Tetrathiafulvalene derivatives as NLO-phores: Synthesis, electrochemistry, Raman spectroscopy, theoretical calculations, and NLO properties of novel TTF-derived donor-π-acceptor dyads

Article abstract of DOI:10.1021/jo010717k

Novel π-conjugated donor-acceptor chromophores, based on the strong electron-donating tetrathiafulvalene moiety and different electron-withdrawing acceptors, exhibit large second-order optical nonlinearities. The effect of increasing the length of the polyenic spacer and the influence of the nature of the acceptor moiety on the NLO properties have been studied by using the electric field-induced second-harmonic generation (EFISH) technique as well as by semiempirical and ab initio theoretical calculations. A charge-transfer band has been observed in the absorption spectra of these D-π-A compounds that undergoes an hypsochromic shift when increasing the number of vinylenic spacer units connecting both donor and acceptor moieties. The degree of the intramolecular charge transfer from the donor to the acceptor has also been analyzed by means of Raman spectroscopy.

Full text of DOI:10.1021/jo010717k

8872
J . Org. Chem. 2001, 66, 8872-8882
Tetr a th ia fu lva len e Der iva tives a s NLO-p h or es: Syn th esis,
Electr och em istr y, Ra m a n Sp ectr oscop y, Th eor etica l Ca lcu la tion s,
a n d NLO P r op er ties of Novel TTF -Der ived Don or -π-Accep tor
Dya d s
Mar Gonza´lez, J ose´ L. Segura, Carlos Seoane, and Nazario Mart´ın*
Departamento de Quı´mica Orga´nica, Facultad de Quı´mica, Universidad Complutense,
E-28040 Madrid, Spain
J avier Gar´ın* and J esu´s Orduna
Departamento de Quı´mica Orga´nica, ICMA, Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain
Rafael Alcala´ and Bele´n Villacampa
Departamento de Fı´sica de la Materia Condensada, ICMA, Universidad de Zaragoza, CSIC,
E-50009 Zaragoza, Spain
V´ıctor Herna´ndez and J uan T. Lo´pez Navarrete*
Departamento de Quı´mica Fı´sica, Facultad de Ciencias, Universidad de Ma´laga, E-29071 Ma´laga, Spain
nazmar@eucmax.sim.ucm.es
Received J uly 16, 2001
Novel π-conjugated donor-acceptor chromophores, based on the strong electron-donating tetra-
thiafulvalene moiety and different electron-withdrawing acceptors, exhibit large second-order optical
nonlinearities. The effect of increasing the length of the polyenic spacer and the influence of the
nature of the acceptor moiety on the NLO properties have been studied by using the electric field-
induced second-harmonic generation (EFISH) technique as well as by semiempirical and ab initio
theoretical calculations. A charge-transfer band has been observed in the absorption spectra of
these D-π-A compounds that undergoes an hypsochromic shift when increasing the number of
vinylenic spacer units connecting both donor and acceptor moieties. The degree of the intramolecular
charge transfer from the donor to the acceptor has also been analyzed by means of Raman
spectroscopy.
In tr od u ction
ceptibility (ø(2)) through high molecular hyperpolarizabil-
ity (â) and fast response time; (ii) they are cheaper to
produce and (iii) easier to fabricate; (iv) they are compat-
ible with existing semiconductor technology; and (v) their
structures can be tailored in myriads of ways allowing
to finely tune NLO properties for desired applications.
A key objective in the development of materials for
nonlinear optical applications is to find highly active
chromophores with large second-order polarizabilities â.
The first hyperpolarizability and, hence, the second-order
NLO response is related to an electronic intramolecular
charge transfer (ICT) excitation between the ground and
excited states of the molecule. Both theoretical and
experimental studies have shown that large hyperpolar-
izabilities generally arise from a combination of a strong
electron donor and acceptor positioned at opposite ends
of a suitable conjugation path. Thus, a variety of donor-
Donor (D)-acceptor (A) substituted organic molecules
with large second-order nonlinear optical (NLO) proper-
ties have been the subject of considerable research efforts
due to their potential applications in areas such as optical
modulation, molecular switching, optical memory, and
frequency doubling.1,2 Although organic molecules are not
as robust as inorganics, they have received a great deal
of interest in the nonlinear optics field given that they
offer many advantages over traditional inorganic crys-
tals: (i) organic materials present high electronic sus-
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10.1021/jo010717k CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/30/2001

Tetrathiafulvalene Derivatives as NLO-phores
J . Org. Chem., Vol. 66, No. 26, 2001 8873
Ch a r t 1
acceptor organic molecules containing different acceptor
units such as nitro,3 nitrile,4 sulfonyl,5 polycyanovinyl,6
4-methylidene-3-phenylisoxazolone,7 4-methylidenedieth-
ylthiobarbituric acid,7 phosphonate,8 1,3-bis(dicyano-
methyliden)indan,9 3-dicyanomethylen-2,3-dihydroben-
zothiophen-2-yliden-1,1-dioxide,10 pyridinium salts11 or
diazonium salts12 and donor units such as dialkyl-
amines,13 alkoxyaryl groups,14 ferrocene,15 guanidyl,16
phosphoranimidyl,16 azulene17 or the 1,3-dithiole ring6a,18,19
have been previously reported (Chart 1).
In this context, we reported in 1997 the first NLO
materials containing the TTF unit as the donor moiety
in D-π-A systems.20 Although TTF and its derivatives
were originally prepared as strong electron-donor mol-
ecules for the development of electrically conducting
materials, during recent years they have shown new and
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Soc., Chem. Commun. 1993, 90. (b) Shu, C.-F.; Tsai, W. J .; Chen, J .-
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R. Adv. Mater. 1996, 8, 672.
in some cases little exploited possibilities.21 After our
investigations have confirmed that TTF derivatives can
display efficient NLO responses,20,22 the combination of
(21) For some recent reviews on TTF, see: (a) Bryce, M. R. Chem.
Soc. Rev. 1991, 20, 355. (b) Khodorkovsky, V.; Becker, J . Y. In Organic
Conductors; Farges, J .-P., Ed.; Dekker: New York, 1994; Chapter 3.
(c) Bryce, M. R. J . Mater. Chem. 1995, 5, 1481. (d) Schukat, G.; Richter,
A. M.; Fangha¨nel, E. Sulfur Rep. 1987, 7, 155. (e) Schukat, G.;
Fangha¨nel, E. Sulfur Rep. 1993, 14, 245. (f) Schukat, G.; Fangha¨nel,
E. Sulfur Rep. 1996, 18, 1. (g) Gar´ın, J . Adv. Heterocycl. Chem. 1995,
62, 249. (h) Simonsen, K. B.; Svenstrup, N.; Lau, J .; Simonsen, O.;
Mørk, P.; Kristensen, G. J .; Becher, J . Synthesis 1996, 407. (i) Otsubo,
T.; Aso, Y.; Takimiya, K. Adv. Mater. 1996, 8, 203. (j) Adam, M.;
Mu¨llen, K. Adv. Mater. 1994, 6, 439. (k) Becher, J .; Lau, J .; Mørk, P.
In Electronic Materials: The Oligomer Approach; Mu¨llen, K., Wegner,
G., Eds.; Wiley-VCH: New York, 1998; pp 198-233. (l) Bryce, M. R.;
Davenport, W.; Goldenberg, L. M.; Wang, C. Chem. Commun. 1998,
945. (m) J ørgensen, T.; Hansen, T. K.; Becher, J . Chem. Soc. Rev. 1994,
41. (n) Simonsen, K. B.; Becher, J . Synlett 1997, 1211. (o) Nielsen, M.
B.; Becher, J . Liebigs Ann./ Recueil 1997, 2177. (p) Coronado, E.;
Go´mez-Garc´ıa, C. J . Chem. Rev. 1998, 98, 273. (q) Roncali, J . J . Mater.
Chem. 1997, 7, 2307. (r) Day, P.; Kurmoo, M. J . Mater. Chem. 1997,
8, 1291. (s) Bryce, M. R. Adv. Mater. 1999, 11, 11. (t) Nielsen, M. B.;
Lomholt, C.; Becher, J . Chem. Soc. Rev. 2000, 29, 153. (u) Bryce, M.
