Synthesis and properties of push-pull chromophores for second-order nonlinear optics derived from π-extended tetrathiafulvalenes (TTFs)

Article abstract of DOI:10.1016/S0040-4020(02)00803-7

Novel π-extended tetrathiafulvalene (exTTF) derivatives connected to a p-nitrophenyl electron-accepting unit through a π-conjugated oligoenic spacer (14a-c-16a-c) show good second-order optical nonlinearities. The effect of the conjugation length of the oligoenic spacer and the presence of a thiophene ring in the π-conjugated bridge (20a-c) have been theoretically (PM3) and/or experimentally (EFISH technique) studied. The redox properties of the novel compounds have been investigated by cyclic voltammetry (CV) and the CV data reveal the good donor ability of the exTTF unit. Although the energy of the intramolecular charge-transfer (ICT) band displayed by these compounds and their redox potentials are fairly insensitive to the nature of the conjugated spacer linking the donor and the acceptor moieties, an increase in their second order nonlinear optical responses is observed on increasing the conjugation lengths. Compounds 20a-c bearing a thiophene ring show a remarkable thermal stability with decomposition temperatures over 400°C. A new series of D-π-A compounds (23a-c) bearing a 1,3-dithiol-2-ylidene donor unit has also been synthesized and studied.

Full text of DOI:10.1016/S0040-4020(02)00803-7

Tetrahedron 58 (2002) 7463–7475
Synthesis and properties of push–pull chromophores
for second-order nonlinear optics derived from p-extended
tetrathiafulvalenes (TTFs)
a
Manuel Otero, M Angeles Herranz, Carlos Seoane, Nazario Martın, Javier Garın,
a
a
a
b
,
a
´
*
´
Jesus Orduna, Rafael Alcala and Belen Villacampa
´
b
c
c
´
´
´
a
´ ´ ´
Departamento de Quımica Organica I, Facultad de Quımica, Universidad Complutense de Madrid,
Avenida Complutense 22, E-28040 Madrid, Spain
´
´
Departamento de Fısica de la Materia Condensada, ICMA, Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain
b
´
Departamento de Quımica Organica, ICMA, Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain
c
Received 14 March 2002; revised 6 June 2002; accepted 10 July 2002
Abstract—Novel p-extended tetrathiafulvalene (exTTF) derivatives connected to a p-nitrophenyl electron-accepting unit through a
p-conjugated oligoenic spacer (14a–c–16a–c) show good second-order optical nonlinearities. The effect of the conjugation length of the
oligoenic spacer and the presence of a thiophene ring in the p-conjugated bridge (20a–c) have been theoretically (PM3) and/or
experimentally (EFISH technique) studied. The redox properties of the novel compounds have been investigated by cyclic voltammetry (CV)
and the CV data reveal the good donor ability of the exTTF unit. Although the energy of the intramolecular charge-transfer (ICT) band
displayed by these compounds and their redox potentials are fairly insensitive to the nature of the conjugated spacer linking the donor and the
acceptor moieties, an increase in their second order nonlinear optical responses is observed on increasing the conjugation lengths.
Compounds 20a–c bearing a thiophene ring show a remarkable thermal stability with decomposition temperatures over 4008C. A new series
of D-p-A compounds (23a–c) bearing a 1,3-dithiol-2-ylidene donor unit has also been synthesized and studied. q 2002 Elsevier Science
Ltd. All rights reserved.
1. Introduction
important requirements for molecular organic materials to
be incorporated into more practical nonlinear optical
polymers.1
The synthesis of molecular and polymeric materials
exhibiting nonlinear optical (NLO) properties is currently
a major task in chemistry due to their applications in the
domain of opto-electronics and photonics.1 Molecular
NLO-phores are traditionally constituted by electron
donor and acceptor moieties covalently connected through
a conjugated bridge, and a wide variety of p-conjugated and
homo- and heterobridges have been investigated.2 In this
regard, Marder has shown that bond length alternation,
i.e. the average difference in length between single and
double bonds in the molecule, is the relevant parameter in
the optimization of the hyperpolarizability of molecules.3
In the search of new NLO-phores, during the last years, we
have reported the synthesis and second order NLO proper-
ties of push–pull tetrathiafulvalenes (TTFs) connected
through an oligoenic bridge to different acceptor moieties
(1–3).5 In these systems, the degree of intramolecular
charge transfer from the donor to the acceptor has been
recently analyzed by means of Raman spectroscopy.6
TTF and its derivatives are nonaromatic (14 p electrons)
planar p-electron-donor molecules which are easily oxi-
dized to form reversibly the radical cation and dication
species.7 Both species are thermodynamically very stable
due to the aromatic character (six p-electrons) of the
resulting 1,3-dithiolium cation. Therefore, TTFs fulfill the
requirement of gain in aromaticity in the oxidized state. In
addition, these TTF-phores show a good degree of thermal
stability as evidenced by the decomposition temperatures
around 2008C.6
Another important aspect in the design of molecules
exhibiting NLO properties has been directed to the synthesis
of systems where the loss of aromaticity in the ground state
is compensated by a gain in aromaticity in the charge
separated form.4 Finally, a good thermal and chemical
stability as well as low optical loss (high transparency) are
Keywords: D-p-A compounds; 1,3-dithiol-2-ylidene; p-extended
tetrathiafulvalene (exTTF); nonlinear optics (NLO); electrochemistry.
The effect of methyl substituents in the TTF moiety and the
nature of the conjugated bridge on the NLO properties have
also been recently studied.8
*
Corresponding author. Tel.: þ34-91-394-4227; fax: þ34-91-394-4103;
e-mail: nazmar@quim.ucm.es
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00803-7

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M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
p-Extended TTFs (exTTFs) with quinonoid structures (4, 5)
have been much less studied as NLO-phores despite
their good hyperpolarizabilities (mb¼230–550£10248 esu)
and excellent thermal stabilities with decomposition
temperatures close to 3008C.9
More recently, exTTFs have been studied in the preparation
of photovoltaic systems (6,7)12 and in chemical sensors and
redox-switchable ligands (8).13
In this paper, we describe the synthesis of new series of
exTTF-containing molecules in which a p-nitrophenyl
group has been used as the acceptor component in these
push–pull systems. Thus, we have systematically modified
the length of the oligoenic spacer connecting both donor and
acceptor moieties. In addition, we have studied the effect of
the substituents on the 1,3-dithiole rings of the exTTF unit,
as well as the presence of a thiophene ring in the p-extended
bridge. A series of D-p-A compounds endowed with a
Quinonoid p-extended TTFs are an important class of
modified TTFs which, in contrast to the parent TTF,
undergo a two-electron oxidation to form the dication
species at potential values close to that of TTF.10 exTTFs
have been successfully used as donor units in the
preparation of charge transfer (CT) complexes with high
electrical conductivities (srt¼60 S cm21).11
Scheme 1.

