Fluorescent self-assembled nanowires of AIE fluorogens

Article abstract of DOI:10.1039/c4tc00788c

The self-assembly of fluorescent molecules is of general interest due to the potential fabrication of nanostructured materials. The fabrication of fluorescent nanowires remains challenging because the inherent aggregation in the self-assembly process quen

Full text of DOI:10.1039/c4tc00788c

Journal of
Materials Chemistry C
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PAPER
Fluorescent self-assembled nanowires of AIE
fluorogens†
ab
Cite this: J. Mater. Chem. C, 2014, 2,
326
6
ab
b
b
c
Rongrong Hu, Jacky W. Y. Lam, Haiqin Deng, Zhegang Song, Chao Zheng
abc
and Ben Zhong Tang*
The self-assembly of fluorescent molecules is of general interest due to the potential fabrication of
nanostructured materials. The fabrication of fluorescent nanowires remains challenging because the
inherent aggregation in the self-assembly process quenches the fluorescence of the molecules in many
cases. In this work, new aggregation-induced emission-active tetraphenylethene derivatives were used
to fabricate fluorescent nanowires facilely by self-assembly processes. Moreover, the fluorescent
nanowires can further self-assemble to form macroscopic fluorescent thin films in the solution. The
detailed self-assembly processes from nanospheres to nanowires, and further to fluorescent
macroscopic thin films were elucidated and evidenced by SEM imaging. A phenomenon of photo-
induced emission enhancement was observed, owing to the photo-induced ring-closing oxidative
reaction of the tetraphenylethene core.
Received 18th April 2014
Accepted 30th May 2014
DOI: 10.1039/c4tc00788c
www.rsc.org/MaterialsC
In general, the cooperative effect of noncovalent forces, such
as hydrogen bonding, p–p stacking, dipolar and van der Waals
Introduction
Nanostructured materials provide opportunities for the fabri- interactions is the main driving force for molecular self-
7
cation of miniaturized high performance photonic and elec- assembly. As a result, uorophores with self-assembly capa-
tronic devices and thus play an important role in bility normally possess coplanar p-conjugated systems with
1
8
nanotechnology. Among them, one-dimensional (1D) nano- long alkyl chains or potential hydrogen bonds. However, the
wires have attracted particular interest because of their small emission of many organic dyes is quenched when they aggre-
size, high aspect ratio, and possible quantum connement gate or self-assemble, due to the common knowledge of aggre-
2
3
9
effects. Whereas inorganic nanowires are extensively studied,
gation-caused emission quenching problem. For example,
their organic counterparts are less explored although they may when H-aggregates are formed, low or no uorescence is
4
possess distinct advantages. For example, uorescent nano- generally observed with a hypsochromically shied emission
wires prepared from p-conjugated organic molecules through a maximum. Thus, the preparation of 1D nanowires with efficient
low-cost, in situ self-assembled approach are expected to emission is challenging. There have been few reports regarding
possess high diversity and exibility, high volume production the preparation of uorescent 1D nanowires through ordered
5
10
and easy modulation of optoelectrical properties. They are thus stacking of molecules, such as J-aggregate formation and
11
considered as promising materials for innovative nanodevices crystallization.
and applications such as nanoscale optoelectronics, uorescent
sensors and biological devices.
We have recently developed a new type of luminescent
6
material with aggregation-induced emission (AIE) characteris-
12
tics. Different from traditional organic dyes, these propeller-
shaped molecules are induced to emit intensely by aggregate
a
HKUST-Shenzhen Research Institute, No. 9 Yuexing 1st RD, South Area, Hi-tech Park,
13
formation due to the restriction of intramolecular rotation. In
such systems, without ordered stacking of the molecules,
amorphous aggregates still possess strong emission. In this
Nanshan, Shenzhen, 518057, China
b
Department of Chemistry, Institute for Advanced Study, Institute of Molecular
Functional Materials, Division of Biomedical Engineering, Division of Life Science
and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of work, we have designed and synthesized two AIE-active tetra-
Science & Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong. E-mail:
phenylethene (TPE) derivatives (Chart 1). Although these lumi-
nogens possess highly twisted conformation without long alkyl
chains and form no hydrogen bond, they can readily self-
assemble to form uorescent nanowires. Moreover, these
tangbenz@ust.hk
c
Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory,
State Key Laboratory of Luminescent Materials and Devices, South China University
of Technology (SCUT), Guangzhou 510640, China
nanowires can be further assembled to form macroscopic
†
Electronic supplementary information (ESI) available: HRMS spectra of 1 and 2,
PL spectra of
2
in THF–water mixtures with different water fractions, uorescent thin lms in solution.
