Strong charge-transfer chromophores from [2+2] cycloadditions of TCNE and TCNQ to peripheral donor-substituted alkynes

Article abstract of DOI:10.1002/ejoc.201101009

Peripheral donor-substituted N,N-dimethyl-4-[(7-nitrobenzo[c][1,2,5] thiadiazol-4-yl)ethynyl]aniline (1a), 4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)- N,N-dimethylaniline (1b), and 4,4′-{benzo[c][1,2,5]thiadiazole-4,7- diylbis(ethyne-2,1-diyl)}bis(N,N-dime

Full text of DOI:10.1002/ejoc.201101009

FULL PAPER
DOI: 10.1002/ejoc.201101009
Strong Charge-Transfer Chromophores from [2+2] Cycloadditions of TCNE
and TCNQ to Peripheral Donor-Substituted Alkynes
Songhua Chen,[a,b] Yongjun Li,*[a] Chao Liu,[a,b] Wenlong Yang,[a,b] and Yuliang Li*[a]
Keywords: Donor–acceptor systems / Cycloaddition / Charge transfer / Aggregate morphology
Peripheral donor-substituted N,N-dimethyl-4-[(7-nitrobenzo- analysis revealed the nonplanarity of these donor–acceptor
[c][1,2,5]thiadiazol-4-yl)ethynyl]aniline (1a), 4-(benzo[c]-
[1,2,5]thiadiazol-4-ylethynyl)-N,N-dimethylaniline (1b), and
4,4Ј-{benzo[c][1,2,5]thiadiazole-4,7-diylbis(ethyne-2,1-diyl)}-
bis(N,N-dimethylaniline) (2) were prepared by Sonogashira
cross-coupling reactions. Compounds 1a, 1b, and 2 sub-
sequently reacted with tetracyanoethylene (TCNE) or
7,7,8,8-tetracyanoquinodimethane (TCNQ) to afford the
charge-transfer chromophores 3–8. X-ray crystallographic
(D–A) chromophores. Cyclic voltammetry (CV) exhibited a
multistep reduction wave. UV/Vis spectra and theoretical
calculations identified efficient intramolecular charge-trans-
fer interactions. Moreover, scanning electron microscopy
(SEM) showed the morphology transition and reconstruction
process of 5 from 0D hollow nanospheres to 1D tubular mi-
crostructures.
been seen to form charge-transfer (CT) complexes[9] and
salts,[10] some of which exhibit high electronic conductivity
and magnetic phenomena.[11] It has been reported that the
reaction of electron-rich alkynes with TCNE afforded [2+2]
cycloaddition products, which gave 1,1,4,4-tetracyano-1,3-
butadienes (TCBD) in high to quantitative yields.[12]
Herein, we show the fast [2+2] cycloaddition reaction of
TCNE/TCNQ to alkynes substituted by electron-donating
and electron-withdrawing groups, where the donor consists
of N,N-dimethylaniline units, and benzothiadiazole or nitro
groups function as the acceptor. Their structures have been
characterized by X-ray crystallography, optical absorption
spectroscopy, electrochemistry, and theoretical calculations.
We have also utilized strong D–A dipole–dipole interactions
as the main driving force to direct the growth of tubular
microstructures.[13]
Introduction
Over recent decades, push–pull chromophores (D–π–A)
with strong electron donors (D) connected by π-conjugated
spacers to strong electron acceptors (A) have been investi-
gated because of their promising optoelectronic properties,
such as large second- and third-order nonlinear optical ef-
fects.[1] Appropriate choices of the D and A units has led
to new high-performance molecular materials such as dye-
sensitized solar cells, light-energy conversion, optical de-
vices, and sensors.[2] Furthermore, D–A-substituted conju-
gated molecules are highly polarized, intramolecular
charge-transfer (ICT) compounds, which can be used to
construct low-dimensional organic nanostructures[3] and
provide possibilities for the design and fabrication of well-
defined, morphology-controlled nanostructures with desir-
able sizes, shapes, and functions. Low-dimensional supra-
molecular micro- or nanostructures have been successfully
constructed from low-molecular-weight D–A-substituted
ICT compounds with the help of D–A dipole–dipole inter-
actions.[3a–3c,4]
Results and Discussion
Synthesis
As strong electron acceptors, tetracyanoethylene (TCNE)
and 7,7,8,8-tetracyanoquinodimethane (TCNQ) are of
interest in the fabrication of optical and electrical re-
cording,[5] energy and data storage,[6] sensors,[7] and elec-
trochromic and magnetic devices.[8] Their derivatives have
The synthesis of the CT chromophores 3–8 is outlined in
(Scheme 1). 4-bromobenzo[c][1,2,5]thiadiazole, 4-bromo-7-
nitrobenzo[c][1,2,5]thiadiazole and 4,7-dibromobenzo[c]-
[1,2,5]thiadiazole were prepared according to literature
methods.[14] Standard Sonogashira coupling gave monoad-
ducts N,N-dimethyl-4-[(7-nitrobenzo[c][1,2,5]thiadiazol-4-
yl)ethynyl]aniline (1a) and 4-(benzo[c][1,2,5]thiadiazol-4-
ylethynyl)-N,N-dimethylaniline (1b) in 83 and 65% isolated
yield, respectively. Bisadduct 4,4Ј-[benzo[c][1,2,5]thiadi-
azole-4,7-diylbis(ethyne-2,1-diyl)]bis(N,N-dimethylaniline)
(2) was also synthesized in a similar Pd-catalyzed reaction
in 45% yield.[15] Compounds 1 and 2 were subsequently
[a] Beijing National Laboratory for Molecular Sciences (BNLMS),
CAS Key Laboratory of Organic Solids, Institute of Chemistry,
Chinese Academy of Sciences,
Beijing 100190, P. R. China
E-mail: ylli@iccas.ac.cn; liyj@iccas.ac.cn
[b] Graduate University of Chinese Academy of Sciences,
Beijing 100049, P. R. China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201101009.
