Synthesis and nonlinear optical properties of chromophores for photorefractive polymer materials

Article abstract of DOI:10.1016/j.tet.2009.03.099

The synthesis and nonlinear optical (NLO) properties of a series of nitrostilbene-, dinitrostilbene-, and dicyanomethylenedihydrofuran-based chromophores potentially useful in photorefractive multifunctional polymers are reported. Electronic absorption sp

Full text of DOI:10.1016/j.tet.2009.03.099

Tetrahedron 65 (2009) 4513–4520
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and nonlinear optical properties of chromophores for photorefractive
polymer materials
a
a
a
b
´
´
´
Enrique Font-Sanchis , Francisco J. Cespedes-Guirao , Angela Sastre-Santos , Belen Villacampa ,
c
b
a,
*
´
´
´
Jesus Orduna , Raquel Alicante , Fernando Fernandez-Lazaro
a
´
´
´
´
´
Division de Quımica Organica, Instituto de Bioingenierıa, Universidad Miguel Hernandez, Elche 03202 (Alicante), Spain
b Departamento de F´ısica de la Materia Condensada, ICMA, Universidad de Zaragoza-CSIC, Zaragoza 50009, Spain
c
´
Departamento de Qu´ımica Organica, ICMA, Universidad de Zaragoza-CSIC, Zaragoza 50009, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and nonlinear optical (NLO) properties of a series of nitrostilbene-, dinitrostilbene-, and
dicyanomethylenedihydrofuran-based chromophores potentially useful in photorefractive multifunc-
tional polymers are reported. Electronic absorption spectra have been measured in different solvents.
Electric field induced second harmonic (EFISH) generation results show that the 2-dicyanomethylen-3-
cyano-5,5-dimethyl-2,5-dihydrofuran moieties lead to the best NLO performances. Dinitrophenyl-based
chromophores have shown a reduced nonlinear response as compared with the mononitro analogues.
Nonlinear optical properties of a selected nitro–dinitro couple have been also determined theoretically.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 20 February 2009
Received in revised form 25 March 2009
Accepted 30 March 2009
Available online 5 April 2009
1. Introduction
showing one or two of the functional properties needed to origi-
nate PR effect, and doped with molecules responsible for the rest of
Under the name of photorefractive (PR) effect lies the synergistic
collaboration of four physical processes, namely charge photo-
generation, charge transport, charge trapping and electrooptic re-
sponse, which altogether lead to a spatial modulation of the
refraction index after irradiation of the material with a laser light
intensity pattern.1 Once these conditions are achieved, an internal
redistribution of charges takes place, which induces the variation
on the refraction index. This effect was first observed in inorganic
materials like LiNbO3, BaTiO3 and GaAs.2 However, the application
of these materials has been limited by technical problems like
sample preparation. On the other hand, organic PR materials ex-
hibit some PR performances, which are better than the corre-
sponding of inorganic materials, with the exception of speed of
grating formation. Moreover, organic materials are produced and
processed easier and at lower cost than the inorganic ones. This is
why they are candidates for applications in optical holographic data
storage, real-time image processing and phase conjugation.3
There are three main strategies to achieve photorefractivity in
organic materials. The first one consists in the mixing as a blend of
an inert polymer with different molecules, each of them re-
sponsible for one, or even two, of the required physical processes.
The second one is the preparation of a functional homopolymer
the functional properties. The last possibility is the synthesis of
a multifunctional copolymer by using all the required physically
active molecules as comonomers.4 All these strategies have their
own advantages, disadvantages and limitations.
In recent times, we have devoted some effort to the preparation
of improved photosensitizers, i.e., molecules for charge photo-
generation, in a successful attempt to increase the photorefractive
speed. Thus, we have designed and synthesized some trinitro-
fluorenone-C60 dyads that generated PR compositions showing
faster photorefractive responses than the corresponding composi-
5
tions containing either trinitrofluorenone or C60
.
Now, we have
focused our research in the study of the effect of material prepa-
ration (blend, multifunctional polymer, sol–gel hybrid organic–in-
organic material) on the PR performances. Hence, we have
designed and studied some series of nonlinear optical (NLO) com-
pounds, bearing a hydroxy group to allow for further anchoring to
a polymer chain.
Among other properties, chromophores for PR applications
should posses large dipole moment (
) values, besides a high linear polarizability anisotropy.3,4,6 It is
well known that the use of -conjugated bridges endcapped with
strong electron donor and acceptor groups (D– –A systems) leads
m) and first hyperpolarizability
(b
p
p
to molecules with high mb values, but usually with red shifted
electronic spectra, detrimental for many applications.7 In the 1990s,
a systematic relation between the ground state polarization, which
depends on both the strength of the terminal groups and the length
* Corresponding author.
E-mail addresses: bvillaca@unizar.es (B. Villacampa), fdofdez@umh.es (F.
and nature of the p-bridge, and b
values was proposed.8 Among the
´
´
Fernandez-Lazaro).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.03.099

4514
E. Font-Sanchis et al. / Tetrahedron 65 (2009) 4513–4520
OH
OH
O
O
O
O2N
O2N
O
O
1
2
OH
OH
OH
O
O
O
O2N
O2N
O2N
3
4
5
NO2
NO2
NO2
OH
O
O
O
O
O
NC
NC
NC
O
CN
CN
CN
CN
6
7
8
CN
CN
Chart 1.
different approaches followed to increase the NLO efficiency, mol-
ecules having novel electron deficient heterocyclic acceptors have
been studied. In particular, 2,5-dihydrofuran-substituted chromo-
phores have shown very high mb values9 and good thermal stability
and some of them have been successfully incorporated into PR
polymer composites.10 On the other hand, in order to eliminate
some of the problems (as phase separation or sublimation) arising
when using blends, the chemical incorporation of NLO moieties
into a polymeric structure has attracted much attention.3,4a Given
the better thermal and temporal stabilities of these systems, the
possibility of easy covalent insertion in polymeric chains is an in-
teresting molecular characteristic.
Here, we present the synthesis, characterization and nonlinear
optical study of new push–pull chromophores 1–8, which can
be used in a PR composition, as a blend, or can be attached to form
a multifunctional PR polymer. To the best of our knowledge, this is
the first time that the NLO properties of 2-dicyanomethylen-3-
cyano-5,5-dimethyl-2,5-dihydrofuran-based chromophores bearing
oxygen atoms as donors are described. The preparation of the poly-
mers and the study of the PR properties of the blends and polymers
are out of the scope of this paper and will be presented elsewhere.
