Dinitriles bearing AIE-active moieties: Synthesis, E/Z isomerization, and fluorescence properties

Article abstract of DOI:10.1002/chem.201406128

Dinitriles bearing aggregation-induced emission (AIE)-active moieties [tetraphenylethylene (TPE) or diphenylphenanthrene (DPP)] were prepared. Compounds 4 (TPElinked) and 8 (DPP-linked) showed considerably redshifted emission resulting from their large St

Full text of DOI:10.1002/chem.201406128

DOI: 10.1002/chem.201406128
Full Paper
&
Aggregation-Induced Emission
Dinitriles Bearing AIE-Active Moieties: Synthesis, E/Z
Isomerization, and Fluorescence Properties**
Thiago Teixeira Tasso, Taniyuki Furuyama, and Nagao Kobayashi*[a]
Abstract: Dinitriles bearing aggregation-induced emission
(AIE)-active moieties [tetraphenylethylene (TPE) or diphenyl-
phenanthrene (DPP)] were prepared. Compounds 4 (TPE-
linked) and 8 (DPP-linked) showed considerably redshifted
emission resulting from their large Stokes shifts and also
strong fluorescence in the aggregated and solid states. Pure
E and Z stereoisomers of both dinitriles were easily separat-
ed, and their isomerization equilibria and fluorescence prop-
erties were investigated. In addition to their pronounced
AIEE behavior, 4 and 8 also showed various reversible chro-
mic responses to external stimuli, namely, solvato-, piezo-,
vapo-, and thermochromism, which make them potential
candidates for smart materials.
Introduction
on aggregation intramolecular rotations become restricted and
the radiative channel is opened. Furthermore, the propeller-
shaped orientation of the phenyl rings imposes severe steric
hindrance on the chromophore unit, which prevents p–p ag-
gregation and fluorescence quenching. In most cases, however,
TPE-modified fluorophores show blue/green fluorescence[9]
due to small p conjugation and absence of intramolecular
charge-transfer transitions.
The demand for next-generation dyes that can effectively
absorb and emit light in the near-infrared (NIR) region has in-
creased recently due to their applicability in solar cells,[1] as
probes for bioimaging,[2] and as photosensitizing agents.[3] In
this regard, p-conjugated organic compounds are good candi-
dates, since their properties can be fine-tuned by means of ap-
propriate synthetic modifications. Redshifted absorption/emis-
sion can be achieved by lowering the energy gap between the
HOMO and LUMO levels of the chromophores through exten-
sion of the p conjugation[4] and/or modification with push–pull
substituents.[5] However, most p-conjugated planar fluoro-
phores suffer from aggregation-caused quenching, in which
their emission in the solid state is completely quenched due to
formation of excimers.[6] This is a serious limitation to their ap-
plicability in imaging and efficiency in photovoltaic devices
such as OLED displays, since strong luminescence in the solid/
aggregate state is crucial for proper color contrast in these
fields.
In an attempt to obtain novel AIE fluorophores with redshift-
ed absorption/emission, we designed the TPE-modified dinitrile
4 (Scheme 1). The vinylene bridge is expected to expand the
overall p conjugation of the molecule by communicating be-
Recently, a new class of chromophores showing weak emis-
sion in solution and strong emission in the solid state owing
to aggregation-induced emission (AIE) behavior was discov-
ered,[7] and this opened the way for the design of improved
compounds and advanced materials.[8] The tetraphenylethylene
(TPE) moiety has been widely used for the design of AIE-active
compounds due to its ease of preparation and outstanding AIE
effect.[6a] The rotatable phenyl rings are responsible for nonra-
diative deactivation of the excited state in solution, whereas
Scheme 1. Molecular structures of dinitriles 4 and 8.
tween the TPE moieties, while the two cyano groups can en-
hance its polarizability to result in large Stokes shifts, and thus
their emission may occur at lower energy. Since the fluores-
cence turn-on of AIE-active chromophores is directly related to
the rotational freedom of the phenyl rings in the packing
structure, we also synthesized dinitrile 8 containing diphenyl-
phenanthrene (DPP) moieties. DPP is a TPE analogue in which
two of the four benzene rings are locked by a covalent bond
to form a phenanthrene unit. The photophysical properties of
partially locked TPE derivatives have already been reported,[10]
but these studies were limited to simple model molecules,
[a] T. T. Tasso, Dr. T. Furuyama, Prof. Dr. N. Kobayashi
Department of Chemistry, Graduate School of Science
Tohoku University, Sendai, 980-8578 (Japan)
E-mail: nagaok@m.tohoku.ac.jp
[**] AIE: aggregation-induced emission.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201406128.
