Novel Fused D-A Dyad and A-D-A Triad Incorporating Tetrathiafulvalene and p-Benzoquinone

Novel F u sed D-A Dya d a n d A-D-A Tr ia d In cor p or a tin g

Tetr a th ia fu lva len e a n d p-Ben zoqu in on e

Fre´de´ric Dumur, Nicolas Gautier, Nuria Gallego-Planas, Yu¨cel S¸ ahin,^†Eric Levillain,

Nicolas Mercier, and Pie´trick Hudhomme*

Inge´nierie Mole´culaire et Mate´riaux Organiques, UMR 6501, Boulevard Lavoisier, Universite´ d’Angers,

F-49045 Angers, France

Matteo Masino and Alberto Girlando

Dipartimento Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Universita` di Parma,

Parco Area delle Scienze, I-43100, Parma, Italy

Vega Lloveras, J ose´ Vidal-Gancedo, J aume Veciana, and Concepcio´ Rovira

Institut de Cie`ncia de Materials de Barcelona (C.S.I.C), Campus de la U.A.B, 08193 Bellaterra, Spain

pietrick.hudhomme@univ-angers.fr

Received November 17, 2003

Novel fused donor-acceptor dyad (TTF-Q or D-A) and acceptor-donor-acceptor triad (Q-TTF-Q

or A-D-A) incorporating the donor tetrathiafulvalene (TTF) and the acceptor p-benzoquinone (Q)

have been synthesized. The solution UV-vis spectra of these molecules display a low-energy

absorption band that is attributed to an intramolecular charge transfer between both antagonistic

units. The presence of reversible oxidation and reduction waves for the donor and acceptor moieties

was shown by cyclic voltammetry, in agreement with the ratio TTF/quinone(s) units. The successive

generation from these compounds of the cation radical and anion radical obtained upon (electro)-

chemical oxidation and reduction, respectively, was monitored by optical and ESR spectroscopies.

The anion radical Q-TTF-Q^-•triad was demonstrated to be a class II mixed-valence system with

the existence of a temperature-dependent intramolecular electron transfer. The crystallographic

tendency of these fused systems to overlap in mixed stacks of alternating A-D-A units is also

discussed.

In tr od u ction

vices. Development of new donor-acceptor architectures

affording highly polarizable molecules is particularly

important in order to progress in these fields. These

compounds are characterized by low excitation energies

leading to interesting optical properties. These could also

be candidates for single one-component conductors show-

ing intrinsic conductivities when relative donating and

accepting abilities are controlled.⁵Moreover, the chal-

lenge of verifying experimentally the Aviram-Ratner

concept of unimolecular electrical rectification on D-σ-A

system,⁶in which the donor tetrathiafulvalene (TTF) and

the acceptor tetracyanoquinodimethane (TCNQ) are con-

nected via a saturated link, was recently achieved on the

D-π-A hexadecylquinolinium tricyanoquinodimetha-

nide molecule: the excited neutral state was found to be

relatively accessible from the zwitterionic ground state

D⁺-π-A^-.⁷Tetrathiafulvalene has attracted much inter-

est for its high electron-donating ability in this field of

intramolecular charge-transfer materials.⁸But, to avoid

the major problem in the synthesis of TTF-spacer-

acceptor compounds resulting in the formation of the

Much attention is still devoted to the investigation of

D-A dyads and D-A-D and A-D-A triads in order to

control the stoichiometry of both donor (D) and acceptor

(A) partners, as well as the degree of charge transfer,

which are crucial parameters in the design of organic

metals. This considerable research effort is justified by

the potential applications of these molecular systems,

which are the basis for artificial photosynthetic systems,¹

materials presenting semiconducting or nonlinear optical

properties,²molecular electronic,³and photovoltaic⁴de-

* Corresponding author. Fax: +33 2 41 73 54 05.

^†Permananent address: Department of Chemistry, Anadolu Uni-

versity, T-26470 Eskis¸ehir, Turkey.