Eur. J. Org. Chem. 2011, 6445–6451
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6445

S. Chen, Y. Li, C. Liu, W. Yang, Y. Li
FULL PAPER
Scheme 1. Synthesis of 3–8.
used for the reaction with TCNE/TCNQ to give the desired perature, and a solution containing 7 in CHCl3 was concen-
products 3–8. A previous report[12b] has shown that the re- trated slowly at room temperature to yield a crystal of 7
action of TCNE with N,N-dimethylanilino (DMA)-substi- (Figure 1b). Compound 7 was found to cocrystallize with
tuted alkynes could reach almost quantitative yield (97%) 1 equiv. of CHCl3. Crystallographic data for both molecules
by [2+2] cycloaddition. Similar reactions were carried out are collected in Table S2 (Supporting Information).
with 1a and 1b to yield the corresponding adducts 3 (78%)
and 5 (83%), respectively, at room temperature. Likewise,
the reaction of 2 with TCNE afforded 7 in 91% yield
(Scheme 1).
In contrast to TCNE, TCNQ displays reduced reactivity
in formal cycloadditions with alkynes. Compounds 4
(27%), 6 (20%), and 8 (35%) were obtained in low yields
even with prolonged reaction times, elevated temperatures
(60 °C) or excess TCNQ. The low yields observed are attrib-
uted to steric effects.
Figure 1. Molecular structures of 5 (a) and 7 (b). Solvent molecules
were omitted for clarity in (b).
Identification of 3–8 was confirmed by NMR spec-
troscopy, MS, and elemental analysis. The 13C NMR spec-
The X-ray crystal structures of 5 and 7 are nonplanar
trum of 7 was not obtained because of its low solubility.
Compounds 3–8 are stable, deeply colored, and show no
decomposition even after several weeks at room tempera-
ture.
due to the strong repelling contacts between the benzothia-
diazole moiety and TCBD group. The TCBD moieties of 7
are distorted with an angle of 38.5° relative to the neigh-
boring benzene rings in the benzothiadiazole moiety,
whereas the TCBD moiety of 5 has a torsion angle of 54.7°.
The crystal-packing diagrams show several interesting
short intermolecular contacts. In the crystal-packing ar-
X-ray Structure and Bond-Length Alternation
A single crystal of 5 (Figure 1a) was obtained by slow rangement of 5 (Figure S1a, Supporting Information), mul-
diffusion of n-hexane into a CH2Cl2 solution at room tem- tiple CN···CN interactions [d(N3···C9Ј) 3.11 Å,
=
6446
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 6445–6451

Strong Charge-Transfer Chromophores from [2+2] Cycloadditions
d(N3···C10Ј) = 3.18 Å] between two neighboring molecules thiadiazole units. The longer wavelength absorption is
are formed, as previously observed.[16] Furthermore, the mainly from the HOMO–LUMO transition. It is worth not-
DMA residues of two neighboring molecules undergo anti- ing that the energies of the HOMO-1 and HOMO are al-
parallel stacking at intermolecular C···H distances of most equal in 7, which may be the cause for the larger ab-
around 2.90 Å. The polarized N atoms of a CN moiety in sorption coefficients compared with those in 5.
one molecule interact with a neighboring benzothiadiazole
ring, which plays an important role in the face-to-face pack-
ing. As can be seen from Figure S1b (Supporting Infor-
mation), the conformation of 7 is locked and stabilized not
only by the strong CN dipoles but also by a large number
of intermolecular hydrogen bonds. The hydrogen bonds and
CH–π interactions, such as C17···H18Ј, N3···H19Ј, and
C17–H17···N3ЈЈ, work cooperatively to help the DMA resi-
dues form antiparallel stacks. In addition, a remarkable fea-
ture of the crystal structure is that the CN groups of one
molecule interact with the C(CN)2 moieties of the neigh-
boring molecule. In this alignment, the CN group can form
two CN···CN contacts [d(N4···C11ЈЈ)
d(N4···C9ЈЈ) = 3.10 Å, d(N4···C10ЈЈ) = 3.18 Å].
=
3.22 Å,
Bond-length alternation in the benzene ring of N,N-di-
methylaniline is a good indicator for the efficiency of CT
conjugation from the donor to the benzothiadiazole ac-
ceptor, which can be expressed by the quinoid character (δr)
[Equation (1)]:[17]
Figure 2. UV/Vis spectra of 3–8 in CH2Cl2 (green: 3; cyan: 4; black:
5; red: 6; blue: 7; magenta: 8).
Table 1. Summary of the UV/Vis spectra of 3–8 in CH2Cl2.