M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
7465
differently substituted 1,3-dithiole ring as donor unit has
been synthesized in order to compare its NLO-response with
that of the related exTTF systems.
In these systems (14–16), the ICT band remains nearly
unaltered without showing a clear bathochromic shift in
comparison with the respective aldehydes (10–12). The
same behavior was observed for the differently substituted
exTTFs (see Fig. 1). This behavior is in contrast to that
previously observed for other stronger acceptors such as the
dicyanovinylene group for which a bathochromic shift of
around 100 nm was observed when compared to the related
aldehydes.8
2. Results and discussion
2.1. Synthesis
The preparation of the novel exTTF-p-A (14a–c–16a–c)
was carried out in a multistep synthetic procedure from
the formyl-free compound 10,14 which was in turn
obtained from commercially available 2-hydroxymethyl-
9,10-anthraquinone (9). Higher vinylogues 11 and 12
were prepared from 10 by reaction with triphenyl-
phosphoranylideneacetaldehyde in refluxing toluene as
shown in Scheme 1.
Enhancement of thermal stability in molecules 14a–c–
16a–c can in principle be achieved by introducing
(hetero)aromatic structures along the conjugation path of
the molecules. Therefore, we carried out the synthesis of a
new series of exTTF-p-A molecules (20a–c) incorporating
a thiophene ring in the conjugated bridge.
The synthesis of compounds 20a–c was carried out as
depicted in Scheme 2. The phosphonium salts (17a–c)15
were prepared from 2-hydroxymethyl-exTTF which was
obtained in a three steps synthesis from 2-hydroxymethyl-
9,10-anthraquinone by following the procedure developed
in our laboratory.16 After isolation, compounds 17a–c were
rapidly reacted with potassium tert-butoxide in refluxing
toluene to form the Wittig ylide (18) which reacted with
5-(2-p-nitrophenylvinyl)-2-thiophenecarbaldehyde (19) to
lead to the push–pull molecules 20a–c which were
obtained in low to moderate yield (9–57%) due to the
decomposition of the starting salt.
The target push–pull molecules (14a–c–16a–c) were
synthesized by Wittig reaction from the respective formyl-
exTTFs (10–12) by reaction with the carbanion of
(4-nitrobenzyl)triphenylphosphonium bromide (13)
generated in the presence of potassium tert-butoxide (see
Section 4). Compounds 14a–c–16a–c were obtained as
stable solids in good yields (61–97%).
In is worth mentioning that this reaction was carried out
using different bases (n-BuLi/THF, EtONa/EtOH). How-
ever, the best results were obtained with t-BuOK in
refluxing toluene since the use of high temperatures allowed
to obtain the all-trans compounds as the only reaction
product.
The structure of the obtained compounds was confirmed by
1
analytical and spectroscopic (FT-IR, H NMR, 13C NMR,
MS, UV–Vis) methods. Thus, the NO2 group was observed
in the FT-IR spectra as two bands at around 1508 and
1
1338 cm21. The H NMR spectra of compounds bearing
only one vinyl group (14a–c) show the vinyl protons as
doublets at around 7.3 and 7.1 ppm with coupling constants
of J¼16.1–16.8 Hz. Compounds 15a–c bearing two vinyl
groups show the vinyl protons as two doublets with coupling
constants of J¼15.4–14.8 and 10.4–10.0 Hz. More com-
plex spectra were observed for 16a–c due to the
overlapping signals. However, coupling constants of J¼
15.7–15.0 and 10.3–9.7 Hz were observed (see Section 4).
These coupling constant values (J¼16.8–14.9 Hz) clearly
confirm the formation of trans stereoisomers.
In addition, the 1,3-dithiole protons in compounds (14a–
16a) appear as a singlet at d 6.3 ppm (4H), and when the
dithiole ring bears SMe and S(CH2)2S substituents, these are
observed as singlets at d,2.4 ppm (12H) and 3.3 ppm (8H),
respectively. This assignment is in good agreement with
that previously reported for related TTF derivatives.8
The UV–Vis spectra of compounds 14a–c–16a–c show a
low energy intramolecular charge-transfer (ICT) band
which appears as a clear shoulder in the visible region,
similarly to that observed for the formyl-containing
precursors (10–12). The UV–Vis spectra of the electro-
active p-nitrotoluene and exTTF (24) have been also
included in Fig. 1 for comparison purposes.
Figure 1. (a) UV–Vis spectra of compounds 12a (—), 12b (- - -) and 12c
(-·-·-). (b) UV–Vis spectra fof 14b (—), 15b (—), 16b (—), p-nitrotoluene
(-·-·-) and exTTF (24) (- - -).

7466
M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
Scheme 2.
2-Formylthiophene derivative 19 was in turn obtained by
treatment of phosphonium bromide 13 with potassium tert-
butoxide to form the intermediate ylide, which reacted with
commercially available 2,5-diformylthiophene (21) in
stoichiometric amounts (1:1) to form compound 19 in
70% yield.
In order to compare the push–pull systems bearing the
exTTF donors with other known and efficient donor
chromophores as the 1,3-dithiol-2-ylidene moiety, we
have carried out the synthesis of compounds 23a–c.
These compounds were easily prepared by two consecutive
Wittig–Horner and Wittig olefination reactions as shown in
Scheme 3.
It is worth mentioning that phosphonium salts 17a–c are
important building blocks for the construction of more
sophisticated donor–acceptor systems provided the syn-
thetic versatility of the Wittig reaction with a wide variety of
eletroactive systems endowed with carbonyl groups.
Thus, compounds 22a–c were obtained by reaction of
2,5-diformylthiophene 21 with the respective phosphonate
The 1H NMR spectroscopic data confirm, similarly to
compounds 14–16, the formation of the all-trans isomers as
the only isolated compounds according to the observed
coupling constants (,16 Hz) for these systems (20a–c).
The electronic spectra of 20a–c reveal the presence of a ICT
band which is observed as a shoulder at around 500 nm
overlapping with the p-extended aromatic system (Fig. 2).
As shown in Fig. 2, substitution on the 1,3-dithiole ring in
20a–c has not a significant effect on the lmax values.
Compounds 20a–c exhibit a remarkable thermal stability
with melting points over 4008C. Therefore, these molecules
are appealing systems for further incorporation into poled
polymers in the search of NLO materials.
Figure 2. UV–Vis spectra for 20a (—), 20b (- - -) and 20c (-·-·-).

M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
7467
Scheme 3.
under basic conditions according to the procedure pre-
viously reported in the literature.17 Further olefination
reaction of 22a–c with 4-nitrobenzyl(triphenyl) phos-
phonium bromide (13) afforded compounds 23a–c in high
yields (65–98%).
The first reduction potential of aldehydes 12a–c appear at
more negative values than those containing the p-nitro-
phenyl group (14–16), which indicates the poorer electron–
acceptor character of the carbonyl group.
On the oxidation side, all the exTTF systems show only one
oxidation wave involving two electrons to form the dication
species, similarly to that observed for the reference exTTF
(24).11,19 The oxidation potential values are lower for the
unsubstituted exTTF moiety (compounds 12a, 14a, 15a,
16a, 20a). As expected, substitution on the 1,3-dithiole rings
of the exTTF units with the SMe and S(CH2)2S groups leads
to more positive values and, therefore, to poorer electron
donors.19
The 1H NMR spectra of 23a–c clearly confirm the presence
of the all-trans isomers as the only product formed in the
olefination reaction (J¼16.5 Hz).
The UV–Vis spectra of compounds 23a–c show a low
energy ICT band in the visible region (lmax¼490 nm in
CH2Cl2) as a consequence of the stronger electron-
accepting character of the p-nitrophenyl chromophore, in
comparison with the carbonyl group. A slightly negative
solvatochromism was observed for compound 23b [CH3CN
(1: 35.94) 478 nm; EtOH (1: 24.55) 482; CH2Cl2 (1: 8.93)
490] in agreement with other related structures.17,18 Never-
theless, in our case, the observed solvatochromism could
stem from the difference in refractive indices of solvents.
Interestingly, compounds 23a–c bearing the 1,3-dithiole
ring as electron donor unit exhibit more positive oxidation
potential values, thus confirming their poorer electron donor
ability related to the exTTF unit (see Table 1 and Fig. 3).
The electrochemical redox behavior of 20b was studied
at different temperatures and the voltammograms are shown
Compounds 23a–c showed decomposition temperatures in
the range 190–2608C which are remarkably lower than
those observed for the related exTTF derivatives (20a–c)
(.4008C), thus proving the additional thermal stabilization
provided by the exTTF units.
Table 1. Redox properties of novel push–pull molecules (12, 14, 15, 16,
20, 23)
a
a
a
a
Compounds
E 1red
E 2red
E 1ox(a.p.)
Eox(c.p.)
2.2. Electrochemistry
12a
12b
12c
14a
14b
14c
15a
15b
15c
16a
16b
16c
20a
20b
20c
23a
23b
23c
13
21.37
21.35
21.37
21.01
21.00
21.02
21.01
21.00
20.97
20.97
20.93
20.94
21.06
21.05
21.07
21.10
21.11
21.08
21.00
–
–
–
–
0.45
0.60
0.54
0.51
0.62
0.64
0.45
0.62
0.65
0.47
0.65
0.66
0.48
0.60
0.57
0.65
0.73
0.71
–
0.04
0.24
0.30
0.13
0.43
0.38
0.20
0.43
0.40
0.19
0.37
0.35
20.07
0.21
0.16
0.43
0.53
0.57
–
The redox properties of the novel compounds obtained have
been determined by cyclic voltammetry (CV) at room
temperature in methylene dichloride solutions, using glassy
carbon as the working electrode, SCE as reference, and
tetra-n-butylammonium perchlorate as the supporting elec-
trolyte. The respective data are collected in Table 1 along
with the redox potentials of compound 13 and the parent
unsubstituted exTTF donor (24).
21.49
21.44
21.47
21.37
21.42
21.43
21.37
21.41
21.39
21.47
21.45
21.46
21.62
21.61
21.52
21.57
–
The voltammograms of exTTF derivatives 14–16 and 20
show the presence of two one-electron reduction waves
corresponding to the reduction of the p-nitrophenyl group
similarly to that found for the reference compound 13
(see Table 1). It is worth mentioning that the first reduction
potential of compounds 16a–c appears at slightly less
negative values (anodically shifted) than those of com-
pounds 14 and 15, which can be attributed to the longer
distance to the exTTF donor unit.
24
0.45
20.03
V vs SCE; Bu4NþClO42 as supporting electrolyte; CH2Cl2 as solvent;
200 mV/s; a.p. anodic peak; c.p. cathodic peak; 24: 9,10-bis(1,3-dithiol-
2-ylidene)-9,10-dihydroanthracene.
a