2. Results and discussions
2.1. Synthesis of NLO chromophores
The preparation of the different NLO chromophores (Chart 1)
was accomplished by two different strategies. Thus, the nitro-
stilbene derivatives 1 and 2 were obtained via Heck reaction,11
while the dinitrostilbene derivatives 3–5 and the tricyano de-
rivatives
6–8
were
synthesized
using
Knoevenagel
condensations.12
The synthesis of compound 1 is depicted in Scheme 1. Thus,
bromination of 2-hexyloxyphenol13 followed by alkylation afforded
compound 10 in good yield. However, this compound failed to
couple with 4-nitrostyrene.14 Treatment of compound 10 with
butyllithium and subsequent quenching with N-formylpiperidine
generated aldehyde 11, which also failed to yield 1 by either
Knoevenagel condensation or Wittig reaction. Lithium-mediated
exchange of bromine by iodine in compound 10 led to 12 in low
yield. This compound happened to be very unstable, and was
characterized only by 1H NMR. However, quick handling of 12
allowed for coupling with 4-nitrostyrene to afford 1.
OH
OH
Br
OH
OH
Br
O
OHC
O
ii
i
v
O
O
O
O
9
10
11
vii
vi
iii
3
6
OH
iv
I
O
1
O
12
Scheme 1. (i) Br2, CH2Cl2 (ii) 2-chloroethanol, KI, K2CO3, 120 ꢀC, DMF; (iii) n-BuLi, ꢁ78 ꢀC then I2; (iv) p-nitrostyrene, Pd(OAc)2, triethylamine, DMF; (v) n-BuLi, ꢁ78 ꢀC, THF then N-
formylpiperidine; (vi) dinitrotoluene, AcOH, NH4OAc, pyridine, molecular sieves, 80 ꢀC; (vii) 2-dicyanomethylen-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran, AcOH, NH4OAc, pyri-
dine, molecular sieves, 80 ꢀC.

E. Font-Sanchis et al. / Tetrahedron 65 (2009) 4513–4520
4515
Table 1
OH
UV–vis data and experimental nonlinearities of compounds 1–8
i
I
OH
I
O
Compound lmax (nm) MeOH//DCM//DMSO mba (10ꢁ48 esu) mb(0)a (10ꢁ48 esu)
13
1
2
377//381//397
380//386//398
90ꢂ10
150ꢂ20
130ꢂ20b
54ꢂ6
73
120
103b
42
ii
3
4
400//406//414
405//414//417
90ꢂ20
70
80ꢂ20b
190ꢂ20
360ꢂ30
460ꢂ40
460ꢂ60
62b
145
259
330
324
5
6
7
8
405//423//419
458//462//469
461//465//469
468//476//471
2
Scheme 2. (i) 2-Chloroethanol, KI, K2CO3, 120 ꢀC, DMF; (ii) p-nitrostyrene, Pd(OAc)2,
triethylamine, DMF.
mb(0) values have been deduced using the two-level dispersion model.19
a
Scheme 2 shows the synthesis of compound 2. Thus, alkylation
of 4-iodo-2,5-dimethylphenol15 afforded compound 13, which
underwent Heck reaction with p-nitrostyrene to yield the nitro-
stilbene in moderate yield. Interestingly, Heck reaction using the
bromo analogue 14 yielded only starting materials.
The dinitrostilbene 3 was prepared by Knoevenagel condensa-
tion between 11 and 2,4-dinitrotoluene (Scheme 1). Alkylation of
4-bromo-2,5-dimethylphenol,16 followed by lithium–bromine
exchange and quenching with N-formylpiperidine generated al-
dehyde 16 (Scheme 3), which afforded 4 after condensation with
2,4-dinitrotoluene. Compound 5 was prepared in a similar way
starting from 2-ethylhexyl 4-bromo-2,5-dimethylphenyl ether.17
Knoevenagel condensation of aldehydes 11, 16 and 17 with 2-
dicyanomethylen-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran18 afforded
compounds 6 (Scheme 1), 7 and 8 (Scheme 3), respectively.
In CH2Cl2 at 1.907
In DMSO at 1.907
mm.
b
m
m.
25000
20000
15000
10000
5000
0
2
4
7
The E configuration for alkenes 1–8 was assigned as a result of
the coupling constants (ca. 16 Hz) showed by the olefinic protons in
the corresponding 1H NMR spectra.
350
400
450
λ (nm)
500
550
600
2.2. Optical characterization
Figure 1. UV–vis absorption spectra of compounds 2, 4 and 7 in CH2Cl2.
the otherhand, the absorption bands slightlyshift to lower energy in
the following sequence of donor groups: hydroxyethyl hexyl-
oxyphenyl ether<hydroxyethyl dimethylphenyl ether<ethylhexyl
dimethylphenyl ether.
UV–vis spectra of compounds 1–8, showing a visible wavelength
band, have been measured in methanol, CH2Cl2 and DMSO. The
wavelength of maximal charge transfer absorption (lmax) is shown
in Table 1.
Second order nonlinearities of these compounds have been in-
vestigated by using the EFISH technique at 1.907 mm. The experi-
For a given donor group, a progressive bathochromic shift of lmax
in the sequence: nitrophenyl<dinitrophenyl<dihydrofuran de-
rivative acceptors is observed, as expected according to the in-
creasing withdrawing character of the groups. As an example, the
optical absorption spectra of compounds 2, 4, 7 (bearing the
hydroxyethyl dimethylphenyl ether donor) are shown in Figure 1.
The same behaviour is observed regardless of the donor group. On
mental mb and mb(0) values are also summarized in Table 1.
It can be seen that the higher mb values measured in this work
correspond to compounds 6–8, having the 2-dicyanomethylen-3-
cyano-5,5-dimethyl-2,5-dihydrofuran moiety as acceptor. As we
mentioned above, dihydrofuran-based groups are very efficient
OH
ii
4, R =
5, R =
iii
i
OHC
OR
OH
Br
OR
OH
Br
OH
16, R =
17, R =
14, R =
15, R =
iv
OH
7, R =
8, R =
Scheme 3. (i) For compound 14: 2-chloroethanol, NaOH, H2O, reflux; (ii) n-BuLi, ꢁ78 ꢀC, 12-crown-4, THF, then N-formylpiperidine; (iii) benzene, AcOH, Et2NH, dinitrotoluene,
reflux; (iv) NaH, DMF, 2-dicyanomethylen-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran, reflux.

4516
E. Font-Sanchis et al. / Tetrahedron 65 (2009) 4513–4520
acceptors,9 so it was thus expected that these molecules gave rise to
higher NLO responses than those of the (di)nitrophenyl-substituted
counterparts (compounds 1–5), as confirmed by the experiment.