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mainly to verify the restriction of intramolecular rotation mech-
anism.
DPP derivative 5 as the sole product, since the methyl group is
responsible for regioselective oxidation of the closest phenyl
ring.[13] To illustrate this, the same oxidative reaction was car-
ried out with compound 3 as precursor, and a mixture of two
isomers was obtained in a 6:1 ratio (Scheme S1 in the Support-
Herein, we show that phenyl locking in expanded structures
such as dinitriles 4 and 8 can lead to intriguing differences in
the properties of these compounds. Since the E/Z isomers of
both 4 and 8 could be easily separated by conventional
column chromatography, we also investigated their photo-
physical properties separately. This is a rare case in the chemis-
try of AIE-active chromophores, since the isolation of stereoiso-
mers of TPE derivatives is rather difficult.[11] Not only different
fluorescence profiles, but also distinct chromic responses to ex-
ternal stimuli, were found for the stereoisomers of 4 and 8.
Hence, we believe our work can further contribute to enriching
the understanding of the AIE phenomenon.
1
ing Information), as confirmed by H NMR spectroscopy. This is
explained by the electron-withdrawing nature of the cyano
group, which removes electron density from the closest
phenyl rings, making it more favorable for the reaction to
occur on the opposite side of the TPE moiety.
There are very limited reports on the distinct AIE behavior of
pure E/Z stereoisomers, due to the difficulty of the separation
step. Long alkyl chains can be attached to a TPE derivative to
increase the size of the molecule and facilitate the separation
of stereoisomers, as shown by Tang and co-workers.[11a] Howev-
er, the crystallinity of the pure isomers was lowered by the
long alkyl chains, and this prevented their characterization in
the solid state by single-crystal X-ray analysis. In our case, pure
E and Z isomers of both 4 and 8 were easily separated by
simple chromatography on silica gel without any modification
of the molecular structure. The structures of the pure isomers
were also unambiguously elucidated by single-crystal X-ray dif-
fraction (see below).
Results and Discussion
Synthesis
The synthetic route for dinitriles 4 and 8 is shown in Scheme 2.
Compounds 3 and 7 were prepared by the Kolbe nitrile syn-
thesis, followed by dimerization in the presence of a strong
base. This is a conventional procedure for the preparation of
dinitriles due to its straightforward steps and moderate to
good yields.[12] Dinitriles 4 and 8 were obtained as mixtures of
E and Z isomers. Oxidation of the TPE unit of 1 generated the
E/Z Photoisomerization in Solution
1
The distinct H NMR spectra of 4 and 8 allowed their unambig-
uous characterization, as well as a clear investigation of the E/Z
isomerization process (Figure 1). Peaks of 4Z at about d=7.06
and 6.95 ppm (Figure 1d) are absent for 4E, and the low-field
doublet at d=7.54 ppm is exclusive to the latter (Figure 1a). In
the spectra of 8, on the other hand, the phenanthrene proton
signals are considerably shifted to low field compared to the
phenyl protons, and larger chemical shifts are observed for the
E form. E/Z isomerization on UV irradiation is commonly ob-
served in olefins, and a detailed study on this kind of equilibri-
um is important to obtain information about the stability of
the stereoisomers.[14]
To obtain quantitative data for the isomerization equilibria
of 4 and 8, the sample concentration, distance from the UV
lamp, and time of irradiation were fixed. Starting from solu-
tions of pure E and Z isomers, the isomerization reaction clear-
ly proceeded for both 4 and 8, as shown in Figure 1 and the
Supporting Information (Figures S1 and S2). The interconver-
sion rates were initially fast at the beginning and noticeable
even in the first minutes of irradiation, and slowed down until
equilibrium was reached (Figure 2). Interestingly, not only were
the isomerization kinetics approximately twice as fast for 8 (ca.