photo-induced emission enhancement of 2, PL spectra of 4 aer UV irradiation,
and synthesis and characterization of 8. See DOI: 10.1039/c4tc00788c
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Chart 1 Chemical structures of tetraphenylethene derivatives.
Results and discussion
Synthesis and characterization
Compounds 1 and 2 were readily obtained by the McMurry
coupling reaction and dicyclohexylcarbodiimide (DCC)-assisted
esterication (Scheme 1). The dihydroxylated TPE (3) was
Fig. 1 IR spectra of (A) 1 and (B) 2.
14
prepared according to our previous publication. Its esteri-
cation with (S)-(+)-2-(6-methoxy-2-naphthyl)propionic acid (4)
furnished compound 1 with both cis- and trans-structures and
such cis-/trans-isomers have similar properties. The McMurry
coupling of 5 generated quite an unstable product in air.
Alternatively, 5 was rst reacted with 4 through esterication to
obtain intermediate 6. McMurry coupling of 6 was then carried
out to furnish the TPE derivative 2 with intact ester groups.
All the compounds were fully characterized by standard
spectroscopic techniques, which gave satisfactory data for
analysis corresponding to their molecular structures. As shown
in Fig. 1, the IR spectra of both 1 and 2 exhibited absorption
ꢀ
1
peaks at 1754 and 1392 cm , associated with the C]O and the
1
CH stretching vibrations, respectively. In the H NMR spectra
3
of 4, the protons on the naphthalene (Naph) ring resonate at d
3 3
7.68, 7.41, and 7.12, while those on the OCH and CH–CH
groups of 4 resonate at d 3.91, 3.87 and 1.59, respectively, which
were found at a slightly lower eld in the spectra of 1 and 2
(Fig. 2). The absorptions of the protons on the TPE core
emerged at d 7.06, 6.96 and 6.74 in the spectrum of 1.
Compound 2, on the other hand, exhibited a symmetrical
1
Fig. 2 H NMR spectra of (A) 4, (B) 1 and (C) 2 in chloroform-d.
1
structure and a simpler H NMR spectrum with only two double
1
3
peaks at d 6.86 and 6.69 representing the TPE core. The
C
1
and 1244.4728 (calcd for 2, 1244.4711), respectively (Fig. S2 and
S3†), conrming the structures of the expected compounds.
NMR spectra were also in good agreement with the H NMR
results (Fig. S1†). Moreover, the high resolution mass spectra of
+
1
and 2 gave M peaks at m/z 788.3176 (calcd for 1, 788.3138)
Aggregation-induced emission
Compounds 1 and 2 possessed similar chemical structures as
well as conjugation. Their UV spectra of THF solutions both
peaked at 234 and 318 nm, associated with the absorptions of
the naphthalene and TPE units, respectively (Fig. 3).
The photoluminescence (PL) behaviors of 1 and 2 were then
studied. The uorescence images of 1 in THF–water mixtures
with identical dye concentration are shown in Fig. 4A. Under UV
illumination, no light was emitted from the THF solution of 1.
Addition of a large amount of water, a poor solvent of 1, into the
THF solution aggregated its molecules and induced it to emit
Scheme 1 Synthetic routes to compounds 1 and 2.