However, those values are far from the extremely high molecular
nonlinearities found for other chromophores ended with the same
acceptor group and much stronger donor moieties.9 Regarding
nitrocompounds, the obtained mb values are in good agreement
with the results reported for related nitrostilbene chromophores
bearing oxygen as donor.20 The mb(0) values obtained for the dinitro
derivative 5 and dihydrofuran derivatives 6–8 (in the range 150–
330ꢃ10ꢁ48 esu) are comparable to those of other classical NLO
chromophores utilized in high performance PR composites,3,21,22 as
2,5-dimethyl-4-(2-hydroxyethoxy)-40-nitroazobenzene (DMHNAB)
energy from 2 to 4 obtained by TD-DFT calculations agrees with the
bathochromic shift observed in UV–vis spectra, although theoreti-
cal lmax values are overestimated (lmax¼413 nm and 463 nm for 2
and 4, respectively). This decrease should favour the NLO response
of compound 4, but the calculated mge and Dmge values point into
the opposite sense and then the b(0) value calculated using the
two-level model expression (see above) is higher for 2. The higher
difference between excited and ground state dipole moments
obtained for 2 seems to agree with the stronger solvatochromism
observed when absorption spectra are taken in CH2Cl2 and DMSO
(12 nm vs 3 nm for 2 and 4, respectively). Moreover, the lower
transition dipole moment mge calculated for compound 4 is also in
qualitative accordance with the lower oscillator strength (f) esti-
mated from the area under the measured absorption band of 4 as
compared to 2 (Fig. 1). A ratio of f values close to 0.8 has been
obtained from this comparison.
or 2,5-dimethyl-4-(40-nitrophenylazo)anisole (DMNPAA)23
(mb(0)z
200ꢃ10ꢁ48 esu).
Finally, and concerning the donor end of the molecules, it is
worth mentioning the general trend that 1-alkoxy-2,5-dimethyl
substitution leads to better NLO responses than the 1,2-dialkoxy
pattern, as shown when comparing the 1/2, 3/4 and 6/7 couples.
2.3. Theoretical calculations
Regarding the experimental values of compounds 1/3 and 2/4, it
should be noted that dinitro compounds did not represent an im-
provement over their mononitro analogues. Concerning spectro-
scopic properties, the predictable bathochromic shift of the
absorption band of 3 and 4 relative to 1 and 2, respectively, is ob-
served in the UV–vis spectra taken in CH2Cl2 as well as in DMSO
and MeOH. Although the dinitro substitution usually gives rise to
an enhancement of the NLO response, a decrease of the measured
mb values in a series of dinitrostilbenes when compared to nitro-
stilbenes had been previously reported.20,24 The authors concluded
that there was an important change in the orientation of the dipole
moment and hence the projection of
rection and so the measured mb values were reduced. An analogous
change in the orientation of was confirmed theoretically for
chromophores having 1,3-dithiol-2-ylidene donor and azine
spacer.25 However, in these compounds the change was not as large
and both experimental and calculated mb values increased on
passing from nitro to dinitro substitution. Trying to take some in-
sight into this fact, mb(0) values for model compounds 2 and 4 were
3. Conclusion
The synthesis and NLO characterization of some push–pull al-
kenes have been accomplished. Results show that the 2-dicyano-
methylen-3-cyano-5,5-dimethyl-2,5-dihydrofuran moiety acting as
acceptor leads to the best NLO performances. Somewhat surpris-
ingly, the use of a 2,4-dinitrophenyl group as electron-accepting
subunit results in lower NLO responses when compared to 4-
nitrophenyl-substituted compounds. CPHF calculations, which
b on the dipole moment di-
usually provide b(0) values closer to the experimental ones than
those calculated by TD-DFT, fail to predict the experimental trend.
Bearing in mind that TD-DFT method is used only to take an in-
tuitive description of NLO behaviour, it provides us with the de-
crease of the transition dipole moment, mge, as well as with the
difference Dmge between the excited and ground state dipole mo-
ments, when passing from nitro to dinitro substitution. These re-
sults lead to mb(0) values lower for the compound with double nitro
substitution as observed in the experiment.
m
calculated (CPHF/6-31G
*
//B3P86/6-31G
*
model). While calcula-
on passing from
tions predict again a change in the orientation of
m
2 to 4, it is not large enough to cause a decrease in mb; as shown in
Table 2, CPHF results show a pronounced increase of the NLO re-
sponse going from nitro to dinitro chromophores. Although CPHF-
calculated values are usually closer to the experimental ones than
those calculated by TD-DFT, we have also used the latter method in
order to obtain a more intuitive description of the NLO behaviour of
the studied compounds.
4. Experimental
4.1. Synthesis of NLO chromophores
All chemicals were reagent-grade, purchased from commercial
sources, and used as received, unless otherwise specified. Column
Chromatography: SiO2 (40–63 mm). TLC plates coated with SiO2
60F254 were visualized by UV light. NMR spectra were measured
with a Bruker AC 300 and with a Bruker AVANCE DRX-500. UV–vis
spectra were recorded with a Helios Gamma spectrophotometer
and IR spectra with a Nicolet Impact 400D spectrophotometer.
Mass spectra were obtained from an Agilent 5973 Network Mass
spectrometer. Elemental analyses were performed on a Thermo
Finnigan Flash 1112 CHN elemental analyzer.
Therefore, we have calculated the parameters needed to eval-
uate b0 in the two-level model19 0fDmge m2ge/E2, where Dmge is
(b
the difference between the excited and ground state dipole mo-
ments, me and mg, respectively, mge is the transition dipole moment,
related to the oscillator strength, and E is the excitation energy). A
summary of these parameters is gathered in Table 2. As opposed to
CPHF results, a higher
b(0) value is obtained using TD-DFT pa-
rameters and the two-level approach. The decrease of the transition
4.1.1. Synthesis of 4-bromo-2-hexyloxyphenol (9)
a
cooled solution (0 ꢀC) of 2-hexyloxyphenol13 (4.5 g,
Table 2
To
Calculated NLO properties of compounds 2 and 4
23.20 mmol) in 100 mL of dichloromethane was added dropwise
a solution of bromine (3.7 g, 23.15 mmol) in 50 mL of dichloro-
methane. After addition, the reaction was stirred at room temper-
ature for 1 h, then was washed with 10% sodium hydroxide and
dried with magnesium sulfate; the solvent was distilled off by an
evaporator. The crude product was purified by chromatography on
silica gel (hexane/ethyl acetate, 9:1) to give an oil (4.94 g, 78%). 1H
Compound
TD-DFTa
CPHFb
E (eV)
mg(D)
mge(D)
Dmge(D)
b
(0)c
mb(0)d
2
4
3.00
2.68
8.66
9.10
8.29
7.04
24.27
19.33
216
156
115
470
a
B3P86/6-31G
*
level.
b
c
CPHF/6-31G
*
level.
