Cycloaddition reactions of polyenic donor-π-acceptor systems with an electron-rich alkyne: Access to new chromophores with second-order optical nonlinearities

Article abstract of DOI:10.1039/c2ob26515j

The formal [2 + 2] cycloaddition-cycloreversion (CA-CR) between 4-ethynyl-N,N-dimethylaniline and polyenic Donor-π-Acceptor (D-π-A) systems takes place to yield compounds bearing two donors and one acceptor. Structural, linear and second-order nonlinear optical (NLO) properties of the new molecules reveal the stronger polarization of these systems when compared to analogous merocyanines lacking the dimethylaminophenyl (DMA) ring.

Full text of DOI:10.1039/c2ob26515j

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Organic &
Biomolecular
Chemistry
Cite this: Org. Biomol. Chem., 2012, 10, 8684
www.rsc.org/obc
PAPER
Cycloaddition reactions of polyenic donor–π-acceptor systems with an
electron-rich alkyne: access to new chromophores with second-order optical
nonlinearities†‡
Elena Galán,a Raquel Andreu,*a Javier Garín,a Jesús Orduna,a Belén Villacampab and Beatriz E. Diosdadoc
Received 1st August 2012, Accepted 11th September 2012
DOI: 10.1039/c2ob26515j
The formal [2 + 2] cycloaddition–cycloreversion (CA–CR) between 4-ethynyl-N,N-dimethylaniline and
polyenic Donor–π-Acceptor (D–π-A) systems takes place to yield compounds bearing two donors and
one acceptor. Structural, linear and second-order nonlinear optical (NLO) properties of the new molecules
reveal the stronger polarization of these systems when compared to analogous merocyanines lacking the
dimethylaminophenyl (DMA) ring.
push–pull chromophores possess more than one CvC bond that
might be involved in the reaction, only one regioisomer is
Introduction
Recently, formal [2 + 2] cycloaddition of electron-poor alkenes
to electron-rich alkynes, followed by electrocyclic ring opening
of the initially formed cyclobutene has attracted substantial inter-
est1 and is considered to be a promising methodology to obtain
new Donor–Acceptor (D–A) products with varied applications,
including second-2 and third-order nonlinear optical (NLO)
properties.3
obtained.
Concerning deficient alkenes, most of the examples have been
centered on tetracyanoethene (TCNE)2a,4 and 7,7,8,8-tetracyano-
quinodimethane (TCNQ)4c,5 moieties. Just recently, other olefins
like dicyanoquinonediimides (DCNQIs)3e or dicyanovinyl/
tricyanovinyl derivatives6–8 are starting to be considered. On the
other hand, simple push–pull alkenes (which can be considered
as electronically confused olefins) have only seldom been
studied in this reaction,6,9 and the reactivity of their polyenic
D–π-A analogues remains unexplored.
We report here several examples of [2 + 2] cycloaddition–
cycloreversion (CA–CR) reactions between electron rich alkyne
1 and polyenic D–π-A systems 2–4.10–12 Although the starting
Results and discussion
aDepartamento de Química Orgánica, ICMA, Universidad de Zaragoza-
CSIC, 50009 Zaragoza, Spain. E-mail: randreu@unizar.es
bDepartamento de Física de la Materia Condensada, ICMA,
Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain
Synthesis and crystal structure analysis
Compounds containing acceptors a and b were prepared as
shown in Scheme 1. New chromophores (5–7)a and 5b have
been obtained in low to moderate yields (15–29%). We tried to
favor the reaction by increasing the temperature, prolonging reac-
tion time, using more polar solvents, or by adding excess of
either the D–A system or the alkyne, without reaching the com-
plete consumption of any initial compound.13 No other regio-
isomer was observed. The reduced reactivity of the starting
D–π-A compounds compared to tetracyanoethene (TCNE)4a or
7,7,8,8-tetracyanoquinodimethane (TCNQ)5a arises from the
cServicio de Difracción de Rayos X y Análisis por Fluorescencia, ICMA,
Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain
†Dedicated to the memory of Professor Enrique Meléndez.
‡Electronic supplementary information (ESI) available: General experi-
mental methods, NMR and UV-vis spectra of new compounds, X-ray
crystallographic data and diagrams of the crystal structures of 5a, 7c and
10, computed energies, Cartesian coordinates of optimized geometries
and molecular orbital contour plots for 5a and 7a, and NLO measure-
ments. CCDC 894169 (5a), 894170 (7c) and 894171 (10). For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c2ob26515j
8684 | Org. Biomol. Chem., 2012, 10, 8684–8691
This journal is © The Royal Society of Chemistry 2012

View Article Online
presence of an electron-donating group.6 The same differences in
reactivity have been encountered in the CA–CR reactions of
electronically-confused alkynes.5b,13
also presumed to take place similarly, since the regioisomer
obtained is the one in which the zwitterionic intermediate is
most stabilized (Fig. 2). Moreover, in the synthesis of com-
pounds a there is an aromatization of the thiazole ring that
further stabilizes the considered intermediate.3e,5a
The structure of 5a was unambiguously established by X-ray
diffraction (Fig. 1) and those of 5b, 6a, 7a by spectral data. The
D–π-A skeleton of 5a is essentially planar, with a twisting angle
between the mean planes of the diethylaminophenyl (DEAP)
and thiazole rings of 6.5°, thus ensuring efficient intramolecular
charge transfer (ICT), and in agreement with the X-ray structure
of its precursor 2a.10 On the other hand, the dimethylamino-
phenyl (DMA) group is not coplanar with the π-spacer. More-
over, the polyenic chain has an all-trans geometry. Bond length
alternation in anilino rings is a good indication of the efficiency
of the charge transfer taking place from the donor to the acceptor
moieties, and can be expressed through the δr parameter of the
ring.14 Whereas the DEAP ring exhibits a very high δr value of
0.063 revealing its partly quinoid character due to the ICT
process, the δr of the DMA ring averages to 0.004, which is very
close to that of benzene as a result of its deviation from the
essentially planar π-system. However, this additional anilino
moiety shows a strong electron-donating σ-inductive effect (see
UV-vis absorption section).
