Aggregation-induced emission of tetraphenylethene-hexaphenylbenzene adducts: Effects of twisting amplitude and steric hindrance on light emission of nonplanar fluorogens

Article abstract of DOI:10.1002/chem.201203840

A series of nonplanar tetraphenylethene (TPE)-hexaphenylbenzene (HPB) adducts was designed and synthesized by Diels-Alder reaction of the acetylene precursors and tetraphenylcyclopentadienone. All of the adducts showed aggregation-induced emission features. The twisting amplitude and steric hindrance of the TPE and HPB units were found to play a crucial role in their fluorescence behaviors in the aggregated state. Nonplanar fluorogens: A series of nonplanar tetraphenylethene and hexaphenylbenzene adducts was designed and synthesized (see scheme) to study the aggregation-induced emission process. The twisting amplitude and steric effect of the units were found to be crucial in the fluorescence behavior of the luminogens.

Full text of DOI:10.1002/chem.201203840

FULL PAPER
DOI: 10.1002/chem.201203840
Aggregation-Induced Emission of Tetraphenylethene–Hexaphenylbenzene
Adducts: Effects of Twisting Amplitude and Steric Hindrance on Light
Emission of Nonplanar Fluorogens
Rongrong Hu,[a] Jacky W. Y. Lam,[a] Yi Liu,[a] Xiaoa Zhang,[a] and Ben Zhong Tang*[a, b]
Abstract: A series of nonplanar tetraphenylethene (TPE)–hexaphenylbenzene
(HPB) adducts was designed and synthesized by Diels–Alder reaction of the acety-
Keywords: aggregation · cycloaddi-
lene precursors and tetraphenylcyclopentadienone. All of the adducts showed ag-
tion · fluorescence · luminescence ·
gregation-induced emission features. The twisting amplitude and steric hindrance
steric hindrance
of the TPE and HPB units were found to play a crucial role in their fluorescence
behaviors in the aggregated state.
Introduction
In solution, the active intramolecular rotation of the phenyl
rings of TPE, for example, serves as a relaxation channel for
the excitons to deactivate. In the aggregated state, such
motion is restricted due to the physical constraint, which
blocks the nonradiative pathway and activates radiative
decay.[6] We thus hypothesized that the restriction of intra-
molecular rotation is the cause of the AIE phenomenon.
Thanks to the research enthusiasm of scientists, many AIE
luminogens with different emission colors have been pre-
pared and have found an array of high-tech applications as
chemosensors, bioprobes, solid-state emitters for optical de-
vices, and so forth.[7]
The conformational planarity and structural rigidity are
found to play key roles in determining whether a luminogen
exhibits AIE activity.[8] Little effort, however, has been
placed on studying how the twisting amplitude of the rotors
affects the emission behaviors of nonplanar AIE lumino-
gens. Hexaphenylbenzene (HPB) is an attractive building
block for the construction of materials with novel properties
because of its ready availability and facile modification.[9]
Similar to TPE, HPB is propeller-like in shape, which im-
parts large internal molecular free volume[10] and impedes
p–p stacking in the solid state, as demonstrated by the crys-
tal structures of its derivatives.[11] Unlike TPE, the peripher-
al phenyl rings in HPB cannot rotate freely due to the
severe steric repulsion. Thus, it is an ideal compound, along
with TPE, to investigate the effect of rotational freedom on
the AIE process.
Organic luminophores have attracted considerable interest
for their potential device, sensing, and imaging applica-
tions.[1] Many conventional fluorophores exhibit high fluo-
rescence efficiency in solution but suffer an aggregation-
caused quenching (ACQ) effect in the condensed phase,
which prevents them from finding real-world applications in
an engineering form.[2] Many studies have been carried out
since the 1930s to investigate the aggregation effect on the
optical properties of organic dyes.[3] In 2001, we observed a
phenomenon of aggregation-induced emission (AIE) in
some propeller-like molecules, such as tetraphenylethene
(TPE) and hexaphenylsilole. These luminogens are nonemis-
sive when molecularly dissolved in their good solvents, such
as toluene, THF, and chloroform, but become highly lumi-
nescent in the aggregated state.[4] We have considered a
number of possible mechanistic pathways, including confor-
mational planarization, J-aggregate formation, hydrophobic
effect, Z/E isomerization, and twisted intramolecular charge
transfer, as causes for the AIE effect but none of them was
fully supported by the experimental results.[5] Fundamental
physics teaches that any molecular motions consume energy.