Compound λmax [nm] (logε)[a]
λend [nm]
δr = {[(a + aЈ)/2 – (b + bЈ)/2] + [(c + cЈ)/2 – (b + bЈ)/2]}/2
(1)
3
4
5
6
7
8
358 (4.32), 472 (4.43)
760
980
660
910
780
990
338 (4.34), 618 (4.28)
441 (4.34), 550[b] (2.85)
In benzene, the δr value is 0 (see Figure 1a for the defini-
tion of the bonds a, aЈ, b, bЈ, c, cЈ). Calculating from the
X-ray crystal structures, 7 exhibits a δr value of 0.044, and
5 shows a similar value of 0.045. It has been reported that
TCBD compounds with two different molecules in the unit
cell exhibit an average δr value of 0.036,[12b] and some
DMA-substituted cyanoethynylethenes with strong D–A in-
teractions display δr values of 0.033–0.037.[18] Taking this
into account, 5 and 7 exhibit efficient ICT interactions in
which the benzothiadiazole moiety plays an important role.
499 (3.13), 720 (4.36)
378 (4.53), 476 (4.74), 647[b] (2.73)
365 (4.50), 400 (4.49), 628 (4.61)
[a] Measured in 1ϫ10–5 m solution. [b] Shoulder.
UV/Vis Spectroscopy
The D–A systems are dark or black metallic solids, which
are stable at ambient temperature. The UV/Vis spectra re-
corded in CH2Cl2 show multi-ICT bands (Figure 2,
Table 1), which result from different D–A transitions. For
example, 5 displays an intense band with λmax = 441 nm
and one weak shoulder at λmax = 550 nm. In contrast, the
lower energy of the CT band of 3 with an apparent λmax
value of 472 nm clearly reflects the strong D–A interaction
as the result of the insertion of the nitro group, and the
absorbance at about 358 nm is assigned to the πǞπ* transi-
tion of the benzothiadiazole unit.[19] Similarly, 7 has a CT
shoulder at about 647 nm with ε values 2.5 times larger than
that of monomeric 5. The highest occupied molecular or-
Figure 3. Calculated spatial distributions of the HOMO and
LUMO for 5 and 7 [B3LYP/6-31G+(d,p)].
The TCNQ adduct 6 shifts the CT band to 499 nm, with
bital (HOMO) and lowest unoccupied molecular orbital a strong CT band of lower energy appearing at λmax
=
(LUMO) from the calculation are depicted in Figure 3. It 720 nm and λend ≈ 910 nm. Apart from the characteristic
can be seen from the calculated spatial distributions that broad absorbance of 4 at 618 nm, the spectrum shows a
the density in the HOMO is concentrated in the DMA moi- new shoulder at a longer wavelength of 750 nm, which de-
ety, and the density in the LUMO on the TCBD and benzo- pends on more effective CT interactions. Solvatochromism
Eur. J. Org. Chem. 2011, 6445–6451
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6447

S. Chen, Y. Li, C. Liu, W. Yang, Y. Li
FULL PAPER
is a characteristic behavior of dipolar molecules. The ab- duction of the strongly accepting nitro group in 3 facilitated
4
sorption bands of TCBD adducts have been reported to the reduction of the benzothiadiazole moiety (Ered
=
3
be redshifted in polar solvents and blueshifted in nonpolar –1.83 V) compared to 5 (Ered = –2.46 V) with a 630 mV
ones.[12b] We investigated the solvent effect on the CT bands shift. This indicates that the nitro-modified benzothiadia-
of 4, 6, and 8 in solvents with different polarities. The re- zole moiety in 3 is more electron-deficient than the benzo-
sults show that the absorbance maxima are highly depend- thiadiazole group in 5. Similarly, there is a 200 mV shift
ent on the solvent polarity (Table S1, Supporting Infor- between 4 (Ered = –2.08 V) and 6 (Ered = –2.28 V) in the
mation). The CT band of 8 in N,N-dimethylformamide benzothiadiazole moiety reduction step. Furthermore, the
(DMF), CH3OH, CH3CN, tetrahydrofuran (THF), and tol- first and second reversible reduction steps became notably
4
3
uene was at 710, 694, 674, 632, and 602 nm, respectively.
facilitated by the introduction of the nitro group. As ob-
served by Diederich and co-workers,[1b] each TCBD moiety
can accommodate two electrons. Thus, dimeric 7 with two
TCBD moieties accepted four electrons in two reversible
two-electron reduction steps at –0.67 and –0.83 V. The first
reduction potentials of 5 and 7 decreased as the number of
TCBD units increased. This indicates that the TCBD unit
reduces the LUMO level and increases the π-accepting abil-
ity.[24] The electrochemical reduction of 8 exhibited a revers-
ible reduction wave, whose potentials were identified at
–0.64, –0.76, –0.80, –0.94, and –2.57 V by CV, which are
attributed to the formation of a pentaanionic species.
Electrochemistry
The redox properties of 3–8 were studied by CV in
CH2Cl2 with nBu4NPF6 (0.1 m) as the supporting electro-
lyte. The redox potentials vs. Fc+/Fc are listed in Table 2.
Table 2. CV of 3–8 in CH2Cl2 (+0.1 m nBu4NPF6).[a]
1
1
2
3
4
5
Compound
Eox
Ered
Ered
Ered
Ered
Ered
[V]
[V]
[V]
[V]
[V]
[V]
3
4
5
6
7
8
0.82
0.33
0.73
0.25
0.73
0.23
–0.70
–0.62
–0.96
–0.75
–0.67
–0.64
–0.93
–0.79
–1.36
–0.91
–0.83
–0.76
–1.43
–1.41
–2.46
–2.28
–1.64
–0.80
–1.83
–2.08
–
–
–
–
–
–
–
Aggregate Structures of 5
–
–0.94
–2.57
Figure 4 shows typical SEM images of the aggregate
nanostructures of 5 with different morphologies. The prepa-
ration of nanostructures was carried out by a simple solu-
[a] All potentials are given vs. Fc+/Fc (scan rate v = 0.1 Vs–1).