These reactions testified to the high torquoselectivity of the
cyclobutene ring opening.3e,7 Taking 5b as a model compound,
selective ge-1D NOESY experiments confirmed the outward
rotation of the donor group in the conrotatory ring-opening of
the two isomeric cyclobutene intermediates (ESI: Fig. S3–4‡).
When 1,1,3-tricyano-2-phenylpropene-containing chromo-
phores 2c and 4c are used the expected final product, together
with another compound (Scheme 2) resulting from a formal
[4 + 2] cycloaddition,9,16 were isolated. The identities and struc-
tures of the final products were established by X-ray diffraction
(7c, 10) (Fig. 3 and S36 in ESI‡), and spectral data (5c, 9).
Moreover, compound 5c could not be isolated as a pure product,
but as a mixture with its cyclobutene precursor 8, (ratio 5c/8:
10/7) (ESI: Fig. S16‡) and all attempts to purify it failed. Inter-
mediate cyclobutenes have only seldom been isolated.15,17 In the
same way as for the synthesis of chromophores represented in
Scheme 1, yields obtained were also low to moderate, recovering
Previous studies on related [2 + 2] CA–CR reactions point to
a stepwise zwitterionic mechanism.6,15 The present reactions are
Scheme 1 Synthesis of compounds 5a–b, 6a, 7a.
Fig. 1 Molecular structure of 5a.
Fig. 2 Non-concerted dipolar mechanism for the [2 + 2] cycloaddition of 1 with 2a.
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 8684–8691 | 8685

View Article Online
Scheme 2 Reaction of compounds 2c, 4c with 1.
geometry of 7c is similar to that of compound 11c,12 bearing the
same acceptor (Fig. 5). Both compounds, 7c and 11c, are
strongly polarized derivatives with an important zwitterionic
character.12 In order to see how the additional DMA ring in 7c
influences the ICT, the Bird Index (I6)20 of the pyranylidene
rings (7c/11c: 40.6/38.5) and the average bond lengths of the
two CuN groups of the dicyanomethylene fragment (7c/11c:
1.147 Å/1.139 Å) were compared. These results point to a
slightly more polarized structure for 7c as a consequence of the
additional DMA ring, despite its deviation from the planar main
π-system.
UV-vis spectroscopy
The UV-vis absorption data of compounds 5a–b, 6a, 7a,c are
collected in Table 1 (see spectra in ESI‡). For the sake of com-
parison, data for compounds 3a,10 11a,c10,12 (Fig. 5) are also
included.
Fig. 3 Molecular structure of 7c.
Spectra have been registered in four solvents of different
N 21
starting materials apart from cycloaddition products. Moreover,
due to the structural similarity of the final and starting push–pull
compounds, subsequent repeated chromatographic purifications
on silica gel were needed. Both facts (the reduced reactivity and
the difficulties in the purification) contribute to explain the low
to moderate yields.
The [2 + 2] (5c + 8) and the [4 + 2] (9) products are generated
from the same zwitterionic intermediate (ESI: Fig. S25‡). On the
other hand, 7c and 10 arise from the reaction of two different
double bonds of the initial D–A compound (Fig. 4). Whereas 7c
is generated from the most stabilized zwitterionic intermediate,
compound 10 arises from a less stabilized intermediate, allowing
a 1,4-elimination of HCN9,18 leading to aromatisation.
polarity (solvent polarity ET
:
DMF: 0.386, CH2Cl2: 0.309,
CHCl3: 0.259, dioxane: 0.164). Compounds 5a–b, 6a, 7a,c
show intense and broad CT bands in all solvents resulting from
different D–A transitions.4b Concerning the dependence of the
band position on solvent polarity, positive solvatochromism was
observed for compounds 5a–b and 6a and negative for com-
pound 7a. The behavior of compound 7c is different: taking into
account data in DMF, CH2Cl2 and CHCl3 this compound shows
an almost negligible solvatochromism, but when comparing with
dioxane, it exhibits positive solvatochromism. This variety of be-
havior has already been reported for other D–π-A systems,22
including 4H-pyranylidene derivatives.23
The combination of DEAP as main donor and dicyanomethylene-
thiazole as acceptor (5a, 6a) gives rise to the higher solvato-
chromism, reaching Δλ values of 87 and 127 nm respectively
(0.21 and 0.26 eV respectively). When comparing 5a and 6a,
The crystal structure of 7c (Fig. 3) confirms the (Z)-configur-
ation of the two double bonds and that the PhC–C(CN) bond
has an s-trans conformation, typical of this moiety.12,19 The
8686 | Org. Biomol. Chem., 2012, 10, 8684–8691
This journal is © The Royal Society of Chemistry 2012

View Article Online
Fig. 4 Non-concerted dipolar mechanism for the [2 + 2] (continuous line) and [4 + 2] (dotted line) cycloaddition of 1 with 4c in formation of 7c and
10 respectively.
two oxidation steps, the first oxidation involving the
conjugated donor (either DEAP or 4H-pyranylidene moieties)
and the second one corresponding to the additional DMA
donor group, taking into account that Eox for 1 in the same
conditions is 1.04 V.