In 10ꢁ30 esu.
In 10ꢁ48 esu.
NMR (CDCl3):
d
6.97 (d, 1H, J¼8.8 Hz), 6.96 (s, 1H), 6.80 (d, 1H,
d
J¼8.8 Hz), 3.99 (t, 2H, J¼6.6 Hz), 1.72–1.80 (m, 2H), 1.26–1.46 (m,

E. Font-Sanchis et al. / Tetrahedron 65 (2009) 4513–4520
4517
6H), 0.91 (t, 3H, J¼6.9 Hz); 13C NMR (CDCl3):
d
146.6, 144.9, 123.8,
(67.9 mg, 0.3 mmol), and triethylamine (0.5 mL) in 10 mL of dry
DMF was stirred under argon at 130 ꢀC for 24 h. After the mixture
was washed with water, extracted with ether and evaporated, the
residue was purified by flash column chromatography (hexane/
ethyl acetate, 2:1) to afford the corresponding coupled product
115.6, 114.8, 111.4, 69.1, 31.4, 28.9, 25.5, 22.5, 13.9; MS (EI) m/z: 272
(Mþ, 38), 274 (37), 190 (99), 188 (100); IR (KBr): 3541 cmꢁ1. Anal.
Calcd for C12H17BrO: C, 52.76; H, 6.27. Found: C, 52.75; H, 6.42%.
4.1.2. Synthesis of 2-(40-bromo-20-hexyloxyphenoxy)-
ethan-1-ol (10)
(0.42 g, 39%). 1H NMR (CDCl3):
d
8.19 (d, 2H, J¼8.8 Hz), 7.59 (d, 2H,
J¼8.8 Hz), 7.20 (d, 1H, J¼16.3 Hz), 7.10 (s, 1H), 7.08 (d, 1H, J¼8.8 Hz),
6.99 (d, 1H, J¼16.3 Hz), 6.94 (d, 1H, J¼8.8 Hz), 4.15 (t, 2H, J¼4.6 Hz),
4.06 (t, 2H, J¼6.7 Hz), 3.93 (t, 2H, J¼4.6 Hz), 1.78–1.90 (m, 2H), 1.33–
A mixture of 4-bromo-2-hexyloxyphenol 9 (6 g, 22 mmol), po-
tassium carbonate (6 g, 43.5 mmol), potassium iodide (1.8 g,
10.8 mmol), 2-chloroethanol (3 mL), and DMF (30 mL) was heated at
120 ꢀC for 24 h. The reaction mixture was cooled in an ice bath.
Hydrochloric acid (10%, 40 mL) and diethyl ether (20 mL) were
added and the two phases were separated. The water phase was
extracted twice with diethyl ether. The resulting organic phases
were combined and washed with water. The organic extracts were
dried oversodium sulfatean evaporated. The residuewas purified by
chromatography on silica gel (hexane/ethyl acetate, 2:1) to gave an
1.52 (m, 6H), 0.91 (t, 3H, J¼7.0 Hz); 13C NMR (acetone-d6):
d 152.0,
151.5, 148.3, 146.6, 135.2, 132.0, 128.6, 126.1, 125.8, 123.0, 116.4,
114.0, 73.0, 70.8, 62.4, 33.3, 31.0, 27.5, 24.3, 15.3; MS (EI) m/z: 385
(Mþ, 94), 355 (18), 301 (22), 257 (100); IR (KBr): 3425, 1512,
1346 cmꢁ1; mp: 92–93 ꢀC. Anal. Calcd for C22H27NO5: C, 68.55; H,
7.06; N, 3.63. Found: C, 68.61; H, 7.08; N, 3.75%.
4.1.6. Synthesis of 2-(40-iodo-20,50-dimethylphenoxy)-
ethan-1-ol (13)
oil (4.80 g, 69%). 1H NMR (CDCl3):
d
6.97 (m, 2H), 6.77 (d, 1H,
J¼9.0 Hz), 4.05 (t, 2H, J¼4.8 Hz), 3.94 (t, 2H, J¼6.8 Hz), 3.87 (t, 2H,
A mixture of 4-iodo-2,5-dimethylphenol15 (3.8 g, 15.32 mmol),
potassium carbonate (4.3 g, 31.2 mmol), potassium iodide (1.3 g,
7.8 mmol), 2-chloroethanol (2.1 mL) and DMF (30 mL) was heated
at 120 ꢀC overnight. The reaction mixture was cooled in an ice
bath. Hydrochloric acid (10%, 40 mL) and diethyl ether (20 mL)
were added and the two phases were separated. The water phase
was extracted twice with diethyl ether. The resulting organic
phases were combined and washed with water. The organic ex-
tracts were dried over sodium sulfate an evaporated. The residue
was purified by chromatography on silica gel (hexane/ethyl ace-
tate, 2:1) to afford a white solid (2.9 g, 65%). 1H NMR (CDCl3):
J¼4.8 Hz),1.76–1.85 (m, 2H),1.30–1.48(m, 6H), 0.89 (t, 3H, J¼6.9 Hz);
13C NMR (CDCl3):
d 150.4, 147.5, 123.6, 117.1, 116.5, 114.2, 72.1, 69.2,
61.2, 31.4, 28.9, 25.6, 22.5, 13.9; MS (EI) m/z: 316 (Mþ, 35), 318 (34),
234 (39), 232 (41), 190 (99), 188 (100); IR (KBr): 3368 cmꢁ1. Anal.
Calcd for C14H21BrO3: C, 53.01; H, 6.67. Found: C, 52.95; H, 6.68%.
4.1.3. Synthesis of 3-hexyloxy-4-(20-hydroxyethoxy)-
benzaldehyde (11)
To a solution of 2-(40-bromo-20-hexyloxyphenoxy)ethan-1-ol 10
(3.85 g, 12.10 mmol) in tetrahydrofuran (50 mL) at ꢁ78 ꢀC under
nitrogen atmosphere was added butyllithium (12 mL of a 2.5 M
solution in hexanes) and the reaction mixture was stirred 1 h. Then,
3.4 g of N-formylpiperidine were added, and the reaction was kept
at room temperature for 24 h. After cooling in an ice bath, hydro-
chloric acid (10%, 40 mL) was added. The crude was extracted with
diethyl ether and the organic extracts were washed and dried with
anhydrous sodium sulfate. Solvent was removed, and the residue
was purified by chromatography on silica gel (hexane/ethyl acetate,
d
7.53 (s, 1H), 6.72 (s, 1H), 4.04 (t, 2H, J¼4.8 Hz), 3.96 (t, 2H,
J¼4.8 Hz), 2.37 (s, 3H), 2.15 (s, 3H); 13C NMR (CDCl3):
d 156.9,
140.1, 139.5, 126.5, 113.1, 89.8, 69.4, 61.5, 27.9, 15.2; MS(EI) m/z:
292 (Mþ, 98), 248 (100), 121 (62), 91 (40); IR (KBr): 3294 cmꢁ1
;
mp: 110–112 ꢀC. Anal. Calcd for C10H13IO2: C, 41.12; H, 4.49. Found:
C, 41.49; H, 4.48%.