[a] Dr. R. Hu, Dr. J. W. Y. Lam, Y. Liu, X. Zhang, Prof. B. Z. Tang
The Hong Kong University of Science & Technology
Shenzhen Research Institute, Department of Chemistry
State Key Laboratory of Molecular Neuroscience
Institute of Molecular Functional Materials and
Division of Biomedical Engineering
Attachment of HPB to traditional luminophores has
solved their ACQ problem in the condensed phase, and the
bulky, nonplanar structure of HPB prevents the formation
of detrimental species such as excimers by intermolecular
interactions.[12] However, its effect in the AIE system re-
mains less explored. What will be the consequence if HPB
units are incorporated into the AIE systems? Tetrakis(pen-
The Hong Kong University of Science & Technology (HKUST)
Clear Water Bay, Kowloon, Hong Kong (P.R. China)
E-mail: tangbenz@ust.hk
[b] Prof. B. Z. Tang
Guangdong Innovative Research Team
SCUT–HKUST Joint Research Laboratory
State Key Laboratory of Luminescent Materials and Devices
South China University of Technology (SCUT)
Guang Zhou 51064 (P.R. China)
taphenylphenyl)ethylene has been reported to show
a
higher fluorescence quantum yield (FF =13%) than TPE
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203840.
(FF =0.24%)[13] in CH2Cl2, presumably due to the steric
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For example, the high-resolution mass spectra of 1b–3b,
2c, and 3c give M+ peaks at m/z 1042.4562 (1b), 1219.8142
(2b), 1575.6741 (2c), 1396.9825 (3b), and 1752.7534 (3c)
(Figures S1–S7 in the Supporting Information), which are in
1
good agreement with the calculated values. The H NMR
analysis provides more detailed structural information. The
biphenyl protons of 2a, for example, resonate at d=
7.56 ppm, which shifts to d=7.52 ppm in the spectrum of
2b (Figure 1). The broad multiplet observed at d=
6.82 ppm in 2b is associated with the resonances of the
newly formed HPB protons. Three peaks related to the ab-
sorptions of the phenyl protons shared by the HPB and
TPE or biphenyl units are found at d=6.70, 6.59, and
6.55 ppm, thus revealing that only half of the triple bonds
of 2a are converted to HPB units in 2b. In 2c, no peak was
observed at d=7.56 ppm and the resonances at d=6.82,
6.67, 6.61, and 6.52 ppm are intensified, which suggests
completeness of the Diels–Alder reaction. Similar phenom-
ena are observed in the 1H NMR spectra of 1a, 1b, and
3a–3c (Figures S8 and S9 in the Supporting Information).
Although they are constructed from benzene rings, 1a–
3c dissolve readily in common organic solvents, such as tol-
uene, chloroform, and THF, thanks to the twisted TPE and
Scheme 1. Chemical structures of 1a–3c.
bulkiness of the HPB unit, which hampers the intramolecu-
lar rotations and thereby reduces the nonradiative decay of
the excited state. In this work, we designed a series of non-
planar luminogenic molecules constructed from TPE and
HPB building blocks and investigated how the twisted struc-
tures of TPE and HPB affect the fluorescence of the result-
ing hybrid molecules in the solution and aggregated states
(Scheme 1).
Results and Discussion
The TPE–HPB adducts were prepared according to the syn-
thetic routes shown in Scheme 2. TPE-containing precursors
4, 5, and 3a were prepared according to the previously pub-
lished procedures.[14] Palladium-catalyzed Sonogashira cou-
pling of 4 and 5 afforded 1a, which was transformed into 1b
by a Diels–Alder reaction with tetraphenylcyclopentadie-
none 6. On the other hand, diyne 9 was obtained by a cou-
pling reaction of 7 with trimethylsilylacetylene followed by
base-catalyzed hydrolysis in THF. Under the same experi-
mental procedures, 2a was prepared from 9 and an excess
amount of 4. Diels–Alder reaction of 6 with 2a or 3a pro-
duced 2b or 3b with one HPB unit and one unreacted
ethynyl group and 2c or 3c with two HPB units.