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the 60 vol% aqueous mixture (Fig. S4B†). The emission intensity
increased by 73-fold in the 90 vol% aqueous mixture, accom-
panied by a 28 nm-hypsochromic shi, suggesting a more
twisted structure in the aggregated state. Compared to 1, 2 was
more sterically crowded with four bulky substitution groups.
This had restricted the rotation of the phenyl rings on the TPE
core even in the aqueous mixture with a small water fraction,
which resulted in lower uorescence enhancement.
F
The solid state quantum efficiencies (F ) of 1 and 2 were
measured through an integrating sphere. The powder of 1 has a
F value of 8.4%, while the F value of 2 is 18.9%.
F
F
Photo-induced emission-enhancement
Fig. 3 Absorption spectra of 1 and 2 in THF solutions. Concentration:
An interesting phenomenon of photo-induced emission-
enhancement was observed during the PL study. When a THF
solution of 1 was continuously excited by 318 nm UV irradiation
1
0 mM.
from
enhancement was observed. The PL change was recorded at a
0 min-interval during 2 h (Fig. 5A). Under continuous UV
a
uorescence spectrometer, rapid uorescence-
1
irradiation, the emission peak at 356 nm was swily intensied
and a new peak emerged at 375 nm, whose intensity increased
linearly with the irradiation time and enhanced by ꢁ6-fold aer
2
h (Fig. 5B). A similar phenomenon was observed for
compound 2 (Fig. S5†). Upon continuous UV irradiation, the
emission peak at 361 nm intensied and a new peak appeared
at 380 nm, the intensity of which enhanced by ꢁ4-fold aer 100
min irradiation. To further conrm such a phenomenon, the PL
change in 2 was investigated and compared aer its THF solu-
tion was exposed to normal daylight and UV irradiation for 3 h,
respectively. In the absence of UV light, the emission of 2
remained unchanged, while the solution exposed to UV irradi-
ation showed enhanced emission intensity and a new dominant
peak at 380 nm (Fig. 6). The PL enhancement was hence proved
to be caused by UV irradiation.
Fig. 4 (A) Photographs of 1 in THF–water mixtures with different
water volume fractions (f ) taken under UV illumination. (B) Emission
spectra of 1 in THF–water mixtures. (C) Plot of (I/I
versus the compositions of the aqueous mixtures. Concentration:
0 mM; excitation wavelength: 318 nm.
What is the solution peak at 356 nm for compound 1 and
) values of 1 and 2 why its intensity becomes higher upon UV irradiation? A control
w
0
study on the naphthalene-containing precursor 4 showed that
both the emission maximum and the prole of 4 matched with
those of 1 in THF solution (Fig. S6†), suggesting that the peak at
1
blue light. The emission intensity remained low at water
content lower than 70 vol% but became stronger aerwards. A
similar phenomenon was observed in 2 and it started to emit in
an aqueous mixture with 60 vol% water content (Fig. S4A†).
To gain a quantitative picture, the PL of solutions was further
investigated using a spectrometer. The dilute THF solution of 1
showed only a weak emission peak at 356 nm (Fig. 4B). The
spectrum remained unchanged when less than 70 vol% of water
was added into the THF solution. Aerwards, a new emission
peak emerged at 481 nm which represents the typical emission
of the aggregates of TPE derivatives. With the increasing water
content, the peak maximum was blue-shied and the intensity
was enhanced progressively. In the 90 vol% aqueous mixture,
the emission maximum was located at 460 nm with emission
intensity being 186-fold higher than that of pure THF solution
Fig. 5 (A) Photo-induced emission enhancement of 1 in THF. (B)
Change in the peak intensity of 1 (376 nm) and 2 (380 nm) versus
the UV irradiation time. Concentration: 10 mM; excitation wavelength:
(Fig. 4C). Similarly, the THF solution of 2 emitted faintly at
3
60 nm. A new and noticeable peak was observed at 484 nm in 318 nm.