R. J . Mater. Chem. 2000, 10, 589. Segura, J . L.; Mart´ın, N. Angew.
Chem., Int. Ed. 2001, 40, 1372.
(17) (a) Asato, A. E.; Liu, R. S. H.; Rao, V. P.; Cai, Y. M. Tetrahedron
Lett. 1996, 37, 419. (b) Iftime, G.; Lacroix, P. G.; Nakatani, K.; Razus,
A. C. Tetrahedron Lett. 1998, 39, 6853. (c) Lacroix, P. G.; Malfant, I.;
Iftime, G.; Razus, A. C.; Nakatani, K.; Delaire, J . A. Chem. Eur. J .
2000, 6, 2599.
(18) (a) J en, A. K.-Y.; Rao, V. P.; Drost, K. J .; Wong, K. Y.; Cava,
M. P. J . Chem. Soc., Chem. Commun. 1994, 2057. (b) Blanchard-Desce,
M.; Ledoux, I.; Lehn, J . M.; Malthete, J .; Zyss, J . J . Chem. Soc., Chem.
Commun. 1988, 737. (c) Meyers, F.; Breda´s, J . L.; Zyss, J . J . Am. Chem.
Soc. 1992, 114, 2914. (d) Inoue, S.; Mikami, S.; Aso, Y.; Otsubo, T.;
Wada, T.; Sasabe, H. Synth. Met. 1997, 84, 395. (e) Inoue, S.; Aso, Y.;
Otsubo, T. Chem. Commun. 1997, 1105. (f) Moore, A. J .; Bryce, M. R.;
Batsanov, A. S.; Green, A.; Howard, J . A. K.; McKervey, M. A.;
McGuigan, P.; Ledoux, I.; Ort´ı, E.; Viruela, R.; Tarbit, B. J . Mater.
Chem. 1998, 8, 1173. (g) Nguyen, T. T.; Salle´, M.; Delaunay, J .; Riou,
A.; Richomme, P.; Raimundo, J . M.; Gorgues, A.; Ledoux, I.; Dhenaut,
C.; Zyss, J .; Orduna, J .; Gar´ın, J . J . Mater. Chem. 1998, 8, 1185.
(19) Batsanov, A. S.; Bryce, M. R.; Coffin, M. A.; Green, A.; Hester,
R. E.; Howard, J . A. K.; Lednev, I. K.; Mart´ın, N.; Moore, A. J .; Moore,
J . N.; Ort´ı, E.; Sa´nchez, L.; Saviro´n, M.; Viruela, P. M.; Viruela, R.;
Ye, T. Chem. Eur. J . 1998, 4, 2580.
(22) A previous communication on the synthesis of compounds 2a -c
and 4 has been reported: (a) Gar´ın, J .; Orduna, J .; Rupe´rez, J . I.;
Alcala´, R.; Villacampa, B.; Sa´nchez, C.; Mart´ın, N.; Segura, J . L.;
Gonza´lez, M. Tetrahedron Lett. 1998, 39, 3577. (b) Gonza´lez, M.;
Mart´ın, N.; Segura, J . L.; Seoane, C.; Gar´ın, J .; Orduna, J .; Alcala´, R.;
Sa´nchez, C.; Villacampa, B. Tetrahedron Lett. 1999, 40, 8599. (c) For
a recent review, see: Gar´ın, J .; Orduna, J .; Andreu, R. Recent Res.
Devel. Org. Chem. 2001, 5, 77.
(20) (a) Andreu, R.; de Lucas, A. I.; Gar´ın, J .; Mart´ın, N.; Orduna,
J .; Sa´nchez, L.; Seoane, C. Synth. Met. 1997, 86, 1817. (b) De Lucas,
A. I.; Mart´ın, N.; Sa´nchez, L.; Seoane, C.; Andreu, R.; Gar´ın, J .;
Orduna, J .; Alcala´, R.; Villacampa, B. Tetrahedron 1998, 54, 4655.

8874 J . Org. Chem., Vol. 66, No. 26, 2001
Gonza´lez et al.
Ch a r t 2
The key step in the general reaction scheme involves
the reaction of monolithio-TTF (generated from TTF and
lithium diisopropylamide) with the commercially avail-
able N,N-dimethylaminoacrolein (7) to yield 5b and with
5-(N,N-diethylamino)-4-pentadienal (8)27 to obtain 5c by
following J utz’s procedure,28 which has been recently
extended to several organolithium systems by Friendli,
Yang, and Marder.29 All-trans vinylogue amides were
used in all cases as starting materials, and only all-trans
vinylogues were obtained according to the coupling
1
constants observed in the H NMR spectra.
As previously stated, we reported the synthesis of the
first NLO materials containing the TTF unit as the donor
moiety and dicyanomethylene as the acceptor group
(1a ,b).20 Now we have extended these series to 1c by
incorporating another vinylene unit between the donor
and acceptor moieties. This compound was obtained in
60% yield from 5c by Knoevenagel condensation with
malononitrile under basic conditions (Scheme 1). Due to
the presence of the conjugated nitrile group in 1c, bands
at 2230 ad 2219 cm-1 can be observed in the FT-IR
spectra and two signals at ca. 115 ppm are present in
the 13C NMR spectra.
this property with the redox ability of TTF as external
stimuli can be envisaged as a promising strategy for the
molecular engineering of switchable NLO materials.23
Thus, in this paper, we present the synthesis of a series
of TTF-containing molecules in which the acceptor part
as well as the length of the π-spacer have been system-
atically modified in order to optimize second-order NLO
responses. As the acceptor counterpart we have chosen
different moieties that have been successfully used in the
synthesis of efficient NLO-phores. To gain an under-
standing on the observed NLO properties of the novel
TTF-based D-π-A systems as well as on their geometrical
and electronic properties, theoretical calculations at the
semiempirical (PM3) and ab initio level have been carried
out. The electronic and Raman spectra complement this
study.
As noted above, following these first examples of TTF-
containing D-π-A systems, we have extended these series
to new acceptor moieties. Marder has proposed a model
that correlates the molecular hyperpolarizability value
â with the degree of charge separation in the ground
state.30 This research group has shown how stilbenes or
diphenylpolyenes endowed with donor and acceptor
groups exhibit a loss of aromaticity in these moieties,
which produces a deficient contribution of resonance
forms with charge separation. To solve this problem, new
acceptor moieties have been designed having a topology
that allows a gain in aromaticity in the charge-separated
state. These acceptor groups, frequently used in the
design of D-A systems for NLO, are the 3-phenyl-5-
isoxazolone and the N,N′-diethylthiobarbituric acid.7
Thus, we have chosen these groups to combine them with
the TTF moiety in order to extend the study of the NLO
properties of TTF derivatives. The syntheses of these new
series of compounds (2a -c, 3a -c) have been carried out
by Knoevenagel condensation between formyl-TTFs (5a -
c) and the corresponding N,N′-diethylthiobarbituric acid
(9) and 3-phenyl-5-isoxazolone (10), respectively. Best
results have been obtained by simply refluxing stiochio-
metric amounts of both reagents in ethanol, while the
mixture was protected from light and oxygen (Scheme
2). The attempted use of different catalysts, such as
ethylenediammonium diacetate or piperidine, invariably
led to decomposition products.
Resu lts a n d Discu ssion
Syn th esis. The synthesis of TTF-π-A derivatives (1-
4, Chart 2) has been carried out by reaction of ap-
propriately functionalized acceptor moieties with formyl-
TTF and its vinylogues. Lithiation of tetrathiafulvalenes
constitutes the most significant route for the preparation
of TTF derivatives given that the metalated species
formed give rise to a wealth of new derivatives.21g,24 The
synthesis of formyl-TTF (5a ) was first reported by
Green24 by reaction of monolithio-TTF with dimethyl-
formamide. Afterward, Gar´ın, Bryce, and co-workers
thoroughly investigated this reaction with a variety of
formylating reagents in order to increase the yields and
optimize the preparation of formyl-TTF (5a ).25 Subse-
quent Wittig reaction of formyl-TTF with phosphorane
6 leads to the formyl-TTF vinylogue 5b with an overall
yield of 51% starting from TTF (Scheme 1). To the best
of our knowledge, the preparation of higher vinylogues
by following this or any other synthetic route has not yet
been reported.