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Published on Web 02/21/2004

2164

J . Org. Chem. 2004, 69, 2164-2177

Novel Fused D-A Dyad and A-D-A Triad

CHART 1

stable and insoluble intermolecular charge-transfer com-

plex between both counterparts prior to their covalent

linking, an alternative route was developed considering

the linkage of the TTF derivatives to a weak electron

acceptor such as quinone. The subsequent conversion into

the strong TCNQ acceptor was investigated, but despite

several attempts, there appears to be no example of a

TTF-quinone being converted into the corresponding

TTF-TCNQ derivative.

a fixed distance and orientation between the TTF and

the quinone moieties, showed a weak intramolecular

charge-transfer interaction.¹²The molecular type of

conjugated 5¹³or fused 6¹⁴D-A dyads with anthraqui-

none as the acceptor, as well as fused D-A-D 7¹⁵and

A-D-A 8¹⁶triads, were also introduced. In this latter

case, the poor solubility of triad 8 prevented a further

functionalization and also the structural study of this

A-D-A system. Additionally and very surprisingly, the

Several TTF-σ-quinone dyads were previously stud-

ied, but no intramolecular charge-transfer band was

discernible in the UV-visible spectrum for molecules 1,⁹

2,¹⁰and 3¹¹(Chart 1). Molecule 4, with a design having

(10) Moriarty, R. M.; Tao, A.; Gilardi, R.; Song, Z.; Tuladhar, S. M.

Chem. Commun. 1998, 157.

(11) (a) Segura, J . L.; Mart´ın, N.; Seoane, C.; Hanack, M. Tetrahe-

dron. Lett. 1996, 37, 2503. (b) Gonzales, M.; Illescas, B.; Mart´ın, N.;

Segura, J . L.; Seoane, C.; Hanack, M. Tetrahedron 1998, 54, 2853.

(12) Tsiperman, E.; Regev, T.; Becker, J . Y.; Bernstein, J .; Ellern,

A.; Khodorkovsky, V.; Shames, A.; Shapiro, L. Chem. Commun. 1999,

1125.

(13) Pe´rez, I.; Liu, S.-G.; Mart´ın, N.; Echegoyen, L. J . Org. Chem.

2000, 65, 3796.

(14) Gautier, N.; Mercier, N.; Riou, A.; Gorgues, A.; Hudhomme, P.

Tetrahedron Lett. 1999, 40, 5997.

(7) (a) Metzger, R. M.; Chen, B.; Ho¨pfner, U.; Lakshmikantham, M.

V.; Vuillaume, D.; Kawai, T.; Wu, X.; Tachibanan, H.; Hughes, T. V.;

Sakurai, H.; Hosch, C.; Cava, M. P.; Brehmer, L.; Ashwell, G. J . J .

Am. Chem. Soc. 1997, 119, 10455. (b) Metzger, R. M. J . Mater. Chem.

1999, 9, 2027. (c) Metzger, R. M. Acc. Chem. Res. 1999, 32, 950. (d)

Roth, S.; Blumentritt, S.; Burghard, M.; Cammi, E.; Carroll, D.; Curran,

S.; Du¨sberg, G.; Liu, K.; Muster, J .; Philipp, G.; Rabenau, T. Synth.

Met. 1998, 94, 105. (e) Metzger, R. M. Chem. Rev. 2003, 103, 3803.

(8) (a) Segura, J . L.; Mart´ın, N. Angew. Chem., Int. Ed. 2001, 40,

1372. (b) Bryce, M. R. J . Mater. Chem. 2000, 10, 589. (c) Bryce, J . M.

Adv. Mater. 1999, 11, 11.

(15) (a) Adam, M.; Mu¨llen, K. Adv. Mater. 1994, 6, 439. (b) Frenzel,

S.; Mu¨llen, K. Synth. Met. 1996, 175.

(16) (a) Watson, W. H.; Eduok, E. E.; Kashyap, R. P.; Krawiec, M.

Tetrahedron 1993, 49, 3035. (b) The bis(1,4-naphthoquinone)TTF

exhibited a reduction wave at E°_1/2) -0.32 V (NHE), but at both

negative and positive potentials, the current increases sharply with

increasing voltage, giving no distinct oxidation-reduction couples.

