New electron-donor/acceptor-substituted tetraphenylethylenes: Aggregation-induced emission with tunable emission color and optical-waveguide behavior

Article abstract of DOI:10.1002/asia.201300451

Herein, we report the synthesis of new tetraphenylethylene derivatives 1-5 that feature electron-donating (methoxy) and -accepting (dicyanomethane) groups as AIE-active molecules with tunable emission colors. The crystal structures of compounds 3 and 4 ar

Full text of DOI:10.1002/asia.201300451

FULL PAPER
FULL PAPER
Say hello wave goodbye: New elec-
tron-donor/acceptor-substituted tetra-
phenylethylenes exhibit aggregation-
induced emission with tunable emis-
sion colors that range from blue to
red. In addition, their microcrystals
show 2D optical-waveguide behavior.
Aggregation-Induced Emission
Xinggui Gu, Jingjing Yao,
Guanxin Zhang,* Chuang Zhang,
Yongli Yan, Yongsheng Zhao,
Deqing Zhang*
&&&& — &&&&
New Electron-Donor/Acceptor-Substi-
tuted Tetraphenylethylenes: Aggrega-
tion-Induced Emission with Tunable
Emission Color and Optical-Wave-
guide Behavior
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Guanxin Zhang, Deqing Zhang et al.
DOI: 10.1002/asia.201300451
New Electron-Donor/Acceptor-Substituted Tetraphenylethylenes:
Aggregation-Induced Emission with Tunable Emission Color and Optical-
Waveguide Behavior
Xinggui Gu, Jingjing Yao, Guanxin Zhang,* Chuang Zhang, Yongli Yan,
Yongsheng Zhao, and Deqing Zhang*[a]
Dedicated to Professor Chunli Bai on the occasion of his 60th birthday
Abstract: Herein, we report the synthe-
sis of new tetraphenylethylene deriva-
tives 1–5 that feature electron-donating
(methoxy) and -accepting (dicyanome-
thane) groups as AIE-active molecules
with tunable emission colors. The crys-
tal structures of compounds 3 and 4 are
described and the intermolecular inter-
actions within their crystals agree with
the observation that they exhibit strong
solid-state emission. Compounds 1–4
exhibit typical AIE behavior and their
emission maxima are red-shifted in the
order: 1<2<3<4. Such red-shifts are
ascribed to the fact that intramolecular
interactions between the electron
donor and the electron acceptor
become stronger with increasing
number of methoxy groups. The solid-
state emission colors of compounds 1–4
are successfully tuned from yellow-
green to red. Compound 5 shows AIE
behavior, but its emission is only slight-
ly enhanced after aggregation and its
solid shows a low quantum yield. Fur-
thermore, microplates of compound 3
exhibit 2D optical-waveguide behavior.
Keywords: aggregation · electronic
structure
· emission · structure–
activity relationships · tetraphenyl-
ethylenes
Introduction
over, various chemo/biosensors are constructed by taking
advantage of the AIE feature.[7,8] Accordingly, AIE mole-
cules have been intensively explored over the past ten years
and this emerging area has attracted more and more atten-
tion.[9]
Organic molecules that exhibit strong emission in the solid
state have received increasing attention in recent years be-
cause of their promising applications in various areas, in-
cluding OLEDs (organic light-emitting diodes) and relevant
white-light-emitting devices.[1] Typically, organic fluoro-
phores are emissive in solutions, but they become weakly
fluorescent or non-fluorescent after aggregation or in the
solid state.[2] However, Tang and co-workers discovered cer-
tain molecules that exhibited abnormal fluorescent behav-
ior; they were weakly fluorescent (even non-fluorescent) in
solution, but they lit up significantly after aggregation. Such
unusual fluorescent phenomenon was referred to by the au-
thors as aggregation-induced emission (AIE).[3] Silole[4] and
tetraphenylethene (TPE)[5] are typical AIE molecules. These
AIE molecules have been successfully utilized as solid-state
emissive materials in OLEDs and in other devices.[6] More-
Most of the reported AIE molecules emit within the
wavelength range of blue and green light. For instance,
silole and tetraphenylethylene molecules become strongly
fluorescent after aggregation at about 480 nm.[4,5] Clearly,
AIE molecules with tunable emission color are desirable.