Remarkably, Eox value to which the additional DMA ring is
oxidized is strongly modulated by the main donor, being
approximately 150 mV higher for pyranylidene-containing
chromophores than for DEAP derivatives. This trend might be
due to the fact that the additional DMA ring is located at a
greater distance from the main donor in DEAP derivatives, and
thus is more easily oxidized.
Fig. 5 Structures of compounds 11a,c.
As expected, on passing from 5a to 6a, lengthening the spacer
gives rise to a decrease of both first Eox and |Ered| values pointing
to a decrease in the interaction between the donor and acceptor
end groups. Finally, when comparing compounds 5a, 7a,c with
their respective analogues without the DMA ring, (3a, 11a,c) no
substantial changes are observed in either Eox of the conjugated
donor or |Ered|.
there is a vinylene shift of 79 nm in CH2Cl2, pointing to weakly
alternated structures.10
As previously mentioned (crystal structure analysis of com-
pound 5a), the additional DMA moiety, even if nearly ortho-
gonal to the extended π-system, also contributes to the donor
potency, as ascertained by the bathochromic shifts shown (in
CH2Cl2) by 5a, 7a,c when compared to 3a, and 11a,c, lacking
the DMA ring. PCM-B3P86/6-31G* calculations in CH2Cl2
(Table 2) on compounds 5a, 7a, 3a, 11a provide a rationale for
the observed trend in λ. In fact, the additional DMA moiety
causes an increase in energy of the HOMO and the LUMO, the
destabilization of the former being slightly higher than that of
the latter. In other words, the HOMO–LUMO gap and the exci-
tation energy (5a: 1.81 eV, 3a: 1.88 eV, 7a: 1.76 eV, 11a: 1.83
eV) are lowered as a consequence of the modification introduced
(see Fig. S48–49 in ESI‡ for molecular orbital contour plots for
5a and 7a).
Nonlinear optical properties
The second-order NLO properties of 5a, 6a, 7a,c have been
measured by electric field-induced second harmonic generation
(EFISH) in CH2Cl2 at 1907 nm (Table 3). The corresponding
static (zero-frequency) μβ0 values determined using the two-
level model24 are also gathered in Table 3. (For the sake of com-
parison, Disperse Red 1, a common benchmark for organic
NLO-chromophores, gives a μβ0 value of ∼480 × 10−48 esu
under the same experimental conditions.) Reported data for com-
pounds 3a,10 11a,c10,12 are also included. In order to get further
insight into the NLO behavior of these compounds, the βvec0
values have been estimated using the theoretically calculated
ground state dipole moments μg.
Electrochemistry
The redox properties were investigated by cyclic voltammetry
(CV) in CH2Cl2 (Table 1). New chromophores 5a–b, 6a, 7a,c
display three waves corresponding to one reduction step and
New chromophores show positive μβ0 values (in 10−48 esu)
ranging from +300 to +1710 except for 7a which presents a
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 8684–8691 | 8687

View Article Online
Table 1 UV-vis dataa and electrochemical propertiesb
Compd
λmax (DMF) (log ε)
λmax (CH2Cl2) (log ε)
λmax (CHCl3) (log ε)
λmax (dioxane) (log ε)
Eox
Ered
5a
681 (sh)
759 (4.86)
631 (sh)
623 (sh)
684 (4.64)
742 (4.71)
—
593 (sh)
672 (4.29)
+0.84
−0.60
694 (4.64)
747 (4.75)
679 (4.76)
732 (4.83)
609 (sh)
+1.08c
3a10
6a
—
—
+0.85c
−0.61
−0.46
677 (sh)
755 (sh)
844 (4.97)
605 (sh)
750 (4.68)
810 (4.65)
558 (sh)
717 (4.46)
+0.79
672 (sh)
+1.05c
759 (4.76)
826 (4.82)
734 (sh)
7a
779 (4.87)
745 (4.67)
810 (4.85)
677 (sh)
736 (4.59)
806 (4.47)
—
+0.71
+1.23
−0.59c
799 (4.89)
11a10
5b
—
726 (4.80)
790 (5.00)
572 (4.47)
665 (4.45)
582 (sh)
—
+0.71
−0.65
−0.81
−0.79c
598 (4.48)d
562 (4.40)
661 (4.37)
559 (sh)
642 (sh)
694 (4.91)
—
535 (4.39)
608 (4.34)
531 (sh)
635 (4.54)
672 (sh)
—
+0.82c
+1.01c
+0.86
+1.18
7c
584 (sh)
635 (sh)
688 (5.07)
—
641 (sh)
691 (5.00)
629 (4.89)
678 (5.11)
11c12
+0.88
−0.76
b
a In nm. In volts, 10−3 M in CH2Cl2 vs. Ag/AgCl (KCl 3 M), glassy carbon working electrode, Pt counter electrode, 20 °C, 0.1 M Bu4NPF6,
100 mV s−1 scan rate. Ferrocene internal reference E1/2 = +0.46 V. c Reversible wave (E1/2). d Extremely broad band.