Figure 1. 1H NMR spectra of A) 2a, B) 2b, and C) 2c in [D1]chloroform.
The solvent peaks are marked with asterisks.
HPB units, which endow large intermolecular distance and
generate large free volume to accommodate more solvent
molecules. The HPB–TPE adducts are also anticipated to
show high resistance to thermolysis owing to the presence of
numerous aromatic rings.[15] Indeed, they enjoy high thermal
stability, showing 5% weight loss at temperatures up to
4608C under nitrogen and 4228C in air (Figure 2 and Fig-
ures S10 and S11 in the Supporting Information). The high
residual yield up to 40% is retained when these compounds
are heated under nitrogen at 8008C, implying their potential
as ceramic materials.
The structures of the intermediates and products were
characterized by standard spectroscopic methods with satis-
factory results (see the Experimental Section for details).
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Emission of Tetraphenylethene–Hexaphenylbenzene Adducts
FULL PAPER
Figure 2. Thermogravimetric analysis (TGA) thermograms of 3b and 3c
recorded under nitrogen and in air at a heating rate of 108CminÀ1. Td =
decompose temperature.
Table 1. Optical properties of 1a–3c.[a]
Luminogen
lab [nm]
lem [nm]
aAIE
Fsolid [%]
1a
1b
2a
2b
2c
345
331
353
321
310
352
334
324
484
480
482
477
462
501
487
474
479
204
269
204
18
115
137
88
87
48
63
21
10
74
70
75
3a[b]
3b
3c
[a] Abbreviations: lab =absorption maximum in THF (10 mm), lem =emis-
sion maximum in THF/water mixture (1:9, v/v), aAIE =ITHF/water (1:9,v/v)/ITHF
,
Fsolid =solid-state fluorescence quantum yield. [b] Data taken from
ref. [10a].
Scheme 2. Synthetic routes to A) 1a and 1b, B) 2a–2c, and C) 3b and
3c. D-A=Diels–Alder, TMS=trimethylsilyl, TBAF=tetrabutylammoni-
um fluoride.
Figure 3. Normalized absorption spectra of 1a–3c in THF. Solution con-
centration: 10 mm.
The absorption spectra of 1a–3c as dilute solutions in
THF are depicted in Figure 3. The spectra of 1a–3a show
peaks at 345, 353, and 352 nm, respectively (Figure 3 and
Table 1). However, their adducts, 1b–3b, absorb at shorter
wavelengths of 331, 321, and 334 nm, respectively, due to
the steric effect of the HPB unit. Compounds 2c and 3c
carry two HPB units in one molecule, and they absorb at
310 and 324 nm, respectively, which are approximately
10 nm blueshifted from those of 2b and 3b. These results
nicely demonstrate that the electronic transitions of the lu-
minogens are sensitive to their molecular structures, thereby
offering the opportunity to modulate their properties by mo-
lecular engineering endeavors. The absorption of AIE lumi-
nogens is normally not affected by aggregate formation, as
studied in our previous work.[16] A similar observation was
also made for the compounds studied herein. For example,
no significant redshift in the absorption maximum was ob-
served in the UV spectra of 1b in THF/water mixtures with
different amounts of water (Figure S12 in the Supporting In-
formation). Level-off tails are seen in the visible spectral
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B. Z. Tang et al.
much higher than that of 1b
(Figure S13 in the Supporting
Information); aAIE is the AIE
factor defined by the following
equation: aAIE =ITHF/water (1:9,v/v)
/
ITHF Similarly, compound 2a
.
emits no light in THF, but its
nanoaggregates in a 90% aque-
ous mixture emit intensely at
482 nm with a 269-fold higher
intensity (Figure 6A). Lumino-
Figure 4. Photographs of 1a–3c in THF/water mixtures with different water fractions (fw) taken under UV illu-
mination. Solution concentration: 10 mm; percentage water is marked above each image.
region, which are attributed to the light-scattering effect of
the nanoparticles.