The DMA donor in 3–8 undergoes an irreversible oxi- tion process. Compound 5 was dissolved in THF at a con-
dation step with the potential ranging from 0.23 to 0.82 V. centration of 2.0ϫ10–3m. Then, 1 mL of the solution was
Bisadducts 7 and 8 have a single oxidation process, which injected into 5 mL of vigorously stirred hexane (antisolvent)
can be assigned to the simultaneous one-electron oxidation at 30 °C. Immediately after the injection, one drop of the
of the two DMA units. This may be due to the noncopla- suspension was put onto a silicon substrate for SEM exami-
narity of the central 4,7-disubstituted benzothiadiazole ring nation (Figure 4a). Large spherical particles with diameters
and results in negligible electronic interactions between the ranging from 0.5 to 1.5 μm were observed in the SEM
DMA units.[20] The oxidation potential was not signifi- images. A large number of membrane defects on the spheri-
cantly affected in either the monoadducts (0.73 V for 5 and cal structures was also observed. After stirring for 3 min, a
7) or the bisadducts (0.25 and 0.23 V for 6 and 8, respec- drop of suspension was put on to a silicon substrate, and
tively). On the other hand, the oxidation potential observed the morphology was measured in situ (Figure 4b). We
in 3 (Eox = +0.82 V) is more positive than that of 5 (Eox
+0.73 V), which indicates that the DMA unit in 5 is more hollow nature of the structure is observable. SEM (Fig-
electron-rich than that in 3. The TCNQ adducts 4 (Eox ure 4c) was used to observe the sample obtained after
=
found that the wall of the sphere had collapsed, and the
=
+0.33 V), 6 (Eox = +0.25 V), and 8 (Eox = +0.23 V) are 30 min. The result showed that a 1D hollow aggregate
oxidized at lower potentials compared to those of the structure was formed with lengths over 5 μm, which clearly
TCNE adducts 5 and 7 (Eox = +0.73 V). The difference be- demonstrates that the solvent strongly favors not only the
tween the oxidation potentials of 3–8 suggests that the in- formation of a large-scale spherical aggregate structure but
teractions between the donor and the acceptor groups are also a 1D hollow aggregate structure. The driving forces for
strong in the ground state.[21]
the self-organization of spherical and hollow structures of
Noticeably, these chromophores show multireversible re- 5 are mainly intermolecular interactions. The growth and
duction steps centered on the C(CN)2 group as well as the assembly process can be proposed as follows: when the
benzothiadiazole moiety. Electrochemical reduction of 5 solution of 5 in THF was injected into hexane, the solvent
showed a reversible three-stage reduction wave at –0.96, polarity and the chemical environment of the molecules was
–1.36, and –2.46 V. The first and second negative potentials changed and formed the spherical aggregate. During con-
are attributed to the Ered values of the TCBD group, and centration, the THF solution was lost from the spherical
the third is attributed to the Ered value of the benzothiadia- shell, which left defects. The vesicles formed initially had a
zole unit.[22] Compared with 5, 3 exhibits another reduction high curvature, and their fusion could release curvature en-
at –1.43 V, probably due to the reduction of the nitro ergy, which would lead to a thermodynamically more stable
group,[23] which was also observed in 4 (–1.41 V). The intro- structure.[3a,21] Therefore, a hemispherical structure was
6448
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 6445–6451

Strong Charge-Transfer Chromophores from [2+2] Cycloadditions
formed in which the molecules flowed with the solvent and ture applications in devices. The exploration of optical non-
aggregated along the initial opening hole. In the growth linearities of the TCNE and TCNQ derivatives is currently
process to form the hollow tubular microstructures, the underway.
strong intermolecular interactions observed in the crystal
packing are proposed to act as the driving force for the
molecules to aggregate, as confirmed by similar X-ray dif-
Experimental Section
fraction patterns between the aggregate and the crystal
Materials and Characterization: Most of the chemical reagents were
(Figure 4d).[3c,25]
purchased from Alfa Aesar and Aldrich Chemicals and were used
as received unless indicated otherwise. All solvents were purified
by using standard procedures. Column chromatography was per-
formed on silica gel (size 200–300 mesh). 1H and 13C NMR spectra
were recorded with a Bruker ARX400 spectrometer. UV/Vis spec-
tra were measured with a Hitachi U-3010 spectrometer. Organic
nanostructures were prepared by a simple solution process. 4-Bro-
mobenzo[c][1,2,5]thiadiazole, 4-bromo-7-nitrobenzo[c][1,2,5]thiadi-
azole and 4,7-dibromobenzo[c][1,2,5]thiadiazole were synthesized
according to previously described procedures.[14]
General Procedure for the Synthesis of N,N-Dimethyl-4-[(7-nitro-
benzo[c][1,2,5]thiadiazol-4-yl)ethynyl]aniline (1a): To a stirred solu-
tion of 4-ethynyl-N,N-dimethylbenzenamine (290 mg, 2.0 mmol)
and 4-bromo-7-nitrobenzo[c][1,2,5]thiadiazole (518 mg, 2.0 mmol)
in THF and (iPr)2NH (3:1, v/v) were added PdCl2(PPh3)2 (40 mg)
and CuI (20 mg) under an argon flow at room temperature. The
mixture was stirred at room temperature for 1 h. The solvent was
evaporated under reduced pressure, and the mixture was purified
by SiO2 chromatography with CH2Cl2/petroleum ether (1:2, v/v) to
obtain 1a (538 mg, 83%) as a yellow powder. 1H NMR (400 MHz,
CDCl3): δ = 3.06 (s, 6 H), 6.72 (d, J = 8.6 Hz, 2 H), 7.58 (d, J =
8.8 Hz, 2 H), 7.79 (m, J = 8.0 Hz, 1 H), 8.59 (d, J = 8.0 Hz, 1 H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 155.9, 151.4, 146.7, 137.6,
134.1 128.6, 126.1, 111.8, 107.8, 106.0, 85.1, 40.2 ppm. HRMS:
calcd. for [M]+ 324.0681; found 324.0686. C16H12N4O2S (324.36):
calcd. C 59.25, H 3.73, N 17.27; found C 69.17, H 3.75, N 17.20.