Table 2 EHOMO and ELUMO valuesa (eV) for compounds 5a, 3a, 7a,
Table 3 Second-order NLO properties
11a
b,c
d
e
Compd
μβ a,b
μβ0
μg
βvec0
Compd
EHOMO
ELUMO
5a
+2050
+5940
+8400
−6600
−3900
+730
+670
+2080
+1710
−1630
−1010
+300
30.9
28.2
34.7
36.9
34.9
32.2
30.3
+22
+74
+49
−44
−29
+9
5a
−5.79
−5.92
−5.68
−5.77
−3.67
−3.78
−3.64
−3.71
3a10
6a
3a10
7a
7a
11a10
11a10
7c
a Calculated at the PCM-B3P86/6-31G* level in CH2Cl2.
11c12
+1550
+670
+22
a Determined in CH2Cl2 at 1907 nm; experimental accuracy: 15%. b In
10−48 esu. c Experimental μβ0 values calculated using the two-level
model. d In Debye, calculated in CH2Cl2 using the PCM-B3P86/6-31G*
model. e In 10−30 esu, estimated using the experimental μβ0 and the
calculated μg values.
negative μβ0 value of −1630, in agreement with its solvato-
chromic behaviour.
Lengthening the polyenic chain from 5a to 6a, gives rise, as
expected, to an important increase in μβ0, as a result of increased
μg and βvec0 values.
acceptor, present more polarized structures than their analogues
without the DMA ring. As a consequence of the presence of the
DMA moiety an increased negative second-order NLO response
for the new right-hand side25 chromophore 7a was found. More-
over, for molecules containing acceptor c, the resulting product
from a [4 + 2] CAwas also isolated.
The new synthesized systems bear two donors and one accep-
tor and the addition of a DMA group leads to more polarized
chromophores, with a large μg. As a consequence, for left-hand
side25 chromophores (region B) (3a, 11c), introduction of the
DMA ring (5a, 7c) results in a decreased NLO response,
whereas for 11a, located in region C–D of Marder’s plot, this
modification results in 7a having an increased negative NLO
response. The more polarized structure for 5a, 7a,c when com-
pared to 3a, 11a,c respectively, is in agreement with X-ray dif-
fraction data for 7c/11c.
Experimental
For general experimental methods see ESI.‡
Compounds 2a–c,10,11 3a10 and 4a,c10,12 were prepared as
previously described.
Conclusions
The reactivity of a series of polyenic D–π-A systems (electroni-
cally confused alkenes) towards the electron-rich alkyne 1 has
been studied, the formal [2 + 2] cycloaddition taking place on
the CvC bond located closer to the donor end of the molecule.
The final obtained compounds, with two donors and one
Compounds 5a, 6a, 7a. General procedure
To a solution of 4-ethynyl-N,N-dimethylaniline (1) (73 mg,
0.50 mmol) in 1,2-dichloroethane (6 mL), the corresponding
8688 | Org. Biomol. Chem., 2012, 10, 8684–8691
This journal is © The Royal Society of Chemistry 2012

View Article Online
2-[3-Cyano-4-{(3E)-4-{4-(diethylamino)phenyl}-2-{4-
(dimethylamino)phenyl}buta-1,3-dienyl}-5,5-dimethylfuran-2-
ylidene]malononitrile (5b)
thiazole-containing D–π-A compound (2a, 3a, 4a) (0.50 mmol)
was added under argon atmosphere. The reaction was refluxed
overnight, then the solvent was evaporated and the residue was
purified by flash chromatography on silica gel.
To a solution of 4-ethynyl-N,N-dimethylaniline (1) (29 mg,
0.20 mmol) in acetonitrile (6 mL), 2b (70 mg, 0.20 mmol) was
added under argon atmosphere. The reaction was refluxed for
three days (TLC monitoring), then it was cooled down to room
temperature. The solvent was evaporated and the residue was
purified by flash chromatography (silica gel) using CH2Cl2 as
eluent. A further purification through TLC preparative using
diethyl ether as eluent was needed to afford a blue solid (15 mg,
15%). Mp 128–132 °C. Found: C, 76.49; H, 6.39; N, 14.03.
Calc. for C32H33N5O: C, 76.31; H, 6.60; N, 13.91%. IR (Nujol,
cm−1): 2220 (CuN), 1608 (CvC, Ar), 1576 (CvC, Ar), 1522
2-{(E)-5-[(E)-3-{4-(Diethylamino)phenyl}-1-{4-(dimethylamino)-
phenyl}allylidene]-4-phenylthiazol-2-ylidene}malononitrile (5a)
Eluent: CH2Cl2. Yield: green solid (78 mg, 29%). Mp
205–207 °C. Found: C, 74.62; H, 5.76; N, 13.39. Calc. for
C33H31N5S: C, 74.83; H, 5.90; N, 13.22%. IR (Nujol, cm−1):
2195 (CuN), 1601 (CvC, Ar), 1560 (CvC, Ar), 1518 (CvC,
Ar). 1H NMR (300 MHz, CD2Cl2): δ 7.56–7.51 (2H, m),
7.36–7.26 (5H, m), 7.13–7.07 (2H, m), 7.02 (1H, d, J =
14.9 Hz), 6.90 (1H, d, J = 14.9 Hz), 6.63–6.59 (2H, m),
6.59–6.56 (2H, m), 3.43 (4H, q, J = 7.0 Hz), 3.04 (6H, s), 1.20
(6H, t, J = 7.0 Hz). 13C NMR (75 MHz, CD2Cl2): δ 174.2,
159.1, 153.5, 151.5, 150.1, 136.0, 134.1, 132.4, 130.2, 130.1,
129.0, 125.7, 123.8, 123.5, 112.2, 111.9, 45.4, 40.5, 12.9.