All the molecules are AIE active, as suggested by the flu-
orescence images of their solutions in THF and THF/water
mixtures (Figure 4). For example, the solution of 1a in THF
emits no light under UV illumination. Addition of water, a
poor solvent of 1a, to the solution aggregates its molecules
and enhances its emission. The emission remains weak in
aqueous mixtures with low water fractions (ꢀ70%) but be-
comes stronger when more water is added. Similar results
were found with other compounds. Some luminogens
become emissive in the presence of a small amount of water
(ꢁ50%), presumably due to their comparatively lower solu-
bility in the aqueous mixture.
In addition to visual observations, the emission behaviors
of 1a–3c in THF/water mixtures were studied by spectro-
fluorometry. As shown in Figure 5A, compound 1b is practi-
Figure 6. Emission spectra of A) 2a, B) 2b, and C) 2c in THF/water mix-
tures with different water fractions (fw). D) Plots of I/I0 values versus the
compositions of aqueous mixtures of 2a–2c. Solution concentration:
10 mm; excitation wavelength: 353 (2a), 321 (2b), and 310 nm (2c).
gen 2b, with one HPB unit, on the other hand, fluoresces at
477 nm in the aggregated state with an aAIE value (204)
close to that of 2a (Figure 6B and 6D). On the other hand,
compound 2c contains two HPB units and shows a broad
emission peak at 462 nm in THF although the intensity is
weak (Figure 6C). The emission intensity starts to rise when
water is added to the solution in THF and reaches its maxi-
mum value for an 80% aqueous mixture, with a much small-
er aAIE value of 18. A similar trend was observed in the pho-
toluminescence (PL) spectra of 3a–3c (Figure 7 and Fig-
ure S14 in the Supporting Information).
Figure 5. A) Photoluminescence (PL) spectra of 1b in THF/water mix-
tures with different water fractions (fw). B) Plots of I/I0 values versus the
compositions of aqueous mixtures of 1a and 1b. Solution concentration:
10 mm; excitation wavelength: 345 (1a) and 331 nm (1b).
cally nonemissive in THF. When the water fraction in the
solvent mixture is 60%, an emission peak emerges at
480 nm, the intensity of which is enhanced, without causing
any spectral profile change, by further increasing the water
solvent fraction. From the solution in THF to nanoaggre-
gates in a 90% aqueous mixture, the emission intensity rises
by 204-fold (Figure 5B). Under the same circumstances, the
emission enhancement, or the aAIE value, of 1a (479) is
We also investigated the PL of 1a–3c in the solid state.
All the solid powders of 1a–3c show strong light emissions
at wavelengths similar to those of their nanoaggregates in
THF/water suspensions (Figure S15 in the Supporting Infor-
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Emission of Tetraphenylethene–Hexaphenylbenzene Adducts
FULL PAPER
ution, thus reducing the energy loss of the excitons through
nonradiative relaxation channels. Furthermore, it impedes
the close packing of the molecules in the aggregated state,
thus reducing the formation of species that are detrimental
to the light emission. On the other hand, the increment of
the intermolecular distance generates more free volume,
which allows the phenyl rings to rotate to a certain extent.
This weakens the light emission in the aggregated state and
hence decreases the aAIE value.
To gain a quantitative characterization of the phenyl ring
rotations, single-crystal structures of TPE and HPB,[17] as
well as their optimized structures obtained by theoretical
calculations, are compared in Figures 9 and 10. In TPE, the
Figure 7. A) PL spectra of 3c in THF/water mixtures with different water
fractions (fw). B) Plots of I/I0 values versus the compositions of aqueous
mixtures of 3a–3c. Solution concentration: 10 mm; excitation wavelength:
352 (3a), 334 (3b), and 324 nm (3c).
mation). We determined their fluorescence quantum yields
(FF,S) by a calibrated integrating sphere (Table 1) and high
FF,S values up to 87% were deduced from the measure-
ments, manifesting their AIE features. The FF,S values of
1a–3a are higher than those of 1b–3b, 2c, and 3c. This sug-
gests that the incorporation of the HPB unit into AIE lumi-
nogens is harmful to the emission of the resulting adducts.
Why is there such a FF,S difference, considering that both
TPE and HPB units take a twisted, propeller-like structure?