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Scheme 2 Photo-induced ring-closing oxidative reaction of 1 and 2.
diphenylphenanthrene derivatives generated by the photo-
induced oxidative reaction were responsible for the emission
1
enhancement (Scheme 2). Furthermore, H NMR spectra of 1
were investigated before and aer UV irradiation as shown in
Fig. 8. Aer strong UV irradiation was applied on the deuterated
chloroform solution of 1, new peaks emerged at d 8.78–8.24
ppm, and protons on the TPE core of 1 (d 6.96 and 6.73 ppm)
shied to a lower eld, indicating the occurrence of the
UV-induced ring-closing oxidative reaction.
Fig. 6 PL spectra of 2 in THF solutions after being exposed to normal
room illumination and UV irradiation for 3 h.
356 nm was associated with the emission of the naphthalene
chromophore. However, unlike the solutions of 1 and 2, the PL
spectrum of 4 showed no obvious change aer UV irradiation
Self-assembly behaviors
even for a long time (75 min), indicating that the TPE core The self-assembly behaviors of 1 and 2 were then studied by
might have played a key role in the photo-induced emission transmission electron microscopy (TEM). When the solvent was
enhancement.
slowly evaporated from the dilute THF solution of 1, the mole-
Photo-oxidation reaction of TPE derivatives was reported to cules readily formed nanospheres with diameters of 100–
generate diphenylphenanthrene derivatives with enhanced 300 nm (Fig. 9A). Some nanospheres were interconnected as
15
emission. To prove the occurrence of such a reaction, a model revealed by the highlighted circles, indicative of potential
compound (8) was prepared by the FeCl -catalyzed ring-closing further self-assembly. Scanning electron microscopy (SEM)
3
oxidative reaction (Scheme S1†) and fully characterized by images also suggested that round nanoparticles were formed
standard spectroscopic methods (Fig. S7 and S8†). Typically, in upon solvent evaporation, which were capable of further self-
1
the H NMR spectrum, the aromatic protons of 8 shied to a organization (Fig. 9B). Similarly, for the nanoaggregates of both
lower eld (low to d 8.82 ppm) when compared with TPE 7, 1 and 2 in a 90 vol% aqueous mixture, when the solvent was
owing to the deshielding effect of the phenanthrene unit. evaporated, nanospheres were formed as shown in Fig. 9C and
Compound 8 absorbed at 259 and 302 nm (Fig. S9†) and emitted D. Interconnections among the nanospheres were observed and
at 358 and 374 nm (Fig. 7) in THF solution. When it aggregated the nanospheres were assembled to form dimers, trimers,
in the presence of a large amount of water (80–90 vol%), its oligomers or other high-ordered hierarchical structures.
emission was dramatically quenched by 10 times. Meanwhile, a
In order to control the self-assembly process and optimize
new broad peak appeared at 459 nm. It was presumed that the the self-assembly conditions, various mixed solvent systems
covalent locking of the phenyl rings had restricted their intra- and dye concentrations were tested. Chloroform was selected as
molecular rotation and hence affected the AIE characteristics. a good solvent and methanol was chosen as a poor solvent. As
The new peaks formed by UV irradiation in 1 and 2 were located shown in Fig. S10,† the volume ratio of chloroform and
at similar wavelengths to the PL of 8, proving that the
1
Fig. 8 H NMR spectra of 1 (A) before and (A) after UV irradiation for
Fig. 7 Photoluminescence spectra of 8 in THF–water mixtures.
20 min in chloroform-d.
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Fig. 9 (A) TEM and (B) SEM images of 1 formed by natural evaporation
of its THF solution at room temperature. SEM images of nanoparticles
of (C) 1 and (D) 2 formed by natural evaporation of their THF–water
mixtures with 90 vol% water content at room temperature.
Fig. 11 (A) Fluorescence microscopy and (B) SEM images of self-
assembled thin films of 1, (C and D) nanowires of 1, helices of (E) 1
and (F) 2.
edges with uniform thickness (Fig. 11B). Surprisingly, the
magnied images revealed that the lms were weaved with
nanowires (Fig. 11C). Such nanowires possessed diameters of
around 50 nm, lengths up to a few mm and high aspect ratios.