Figure 4. SEM images of 5 prepared at different ageing times in
THF/hexane. (a) immediately, (b) after 3 min, (c) after 30 min; (d)
compares the XRD patterns of the aggregate (I) and the crystal
(II) of 5.
The THF solution was essential for this kind of tubular
formation progress. When the sample was dissolved in
CH2Cl2 (Figure S21, Supporting Information), a 3D net-
work of the flexible endless fibers was formed. Further-
more, when CH2Cl2 was used instead of THF, the changes
in morphology were not as obvious in the mixture with hex-
ane.
4-(Benzo[c][1,2,5]thiadiazol-4-ylethynyl)-N,N-dimethylaniline (1b):
To
a stirred solution of 4-ethynyl-N,N-dimethylbenzenamine
(522 mg, 3.6 mmol) and 4-bromobenzo[c][1,2,5]thiadiazole
(642 mg, 3.0 mmol) in THF and (iPr)2NH (3:1, v/v) were added
PdCl2(PPh3)2 (40 mg) and CuI (20 mg) under an argon flow at
room temperature. The reaction mixture was heated to reflux with
stirring for 10 h, and then cooled to room temperature. The solvent
was then evaporated under reduced pressure, and the mixture was
Except 5, the other compounds with bulkier substituents
do not form well-defined aggregate structures. This indi- purified by SiO2 chromatography with CH2Cl2/petroleum ether
(1:3, v/v) to obtain 1b (544 mg, 65%) as a yellow powder. 1H NMR
(400 MHz, CDCl3): δ = 3.02 (s, 6 H), 6.69 (d, J = 8.8 Hz, 2 H),
cated that the molecular structure, which controls the pack-
ing style, plays as important a role as the dipole–dipole in-
teraction in directing the aggregation.
7.54 (d, J = 5.4 Hz, 2 H), 7.58 (m, J = 7.2 Hz, 1 H), 7.74 (d, J =
7.0 Hz, 1 H), 7.93 (d, J = 8.8 Hz, 1 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 154.9, 154.8, 150.6, 133.4, 131.8, 129.5, 120.8, 118.3,
111.8, 109.3, 97.9, 83.7, 40.3 ppm. EI-MS: m/z = 279 [M]+.
Conclusions
C16H13N3S (279.36): calcd. C 68.79, H 4.69, N 15.04; found C
68.60, H 4.69, N 14.87.
Three peripheral donor-substituted alkynes (1a, 1b, and
4,4Ј-{Benzo[c][1,2,5]thiadiazole-4,7-diylbis(ethyne-2,1-diyl)}bis-
(N,N-dimethylaniline) (2): To a stirred solution of 4-ethynyl-N,N-
dimethylbenzenamine (870 mg, 6.0 mmol) and 4,7-dibromo-
benzo[c][1,2,5]thiadiazole (882 mg, 3.0 mmol) in THF and Et3N
(3:1, v/v) were added PdCl2(PPh3)2 (40 mg) and CuI (20 mg) under
a nitrogen flow. The reaction mixture was heated to reflux with
stirring for 10 h before the solvent was evaporated. The mixture
was purified by SiO2 chromatography with CH2Cl2/petroleum ether
(2:1, v/v) to obtain 2 (569 mg, 45%) as a red powder. 1H NMR
(400 MHz, CDCl3): δ = 3.02 (s, 12 H), 6.68 (d, J = 8.9 Hz, 4 H),
2) were prepared by Sonogashira cross-coupling reactions
and subsequently used in reactions with TCNE or TCNQ
to give 3–8. X-ray crystallographic analysis (for 5 and 7)
revealed the nonplanarity of these D–A chromophores. CV
showed that 3–8 exhibit multistep reduction waves. UV/Vis
spectra and theoretical calculations identified the efficient
ICT interactions. The aggregate structures of 5 were investi-
gated by SEM, and spherical and hollow structures were
formed in the controlled assembly process. These optical
and electronic features make them potentially useful for fu- 7.54 (d, J = 8.9 Hz, 4 H), 7.70 (s,2 H) ppm. 13C NMR (100 MHz,
Eur. J. Org. Chem. 2011, 6445–6451
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6449

S. Chen, Y. Li, C. Liu, W. Yang, Y. Li
FULL PAPER
CDCl3): δ = 154.6, 150.6, 133.4, 131.8, 117.1, 111.8, 109.3, 99.2,
84.3, 40.3 ppm. EI-MS: m/z = 422 [M]+. C26H22N4S (422.55): calcd.
C 73.90, H 5.25, N 13.26; found C 73.69, H 5.25, N 12.94.