The four phenyl rings in TPE can undergo free rotation
with a large twisting amplitude. However, the rotation of
the phenyl rings in HPB is more difficult because of the
severe steric hindrance from the neighborhood. Hence, TPE
shows no discernible emission peak in solution, whereas
HPB emits a weak PL peak at 334 nm in THF (Figure 8). In
an 80% aqueous solvent mixture, the emission from HPB is
increased by 12-fold, accompanied by a 5 nm blueshift in the
emission maximum, thereby displaying a phenomenon of ag-
gregation-enhanced emission. The HPB unit plays dual roles
in the photophysical processes of 1b–3c. Its bulky size re-
stricts the intramolecular rotation of the phenyl rings in sol-
Figure 9. A,C) Single-crystal structure and B,D) optimized calculated
structure of TPE. CCDC-633293 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
four peripheral phenyl rings are twisted out of the central
double-bond plane. The dihedral angle of C20-C10-C1-C2 is
1388, as suggested by the single-crystal structure. This indi-
cates that the phenyl ring in plane 2 deviates from the per-
pendicular position of plane 1 by 488 where the central
double bond lies (Figure 9C). A similar value (438) was ob-
tained from theoretical calculations (Figure 9B and 9D). In
HPB, the peripheral phenyl rings are almost perpendicular
to the central benzene ring. Through the single-crystal struc-
ture, the dihedral angle of C1-C2-C13-C14 is 1028, from
which a twisting angle of 128 is derived. This value is much
smaller than that in TPE, which is suggestive of a smaller
twisting amplitude of the phenyl rings in HPB. Although the
optimized structure reveals a higher twisting angle of 228,
such a value is still small when compared with TPE.
The potential energy curves along the dihedral angle of
the ground state for isolated TPE and HPB molecules are
calculated and shown in Figure 11. The energy barrier of
phenyl-ring rotation in TPE is about 8 kcalmolÀ1, whereas
Figure 8. A) Emission spectra of HPB in THF/water mixtures. B) Plot of
I/I0 values versus the compositions of aqueous mixtures of HPB. Concen-
tration: 10 mm; excitation wavelength: 272 nm.
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B. Z. Tang et al.
fluorogens. Such
a
structure–property relationship will
deepen our mechanistic understanding of this new phenom-
enon and guide the future design of materials.
Experimental Section
Materials: Tetrahydrofuran (THF) and toluene were distilled under
normal pressure from sodium benzophenone ketyl under nitrogen imme-
diately prior to use. Dichlorobis(triphenylphosphine)palladium(II) ([Pd-
AHCTNUGTREN(GNNU PPh3)2Cl2]), copper(I) iodide (CuI), triphenylphosphine (PPh3), tetrabu-
tylammonium fluoride (TBAF), trimethylsilylacetylene, triethylamine
(Et3N), 2,3,4,5-tetraphenylcyclopentadienone (6), and other chemicals
and solvents were all purchased from Aldrich and used as received with-
out further purification. 1-(4-Bromophenyl)triphenylethene (4), 1-(4-
ethynylphenyl)triphenylethene (5), and 1,2-bis{4-[2-(4-triphenylvinylphe-
nyl)ethynyl]phenyl}-1,2-diphenylethene (3a) were prepared according to
the previously published procedures.[14]
Instruments: 1H NMR spectra were measured on a Bruker ARX 400
NMR spectrometer with CDCl3 or CD2Cl2 as solvent and tetramethylsi-
lane (TMS; d=0 ppm) as internal standard. IR spectra were recorded on
Figure 10. A,C) Single-crystal structure and B,D) optimized calculated
structure of HPB. CCDC-177146 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
a
Perkin–Elmer 16 PC FTIR spectrophotometer. Thermogravimetric
analysis (TGA) was carried out under nitrogen or in air on a Perkin–
Elmer TGA 7 analyzer at a heating rate of 108CminÀ1. UV/Vis absorp-
tion spectra were measured on a Milton Roy Spectronic 3000 array spec-
trophotometer. Photoluminescence (PL) spectra were recorded on a
Perkin–Elmer LS 55 spectrofluorometer. High-resolution mass spectra
were recorded on a GCT premier CAB048 mass spectrometer operating
in MALDI-TOF mode. The ground-state geometries of TPE and HPB
were optimized by density functional theory (DFT). The DFT calcula-
tions were carried out by using the B3LYP functionals with the 6-31g-
AHCTUNGTRENNUNG
(d,p) basis set.[18]
Preparation of aggregates: Stock solutions of the molecules in THF were
prepared with a concentration of 0.1mm. An aliquot (1 mL) of this stock
solution was transferred to a volumetric flask (10 mL). After adding an
appropriate amount of THF, water was added dropwise under vigorous
stirring to furnish a 10 mm solution in a THF/water mixture with a specific
water fraction (fw). The water content was varied in the range of 0–
90 vol%. Absorption and emission spectra of the resulting solutions and
aggregates were measured immediately after sample preparation.