HRMS (ESI+): calcd for C33H32N5S 530.2373, found 530.2404
[M + H]+.
1
(CvC, Ar). H NMR (400 MHz, CD2Cl2): δ 7.54–7.50 (2H,
m), 7.39–7.35 (2H, m), 7.14 (1H, d, J = 15.3 Hz), 7.01 (1H, d, J
= 15.3 Hz), 6.77–6.73 (2H, m), 6.71–6.67 (2H, m), 5.81 (1H, s),
3.44 (4H, q, J = 7.1 Hz), 3.07 (6H, s), 1.64 (6H, s), 1.20 (6H, t,
J = 7.1 Hz). 13C NMR (75 MHz, CD2Cl2): δ 178.9, 174.4,
164.0, 153.0, 150.7, 146.8, 132.5, 131.2, 127.3, 123.7, 123.6,
114.0, 113.2, 112.1, 112.0, 110.1, 98.2, 45.1, 40.5, 26.6, 12.9.
HRMS (ESI+): calcd for C32H34N5O 504.2758, found 504.2734
[M + H]+; calcd for C32H33N5NaO 526.2577, found 526.2544
[M + Na]+.
2-{(Z)-5-[(2Z,4E)-5-{4-(Diethylamino)phenyl}-3-{4-(dimethyl-
amino)phenyl}penta-2,4-dienylidene]-4-phenylthiazol-2-ylidene}-
malononitrile (6a)
Compounds (5c + 8, 9) and (7c, 10). General procedure
Eluent: CH2Cl2. Yield: dark green solid (45 mg, 17%). Mp
246–248 °C. Found: C, 75.81; H, 5.80; N, 12.71. Calc. for
C35H33N5S: C, 75.64; H, 5.99; N, 12.60%. IR (Nujol, cm−1):
2197 (CuN), 1606 (CvC, Ar), 1521 (CvC, Ar). 1H NMR
(400 MHz, CD2Cl2): δ 7.71–7.67 (2H, m), 7.63 (1H, d, J =
12.8 Hz), 7.52–7.44 (3H, m), 7.44–7.39 (2H, m), 7.34–7.28
(2H, m), 7.13 (1H, d, J = 15.3 Hz), 6.99 (1H, d, J = 15.3 Hz),
6.79–6.74 (2H, m), 6.70–6.65 (2H, m), 6.62 (1H, d, J =
12.8 Hz), 3.44 (4H, q, J = 7.1 Hz), 3.06 (6H, s), 1.20 (6H, t, J =
7.1 Hz). 13C NMR (75 MHz, CD2Cl2): δ 150.6, 145.9, 141.8,
141.1, 140.9, 135.6, 133.6, 133.0, 132.4, 131.8, 131.4, 130.6,
129.2, 125.9, 124.7, 124.5, 124.0, 117.3, 115.3, 112.2, 112.1,
45.2, 40.6, 40.6, 12.9. HRMS (ESI+): calcd for C35H34N5S
556.2529, found 556.2525 [M + H]+.
To a solution of 4-ethynyl-N,N-dimethylaniline (1) (363 mg,
2.50 mmol) in acetonitrile (20 mL), the corresponding 1,1,3-tri-
cyano-2-phenylpropene-containing chromophore (2c, 4c) (2.50
mmol) was added under argon atmosphere. The reaction was
refluxed for four days (TLC monitoring), then it was cooled
down to room temperature. The solvent was evaporated and the
residue was purified by flash chromatography (silica gel).
Compounds 5c + 8, 9
Eluent: CH2Cl2–diethyl ether (100 : 0.3).
(3E,5E)-6-(4-(Diethylamino)phenyl)-4-(4-(dimethylamino)-
phenyl)-2-phenylhexa-1,3,5-triene-1,1,3-tricarbonitrile (5c) +
2-((1-cyano-4-(4-(diethylamino)phenyl)-2-(4-(dimethylamino)-
phenyl)cyclobut-2-enyl)(phenyl)methylene)malononitrile (8)
2-{(Z)-5-[(E)-4-{2,6-Di-tert-butyl-4H-pyran-4-ylidene}-3-{4-
(dimethylamino)phenyl}but-2-enylidene]-4-phenylthiazol-2-
ylidene}malononitrile (7a)
A mixture of 5c and 8 (ratio 5c/8 10 : 7) was isolated after a
further purification through several TLC preparative using
diethyl ether as eluent. Blue solid. Yield: (416 mg, 28%). IR
(Nujol, cm−1): 2216 (CuN), 2197 (CuN), 1605 (CvC, Ar),
1574 (CvC, Ar), 1522 (CvC, Ar). 1H NMR (300 MHz,
CD2Cl2): δ 7.59–7.53 (6H, m), 7.48–7.23 (11H, m), 7.08–7.00
(2H, m, (5c)), 6.87 (1H, d, J = 15.2 Hz, (5c)), 6.78–6.73 (2H, m,
(8)), 6.72–6.67 (2H, m, (8)), 6.66–6.61 (2H, m, (5c)), 6.59–6.53
(2H, m, (5c)), 6.28 (1H, d, J = 4.2 Hz, (8)), 4.36 (1H, d, J =
4.2 Hz, (8)), 3.47–3.32 (8H, m), 3.01–2.99 (12H, m), 1.22–1.13
(12H, m). 13C NMR (75 MHz, CD2Cl2): δ 169.1, 152.8, 151.5,
150.8, 149.4, 149.1, 143.2, 137.0, 136.0, 134.5, 132.8, 132.5,
131.6, 131.5, 131.0, 130.1, 129.5, 129.1, 129.0, 128.5, 126.6,
Eluent: CH2Cl2–AcOEt (10 : 0.2). Yield: dark green solid
(44 mg, 15%). Mp 286–290 °C. Found: C, 75.83; H, 6.32; N,
9.32. Calc. for C37H38N4OS: C, 75.73; H, 6.53; N, 9.55%. IR
(Nujol, cm−1): 2191 (CuN), 1634 (CvN), 1602 (CvC, Ar),
1551 (CvC, Ar), 1511 (CvC, Ar). 1H NMR (300 MHz,
CD2Cl2): δ 7.63–7.59 (2H, m), 7.46 (1H, d, J = 13.3 Hz),
7.44–7.36 (3H, m), 7.24–7.18 (2H, m), 6.79–6.73 (2H, m), 6.58
(1H, d, J = 13.3 Hz), 6.32 (1H, br s), 6.10 (1H, s), 5.97 (1H, br
s), 3.04 (6H, s), 1.40–1.00 (18H, m). The 13C NMR spectrum
was not registered because of the low solubility of 7a.
