Enhanced AIE and different stimuli-responses in red fluorescent (1,3-dimethyl)barbituric acid-functionalized anthracenes

Article abstract of DOI:10.1039/c5tc03629a

Two structurally simple and red light-emitting AIE luminogens, (1,3-dimethyl)barbituric acid-functionalized anthracenes (B-A and DMB-A), were designed and synthesized. In comparison with DMB-A, B-A shows strikingly enhanced AIE as well as superior thermal stability (T_d, 328.5 °C vs. 280.2 °C). Moreover, distinguishable behaviors of the two red luminogens to stimuli such as (1) dissolution (in 1,4-dioxane), then solidification via removing the solvent in vacuo at 50 °C, (2) thermal treatment following stimuli-I and (3) mechanical grinding were observed. In particular, reversible switching of colours (orange 虠 red), accompanied by a fluorescence shift (Δλ_em ≈ 36 nm) was achieved by repeatedly applying stimuli (I) and (II) on luminogen B-A, whereas almost no change of luminogen DMB-A was found under the same conditions. A mechanism of solvent molecule assisted B-A molecular packing changes was proposed to illustrate the origin of B-A's chromic phenomenon.

Full text of DOI:10.1039/c5tc03629a

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Materials Chemistry C
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Enhanced AIE and different stimuli-responses
in red fluorescent (1,3-dimethyl)barbituric
Cite this:DOI: 10.1039/c5tc03629a
acid-functionalized anthracenes†
Guohui Yin,a Yawen Ma,bc Yao Xiong,b Xiaohui Cao,d Yang Li*bc and
Ligong Chen*bc
Two structurally simple and red light-emitting AIE luminogens, (1,3-dimethyl)barbituric acid-functionalized
anthracenes (B-A and DMB-A), were designed and synthesized. In comparison with DMB-A, B-A shows
strikingly enhanced AIE as well as superior thermal stability (Td, 328.5 1C vs. 280.2 1C). Moreover,
distinguishable behaviors of the two red luminogens to stimuli such as (1) dissolution (in 1,4-dioxane),
then solidification via removing the solvent in vacuo at 50 1C, (2) thermal treatment following stimuli-I
and (3) mechanical grinding were observed. In particular, reversible switching of colours (orange 2 red),
accompanied by a fluorescence shift (Dlem E 36 nm) was achieved by repeatedly applying stimuli (I)
and (II) on luminogen B-A, whereas almost no change of luminogen DMB-A was found under the same
conditions. A mechanism of solvent molecule assisted B-A molecular packing changes was proposed to
illustrate the origin of B-A’s chromic phenomenon.
Received 3rd November 2015,
Accepted 17th December 2015
DOI: 10.1039/c5tc03629a
www.rsc.org/MaterialsC
generally designed and obtained with strongly twisted conjuga-
tion back-bones bearing rotatable aryl moieties. For seeking
Introduction
Luminescent materials with aggregation-induced emission (AIE) luminogens with both AIE characteristics and red emission,
characteristics have recently attracted considerable attention incorporation of AIE units such as tetraphenylethene (TPE) into
since the discovery of the AIE phenomenon by Tang in 2001.1 A flat and extended p-conjugated frameworks or strong donor–
common feature of these materials is that they are non-emissive acceptor skeletons is the main strategy employed now.6–12 However,
in solutions but emit strong fluorescence in aggregated states. this strategy normally requires tedious multistep synthesis and
Due to the unique fluorescence property, AIE-active luminogens usually gives red-emitting AIE materials with bulky and compli-
show great potential for applications in such fields as opto- cated structures. Therefore, exploring AIE-active luminogens with
electronic devices, chemo/biosensors, bio-imaging and smart red emission, especially structurally simple ones, and new design
materials.2–5 Consequently, intensive efforts have been devoted strategies is still greatly interesting and valuable.