Synthesis and characterization: Compounds 1a–3c were synthesized ac-
cording to the synthetic routes shown in Scheme 2. Detailed experimen-
tal procedures are given below. Although the Diels–Alder reaction is
known as a quantitative reaction in many cases, the small polarity differ-
ence between the reactants 1a–3a and products 1b–3b, 2c, and 3c, as
well as their poor solubility in nonpolar solvents such as hexane, lowered
the yield of isolated products significantly.
Figure 11. Potential energy curves along the dihedral angle of the ground
state for isolated TPE (C20-C10-C1-C2) and HPB (C1-C2-C13-C14) mol-
ecules.
4,4’-Bis(2-trimethylsilylethynyl)biphenyl
(8):
Compound 7
(5.00 g,
12.3 mmol), [Pd(PPh3)2Cl2] (0.43 g, 0.62 mmol), CuI (0.12 g, 0.62 mmol),
AHCTUNGTRENNUNG
the value in HPB is doubled, which demonstrates that the
rotation of the phenyl rings in HPB is more difficult. More-
over, the dihedral angle for minimum energy is 508 for TPE
and 688 for HPB, from which twisting angles of 40 and 228
are deduced for TPE and HPB, respectively. All these re-
sults show the higher twisting amplitude in TPE.
PPh3 (0.10 g, 0.37 mmol), and a solvent mixture of THF/Et3N (100/
50 mL) were added to a two-necked round-bottom flask (250 mL) in the
atmosphere of nitrogen. After the catalysts were completely dissolved,
(trimethylsilyl)acetylene (5.22 mL, 36.9 mmol) was injected into the flask
and the mixture was stirred at 708C for 24 h. The formed solid was re-
moved by filtration and washed with diethyl ether. The solvent was re-
moved under reduced pressure and the crude product was purified on a
silica-gel column with hexane as eluent. A pale-brown solid (8) was ob-
1
tained in 96% yield. H NMR (400 MHz, CDCl3): d(TMS)=7.53 (s, 8H),
Conclusion
ꢂ
0.27 ppm (s, 18H); IR (KBr): n˜ =3036, 2956, 2899, 2157 (C C stretching),
1918, 1488, 1399, 1253, 1242, 1220, 1113, 1004, 847, 823, 758, 697, 646,
543 cmÀ1; HRMS (MALDI-TOF): m/z calcd for C22H26Si2: 346.1573 [M]+
; found: 346.1252.
A series of luminogenic materials has been designed and
synthesized from TPE and HPB building blocks. They are
all AIE active with high solid-state fluorescence quantum
yields up to 87%. The twisting amplitude and steric effects
are found to be crucial for the AIE behavior in nonplanar
4,4’-Diethynylbiphenyl (9): A solution of 8 in THF (120 mL, 3.80 g,
11.0 mmol) and TBAF (1m; 44 mL) were placed into a round-bottom
flask (250 mL). After stirring for 3 h, water (120 mL) was added and the
mixture was then extracted three times with dichloromethane. The solu-
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Emission of Tetraphenylethene–Hexaphenylbenzene Adducts
FULL PAPER
tion in CH2Cl2 was washed with twice brine and dried over anhydrous
sodium sulfate. After filtration and solvent evaporation, the crude prod-
uct was purified on a silica-gel column with petroleum ether as eluent. A
light-yellow solid (9) was obtained in 89% yield. 1H NMR (400 MHz,
3025, 2959, 2927, 1600, 1494, 1443, 1074, 1029, 731, 697 cmÀ1; HRMS
(MALDI-TOF): m/z calcd for C124H86: 1574.6730 [M]+; found: 1574.6741.