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M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
are usually required to obtain accurate results can not be
used on large molecules like those presented in this paper
due to their large computational cost. Having this in mind,
we have performed semiempirical calculations using the
PM3 hamiltonian and the Time-Dependent Hartree–Fock
(TDHF) approximation since this method has proved to
reproduce successfully the trends in the NLO response of
tetrathiafulvalene chromophores.5b–c,8,24
Two possible conformations (A and B) were considered for
the calculations of the geometry of compounds 14–16 (Fig.
5).
Theoretical calculations predict in all cases studied
practically the same heats of formation for both confor-
mations (A, B). The difference (0.1 kcal/mol) between their
heats of formation indicates that both conformations should
be possible and, therefore, the calculations of the NLO
properties were carried out on both conformers (A and B).
Figure 3. Cyclic voltammograms of compounds 20b (—) and 23b (- - -).
in Fig. 4. The oxidation potential values are anodically
shifted with decreasing the temperature [Eox(358C)¼0.58 V;
Eox(rt)¼ 0.60 V; Eox(08C)¼0.60 V; Eox(2788C)¼0.64 V] which
indicates the higher difficulty in the formation of the dication
species. A more remarkable effect is the reduction from the
dication to the neutral form, which undergoes a drastic shift
to lower potentials when lowering the temperature
[Ered(358C)¼0.32 V; Ered(rt)¼0.21 V; Ered(08C)¼0.17 V;
Ered(2788C)¼0.02 V] becoming a more electrochemically
irreversible system. This behavior has been previously
observed and indicates the high stability of the formed
dications.19,20
The molecular geometry of conformation A for compound
16a is shown in the Fig. 5. As expected, the exTTF donor
unit shows a highly distorted geometry out of planarity due
to the strong steric interactions between the 1,3-dithiole
rings and the peri hydrogens. To avoid these interactions,
the molecule adopts a butterfly shape with the central ring
upward and the dithiole rings pointing downward. This
geometry is in full agreement with that calculated for other
related systems19 as well as that determined by X-ray
crystallography.11 It has been reported that the PM3 method
provides a good description, even better than ab initio HF/
6-31Gp calculations, for the molecular structure of extended
TTFs with a minimal computational cost.19 A planar
geometry was determined for the conjugated oligoenic
spacer and p-nitrophenyl moiety (Fig. 5).
2.3. Theoretical calculations and NLO properties
In order to gain a better understanding of the geometrical
and electronic properties of the compounds synthesized as
well as on the observed ICT band, which is a prerequisite to
the attainment of high b values,21–23 theoretical calcu-
lations were performed.
The electronic structure of 14–16 shows that the HOMO
is located on the exTTF donor fragment, and the LUMO is
mainly spread on the p-nitrophenyl acceptor moiety and the
oligoenic spacer (Fig. 5). It can be seen that there is an
overlap between the HOMO and LUMO which is an
important requirement to obtain large second order NLO
responses.21
The calculation of the hyperpolarizabilities using quantum
chemical calculations is usually performed on isolated
molecules in the gas phase and at a fixed conformation and
hence are not expected to reproduce quantitatively the
experimental EFISH values obtained in solution. Further-
more, the ab initio models employing large basis sets that
The mb values of the exTTF derivatives (14–16) were
measured using the EFISH technique22 and the values are
presented in Table 2, along with the mb(0) values calculated
assuming a two-level model (compounds 20a–c were not
measured due to their instability under EFISH conditions).
In order to minimize possible resonance effects which
would enhance the NLO response, measurements were
performed at a fundamental wavelength of 1.907 nm. For the
sake of comparison, the mb(0) of DANS is 363£10248 esu
(CHCl3).
As shown in Table 2, while semiempirical calculations
overestimate the experimental NLO response, the calculated
mb values follow the same trend than that observed
experimentally with the only exception of compound 15b
which displays an unexpectedly high NLO response.
The NLO response increases with increasing the p-conju-
gation between both donor and acceptor moieties.
Figure 4. Cyclic voltammograms of compound 20b at different
temperatures.

M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
7469
Figure 5. (a) Two possible conformations (A and B) for compounds 14–16a–c and 20. (b) Calculated molecular geometry (PM3) of compound 16a.
(c) HOMO–LUMO orbitals for compound 16a. (d) HOMO–LUMO orbitals for compound 20a.
However, a most interesting result is that alkylthio
substituents on the 1,3-dithiole ring significantly increase
the mb values.
Although we were not able to measure the experimental mb
values for 20a–c, the calculated values predict a good NLO
response, similar to that of compounds 16a–c bearing three
vinyl units. These values are remarkably higher than those
of the related systems bearing the 1,3-dithiol-2-ylidene as
the donor unit in 23a–c (Table 2).
It is also worthy to note that the NLO responses of
compounds 14a, 15a and 16a are very similar to those of
analogous chromophores containing a tetrathiafulvalene
linked to the p-nitrophenyl acceptor.8
Thermal stability is an important criterion for technological
applications. In this regard, compounds 20a–c show an
outstanding thermal stability (decomposition temperatures
.4008C) and, therefore, these could be interesting systems
for further applications.
The geometry calculated (PM3) for compound 20a was
quite similar to that found for compounds 14–16. Interest-
ingly, a planar geometry is observed for the benzene-p-
acceptor moiety, thus supporting the good NLO response.
As expected, the HOMO is located on the exTTF unit and
the LUMO on the acceptor and vinyl-thiophene fragment
(see Fig. 5).
The mb values determined experimentally for 23a–c show
the same trend observed for compounds 20a–c for the
substitution pattern on the 1,3-dithiole ring. Thus, the NLO

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M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
Table 2. lmax values and calculated and experimental NLO properties of novel systems
max (nm)a
mbexp
mb(0)exp
PM3 Conf. A
mb(0)b
PM3 Conf. B
mb(0)b
a,b
a,b
Compounds
l
mc
mc
14a
14b
14c
15a
15b
15c
16a
16b
16c
20a
20b
20c
23a
23b
23c
,480 (sh)
,480 (sh)
,480 (sh)
,480 (sh)
,480 (sh)
,480 (sh)
,490 (sh)
,490 (sh)
,490 (sh)
,500 (sh)
,500 (sh)
,500 (sh)
490
180
212
205
230
360
255
324
350
331
–
–
–
315
470
370
140
163
155
180
277
191
247
270
250
–
–
–
219
323
266
6.74
7.22
7.38
6.78
7.29
7.43
6.87
7.35
7.54
7.18
7.90
7.97
6.44
6.69
6.78
290
361
367
382
466
468
485
568
578
537
667
649
397
443
481
6.73
7.20
7.40
6.78
7.25
7.32
6.85
7.30
7.54
–
288
354
359
382
452
432
484
554
567
–
–
–
–
–
–
–
–
–
490
490
–
–
a
In CH2Cl2.
In 10248 esu units.
In Debye.
b
c
response increases with the presence of alkylthio sub-
stituents on the 1,3-dithiole ring (Table 2). In contrast to the
exTTF derivatives, PM3 method did not lead to a good
correlation with experimental mb values, since they predict
an anti conformation of the vinyl group with the sulfur atom
of the thiophene ring, which is in contrast to the
experimental geometries determined by X-ray crystal-
lography.25
All the D-p-A systems prepared show the presence of a low
energy intramolecular charge-transfer band (ICT) in their
electronic spectra which is nearly independent of the donor
ability of the donor moiety and the length of the oligoenic
spacer.
In agreement with their nature, the studied compounds
(14a–c–16a–c, 23a–c) showed second order NLO
responses that were measured by using the EFISH
technique. Therefore, p-extended TTFs are interesting
NLO-phores which exhibit good mb values and thermal
stabilities for further practical applications. Work is in
progress to optimize the NLO response by using other
stronger acceptors as well as to embody them into polymeric
systems.
Therefore, and for comparison purposes, we calculated the
mb(0) value for 23a–c using the more reliable conformation
with a syn geometry. The calculated values show a similar
correlation with those experimental values found for the
exTTF derivatives (Table 2).
3. Summary and conclusions
4. Experimental
In summary, we describe the synthesis of novel p-extended
TTF derivatives in which the exTTF unit is connected to
a p-nitrophenyl acceptor through different bridges (14–16).
A systematic study has been carried out on the length of the
oligoenic spacer as well as on the substitution on
the exTTF moiety. The electrochemical study reveals
the good donor character of the p-extended TTF unit
and the effect of the alkylthio substituents on the donor
ability.
All melting points were measured with a Gallenkamp
apparatus and are uncorrected. IR spectra were recorded
either as KBr pellets or as films with NaCl plates with a
Perkin–Elmer 257 spectrometer. UV–Vis spectra were
recorded with a Perkin–Elmer Lambda 3 instrument. 13C-
and 1H NMR spectra were recorded with a Varian VXR-300
spectrometer (300 and 75 MHz for 1H and 13C, respectively.
Chemical shifts are given as d values (int. Standard: TMS).
Fourier Transform Infrared absorption (FT-IR) measure-
ments were made with a Perkin–Elmer Model 1760 X
spectrometer. All spectra were collected using a resolution
of 2 cm21, and the mean of 50 scans was obtained.
Interference from atmospheric water vapor was minimized
by purging the instrument for 10–15 min with dry argon
before beginning data collection. Elemental analyses were
performed with a Perkin–Elmer CHN 2400 apparatus. MS
were recorded with a Hewlett–Packard HP5989A spectro-
meter. Cyclic voltammograms were recorded on a poten-
tiostat/galvanostat Versastat EG&G PAR, equipped with a
software electrochemical analysis Model 250 by using a
GCE (glassy carbon) as working electrode, SCE as
reference electrode, Bu4NþClO4 as supporting electrolyte,
In order to improve the thermal properties of these
compounds, a thiophene ring has been inserted in the
conjugated oligoenic spacer. Theoretical calculations (PM3)
predict a good NLO response for these molecules (20a–c)
which exhibit a remarkable thermal stability with decompo-
sition temperatures over 4008C.
A new series of D-p-A systems bearing a 1,3-dithiol-2-
ylidene donor connected to the same p-nitrophenyl group as
acceptor NLO-phore has been synthesized. Although a
comparison of the experimental mb(0) values of compounds
20a–c and 23a–c has not been possible, the latter also show
good NLO responses.