90 min) compared to 4 (ca. 180 min), but also the final mixture
differed from the 50/50 E/Z ratio in both cases. When equilibri-
um was reached, the E/Z ratios found for 4 and 8 were 59/41
and 46/54, respectively, that is, the most stable stereoisomer is
also different for these dinitriles. No isomerization was ob-
served on irradiation of the samples with light in the solid
state, due to the locked conformation of the compounds in
the packing structure. To further support the observed results,
we carried out theoretical calculations on the total energy of
Scheme 2. Synthesis of the compounds studied in this work. Reagents and
conditions: i) NBS, benzoyl peroxide, CCl4, reflux, overnight; ii) KCN, DMSO,
908C, 2 h; iii) NaOMe, I2, diethyl ether, 08C, 30 min; iv) 2,3-dichloro-5,6-dicya-
nobenzoquinone, MeSO3H, CH2Cl2, 08C, 30 min; v) NaOMe, I2, THF, ꢀ358C,
10 min.
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Figure 2. Plot of the percentage of E isomer present in solutions of the dini-
triles after each UV irradiation interval.
up the fluorescence pathway. The 12-fold increase in the FF
values of 4E and 4Z that was observed on aggregation in solu-
tion confirms the aggregation-induced emission enhancement
(AIEE) behavior (Supporting Information, Figure S4). Dinitriles
8E and 8Z, on the other hand, showed almost constant emis-
sion efficiency up to 80% water, followed by a sharp increase
in fluorescence for the mixture with 99% water. An approxi-
mate fourfold increase in FF was observed for 8E and 8Z,
which thus show a weaker AIEE effect compared to 4.
Compounds 4 and 8 are composed of TPE/DPP and CN
units, which act as electron-donating and electron-accepting
moieties, respectively. This push–pull structure results in transi-
tions with strong intramolecular charge-transfer (CT) character,
which can be tuned by varying the polarity of the solution.
With this in mind, we investigated the absorption and emis-
sion spectra of these compounds in a series of solvents, as
shown in Figure 4A and B for 4E and 8Z and Figure S5 of the
1
Figure 1. Top : H NMR spectra of CDCl3 solutions of 4E and 4Z before (a, d)
1
and after UV irradiation for 180 min (b, c). Bottom: H NMR spectra of CDCl3
solutions of 8E and 8Z before (e, h) and after UV irradiation for 90 min (f, g).
the molecules (see Supporting Information for details). The dif-
ference in Gibbs free energy of the E and Z isomers (DG=
GEꢀGZ) for 4 was found to be ꢀ0.58 kcalmolꢀ1, which indicates
a slightly higher thermodynamic stability of the E form. In con-
trast, the positive DG value of 28.4 kcalmolꢀ1 found
for 8 suggests higher stability of the Z isomer. These
trends support the experimental data obtained by
1H NMR spectroscopy.
Photophysical Properties in Solution
The AIE behavior of the stereoisomers was investi-
gated in THF/water (Figure 3 and Figure S3 in the
Supporting Information). The dinitriles are emissive
to some extent in pure THF solution, with a broad
emission peak around 640 nm for 4 and 560 nm for
8. The fluorescence intensity of nitriles 4E and 4Z de-
creased progressively with increasing fraction of
water in the mixtures, due to the increase in the po-
larity of the medium. In mixtures containing 60%
water, the fluorescence peak was blueshifted and the
intensity sharply increased with increasing water
content, until a maximum quantum yield FF of
about 40% was reached in pure water, which is simi-
lar to the FF values found in the solid state (see
above). This indicates that the molecules aggregate
with increasing amount of poor solvent above 60%;
this prevents rotation of the phenyl rings and opens
Figure 3. Fluorescence spectra of A) 4E and C) 8Z and fluorescence quantum yields FF of
B) 4E/4Z and D) 8E/8Z in water/THF mixtures.
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the dipole moments in the excited and ground states, respec-
tively. The calculation of the solvent polarity parameter is
shown in Equation (S1) and all data are summarized in Table S1
(Supporting Information). The correlation plots between Dn
and Df for the dinitriles (Figure 4C) show an ascendant linear
tendency with increasing solvent polarity, that is, solvatochro-
micity. On linear fitting, large slopes were found for 4E (7940)
and 4Z (7500), which represent stronger solvatochromism than
for 8E (3860), 8Z (6180), and those reported for other donor–
acceptor AIE-active chromophores.[16] In addition, the larger
Stokes shifts observed for 4 compared to 8 further push the
emission towards the NIR region, and makes them more ap-
propriate candidates for the design of NIR-emitting materials.