Compounds 3b and 3c: Compound 3a (0.30 g, 0.29 mmol), 6 (0.44 g,
1.15 mmol), and diphenyl ether (5 mL) were added to a round-bottom
flask. After heating at reflux for 48 h under nitrogen, the mixture was
cooled to room temperature and diluted with ethanol. The precipitate
was separated by filtration and washed with ethanol. The crude product
was purified by silica-gel column chromatography with petroleum ether
as eluent. Compounds 3b and 3c were obtained in 21 and 44% yield, re-
ꢂ
CD2Cl2): d(TMS)=7.56 (s, 8H), 3.14 ppm (s, 2H); IR (KBr), n˜ =3467 (
À
ꢂ
C H stretching), 3273, 3035, 2106 (C C stretching), 1919, 1694, 1660,
1604, 1489, 1393, 1252, 1108, 1004, 857, 825, 678, 658, 647, 632, 565, 546,
513 cmÀ1; HRMS (MALDI-TOF): m/z calcd for C16H10: 202.0783 [M]+;
found: 202.0774.
1
spectively. 3b: H NMR (400 MHz, CDCl3): d(TMS)=7.20 (m, 4H), 7.06
4,4’-Bis(1,2,2-triphenylvinyl)diphenylacetylene (1a): A two-necked flask
(m, 36H), 6.86 (m, 28H), 6.56 (m, 4H), 6.51 ppm (m, 4H); IR (KBr), n˜ =
3441, 3055, 3026, 2959, 2927, 1945, 1884, 1802, 1727, 1600, 1493, 1443,
1262, 1074, 1029, 803, 751, 730, 698 cmÀ1; HRMS (MALDI-TOF): m/z
was charged with
ACHTUNGTRENNUNG(PPh3)2Cl2] (16 mg, 0.02 mmol), PPh3 (3 mg, 0.01 mmol), and CuI (4 mg,
4 (0.51 g, 1.24 mmol), 5 (0.40 g, 1.12 mmol), [Pd-
0.02 mmol). The flask was degassed and filled with nitrogen. A mixture
of THF (12 mL) and Et3N (6 mL) was then added by syringe. The mix-
ture was stirred at reflux for 24 h under nitrogen. The solution was al-
lowed to cool to room temperature and washed with saturated aqueous
NH4Cl. The mixture was extracted with CH2Cl2 and washed with brine.
The organic extracts were separated, combined, and dried over anhy-
drous MgSO4. After filtration and solvent removal under vacuum, the
residue was purified by silica-gel column chromatography with petroleum
ether as eluent. A yellow solid (1a) was isolated in 89% yield. 1H NMR
(400 MHz, CDCl3): d(TMS)=7.21 (d, J=8 Hz, 4H), 7.10 (m, 18H), 7.02
(m, 12H), 6.98 ppm (d, J=8 Hz, 4H); IR (KBr), n˜ =3056, 3021, 1598,
1491, 1441, 1075, 1029, 853, 824, 748, 699 cmÀ1; HRMS (MALDI-TOF):
m/z calcd for C54H38: 686.2974 [M]+; found: 686.2964.
calcd for C110H76
:
1396.5947 [M]+; found: 1396.9825. 3c: 1H NMR
(400 MHz, CDCl3): d(TMS)=7.08 (d, J=8.4 Hz, 4H), 7.03 (m, 8H), 6.97
(d, J=7.2 Hz, 4H), 6.90 (m, 16H), 6.82 (m, 52H), 6.68 (d, J=7.2 Hz,
4H), 6.61 (d, J=8.4, 4H), 6.53 ppm (d, J=8.4 Hz, 4H); IR (KBr), n˜ =
3023, 1585, 1485, 1442, 1390, 1234, 1074, 1022, 750, 726, 697 cmÀ1; HRMS
(MALDI-TOF): m/z calcd for C138H96: 1752.7512 [M]+; found: 1752.7534.