4.1.7. Synthesis of (E)-1-[20,50-dimethyl-40-(200-hydroxyethoxy)-
phenyl]-2-(40-nitrophenyl)-ethene (2)
2:1) to yield an oil (1.19 g, 37%). 1H NMR (acetone-d6):
d 9.85 (s, 1H),
7.50 (dd, 1H, J¼8.2, 1.9 Hz), 7.42 (d, 1H, J¼1.9 Hz), 7.17 (d, 1H,
J¼8.2 Hz), 4.20 (t, 2H, J¼4.8 Hz), 4.10 (t, 2H, J¼6.8 Hz), 3.9 (t, 2H,
J¼4.8 Hz), 1.77–1.85 (m, 2H), 1.35–1.53 (m, 6H), 0.90 (t, 3H,
A mixture of 2-(40-iodo-20,50-dimethylphenoxy)ethan-1-ol 13
(2.34 g, 8.01 mmol), 4-nitrostyrene (1.56 g, 10.45 mmol), Pd(OAc)2
(43 mg, 0.19 mmol), and triethylamine (1.7 mL) in 30 mL of dry
DMF was refluxed under argon for 17 h. After the mixture was
washed with water, extracted with ethyl acetate and evaporated,
the residue was purified by flash column chromatography (hex-
ane/ethyl acetate, 2:1) to generate an orange solid (1.2 g, 48%). 1H
J¼6.9 Hz); 13C NMR (acetone-d6):
d 192.3, 156.4, 151.4, 132.4, 127.5,
114.7, 113.4, 72.7, 70.7, 62.2, 33.3, 31.0, 27.4, 24.3, 15.3; MS (EI) m/z:
266 (Mþ, 44), 182 (48), 138 (100); IR (KBr): 3437, 1689 cmꢁ1. Anal.
Calcd for C15H22O4: C, 67.65; H, 8.33. Found: C, 67.64; H, 8.24%.
NMR (CDCl3):
d
8.18 (d, 2H, J¼8.8 Hz), 7.58 (d, 2H, J¼8.8 Hz), 7.42
4.1.4. Synthesis of 2-(20-hexyloxy-40-iodophenoxy)ethan-1-ol (12)
To a solution of 2-(40-bromo-20-hexyloxyphenoxy)ethan-1-ol 10
(7.87 g, 21.61 mmol) in tetrahydrofuran (40 mL) at ꢁ78 ꢀC under
nitrogen atmosphere was added butyllithium (17.3 mL of a 2.5 M
solution in hexanes) and the mixture was stirred 1 h. Then, a solu-
tion of iodine (5.58 g) in tetrahydrofuran (10 mL) was added over
15 min. The reaction was kept at room temperature for 45 min and
water (30 mL) was added. The crude was extracted with diethyl
ether and the organic extracts were washed and dried with anhy-
drous sodium sulfate. Solvent was removed, and the residue was
purified by chromatography on silica gel (hexane/ethyl acetate, 2:1)
(s, 1H), 7.43 (d, 1H, J¼16.1 Hz), 6.93 (d, 1H, J¼16.1 Hz), 6.66 (s, 1H),
4.11 (t, 2H, J¼5.0 Hz), 4.0 (t, 2H, J¼5.0 Hz), 2.42 (s, 3H), 2.25 (s,
3H); 13C NMR (acetone-d6):
d 159.5, 148.1, 146.9, 137.6, 132.5,
129.5, 129.1, 128.6, 126.6, 126.3, 125.7, 115.0, 71.7, 62.4, 20.8, 17.0;
MS (EI) m/z: 313 (Mþ, 100), 283 (17), 269 (55), 208 (28), 179 (20);
IR (KBr): 3291, 1589, 1338 cmꢁ1; mp: 112–114 ꢀC. Anal. Calcd for
C18H19NO4: C, 68.99; H, 6.16; N, 4.47. Found: C, 69.00; H, 6.16; N,
4.63%.
4.1.8. Synthesis of 2-(40-bromo-20,50-dimethylphenoxy)-
ethan-1-ol (14)
to yield an oil (1.76 g, 22%). 1H NMR (CDCl3):
d
7.19 (dd, 1H, J¼8.4,
A mixture of 4-bromo-2,5-dimethylphenol16 (20.1 g, 0.1 mol), 2-
chloroethanol (16.1 g, 0.2 mol), sodium hydroxide (0.10 mol) and
water (40 mL) was refluxed for 24 h. The reaction mixture was
cooled in an ice bath followed by suction filtration to afford the
crude product. Purification by chromatography on silica gel (hex-
ane/ethyl acetate, 2:1) gave a white solid (18.87 g, 77%). 1H NMR
2.0 Hz), 7.13 (d, 1H, J¼2.0 Hz), 6.65 (d, 1H, J¼8.4 Hz), 4.03 (t, 2H,
J¼4.8 Hz), 3.92 (t, 2H, J¼6.8 Hz), 3.85 (t, 2H, J¼4.8 Hz), 1.76–1.85 (m,
2H), 1.28–1.50 (m, 6H), 0.90 (t, 3H, J¼6.9 Hz).
4.1.5. Synthesis of (E)-1-[30-hexyloxy-40-(200-hydroxyethoxy)-
phenyl]-2-(40-nitrophenyl)-ethene (1)
A mixture of 2-(20-hexyloxy-40-iodophenoxy)ethan-1-ol 12 (1 g,
2.75 mmol), 4-nitrostyrene14 (0.51 g, 3.44 mmol), Pd(OAc)2
(CDCl3):
d
7.20 (s, 1H), 6.62 (s, 1H), 3.98 (t, 2H, J¼4.8 Hz), 3.88 (t, 2H,
J¼4.8 Hz), 2.27 (s, 3H), 2.10 (s, 3H); 13C NMR (CDCl3):
d 155.8, 135.8,
133.8, 126.2, 115.2, 113.9, 69.6, 61.5, 22.8, 15.5; MS (EI) m/z: 244 (Mþ,

4518
E. Font-Sanchis et al. / Tetrahedron 65 (2009) 4513–4520
55), 246 (54), 200 (100), 198 (98), 121 (99), 91 (44); IR (KBr):
3291 cmꢁ1; mp: 108–110 ꢀC. Anal. Calcd for C10H13BrO2: C, 49.00;
H, 5.35. Found: C, 49.45; H, 5.33%.