3,3Ј-(Benzo[c][1,2,5]thiadiazole-4,7-diyl)bis[2-{4-(dimethylamino)-
phenyl}buta-1,3-diene-1,1,4,4-tetracarbonitrile] (7): TCNE (77 mg,
0.6 mmol) was added to a solution of 2 (126mg, 0.3 mmol) in
CH2Cl2 (60 mL) at room temperature. The mixture was stirred at
room temperature for 30 min. The solvent was removed in vacuo,
and the product was purified by SiO2 chromatography with CH2Cl2
as the eluent to yield 7 as a dark green solid (185 mg, 91%). M.p.
2-[4-(Dimethylamino)phenyl]-3-(7-nitrobenzo[c][1,2,5]thiadiazol-4-
yl)buta-1,3-diene-1,1,4,4-tetracarbonitrile (3): TCNE (64 mg,
0.5 mmol) was added to a solution of 1a (162 mg, 0.5 mmol) in
CH2Cl2 (20 mL). The mixture was stirred at room temperature for
1 h. The solvent was removed in vacuo, and the product was puri-
fied by SiO2 chromatography with CH2Cl2 as the eluent to yield 3
as a dark brown solid (165 mg, 78 %). M.p. 136 °C. 1H NMR
(400 MHz, CDCl3): δ = 3.14 (s, 6 H), 6.68 (d, J = 9.2 Hz, 2 H),
7.78 (d, J = 9.2 Hz, 2 H), 8.11 (d, J = 7.9 Hz, 1 H), 8.59 (d, J =
7.9 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 163.2, 161.8,
154.5, 152.6, 146.5, 141.8, 132.8, 130.9, 130.6, 126.0, 118.0, 114.0,
113.7, 112.3, 111.0, 110.3, 95.5, 75.9, 40.2 ppm. HRMS: calcd. for
[M]+ 425.0804; found 452.0810.
1
301 °C. H NMR (400 MHz, CDCl3): δ = 3.14 (s, 12 H), 6.68 (d,
J = 9.4 Hz, 4 H), 7.76 (d, J = 8.1 Hz, 4 H), 8.05 (s, 2 H) ppm. MS
(MALDI-TOF): 679.5 [M + 1]+. HRMS: calcd. for [M]+ 678.1811;
found 678.1822.
2,2Ј-(Benzo[c][1,2,5]thiadiazole-4,7-diylbis{2-[4-(dicyanomethylene)-
cyclohexa-2,5-dien-1-ylidene]-2-[4-(dimethylamino)phenyl]eth-1-yl-1-
ylidene})dimalononitrile (8): To a stirred solution of 2 (126 mg,
0.3 mmol) in CH2Cl2 (60 mL) was added TCNQ (122mg,
0.6 mmol). The reaction mixture was heated to reflux with stirring
for 48 h before the solvent was evaporated. The mixture was puri-
fied by SiO2 chromatography with CH2Cl2 to obtain 8 (87 mg,
2-[4-(3,3-Dicyano-1-{(4-(dimethylamino)phenyl}-2-{7-nitrobenzo[c]-
[1,2,5]thiadiazol-4-yl}allylidene)cyclohexa-2,5-dien-1-ylidene]malono-
nitrile (4): TCNQ (102 mg, 0.5 mmol) was added to a solution of
1a (162 mg, 0.5 mmol) in THF (40 mL). The mixture was stirred
for 20 h at 60 °C. The solvent was removed in vacuo, and the prod-
uct was purified by SiO2 chromatography with CH2Cl2/CH3OH
(100:1) as the eluent to yield 4 as a dark black solid (71 mg, 27%).
1
35%) as a dark black powder. M.p. 213 °C. H NMR (400 MHz,
CDCl3): δ = 3.09 (s, 12 H), 6.64 (d, J = 8.4 Hz, 4 H), 7.20 (d, J =
7.3 Hz, 2 H),7.27 (m, 8 H),7.38 (d, J = 9.6 Hz, 2 H) 7.76 (s, 2 H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 167.1, 153.9, 153.1, 151.4,
150.5, 136.1, 134.7, 134.3, 133.7, 132.1, 130.6, 126.0, 125.6, 122.7,
114.6, 112.5, 112.2, 111.7, 93.5, 73.2, 40.3 ppm. MS (MALDI-
TOF): m/z = 831.6. C50H30N12S (830.93): calcd. C 72.27, H 3.64,
N 20.23; found C 72.35, H 3.60, N 19.94.
1
M.p. 145 °C. H NMR (400 MHz, CDCl3): δ = 3.07 (s, 6 H), 6.59
(d, J = 8.8 Hz, 2 H), 7.21 (d, J = 8.9 Hz, 2 H), 7.29 (d, J = 5.1 Hz,
2 H), 7.34 (m, 2 H), 7.92 (d, J = 7.8 Hz, 1 H), 8.52 (d, J = 7.8 Hz,
1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 166.3, 153.8, 152.9,
152.8, 150.1, 146.4, 141.2, 136.1, 134.5, 134.3, 134.2, 129.9, 129.3,
126.2, 126.0, 125.8, 122.4, 114.5, 114.4, 112.3 112.0, 111.5,
94.0,73.4, 40.1 ppm. HRMS: calcd. for [M]+ 528.1117; found
528.1122.
CCDC-814624 (for 5) and -814625 (for 7) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supporting Information (see footnote on the first page of this arti-
cle): Cyclic voltammetry, molecular orbital and SEM images.