The photophysical data of these dinitriles in solution showed
that the control of the number of rotatable rings in these
types of chromophore not only affects their AIE(E) output, but
also can be used to fine-tune their emission profile and solva-
tochromic response.
Photophysical Properties in the Solid State
The AIEE behavior observed for the dinitriles in water/THF sug-
gests that these compounds should also have strong fluores-
cence in the solid state. Indeed, the fluorescence spectra of
dried powders of 4 and 8 showed a strong emission band in
the 500–600 nm region, which is broader than in solution and
extends further into the NIR region (Figure S7 of the Support-
ing Information). Their emission maxima and fluorescence
quantum yields are summarized in Table 1.
Table 1. Emission wavelength maxima lem and absolute fluorescence
quantum yields FF of fluorophore samples with different morphologies.[a]
Figure 4. Absorption and fluorescence spectra (excited at 390 nm) for A) 4E
and B) 8Z in different solvents. Interference peaks were removed for clarity.
C) Lippert–Mataga plots for all dinitriles.
Compd.
As-ob-
tained
Pressed
powder
Fumed
powder[b]
Film[c]
Aggregate[d]
powder
lem
FF lem
FF lem
FF lem
FF lem
FF
Supporting Information for 4Z and 8E. Although only small
changes in the absorption spectra of the four dinitriles were
observed, their emission spectra were significantly redshifted
on increasing the solvent polarity from toluene to ethanol. The
emission shift from 584 nm (toluene) to 639 nm (ethanol) for
4E, for example, was enough to produce a visible color change
in the solution from yellow to dark red (Figure S6 of the Sup-
porting Information). However, 8E and 8Z showed an initial
green fluorescence as a result of their blueshifted emission,
and the visible color change was marginal compared to 4. To
quantify the solvatochromism of these compounds we used
the Lippert–Mataga equation [Eq. (1)], which correlates the
Stokes shift Dn with the solvent polarity parameter Df[15]
[nm] [%] [nm] [%] [nm] [%] [nm] [%] [nm] [%]
4E
4Z
8E
8Z
549
587
576
591
52.2 579
47.9 599
52.3 580
25.1 591
45.4 549
43.7 579
59.9 560
24.8 558
43.2 601
55.5 613
57.9 569
45.5 585
50.9 590
44.7 637
28.9 564
22.8 572
41.8
33.7
26.9
16.8
[a] Excitation at 390 nm. [b] Fumed with CHCl3 for 3 min. [c] Prepared by
dropping a concentrated solution of the dinitrile in CHCl3 onto the sub-
strate. [d] At a water fraction of 99%.
Photofunctional materials that respond to thermal, optical,
and mechanical stimuli are promising for various applica-
tions.[17] As shown in Figure 5 and Figure S8 of the Supporting
Information, the emission band of 4E powder underwent
a 30 nm redshift from 549 to 579 nm on mechanical stimulus
(grinding or manually pressing), which was enough to produce
a visible color change in the powder from yellow to orange.
When the pressed powder was exposed to CHCl3 vapor for
3 min, the emission band blueshifted back to 549 nm, and the
original yellow color was regenerated. Indeed, the color
change was visible even during the first 10 s of exposure to
2 Df
hca3
2
ð1Þ
Dn ¼ na ꢀ nf ¼
ðmE ꢀ mGÞ þconstant
where na and nf are the absorption and fluorescence peak
wavelengths, respectively, h is the Planck constant, c the speed
of light, a the Onsager solvent cavity radius, and mE and mG are
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Figure 5. Changes in the fluorescence spectra of A) 4E and B) 4Z on external
stimuli. Excitation at 365 nm.
Figure 6. Reversibility of the fluorescence emission wavelength of A) 4E and
B) 4Z on manual pressurization and fuming with CHCl3 or heating at 1408C
for 3 min.
CHCl3, and thus represents a rapid vapochromic response.
Compound 4Z showed a similar response, but the shift of the
emission band on pressing/fuming was smaller (20 nm), and
the color change was also less noticeable, mainly due to its
longer emission wavelength compared to 4E.