Tang and co-workers reported new AIE molecules with
emissions in the long-wavelength region by conjugating TPE
moieties at the periphery of normal fluorophores (e.g., pery-
lene bisimide, pyrene, naphthalene, anthracene, and phenan-
thracene).[10] The authors also reported new AIE molecules
by connecting two TPE moieties with conjugated groups,
such as benzo-2,1,3-thiadiazole and thiophene.[11] Herein, we
report an alternative strategy for developing new AIE mole-
cules with tunable emission colors by connecting electron-
donating and -accepting groups onto a TPE framework. The
molecular design is based on the consideration that the in-
corporation of electron-donating (methoxy) and -accepting
(dicyanovinyl) groups into a TPE framework will tune the
HOMO/LUMO energies and, hence, the emission wave-
lengths can be tuned. The number of methoxy groups in-
creases from compounds 1–5 (Scheme 1) and compounds 4
and 5 are different in the substitution pattern of the dicya-
novinyl moiety. The results show that compounds 1–4, which
feature methoxy and dicyanovinyl groups, show AIE behav-
[a] X. Gu, J. Yao, Dr. G. Zhang, C. Zhang, Dr. Y. Yan,
Prof. Dr. Y. Zhao, Prof. Dr. D. Zhang
Beijing National Laboratory for Molecular Sciences
Organic Solids Laboratory and Photochemistry Laboratory
Institute of Chemistry, Chinese Academy of Sciences
Beijing 100190 (P. R. China)
Fax : (+86)10-62562693
E-mail: dqzhang@iccas.ac.cn
gxzhang@iccas.ac.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201300451.
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Scheme 2. Synthetic route to compound 1. Reaction conditions: a) TiCl4,
Zn in THF (31% yield); b) nBuLi, DMF, À788C (64% yield);
c) CH2(CN)2, Et3N, RT (95% yield).
tures were determined. Disappointingly, efforts to grow
good-quality crystals of compounds 1, 2, and 5 were unsuc-
cessful. The molecular structures of compounds 3 and 4 are
shown in Figure 1. Their bond lengths and angles are within
the typical range. As anticipated, both compounds 3 and 4
adopt twisted conformations and the phenyl rings are not
Scheme 1. Chemical structures of compounds 1–7.
ior with different emission colors that range from green to
red. Moreover, crystals of compound 3 display 2D optical-
waveguide behavior.
À
À
À
À
À
coplanar. For example, the C3 C4 C5 C6 C7 C8 phenyl
Results and Discussion
As an example, the synthesis of compound 1 is shown in
Scheme 2. Compound 1-Br was obtained by a McMurry re-
action in the presence of Zn and TiCl4 in 31% yield. Then,
compound 1-Br was reacted with nBuLi and DMF to yield
compound 1-CHO in 64% yield. Compound 1 was obtained
in almost-quantitative yield after the reaction of compound
1-CHO with dicyanomethane in the presence of Et3N. Com-
pounds 2–5 were synthesized in a similar manner (for the
synthetic details, see the Supporting Information). The
chemical structures of compounds 1–5 were characterized
by NMR spectroscopy and by MS (see the Experimental
Section).
Single crystals of compounds 3 and 4 suitable for X-ray
analysis were successfully obtained and their crystal struc-
Abstract in Chinese:
Figure 1. Molecular structures of compounds 3 and 4 depicted as thermal
ellipsoids.
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ring in compound 3 forms a dihedral angle of 71.718 with
À
À
À
À
À
the neighboring phenyl ring (C9 C10 C11 C12 C13 C14).
À
À
À
À
À
Similarly, in compound 4, the C3 C4 C5 C6 C7 C8
phenyl ring is not coplanar with the neighboring phenyl ring
À
À
À
À
À
(C17 C18 C19 C20 C21 C22), with a dihedral angle of
À
73.588. In compound 3, the C12 C15 bond length (1.448 ꢁ),
which connects the dicyanomethane group to the TPE
framework, is comparably shorter than that of the respective
À
C27 C30 bond (1.462 ꢁ) in compound 4; however, the
À
C15 C16 bond (1.356 ꢁ) in compound 3 is relatively longer
À
than the respective C30 C31 bond (1.324 ꢁ) in compound
4. Such a difference can be attributed to the intramolecular
interactions between the electron-donor and -acceptor
groups within compounds 3 and 4. The addition of one more
methoxy group in compound 4 will enhance the electron-do-
nating ability of the TPE framework and, accordingly, it is
expected that the interactions between the electron-donor
and -acceptor groups in compound 4 will be stronger than in
compound 3.