to the construction of AIE luminogens. However, most of the
Herein, we present two red AIE-active and structurally simple
AIE-active molecules developed so far dominantly emit blue luminogens B-A and DMB-A based on the RIR and twisted
or green fluorescence, while very few of them are red emitting intramolecular charge transfer (TICT)15 (Scheme 1). It indicates
ones.6–15
that twisted-p bridging electron donor (D) and acceptor (A)
Restriction of intramolecular rotation (RIR) has been ration- groups could be used as an alternative strategy to explore red-
alized as the cause of AIE. Thus, AIE molecules or units are emitting AIE materials.10,15,16 The strong aggregated capability
of the barbituric acid unit via intermolecular hydrogen bonding
interactions (N–Hꢀ ꢀ ꢀO) has been well documented in literature
a School of Science, Tianjin University, Tianjin 300072, China
reports.17,18 As a result, luminogen B-A was expected to
b School of Chemical Engineering and Technology, Tianjin University,
show enhanced AIE in comparison with DMB-A because of
Tianjin 300072, China. E-mail: lgchen@tju.edu.cn, liyang777@tju.edu.cn
c Collaborative Innovation Centre of Chemical Science and Engineering (Tianjin),
the potential formation of intermolecular hydrogen bonds that
help to lock and rigidify its conformation.19 More interestingly,
these two red luminogens display different stimuli-responses,
and reversible switching of colours (orange 2 red), accom-
panied by a fluorescence shift (Dlem E 36 nm) was achieved
via repeatedly applying re-solidifying and heating stimuli on
B-A. To account for such a chromic phenomenon of B-A,
Tianjin 300072, China
d School of Chemical Engineering and Technology, Hebei University of Technology,
Tianjin 300130, China
† Electronic supplementary information (ESI) available: Copies of NMR spectra
and HRMS, photographs, TGA, time-resolved decay curves, fluorescence micro-
scopic images, and crystal data for DMB-A. CCDC 1432611. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c5tc03629a
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Scheme 1 Design strategy and molecular structures of B-A and DMB-A.
a mechanism of solvent molecule assisted luminogen molecular of B-A and DMB-A. Simulation results (Fig. 1c) show that the
packing changes was proposed, which might provide a fresh electron clouds of the highest occupied molecular orbital (HOMO)
strategy for developing chromic materials.
are mainly distributed on the anthracene group, whereas the
lowest unoccupied molecular orbitals (LUMO) are primarily
localized over the vinyl segment and the adjacent part of the
(1,3-dimethyl)barbiturate unit. In addition, it is worth noting
that the optimized geometric structures of B-A and DMB-A show
Results and discussion
The target luminogens B-A and DMB-A were one-step synthesized twisted conformation with a dihedral angle of 54.431 and 57.031,
by the Knoevenagel condensation of anthracene-9-carbaldehyde respectively. These results agree well with our anticipation on the
with (1,3-dimethyl)barbituric acid in 96% and 94% yields, respec- TICT process in B-A and DMB-A.
tively. Then, these two luminogens were characterized by 1H NMR,
13C NMR and high-resolution mass spectra (HRMS).
To check whether B-A and DMB-A are AIE active, their
photoluminescence (PL) behaviours were investigated in 1,4-
With the desired luminogens in hand, initially, the TICT dioxane–water mixtures with different water (poor solvent)
characters of B-A and DMB-A were investigated by using UV fractions ( fw). As depicted in Fig. 2, both B-A and DMB-A are
absorption spectra and theoretical calculation methods. As shown practically non-luminescent in 1,4-dioxane and their spectral
in Fig. 1a, these two red luminogens exhibit quite similar UV patterns alter little even at fw of 50% and 70%, respectively.
absorption spectra in 1,4-dioxane solutions. The absorption bands Subsequently, red fluorescence, followed by emission enhance-
ranging between 280 and 400 nm are assigned to p–p* transitions, ment, was witnessed upon increasing the water content. These
of which typical absorption features of an anthracene chromo- observations truly demonstrate that B-A and DMB-A are both of
phore were observed in the range of 320–400 nm.20 While the AIE activity. The emission maximum of B-A (605 nm) is red-
absorption peak located at around 450 nm can be attributed to shifted 11 nm from that of DMB-A, in agreement with preceding
intramolecular charge transfer (ICT) from the anthracene unit to simulation data that the optimized geometric structure of B-A shows
the (1,3-dimethyl)barbiturate moiety.16,21 Density functional a smaller dihedral angle. Significantly, B-A exhibits enhanced
theory (DFT) calculations also confirmed the ICT possibilities AIE compared to that of DMB-A as expected: at fw = 90%, the PL
Fig. 1 (a) UV absorption spectra of B-A and DMB-A in 1,4-dioxane. (b) Optimized geometric structures. (c) HOMO and LUMO frontier molecular orbitals
(isovalue = 0.05) of B-A and DMB-A at the B3LYP/6-31G(d) level.