M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
7471
dichloromethane as solvent, and at a scan rate of 200 mV/s.
2-Hydroxymethyl-9,10-anthraquinone, 2,5-diformylthio-
phene and (4-nitrobenzyl)triphenylphosphonium bromide
are commercially available and were used without further
purification. EFISH measurements were taken with a
nonlinear optics spectrometer from SOPRA. The funda-
mental light at 1.907 mm was the first Stokes peak of a
hydrogen Raman cell pumped by the 1.064 mm light from a
Q-switched Nd:YAG laser (Quantel YG 781, 10 pps, 8 ns,
pulse). That light was passed through a linear polariser and
focused on the EFISH cell. The polarising dc voltage
(parallel to the light polarization) used in this cell was 6 kV.
The output light from the cell was passed through an
interference filter to select the second harmonic light
(0.954 mm) which was finally detected with a R642
photomultiplier from Hamamatsu. Static mb(0) values
were deduced from the experimental values using a
two-level dispersion model.
J¼8.1 Hz), 7.75–7.70 (m, 1H), 7.67 (s, 1H), 7.63–7.53 (m,
3H), 7.45 (d, 1H, J¼8.4 Hz), 7.36–7.32 (m, 2H), 7.07–7.04
(m, 2H), 6.32 (dd, 1H, J1¼15.1 Hz, J2¼8.1 Hz), 2.40 (s,
12H); 13C NMR (75 MHz, CDCl3) d 167.8, 151.9, 141.8,
135.9, 135.3, 134.3, 133.5, 132.6, 132.4, 131.9, 131.8, 130.9
(2C), 128.8 (2C), 126.8, 126.5, 126.4, 126.1, 125.9, 125.8,
125.4, 125.3, 124.4, 123.0, 19.2 (2C), 19.1 (2C); MS (m/z)
644 (Mþ, 100); UV–Vis (CH2Cl2) lmax (log 1 ) 462 (4.22),
412 (4.32), 340 (4.52), 284 (4.29), 244 (4.44) nm.
4.1.3. 2-(4-Formyl-1,3-butadienyl)-9,10-bis(4,5-ethylen-
dithio-1,3-dithiol-2-ylidene)-9,10-dihydroanthracene
(12c). Yield 35%; mp 190–1928C (dec.); FT-IR (KBr)
2924, 2854, 1728, 1672, 1618, 1599, 1508, 1460, 1379,
1277, 1121, 1074, 1040, 1007, 980, 754, 706, 679,
611 cm21 1H NMR (300 MHz, CDCl3) d 9.64 (d, 1H,
;
J¼7.9 Hz), 7.74–7.69 (m, 1H), 7.63 (s, 1H), 7.56–7.48 (m,
3H), 7.44 (dd, 1H, J1¼8.0 Hz, J2¼1.5 Hz), 7.37–7.32 (m,
2H), 6.37–6.28 (m, 2H), 6.32 (dd, 1H, J1¼15.2 Hz,
J2¼8.0 Hz), 3.31 (s, 8H); 13C NMR (50 MHz, CDCl3) d
167.7, 151.9, 141.8, 135.9, 135.3, 134.4, 133.6, 132.4,
131.7, 130.9 (2C), 130.6, 128.8 (2C), 126.5, 126.4, 126.0,
125.6, 125.5, 124.4, 123.4, 111.3, 111.2, 111.0, 110.7, 29.6
(2C); MS ((m/z)) 640 (Mþ, 67); UV–Vis (CH2Cl2) lmax
(log 1 ) 468 (4.38), 426 (4.44), 344 (4.70), 286 (4.51), 242
(4.69) nm.
Molecular orbital calculations for compounds 14–16a–c
were carried out using the version PC-GAMESS 6.026 of the
GAMESS program.27
4.1. Synthesis of starting aldehydes
Aldehydes 10a–c14 and 11a–c9 were prepared by following
the procedures previously reported in the literature.
Aldehydes 12a–c were prepared according to the following
general procedure:
4.2. Synthesis of donor-p-acceptor compounds
(14–16a–c)
A solution of (tiphenylphosphoranylidene)acetaldehyde
(0.9 mmol) and the corresponding carbonyl compound
(11a–c) (0.3 mmol) in toluene, was refluxed under argon
atmosphere for 16 h. The solvent was removed under
reduced pressure, and the crude material washed with water
(50 mL) and extracted with methylene dichloride
(3£50 mL). The organic extracts were dried, and the solvent
was removed under reduced pressure. The resulting mixture
was purified by silica gel chromatography using methylene
dichloride as eluent.
A toluene solution of (4-nitrobenzyl)triphenylphosphonium
bromide (268 mg, 0.56 mmol) and potassium tert-butoxide
(149 mg, 1.33 mmol) was heated to reflux under argon
atmosphere. After 30 min, a solution of the corresponding
aldehyde (10–12a–c) (0.22 mmol) was added and refluxed
for 16 h. The solvent was removed under reduced pressure
and the residue washed with water and extracted with
methylene dichloride. The organic extract was dried, and
the solvent was removed under reduced pressure. The
resulting solid was purified by silica gel chromatography
using hexane/methylene dichloride (1:1) as eluent.
4.1.1. 2-(4-Formyl-1,3-butadienyl)-9,10-bis(1,3-dithiol-2-
ylidene)-9,10-dihydroanthracene (12a). Yield 65%; mp
190–1938C (dec.); FT-IR (KBr) 1670, 1655, 1618, 1585,
1545, 1500, 1452, 1287, 1151, 1119, 1012, 987, 800, 756,
646, 615 cm21; 1H NMR (300 MHz, CDCl3) d 9.64 (d, 1H,
J¼8.0 Hz), 7.86 (d, 1H, J¼1.5 Hz), 7.74–7.64 (m, 3H),
7.57–7.54 (m, 1H), 7.43 (dd, 1H, J1¼8.1 Hz, J2¼1.5 Hz),
7.35–7.29 (m, 2H), 7.08–7.03 (m, 2H), 6.36–6.33 (m, 4H),
6.30 (dd, 1H, J1¼15.1 Hz, J2¼9.1 Hz); 13C NMR (50 MHz,
CDCl3) d 167.7, 152.2, 142.2, 139.2, 136.7, 136.0, 135.1,
133.1, 132.4, 131.4, 130.9 (2C), 128.8 (2C), 126.1, 126.0,
125.4, 124.9, 123.8, 121.6, 121.5, 117.4, 117.3, 116.9,
114.0; MS (m/z ) 460 (Mþ, 100); UV–Vis (CH2Cl2) lmax
(log 1 ) 460 (4.19), 408 (4.40), 336 (4.57), 286 (4.22), 244
(4.37) nm.
4.2.1. 2-(2-p-Nitrophenylvinyl)-9,10-bis(1,3-dithiol-2-yli-
dene)-9,10-dihydroanthracene (14a). Yield 75%; mp
206–2088C (dec.); FT-IR (KBr) 1591, 1543, 1508, 1456,
1419, 1338, 1259, 1107, 1026, 951, 866, 843, 802, 756, 690,
650, 634 cm21; 1H NMR (300 MHz, CDCl3) d 8.23 (d, 2H,
J¼8.5 Hz), 7.90 (s, 1H), 7.74–7.70 (m, 3H), 7.66 (d, 2H,
J¼8.5 Hz), 7.45 (d, 1H, J¼7.6 Hz), 7.34–7.29 (m, 2H),
7.31 (d, 1H, J¼16.2 Hz), 7.18 (d, 1H, J¼16.2 Hz), 6.34 (s,
4H); 13C NMR (75 MHz, CDCl3) d 146.6, 143.9, 136.6,
136.3, 136.2, 136.0, 135.9, 135.4, 135.2, 135.1, 133.7,
133.0, 126.8 (2C), 126.1 (2C), 125.4, 124.9 (2C), 124.2
(2C), 123.3, 121.8, 121.7, 117.4, 117.3, 117.2, 116.9; MS
(m/z) 527 (Mþ, 5), 497 (Mþ230, 100); UV–Vis (CH2Cl2)
lmax (log 1 ) ,480 (sh), 410 (4.31), 352 (4.34), 234
(4.33) nm. Anal. calcd for C28H17S4NO2·CH2Cl2·C6H14
(%): C 60.16, H 4.76, N 2.00, S 18.35. Found (%): C
60.39, H 4.51, N 2.24, S 18.57.
4.1.2. 2-(4-Formyl-1,3-butadienyl)-9,10-bis(4,5-dimethyl-
thio-1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (12b).
Yield 34%; mp 185–1878C; FT-IR (KBr) 2924, 2852, 1676,
1657, 1612, 1597, 1562, 1547, 1529, 1510, 1493, 1444,
1412, 1394, 1319, 1275, 1262, 1151, 1117, 1012, 981, 769,
4.2.2. 2-(2-p-Nitrophenylvinyl)-9,10-bis(4,5-dimethyl-thio-
1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (14b). Yield
97%; mp 242–2458C (dec.); FT-IR (KBr) 2922, 2852, 1629,
756 cm21 1H NMR (300 MHz, CDCl3) d 9.63 (d, 1H,
;