Attempts to obtain compound 3a invariably led to a
mixture of decomposition products while derivatives 3b,c
have been obtained in 72 and 69% yield, respectively. The
structure of these compounds has been confirmed by their
spectroscopic and analytical data. The signals corre-
sponding to the ethylenic protons in the 1H NMR spectra
To systematically increase the length of the polyenic
spacer between the donor and acceptor units in these
D-π-A systems, the synthesis of longer vinylogues of 5a
were required. Thus, we have recently reported in a
preliminary communication an alternative one-pot syn-
thesis of 5b as well as the synthesis of the higher
vinylogue 5c (Scheme 1).26
(26) Gonza´lez, M.; Mart´ın, N.; Segura, J . L.; Gar´ın, J .; Orduna, J .
Tetrahedron Lett. 1998, 39, 3269.
(27) Becher, J . Synthesis 1980, 589.
(28) J utz, C. Chem. Ber. 1958, 91, 1867.
(29) Friendli, A. C.; Yang, E.; Marder, S. R. Tetrahedron 1997, 53,
2717 (Corrigendum 1997, 53, 6233).
(30) (a) Marder, S.; Beratan, D. Science 1991, 252, 103. (b) Meyers,
F.; Marder, S.; Pierce, B.; Bre´das, J . L. J . Am. Chem. Soc. 1994, 116,
10703.
(23) Coe, B. J . Chem Eur. J . 1999, 5, 2464.
(24) Green, D. C. J . Org. Chem. 1979, 44, 1476.
(25) Gar´ın, J .; Orduna, J .; Uriel, S.; Moore, A. J .; Bryce, M. R.;
Wegener, S.; Yufit, D. S.; Howard, J . A. K. Synthesis, 1994, 489.

Tetrathiafulvalene Derivatives as NLO-phores
J . Org. Chem., Vol. 66, No. 26, 2001 8875
Sch em e 1
Sch em e 2
Sch em e 3
with J ) 13-15 Hz indicate an all-trans configuration
for the double bonds.
Other acceptor groups that have been successfully used
for the synthesis of effective NLO materials are 3-(di-
cyanomethylen)indan-1-one (11) and 1,3-bis(dicyano-
methylen)indan (12).9 Thus, we have prepared com-
pounds 4a -c by refluxing stoichiometric amounts of
both formyl-TTFs (5a -c) and 3-dicyanovinylindan-1-one
(11) in acetic anhydride while the mixture was protected
from light and oxygen (Scheme 3).
Derivatives 4a -c were obtained as stable crystalline
solids in moderate yields (45-52%). Their structure were
confirmed by the spectroscopic and analytical data. Their
FT-IR spectra exhibit bands at 2215 and 1700 cm-1
corresponding to the nitrile and carbonyl groups repec-
tively. Interestingly, when a similar reaction was carried
out using 1,3-bis(dicyanomethylene)indan as the acceptor
moiety, highly insoluble dark materials were obtained.
As a consequence of the strong donor ability of the TTF
moiety and the strong acceptor character of the 1,3-bis-
(dicyanomethylene)indan system, formation of a charge-
transfer complex in solution between the two molecules
has to be taken into consideration. In fact, Batsanov et
al. have reported that TTF and 1,3-bis(dicyanomethyl-
ene)indan form a 1:1 complex exhibiting semiconducting
properties.31 This fact strongly suggests that after com-
bination of the TTF derivative with the tetracyano
derivative of the indandione, a concurrence between the
two reaction takes place, and the faster electron transfer
process yields mainly the corresponding charge-transfer
complexes.
Electr och em istr y. The electrochemical properties of
the new TTF-based NLO chromophores 1-4 have been
(31) Batsanov, A. S.; Bryce, M. R.; Davies, S. R.; Howard, J . A. K.;
Whitehead, R.; Tanner, B. K. J . Chem. Soc., Perkin Trans. 2 1993,
313.

8876 J . Org. Chem., Vol. 66, No. 26, 2001
Ta ble 1. Red ox P oten tia ls for Com p ou n d s 1-4
Gonza´lez et al.
a
a
a
compd
E1
E2
E1
1/2,ox
1/2,ox
red
1a
1b
1c
2a
2b
2c
3b
3c
4a
4b
4c
TTF
0.63
0.54
0.50
0.60
0.60
0.56
0.53
0.49
0.46
0.47
0.45
0.37
0.87
0.84
0.83
0.97
1.00
0.90
0.86
0.83
0.75
0.75
0.75
0.73
-0.89
-0.87
-0.87
-0.63
-0.57
-0.52
-0.88
-0.91
-0.96
-0.96
-0.97
-
a
-
In volts vs SCE; CH2Cl2 as solvent, Bu4N+ClO4 0.1 M; 200
mV/s.
Ta ble 2. Exp er im en ta l µâ Va lu es a n d Low est En er gy
Absor p tion Ba n d s for Com p ou n d s 1-4
F igu r e 1. UV-vis spectrum of compound 4b.
a
a
compd
µâexp
µâ0exp
λmax (nm, in CH2Cl2)
1a
1b
1c
2a
2b
2c
3b
3c
4b
4c
624
618
608
718
672
648
658
630
726
690
470b
630b
480c
234b
320b
180c
347c
455c
295d
611d
259d
570d
760c
960c
625d
1200d
700d
1350d
a
b
All µâ values in (10-48 esu). Measured in chloroform at 1907
nm. c Measured in DMSO at 1907 nm. Measured in dichlo-
d
romethane at 1907 nm.
studied by cyclic voltammetry at room temperature in
dichloromethane solutions, using glassy carbon as the
working electrode, SCE as reference, and tetra-n-butyl-
ammonium perchlorate as the supporting electrolyte. The
corresponding data are collected in Table 1 along with
the redox potentials of the unsubstituted tetrathiaful-
valene (TTF) used as reference.
F igu r e 2. FT-Raman spectra of compounds 1a -c in the
1600-1000 cm-1 Raman shift region.
All the voltammograms show two reversible one-
electron oxidation waves corresponding to the TTF
moiety, and one irreversible reduction wave, correspond-
ing to the acceptor moiety. In all cases the oxidation
potential values are shifted toward more positive values
in comparison with unsubstituted TTF measured under
the same experimental conditions, which is consistent
with an increase in the oxidation potential produced by
the presence of the acceptor moieties. The general trend
is that this shift is bigger as the length of the spacer
decreases indicating a stronger interaction between the
donor and acceptor groups when they are closer.
Concerning the cathodic region of these voltammo-
grams, the diethylthiobarbituric acid moiety shows the
best electron acceptor properties, whereas derivatives 1,
3, and 4 present similar reduction potentials.
UV-vis, IR, a n d Ra m a n Sp ectr oscop y. The lowest
energy absorption bands in electronic spectra observed
for compounds 1-4 are given in Table 2. These bands
(Figure 1) can be assigned to an intramolecular charge
transfer (ICT) process and are subject to two general
trends: (i) a red shift of the lowest energy absorption
band is observed when increasing the acceptor ability of
the acceptor moiety. The more red-shifted values of λmax
for derivatives 4 in comparison with that of derivatives
2 are an exception to this rule. (ii) The ICT band upshifts
when the length of the oligoenic spacer is increased. This
fact suggests that the extension of the charge transfer is
F igu r e 3. FT-Raman spectra of compounds 2a -c in the
1600-1000 cm-1 Raman shift region.
reduced due to the inclusion of extra vinylenic double
bonds in the spacer unit.
To analyze these experimental observations, we have
carried out an IR and Raman spectroscopy study on these
systems.
The Raman spectra of compounds 1a -c and 2a -c in
the 1600-1000 cm-1 Raman shift region are shown in
Figures 2 and 3, respectively. In view of the B3LYP32/6-
31G**33 vibrational eigenvectors plotted in Figure 4, the

Tetrathiafulvalene Derivatives as NLO-phores
J . Org. Chem., Vol. 66, No. 26, 2001 8877
F igu r e 4. Schematic B3LYP/6-31G** atomic vibrational displacements associated with some of the most intense Raman lines of
compounds 1a -c.
Raman line around 1585-1540 cm-1 can be assigned to
a ν(CdC) stretching mode of the vinylenic spacer coupled
to some extent with a νs(CdC) stretching of the TTF
donor unit, whereas the line near 1495-1470 cm-1 arises
from a ν(CdC) stretching vibration mainly located on the
TTF group, which extends toward the vinylenic spacer.