Exposure of the pressed powder to CHCl3, THF, and CH2Cl2
resulted in similar responses, whereas hexane and ethanol in-
duced a weaker emission response (data not shown). Since the
solubility of the dinitrile is much higher in the first three sol-
vents than the last two, the fluorescence change may involve
an interaction between 4E and solvent molecules, rather than
a response to solvent polarity.
was observed (Supporting Information, Figure S10). Interesting-
ly, whereas the FF values for the E isomers of 4 and 8 showed
no significant change during the pressurization/fuming or
pressurization/heating cycles, the values for the Z isomers
were dependent on the crystallinity of the sample. As shown
in Table 1 and Figure S10B (Supporting Information), 8Z in par-
ticular showed a remarkable decrease in fluorescence from the
fumed powder (45.5%) to the pressed powder (24.8%), which
was also reversible on cycling. This is an example of crystalliza-
tion-induced emission enhancement (CIEE), which has been
observed for only a very limited number of compounds to
date.[18] Similarly to the pressed powders, thin films of the dini-
triles (Figure 5 and Figure S8 in the Supporting Information)
showed redshifted emission bands owing to their amorphous
structure. A closer look at their fluorescence quantum yields
(Table 1) reveals that the values decrease from 4E to 8Z with
a similar trend to that observed for the aggregates in the
water/THF mixtures, while the FF values of the samples with
the best crystallinity (fumed powders) are high for all fluoro-
phores (43–58%). This indicates that the sample morphology,
and thus the molecular packing, has a strict relationship with
the position of the emission maxima and the fluorescence effi-
ciency.
We further investigated the fluorescence response of these
luminophores on thermal treatment of their powders. As
shown in Figure 6, heating pressed powders of 4E and 4Z at
1408C was also efficient for promoting reorganization of the
molecular packing and consequently blueshifted their emission
by 20–30 nm. For both pressurization/fuming and pressuriza-
tion/heating cycles, the samples showed good reversibility and
stability. The DPP-substituted dinitriles 8E and 8Z showed
piezo- and vapochromic behavior as well, with a color change
from orange (pressed powder) to yellow (fumed powder)
under the same experimental conditions (Supporting Informa-
tion, Figure S9). On the other hand, their emission response to
thermal treatment was much poorer than those of 4E and 4Z.
For 8E, no changes were observed in the fluorescence band at
1408C, even after several minutes of heating, and at 2108C the
emission maxima was shifted by only 12 nm. Compound 8Z
showed no thermal response, even on heating the sample
near its melting point (1908C) for several minutes. The pressur-
ization/fuming (8E and 8Z) and pressurization/heating (8E)
cycles were reversible, and no decomposition of the samples
X-ray Crystal Structures
To gain further insight into the organization of the molecules
in the solid state, single crystals of all the dinitriles were ob-
tained for X-ray diffraction analysis. The X-ray structures of the
dinitriles are shown in Figure 7. The phenyl rings in the TPE
units of 4E and 4Z are oriented in a propeller-shaped manner,
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mation, Figure S11). The as-obtained powder showed sharp re-
flection peaks due to its microcrystalline structure. On pressuri-
zation, the peaks became weaker and broader, and thus indi-
cated a more amorphous character of the powder due to par-
tial disruption of the molecular packing. After fuming with
CHCl3 for 3 min, the intensity and sharpness of the reflection
peaks were regenerated, and this suggests that CHCl3 mole-
cules are effective in reordering the microcrystalline structure.
Finally, the mechanochromic applicability was demonstrated.
The powder of 4E was dispersed on filter paper, and the Chi-
nese characters for “Tohoku University” were written by
scratching the paper with a spatula (Supporting Information,
Figure S12). Under UV irradiation, the yellow background fluo-
rescence and the orange emission from the characters pro-
duced strong contrast for a clear image of the written content.
On fuming the paper with CHCl3 or CH2Cl2, or heating it at
1408C for 5 min, the crystallinity of the scratched powder was
regenerated and the letters became invisible under UV light.
This writing/erasing process could be repeated reversibly with-
out decomposition of the chromophore, and thus the dinitriles
have potential applications for rewritable data storage, sens-
ing, and security printing.[21]
Figure 7. X-ray crystal structures (hydrogen atoms omitted) and packing dia-
grams of A) 4E, B) 4Z, C) 8E, and D) 8Z. The thermal ellipsoids are scaled to
50% probability. Solvent molecules are omitted for clarity.
with torsion angles varying between 41 and 638. The phenyl
rings connected to the central ethylene bridge are also twisted
from its plane, by 28 and 348 for 4E and 4Z, respectively. This
deviation from planarity leads to poorer overall conjugation in
the molecule and explains why the crystalline samples show
blueshifted emission compared to the amorphous state, in
which the phenyl moieties are more free to rotate. The larger
separation between the bulky TPE units in 4E compared to 4Z
supports the premise that 4E is more stable in solution. Com-
pounds 8E and 8Z showed more pronounced distortions, with
phenyl–phenanthrene torsion angles of 69–808 and phenan-
threne–ethylene angles of 35 and 408, respectively.