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M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
1591, 1560, 1512, 1491, 1458, 1450, 1419, 1381, 1338,
1
378 (4.59), 240 (4.54) nm. Anal. calcd for C34H27S8NO2
(%): C 55.3, H 3.7, N 1.9. Found (%): C 56.0, H 4.3, N 2.2.
1281, 1109, 966, 835, 771, 746, 694, 682, 671 cm21; H
NMR (300 MHz, CDCl3) d 8.25 (d, 2H, J¼8.8 Hz), 7.71 (s,
1H), 7.68 (d, 2H, J¼8.8 Hz), 7.60–7.56 (m, 2H), 7.58 (d,
1H, J¼8.5 Hz), 7.49 (dd, 1H, J1¼8.5 Hz, J2¼1.5 Hz),
7.36–7.31 (m, 2H), 7.32 (d, 1H, J¼16.1 Hz, CH), 7.19 (d,
1H, J¼16.1 Hz), 2.42–2.39 (m, 12H); 13C NMR (50 MHz,
CDCl3) d 146.8, 143.7, 135.2, 135.0, 134.4, 134.2, 132.7,
132.0, 131.6, 130.6, 129.8, 127.4, 126.9, 126.6, 126.5,
126.4, 126.1, 125.9, 125.7, 125.4, 125.3, 125.0, 124.2,
124.1, 124.0, 123.8, 123.3, 123.1, 19.3 (4C); MS (m/z) 711
(Mþ, 25), 681 (Mþ230, 12); UV–Vis (CH2Cl2) lmax
(log 1) ,480 (sh), 416 (4.48), 356 (4.62), 234 (4.64) nm.
4.2.6. 2-(4-p-Nitrophenyl-1,3-butadienyl)-9,10-bis(4,5-
ethylendithio-1,3-dithiol-2-ylidene)-9,10-dihydroanthra-
cene (15c). Yield 80%; mp 196–1988C (dec.); FT-IR (KBr)
2924, 2852, 1589, 1508, 1458, 1337, 1279, 1109, 981, 852,
756, 744, 604 cm21; 1H NMR (300 MHz, CDCl3) d 8.28 (d,
1H, J¼8.8 Hz), 8.21 (d, 1H, J¼8.8 Hz), 7.72 (s, 1H), 7.70
(d, 1H, J¼8.8 Hz), 7.57 (d, 1H, J¼8.8 Hz), 7.61–7.49 (m,
3H), 7.40 (dd, 1H, J1¼7.9 Hz, J2¼1.5 Hz), 7.38–7.30 (m,
2H), 7.15 (dd, 1H, J1¼15.1 Hz, J2¼10.3 Hz), 7.03 (dd, 1H,
J1¼15.1 Hz, J2¼10.3 Hz), 6.85 (d, 1H, J¼15.1 Hz), 6.76 (d,
1H, J¼15.1 Hz), 3.32 (s, 8H); 13C NMR (50 MHz, CDCl3) d
146.6, 144.4, 135.5, 135.2, 134.8, 134.6, 134.5, 133.8, 130.8,
130.6, 130.4, 129.7, 128.8, 128.7, 127.4, 126.4, 126.0, 125.6,
124.5, 124.2, 124.0, 123.9, 123.8, 123.7, 123.6, 123.5, 111.2,
111.1, 111.0, 110.7, 29.7 (2C), 29.6 (2C); MS (m/z) 733
(Mþ, 25); UV–Vis (CH2Cl2) lmax (log 1) ,480 (sh), 452
(4.29), 428 (4.37), 376 (4.50), 244 (4.49) nm.
4.2.3. 2-(2-p-Nitrophenylvinyl)-9,10-bis(4,5-ethylendi-thio-
1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (14c). Yield
61%; mp 208–2108C (dec.); FT-IR (KBr) 2924, 2852, 1630,
1593, 1562, 1547, 1510, 1450, 1338, 1279, 1109, 852, 756,
694, 634 cm21, 1H NMR (300 MHz, CDCl3) d 8.24 (d, 2H,
J¼8.8 Hz), 7.72–7.64 (m, 3H), 7.59–7.44 (m, 4H), 7.40–
7.28 (m, 2H), 7.32 (d, 1H, J¼16.8 Hz), 7.18 (d, 1H, J¼
16.8 Hz), 3.31 (s, 8H); 13C NMR (50 MHz, CDCl3) d 146.8,
144.0, 143.8, 135.3, 135.1, 134.6, 134.4, 134.3, 132.8,
130.7, 130.4, 130.0, 128.7, 127.0, 126.6, 126.5, 126.0,
125.5, 125.0, 124.2, 124.1, 124.0, 123.7, 123.6, 111.2,
111.1, 111.0, 110.7, 29.6 (4C); MS (m/z) 707 (Mþ, 99);
UV–Vis (CH2Cl2) lmax (log 1) ,480 (sh), 432 (4.44), 358
(4.56), 248 (4.63) nm. Anal. calcd for C32H21S8NO2 (%): C
54.3, H 3.0, N 2.0. Found (%): C 55.2, H 3.5, N 2.2.
4.2.7. 2-(6-p-Nitrophenyl-1,3,5-hexatrienyl)-9,10-bis(1,3-
di-thiol-2-ylidene)-9,10-dihydroanthracene (16a). Yield
65%; mp 268–2708C (dec.); FT-IR (KBr) 1635, 1578, 1558,
1541, 1508, 1458, 1419, 1338, 1257, 1109, 997, 976, 860,
800, 744, 692, 636, 611 cm21; 1H NMR (300 MHz, CDCl3)
d 8.28 (d, 2H, J¼8.8 Hz), 7.79 (s, 1H), 7.75–7.64 (m, 5H),
7.35 (d, 1H, J¼8.8 Hz), 7.34–7.25 (m, 2H), 7.06 (dd, 1H,
J1¼15.7 Hz, J2¼10.3 Hz), 6.96 (dd, 1H, J1¼15.0 Hz, J2¼
10.3 Hz), 6.77–6.51 (m, 4H), 6.33 (s, 4H); 13C NMR
(75 MHz, CDCl3) d 142.8, 142.2, 136.9, 136.1, 135.8,
135.2, 134.5, 133.7, 132.5, 132.3, 131.3, 130.6, 130.1,
129.8, 129.7, 129.3, 128.8, 128.7, 128.6, 127.5, 126.6,
126.0, 124.9, 124.3, 124.1, 123.9, 123.8, 123.5, 117.3 (2C),
117.0 (2C); MS (m/z ) 579 (Mþ, 100), 549 (Mþ230, 56);
UV–Vis (CH2Cl2) lmax (log 1) ,490 (sh), 426 (4.59), 398
(4.53), 240 (4.46) nm.
4.2.4. 2-(4-p-Nitrophenyl-1,3-butadienyl)-9,10-bis(1,3-di-
thiol-2-ylidene)-9,10-dihydroanthracene (15a). Yield
64%; mp 190–1928C (dec.); FT-IR (KBr) 1583, 1543,
1508, 1450, 1338, 1275, 1181, 1107, 984, 852, 812, 758,
746 cm21 1H NMR (300 MHz, CDCl3) d 8.20 (d, 2H,
;
J¼8.6 Hz), 7.82 (s, 1H), 7.73–7.64 (m, 3H), 7.56 (d, 2H,
J¼8.6 Hz), 7.37 (d, 1H, J¼8.0 Hz), 7.33–7.29 (m, 2H),
7.15 (dd, 1H, J1¼15.2 Hz, J2¼10.4 Hz), 7.02 (dd, 1H,
J1¼14.8 Hz, J2¼10.4 Hz), 6.85 (d, 1H, J¼14.8 Hz), 6.73 (d,
1H, J¼15.2 Hz), 6.33 (s, 4H); 13C NMR (50 MHz, CDCl3) d
146.5, 144.0, 136.0, 135.9, 135.5, 135.2, 135.1, 134.2,
133.9, 130.6, 130.0, 129.8, 128.2, 127.9, 127.5, 126.6,
126.1, 126.0, 125.3, 124.9, 124.6, 124.3, 124.2, 123.0,
122.0, 121.9, 117.4, 117.3, 117.2, 117.0; MS (m/z) 553
(Mþ, 100), 523 (Mþ230, 11); UV–Vis (CH2Cl2) lmax
(log 1) ,480 (sh), 418 (4.55), 378 (4.53), 238 (4.44) nm.
4.2.8. 2-(6-p-Nitrophenyl-1,3,5-hexatrienyl)-9,10-bis(4,5-
dimethylthio-1,3-dithiol-2-ylidene)-9,10-dihydroanthra-
cene (16b). Yield 77%; mp 220–2228C (dec.); FT-IR (KBr)
2923, 2854, 1637, 1593, 1577, 1508, 1452, 1419, 1338,
1
1272, 1178, 1107, 995, 956, 850, 752, 692, 638 cm21; H
NMR (300 MHz, CDCl3) d 8.20 (d, 2H, J¼8.8 Hz), 7.61 (d,
1H, J¼1.5 Hz), 7.60–7.50 (m, 5H), 7.38 (dd, 1H, J1¼
7.9 Hz, J2¼1.5 Hz), 7.35–7.30 (m, 2H), 7.07 (dd, 1H,
J1¼15.6 Hz, J2¼10.1 Hz), 6.97 (dd, 1H, J1¼15.6 Hz, J2¼
10.0 Hz), 6.77–6.55 (m, 4H), 2.41 (s, 12H); 13C NMR
(50 MHz, CDCl3) d 146.5, 143.9, 136.6, 135.1, 134.5,
134.4, 134.3, 133.6, 132.9, 132.5, 131.5, 131.4, 130.9,
130.7, 130.6, 130.1, 129.7, 129.3, 129.0, 128.8, 128.7,
127.5, 126.6, 126.4, 125.8, 125.5, 125.4, 124.3, 124.1,
123.9, 123.8, 123.5, 19.3 (2C), 19.1 (2C); MS (m/z ) 763
(Mþ, 6), 733 (Mþ230, 8); UV–Vis (CH2Cl2) lmax (log 1 )
,490 (sh), 428 (4.53), 382 (4.51), 242 (4.47) nm.
4.2.5. 2-(4-p-Nitrophenyl-1,3-butadienyl)-9,10-bis(4,5-
dimethylthio-1,3-dithiol-2-ylidene)-9,10-dihydroanthra-
cene (15b). Yield 95%; mp 170–1738C (dec.); FT-IR (KBr)
2920, 2852, 1637, 1585, 1560, 1508, 1490, 1450, 1419,
1337, 1279, 1109, 987, 854, 756, 611 cm21 1H NMR
;
(300 MHz, CDCl3) d 8.21 (d, 2H, J¼8.8 Hz), 7.64 (s, 1H),
7.60–7.54 (m, 5H), 7.41 (d, 1H, J¼8.1 Hz), 7.36–7.29 (m,
2H), 7.16 (dd, 1H, J1¼15.0 Hz, J2¼10.0 Hz), 7.03 (dd, 1H,
J1¼15.4 Hz, J2¼10.0 Hz), 6.85 (d, 1H, J¼15.0 Hz), 6.76 (d,
1H, J¼15.4 Hz), 2.41 (s, 12H); 13C NMR (50 MHz, CDCl3)
d 146.6, 143.8, 135.5, 135.1, 134.8, 134.6, 134.4, 133.7,
132.3, 132.1, 131.7, 131.4, 130.4, 128.6, 128.3, 127.5,
126.6, 126.5, 126.4, 126.0, 125.8, 125.4, 125.3, 125.1,
124.6, 124.2, 124.1, 123.7, 123.5, 123.3, 19.2 (2C), 19.0
(2C); MS (m/z) 737 (Mþ, 39), 707 (Mþ230, 46); UV–Vis
(CH2Cl2) lmax (log 1) ,480 (sh), 454 (4.43), 420 (4.58),
4.2.9. 2-(6-p-Nitrophenyl-1,3,5-hexatrienyl)-9,10-bis(4,5-
ethylendithio-1,3-dithiol-2-ylidene)-9,10-dihydroanthra-
cene (16c). Yield 63%; mp 190–1928C (dec.); FT-IR (KBr)
2924, 2852, 1508, 1456, 1337, 1284, 1109, 995, 850, 746,
692 cm21 1H NMR (300 MHz, CDCl3) d 8.27 (d, 2H,
;
J¼8.8 Hz), 7.58–7.45 (m, 6H), 7.39–7.28 (m, 3H), 7.06
(dd, 1H, J1¼15.4 Hz, J2¼9.7 Hz), 6.96 (dd, 1H,