The two Raman lines undergo an upshift with increas-
ing length of the π-spacer: 1544 and 1469 cm-1 (1a ), 1579
and 1481 cm-1 (1b), and 1584 and 1493 cm-1 (1c) for the
series of the dicyanomethylene acceptor group and 1543
and 1462 cm-1 (2a ), 1576 and 1459 cm-1 (2b), and 1575
and 1483 cm-1 (2c) for the series of the N,N′-diethylthio-
barbituric acid acceptor group.
Matsuzaki et al. have reported a Raman study of some
mixed-valent and charge-transfer salts of TTF to deter-
mine either the formal charge or the degree of charge
transfer, F, of the molecule or ion that forms the one-
dimensional stack.34-36 The plot of the Raman frequencies
of the TTF salts vs F gives a straight line, and the formal
charges of TTF estimated from the empirical relation
agree well with those obtained from neutron and X-ray
scatterings. The so-called ν3 mode of TTF (associated to
the stretching vibration of the central CdC bond) is
measured at 1516 cm-1 in the neutral molecule (F ) 0)
and at 1420 cm-1 in the monocation (F ) 1), and it shows
the largest frequency shift with increasing F (ca. 100
cm-1), thus giving the most reliable estimation of the
formal charge or degree of charge transfer.
The ν3 mode of the TTF moiety correlates with the
Raman line near 1495-1470 cm-1 of our NLO chro-
mophores. Under the assumption of general applicability
of the linear relation ν3 vs F proposed by these authors,
the degree of intramolecular charge transfer can be
estimated to be approximately 0.48 (1a ), 0.37 (1b), and
0.25 (1c) for the series of the dicyanomethylene acceptor
group and 0.57 (2a ), 0.59 (2b), and 0.35 (2c) for the series
of the N,N′-diethylthiobarbituric acid acceptor group.
Thus, the values of F are found to be larger for the 2a -c
than for the 1a -c compounds. These Raman results are
in full agreement with the better electron acceptor
properties of the diethylthiobarbituric acid as compared
with the dicyanomethylene group. This Raman spectros-
copy study reveals that of the six NLO-phores studied,
2b displays the more effective intramolecular charge
transfer. The increasing weight of the zwitterionic ca-
nonical structure (where an electron is fully transferred
from the donor to the acceptor) in the stabilization of the
electronic ground state could justify the high positive
(32) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.
(33) Francl, M. M.; Pietro, W. J .; Hehre, W. J .; Binkley, J . S.; Gordon,
M. S.; Defrees, D. J .; Pople, J . A. J . Chem. Phys. 1982, 77, 3654.
(34) Matsuzaki, S.; Moriyama, T.; Toyoda, K. Solid State Commun.
1980, 34, 857.
(35) Matsuzaki, S.; Onomichi, M.; Tomura, H.; Yoshida, S.; Toyoda,
K. Mol. Cryst. Liq. Cryst. 1985, 120, 93.
(36) Del Zoppo, M.; Castiglioni, C.; Zuliani, P. In Handbook of
Conductive Polymers, 2; Skotheim, T. A., Elsembaumer, R. L., Rey-
nolds, J ., Eds.; Marcel Dekker: New York, 1998.
E1
and E2
values of 2b (see Table 1).
1/2,ox
1/2,ox
In accordance with the trend of variation of the
oxidation potentials on the chemical structure of these
TTF-based NLO-phores, we observe that the Raman ν3
mode of the TTF moiety upshifts in frequency as the

8878 J . Org. Chem., Vol. 66, No. 26, 2001
Gonza´lez et al.
the donor to the acceptor end groups goes down roughly
as 1/L (where L is the molecular length) and that the
corresponding L∆q contribution to the total dipole mo-
ment vary relatively slowly with length along a given
series of chromophores with the same pair of donor and
acceptor. The length dependence of â for such molecules
is dominated by that of γ/R of the corresponding unsub-
stituted π-conjugated bridge (where γ and R are the third-
order and linear polarizabilities, respectively) or roughly
quadratic (L2) as found experimentally (since R ≈ L3 and
γ ≈ L5).
It has also been hypothesized39 that the ground-state
polarization and bond length alternation (BLA) (i.e., the
difference between average length of carbon-carbon
double and single bonds in a polyenic chain) are useful
parameters to consider when establishing structure-
property relationships for NLO molecules. BLA varies
from negative values for the neutral polyene structure,
through zero for the polar cyanine-like structure, to
positive values for the highly polar zwitterionic polyene
structure. Also, as BLA changes from negative to positive
values, the ground-state dipole moment, µ, increases, and
at the same time, â initially increases, reaches a maxi-
mum, and begins to decrease, crossing through zero at
BLA ) 0 Å, and ultimately becomes negative when BLA
is positive. This dependence of â on the ground-state
polarization and BLA for a series of donor-acceptor
disubstituted polyenes has been experimentally demon-
strated.40 The B3LYP/6-31G** geometry optimizations
performed for compounds 1a -c indicate that BLA
amounts nearly the same negative value for the three
compounds (ca. -0.064 Å), and these results are therefore
consistent with the observed positive â values. Thus, the
trend of variation of â along the series of compounds
studied in this work seems to be mainly determined by
the quadratic dependence on L.
Secon d -Or d er Non lin ea r Op tica l P r op er ties. The
µâ values of compounds 1-4 measured using the EFISH
technique are gathered in Table 2 along with the µâ(0)
values calculated assuming a two-level model (com-
pounds 1a and 4a were not measured due to their
instability under the EFISH conditions). In comparison,
the relevant application parameter µâ(0) for the classical
NLO dye DR1 is ca. 600 × 10-48 esu. It can be seen that
the nonlinear optical activity is larger for compounds
containing better acceptors and that µâ values increase
with increasing the length of the ethylenic spacer.
F igu r e 5. Infrared absorptions due to the CN end groups of
compounds 1a -c.
length of the π-bridge becomes longer, thus suggesting
that the intramolecular charge transfer is less effective
with increasing number of vinylenic units in the π-spacer.
The presence in push-pull molecules of a highly
delocalized π-system gives rise to Raman spectra of a
rather simple appearance: usually two to four lines with
overwhelmingly strong activity dominate the whole
spectrum. On the other hand, the electron-acceptor group
withdraws electronic charge from the donor through the
conjugated spacer, giving rise to a relevant molecular
dipole moment roughly coincident with the chain axis of
the molecule. For this reason, the shorter the chain
length the stronger the bond polarization and more
efficient the activation in the IR of the normal modes
associated to the intramolecular charge transfer. On the
contrary, the intensities of the few Raman bands experi-
mentally observed continuously increase as the length
of the spacer becomes longer, due to the increasing
polarizability of the π-conjugated skeleton.
It has already been suggested the existence of a critical
chain length in the class of the push-pull polyenes shown
above in which the interaction between donor and ac-
ceptor groups is inhibited.36,37 For chains with a length
longer than the critical value, the bond polarization is
confined within a few bonds close to the polar end groups,
whereas the bonds in the middle of the π-bridge are
practically apolar and still keep a strongly alternating
polyene-like structure.
We observe that the frequencies of the infrared absorp-
tion bands due to the ν(C≡N) stretching modes also
increase with increasing the length of the π-spacer: 2212
and 2217 cm-1 (1a ), 2221 cm-1 (1b), and 2220 and 2229
cm-1 (1c) (see Figure 5). This finding has a straightfor-
ward explanation: as the chain length of the spacer
becomes shorter (and more electronic charge is trans-
ferred from the donor to the acceptor end groups), the
loss of triple bond character of the cyano groups (since
the C≡N groups enter in the resonant stabilization of
the zwitterionic form of the molecule) is more pro-
nounced.
Thermal stability is also an important criterion for
technological applications. These compounds show a good
degree of thermal stability as evidenced by the decom-
position temperatures of compounds 2a (194 °C), 2b (195
°C), and 2c (206 °C).
To gain further understanding of the NLO behavior of
these compounds, we have performed theoretical calcula-
tions41 starting with the Finite Field (FF) PM342 method,
(38) (a) Hutchinson, M. H.; Sutton, L. E. J . Chem. Soc. 1958, 4382.