Figure 2. Normalized absorption spectra of compounds 1, 2, 3, 4, 6, and 7
in THF; inset shows the absorption spectra of compound 5 in THF. The
concentration of all compounds was 2.5ꢂ10À5 m.
The intermolecular orientation and arrangement within
the crystals of compounds 3 and 4 are shown in the Support-
ing Information, Figures S1 and S2, respectively. Intermolec-
À
ular p p interactions are not detected in either compounds
3 or 4; however, multiple short interatomic contacts exist
within the crystals: O1···H (2.629, 2.505 ꢁ), O2···H
(2.502 ꢁ), N1···H (2.621 ꢁ), and N2···H (2.697 ꢁ) interac-
tions in compound 3 and O2···H (2.648 ꢁ), O3···H (2.698,
2.645, 2.642 ꢁ), N1···H (2.608, 2.701 ꢁ), N2···H (2.658,
Figure 3. HOMO and LUMO of compounds 3 and 5, based on the DFT
calculations.
À
2.713 ꢁ) interactions in compound 4. Furthermore, C H···p
interactions are detected in compound 3 (2.799, 2.797, and
2.645 ꢁ) and compound 4 (2.840, 2.896, 2.761, 2.866, 2.839,
2.857, 2.648, 2.886, and 2.579 ꢁ). These weak intermolecular
interactions fix the molecular conformations of compounds
3 and 4 in the solid state, thus inhibiting the internal rota-
tions and block their non-radiative relaxation, according to
previous studies.[12] This result agrees well with the observa-
tion that both compounds 3 and 4 show strong emissions in
the solid state, as discussed below.
Figure 2 shows the absorption spectra of compounds 1–4
in solution, as well as those of compounds 6 and 7 for com-
parison. Compounds 1–4 exhibit new, broad absorptions at
around 394, 410, 425, and 440 nm, respectively, whereas
compounds 6 and 7 absorb below 350 nm. Clearly, the ab-
sorption maximum is red-shifted in the order: 1<2<3<4.
The appearance of such absorptions can be ascribed to in-
tramolecular interactions between the electron-donor (me-
thoxy) and -acceptor (dicyanomethane) groups in com-
pounds 1–4; furthermore, the number of methoxy groups in-
creases from compound 1 to compound 4 and, accordingly,
the intramolecular electron-acceptor interactions gradually
become stronger from compound 1 to compound 4. For ex-
ample, DFT calculations were performed for compound 3.
The HOMO is mainly localized on TPE and on the methoxy
groups, but the dicyanomethane group also makes a slight
contribution, as shown in Figure 3. Similarly, the LUMO is
mainly localized on the dicyanomethane group, but the TPE
fragment also contributes, albeit slightly. These calculation
results clearly indicate the presence of intramolecular inter-
action between the electron-donor and -acceptor groups in
compound 3.[13]
Compounds 3 and 5 are only different in terms of the sub-
stitution position of the dicyanomethane group, which is
connected to TPE at the para and meta positions, respective-
ly. However, their absorption spectra are completely differ-
ent and compound 5 only shows absorption at around
320 nm, as shown in Figure 2, inset. Thus, the electronic
structures of compounds 3 and 5 are largely affected by the
substitution position of the dicyanomethane group. Indeed,
this result is in agreement with the DFT calculations of com-
pound 5. As shown in Figure 3, the HOMO is completely lo-
calized on the TPE and methoxy groups, whereas the
LUMO completely resides on the dicyanomethane group.
Therefore, the intramolecular interactions between the elec-
tron-donor and -acceptor groups in compound 5 should be
rather weak. This result agrees with the difference between
the absorption spectra of compounds 3 and 5 (Figure 2 and
inset).