Fig. 11D shows that the free nanowires interconnected with
each other to form a single-layer network. Meanwhile, helically
twisted single nanowires were observed for both 1 and 2
Fig. 10 Self-assembled fluorescent thin films of 1 prepared from (A
3
and B) CHCl –methanol mixture (1 : 3 v/v) with a dye concentration of
ꢀ
1
1
3
3 mg mL and (C and D) CHCl –methanol mixture (1 : 4 v/v) with a
ꢀ1
dye concentration of 10 mg mL . (E and F) Fluorescent thin films of 1
in methanol. Photos were taken under (A, C and E) daylight and (B, D
and F) UV irradiation.
methanol (vCHCl3/vmethanol) was tuned from 1 : 3 to 2 : 3, and the
ꢀ1
concentration of 1 was gradually tuned from 10 mg mL to
ꢀ1
4
0 mg mL . Aer the clear solutions were prepared, they were
stored in capped bottles for 24 hours to obtain different struc-
tures. When the vCHCl3/vmethanol was 1 : 3 and the dye concen-
ꢀ
1
tration was 13 mg mL (Fig. 10A and B), a oating thin lm was
slowly formed in the solution. Further increasing the volume
ratio of methanol and decreasing the dye concentration gener-
ated a oating thin lm on top of the solution. When observed
under UV irradiation through the naked eye, the lms emitted
bright greenish-blue light (Fig. 10B, D and F). Fluorescence
microscopy images also showed the bright emission of the thin

lm (Fig. 11A). SEM analysis suggested that the lms had sharp Fig. 12 SEM images of the edges of the self-assembled thin films.
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(Fig. 11E and F), probably induced by the chiral centers of the the light source of 350 nm SHG of Ti:sapphire mode-locked
compounds. laser and the signals were collected with an Ocean Optics
Careful inspection of the lm edges provided evidence for USB2000 CCD spectrometer. The uorescence photos were
the self-assembly process. The round nanoparticles were self- taken on an optical microscope (Nikon ECLIPSE 80i) under UV
assembled to form well-aligned lines, resembling strings of light or a blue light source. The structures of the nanospheres
pearls. Transition states can be clearly identied, revealing a were investigated by high-resolution transmission electron
“polymerization” process of these nanospheres (Fig. 12A and B). microscopy JEOL 2010F TEM. Morphologies of the uorescent
The aligned nanoparticles further merged to form nanowires, thin lm and nanowires were investigated by a JEOL-6700
which then intertwined and overlaid to form a macroscopic thin scanning electron microscope (SEM).

lm (Fig. 12C and D). 1 does not possess any coplanar aromatic
core, long alkyl units or potential hydrogen bonds, and hence
the p–p interaction between the naphthalene units might be
Synthesis and characterization
the possible driving force for it to self-assemble into various The synthetic routes to compound 1 and 2 are shown in Scheme
morphologies.