HRMS (ESI+): calcd for C37H39N4OS 587.2839, found
587.2810 [M + H]+.
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 8684–8691 | 8689

View Article Online
123.8, 123.5, 123.0, 121.8, 118.5, 118.2, 116.4, 115.9, 114.9,
114.1, 114.0, 112.7, 112.1, 111.9, 111.8, 111.8, 48.8, 45.1, 44.7,
40.5, 40.4, 12.8, 12.8. HRMS (ESI+): calcd for C33H32N5
498.2652, found 498.2623 [M + H]+.
nm 411 (log ε: 4.42). IR (Nujol, cm−1): 2218 (CuN), 1666,
1610 (CvC, Ar), 1554 (CvC, Ar), 1553 (CvC, Ar), 1521
(CvC, Ar). 1H NMR (300 MHz, CD2Cl2): δ 7.69 (1H, s),
7.59–7.49 (7H, m), 6.85–6.78 (2H, m), 6.52 (1H, d, J = 1.6 Hz),
5.93–5.91 (2H, m), 3.04 (6H, s), 1.27 (9H, m), 1.24 (9H, s). 13
C
NMR (75 MHz, CD2Cl2): δ 167.7, 165.7, 152.2, 151.8, 149.4,
147.0, 138.4, 137.4, 130.4, 130.1, 129.8, 129.1, 126.6, 125.5,
118.3, 117.3, 112.4, 109.5, 107.1, 106.2, 106.0, 99.0, 40.6, 36.6,
36.2, 28.2, 28.1. HRMS (ESI+): calcd for C36H38N3O 528.3009,
found 555.3025 [M + H]+.
4-Diethylamino-4′′-dimethylamino-2′,4′-dicarbonitrile-3′-phenyl-
[1,1′:5′,1′′-terphenyl] (9)
To obtain 9 as a pure sample, it was further dissolved in the
minimum amount of CH2Cl2 and then hexane was added. The
precipitate was filtered, washed with hexane and dried to afford a
yellow solid (402 mg, 29%). Mp 240–241 °C. Found: C, 81.94;
H, 6.52; N, 11.57. Calc. for C32H30N4: C, 81.67; H, 6.43; N,
11.91%. λmax (CH2Cl2)/nm 392 (log ε: 4.36). IR (Nujol, cm−1):
2221 (CuN), 1606 (CvC, Ar), 1580 (CvC, Ar), 1569 (CvC,
Ar), 1523 (CvC, Ar). 1H NMR (400 MHz, CDCl3): δ
7.59–7.51 (10H, m), 6.83–6.78 (2H, m), 6.77–6.73 (2H, m),
3.42 (4H, q, J = 7.1 Hz), 3.04 (6H, s), 1.21 (6H, t, J = 7.1 Hz).
13C NMR (100 MHz, CD2Cl2): δ 152.5, 151.8, 149.9, 149.8,
149.3, 137.2, 130.7, 130.4, 130.1, 129.8, 129.7, 129.1, 124.8,
123.7, 118.0, 117.9, 112.3, 111.6, 109.5, 109.5, 44.9, 40.5, 12.8.
HRMS (ESI+): calcd for C32H31N4 471.2543, found 471.2517
[M + H]+; calcd for C32H30N4Na 493.2363, found 493.2337
[M + Na]+.
Acknowledgements
Financial support from MICINN-FEDER (CTQ2011-22727 and
MAT2011-27978-C02-02) and Gobierno de Aragón-Fondo
Social Europeo (E39) and a predoctoral fellowship to E. Galán
(CSIC, JAE 2008) are gratefully acknowledged.
Notes and references
1 See for example: (a) S.-i. Kato and F. Diederich, Chem. Commun., 2010,
46, 1994–2006 and references cited therein; (b) T. Michinobu, Pure Appl.
Chem., 2010, 82, 1001–1009 and references cited therein.