A closer look at the molecular structure of 8Z also suggests
the presence of intramolecular parallel-displaced p–p stack-
ing[19] between the phenanthrene units, with a centroid–cent-
roid separation Rcen of 4.46 ꢁ and parallel-displacement angle q
of 308 (Supporting Information, Scheme S2). This distance is
even shorter than those found for anthracene-based aromatic
compounds that show strong p–p interaction[20] and results in
an effective energetic contribution for this stereoisomer. Such
interaction may account for the higher thermodynamic stabili-
ty of 8Z over 8E in solution. No intermolecular p–p stacking
was found in the packing structure of the dinitriles, owing to
Conclusion
Modification of the blue-emitting TPE and DPP moieties with
electron-withdrawing cyano groups and vinylene linkages
yielded dinitriles 4 and 8 as pure E/Z isomers, which exhibited
redshifted absorption and emission bands as well as large
Stokes shifts. The E/Z isomerization experiments in solution
showed that the number of rotatable phenyl groups in the di-
nitriles determines the E/Z interconversion kinetics and ther-
modynamic stability of the stereoisomers due to the difference
in the bulkiness of the groups and the presence or absence of
intramolecular interactions. TPE-substituted dinitrile 4 showed
more pronounced fluorescence enhancement on aggregation
(12-fold increase) as well as larger Stokes shifts and solvato-
chromism compared to 8. On grinding or pressurization of the
powder samples of 4 and 8, their emission bands were red-
shifted by about 20–30 nm, which was enough to produce
a visible color change from yellow to orange (mechano/piezo-
chromism). Fuming the powders for several seconds was
enough to regenerate their original yellow color (vapochrom-
ism). Moreover, heating the samples for several minutes also
blueshifted their fluorescence emission (thermochromism). This
their twisted nature. However, intermolecular CꢀH···p and Cꢀ shows that the molecular organization in the packing structure
N···H interactions with distances of about 3.0 and 2.4 ꢁ were
observed, leading to locking of the phenyl rotors in the crystal.
The absence of p–p stacking and blocking of the rotation of
the phenyl rings are responsible for the strong fluorescence of
these compounds in the crystalline state.
has a critical influence on the fluorescence response. Interest-
ingly, 8Z is a rare example of CIEE, which demonstrates that
completely different properties may arise from stereoisomers
of a single AIE-active fluorophore. The AIEE behavior and the
various chromic responses observed for 4 and 8 make them
potential candidates for the design of smart materials for vari-
ous purposes.
To further interpret the mechanochromic behavior, we con-
ducted powder XRD measurements on 4E (Supporting Infor-
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and then the reaction mixture was quenched with saturated aque-
ous Na2S2O3. The organic layer was washed with water, dried over
MgSO4, filtered, and concentrated. The crude product was purified
by silica-gel column chromatography with CHCl3/hexane (1/2 v/v)
as eluent. Yield: 900 mg, 71%. MALDI-TOF-MS: m/z calcd for [M]+:
Experimental Section
Instrumentation
1H NMR and 13C NMR spectra were obtained on a Bruker AVANCE III
500 spectrometer. The spectra were referenced to the residual sol-
vent proton peaks as internal standard. MALDI-TOF mass spectra
were obtained on an AB Sciex 4800Plus TOF/TOF Analyzer. Elec-
tronic absorption spectra and fluorescence spectra were recorded
on JASCO V-570 and HITACHI F-4500 spectrophotometers, respec-
tively. Absolute fluorescence quantum yields were measured by
1
422.1; found: 422.9; H NMR in CDCl3: d=8.80 (s, 1H), 8.79 (d, J=
5.5 Hz, 1H), 7.69 (m, 2H), 7.53 (m, 4H), 7.25–7.12 (m, 9H), 4.78 ppm
(s, 2H); 13C NMR in CDCl3: d=139.36, 137.96, 136.96, 135.69,
132.14, 131.77, 131.01, 130.08, 129.73, 128.66, 127.99, 127.67,
127.38, 126.96, 126.63, 123.03, 122.51, 34.19 ppm.