1. Detailed experimental procedures are given below.
,2-Bis(1,4-phenylene)-diphenylvinyl bis[(S)-2-(6-methoxy-2-
1
naphthyl)propionate] (1). In a 500 mL round-bottom ask were
dissolved 2.00 g (5.48 mmol) of 3, 4.52 g (21.9 mmol) of DCC,
Conclusions
0
2
.33 g (2.74 mmol) of DMAP and 0.52 g (2.74 mmol) of TsOH in
00 mL of dry DCM. The solution was cooled to 0 C with an ice-
In this work, two tetraphenylethene derivatives were designed
and synthesized through the McMurry coupling reaction and
DCC-assisted esterication. They were both faintly emissive in
the solution state but emitted intensely when aggregated in a
poor solvent, demonstrating their aggregation-induced emis-
sion characteristics. A phenomenon of photo-induced emission
enhancement was observed in the solutions of 1 and 2, owing to
the photo-induced ring-closing oxidative reaction of the TPE
core. The compounds could readily self-assemble to form
ꢂ
water bath, into which 3.79 g (16.5 mmol) of (S)-(+)-2-(6-
methoxy-2-naphthyl)propionic acid (4) dissolved in 20 mL of
DCM was added under stirring by using a syringe. The reaction
mixture was stirred overnight. Aer ltration, the solution was
concentrated by using a rotary evaporator. The crude product
was puried by a silica gel column using a petroleum ether–
ethyl acetate mixture (4 : 1 v/v) as the eluent to give 1 as a white
ꢀ1
solid in 51% yield. IR (KBr), n (cm ): 2938, 1754, 1606, 1504,

uorescent nanowires, taking advantage of their AIE charac-
1
1
(
(
392, 1267, 1200, 1164, 1135, 1070, 1031, 851. H NMR
300 MHz, CDCl ), d (TMS, ppm): 7.74–7.70 (m, 6H), 7.47–7.44
m, 2H), 7.17–7.11 (m, 4H), 7.06–7.05 (m, 10H), 6.96–6.91 (m,
teristics and self-assembly. The self-assembly process from
nanospheres to nanowires and nally to macroscopic uores-
cent thin lms was reported.
3
8H), 6.74–6.70 (m, 4H), 4.03 (q, 2H, CH), 3.92 (s, 6H, OCH ), 1.65
3
+
(
d, J ¼ 7.2 Hz, 6H, CH
3
). HRMS (MALDI-TOF): m/z 788.3176 (M ,
Experimental section
Materials
calcd 788.3138).
0
4,4 -Carbonylenediphenyl bis[(S)-2-(6-methoxy-2-naphthyl)-
propionate] (6). In a 500 mL round-bottom ask were dissolved
Tetrahydrofuran (THF) was distilled under normal pressure
from sodium benzophenone ketyl under nitrogen immediately
prior to use. Dichloromethane (DCM) was distilled over calcium
0
1
.86 g (8.68 mmol) of 4,4 -dihydroxylbenzophenone (5), 6.00 g
(
26.0 mmol) of DCC, 0.53 g (4.34 mmol) of DMAP and 0.83 g
0
(4.34 mmol) of TsOH in 70 mL of dry DCM. The solution was
hydride. 4,4 -Dihydroxylbenzophenone (5), (S)-(+)-2-(6-methoxy-
ꢂ
cooled to 0 C with an ice-water bath, into which 6.00 g (26.0
2
-naphthyl)propionic acid (4), zinc powder, titanium(IV) chlo-
ride (TiCl ), 1,3-dicyclohexylcarbodiimde (DCC), 4-dimethyl-
aminopyridine (DMAP), p-toluenesulfonic acid monohydrate
TsOH), and all other chemicals were purchased from Aldrich
mmol) of (S)-(+)-2-(6-methoxy-2-naphthyl)propionic acid (4)
dissolved in 30 mL of DCM was added under stirring by using a
syringe. The reaction mixture was stirred overnight. Aer
4
(

ltration, the solution was concentrated by using a rotary
and used as received without further purication.
evaporator. The crude product was puried by a silica gel
column using a petroleum ether–ethyl acetate mixture (4 : 1 v/
Instruments
v) as the eluent to give 6 as a white solid in 67% yield. IR (KBr),
1
13
ꢀ1
H and C NMR spectra were recorded on a Bruker ARX 400 n (cm ): 2937, 1753, 1643, 1601, 1504, 1267, 1212, 1162, 1070.