(b) Dulcic, A.; Flytzanis, C.; Tang, C. L.; Pe´pin, D.; Fe´tizon, M.;
Hoppilliard, Y. J . Chem. Phys. 1981, 74, 1559.
(39) Ortiz, R.; Marder, S. R.; Cheng, L.; Tiemann, B. G.; Cavagnero,
S.; Ziller, J . W. Chem. Commun. 1994, 2263.
(40) Bourhill, G.; Bre´das, J .-L.; Cheng, L.-T.; Marder, S. R.; Meyers,
F.; Perry, J . W.; Tiemann, B. G. J . Am. Chem. Soc. 1994, 116, 2619.
(41) For reviews on the calculation of second-order nonlinearities
using quantum chemical methods, see: (a) Kanis, D. R.; Ratner, M.
A.; Marks, T. J . Chem. Rev. 1994, 94, 195. (b) Morley, J . O.; Pugh, D.
In Nonlinear Optics of Organic Molecules and Polymers; Nalwa, H.
S., Miyata, S., Eds.; CRC: Boca Raton, 1997; p 29.
It has been suggested38 on the basis of a one-dimen-
sional model for the class of disubstituted D-π-A mol-
ecules, that the intramolecular charge transfer, ∆q, from
(37) Del Zoppo, M.; Castiglioni, C.; Zuliani, P.; Razelli, A.; Tom-
masini, M.; Zerbi, G.; Blanchard-Desce, M. J . Appl. Polym Sci. 1998,
70, 1311.

Tetrathiafulvalene Derivatives as NLO-phores
J . Org. Chem., Vol. 66, No. 26, 2001 8879
Ta ble 3. Exp er im en ta l a n d Ca lcu la ted NLO P r op er tiesa of Com p ou n d s 1-4
exp
FF-PM3
HF/6-31G*//HF/6-31G*
HF/6-31+G*//HF/6-31G*
HF/6-31G*//B3P86/6-31G*
µâ(0)
m
âtot
µâ(0)
m
âtot
µâ(0)
m
âtot
µâ(0)
m
âtot
µâ(0)
1a
1b
1c
2a
2b
2c
3b (Z)
3b (E)
3c (Z)
3c (E)
4b
4.68
5.00
5.17
5.29
6.19
6.55
5.90
6.70
6.13
6.80
3.63
3.52
25
42
59
37
64
92
47
35
64
52
63
81
109
177
266
167
334
537
104
232
172
351
96
7.16
7.66
8.25
5.60
6.67
7.42
7.01
8.72
7.45
8.91
5.23
5.22
15
30
49
16
36
59
35
23
53
39
59
87
95
202
367
76
214
411
76
189
159
333
165
262
7.34
7.91
8.51
5.62
6.73
7.52
7.12
8.94
7.44
9.12
5.31
5.32
16
32
53
19
41
68
39
25
59
43
64
95
102
225
410
91
252
476
83
212
210
370
193
304
7.73
8.63
9.63
6.03
7.60
8.76
7.77
9.87
8.47
10.30
6.06
6.40
19
42
78
24
59
96
53
33
92
66
93
153
129
320
680
120
386
777
150
316
367
659
396
746
234b
320b
180c
347c
455c
295d
611d
259d
570d
4c
106
a
b
Dipole moments in debye, hyperpolarizabilities in (10-30 esu) and µâ in (10-48 esu). Measured in chloroform at 1907 nm. c Measured
d
in DMSO at 1907 nm. Measured in dichloromethane at 1907 nm.
which has proved to be very accurate in the prediction
of the NLO properties of TTF-derived chromophores at
a minimal computational cost.43 These calculations pre-
dicted the s-cis conformation of the bond linking the TTF
core to the ethylenic spacer as the most stable one, and
the FF procedure afforded the results gathered in Table
3. It can be seen that FF-PM3 provides an adequate
description of the NLO properties of compounds 1 and 2
but underestimates largely the activity of compounds 3
and 4. It is noteworthy that in the case of compounds 3,
the less stable E isomers are predicted to display larger
µâ values.
F igu r e 6. Hyperpolarizability and dipole moment vectors
calculated using the HF/6-31G* (left) and B3P86/6-31G* (right)
In an attempt to obtain a better agreement between
the observed and calculated µâ(0) values, we have
performed ab initio calculations using the coupled per-
turbed Hartree-Fock (CPHF) method and the medium-
size 6-31G* basis set.44 Although ab initio calculations
differ from PM3 in the prediction of the s-trans confor-
mation of the bond linking the TTF moiety to the
ethylenic spacer, the calculated µâ(0) values displayed
in Table 3 are analogous to FF-PM3 ones and are unable
to explain the NLO response of compounds 3 and 4.
Furthermore, while it has been reported that diffuse
functions are necessary to obtain accurate hyperpolar-
izabilities,45 the use of the 6-31+G* basis set incorporat-
ing diffuse functions on heavy atoms causes the predic-
tion of increased µâ(0) values but does not modify the
predicted trends in NLO activity (Table 3).
A possible explanation to poor property prediction
displayed by semiempirical and Hartree-Fock methods
can be found in the used ground-state geometries that
are a consequence of the low charge transfer predicted
by these methods. Thus, the calculated bond lengths in
the ethylenic spacers are 1.45-1.46 Å for single C-C
bonds and 1.33-1.34 Å for double CdC bonds, being
nearly identical to those of unsubstituted polyenes and
corresponding to a bond length alternation30b,46 (BLA) of
0.11 Å, which should be related to a poor charge transfer
in the ground state and a small â value. To obtain better
molecular geometries, we have performed optimizations
using the B3P8647/6-31G* model chemistry that has been
geometries of compound 4c.
successfully applied to TTF derivatives48 and provides
better C-S bond lengths than the commonly used B3LYP
functional.49 The geometries calculated in this way
display distances of 1.42-1.43 and 1.36-1.37 Å for single
and double C-C bonds, respectively, corresponding to a
BLA of ca. 0.06 Å that is near the optimum value in the
search for large hyperpolarizabilities. Unfortunately,
DFT methods are unable to predict accurately hyperpo-
larizabilities due to an incomplete screening of the
external electric field,50 and consequently, we decided to
calculate HF hyperpolarizabilities on DFT geometries.
The effect of the geometry on the calculated µâ(0)
values of 4c is depicted in Figure 6. The DFT geometry
gives rise to enhanced µ and â values and causes a
redirection of the µ vector due to the increased charge
transfer from TTF to the acceptor moiety in the ground
state.
The µâ(0) values calculated using HF/6-31G*//B3P86/
6-31G* are gathered in Table 3, it can be seen that while
most of them are somewhat overestimated with respect
to the experimental values, this model chemistry yields
the best correlation of all the described calculations.
The results obtained for compounds 3 must be com-
mented on separately. While all the theoretical methods
(47) The B3P86 functional consists of Becke’s three parameter
hybrid functional with the nonlocal correlation provided by Perdew:
J . P. Perdew, Phys. Rev. B 1986, 33, 8822.
(48) (a) Terkia-Derdra, N.; Andreu, R.; Salle´, M.; Levillain, E.;
Orduna, J .; Gar´ın, J .; Ort´ı, E.; Viruela, R.; Pou-Amerigo, R.; Sahraoui,
B.; Gorgues, A.; Favard, J .-F.; Riou, A. Chem. Eur. J . 2000, 6, 1199.
(b) Viruela, R.; Viruela, P. M.; Pou-Amerigo, R.; Ort´ı, E. Synth. Met.
1999, 103, 1991.
(49) Ma, B.; Lii, J .-H.; Schaefer, H. F., III; Allinger, N. L. J . Phys.
Chem. 1996, 100, 8763.
(50) Champagne, B.; Perpe`te, E. A.; J acquemin, D.; Van Gisbergen,
S. J . A.; Baerends, E.-J .; Soubra-Ghaoui, C.; Robins, K. A.; Kirtman,
B. J . Phys. Chem. 2000, 104, 4755.
(42) (a) Stewart, J . J . P. J . Comput. Chem., 1989, 10, 209. (b)
Stewart, J . J . P. J . Comput. Chem. 1989, 10, 221.
(43) Gar´ın, J .; Orduna, J .; Andreu, R. Synth. Met. 1999, 102, 1531.
(44) Hariharan, P. C.; Pople, J . A. Chem. Phys. Lett. 1972, 16, 217.