4.1.12. Synthesis of (E)-1-[20,50-dimethyl-40-(200-hydroxyethoxy)-
phenyl]-2-(20,40-dinitrophenyl)-ethene (4)
A solution of 4-(20-hydroxyethoxy)-2,5-dimethylbenzaldehyde
16 (1.94 g, 10.00 mmol), 2,4-dinitrotoluene (2 g, 10.98 mmol),
diethylamine (4 mL) and glacial acetic acid (2 mL) in benzene was
refluxed for 24 h using a Dean–Stark trap. The reaction solution
was cooled to room temperature and the solvent removed. Af-
terwards, the residue was purified by chromatography on silica
gel (hexane/ethyl acetate, 1:2) to give a yellow solid (1.47 g, 41%).
4.1.9. Synthesis of 4-(20-hydroxyethoxy)-2,5-dimethyl-
benzaldehyde (16)
To a solution of 2-(40-bromo-20,50-dimethylphenoxy)ethan-1-ol
14 (5 g, 20.41 mmol) and 12-crown-4 (3.52 g, 20 mmol) in tetra-
hydrofuran (40 mL) at ꢁ78 ꢀC under nitrogen atmosphere was
added slowly butyllithium (18 mL of 2.5 M solution in hexanes) and
the mixture reaction was stirred 1 h. Then, 3 g of N-for-
mylpiperidine were added, and the reaction was kept at room
temperature for 24 h. After cooling in an ice bath, dilute hydro-
chloric acid (40 mL) was added. The crude was extracted with
diethyl ether and the organic extracts were washed and dried with
anhydrous sodium sulfate. Solvent was removed, and the residue
was purified by chromatography on silica gel (hexane/ethyl acetate,
1H NMR (CDCl3):
d
8.71 (d, 1H, J¼2.3 Hz), 8.43 (dd, 1H, J¼8.8,
2.3 Hz), 8.29 (d, 1H, J¼8.8 Hz), 7.64 (d, 1H, J¼15.9 Hz), 7.49 (s, 1H),
7.26 (d, 1H, J¼15.9 Hz), 6.83 (s, 1H), 4.01 (t, 2H, J¼4.8 Hz), 3.74 (t,
2H, J¼4.8 Hz), 2.43 (s, 3H), 2.17 (s, 3H); 13C NMR (DMSO-d6):
d
157.8, 146.9, 145.2, 138.2, 136.5, 134.8, 129.0, 127.8, 126.9, 126.2,
124.0, 120.2, 119.1, 113.3, 69.6, 59.5, 19.3, 15.5; MS (EI) m/z: 358
(Mþ, 58), 314 (15), 193 (29), 165 (20), 149 (100), 91 (16); IR (KBr):
3426, 1508, 1346 cmꢁ1
;
mp: 177–178 ꢀC. Anal. Calcd for
2:1) to give a yellow solid (2.06 g, 52%). 1H NMR (CDCl3):
d
10.05 (s,
C18H18N2O6$1⁄4 H2O: C, 59.58; H, 5.14; N, 7.72. Found: C, 59.54; H,
1H), 7.53 (s, 1H), 6.62 (s, 1H), 4.14 (t, 2H, J¼4.8 Hz), 4.00 (t, 2H,
5.02; N, 7.86%.
J¼4.8 Hz), 2.59 (s, 3H), 2.21 (s, 3H); 13C NMR (CDCl3):
d 191.2, 160.9,
141.0, 133.9, 126.8, 124.5, 113.2, 69.3, 60.8, 19.1, 15.3; MS (EI) m/z:
194 (Mþ, 69), 149 (100), 121 (20), 91 (18), 77 (26); IR (KBr): 3313,
1687 cmꢁ1; mp: 72–74 ꢀC. Anal. Calcd for C11H14O3: C, 68.02; H,
7.27. Found: C, 67.58; H, 7.25%.
4.1.13. Synthesis of (E)-1-(20,40-dinitrophenyl)-2-[40-(200-
ethylhexyloxy)-20,50-dimethylphenyl]-ethene (5)
A flask was equipped with a Dean–Stark trap and a reflux
condenser. The flask was charged with 4-(20-ethylhexyloxy)-2,5-
dimethylbenzaldehyde 17 (1.5 g, 5.7 mmol), 2,4-dinitrotoluene
(1.09 g, 6 mmol), diethylamine (2 mL) and glacial acetic acid
(1 mL) in 100 mL of benzene. The mixture was heated under
reflux for 24 h and was allowed to cool to ambient temperature
and rotary evaporated. The residue was recrystallized from
diethyl ether/hexane to give the product as an orange solid (1.1 g,
4.1.10. Synthesis of 4-(20-ethylhexyloxy)-2,5-dimethyl-
benzaldehyde (17)
To
a
solution of 1-bromo-4-(20-ethylhexyloxy)-2,5-dime-
thylbenzene17 15 (4.6 g, 14.68 mmol) in tetrahydrofuran (50 mL) at
ꢁ78 ꢀC under nitrogen atmosphere was added butyllithium (10 mL
of a 1.6 M solution in hexanes) and the mixture reaction was stirred
1 h. Then, 3.4 g of N-formylpiperidine were added, and the reaction
was kept at room temperature for 12 h. After cooling in an ice bath,
hydrochloric acid (10%, 40 mL) was added. The crude was extracted
with diethyl ether and the organic extracts were washed and dried
with anhydrous sodium sulfate. Solvent was removed, and the
residue was purified by chromatography on silica gel (hexane/ethyl
45%). 1H NMR (CDCl3):
d
8.78 (d, 1H, J¼2.3 Hz), 8.38 (dd, 1H, J¼8.8,
2.3 Hz), 7.95 (d, 1H, J¼8.8 Hz), 7.50 (d, 1H, J¼15.8 Hz), 7.43 (s, 1H),
7.40 (d, 1H, J¼15.8 Hz), 6.65 (s, 1H), 3.88 (d, 2H, J¼5.5 Hz), 2.44 (s,
3H), 2.22 (s, 3H), 1.72–1.78 (m, 1H), 1.32–1.52 (m, 8H), 0.95 (t, 3H,
J¼7.0 Hz), 0.92 (t, 3H, J¼7.0 Hz); 13C NMR (acetone-d6):
d 157.9,
146.9, 145.2, 138.2, 136.6, 134.9, 129.0, 127.8, 127.0, 126.2, 123.8,
120.2, 119.0, 113.1, 69.8, 30.6, 30.0, 28.4, 23.5, 22.4, 19.3, 15.4, 13.8,
11.0; MS (EI) m/z: 426 (Mþ, 46), 314 (14), 282 (23), 150 (100); IR
acetate, 9:1) to yield an oil (3.35 g, 87%). 1H NMR (CDCl3):
d 10.09 (s,
1H), 7.56 (s,1H), 6.63 (s,1H), 3.91 (d, 2H, J¼5.5 Hz), 2.63 (s, 3H), 2.21
(KBr): 1585, 1346 cmꢁ1 mp: 123–125 ꢀC. Anal. Calcd for
;
(s, 3H), 1.72–1.80 (m, 1H), 1.29–1.55 (m, 8H), 0.88–0.96 (m, 6H); 13C
C24H30N2O5: C, 67.59; H, 7.09; N, 6.57. Found: C, 67.67; H, 7.21; N,
6.43%.