(9) Scheib, S.; Cava, M. P.; Baldwin, J . W.; Metzger, R. M. J . Org.

Chem. 1998, 63, 1198.

J . Org. Chem, Vol. 69, No. 6, 2004 2165

Dumur et al.

SCHEME 1^a

a

Reagents: (a) p-benzoquinone then glacial AcOH, 80 °C, 96% (lit.^19a63%). (b) Na₂S‚9H₂O, MeOH, 98% (lit.^19a71%). (c) Ac₂O, Et₃N,

80% for 14a ; Ph₂tBuSiCl, DMF, imidazole, 86% for 14b. (d) Hg(OAc)₂, CH₂Cl₂/glacial AcOH, 88% for 15a , 85% for 15b. (e) ∆ P(OEt)₃, 45%

(lit.^19a47% using P(OEt)₃/toluene). (f) (i) MeONa/MeOH; (ii) PTSA, H₂O; (iii) DDQ, 57%. (g) phosphonate 17, n-BuLi, THF, -78 to 20 °C,

90%. (h) (i) n-Bu₄NF/THF; (ii) p-benzoquinone, 75%.

cyclic voltammetry study did not exhibit the oxidation

waves corresponding to the TTF donor fragment.¹⁶On

the other hand, the cyclic voltammetry of compound 7

revealed the presence of two two-electron oxidation waves

corresponding to both TTF moieties, but no data were

reported on the electrochemical behavior of the p-benzo-

quinone fragment.¹⁵

In this work we report the synthesis, theoretical

calculations, spectroscopic and electrochemical properties

of A-D-A triad 9 (Q-TTF-Q) and D-A (TTF-Q) dyad

10 corresponding to fused TTF-quinone(s) assemblies,

also considered to be potential precursors for fused

donor-acceptor oligomers or TTF-TCNQ systems. The

study of the derived oxidized and reduced species is also

presented in which previous results demonstrated that

intramolecular electron transfer (IET) process occurred

in the mixed-valence Q-TTF-Q^-•system.¹⁷Moreover,

we present the study of the crystallographic arrangement

of the fused Q-TTF-Q 9 to check if the previously

proposed concept of designing organic metals with A-D-A

type molecules, where the donors and acceptors are

covalently linked via a saturated methylene spacer or a

sulfur atom,¹⁸can be extended to fused systems.

pound 11 in 97% yield. The latter was further oxidized

using p-benzoquinone, and the following cyclization upon

treatment with glacial acetic acid led to the iminium salt

12 in 96% yield for the two steps.¹⁹After quantitative

conversion to the corresponding 2-thioxo-1,3-dithiole 13

using sodium sulfide, the hydroquinone functionalities

were protected using the acetyl or silyl groups. Well-

established procedures afforded compounds 14a and 14b

in 80 and 86% yields, respectively. The transchalcoge-

nation upon treatment with mercuric acetate furnished

the 2-oxo-1,3-dithiole derivatives 15 in excellent yields.

The triethyl phosphite coupling methodology was ap-

plied to 15a , and the resulting tetrathiafulvalene 16 was

isolated as yellow crystals in 45% yield. Subsequent

methanolysis using a methoxide solution in THF/MeOH

afforded TTF-bis(1,4-hydroquinone) after treatment with

p-toluenesulfonic acid (PTSA).²⁰Without isolating the

fused TTF-bis(1,4-hydroquinone) intermediate, the oxi-

dation was carried out using DDQ to yield the fused

A-D-A system 9 as green-blue crystals after classical

workup and chromatography on florisil using CH₂Cl₂/

EtOAc (99/1) as the mixture of eluents.