2 (a) C. Cai, I. Liakatas, M.-S. Wong, M. Bösch, C. Bosshard, P. Günter,
S. Concilio, N. Tirelli and U. W. Suter, Org. Lett., 1999, 1, 1847–1849;
(b) H. Ma, B. Chen, T. Sassa, L. R. Dalton and A. K.-Y. Jen, J. Am.
Chem. Soc., 2001, 123, 986–987; (c) J. Luo, H. Ma, M. Haller,
A. K.-Y. Jen and R. R. Barto, Chem. Commun., 2002, 888–889; (d) Y. Li,
K. Tsuboi and T. Michinobu, Macromolecules, 2010, 43, 5277–5286.
3 See for example: (a) B. Esembeson, M. L. Scimeca, T. Michinobu,
F. Diederich and I. Biaggio, Adv. Mater., 2008, 20, 4584–4587;
(b) B. B. Frank, M. Kivala, B. Camafort Blanco, B. Breiten,
W. B. Schweizer, P. R. Laporta, I. Biaggio, E. Jahnke, R. R. Tykwinski,
C. Boudon, J.-P. Gisselbrecht and F. Diederich, Eur. J. Org. Chem., 2010,
2487–2503; (c) B. Breiten, I. Biaggio and F. Diederich, Chimia, 2010,
64, 409–413; (d) M. T. Beels, M. S. Fleischman, I. Biaggio, B. Breiten,
M. Jordan and F. Diederich, Opt. Mater. Express, 2012, 2, 294–303;
(e) M. Chiu, B. Jaun, M. T. R. Beels, I. Biaggio, J.-P. Gisselbrecht,
C. Boudon, W. B. Schweizer, M. Kivala and F. Diederich, Org. Lett.,
2012, 14, 54–57.
4 See for example: (a) T. Michinobu, J. C. May, J. H. Lim, C. Boudon,
J.-P. Gisselbrecht, P. Seiler, M. Gross, I. Biaggio and F. Diederich, Chem.
Commun., 2005, 737–739; (b) T. Michinobu, C. Boudon,
J.-P. Gisselbrecht, P. Seiler, B. Frank, N. N. P. Moonen, M. Gross and
F. Diederich, Chem.–Eur. J., 2006, 12, 1889–1905; (c) M. Jordan,
M. Kivala, C. Boudon, J.-P. Gisselbrecht, W. B. Schweizer, P. Seiler and
F. Diederich, Chem.–Asian J., 2011, 6, 396–401.
5 (a) M. Kivala, C. Boudon, J.-P. Gisselbrecht, P. Seiler, M. Gross and
F. Diederich, Chem. Commun., 2007, 4731–4733; (b) P. Reutenauer,
M. Kivala, P. D. Jarowski, C. Boudon, J.-P. Gisselbrecht, M. Gross and
F. Diederich, Chem. Commun., 2007, 4898–4900.
6 P. D. Jarowski, Y.-L. Wu, C. Boudon, J.-P. Gisselbrecht, M. Gross,
W. B. Schweizer and F. Diederich, Org. Biomol. Chem., 2009, 7, 1312–
1322.
7 F. Silvestri, M. Jordan, K. Howes, M. Kivala, P. Rivera-Fuentes,
C. Boudon, J.-P. Gisselbrecht, W. B. Schweizer, P. Seiler, M. Chiu and
F. Diederich, Chem.–Eur. J., 2011, 17, 6088–6097.
Compounds 7c, 10
Eluent: CH2Cl2–AcOEt (100 : 1).
(3E,5Z)-7-(2,6-Di-tert-butyl-4H-pyran-4-ylidene)-6-(4-
(dimethylamino)phenyl)2-phenylhepta-1,3,5-triene-1,1,3-
tricarbonitrile (7c)
A further purification through flash chromatography using
CH2Cl2–AcOEt (100 : 0.5) was needed. Then, the residue was
dissolved in the minimum amount of CH2Cl2, hexane was added
and the precipitate was filtered, washed with hexane and dried to
afford a blue solid (14 mg, 5%). Mp 272–276 °C. Found: C,
80.32; H, 6.75; N, 10.34. Calc. for C37H38N4O: C, 80.11; H,
6.90; N, 10.10%. IR (Nujol, cm−1): 2212 (CuN), 2202 (CuN),
1644 (CvC, Ar), 1610 (CvC, Ar). 1H NMR (400 MHz,
CD2Cl2): δ 7.45–7.38 (3H, m), 7.30–7.25 (2H, m), 7.11 (1H, d,
J = 13.2 Hz), 7.06–7.00 (2H, m), 6.79 (1H, d, J = 13.2 Hz),
6.65–6.60 (2H, m), 6.19 (1H, s), 5.98 (1H, s), 5.87 (1H, br s),
2.99 (6H, s), 1.26 (9H, s), 1.04 (9H, s). 13C NMR (75 MHz,
CD2Cl2): δ 166.9, 166.8, 154.9, 152.5, 149.7, 136.4, 131.3,
131.1, 129.9, 129.1, 125.7, 122.1, 116.9, 116.9, 116.1, 115.4,
112.6, 110.0, 105.0, 97.0, 40.6, 36.7, 28.1, 28.0. HRMS (ESI+):
calcd for C37H39N4O 555.3118, found 555.3090 [M + H]+;
calcd for C37H38N4ONa 577.2938, found 577.2890 [M + Na]+.
8 D. T. S. Rijkers, F. de Prada López, R. M. J. Liskamp and F. Diederich,
Tetrahedron Lett., 2011, 52, 6963–6967.