1
NMR spectrometer using chloroform-d as the solvent and tet-
ramethylsilane (TMS; d ¼ 0 ppm) as the internal reference. IR 7.49 (dd, J
spectra were recorded on a Perkin-Elmer 16 PC FT-IR spectro- (d, 4H), 4.12 (q, 2H, CH), 3.93 (s, 6H, OCH
photometer. High resolution mass spectra (HRMS) were recor- 6H, CH ). HRMS (MALDI-TOF): m/z 638.2305 (M , calcd
ded on a GCT premier CAB048 mass spectrometer operating in 638.2305).
a MALDI-TOF mode. UV-vis absorption spectra were recorded 1,1,2,2-Tetrakis(1,4-phenylene)vinyl tetrakis[(S)-2-(6-methoxy-
H NMR (300 MHz, CDCl
¼ 8.4 Hz, J ¼ 1.6 Hz, 2H), 7.18–7.14 (m, 4H), 7.09
), 1.70 (d, J ¼ 7.2 Hz,
3
), d (TMS, ppm): 7.77–7.73 (m, 10H),
1
2
3
+
3
on a Milton Roy Spectronic 3000 array spectrophotometer. 2-naphthyl)propionate] (2). Into a 500 mL two-necked round-
Photoluminescence spectra were recorded on a Perkin-Elmer LS bottom ask with a reux condenser were added 4.77 g (7.47
55 spectrouorometer. The solid state uorescence quantum mmol) of 6 and 0.98 g (14.9 mmol) of zinc dust. The ask was
yields were measured by a Labsphere integrating sphere with evacuated under vacuum and ushed with dry nitrogen three
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times. 150 mL of THF was then added. The mixture was cooled
Acknowledgements
to ꢀ78 ꢂC, and 0.82 mL (7.47 mmol) of TiCl4 was added
dropwise by using a syringe. The mixture was slowly warmed This work was partially supported by the National Basic
to room temperature and stirred for 0.5 h, then reuxed for 24 Research Program of China (973 Program; 2013CB834701), the
h. The reaction was then quenched with 10% aqueous K
aqueous solution. The resulting mixture was ltered and the N_HKUST620/11) and the University Grants Committee of HK
ltrate was extracted with dichloromethane three times. The (AoE/P-03/08). B.Z.T. thanks the support of the Guangdong
2
CO
3
Research Grants Council of Hong Kong (HKUST2/CRF/10 and

organic layer was washed with water and dried over Na
Aer solvent evaporation, the residue was puried by silica gel
chromatography using petroleum ether–ethyl acetate
mixture (4 : 1 v/v) as the eluent to give 2 as a white solid in
2
SO
4
.
Innovative Research Team Program (201101C0105067115).
a
Notes and references
ꢀ
1
3
1
0% yield. IR (KBr), n (cm ): 2935, 1754, 1606, 1504, 1392,
267, 1200, 1164, 1135, 1070, 1031, 851. H NMR (300 MHz,
1
C. P. Poole, Introduction to nanotechnology, John Wiley &
Sons, Hoboken, New Jersey, USA, 2003.
1
CDCl
3
), d (TMS, ppm): 7.71 (m, 12H), 7.44 (d, J ¼ 8.4 Hz, 4H),
.16–7.12 (m, 8H), 6.86 (d, J ¼ 8.8 Hz, 8H), 6.69 (d, J ¼ 8.8 Hz,
H), 4.01 (q, 4H, CH), 3.92 (s, 12H, OCH
), 1.63 (d, J ¼ 7.2 Hz,
2H, CH ). HRMS (MALDI-TOF): m/z 1244.4728 (M , calcd
244.4711).
,2-Diphenylphenanthrene (8). Into a 100 mL two-neck
2
B. Z. Tian, J. Liu, T. Dvir, L. H. Jin, J. H. Tsui, Q. Qing,
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1
2
004, 34, 83.