The fluorescence spectra of compounds 1–5 in solution
were also recorded. As expected, these compounds are
almost non-fluorescent in solution (Figure 4 and the Sup-
porting Information, Figure S3), owing to internal rotations,
according to previous studies.[2–5] However, the fluorescence
of compounds 1–4 “turns on” upon aggregation. As an ex-
ample, Figure 4 shows the fluorescence spectra of compound
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The emission properties of solid samples of compounds 1–
4 that precipitated out from their respective solutions in
THF after the addition of water were also examined. Table 1
summarizes the solid-state emission maxima of compounds
1–4, as well as their emission quantum yields and lifetimes.
Their emission quantum yields are relatively high, reaching
0.61 for the solid sample of compound 2. They also show
relatively long emission lifetimes in the nanosecond range.
Clearly, the solid-state emissions of compounds 1–4 are red-
shifted in the order: 1<2<3<4. Figure 5 shows fluores-
cence spectra and photographs of solid samples of com-
pounds 1–4 under UV illumination. For comparison, the
emission spectra of solids of compounds 6 and 7 are also in-
Figure 4. A) Fluorescence spectra of compound 3 (2.5ꢂ10À5 m) in THF
after the addition of various amounts of water (excitation wavelength:
430 nm). B) Plot of the relative fluorescence enhancement of compound
3 versus the volume fraction of water in THF/water mixtures; inset
shows photographs of solutions of compound 3 in THF and THF/water
(v/v, 5:95) under UV illumination (365 nm).
Figure 5. Normalized fluorescence spectra of (from left to right) com-
pounds 1, 2, 3, 4, 6, and 7 in the solid state; inset shows photographs of
compounds 1, 2, 3, 4, 6, and 7 under UV illumination (365 nm).
3 in THF after the addition of different amounts of water.
Clearly, the fluorescence intensity of compound 3 is signifi-
cantly enhanced when the volume percentage of water is
larger than 60%, as shown in Figure 4B. Such fluorescence
enhancement can be detected by the naked eye, as shown in
Figure 4B, inset, which shows photographs of compound 3
in THF and THF/water (5:95, v/v) under UV irradiation. As
shown in the Supporting Information, Figure S2, the fluores-
cence intensities of solutions of compounds 1, 2, and 4 in
THF also remarkably increase on the addition of water.
Such fluorescence enhancement for compounds 1–4 is due
to the formation of aggregates because these compounds
are not water soluble[14] and, thus, the addition of water to
their solutions in THF induces their aggregation, according
to previous studies.[2–5] Therefore, compounds 1–4
cluded in Figure 5. Clearly, the emission colors of com-
pounds 6 and 7 and of compounds 1–4 vary from blue to
green, yellow, orange, and even red. Thus, the emission
colors of TPE compounds can be tuned by linking electron-
donating (methoxy) and -accepting (dicyanomethane)
groups.
The fluorescence spectra of compound 5 in THF after the
addition of different amounts of water were also recorded.
After aggregation, compound 5 shows an emission at
around 595 nm, which is blue-shifted by 33 nm compared to
that of compound 3 (see the Supporting Information, Fig-
ure S3). This shift is probably due to the fact the weak intra-
molecular interactions between the electron-donor and -ac-
show typical AIE behavior. Furthermore, com-
pounds 1–4 show AIE emission maxima at 564, 603,
628, and 645 nm, respectively; thus, their emissions
after aggregation are red-shifted with increasing
number of methoxy groups. Accordingly, the emis-
sion colors of compounds 1–4 after aggregation can
be successfully tuned, again owing to the fact that
intramolecular interactions between the electron-
donor and -acceptor groups become stronger with
increasing number of methoxy groups in com-
pounds 1–4.[15]
Table 1. Photophysical properties of solid compounds 1–5.
Compound
Fl (lmax) [nm]
Ff[a]
t1 [ns]/A1 [%]
t2 [ns]/A2 [%]
<t>[b] [ns]
1
2
3
4
5
564
603
628
645
595
0.54
0.61
0.52
0.48
0.03
0.508/58.2
0.564/45.8
0.575/43.1
0.459/46.5
2.058/31.9
3.223/41.8
3.011/54.2
2.646/56.9
4.195/53.5
9.851/68.1
1.643
1.890
1.753
2.458
7.365
[a] Ff was measured by using a calibrated integrating sphere system. [b] An apparent
decay time constant, <t>, was determined by using the relationship <t> =ꢀ(Aiꢂti)/
ꢀAi (i=1Àn, nꢀ2–3), where ti and ai represent the individual exponential decay-time
constant and the corresponding pre-exponential factor, respectively.[16] Fl=fluores-
cence.