(45) Andre´, J .-M.; Delhalle, J . Chem. Rev. 1991, 91, 843.
(46) (a) Marder, S. R.; Cheng, L.-T.; Tiemann, B. G.; Friedli, A. C.;
Blanchard-Desce, M.; Perry, J . W.; Skindhøj, J . Science 1994, 263, 511.
(b) Marder, S. R.; Gorman, C. B.; Meyers, F.; Perry, J . W.; Bouhill, G.;
Bre´das, J .-L.; Pierce, B. M. Science 1994, 265, 632.

8880 J . Org. Chem., Vol. 66, No. 26, 2001
Gonza´lez et al.
which the donor TTF unit is connected to different
acceptor moieties through an oligoenic spacer of variable
length. The CV measurements reveal an amphoteric
behavior showing two reversible oxidation waves corre-
sponding to the formation of the radical cation and
dication species of the TTF moiety and an irreversible
reduction wave corresponding to the electron-accepting
moiety.
F igu r e 7. Hyperpolarizability and dipole moment vectors
calculated using the HF/6-31G*//B3P86/6-31G* model chem-
istry for the Z and E isomers of compound 3c.
The barbituric acid derivatives (2a -c) showed stronger
electron-acceptor properties than the remaining accep-
tors, as judged from their reduction potential values.
All the D-π-A systems showed an intramolecular
charge transfer band in their electronic spectra which is
strongly influenced by the acceptor ability of the acceptor
moiety as well as by the length of the oligoenic spacer.
Thus, a red shift of the lowest energy absorption band
was observed when increasing the acceptor strength.
However, a most interesting observation was the hypso-
chromic shift when increasing the length of the oligoenic
spacer. This fact, which at present has not a clear
explanation, has been analyzed by UV-vis and Raman
spectroscopy. In particular, we have found that the
characteristic Raman-active ν3 mode associated to the
TTF moiety (identified on the basis of B3LYP/6-31G**
force field quantum chemical calculations) undergoes an
upshift with increasing length of the π-spacer, thus
suggesting a less effective intramolecular charge transfer
as derived from previous empirical relations.
All the studied compounds (1-4) showed high second-
order NLO responses that were measured by using the
EFISH technique. The higher µâ values were obtained
for those TTF derivatives bearing the stronger acceptors
and larger oligoenic spacers.
Theoretical calculations carried out at the semiempiri-
cal (FF-PM3) and ab initio (HF/6-31G* and HF/6-31+G*)
levels reveal a good agreement with the µâ(0) experi-
mental values, although these values were somewhat
overestimated when HF/6-31G*//B3P86/6-31G* was used.
The topologies and energies of molecular orbitals were
studied by B3P86/6-31G* showing that the HOMO-
LUMO energy gaps account for the observed intramo-
lecular charge transfer from the donor TTF to the LUMO,
which is mainly located on the acceptor moiety.
F igu r e 8. HOMO (-5.65 eV, left) and LUMO (-3.97 eV,
right) of compound 4c calculated by B3P86/6-31G*.
used predict a slightly higher stability of the Z isomers
compared to the E ones, the high electric field used in
the EFISH experiments is expected to render the E
isomers more stable due to their larger dipole moments,
and it is feasible that the E isomers are responsible for
the measured µâ values due to an isomerization under
the experimental conditions. This surprising behavior is
analogous to the preference for the conformer of higher
dipole moment observed on some azo dyes under the
EFISH conditions.51
The differences in the NLO behavior of the E and Z
isomers of compounds 3 are displayed in Figure 7. It can
be seen that while the âtot value calculated for 3c (E) is
smaller than that of the Z isomer, the better alignement
of the µ and â vectors renders the former more active in
the EFISH measurements.
The topologies and energies of molecular orbitals have
been studied by means of the B3P86/6-31G* model
chemistry. The HOMO-LUMO energy gaps calculated
in this way, from 1.68 to 2.20 eV, account for this
transition as being responsible for the lowest energy
absorption in every case. Furthermore, a recent TD-DFT
study on compounds 2a -c correctly reproduces the
hypsochromic effect observed on lengthening the ethyl-
enic spacer.52 The charge-transfer character of the
HOMO-LUMO transition is demonstrated by the topol-
ogy of these orbitals (see Figure 8).
Work is currently in progress directed to the prepara-
tion of other TTF derivatives exhibiting NLO properties
which throw some light on the most unusual observed
hypsochromic shifts in these TTF-π-A compounds when
increasing the conjugation of the π-system.
Exp er im en ta l Section
The HOMO is analogous to the HOMO of most TTF
derivatives and is located mainly on the TTF moiety,
while the LUMO extends from the acceptor to the nearest
atoms of TTF across the ethylenic spacer. These orbital
topologies show the HOMO-LUMO overlap that is a
prerequisite41a to increase the allowedness of the charge
transfer transition and consequently the nonlinear optical
response.
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
1
with a Perkin-Elmer Lambda 3 instrument. 13C and H NMR
spectra were recorded with a Varian VXR-300 spectrometer
(300 and 75 MHz for 1H and 13C, respectively; chemical shifts
are given as δ values (int. Standard: TMS). Fourier Transform
Infrared absorption (FT-IR) measurements were made with a
Perkin-Elmer Model 1760 X spectrometer. All spectra were
collected using a resolution of 2 cm-1, 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. Fourier transform
Raman (FT-Raman) spectra were recorded using a Bruker
FRA106/S apparatus with a germanium photoresistor operat-
ing at liquid nitrogen temperatures as the near-infrared
Su m m a r y a n d Con clu sion s
In summary, we describe the synthesis of novel TTF-
based π-conjugated donor-acceptor systems (1-4) in
(51) Morley, J . O.; Hutchings, M. G.; Zyss, J .; Ledoux, I. J . Chem.
Soc., Perkin Trans. 2 1997, 1139.
(52) Andreu, R.; Gar´ın, J .; Orduna, J . Tetrahedron 2001, 57, 7883.

Tetrathiafulvalene Derivatives as NLO-phores
J . Org. Chem., Vol. 66, No. 26, 2001 8881
detector. Radiation of 1064 nm from a Nd:YAG laser was used
for Raman excitation with the operating power adjusted to 100
mW. Light reflected and scattered off the samples was filtered
to remove that elastically scattered and then passed through
a Michelson interferometer in a backscattering arrangement.
Samples were analyzed as pure solids in sealed capillaries.
One thousand scans were added to increase the signal-to-noise
ratio. Spectra were plotted after baseline correction to remove
the fluorescence showed by the samples in the near-infrared
region. Elemental analyses were performed with a Perkin-
Elmer CHN 2400 apparatus. MS were recorded with a Hewlet-
Packard HP5989A spectrometer. EFISH measurements were
taken with a nonlinear optics spectrometer from SOPRA. The
fundamental light at 1.907 µm was the first Stokes peak of a
hydrogen Raman cell pumped by the 1.064 µm light from a
Q-switched Nd:YAG laser (Quantel YG 781, 10 pps, 8 ns,
pulse). That light was passed through a linear polarizer and
focused on the EFISH cell. The polarizing 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 µm), which was
finally detected with a R642 photomultiplier from Hamamatsu.
Static µâ(0) values were deduced from the experimental values
using a two-level dispersion model. Cyclic voltammograms
were recorded on a potentiostat/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, Bu4N+ClO4 as support-
ing electrolyte, dichloromethane as solvent, and at a scan rate
of 200 mV/s. Tetrathiafulvalene (TTF), N,N-dimethylamino-
acroleine, N,N-diethylthiobarbituric acid, 3-phenyl-5-isoxazolo-
ne and 1,3-indandione are commercially available and were
used without further purification. Ethanol and tetrahydrofu-
ran were dried with sodium and were distilled before use.