NMR (CDCl3):
d 191.2, 161.7, 141.1, 134.0, 126.8, 124.8, 113.2, 70.4,
39.4, 30.6, 29.0, 23.9, 22.9, 19.5, 15.6, 14.0, 11.2; MS (EI) m/z: 262
(Mþ, 26), 150 (100); IR (KBr): 1697 cmꢁ1. Anal. Calcd for C17H26O2:
C, 77.82; H, 9.99. Found: C, 77.34; H, 10.04%.
4.1.14. Synthesis of 3-cyano-4-{(E)-20-[300-hexyloxy-400-(2%-
hydroxyethoxy)phenyl]-10-ethenyl}-5,5-dimethyl-2-
propanylidendinitrile-2,5-dihydrofuran (6)
4.1.11. Synthesis of (E)-1-(20,40-dinitrophenyl)-2-[30-hexyloxy-40-
(200-hydroxyethoxy)phenyl]-ethene (3)
To a solution of dry pyridine (20 mL), glacial acetic acid
(0.12 mL), ammonium acetate (32 mg) and molecular sieves
(3 Å pellets, 2 g) was added 3-hexyloxy-4-(20-hydroxyethoxy)-
benzaldehyde 11 (0.6 g, 2.3 mmol) and 3-cyano-4,5,5-trimethyl-
2-propanylidendinitrile-2,5-dihydrofuran18 (0.5 g, 2.5 mmol).
After the solution was stirred for 48 h at 80 ꢀC, the reaction
mixture was cooled to room temperature, diluted with ethyl
acetate (20 mL) and filtered. After removal of solvent under re-
duced pressure, the residue was purified by chromatography on
silica gel (hexane/ethyl acetate, 1:3) to yield a red solid (0.31 g,
To a solution of dry pyridine (10 mL), glacial acetic acid
(0.12 mL), ammonium acetate (32 mg) and molecular sieves
(3 Å pellets, 2 g) was added 3-hexyloxy-4-(20-hydroxyethoxy)-
benzaldehyde (0.6 g, 2.3 mmol) and 2,4-dinitrotoluene (0.5 g,
2.7 mmol). After the solution was stirred for 48 h at 80 ꢀC, the re-
action mixture was cooled to room temperature, diluted with ethyl
acetate (10 mL) and filtered. After removal of solvent under reduced
pressure, the residue was purified by chromatography on silica gel
(hexane/ethyl acetate, 1:2) to yield a orange solid (0.41 g, 41%). 1H
30%). 1H NMR (CDCl3):
d
7.57 (d, 1H, J¼16.3 Hz), 7.23 (dd, 1H,
NMR (CDCl3):
d
8.80 (d, 1H, J¼2.4 Hz), 8.39 (dd, 1H, J¼8.8, 2.4 Hz),
J¼8.4, 2.0 Hz), 7.10 (d, 1H, J¼2.0 Hz), 6.96 (d, 1H, J¼8.4 Hz), 6.87
(d, 1H, J¼16.3 Hz), 4.20 (t, 2H, J¼4.9 Hz), 4.06 (t, 2H, J¼6.6 Hz),
4.00 (t, 2H, J¼4.9 Hz), 1.76–1.84 (m, 2H), 1.34–1.53 (m, 6H), 0.91
7.95 (d,1H, J¼8.8 Hz), 7.49 (d,1H, J¼16.0 Hz), 7.23 (d,1H, J¼16.0 Hz),
7.1–7.2 (m, 2H), 6.94 (d, 1H, J¼8.0 Hz), 4.16 (t, 2H, J¼4.8 Hz), 4.06 (t,
2H, J¼6.8 Hz), 3.96 (t, 2H, J¼4.8 Hz), 1.83–1.89 (m, 2H), 1.33–1.52
(t, 3H, J¼7.0 Hz); 13C NMR (acetone-d6):
d 178.6, 177.2, 155.5,
(m, 6H), 0.91 (t, 3H, J¼7.1 Hz); 13C NMR (CDCl3):
d
150.1, 149.6, 147.1,
151.5, 149.9, 129.7, 126.9, 115.5, 115.3, 114.8, 114.1, 113.4, 112.6,
100.5, 100.0, 72.7, 71.0, 62.2, 56.8, 33.3, 31.0, 27.4, 27.1, 24.3, 15.3;
MS (EI) m/z: 447 (Mþ, 18), 324 (24), 319 (48), 240 (10), 44 (100);
IR (KBr): 3472, 2226 cmꢁ1; mp: 178–180 ꢀC. Anal. Calcd for
C26H29N3O4$1H2O: C, 67.08; H, 6.71; N, 9.03. Found: C, 67.35; H,
6.45; N, 9.47%.
145.8, 138.8, 138.0, 129.5, 128.5, 127.0, 121.8, 120.7, 119.2, 114.8, 111.5,
71.3, 69.2, 61.1, 31.5, 29.1, 25.6, 22.5, 14.0; MS (EI) m/z: 430 (Mþ, 10),
266 (15), 251 (20), 138 (32), 44 (100); IR (KBr): 3430, 1591,
1348 cmꢁ1; mp: 59–60 ꢀC. Anal. Calcd for C22H26N2O7: C, 61.39; H,
6.09; N, 6.51. Found: C, 61.28; H, 6.17; N, 6.21%.