Y. L. Yan, C. Zhang, J. N. Yao and Y. S. Zhao, Adv. Mater.,
013, 25, 3627.
round-bottom ask tetraphenylethene (1.00 g, 3.01 mmol)
was added. The ask was evacuated under vacuum and
2

ushed with dry nitrogen for three times. 50 mL dichloro-
H. Jintoku, T. Sagawa, M. Takafuji and H. Ihara, Org. Biomol.
Chem., 2009, 7, 2430.
methane was then added to dissolve the compound. The
ꢂ
mixture was cooled to 0 C and a solution of FeCl
3
(1.27 g,
6
7
8
B. C. Sih and M. O. Wolf, Chem. Commun., 2005, 3375.
J. Lv, H. B. Liu and Y. L. Li, Pure Appl. Chem., 2008, 80, 639.
S. J. George and A. Ajayaghosh, Chem.–Eur. J., 2005, 11, 3217;
A. Ajayaghosh and V. K. Praveen, Acc. Chem. Res., 2007, 40,
8
3 2
.83 mmol) in CH NO (5.69 g, 5 mL) was then added drop-
wise via a syringe. Aer the mixture was stirred for 2 h, 50 mL
methanol was added to quench the reaction. The resulting
mixture was washed with 70 mL water for three times and the
644; J. van Herrikhuyzen, S. J. George, M. R. J. Vos,
2 4
organic layer was dried over Na SO . Aer solvent evapora-
N. A. J. M. Sommerdijk, A. Ajayaghosh, S. C. J. Meskers and
A. P. H. J. Schenning, Angew. Chem., Int. Ed., 2007, 46, 1825.
J. Luo, T. Lei, L. Wang, Y. G. Ma, Y. Cao, J. Wang and J. Pei, J.
Am. Chem. Soc., 2009, 131, 2076.
tion, the residue was puried by silica gel chromatography
using petroleum ether as the eluent to give 8 as a white solid
9
ꢀ
1
in 83% yield. IR (KBr), n (cm ): 3444, 3046, 3026, 1487,
1
1
441, 1417, 1072, 1026, 760, 725, 700, 629, 580. H NMR
1
0 B. K. An, S. H. Gihm, J. W. Chung, C. R. Park, S. K. Kwon and
S. Y. Park, J. Am. Chem. Soc., 2009, 131, 3950; B. K. An,
D. S. Lee, J. S. Lee, Y. S. Park, H. S. Song and S. Y. Park, J.
Am. Chem. Soc., 2004, 126, 10232.
(
(
1
3
400 MHz, CDCl ), d (TMS, ppm): 8.82 (d, J ¼ 8.4 Hz, 2H), 7.67
3
t, 2H), 7.56 (d, J ¼ 7.6 Hz, 2H), 7.49 (t, 2H), 7.25–7.15 (m,
+
0H). HRMS (MALDI-TOF): m/z 330.1499 (M , calcd
30.1409).
11 C. G. Chandaluri and T. P. Radhakrishnan, J. Mater. Chem. C,
2013, 1, 4464.
1
2 J. D. Luo, Z. L. Xie, J. W. Y. Lam, L. Cheng, H. Y. Chen,
C. F. Qiu, H. S. Kwok, X. W. Zhan, Y. Q. Liu, D. B. Zhu and
B. Z. Tang, Chem. Commun., 2001, 1740.
Preparation of aggregates
Stock THF solutions of the molecules with a concentration of
0
.1 mM were prepared. An aliquot (1 mL) of this stock solution 13 Y. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Soc. Rev., 2011,
was transferred to a 10 mL volumetric ask. Aer adding an 40, 5361.
appropriate amount of THF, water was added dropwise under 14 R. R. Hu, J. W. Y. Lam, Y. Yu, H. H. Y. Sung, I. D. Williams,
vigorous stirring to furnish a 10 mM THF–water mixture with a M. M. F. Yuen and B. Z. Tang, Polym. Chem., 2013, 4, 95.
specic water fraction (f ). The water content was varied in the 15 M. P. Aldred, C. Li and M. Q. Zhu, Chem.–Eur. J., 2012, 18,
w
range of 0–90 vol%. Absorption and emission spectra of the
resulting solutions and aggregates were measured immediately
aer the sample preparation.
16037; G. X. Huang, B. D. Ma, J. M. Chen, Q. Peng,
G. X. Zhang, Q. H. Fan and D. Q. Zhang, Chem.–Eur. J.,
2012, 18, 3886.
6332 | J. Mater. Chem. C, 2014, 2, 6326–6332
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