9 G. Jayamurugan, J.-P. Gisselbrecht, C. Boudon, F. Schoenebeck,
W. B. Schweizer, B. Bernet and F. Diederich, Chem. Commun., 2011, 47,
4520–4522.
4-Dimethylamino-5′-(2,6-di-tert-butyl-4H-pyran-4-
ylidenemethyl)[1,1′:3′,1′′-terphenyl]-2′,4′-dicarbonitrile (10)
10 R. Andreu, E. Galán, J. Orduna, B. Villacampa, R. Alicante, J. T. López
Navarrete, J. Casado and J. Garín, Chem.–Eur. J., 2011, 17, 826–838.
11 (a) L. Han, Y. Jiang, W. Li, Y. Li and P. Hao, Spectrochim. Acta, Part A,
2008, 71, 86–89; (b) S. Tada and Y. Ito, Jp. Pat., 61103862 A, 1986
(Chem. Abstr., 1987, 106, 76075).
A further purification through flash chromatography on silica gel
using CH2Cl2–AcOEt (100 : 0.5) was needed first, and then a
TLC preparative using hexane–AcOEt (7 : 3) as eluent to afford
a yellow solid (30 mg, 12%). Mp 239–242 °C. λmax (CH2Cl2)/
8690 | Org. Biomol. Chem., 2012, 10, 8684–8691
This journal is © The Royal Society of Chemistry 2012

View Article Online
12 R. Andreu, L. Carrasquer, S. Franco, J. Garín, J. Orduna, N. Martínez de
Baroja, R. Alicante, B. Villacampa and M. Allain, J. Org. Chem., 2009,
74, 6647–6657.
13 M. Kivala, C. Boudon, J.-P. Gisselbrecht, B. Enko, P. Seiler, I. B. Müller,
N. Langer, P. D. Jarowski, G. Gescheidt and F. Diederich, Chem.–Eur. J.,
2009, 15, 4111–4123.
14 C. Dehu, F. Meyers and J.-L. Brédas, J. Am. Chem. Soc., 1993, 115,
6198–6206.
15 Y.-L. Wu, P. D. Jarowski, W. B. Schweizer and F. Diederich, Chem.–Eur.
J., 2010, 16, 202–211.
22 See for example: (a) J. A. Davies, A. Elangovan, P. A. Sullivan,
B. C. Olbricht, D. H. Bale, T. R. Ewy, C. M. Isborn, B. E. Eichinger,
B. H. Robinson, P. J. Reid, X. Li and L. R. Dalton, J. Am. Chem. Soc.,
2008, 130, 10565–10575; (b) M. C. Ruiz Delgado, J. Casado,
V. Hernández, J. T. López Navarrete, J. Orduna, B. Villacampa,
R. Alicante, J.-M. Raimundo, P. Blanchard and J. Roncali, J. Phys.
Chem. C, 2008, 112, 3109–3120.
23 E. Galán, R. Andreu, J. Garín, L. Mosteo, J. Orduna, B. Villacampa and
B. E. Diosdado, Tetrahedron, 2012, 68, 6427–6437.
24 (a) J. L. Oudar and D. S. Chemla, J. Chem. Phys., 1977, 66, 2664–2668;
(b) D. R. Kanis, M. A. Ratner and T. J. Marks, Chem. Rev., 1994, 94,
195–242.
16 R. Gompper and H.-U. Wagner, Angew. Chem., Int. Ed., 1988, 27, 1437–
1455.
17 S.-i. Kato, M. T. R. Beels, P. La Porta, W. B. Schweizer, C. Boudon,
J.-P. Gisselbrecht, I. Biaggio and F. Diederich, Angew. Chem., Int. Ed.,
2010, 49, 6207–6211.
18 R. M. Acheson and J. Woollard, J. Chem. Soc., Perkin Trans. 1, 1975,
744–748.
19 (a) S. Alías, R. Andreu, M. J. Blesa, S. Franco, J. Garín, A. Gragera,
J. Orduna, P. Romero, B. Villacampa and M. Allain, J. Org. Chem.,
2007, 72, 6440–6446; (b) R. Andreu, L. Carrasquer, J. Garín,
M. J. Modrego, J. Orduna, R. Alicante, B. Villacampa and M. Allain,
Tetrahedron Lett., 2009, 50, 2920–2924.
25 (a) G. Bourhill, J.-L. Brédas, L.-T. Cheng, S. R. Marder, F. Meyers,
J. W. Perry and B. G. Tiemann, J. Am. Chem. Soc., 1994, 116, 2619–
2620; (b) For D–A polyenes, β can be maximized when there is an
optimal degree of mixing between neutral and charge-separated canonical
forms. As a function of increasing polarization, and starting from chromo-
phores with weak D and A groups, β is positive, first increases, peaks in a
positive sense, decreases, crosses through zero at the cyanine limit, and
then becomes negative when the ground state of the molecule becomes
zwitterionic. The rationalization of this behavior has allowed the estab-
lishment of very useful guidelines for the design of NLO chromophores.
Molecules showing high positive (negative) β values with ground-states
lying halfway between the neutral (zwitterionic) and the cyanine limit
forms have been named left (right)-hand side chromophores.
20 C. W. Bird, Tetrahedron, 1986, 42, 89–92.
21 C. Reichardt and T. Welton, Solvents and Solvents Effects in Organic
Chemistry, Wiley-VCH Verlag GmbH & Co., Weinheim, 4th edn, 2010.
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 8684–8691 | 8691