. Amb
and J. R. Reynolds, Acc. Chem. Res., 2010, 43, 1396; (e)
X. Shan, F. Jiang, L. Chen, M. Wu, J. Pan, X. Wan and
M. Hong, J. Mater. Chem. C, 2013, 1, 4339.
2 (a) Y. Sagara, S. Yamane, T. Mutai, K. Araki and T. Kato, Adv.
Funct. Mater., 2009, 19, 1869; (b) C. Dou, L. Han, S. Zhao,
H. Zhang and Y. Wang, J. Phys. Chem. Lett., 2011, 2, 666; (c)
X. Luo, W. Zhao, J. Shi, C. Li, Z. Liu, Z. Bo, Y. Q. Dong and
B. Z. Tang, J. Phys. Chem. C, 2012, 116, 21967.
3 J. W. Chung, Y. You, H. S. Huh, B. K. An, S. J. Yoon, S. H. Kim,
S. W. Lee and S. Y. Park, J. Am. Chem. Soc., 2009, 131, 8163.
4 Q. Oms, K. Hakouk, R. Dessapt, P. Deniard, S. Jobic,
A. Dolbecq, T. Palacin, L. Nadjo, B. Keita, J. Marrot and
P. Mialane, Chem. Commun., 2012, 48, 12103.
5 (a) Y. Zhang, W. Li, X. Wang, B. Yang, M. Li and S. X. Zhang,
Chem. Commun., 2014, 50, 1420; (b) Y. Zhang, M. Li, W. Li,
Z. Huang, S. Zhu, B. Yang, X. Wang and S. X. Zhang, J.
Mater. Chem. C, 2013, 1, 5309.
6 (a) Z. Yang, W. Qin, J. W. Y. Lam, S. Chen, H. H. Y. Sung,
I. D. Williams and B. Z. Tang, Chem. Sci., 2013, 4, 3725; (b)
R. Rao, C. W. Liao and S. S. Sun, J. Mater. Chem. C, 2013, 1,
6386.
7 (a) J. Luo, L. Y. Li, Y. L. Song and J. Pei, Chem.–Eur. J., 2011,
17, 10515; (b) M. J. Teng, X. R. Jia, S. Yang, X. F. Chen and
Y. Wei, Adv. Mater., 2012, 24, 1255; (c) M. S. Kwon,
J. Gierschner, S. J. Yoon and S. Y. Park, Adv. Mater., 2012,
24, 5487; (d) R. M. Rao, C. W. Liao, W. L. Su and S. Sun, J.
Mater. Chem. C, 2013, 1, 5491; (e) Y. J. Zhang, J. W. Sun,
X. J. Lv, M. Ouyang, F. Cao, G. X. Pan, L. P. Pan, G. B. Fan,
W. W. Yu, C. He, S. S. Zheng, F. Zhang, W. Wang and
C. Zhang, CrystEngComm, 2013, 15, 8998; (f) Y. J. Zhang,
J. W. Sun, F. Cao, G. X. Pan, M. Ouyang, C. Zhang and
Z. W. Yu, J. Mater. Chem. C, 2014, 2, 195.
8 W. Z. Yuan, Y. Tan, Y. Gong, P. Lu, J. W. Y. Lam, X. Y. Shen,
C. Feng, H. H.-Y. Sung, Y. Lu, I. D. Williams, J. Z. Sun,
Y. Zhang and B. Z. Tang, Adv. Mater., 2013, 25, 2837.
9 (a) Y. Dong, B. Xu, J. Zhang, X. Tan, L. Wang, J. Chen, H. Lv,
S. Wen, B. Li, L. Ye, B. Zou and W. Tian, Angew. Chem., Int.
Ed., 2012, 51, 10782; (b) Y. Dong, J. Zhang, X. Tan,
L. Wang, J. Chen, B. Li, L. Ye, B. Xu, B. Zou and W. Tian, J.
Mater. Chem. C, 2013, 1, 7554.
16 (a) W. Qin, D. Ding, J. Liu, W. Z. Yuan, Y. Hu, B. Liu and
B. Z. Tang, Adv. Funct. Mater., 2012, 22, 771; (b)
G. F. Zhang, M. P. Aldred, W. L. Gong, C. Li and
M. Q. Zhu, Chem. Commun., 2012, 48, 7711.
17 (a) Y. Gong, Y. Tan, J. Liu, P. Lu, C. Feng, W. Z. Yuan, Y. Lu,
J. Z. Sun, G. He and Y. Zhang, Chem. Commun., 2013, 49,
4009; (b) G. Li, F. Song, D. Wu, J. Lan, X. Liu, J. Wu,
S. Yang, D. Xiao and J. You, Adv. Funct. Mater., 2014, 24, 747.
18 T. Hsiao, T. Chen, W. Chien and J. Hong, Dyes Pigm., 2014,
103, 161.
19 (a) J. C. Sharp, F. Bebensee, J. H. Baricuatro, H. P. Steinruck,
J. M. Gottfried and C. T. Campbell, J. Phys. Chem. C, 2013,
117, 23781; (b) G. Beamson and D. Briggs, High Resolution
XPS of Organic Polymers: the Scienta ESCA300 Database,
Wiley, Chichester, New York, 1992.
20 Y. Li, F. Li, H. Zhang, Z. Xie, W. Xie, H. Xu, B. Li, F. Shen,
L. Ye, M. Hanif, D. Ma and Y. Ma, Chem. Commun., 2007,
231.
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