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Fig. 2 PL spectra of (a) B-A and (b) DMB-A in 1,4-dioxane–water mixtures with different water fractions (fw). Concentration: 100 mM; excitation wavelength:
470 nm. (c) Plot of relative emission intensity of B-A and DMB-A versus the water fraction in the aqueous mixtures. The inset is the photographs of B-A and
DMB-A at fw = 90% taken under 365 nm light.
intensity of B-A is E144-fold higher than that in 1,4-dioxane in Fig. 3, the as prepared red B-A and DMB-A powders emit red
and the fluorescence quantum yield (FF) increases from 2.43% fluorescence with an emission maximum at 635 nm and 627 nm,
to 5.10%, while DMB-A’s maximum emission enhancement respectively. After being dissolved in 1,4-dioxane (heating
(I90/I0) is only E22-fold (FF: 1.92% to 6.19%). Meanwhile, was necessary for a certain amount of B-A), followed by
pristine B-A powders also display much brighter red fluores- re-solidification through removing the solvent in vacuo at 50 1C
cence than that of DMB-A (Fig. S2, ESI†) with FF of 3.31% and (stimuli-I), the red colour of B-A visibly turned to orange and the
2.04%, respectively. As mentioned earlier, B-A’s better AIE emission peak blue-shifted to 599 nm, showing a emission
performance can be ascribed to the H-bonding contact, which wavelength change of 36 nm.27,28 In contrast, such a stimuli-I
helps to further solidify the molecular conformation in the treatment just deepened DMB-A’s colour a little and induced a
aggregated state and block the non-radioactive pathways. At slight spectral red-shift of 5 nm. Interestingly, when the
higher water content, the PL intensity of B-A (fw = 99%) and re-solidified samples of B-A and DMB-A were heated at 100 1C
DMB-A (fw Z 95%) decreases, which is probably due to the for 2 h (stimuli-II), both the colour and emission of B-A were
formation of amorphous aggregates.22,23 Interestingly, the two recovered, whereas almost no changes were observed for the
usually observed features of the TICT effect: red-shifted emis- DMB-A sample. Furthermore, the reversible behaviours of B-A
sion and decreased emission intensity with increasing solvent to stimuli (I and II) can be repeated many times (Fig. S5, ESI†),
polarity15 are not witnessed as the increase of the water fractions.24 suggesting the promising future of B-A as stimuli responsive
Highly twisted conformation of B-A and DMB-A as well as the smart materials. Mechanical force is one of the most common
relatively weak electron-donating capability of the anthracene unit external stimuli that is used to evaluate the potential of AIE
might account for such observations.
luminogens as smart materials.29,30 Upon grinding with a
Time-resolved emission-decay behaviors of the two com- pestle and mortar (stimuli-III), the pristine B-A exhibited no
pounds were also studied (Fig. S3, ESI†). Their excited states mechanochromic properties, while DMB-A was found to display
in the dioxane decay in a single exponential fashion with t of a spectral blue-shift of 9 nm, probably attributing to a reduction
4.15 ns and 4.02 ns, respectively; while pristine B-A and DMB-A in the overlapping area of two p-stacked anthracenes after
powders show bi-exponential decay and the lifetimes are grinding.31–34 Apparently, the driving force, provided by grinding
shorter (B-A: hti = 0.96 ns, DMB-A: hti = 0.81 ns). Similar results treatment, is insufficient for the rearrangement of the B-A
can be seen in other literature reports.15,24 Perhaps the shortening molecules in the solid state. These results are in fine accord with
of emission lifetimes in the solid state is ascribed to the charge the speculation that B-A molecules in the aggregated state pack
transfer and p–p stacking effect, which activate non-radiative more tightly compared to DMB-A, owing to the intermolecular
quenching processes.25,26
hydrogen bonding of the barbituric acid segment.