ACHTUNGTRENNUNG
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ceptor groups in compound 5, as discussed above. As shown
in the Supporting Information, Figure S3, the fluorescence
of compound 5 is also enhanced after aggregation in THF/
water (5:95, v/v). However, the aggregation-induced fluores-
cence enhancement for compound 5 is remarkably small
compared to that for compound 3 under the same condi-
tions. As listed in Table 1, the emission quantum yield of
a solid sample of compound 5 is 0.03, much lower than that
of compound 3 (F=0.52). One possible explanation for this
result is that the intermolecular packing within the aggre-
gates of compound 5 is loose[17] and, as a result, the internal
rotations are only inhibited for a limited number of mole-
cules within the aggregates, thus leading to a slight fluores-
cence enhancement. However, the emitted molecules within
the solid sample of compound 5 exhibit a relatively long
emission lifetime (Table 1).
Microplates of compound 3 (quasi-rectangular shape)
were successfully obtained by crystallization. Near-field
scanning optical microscopy (NSOM) was used to investi-
gate the solid-state emission behavior of microplates of
compound 3. Figure 6A shows the photoluminescence (PL)
of microplates of compound 3 under UV illumination (330–
380 nm). Clearly, bright, red-light emissions were detected
from the four edges, whilst those from the body of micro-
plates were remarkably weak. Such solid-state emission be-
havior is characteristic for optical waveguides.[18] As shown
in Figure 6B, red-light emissions were detected at six spots
around the edges of the microplate of compound 3 after ex-
citation in its center with a focused laser (351 nm). In gener-
al, the emission light can only be observed at the local area
of the excited position. The appearance of the out-coupling
light at the edges of the microplates of compound 3 is a typi-
cal characteristic of 2D waveguide behavior. Because the
waveguided light is generated from the PL, microplates of
compound 3 can be classified as active 2D waveguides,
based on previous reports.[19]
The corresponding emission spectra at the six spots and in
the center were collected (Figure 6C). Compared to that at
the center, the emission spectra at the six spots are both
red-shifted and weakened. Because there is overlap between
the corresponding absorption and fluorescence spectra of
compound 3 in the solid state (see the Supporting Informa-
tion, Figure S4), self-absorption may be responsible for the
observed red-shifts and optical loss. In addition, the optical
loss can be also induced by: 1) the effect of the glass sub-
strate and 2) Rayleigh scattering, owing to defects within
the microplates, which will lead to local variation of the re-
fractive index within the microplates.[18,19]
Figure 6. A) Photoluminescence (PL) image of the microplates of com-
pound 3. B) Micro-area PL image that was obtained by exciting the
center of the microplate of compound 3. C) Corresponding spatially re-
solved PL spectra at the excitation position (A0) and of the out-coupled
light (A1–A6).
guided emissions were red-shifted and weakened compared
to the respective emissions at the excited spots (see the Sup-
porting Information, Figure S5).
Alternatively, guided red-light emissions were only detect-
ed at the two ends of the edge of the microplate of com-
pound 3 at which the excitation laser was focused (see the
Supporting Information, Figure S5). When the excitation
laser was focused on one of the four corners of the micro-
plate of compound 3, the guided red-light emission mainly
appeared at the respective end of the edge (see the Support-
ing Information, Figure S5). The emission spectra at the re-
spective ends of the edges were recorded; similarly, the
Conclusions
New tetraphenylethylene derivatives 1–5, which feature
electron-donating (methoxy) and -accepting (dicyanome-
thane) groups, have been designed and investigated as AIE-
active molecules with tunable emission colors. Absorption
spectroscopic analysis revealed that intramolecular electron-
donor/acceptor interactions existed within compounds 1–4.
Crystal structures of compounds 3 and 4 were also deter-
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Guanxin Zhang, Deqing Zhang et al.