2-(9,10-Diphenylphenanthren-3-yl)acetonitrile (7): In a round-
bottom flask, KCN (182 mg, 2.8 mmol) was dissolved in DMSO
using
a Hamamatsu C9920-03G calibrated integrating-sphere
system.
(10 mL) at 908C. Compound
6 (600 mg, 1.4 mmol) and NaI
(104.9 mg, 0.71 mmol) were then added to the flask and the mix-
ture allowed to react for 3 h. After cooling to room temperature,
the mixture was poured into 100 mL of satuated aqueous NaHCO3
and extracted with CHCl3. The organic layer was concentrated and
the crude product purified by silica-gel column chromatography
with CH2Cl2/hexane as eluent. Yield: 326 mg, 63%. MALDI-TOF-MS:
Materials and Methods
All solvents and reagents were used without purification unless
otherwise specified. Dehydrated DMSO was purchased from Wako
Pure Chemicals Industries Ltd., and CH2Cl2 and CCl4 were distilled
from CaH2 and stored over molecular sieves prior to use. N-Bromo-
succinimide (NBS) was recrystallized by slow cooling of a saturated
solution in boiling water. Compounds 1, 2, and 5 were synthesized
according to previous literature.[13,22] The isomerization experiments
were conducted by using NMR tubes containing 4.5 mm solutions
of pure 4E/4Z or 8E/8Z in CDCl3. The tubes were placed 5 cm from
a UV lamp (365 nm, 9.0 W) and were irradiated for 4 h, during
1
m/z calcd for [M]+: 369.1; found: 369.0. H NMR in CDCl3: d=8.80
(d, J=8.5 Hz, 1H), 8.76 (s, 1H), 7.70 (td, 1H), 7.57 (d, J=8.0 Hz,
1H), 7.52 (d, J=7.0 Hz, 1H), 7.48 (d, J=7.0 Hz, 1H), 7.39 (dd, 1H),
7.24–7.12 (m, 10H), 4.03 ppm (s, 2H); 13C NMR in CDCl3: d=139.26,
137.88, 136.82, 132.22, 131.82, 131.47, 130.98, 130.35, 129.48,
128.93, 128.01, 127.71, 127.17, 126.72, 126.12, 122.51, 121.86,
117.95, 24.10 ppm.
1
which the H NMR spectra were recorded at defined intervals. The
2,3-Bis(9,10-diphenylphenanthren-3-yl)but-2-enedinitrile
(8):
THF/water experiments were performed by preparing a 1.0 mm
stock solution of samples in THF and adding 20 mL of this solution
to each THF/water mixture with a final volume of 3 mL. After ho-
mogenizing the solution, the fluorescence quantum yields were
measured immediately.
Compound 7 (100 mg, 0.27 mmol), I2 (68.7 mg, 0.27 mmol), and
THF (5 mL) were placed in a round-bottom flask and cooled to
ꢀ358C. Sodium methoxide (Na 14 mg, 0.6 mmol) in methanol solu-
tion (1 mL) was then added dropwise to the stirred mixture, which
was left to react for further 10 min. The mixture was diluted with
CHCl3, washed with saturated aqueous Na2S2O3, and the organic
layer collected and dried over MgSO4. The E and Z isomers were
isolated by silica-gel chromatography with CHCl3/hexane (9/1) as
eluent. Yield: 14 mg of 8E (14%) and 10 mg of 8Z (10%). 8E: m.p.