Then, the thermal properties of B-A and DMB-A were inves-
Spectroscopic properties of luminogens in the solid state are
tigated by thermogravimetric analysis (TGA). Both of them strongly dependent on the molecular packing.35,36 In fact, the
exhibit good thermal stability as demonstrated by their TGA colours of B-A solution in 1,4-dioxane and re-solidified B-A solid
curves (Fig. S4, ESI†), interestingly, of which B-A shows higher are quite similar. Considering that 1,4-dioxane is a hydrogen-
decomposition temperature (Td, 5% weight loss temperature) bonding-acceptor solvent and the barbituric acid unit in B-A
than that of DMB-A (328.5 1C vs. 280.2 1C). The tight packing of has two N-H hydrogen-bonding donors, the thus re-solidified
B-A molecules in the solid state, due to intermolecular hydro- B-A sample is deemed as complexes of B-A and 1,4-dioxane
gen bonding of the barbituric acid unit, was likewise supposed (Fig. 4a). The bridging effect of 1,4-dioxane results in loose B-A
to account for the superior thermal stability of B-A.
molecular packing, and consequently, colour and emission
Apart from distinguishable AIE and thermal properties, B-A changes were observed. Upon heating, the 1,4-dioxane in
and DMB-A also display different stimuli-responses, which were re-solidified B-A would be removed, the packing of B-A as well
1
explored by studying their solid-state emissions. As shown as its colour and emission thereby was recovered. H NMR of
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Fig. 3 Normalized solid-state PL spectra of (a) B-A and (b) DMB-A upon external stimuli. Excitation wavelength: 470 nm. The photographs of (c) B-A and
(d) DMB-A taken under 365 nm light.
Fig. 4 (a) Hypothetical structures of re-solidified B-A. (b) 1H NMR of pristine, re-solidified and heated B-A samples.
re-solidified and heated B-A samples confirmed the existence
To better understand the stimuli-responsive behaviors of
and reduction of 1,4-dioxane, respectively (Fig. 4b). Additionally, it B-A and DMB-A, powder X-ray diffraction (PXRD) measurements
was found that when heated at 120 1C, a temperature higher than were also carried out. All the diffraction patterns of B-A and
the boiling point of 1,4-dioxane (101 1C), the chromic process of re- DMB-A solids in various states exhibit sharp and intense reflec-
solidified B-A was accomplished in less than 10 minutes. These tions that are indicative of crystalline order (Fig. 5). For B-A, its
results suggest that the 1,4-dioxane molecule probably plays an re-solidified sample displays a quite different PXRD curve from
important role in the reversible switching of colours (orange 2 red) that of pristine one, indicating the transition of stacking modes.
and emission upon re-solidifying and heating. We also carried out The re-solidified B-A upon heating shows combined diffraction
similar measurements employing cyclohexane and ethyl acetate that features of the corresponding pristine and re-solidified samples,
are hard to form hydrogen bonding with B-A. The corresponding e.g. the double peaks near 51and 101; and weakened reflection
solutions are prepared by the filtration of hot mixtures of B-A and peaks at around 121, 141 and 261. This observation implies the
cyclohexane (ethyl acetate) using a syringe filter. After removing the recovery of altered molecular packing to some extent. In keeping
solvent in vacuo at 50 1C, we obtained a few red B-A solids. This with the poor mechanochromic properties, as-prepared B-A
result further supports the above proposed mechanism.
after grinding exhibits a similar diffraction pattern to that of
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Fig. 5 The PXRD patterns of (a) B-A and (b) DMB-A.
Fig. 6 (a) Basic unit and (b) the lattice structure of the DMB-A crystals.
pristine one. In the case of DMB-A, its pristine, re-solidified and of the single crystals is formed by two DMB-A molecules with a
ground solids demonstrate alike PXRD curves that are consis- torsion angle of 65.621 and 67.151, respectively. Furthermore,
tent with the simulated diffraction pattern from the crystal data multiple kinds of intermolecular contacts, including C–Hꢀ ꢀ ꢀp,
of DMB-A, suggesting that little changes occur in the molecular C–Hꢀ ꢀ ꢀO, pꢀ ꢀ ꢀp, CQOꢀ ꢀ ꢀp and C–Hꢀ ꢀ ꢀH–C and a compact
packing. Clearly, the rearrangement of molecules should be stacking mode of DMB-A molecules are observed in the crystals,
responsible for these two red luminogens’ stimuli-responsive which explains the poor stimuli-responsive properties of DMB-A.
properties. Additionally, there are morphology changes of B-A
and DMB-A upon stimuli, which can be clearly observed in the
fluorescence microscopy images (Fig. S6, ESI†).