Optical-Waveguide Behavior
mined. Compounds 1–4 exhibited typical AIE behavior and
their emission maxima were red-shifted in the order: 1<2<
3<4. Such red-shifts are due to the fact that intramolecular
interactions between the electron-donor and electron-ac-
ceptor groups become stronger on increasing the number of
methoxy groups in compounds 1–4. The solid-state emission
of compounds 1–4 was also investigated; these compounds
exhibited high emission quantum yields and their emission
colors varied from yellow to red. Interestingly, alteration of
the substitution pattern of the dicyanomethane group from
para (in 3) to meta (in 5) significantly affected the emissive
feature of compound 5. Compound 5 showed AIE behavior,
but its emission was only slightly enhanced after aggregation
and its solid showed a low quantum yield. Furthermore, mi-
croplates of compound 3 exhibited 2D optical-waveguide
behavior. These results indicate that the connection of elec-
tron-donating and -accepting groups onto the TPE frame-
work is a useful strategy for inventing new AIE-active mole-
cules with tunable emission colors. Further functionalization
of these new AIE molecules (in particular for compound 4
with red AIE) is underway for applications in biosensing
and bioimaging.
To measure the micro-area PL spectra of microplates of compound 3,
a dispersion of the microplates over a glass cover-slip was excited with
a UV laser (l=351 nm, Beamlok, Spectra-Physics). The excitation laser
was filtered with a band-pass filter (330–380 nm) and then focused to
excite the microplates with an objective lens (ꢂ50, N.A.=0.80; N.A., nu-
merical aperture).
Typical Synthesis of Compound 1
Both compounds 1-Br and 1-CHO were synthesized according to litera-
ture procedures.[21] 1-CHO (360 mg, 1.0 mmol) and CH2(CN)2 (99.8 mg,
1.5 mmol) were dissolved in dry CH2Cl2 (10 mL) and one drop of Et3N
was added to the solution. The mixture was stirred for about 2 h at RT.
Then, the mixture was washed with water (3ꢂ50 mL) and dried with an-
hydrous Na2SO4. After removal of the solvents, the residue was purified
by column chromatography on silica gel to afford compound
1 (387.5 mg). Compounds 2–5 were synthesized in a similar manner.
1
Compound 1: Yield: 95%; H NMR (400 MHz, CDCl3): d=7.65 (d, 2H),
7.61 (s, 1H), 7.22–7.08 (m, 11H), 7.07–6.94 ppm (m, 6H); 13C NMR
(100 MHz, CDCl3): d=159.1, 151.1, 144.0, 142.7, 142.6, 142.5, 139.2,
132.4, 131.2, 131.1, 130.2, 128.8, 128.0, 127.7, 127.3, 127.0, 114.0, 112.8,
81.2 ppm; HRMS (EI): m/z calcd for C30H20N2: 408.1626; found:
408.1632; elemental analysis calcd (%) for C30H20N2·0.1CH2Cl2: C 86.70,
H 4.88, N 6.72; found: C 86.73, H 4.95, N 6.83.
1
Compound 2: Yield: 95%; H NMR (400 MHz, CDCl3): d=7.66 (d, 1H),
7.64–7.58 (m, 2H), 7.16 (t, 8H), 7.03 (d, 4H), 6.92 (d, 2H), 6.65 (t, 2H),
3.77–3.74 ppm (d, 3H); 13C NMR (100 MHz, CDCl3): d=159.1, 158.6,
151.6, 151.5, 143.7, 143.0, 142.9, 138.3, 138.2, 135.1, 132.6, 132.5, 132.4,
131.3, 130.3, 130.2, 128.6, 128.1, 128.0, 127.6, 127.3, 126.8, 114.0, 113.4,
113.1, 112.8, 81.0, 55.1, 55.0 ppm; HRMS (EI): m/z calcd for C31H22N2O:
438.1732; found: 438.1738; elemental analysis calcd (%) for
C31H22N2O·0.1CH2Cl2: C 83.56, H 5.01, N 6.27; found: C 83.30, H 5.00,
N 6.23.
Experimental Section
General
All chemicals were purchased from Alfa Aesar and used without further
purification. Water was purified by using a Millipore filtration system.