Theoretical calculations were performed with the Gaussian 94
and Gaussian 9853 programs. Geometry optimizations were
performed on isolated entities using the default convergence
criteria, and harmonic vibrational frequencies and molecular
hyperpolarizabilities were calculated analytically using the
CPHF procedure. Semiempirical FF-PM3 calculations were
performed using MOPAC 6.0.54
Afterward, the mixture was poured over a 2 M aqueous
solution of hydrochloric acid. The organic layer was extracted
with diethyl ether and dried over sodium sulfate. After vacuum
elimination of the solvent, the residue obtained was chromato-
graphed (hexane/dichloromethane) to yield 91 mg (32%) of 5b
as a red solid: mp 151-152 °C; 1H NMR (CDCl3, 300 MHz) δ
9.59 (d, J ) 7.8 Hz, 1H), 7.12 (dd, J ) 15.3, 11.4 Hz, 1H), 6.75
(d, J ) 15.3 Hz, 1H), 6.61 (s, 1H), 6.35 (s, 2H), 6.27 (dd, J )
14.7, 11.4 Hz, 1H), 6.22 (dd, J ) 14.7, 7.8 Hz, 1H); 13C NMR
(CDCl3, 75 MHz) δ 193.1, 150.4, 135.2, 132.3, 131.9, 128.7,
125.1, 119.1, 118.9, 114.1, 106.1; FTIR (KBr, cm-1) 1660, 1605,
1582, 1504, 114, 1160; UV-vis (CH2Cl2) λmax (nm) 520, 334;
MS m/z (rel intensity) 284 (M+, 100). Anal. Calcd for C11H8-
OS4: C, 46.49; H, 2.84. Found: C, 46.82; H, 2.97.
2-(6,6-Dicya n oh exa tr ien yl)tetr a th ia fu lva len e (1c). A
solution of 227 mg (0.8 mmol) of 5-(tetrathiafulvalenyl)penta-
2,4-dienal (5c), 244 mg (3.30 mmol) of malononitrile, 0.18 mL
of ammonium acetate, and 0.18 mL of acetic acid in 25 mL of
toluene was refluxed, under azeotropic removal of water, for
24 h. The solvent was evaporated, and the crude product was
purified by flash chromatography by using hexane/methylene
chloride as the eluent to afford 160 mg (60%) of 1c as a red
1
solid: mp 201-202 °C; H NMR (DMSO-d6, 300 MHz) δ 8.14
(d, J ) 11.2 Hz, 1H), 7.29 (s, 1H), 7.24 (dd, J ) 13.7, 12.7 Hz,
1H), 7.08 (d, J ) 13.7 Hz, 1H), 6.93 (dd, J ) 12.7, 12.7 Hz,
1H), 6.75 (s, 2H), 6.51 (dd, J ) 12.7, 11.2 Hz, 1H); 13C NMR
(DMSO-d6, 75 MHz) δ 161.07, 150.50, 148.29, 144.12, 135.13,
133.69, 129.99, 128.79, 127.48, 120.17, 114.71, 114.50, 112.67,
112.47; FTIR (KBr, cm-1) 2230, 2219, 1584, 1538, 1496, 1363,
1287, 1153; UV-vis (CH2Cl2) λmax (nm) 608, 392; MS m/z (rel
intensity) 332 (M+, 100). Anal. Calcd for C14H8N2S4: C, 50.61;
H, 2.40; N, 8.44. Found: C, 51.02; H, 2.57; N, 8.79.
Syn th esis of TTF Der iva tives 2a -c. Gen er a l P r oce-
d u r e. A 200 mg (1 mmol) sample of diethylthiobarbituric acid
(9) was added to a solution of 1 mmol of the corresponding
formyl-TTF derivative (5a -c) in 15 mL of dry ethanol. The
solution was refluxed under argon atmosphere with exclusion
of light for 2 h. After this time, the precipitated solid was
filtered, washed thoroughly with ethanol, and purified by flash
chromatography (hexane/dichloromethane) to afford deriva-
tives 2a -c as red solids.
(E)-3-(Tetr a th ia fu lva len yl)a cr yla ld eh yd e (5b). Under
argon atmosphere, at -78 °C, 0.73 mL (1.09 mmol) of a 1.5 M
solution of lithium diisopropylamide (LDA) in tetrahydrofuran/
heptane was added to a solution of 204 mg (1 mmol) of TTF in
10 mL of dry THF. Then, 99 mg (1 mmol) of 3-(dimethylamino)-
acrolein (7) was added and the reaction was allowed to reach
room temperature overnight. Afterward, the mixture was
poured over a 2 M aqueous solution of hydrochloric acid. The
organic layer was extracted with diethyl ether and dried over
sodium sulfate. After vacuum elimination of the solvent, the
residue obtained was chromatographed (hexane/dichloro-
methane) to yield 155 mg (60%) of 5b as a red solid: mp 121-
122 °C (lit.25 mp 121-122 °C).
5-(Tetr a th ia fu lva len yl)p en ta -2,4-d ien -1-a l (5c). Under
argon atmosphere, at -78 °C, 0.73 mL (1.09 mmol) of a 1.5 M
solution of lithium diisopropylamide (LDA) in tetrahydrofuran/
heptane was added to a solution of 204 mg (1 mmol) of TTF in
10 mL of dry THF. Then, 125 mg (1 mmol) of 5-(N,N-
diethylamino)-2,4-pentadienal27 (8) was added, and the reac-
tion was allowed to reach room temperature overnight.
1,3-Dieth yl-5-(tetr a th ia fu lva len ylm eth ylid en e)-2-th io-
ba r bitu r ic Acid (2a ). By following the above general proce-
dure and using formyl-TTF (5a ) as the reagent, derivative 2a
was obtained in a 67% yield: mp 215-216 °C; 1H NMR
(DMSO-d6, 300 MHz) δ 7.93 (s, 1H), 7.66 (s, 1H), 6.35 (m, 2H),
4.51 (m, 4H), 1.28 (m, 6H); FTIR (KBr, cm-1) 3042, 2975, 2928,
1685, 1652, 1541, 1379, 1363, 1097; UV-vis (CH2Cl2) λmax (nm)
718, 384, 316, 266; MS. m/z (rel intensity) 414 (M+, 100). Anal.
Calcd for C15H14N2O2S5: C, 43.46; H, 3.40; N, 6.76. Found: C,
43.99; H, 3.21; N, 7.28.
1,3-Dieth yl-5-(3-tetr a th ia fu lva len yl-2-p r op en ylid en e)-
2-th ioba r bitu r ic Acid (2b). By following the above general
procedure and using (E)-3-(tetrathiafulvalenyl)acrylaldehyde
(5b) as the reagent, derivative 2b was obtained in a 65%
yield: mp 205-206 °C; 1H NMR (DMSO-d6, 300 MHz) δ 8.03
(d, J ) 12.7 Hz, 1H), 7.75 (dd, J ) 14.1 Hz, J ′ ) 11.7 Hz, 1H),
7.10 (d, J ) 14.7 Hz, 1H), 6.96 (s, 1H), 6.35 (m, 2H), 4.52 (m,
4H), 1.27 (m, 6H); FTIR (KBr, cm-1) 3057, 2966, 2924, 1652,
1544, 1449, 1386, 1079; UV-vis (CH2Cl2) λmax (nm) 672, 404,
312. Anal. Calcd for C17H16N2O2S5: C, 46.37; H, 3.66; N, 6.37.
Found: C, 46.88; H, 4.09; N, 6.79.
(53) Gaussian 98, Revision A.7: Frisch, M. J .; Trucks, G. W.;
Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J . R.;
Zakrzewski, V. G.; Montgomery, J . A., J r.; Stratmann, R. E.; Burant,
J . C.; Dapprich, S.; Millam, J . M.; Daniels, A. D.; Kudin, K. N.; Strain,
M. C.; Farkas, O.; Tomasi, J .; Barone, V.; Cossi, M.; Cammi, R.;
Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J .;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J . B.; Cioslowski, J .; Ortiz,
J . V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J .; Keith, T.;
Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Chal-
lacombe, M.; Gill, P. M. W.; J ohnson, B.; Chen, W.; Wong, M. W.;
Andres, J . L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople,
J . A. Gaussian, Inc., Pittsburgh, PA, 1998.