2-(Benzo[c][1,2,5]thiadiazol-4-yl)-3-[4-(dimethylamino)phenyl]buta-
1,3-diene-1,1,4,4-tetracarbonitrile (5): TCNE (64 mg, 0.5 mmol)
was added to a solution of 1b (140 mg, 0.5 mmol) in CH2Cl2
(40 mL). The mixture was stirred at room temperature for 1 h. The
solvent was removed in vacuo, and the product was purified by
SiO2 chromatography with CH2Cl2 as the eluent to yield 5 as a
dark brown solid (169 mg, 83 %). M.p. 196 °C. 1 H NMR
(400 MHz, CDCl3): δ = 3.12 (s, 6 H), 6.67 (d, J = 9.1 Hz, 2 H),
7.75 (t, J = 7.9 Hz, 1 H), 7.81 (d, J = 9.1 Hz, 2 H), 8.02 (d, J =
7.1 Hz, 1 H), 8.26 (d, J = 8.8 Hz, 1 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 165.4, 163.4, 155.0, 154.4, 151.0, 132.9, 132.6, 128.9,
127.4, 125.6, 118.6, 114.5, 113.9, 112.2, 111.8, 111.2, 92.8, 75.9,
40.3 ppm. HRMS: calcd. for [M]+ 407.0953; found 407.0959.
C16H13N3S (279.36): calcd. C 64.85, H 3.22, N 24.06; found C
64.70, H 3.28, N 24.19.
Acknowledgments
We are grateful for financial support from the National Nature
Science Foundation of China (21031006, 20831160507, 20721061,
and 90922017) and the National Basic Research 973 Program of
China.
[1] a) T.-G. Zhang, Y. Zhao, I. Asselberghs, A. Persoons, K. Clays,
M. J. Therien, J. Am. Chem. Soc. 2005, 127, 9710–9720; b) M.
Kivala, C. Boudon, J.-P. Gisselbrecht, P. Seiler, M. Gross, F.
Diederich, Angew. Chem. 2007, 119, 6473; Angew. Chem. Int.
Ed. 2007, 46, 6357–6360.
[2] a) A. P. Kulkarni, C. J. Tonzola, A. Babel, S. A. Jenekhe, Chem.
Mater. 2004, 16, 4556–4573; b) P. T. Furuta, L. Deng, S. Ga-
ron, M. E. Thompson, J. M. J. Fréchet, J. Am. Chem. Soc.
2004, 126, 15388–15389.
[3] a) J. Xu, X. Liu, J. Lv, M. Zhu, C. Huang, W. Zhou, X. Yin,
H. Liu, Y. Li, J. Ye, Langmuir 2008, 24, 4231–4237; b) X.
Zhang, X. Zhang, K. Zou, C.-S. Lee, S.-T. Lee, J. Am. Chem.
Soc. 2007, 129, 3527–3532; c) X. J. Zhang, X. H. Zhang, W. S.
Shi, X. M. Meng, C. S. Lee, S. T. Lee, Angew. Chem. 2007, 119,
1547; Angew. Chem. Int. Ed. 2007, 46, 1525–1528; d) H. B. Liu,
J. L. Xu, Y. J. Li, Y. L. Li, Acc. Chem. Res. 2010, 43, 1496–
1508.
[4] a) C. Zhang, X. Zhang, X. Zhang, X. Fan, J. Jie, J. C. Chang,
C.-S. Lee, W. Zhang, S.-T. Lee, Adv. Mater. 2008, 20, 1716–
1720; b) Y. Yamamoto, T. Fukushima, Y. Suna, N. Ishii, A.
Saeki, S. Seki, S. Tagawa, M. Taniguchi, T. Kawai, T. Aida,
Science 2006, 314, 1761–1764; c) J. Xu, L. Wen, W. Zhou, J.
Lv, Y. Guo, M. Zhu, H. Liu, Y. Li, L. Jiang, J. Phys. Chem. C
2009, 113, 5924–5932.
2-[1-(Benzo[c][1,2,5]thiadiazol-4-yl)-2-{4-(dicyanomethylene)cyclo-
hexa-2,5-dienylidene}-2-{4-(dimethylamino)phenyl}ethylidene]-
malononitrile (6): TCNQ (102 mg, 0.5 mmol) was added to a solu-
tion of 1b (107 mg, 0.5 mmol) in CH2Cl2 (40 mL). The mixture was
stirred at room temperature for 30 h. The solvent was removed in
vacuo, and the product was purified by SiO2 chromatography with
CH2Cl2 as the eluent to yield 5 as a dark black solid (48 mg, 20%).
1
M.p. 244 °C. H NMR (400 MHz, CDCl3): δ = 3.08 (s, 6 H), 6.63
(d, J = 8.7 Hz), 7.19 (d, J = 9.4 Hz, 1 H), 7.28 (m, 4 H), 7.41 (d,
J = 9.6 Hz, 1 H), 7.67 (t, J = 7.8 Hz, 1 H), 7.81 (d, J = 6.9 Hz, 1
H), 8.17 (d, J = 8.7 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl3):
δ = 168.9, 154.9, 154.2, 152.9, 151.9, 151.3, 136.4, 134.9, 134.7,
133.6, 131.9, 128.8, 126.4, 125.7, 125.3, 123.6, 114.8, 114.7, 112.7,
112.3, 112.1, 92.3, 72.6, 40.3 ppm. MS: m/z = 483 [M]+. C28H17N7S
(483.55): calcd. C 69.55, H 3.54, N 20.28; found C 69.43, H 3.52,
N 20.18.