Acknowledgements
We thank Luming Meng and Prof. Xuhui Huang for technical support on
theoretical calculations. This work was partially supported by the Nation-
al Basic Research Program of China (973 Program; 2013CB834701), the
RPC and SRFI Grants of HKUST (RPC11SC09 and SRFI11SC03PG),
the Research Grants Council of Hong Kong (HKUST2/CRF/10 and
N_HKUST620/11), the Innovation and Technology Commission (ITCPD/
17-9), and the University Grants Committee of HK (AoE/P-03/08).
B.Z.T. is grateful for the support of the Guangdong Innovative Research
Team Program (201101C0105067115).
1,2-Bis[4-(1,2,2-triphenylvinyl)phenyl]-3,4,5,6-tetraphenylbenzene
(1b):
Compound 1a (0.25 g, 0.36 mmol), 6 (0.17 g, 0.44 mmol), and diphenyl
ether (5 mL) were added to a round-bottom flask. After heating at reflux
for 48 h under nitrogen, the solution was cooled to room temperature
and diluted with ethanol. The precipitate was separated by filtration and
washed with ethanol. The crude product was purified by silica-gel column
chromatography with petroleum ether as eluent. A yellow solid was iso-
lated (1b) in 32% yield. 1H NMR (400 MHz, CDCl3): d(TMS)=7.34 (t,
J=8.0 Hz, 2H), 6.99 (m, 50H), 6.57 (d, J=8.4 Hz, 2H), 6.50 ppm (d, J=
8.0 Hz, 2H); IR (KBr), n˜ =3056, 3025, 2924, 1725, 1583, 1487, 1442, 1236,
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:
4,4’-Bis{2-[4-(1,2,2-triphenylvinyl)phenyl]ethynyl}biphenyl (2a):
necked flask was charged with (3.00 g, 7.29 mmol),
2.43 mmol), [Pd(PPh3)2Cl2] (136 mg, 0.19 mmol), PPh3 (64 mg,
A
two-
9
4 (0.49 g,
ACHTUNGTRENNUNG
0.24 mmol), and CuI (28 mg, 0.14 mmol). The flask was degassed and
filled with nitrogen. A mixture of THF (100 mL) and Et3N (50 mL) was
then added by syringe. After stirring at reflux for 24 h under nitrogen,
the mixture was cooled to room temperature and washed with saturated
aqueous NH4Cl. The mixture was extracted with CH2Cl2 and washed
with brine. The organic extracts were separated and dried over anhy-
drous MgSO4. After filtration and solvent evaporation under vacuum, the
residue was purified by silica-gel column chromatography with petroleum
ether as eluent to give 2a as a yellow solid in 25% yield. 1H NMR
(400 MHz, CDCl3): d(TMS)=7.56 (m, J=2 Hz, 8H), 7.28 (m, J=8.4 Hz,
4H), 7.11 (m, 18H), 7.03 ppm (m, 16H); IR (KBr), n˜ =2925, 2856, 1509,
1491, 1462, 1443, 1378, 822, 700 cmÀ1; HRMS (MALDI-TOF): m/z calcd
for C68H46: 862.3600 [M]+; found: 862.3597.
Compounds 2b and 2c: Compound 2a (0.30 g, 0.35 mmol), 6 (0.53 g,
1.39 mmol), and diphenyl ether (5 mL) were added to a round-bottom
flask. After heating at reflux for 48 h under nitrogen, the solution was
cooled to room temperature and diluted with ethanol. The precipitate
was separated by filtration and washed with ethanol. The crude product
was purified by silica-gel column chromatography with petroleum ether
as eluent. Compounds 2b and 2c were obtained in 39 and 37% yield, re-
1
spectively. 2b: H NMR (400 MHz, CDCl3): d(TMS)=7.52 (m, 8H), 7.09
(m, 18H), 6.88 (m, 28H), 6.70 (d, J=6.8 Hz, 4H), 6.59 (d, J=8.4 Hz,
4H), 6.55 ppm (d, J=8.4 Hz, 4H); IR (KBr), n˜ =3026, 2925, 2347, 1730,
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4H), 6.61 (d, J=8.0 Hz, 4H), 6.52 ppm (d, J=8.4 Hz, 4H); IR (KBr), n˜ =
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Received: October 27, 2012
Revised: January 7, 2013
Published online: March 5, 2013
5624
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Chem. Eur. J. 2013, 19, 5617 – 5624