1,3-Diet h yl-5-(5-t et r a t h ia fu lva len yl-2,4-p en t a d ien yli-
d en e)-2-th ioba r bitu r ic Acid (2c). By following the above
general procedure and using 5-(tetrathiafulvalenyl)penta-2,4-
dienal (5c) as the reagent, derivative 2c was obtained in a 58%
yield: mp 199-200 °C; 1H NMR (DMSO-d6, 300 MHz) δ 8.07
(d, J ) 12.9 Hz, 1H), 7.70 (m, 1H), 7.54 (m, 1H), 7.12 (m, 1H),
6.78 (d, J ) 14.1 Hz, 1H), 6.68 (s, 1H), 6.33 (m, 2H), 4.53 (m,
4H), 1.29 (m, 6H); FTIR (KBr, cm-1) 2977, 2928, 2854, 1686,
1575, 1521, 1493, 1376; UV-vis (CH2Cl2) λmax (nm) 648, 430,
310; MS m/z (rel intensity) 466 (M+, 100). Anal. Calcd for
C
19H18N2O2S5: C, 48.93; H, 3.89; N, 6.01. Found: C, 48.79; H,
(54) MOPAC 6.0: J . J . P. Stewart, QCPE, 1990, 10, 455.
3.77; N, 6.45.

8882 J . Org. Chem., Vol. 66, No. 26, 2001
Gonza´lez et al.
Syn th esis of TTF Der iva tives 3b,c. Gen er a l P r oce-
d u r e. A 161 mg (1 mmol) sample of 3-phenyl-5-isoxazolone
(10) was added to a solution of 1 mmol of the corresponding
formyl-TTF derivative (5a -c) in 15 mL of dry ethanol. The
solution was refluxed under argon atmosphere with exclusion
of light for 2 h. After this time, the precipitated solid was
filtered, washed thoroughly with ethanol, and purified by flash
chromatography (hexane/dichloromethane) to afford deriva-
tives 3b,c as red solids.
purified by flash chromatography (hexane/dichloromethane)
to afford derivatives 4a -c as red solids.
3-Dicyan om eth ylen -2-(tetr ath iafu lvalen ylm eth yliden )-
1-in d a n on e (4a ). By following the above general procedure
and using formyl-TTF (5a ) as the reagent, derivative 4a was
1
obtained in a 52% yield: mp > 300 °C; H NMR (DMSO-d6,
300 MHz) δ 8.69 (d, 1H), 8.22 (s, 1H), 7.93 (d, 1H), 7.78 (m,
2H), 7.66 (s, 1H), 6.41 (d, 1H), 6.36 (d, 1H); 13C NMR (DMSO-
d6, 75 MHz) δ 176.3, 169.6, 147.1, 135.5, 131.2, 129.4, 127.1,
123.8, 121.3, 120.7, 113.7, 110.8, 109.5, 108.5, 107.9, 106.8,
104.7, 104.5, 103.2; FTIR (KBr, cm-1) 2214, 1701, 1589, 1541,
1471, 1456, 1375, 1342; UV-vis (CH2Cl2) λmax (nm) 798, 390,
310, 230. Anal. Calcd for C19H8N2OS4: C, 55.89; H, 1.98; N,
6.87. Found: C, 56.49; H, 2.24; N, 7.51.
3-P h en yl-4-(3-t et r a t h ia fu lva len yl-2-p r op en ylid en )-5-
isoxa zolon e (3b). By following the above general procedure
and using (E)-3-(tetrathiafulvalenyl)acrylaldehyde (5b) as the
reagent, derivative 3b was obtained in a 72% yield: mp 214-
216 °C; 1H NMR (DMSO-d6, 300 MHz) δ 7.72 (d, J ) 14.7 Hz,
1H), 7.68-7.57 (m, 5H), 7.35 (s, 1H), 7.29 (d, J ) 14.4 Hz,
1H), 6. 79 (m, 2H), 5.90 (dd, J ) 14.7 Hz, J ′ ) 11.7 Hz, 1H);
13C NMR (DMSO-d6, 75 MHz) δ 169.1, 164.9, 161.9, 149.9,
141.7, 135.7, 135.0, 131.0, 129.2, 128.5, 128.2, 127.1, 123.8,
120.3, 120.1, 115.9, 114.8, 104.8; FTIR (KBr, cm-1) 3066, 1750,
1606, 1574, 1523, 1490, 1385, 1196, 1165, 1104; UV-vis (CH2-
Cl2) λmax (nm) 658, 382, 320; MS m/z (rel intensity) 01 (M+,
100). Anal. Calcd for C18H11NO2S4: C, 53.87; H, 2.76; N, 3.49.
Found: C, 54.46; H, 3.12; N, 3.89.
3-Dicya n om eth ylen -2-(3-tetr a th ia fu lva len yl-2-p r op en -
ylid en )-1-in d a n on e (4b). By following the above general
procedure and using (E)-3-(tetrathiafulvalenyl)acrylaldehyde
(5b) as the reagent, derivative 4b was obtained in a 47%
yield: mp > 300 °C; 1H NMR (DMSO-d6, 300 MHz) δ 8.51 (d,
1H), 8.19 (d, 1H), 7.96 (m, 2H), 7.89 (d, 1H), 7.78 (m, 1H), 7.74
(s, 1H), 7.55 (d, 1H), 6.80 (s, 2H); FTIR (KBr, cm-1) 2218, 1697,
1591, 1569, 1541, 1481, 1456, 1359, 1342; UV-vis (CH2Cl2)
λmax (nm) 726, 428, 308, 218 Anal. Calcd for C21H10N2OS4: C,
58.07; H, 2.32; N, 6.45. Found: C, 58.62; H, 2.59; N, 7.02.
3-Dicya n om eth ylen -2-(5-tetr a th ia fu lva len yl-2,4-p en ta -
d ien ylid en )-1-in d a n on e (4c). By following the above general
procedure and using 5-(tetrathiafulvalenyl)penta-2,4-dienal
(5c) as the reagent, derivative 4c was obtained in a 45%
yield: mp > 300 °C; FTIR (KBr, cm-1) 2212, 1697, 1575, 1522,
1483, 1458, 1379, 1340; UV-vis (CH2Cl2) λmax (nm) 690, 458,
300, 222; MS m/z (rel intensity) 466 (M+, 100). Anal. Calcd
for C23H12N2OS4: C, 60.00; H, 2.63; N, 6.09. Found: C, 60.55;
H, 3.22; N, 6.71.
3-P h en yl-4-(5-tetr ath iafu lvalen yl-2,4-pen tadien yliden )-
5-isoxa zolon e (3c). By following the above general procedure
and using 5-(tetrathiafulvalenyl)penta-2,4-dienal (5c) as the
reagent, derivative 3c was obtained in a 69% yield: mp 207-
209 °C dec; 1H NMR (DMSO-d6, 300 MHz) δ 7.81 (dd, J ) 13.8
Hz, J ′ ) 11.5 Hz, 1H), 7.79 (d, J ) 14.7 Hz, 1H), 7.70-7.57
(m, 5H), 7.45 (dd, J ) 15.1 Hz, J ′ ) 10.8 Hz, 1H), 7.36 (s, 1H),
7.04 (d, J ) 14.7 Hz, 1H), 6.77 (s, 2H), 6.52 (dd, J ) 15.3 Hz,
J ′ ) 11.4 Hz, 1 H); 13C NMR (DMSO-d6, 75 MHz) δ 169.0,
164.9, 163.4, 162.3, 153.3, 150.5, 147.7, 135.4, 133.5, 131.0,
130.8, 129.3, 129.2, 128.3, 127.6, 127.3, 120.3, 120.1, 114.0,
106.1; UV-vis (CH2Cl2) λmax (nm) 630, 408, 320; MS m/z (rel
intensity) 427 (M+, 100). Anal. Calcd for C20H13NO2S4: C,
56.21; H, 3.07; N, 3.28. Found: C, 55.99; H, 3.26; N, 3.79.
Ack n ow led gm en t. This work has been partially
supported by the DGESIC of Spain (Projects PB98-0818,
BQU2000-0790, MAT99-1009-C02-02, FD97-1765-C03,
and BQU2000-1156).
Syn th esis of TTF Der iva tives 4a -c. Gen er a l P r oce-
d u r e. A 194 mg (1 mmol) sample of dicyanomethyleneindan-
dione (11)9 was added to a solution of 1 mmol of the corre-
sponding formyl-TTF derivative (5a -c) in 15 mL of acetic
anhydride. The solution was refluxed under argon atmosphere
with exclusion of light for 2 h. After this time, the precipitated
solid was filtered, washed thoroughly with ethanol, and
Su p p or tin g In for m a tion Ava ila ble: B3P86/6-31G* ge-
ometries (Cartesian coordinates) and energies (atomic units)
of compounds 1a -c, 2a -c, 3b,c, and 4b,c. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O010717K