1H NMR and 13C NMR spectra were recorded on a Bruker Avance
400 MHz spectrometer. MS (MALDI-TOF) were recorded on
1
Compound 3: Yield: 95%; H NMR (400 MHz, CDCl3): d=7.64 (d, 2H),
7.60 (s, 1H), 7.15 (d, 5H), 6.99 (d, 2H), 6.96–6.84 (m, 4H), 6.65 (dd, 4H),
3.77 (s, 3H), 3.74 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=159.0,
158.8, 158.5, 152.0, 143.5, 143.1, 137.4, 135.3, 135.2, 132.7, 132.6, 132.4,
131.3, 130.3, 128.4, 128.0, 126.7, 114.1, 113.4, 113.0, 112.9, 80.7, 55.1,
55.0 ppm; HRMS (EI): m/z calcd for C32H24N2O2: 468.1838; found:
468.1845; elemental analysis calcd (%) for C32H24N2O2·0.05CH2Cl2:
C 81.42, H 5.14, N 5.93; found: C 81.27, H 5.12, N 6.02.
a
BEFLEX III spectrometer. Absorption spectra were recorded on
a JASCO V-570 UV/Vis spectrophotometer. Steady-state fluorescence
spectra were recorded on Hitachi (F-4500) spectrophotometers at 258C.
All photographs were taken with a Canon digital camera. Density func-
tional theory (DFT) calculations were performed at the B3LYP/6-31G*
level of theory by using the Gaussian 09 program package (revisio-
n A.02).[20]
1
Compound 4: Yield: 95%; H NMR (400 MHz, CDCl3): d=7.64 (d, 2H),
7.60 (s, 1H), 7.16 (d, 2H), 6.92 (dd, 6H), 6.67 (d, 6H), 3.76 ppm (s, 9H);
13C NMR (100 MHz, CDCl3): d=159.1, 158.7, 158.4, 158.2, 152.3, 142.6,
137.1, 135.6, 135.5, 132.7, 132.5, 132.4, 130.3, 128.4, 114.2, 113.4, 113.3,
113.1, 112.9, 80.5, 55.1 ppm; HRMS (EI): m/z calcd for C33H26N2O3: m/z
498.1943; found: 498.1949.
Crystal-Structure Analysis
Crystals of compounds 3 and 4 were grown by the slow evaporation of
their solutions in CH2Cl2/petroleum ether. All diffraction data were col-
lected on a Rigaku Saturn diffractometer with a CCD area detector. All
calculations were performed by using SHELXL97 and the crystallograph-
ic software packages. CCDC 889341 (3) and CCDC 889342 (4) contain
the supplementary crystallographic 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.
1
Compound 5: Yield: 95%; H NMR (400 MHz, CDCl3): d=7.77 (d, 1H),
7.53 (s, 1H), 7.39 (s, 1H), 7.28 (s, 2H), 7.13 (s, 3H), 7.00 (d, 2H), 6.93 (d,
4H), 6.65 (t, 4H), 3.76 (s, 3H), 3.74 ppm (s, 3H); 13C NMR (100 MHz,
CDCl3): d=159.9, 158.4, 158.3, 146.1, 143.1, 142.1, 137.6, 136.8, 135.3,
135.2, 134.6, 132.6, 132.4, 131.2, 130.5, 129.0, 128.0, 127.2, 126.6, 113.7,
113.3, 113.0, 112.4, 82.2, 55.1, 55.0 ppm; HRMS (EI): m/z calcd for
C32H24N2O2: 468.1838; found: 468.1843; elemental analysis calcd (%) for
C32H24N2O2: C 82.03, H 5.16, N 5.98; found: C 81.95, H 5.40, N 5.90.
Photophysical Studies
Quantum efficiencies of compounds 1–5 in the solid state were deter-
mined on a FLSP 920 fluorescence spectrometer with a calibrated inte-
grating sphere system. Fluorescence lifetimes of compounds 1–5 were
measured, based on time-resolved PL experiments with a regenerative
amplified Ti:sapphire laser (Spectra-Physics, Spitfire) at 400 nm (pulse
width: 150 fs, second harmonic). The PL spectra were recorded by using
a streak camera (C5680, Hamamatsu Photonics) that was attached to
a polychromator (Chromex, Hamamatsu Photonics), for which the tem-
poral and spectroscopic resolutions of the detector were about 10 ps and
2 nm, respectively. All of the spectroscopic measurements were per-
formed at RT.
Acknowledgements
This research was financially supported by the Chinese Academy of Sci-
ences, the NSFC, and the State Key Basic Research Program. This work
was also supported by the China–Germany Joint Project (TRR61).
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Received: April 2, 2013
Published online: && &&, 0000
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ÝÝ These are not the final page numbers!