M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
7473
J1¼15.4 Hz, J2¼10.1 Hz), 6.78–6.50 (m, 4H), 3.31 (s, 8H);
13C NMR (75 MHz, CDCl3) d 147.9, 146.9, 144.4, 142.9,
137.1, 135.5, 134.9, 134.7, 134.6, 134.1, 133.2, 132.8,
131.3, 131.1, 130.5, 129.5, 129.2, 129.1, 127.9, 127.0,
126.9, 126.3, 126.0, 124.7, 124.5, 124.4, 124.2, 123.9,
111.5, 111.4 (2C), 111.1, 30.8, 30.1, 30.0, 29.3; MS (m/z)
759 (Mþ, 14); UV–Vis (CH2Cl2) lmax (log 1 ) ,490 (sh),
434 (4.44), 382 (4.47), 240 (4.46) nm. Anal. calcd for
C36H25S8NO2 (%): C 56.9, H 3.3, N 1.8. Found (%): C 57.3,
H 4.0, N 2.1.
(d, 1H, J¼3.9 Hz), 7.09 (d, 1H, J¼15.4 Hz), 7.04 (d, 1H,
J¼15.4 Hz), 6.79–6.73 (m, 4H); 13C NMR (75 MHz,
DMSO-d6) d 147.9, 146.9, 1445, 144.1, 142.3, 141.6,
137.9, 137.8, 136.1, 135.4, 135.2, 135.0, 131.0, 129.3,
129.2, 129.1, 128.7, 128.0, 127.9, 127.5, 127.2, 126.6,
126.0, 125.6, 125.3, 125.0, 123.9, 123.4, 123.0, 121.3,
119.2, 119.1, 119.0, 118.9; MS (m/z) (%) 635 (Mþ, 100),
605 (Mþ230, 85); UV–Vis (CH2Cl2) lmax (log 1 ) ,500
(sh), 434 (4.72), 244 (4.55) nm. Anal. calcd for
C34H21S5NO2 (%): C 64.2, H 3.3, N 2.2. Found (%): C
63.9, H 4.0, N 1.6.
4.2.10. Synthesis of 5-(2-p-nitrophenylvinyl)-2-thiophene-
carbaldehyde (19). (4-nitrobenzyl)triphenylphosphonium
bromide 13 (341 mg, 0.71 mmol) and potassium tert-
butoxide (79 mg, 0.71 mmol) were dissolved in toluene
under argon atmosphere and the reaction was vigorously
stirred at room temperature for one hour. After this time,
a toluene solution of 2,5-thiophenedicarbaldehyde 21
(100 mg, 0.71 mmol) was added. After 5 h, the reaction
was heated to reflux for 10 h. The solvent was removed
under reduced pressure and the residue washed with water
and extracted with methylene dichloride. The organic layer
was dried and the solvent was removed under reduced
pressure. The resulting solid was purified by silica gel
chromatography using hexane/methylene dichloride (3:1) as
eluent.
4.3.2. 2-{2-[5-(2-p-Nitrophenylvinyl)-2-thienyl]vinyl}-
9,10-bis(4,5-dimethylthio-1,3-dithiol-2-ylidene)-9,10-
dihydroanthracene (20b). Yield 11%; mp .4008C; FT-IR
(KBr) 1589, 1514, 1497, 1452, 1419, 1337, 1313, 1281,
1109, 945, 827, 754 cm21; 1H NMR (300 MHz, DMSO-d6)
d 8.21 (d, 2H, J¼8.9 Hz), 7.84 (d, 2H, J¼8.9 Hz), 7.74 (d,
1H, J¼16.1 Hz), 7.69 (s, 1H), 7.67–7.50 (m, 4H), 7.47–
7.34 (m, 3H), 7.30 (d, 1H, J¼3.8 Hz), 7.26 (d, 1H, J¼
3.8 Hz), 7.09 (d, 1H, J¼16.1 Hz), 7.08 (d, 1H, J¼16.1 Hz),
2.43 (m, 12H); 13C NMR (75 MHz, CDCl3) d 146.5, 143.7,
143.5, 140.7, 135.1, 134.7, 134.5, 134.4, 134.2, 134.0, 131.4
(2C), 131.2, 129.4, 129.1, 127.5, 126.6, 126.5, 126.3, 126.2,
125.9, 125.8, 125.7, 125.4 (2C), 125.2, 124.3, 124.2, 123.5,
123.3, 121.9, 120.5, 120.1, 119.7, 19.1 (4C); MS (m/z) (%)
819 (Mþ, 100), 789 (Mþ230, 3); UV–Vis (CH2Cl2) lmax
(log 1 ) ,500 (sh), 440 (4.72), 246 (4.70) nm. Anal. calcd
for C38H29S9NO2 (%): C 55.6, H 3.6, N 1.7. Found (%): C
54.9, H 4.1, N 1.5.
Yield 70%; mp 191–1928C; FT-IR (KBr) 1659, 1584, 1508,
1491, 1448, 1387, 1338, 1263, 1227, 1194, 1105, 1049, 951,
1
868, 833, 806, 775, 746, 687, 669, 631 cm21; H NMR
(300 MHz, CDCl3) d 9.90 (s, 1H), 8.23 (d, 2H, J¼8.9 Hz),
7.99 (d, 1H, J¼3.9 Hz), 7.88 (d, 2H, J¼8.9 Hz), 7.80 (d, 1H,
J¼16.4 Hz), 7.51 (d, 1H, J¼3.9 Hz), 7.41 (d, 1H, J¼
16.4 Hz); 13C NMR (75 MHz, CDCl3) d 184.3, 150.4,
146.9, 142.9, 142.6, 138.9. 130.1, 129.3, 128.0 (2C), 125.8,
124.2 (2C); MS (m/z) 259 (Mþ, 5), 229 (Mþ230, 100);
UV–Vis (CH2Cl2) lmax (log 1) 382 (7.25), 240 (4.05) nm.
Anal. calcd for C13H9SNO3 (%): C 60.2, H 3.5, N 5.4, S
12.4. Found (%): C 60.0, H 3.8, N 5.3, S 12.0.
4.3.3. 2-{2-[5-(2-p-Nitrophenylvinyl)-2-thienyl]vinyl}-
9,10-bis(4,5-ethylendithio-1,3-dithiol-2-ylidene)-9,10-
dihydroanthracene (20c). Yield 9%; mp .4008C; FT-IR
(KBr) 1589, 1508, 1452, 1419, 1337, 1109, 945, 862, 795,
754, 739, 725, 712, 685, 669, 615 cm21
;
1H NMR
(300 MHz, DMSO-d6) d 8.18 (d, 2H, J¼8.9 Hz), 7.80 (d,
2H, J¼8.9 Hz), 7.70 (d, 1H, J¼15.9 Hz), 7.62 (s, 1H),
7.57–7.45 (m, 4H), 7.43–7.31 (m, 3H), 7.26 (d, 1H, J¼
3.7 Hz), 7.23 (d, 1H, J¼3.7 Hz), 7.06 (d, 2H, J¼15.9 Hz),
3.32 (s, 8H); 13C NMR (75 MHz, CDCl3) d 146.5, 143.8,
143.5, 140.7, 140.3, 135.2, 134.7, 134.5, 134.4, 134.2, 130.1,
129.4, 129.0, 127.5, 126.5 (3C), 126.4, 126.2, 126.0, 125.7,
125.6, 125.5, 124.4, 124.2 (2C), 123.9, 123.8, 123.4, 121.9,
111.0 (2C), 110.6 (2C), 29.7 (2C), 29.6 (2C); MS (m/z) (%)
815 (Mþ, 100), 785 (Mþ230); UV–Vis (CH2Cl2) lmax
(log 1) ,500 (sh), 448 (4.38), 280 (4.14), 244 (4.40) nm.
4.3. Synthesis of donor-p-acceptor compounds (20a–c)
The corresponding salt of p-extended TTF (17a–c)
(0.22 mmol) and potassium tert-butoxide (54 mg,
0.48 mmol) were dissolved in toluene and heated to reflux.
After 1 h, a solution of compound 19 in toluene was added
and the reaction was heated to reflux for 12 h. The solvent
was removed under reduced pressure and the resulting
mixture washed with water and extracted with methylene
dichloride. The organic layer was dried and the solvent was
removed under reduced pressure. The resulting solid was
purified by silica gel chromatography using hexane/methyl-
ene dichloride (5:1) as eluent.
4.4. Synthesis of donor-p-acceptor compounds (23a–c)
A toluene solution of (4-nitrobenzyl)triphenylphosphonium
bromide 13 (304 mg, 0.64 mmol) and potassium tert-
butoxide (90 mg, 0.81 mmol) was heated to reflux. After
1 h, a solution of the corresponding aldehyde (22a–c)
(0.25 mmol) in toluene was added and heated to reflux for
16 h. The reaction crude was washed with water and
extracted with methylene dichloride. The organic layer was
dried and the obtained solid was purified by silica gel
chromatography using hexane/methylene dichloride (1:1) as
eluent.
4.3.1. 2-{2-[5-(2-p-Nitrophenylvinyl)-2-thienyl]vinyl}-
9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene
(20a). Yield 57%; mp .4008C; FT-IR (KBr) 1544, 1508,
1450, 1419, 1337, 1109, 1047, 1030, 945, 862, 825, 800,
758, 746, 636, 604 cm21; 1H NMR (300 MHz, DMSO-d6) d
8.21 (d, 2H, J¼8.9 Hz), 7.85 (d, 1H, J¼1.5 Hz), 7.84 (d, 2H,
J¼8.9 Hz), 7.74 (d, 1H, J¼16.0 Hz), 7.67–7.62 (m, 3H),
7.57 (dd, 1H, J1¼8.2 Hz, J2¼1.5 Hz), 7.51 (d, 1H, J¼
16.0 Hz), 7.39–7.33 (m, 2H), 7.29 (d, 1H, J¼3.9 Hz), 7.24
4.4.1. 2-(E-2-p-Nitrophenylvinyl)-5-(1,3-dithiol-2-ylidene-
methyl)thiophene (23a). Yield 72%; mp 245–2478C