E. Font-Sanchis et al. / Tetrahedron 65 (2009) 4513–4520
4519
4.1.15. Synthesis of 3-cyano-4-{(E)-20-[400-(2%-hydroxyethoxy)-
200,500-dimethylphenyl]-10-ethenyl}-5,5-dimethyl-2-
propanylidendinitrile-2,5-dihydrofuran (7)
diluted. In the case of compound 4, it was necessary to use even
lower concentrations. Its quite low NLO response made it difficult
to obtain accurate mb values in CH2Cl2. Therefore, the molecular non
linearity of compound 4 was measured in a highly polar solvent as
DMSO. For sake of comparison, compound 2 was measured in
DMSO as well. Under the same experimental conditions, the mb
value of the azo dye Disperse Red 1 (DR1) was determined to be
670ꢃ10ꢁ48 esu in CH2Cl2 and 600ꢃ10ꢁ48 esu in DMSO.
A mixture of 4-(20-hydroxyethoxy)-2,5-dimethylbenzaldehyde
16 (1.98 g, 10.24 mmol), 3-cyano-4,5,5-trimethyl-2-propanylidendi-
nitrile-2,5-dihydrofuran (2.80 g, 14.05 mmol), sodium hydride
(0.01 g, 0.42 mmol) and anhydrous N,N-dimethylformamide
(20 mL) was refluxed for 24 h. The mixture was poured into water
(50 mL) followed by extraction with dichloromethane. The organic
extract was washed with water and dried. After removal of solvent
under reduced pressure, the residue was purified by chromato-
graphy on silica gel (hexane/ethyl acetate, 1:3) to afford a red solid
4.3. Computational procedures
Theoretical calculations were performed by means of the
Gaussian 03 program. TD-DFT calculations used the B3P864 func-
tional and the 6-31G(d) basis set. Molecular hyperpolarizabilities at
zero frequency were calculated by the Coupled Perturbed Hartree
(1.96 g, 51%). 1H NMR (acetone-d6):
d
8.38 (d, 1H, J¼16.1 Hz), 7.87 (s,
1H), 7.12 (d,1H, J¼16.1 Hz), 6.95 (s,1H), 4.19 (t,1H, J¼4.8 Hz), 3.93 (t,
1H, J¼4.8 Hz), 2.50 (s, 3H), 2.21 (s, 3H), 1.85 (s, 6H); 13C NMR
(DMSO-d6):
d 177.5, 176.1, 160.7, 144.8, 140.6, 129.2, 125.0, 127.4,
Fock Method (CPHF) using the HF/6-31G model chemistry and the
*
113.5, 112.9, 112.3, 112.1, 112.0, 99.0, 94.6, 70.0, 59.7, 59.4, 53.1, 24.8,
19.0, 15.4; MS (EI) m/z: 375 (Mþ, 100), 331 (58), 316 (18), 149 (20),
115 (8), 91 (16); IR (KBr): 3436, 2229 cmꢁ1; mp: 235–237 ꢀC. Anal.
Calcd for C22H21N3O3$1H2O: C, 67.16; H, 5.89; N, 11.68. Found: C,
67.27; H, 5.79; N, 11.95%.
default parameters provided by the ‘polar’ keyword.
Acknowledgements
Support of this work from the Spanish Government (CICYT
grants No. MAT2005-07369-C03-02, MAT2005-06373-C02-02,
CTQ2005-01368, CTQ2007-67888/BQU, CTQ2008-05901/BQU and
Consolider-Ingenio 2010 project HOPE CSD2007-00007) and the
Generalitat Valenciana (grants No. ACOMP06/054 and GV01-81) is
acknowledged. F.J.C.-G. and R.A. thank the spanish Ministerio de
4.1.16. Synthesis of 3-cyano-4-{(E)-20-[400-(2%-ethylhexyloxy)-
200,500-dimethylphenyl]-10-ethenyl}-5,5-dimethyl-2-
propanylidendinitrile-2,5-dihydrofuran (8)
A mixture of 4-(20-ethylhexyloxy)-2,5-dimethylbenzaldehyde
17 (1.34 g, 5.12 mmol), 3-cyano-4,5,5-trimethyl-2-propanylidendi-
nitrile-2,5-dihydrofuran (1.4 g, 7.03 mmol), sodium hydride (5 mg,
0.21 mmol) and dry DMF (25 mL) was refluxed for 24 h under inert
atmosphere. The mixture was poured into water (25 mL) followed
by extraction with dichloromethane. The organic extract was
washed with water and dried. After removal of solvent under re-
duced pressure, the residue was purified by chromatography on
silica gel (hexane/ethyl acetate, 1:3) to afford a red solid (1.25 g,
´
Ciencia e Innovacion for a FPU fellowship.
References and notes
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Photorefractive Materials; Clarendon: Oxford, 1996.
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E.; Grunnet-Jepsen, A.; Thompson, C. L. Annu. Rev. Mater. Sci. 1997, 27, 585–623.
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M.; Boj, P.; Dı´az-Garcı´a, M. A.; Rivera, J.; Stepleton, S.; Cox, C.; Echegoyen, L.
Chem. Mater. 2004, 16, 5021–5026; (b) Quintana, J. A.; Boj, P. G.; Villalvilla, J. M.;
Ortiz, J.; Ferna´ndez-La´zaro, F.; Sastre-Santos, A.; Dı´az-Garcı´a, M. A. Appl. Phys.
55%). 1H NMR (CDCl3):
d
8.12 (d, 1H, J¼16.1 Hz), 7.56 (s, 1H), 6.77 (d,
1H, J¼16.1 Hz), 6.69 (s, 1H), 3.92 (d, 1H, J¼5.5 Hz), 2.47 (s, 3H), 2.22
(s, 3H), 1.77 (s, 6H), 1.30–1.53 (m, 8H), 0.94 (t, 3H, J¼7.0 Hz), 0.90 (t,
3H, J¼7.0 Hz); 13C NMR (acetone-d6):
d 178.9, 177.7, 163.3, 146.9,
142.8, 130.8, 127.4, 127.0, 115.3, 114.2, 114.1, 113.5, 100.4, 97.8, 72.3,
56.4, 41.2, 32.3, 30.7, 26.9, 25.7, 24.7, 20.7, 16.9, 15.3, 12.4; MS (EI)
m/z: 443 (Mþ, 23), 331 (100); IR (KBr): 2226 cmꢁ1; mp: 174–175 ꢀC.
Anal. Calcd for C28H33N3O2$1⁄2 H2O: C, 74.31; H, 7.57; N, 9.28.
Found: C, 74.14; H, 7.57; N, 9.28%.
´
´
´
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Meerholz, K. ChemPhysChem 2002, 3, 17–31.
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Org. Chem. 1999, 32, 121–217.
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