>3008C; MALDI-TOF-MS: m/z calcd for [M]+: 734.27; found:
Synthesis
2-[4-(1,2,2-Triphenylvinyl)phenyl]acetonitrile (3): In
bottom flask, potassium cyanide (247 mg, 3.8 mmol) was dissolved
in dehydrated DMSO (20 mL) at 908C. Compound (1.5 g,
a round-
2
1
734.13;. H NMR in CDCl3: d=9.42 (s, 2H), 8.90 (d, J=8.4 Hz, 2H),
3.5 mmol) was then added to the mixture, which was stirred at the
same temperature for 2 h. After cooling the flask to room tempera-
ture, the reaction mixture was poured into water (100 mL) and ex-
tracted with ethyl acetate. The organic layers were collected, dried
over MgSO4, and the solvent removed. Purification by silica-gel
column chromatography with CHCl3/hexane (9/1 v/v) as eluent
yielded the pure compound as a yellow powder. Yield: 814 mg,
8.00 (d, J=8.6 Hz, 2H), 7.74 (t, 4H), 7.61 (d, J=7.5 Hz, 2H), 7.56 (t,
2H), 7.28–7.22 (m, 12H), 7.19–7.17 ppm (m, 8H). 8Z: m.p. 190–
1958C. MALDI-TOF-MS: m/z found: 734.15; 1H NMR in CDCl3: d=
8.95 (s, 2H), 8.47 (d, J=8.2 Hz, 2H), 7.60 (t, 2H), 7.56 (d, J=6.9 Hz,
2H), 7.52 (d, J=7.0 Hz, 2H), 7.40 (d, J=8.7 Hz, 2H), 7.36 (d, 2H),
7.23–7.10 (m, 16H), 7.03 ppm (m, 4H).
1
63%. H NMR in CDCl3: d=7.09–6.98 (m, 19H), 3.64 ppm (s, 2H).
2,3-Bis[4-(1,2,2-triphenylvinyl)phenyl]but-2-ene-dinitrile
(4):
Sodium methoxide (Na, 62 mg, 2.68 mmol) in methanol (3 mL) so-
lution was added dropwise to a mixture of 3 (500 mg, 1.34 mmol),
I2 (339 mg, 1.34 mmol), and diethyl ether (8 mL) over 20 min with
stirring at 08C. The mixture was allowed to react for 30 min, fil-
tered, and washed with cold methanol to remove any excess of
iodine. The title compound was obtained as a mixture of re-
gioisomers (4E and 4Z, 240 mg, 49%). Finally, 4E and 4Z were sep-
arated by silica-gel column chromatography with CHCl3 as eluent.
To avoid isomerization, solutions of pure isomers were protected
from light exposure during all procedures. 4Z: m.p. 210–2158C;
Acknowledgements
This work was partly supported by a Grant-in-Aids for Scientific
Research on Innovative Areas (25109502, “Stimuli-responsive
Chemical Species”), Scientific Research (B) (No. 23350095),
Challenging Exploratory Research (No. 25620019), and Young
Scientist (B) (No. 24750031) from the Ministry of Education,
Culture, Sports, Science, and Technology (MEXT). The authors
thank Prof. Takeaki Iwamoto and Dr. Shintaro Ishida (Tohoku
University) for the single-crystal X-ray measurements, and Dr.
Eunsang Kwon (Tohoku University) for the powder X-ray meas-
urements. Some of the calculations were performed by using
supercomputing resources at the Cyberscience Center of
Tohoku University.
1
MALDI-TOF-MS: m/z calcd for [M]+: 738.31; found: 738.39; H NMR
in CDCl3: d=7.13–6.94 ppm (m, 38H). 4E: m.p. 2578C; MALDI-TOF-
MS: m/z found: 738.40. 1H NMR in CDCl3: d=7.53 (d, 4H), 7.14–
7.08 (m, 22H), 7.03–7.00 ppm (m, 12H).
3-(Bromomethyl)-9,10-diphenylphenanthrene (6): Compound 5
(1.0 g, 3.0 mmol), NBS (622 mg, 3.5 mmol), and benzoyl peroxide
(7 mg, 0.03 mmol) were heated to reflux in CCl4 (60 mL) for 12 h,
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Published online on && &&, 0000
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FULL PAPER
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Aggregation-Induced Emission
T. T. Tasso, T. Furuyama, N. Kobayashi*
&& – &&
Dinitriles Bearing AIE-Active Moieties:
Synthesis, E/Z Isomerization, and
Fluorescence Properties
What it takes to shine: Dinitriles bear-
ing tetraphenylethylene (TPE) or diphe-
nylphenanthrene (DPP) units showed
distinct aggregation-induced emission
(AIE) and various reversible chromic re-
sponses to external stimuli (solvato-,
piezo-, vapo-, and thermochromism),
depending on the isomer conformation
and number of rotatable phenyl rings in
the molecule.
Chem. Eur. J. 2015, 21, 1 – 9
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ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers! ÞÞ