7474
M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
Polymers for Second-Order Nonlinear Optics. ACS
Symposium Series, Lindsay, G. A., Singer, K. D., Eds.;
American Chemical Society: Washington, DC, 1995; Vol.
601. (f) Kajzar, F.; Swalen, J. Organic Thin Films for
(dec.); FT-IR (KBr) 1581, 1545, 1499, 1437, 1329, 1310,
1109, 947, 866, 673, 609 cm21 1H NMR (300 MHz,
;
DMSO-d6) d 8.18 (d, 2H, J¼9.0 Hz), 7.81 (d, 2H, J¼
9.0 Hz), 7.73 (d, 1H, J¼16.5 Hz), 7.68 (d, 1H, J¼3.8 Hz),
7.24 (d, 1H, J¼3.8 Hz), 7.07 (s, 1H), 7.60 (d, 1H, J¼
16.5 Hz), 6.90 (m, 2H); 13C NMR (75 MHz, CDCl3) d
143.9, 139.4, 132.4, 132.2, 130.9, 128.8, 128.6, 128.4,
127.5, 126.2, 124.3, 124.2, 123.9, 123.5, 118.6, 118.5; MS
(m/z) 345 (Mþ, 100), 315 (Mþ230, 16); UV–Vis (CH2Cl2)
Waveguiding Nonlinear Optics. Gordon
& Breach:
Amsterdam, 1996. (g) Miyata, S.; Sasabe, H. Poled Polymers
and Their Applications to SHG and EO Devices. Gordon &
Breach: Amsterdam, 1997. (h) Nalwa, H. S. Nonlinear Optics
of Organic Molecules and Polymers. CRC: Boca Raton, FL,
1997. (i) Kuzyk, M. G.; Singer, K. D.; Twieg, R. J. J. Opt. Soc.
Am. B. Opt. Phys. 1998, 15, 254.
l
max (log 1) 490 (4.31), 358 (3.95), 278 (3.93), 278 (3.93),
238 (3.95) nm. Anal. calcd for C16H11S3NO2 (%): C 55.6, H
3.2, N 4.1. Found (%): C 55.1, H 3.9, N 3.5.
2. For a review, see: Verbiest, T.; Houbrechts, S.; Kauranen, M.;
Clays, K.; Persoons, A. J. Mater. Chem. 1997, 7, 2175.
3. Marder, S. R.; Gorman, G. B.; Tiemann, B. G.; Cheng, L.-T.
J. Am. Chem. Soc. 1993, 115, 3006.
4.4.2. 2-(E-2-p-Nitrophenylvinyl)-5-(4,5-dimethylthio-1,3-
dithiol-2-ylidenemethyl)thiophene (23b). Yield 98%; mp
190–1988C (dec.); FT-IR (KBr) 1587, 1508, 1485, 1439,
4. (a) Rao, V. P.; Jen, A. K. Y.; Wong, K. Y.; Drost, K. J. J. Chem.
Soc., Chem. Commun. 1993, 1118. (b) Rao, V. P.; Jen, A. K.
Y.; Wong, K. Y.; Drost, K. J. Tetrahedron Lett. 1993, 34,
1747. (c) Rao, V. P.; Jen, A. K. Y.; Wong, K. Y.; Drost, K. J.
J. Chem. Soc., Chem. Commun. 1993, 90. (d) Rao, V. P.; Jen,
A. K. Y.; Cai, Y. Chem. Commun. 1996, 1237. (e) Pauley,
M. A.; Wang, C. H.; Jen, A. K. Y. J. Chem. Phys. 1995, 102,
6400.
1335, 1310, 1107, 943, 864, 825, 781, 746, 688, 609 cm21
;
1H NMR (300 MHz, CDCl3) d 8.21 (d, 2H, J¼9.0 Hz), 7.57
(d, 2H, J¼9.0 Hz), 7.38 (d, 1H, J¼16.1 Hz), 7.10 (d, 1H,
J¼3.8 Hz), 6.90 (d, 1H, J¼16.1 Hz), 6.79 (d, 1H, J¼
3.8 Hz), 6.70 (s, 1H), 2.50 (s, 3H), 2.47 (s, 3H); 13C NMR
(75 MHz, CDCl3) d 146.3, 143.8, 141.4, 141.3, 140.3,
132.9, 129.2, 128.8, 126.3 (2C), 126.2, 124.7, 124.5, 124.2
(2C), 108.0, 19.2, 18.9; MS (m/z) 437 (Mþ, 42), 407
(Mþ230, 100); UV–Vis (CH2Cl2) lmax (log 1) 490 (4.41),
360 (4.13), 270 (4.09), 242 (4.11) nm. Anal. calcd for
C18H15S5NO2 (%): C 49.4, H 3.5, N 3.2. Found (%): C 50.1,
H 4.1, N 3.2.
´ ´
5. (a) Andreu, R.; de Lucas, A. I.; Garın, J.; Martın, N.; Orduna,
´
J.; Sanchez, L.; Seoane, C. Synth. Met. 1997, 86, 1817.
´ ´
(b) De Lucas, A. I.; Martın, N.; Sanchez, L.; Seoane, C.;
´ ´
Andreu, R.; Garın, J.; Orduna, J.; Alcala, R.; Villacampa, B.
´
Tetrahedron 1998, 54, 4655. (c) Garın, J.; Orduna, J.; Ruperez,
´
´ ´
J. I.; Alcala, R.; Villacampa, B.; Sanchez, C.; Martın, N.;
´
4.4.3. 2-(E-2-p-Nitrophenylvinyl)-5-(4,5-ethylenedithio-
1,3-dithiol-2-ylidenemethyl)thiophene (23c). Yield 65%;
mp 258–2608C (dec.); FT-IR (KBr) 1583, 1545, 1500,
1439, 1425, 1375, 1333, 1306, 1180, 1107, 1051, 943, 858,
´
Segura, J. L.; Gonzalez, M. Tetrahedron Lett. 1998, 39, 3577.
´ ´
(d) Gonzalez, M.; Martın, N.; Segura, J. L.; Seoane, C.; Garın,
´
´ ´
J.; Orduna, J.; Sanchez, C.; Alcala, R.; Villacampa, B.
Tetrahedron Lett. 1999, 40, 8599.
1
789, 744, 688, 631 cm21; H NMR (300 MHz, CDCl3) d
´ ´ ´
6. Gonzalez, M.; Segura, J. L.; Seoane, C.; Martın, N.; Garın, J.;
´ ´
8.19 (d, 2H, J¼8.8 Hz), 7.82 (d, 2H, J¼8.8 Hz), 7.74 (d, 1H,
J¼16.0 Hz), 7.29 (d, 1H, J¼3.9 Hz), 7.13 (s, 1H), 7.08 (d,
1H, J¼16.0 Hz), 6.94 (d, 1H, J¼3.9 Hz), 3.44 (s, 4H); MS
(m/z) 435 (Mþ, 100), 405 (Mþ230, 22); UV–Vis (CH2Cl2)
lmax (log 1) 490 (4.36), 368 (4.13), 266 (4.07), 248
(4.13) nm.
´
Orduna, J.; Alcala, R.; Villacampa, B.; Hernandez, V.; Lopez
Navarrete, J. T. J. Org. Chem. 2001, 66, 8872.
7. For a recent review on TTFs, see: Segura, J. L.; Martın, N.
´
Angew. Chem. Int. Ed. 2001, 40, 1372.
8. Bryce, M. R.; Green, A.; Moore, A. J.; Perepichka, D. F.;
´
Batsanov, A. S.; Howard, J. A. K.; Ledoux-Rak, I.; Gonzalez,
´ ´ ´
M.; Martın, N.; Segura, J. L.; Garın, J.; Orduna, J.; Alcala, R.;
Villacampa, B. Eur. J. Org. Chem. 2001, 1927.
´ ´
9. Herranz, M. A.; Martın, N.; Sanchez, L.; Garın, J.; Orduna, J.;
´
Acknowledgments
´
´
Alcala, R.; Villacampa, B.; Sanchez, C. Tetrahedron 1998, 54,
11651.
10. For a recent review on quinonoid p-extended TTFs, see:
We thank DGICYT of Spain (Projects: PR BQU2000-0790,
PB98-0818 and MAT99-1009-C02-02) and Gobierno de
´
Aragon-Fondo Social Europeo (P009/2001) for financial
support.
´
´
Martın, N.; Ortı, E. Handbook of Advanced Electronic and
Photonic Materials and Devices, Nalwa, H. S., Ed.;
Academic: New York, 2001; Vol. 3, pp 245–265.
11. Bryce, M. R.; Moore, A. J.; Hasan, M.; Ashwell, G. J.; Fraser,
A. T.; Clegg, W.; Karanlov, A. I. Angew. Chem. Int. Ed. Engl.
1990, 29, 1450.
References
´
12. Martın, N.; Sanchez, L.; Guldi, D. M. Chem. Commun. 2000,
´
113.
1. (a) In Nonlinear Optical Properties of Organic Molecules and
Crystal. Chemla, D. S., Zyss, J., Eds.; Academic: New York,
1987. (b) In Materials for Nonlinear Optics: Chemical
Perspectives. ACS Symposium Series, Marder, S. R., Sohn,
J. E., Stucky, G. D., Eds.; American Chemical Society:
Washington, DC, 1991. (c) Special issue on optical non-
linearities in chemistry. Burland, D. M. Ed. Chem. Rev. 1994
1–278. (d) Bosshard, C.; Sutter, K.; Pretre, P.; Hulliger, J.;
13. (a) Godbert, N.; Batsanov, A. S.; Bryce, M. R.; Howard, J. A.
K. J. Org. Chem. 2001, 66, 713. (b) Christensen, C. A.;
Batsanov, A. S.; Bryce, M. R.; Howard, J. A. K. J. Org. Chem.
2001, 66, 3313. (c) Bryce, M. R.; Batsanov, A. S.; Finn, T.;
Hansen, T. K.; Howard, J. A. K.; Kamenjicki, M.; Lednev,
I. K.; Asher, S. A. Chem. Commun. 2000, 295.
´ ´ ´
14. Martın, N.; Perez, I.; Sanchez, L.; Seoane, C. J. Org. Chem.
¨
Florsheimer, M.; Kaatz, P.; Gunter, P. Organic Nonlinear
¨
1997, 62, 5690.
´
15. Perez, I. PhD Dissertation, Universidad Complutense, 2002.
Optical Materials. Gordon & Breach: Basel, 1995. (e) In