Conclusions
Single crystal X-ray diffraction (SXRD) analysis could provide a
direct insight into the molecular conformation and the packing In summary, two structurally simple, thermally stable and red
structure of one compound. Although efforts to grow good-quality emissive luminogens B-A and DMB-A with AIE characteristics
crystals of B-A were failing, suitable single crystals of DMB-A for have been designed and synthesized. UV absorption spectra and
SXRD analysis were successfully obtained through slow solvent theoretical calculation reveal the ICT possibilities of B-A and
evaporation of a DMB-A solution (CH2Cl2/petroleum ether). DMB-A from the anthracene unit to the (1,3-dimethyl)barbiturate
As depicted in Fig. 6, the DMB-A molecule adopts a twisted moiety. It indicates that twisted-p bridging electron donor
conformation due to the steric effect between the anthracene and acceptor groups could be used as an alternative strategy
unit and the 1,3-dimethylbarbiturate moiety, and the basic unit for exploring AIE-active molecules with red emission. Notably,
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B-A was found to show striking enhanced AIE as well as superior HRMS (ESI): calcd for C19H12N2O3Na: 339.0740 (M + Na)+,
thermal stability compared with DMB-A, probably attributed to found 339.0741.
the formation of intermolecular hydrogen bonds. Furthermore,
5-(Anthracen-9-ylmethylene)-1,3-dimethylbarbituric acid
these two luminogens display different responses to stimuli, of (DMB-A). Red solid (1.62 g, yield: 94%). 1H NMR (600 MHz,
which reversible switching of colours (orange 2 red), accom- DMSO-d6) d: 9.08 (s, 1H), 8.67 (s, 1H), 8.14 (d, J = 8.4 Hz, 2H),
panied by a fluorescence shift (Dlem E 36 nm), was achieved by 7.93 (d, J = 8.4 Hz, 2H), 7.48–7.56 (m, 4H), 3.34 (s, 3H), 2.97
repeatedly applying re-solidifying and heating treatments on (s, 3H). 13C NMR (150 MHz, DMSO-d6) d: 161.2, 159.3, 152.7,
luminogen B-A. Such colour and fluorescence changing perfor- 151.4, 130.6, 129.7, 128.7, 127.8, 127.6, 126.3, 125.6, 125.5,
mances of B-A was thought to result from solvent molecule 125.0, 28.6. HRMS (ESI): calcd for C21H16N2O3Na: 367.1053
assisted B-A molecular packing changes. This work perhaps (M + Na)+, found 367.1053.
opens up a different path to chromic materials and also suggests
that B-A may be a potential candidate for applications as sensors
and organic light-emitting materials.
Notes and references
1 J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu,
H. S. Kwok, X. Zhan, Y. Liu, D. Zhu and B. Z. Tang, Chem.
Commun., 2001, 1740.
2 Y. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Commun., 2009,
4332.
3 Y. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Soc. Rev., 2011,
40, 5361.
4 R. Hu, N. L. C. Leung and B. Z. Tang, Chem. Soc. Rev., 2014,
43, 4494.
5 J. Mei, Y. Hong, J. W. Y. Lam, A. Qin, Y. Tang and B. Z. Tang,
Adv. Mater., 2014, 26, 5429.
6 H. Li, Z. Chi, X. Zhang, B. Xu, S. Liu, Y. Zhang and J. Xu,
Chem. Commun., 2011, 47, 11273.
7 Q. Zhao, S. Zhang, Y. Liu, J. Mei, S. Chen, P. Lu, A. Qin,
Y. Ma, J. Z. Sun and B. Z. Tang, J. Mater. Chem. C, 2012,
22, 7387.