6450
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 6445–6451

Strong Charge-Transfer Chromophores from [2+2] Cycloadditions
[5] H. Peng, Z. Liu, Coord. Chem. Rev. 2010, 254, 1151–1168.
[6] C. Ran, H. Peng, W. Zhou, X. Yu, Z. Liu, J. Phys. Chem. B
2005, 109, 22486–22490.
[7] a) T. J. Wooster, A. M. Bond, Analyst 2003, 128, 1386–1390; b)
T. J. Wooster, A. M. Bond, M. J. Honeychurch, Anal. Chem.
2003, 75, 586–592.
[8] D. F. Perepichka, M. R. Bryce, C. Pearson, M. C. Petty, E. J. L.
McInnes, J. P. Zhao, Angew. Chem. 2003, 115, 4784; Angew.
Chem. Int. Ed. 2003, 42, 4636–4639.
[9] a) K. Tahara, T. Fujita, M. Sonoda, M. Shiro, Y. Tobe, J. Am.
Chem. Soc. 2008, 130, 14339–14345; b) H. B. Liu, Q. Zhao,
Y. L. Li, Y. Liu, F. S. Lu, J. P. Zhuang, S. Wang, L. Jiang, D. B.
Zhu, D. P. Yu, L. F. Chi, J. Am. Chem. Soc. 2005, 127, 1120–
1121.
[15]
[16]
[17]
S. Chen, Y. Li, W. Yang, N. Chen, H. Liu, Y. Li, J. Phys. Chem.
C 2010, 114, 15109–15115.
J. L. Alonso-Gómez, P. Schanen, P. Rivera-Fuentes, P. Seiler,
F. Diederich, Chem. Eur. J. 2008, 14, 10564–10568.
a) C. Dehu, F. Meyers, J. L. Bredas, J. Am. Chem. Soc. 1993,
115, 6198–6206; b) A. Hilger, J.-P. Gisselbrecht, R. R. Tykwin-
ski, C. Boudon, M. Schreiber, R. E. Martin, H. P. Luthi, M.
Gross, F. Diederich, J. Am. Chem. Soc. 1997, 119, 2069–2078.
N. N. P. Moonen, F. Diederich, Org. Biomol. Chem. 2004, 2,
2263–2266.
H. Zhang, X. Wan, X. Xue, Y. Li, A. Yu, Y. Chen, Eur. J. Org.
Chem. 2010, 1681–1687.
K. Danel, T.-H. Huang, J. T. Lin, Y.-T. Tao, C.-H. Chuen,
[18]
[19]
[20]
[10] M. Kivala, C. Boudon, J. P. Gisselbrecht, B. Enko, P. Seiler,
I. B. Muller, N. Langer, P. D. Jarowski, G. Gescheidt, F. Died-
erich, Chem. Eur. J. 2009, 15, 4111–4123.
[11] T. Akutagawa, T. Hasegawa, T. Nakamura, T. Inabe, G. Saito,
Chem. Eur. J. 2002, 8, 4402–4411.
Chem. Mater. 2002, 14, 3860–3865.
[21] D. M. Vriezema, J. Hoogboom, K. Velonia, K. Takazawa,
P. C. M. Christianen, J. C. Maan, A. E. Rowan, R. J. M. Nolte,
Angew. Chem. 2003, 115, 796; Angew. Chem. Int. Ed. 2003, 42,
772–776.
[12] a) M. I. Bruce, J. R. Rodgers, M. R. Snow, A. G. Swincer, J.
Chem. Soc., Chem. Commun. 1981, 271–272; b) T. Michinobu,
C. Boudon, J.-P. Gisselbrecht, P. Seiler, B. Frank, N. N. P.
Moonen, M. Gross, F. Diederich, Chem. Eur. J. 2006, 12, 1889–
1905; c) C. Cai, I. Liakatas, M.-S. Wong, M. Bösch, C. Bossh-
ard, P. Günter, S. Concilio, N. Tirelli, U. W. Suter, Org. Lett.
1999, 1, 1847–1849; d) P. Reutenauer, M. Kivala, P. D. Jarow-
ski, C. Boudon, J.-P. Gisselbrecht, M. Gross, F. Diederich,
Chem. Commun. 2007, 4898–4900.
[13] J. Xu, H. Zheng, H. Liu, C. Zhou, Y. Zhao, Y. Li, Y. Li, J.
Phys. Chem. C 2010, 114, 2925–2931.
[14] a) K. Pilgram, M. Zupan, R. Skiles, J. Heterocycl. Chem. 1970,
7, 629–633; b) K. Pilgram, M. Zupan, J. Org. Chem. 1971, 36,
207–209.
[22] H. Sakurai, M. T. S. Ritonga, H. Shibatani, T. Hirao, J. Org.
Chem. 2005, 70, 2754–2762.
[23] P. Allongue, M. Delamar, B. Desbat, O. Fagebaume, R. Hitmi,
J. Pinson, J.-M. Savéant, J. Am. Chem. Soc. 1997, 119, 201–
207.
[24] T. Shoji, S. Ito, K. Toyota, M. Yasunami, N. Morita, Chem.
Eur. J. 2008, 14, 8398–8408.
[25] X. J. Zhang, X. H. Zhang, K. Zou, C. S. Lee, S. T. Lee, J. Am.
Chem. Soc. 2007, 129, 3527–3532.
Received: July 12, 2011
Published Online: September 16, 2011
Eur. J. Org. Chem. 2011, 6445–6451
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6451