M. Otero et al. / Tetrahedron 58 (2002) 7463–7475
7475
´
16. Gonzalez, S. PhD Dissertation, Universidad Complutense,
´
24. Garın, J.; Orduna, J.; Andreu, R. Synth. Met. 1999, 102, 1531.
`
25. (a) Roncali, J.; Rasmussen, L.; Thobie-Gautier, C.; Frere, P.;
2001.
17. De Lucas, A. I.; Martın, N.; Sanchez, L.; Seoane, C.; Garın, J.;
´
Orduna, J.; Alcala, R.; Villacampa, B. Tetrahedron Lett. 1997,
´
´
´
´
Brisset, H.; Salle, M.; Becher, J.; Simonsen, O.; Hansen, T. K.;
´
Benahmed-Gasmi, A.; Orduna, J.; Garın, J.; Jabault, M.;
38, 6107.
18. Inove, S.; Aso, Y.; Otsubo, T. Chem. Commun. 1997, 1105.
Gorgues, A. Adv. Mater. 1994, 6, 841. (b) De Lucas, A. I.;
´
Martın, N.; de Miguel, P.; Seoane, C.; Albert, A.; Cano, F. H.
´
´
´
19. Martın, N.; Sanchez, L.; Seoane, C.; Ortı, E.; Viruela, P. M.;
Viruela, R. J. Org. Chem. 1998, 63, 1268.
20. Moore, A. J.; Bryce, M. R. J. Chem. Soc., Perkin Trans. 1
1991, 157.
J. Mater. Chem. 1995, 5, 1145.
26. Granovsky, A. http://www.classic.chem.msu.su/gran/gamess/
index.html.
27. Schmidt, M. W.; Baldridge, K. K.; Boats, J. A.; Elbert, S. T.;
Gordon, M. S.; Jensen, J. J.; Koseki, S.; Matsunaga, N.;
Nguyen, K. A.; Su, S.; Windus, T. L.; Dupuis, M.;
Montgomery, J. A. J. Comput. Chem. 1993, 14, 1347.
21. Kanis, D. R.; Ratner, M. A.; Marks, T. J. Chem. Rev. 1994, 94,
195.
22. Oudar, J. L. J. Chem. Phys. 1977, 67, 446.
23. Oudar, J. L.; Chemla, D. S. J. Phys. Chem. 1977, 66, 2664.