Experimental section
Materials and instrumentation
All reagents were purchased from commercial sources and used
as received unless otherwise stated. 1H NMR and 13C NMR spectra
were measured on a Bruker Avance III 600 MHz spectrometer
using DMSO-d6 as the solvent. High-resolution mass spectra
(HRMS) were performed on a Bruker Daltonics micrOTOF-Q II
instrument (ESI†). UV-Vis spectra were determined using an
Evolution 300 spectrophotometer. All the solid phase and solution
phase fluorescence spectra were recorded on a Horiba Jobin Yvon
Fluorolog-3 spectrophotometer. Absolute fluorescence quantum
yields (FF) of solutions were recorded in a conventional quartz cell
(light path 10 mm) using a Varian Cary Eclipse spectrometer that
was equipped with a Varian Cary single-cell Peltier accessory to
control temperature. Fluorescence lifetimes (t) of B-A and DMB-A
in solution were determined by a Horiba Jobin Yvon Fluorolog-3
8 Z. Zhao, J. Geng, Z. Chang, S. Chen, C. Deng, T. Jiang,
W. Qin, J. W. Y. Lam, H. S. Kwok, H. Qiu, B. Liu and
spectrofluorometer. Solid-state emission quantum yields (FF) and
B. Z. Tang, J. Mater. Chem. C, 2012, 22, 11018.
luminescence lifetimes were measured using an Edinburgh
FLS920 spectrometer. Thermal gravimetric analysis (TGA) was
9 M. P. Aldred, G. F. Zhang, C. Li, G. Chen, T. Chen and
M. Q. Zhu, J. Mater. Chem. C, 2013, 1, 6709.
10 K. Li, W. Qin, D. Ding, N. Tomczak, J. Geng, R. Liu, J. Liu,
X. Zhang, H. Liu, B. Liu and B. Z. Tang, Sci. Rep., 2013,
3, 1150.
11 E. Wang, J. W. Y. Lam, R. Hu, C. Zhang, Y. S. Zhao and
conducted on a TA Q500 instrument with a heating rate of
10 1C minꢁ1 in a nitrogen atmosphere. Powder X-ray diffraction
(PXRD) patterns were taken on a Rigaku Miniflex 600 diffracto-
meter at a rate of 51 minꢁ1. Fluorescent microscopic images
were taken using an Olympus IX73 fluorescence microscope.
The density functional theory (DFT) calculations were carried
B. Z. Tang, J. Mater. Chem. C, 2014, 2, 1801.
12 Z. Wang, L. Yan, L. Zhang, Y. Chen, H. Li, J. Zhang,
out at the B3LYP/6-31G(d) level in the Gaussian 09 program
Y. Zhang, X. Li, B. Xu, X. Fu, Z. Sun and W. Tian, Polym.
Chem., 2014, 5, 7013.
(IEFPCM: 1,4-dioxane).37
13 G. Liu, D. Chen, L. Kong, J. Shi, B. Tong, J. Zhi, X. Feng and
General procedure for the synthesis of luminogens
Y. Dong, Chem. Commun., 2015, 51, 8555.
Anthracene-9-carbaldehyde 1.03 g (5.0 mmol), ethanol (30 mL), 14 C. Yang, Q. T. Trinh, X. Wang, Y. Tang, K. Wang, S. Huang,
distilled water (30 mL) and (1,3-dimethyl)barbituric acid
(15.0 mmol) were refluxed at 80 1C for 4 h. The formed solids
X. Chen, S. H. Mushrif and M. Wang, Chem. Commun., 2015,
51, 3375.
were collected by filtration and washed with hot water and 15 R. Hu, E. Lager, A. Aguilar-Aguilar, J. Liu, J. W. Y. Lam,
˜
ethanol. Then, the solids obtained were dried in vacuo for 12 h.
5-(Anthracen-9-ylmethylene)barbituric acid (B-A). Red solid
H. H. Y. Sung, I. D. Williams, Y. Zhong, K. S. Wong, E. Pena-
Cabrera and B. Z. Tang, J. Phys. Chem. C, 2009, 113, 15845.
(1.52 g, yield: 96%). 1H NMR (600 MHz, DMSO-d6) d: 11.56 16 M. Shimizu, R. Kaki, Y. Takeda, T. Hiyama, N. Nagai,
(s, 1H), 11.11 (s, 1H), 8.98 (s, 1H), 8.66 (s, 1H), 8.13 (d, J = 8.4 Hz,
2H), 7.95 (d, J = 8.4 Hz, 2H), 7.49–7.56 (m, 4H). 13C NMR
H. Yamagishi and H. Furutani, Angew. Chem., Int. Ed.,
2012, 51, 4095.
(150 MHz, DMSO-d6) d: 162.5, 160.6, 151.3, 150.6, 130.6, 17 R. Misra, T. Jadhav, B. Dhokale and S. M. Mobin, Chem.
129.6, 128.8, 127.9, 127.7, 126.3, 125.7, 125.6, 125.4.
Commun., 2014, 50, 9076.
J. Mater. Chem. C
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View Article Online
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Paper
18 R. Li, S. Xiao, Y. Li, Q. Lin, R. Zhang, J. Zhao, C. Yang, 30 Y. Xiong, X. Yan, Y. Ma, Y. Li, G. Yin and L. Chen, Chem.
K. Zou, D. Li and T. Yi, Chem. Sci., 2014, 5, 3922. Commun., 2015, 51, 3403.
19 Z. H. Guo, Z. X. Jin, J. Y. Wang and J. Pei, Chem. Commun., 31 S. Varughese, J. Mater. Chem. C, 2014, 2, 3499.
2014, 5, 6088.
32 H. Naito, Y. Morisaki and Y. Chujo, Angew. Chem., Int. Ed.,
2015, 54, 5084.
20 S. Yagai, Y. Goto, X. Lin, T. Karatsu, A. Kitamura,
D. Kuzuhara, H. Yamada, Y. Kikkawa, A. Saeki and S. Seki, 33 H. Zhang, Z. Zhang, K. Ye, J. Zhang and Y. Wang, Adv.
Angew. Chem., Int. Ed., 2012, 51, 6643. Mater., 2006, 18, 2369.
21 S. Yagai, M. Suzuki, X. Lin, M. Gushiken, T. Noguchi, 34 Z. Zhang, Y. Zhang, D. Yao, H. Bi, I. Javed, Y. Fan, H. Zhang
T. Karatsu, A. Kitamura, A. Saeki, S. Seki, Y. Kikkawa, and Y. Wang, Cryst. Growth Des., 2009, 9, 5069.
Y. Tani and K. Nakayama, Chem. – Eur. J., 2014, 20, 16128. 35 S. Varghese and S. Das, J. Phys. Chem. Lett., 2011, 2, 863.
22 Q. Lu, X. Li, J. Li, Z. Yang, B. Xu, Z. Chi, J. Xu and Y. Zhang, 36 T. Mutai, H. Satou and K. Araki, Nat. Mater., 2005, 4, 685.
J. Mater. Chem. C, 2015, 3, 1225.
37 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, G. Cheeseman, J. R. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N.
Kudin, V. N. Staroverov, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas,
J. B. Foresman, J. V. Ortiz and J. Cioslowski, Gaussian 09,
revision B.01, Gaussian, Inc., Wallington, CT, 2010.
23 Y. Dong, J. W. Y. Lam, A. Qin, Z. Li, J. Sun, H. H.-Y. Sung,
I. D. Williams and B. Z. Tang, Chem. Commun., 2007, 40.
24 C. F. A. Gomez-Duran, R. Hu, G. Feng, T. Li, F. Bu,
˜
M. Arseneault, B. Liu, E. Pena-Cabrera and B. Z. Tang,
ACS Appl. Mater. Interfaces, 2015, 7, 15168.
25 Z. Zhu, J. Qian, X. Zhao, W. Qin, R. Hu, H. Zhang, D. Li,
Z. Xu, B. Z. Tang and S. He, ACS Nano, 2015, DOI: 10.1021/
acsnano.5b05606.
26 J. Qian, Z. Zhu, A. Qin, W. Qin, L. Chu, F. Cai, H. Zhang,
Q. Wu, R. Hu, B. Z. Tang and S. He, Adv. Mater., 2015, 27, 2332.
27 Y. Lei, Y. Liu, Y. Guo, J. Chen, X. Huang, W. Gao, L. Qian,
H. Wu, M. Liu and Y. Cheng, J. Phys. Chem. C, 2015, 119, 23138.
28 Y. Liu, Y. Lei, F. Li, J. Chen, M. Liu, X. Huang, W. Gao,
H. Wu, J. Ding and Y. Cheng, J. Mater. Chem. C, 2016, DOI:
10.1039/C5TC02932E.
29 Z. Chi, X. Zhang, B. Xu, X. Zhou, C. Ma, Y. Zhang, S. Liu and
J. Xu, Chem. Soc. Rev., 2012, 41, 3878.
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