To reach the fused D-A assembly 10a , we applied a

nonclassical Horner-Wadsworth-Emmons olefination to

create the TTF core involving the 2-oxo-1,3-dithiole

functionality.²¹After reaction of 15b with the anion of

phosphonate 17²²in THF and silicagel column chroma-

Resu lts a n d Discu ssion

Syn th esis. The synthesis of triad A-D-A 9 and dyad

D-A 10 was performed using the same key intermediate

2-oxo-1,3-dithiole derivative 15 (Scheme 1). p-Benzo-

quinone was reacted with the dithiocarbamate salt

(isolated from the addition of piperidine to carbon disul-

fide) in the presence of glacial acetic acid in a mixture of

DMF/DMSO as solvents. The corresponding Michael

addition followed by the aromatization produced com-

(19) (a) Synthesis of this compound was carried out according to a

previously described methodology, several yields being improved by

small modifications of experimental procedures: Sun, D.; Krawiec, M.;

Watson, W. H. J . Chem. Crystallogr. 1997, 27, 515. (b) Yields were

particularly improved by using piperidine instead of pyrrolidine:

Gautier, N.; Gallego-Planas, N.; Mercier, N.; Levillain, E.; Hudhomme,

P. Org. Lett. 2002, 4, 961.

(20) We should note that an identical reaction using inorganic acids

such as hydrochloric acid or sulfuric acid solutions was unsuccessful.

In these cases, the resulting precipitate could be the result of

concomitant protonation of the TTF core.

(21) Boulle, C.; Desmars, O.; Gautier, N.; Hudhomme, P.; Cariou,

M.; Gorgues, A. Chem. Commun. 1998, 2197.

(17) Some parts of this work have been previously reported: Gautier,

N., Dumur, F.; Lloveras, V.; Vidal-Gancedo, J .; Veciana, J .; Rovira,

C.; Hudhomme, P. Angew. Chem., Int. Ed. 2003, 42, 2765.

(18) Khodorkovsky, V.; Becker J . Y. Organic Conductors, Funda-

mentals and Applications; Farges, J . P., Ed.; New York, 1994.

2166 J . Org. Chem., Vol. 69, No. 6, 2004

Novel Fused D-A Dyad and A-D-A Triad

F IGURE 1. HOMO orbital (left) and LUMO orbital (right) of triad 9 obtained by DFT calculations.

tography (CH₂Cl₂/petroleum ether (1/4) as the mixture

of eluents), we could isolate compound 18 as yellow

crystals in 90% yield. The deprotection of the silyl group

was carried out using tetrabutylammonium fluoride, and

then subsequent oxidation using p-benzoquinone afforded

compound 10a as green crystals in 75% yield after

column chromatography on florisil using CH₂Cl₂/petro-

leum ether (1/1) as the mixture of eluents.

Th eor etical Calcu lation s an d Spectr oscopic P r op-

er ties of 9 a n d 10. Density Functional Theory (DFT)

calculations were performed using Gaussian 98²³at the

B3LYP/6-31G* level of theory for a full geometry opti-

mization, with no symmetry contraints, of the fused D-A

and A-D-A systems. Even if no symmetry was imposed,

F IGURE 2. Raman spectra of 9 (continuous line) and 10a

the optimized geometry obtained confirmed the high

symmetry of this A-D-A molecule (D_2hsymmetry). For

the A-D-A assembly 9, the molecular orbital analysis

of both compounds showed that the largest coefficients

in the HOMO orbital are mainly located on the central

TTF core (the S₂CdCS₂fragment) and the calculated

energy value for this HOMO orbital was -5.35 eV (Figure

1). As expected, the coefficients in the LUMO orbital were

centered on the quinone moieties, showing an alternation

of π-bond signs in these rings, but this LUMO orbital was

characterized by two quasi-degenerated orbitals: the

LUMO (-3.89 eV) and the LUMO +1 (-3.84 eV).

Consequently, the calculated HOMO-LUMO gap was

estimated to be 1.46 eV. The degenerated LUMO orbital

is due to alternating signs of the wave function coef-

ficients in the π-molecular orbitals, as shown in Figure

1. A perpendicular plane reflects the same coefficients

and signs of the wave function of each quinone unit.

Geometry optimization was also performed on the D-A

system 10a and 10b, and the same conclusions were

reached in terms of the localization of the HOMO and

LUMO coefficients and energies (for 10a , HOMO ) -5.04

eV, LUMO ) -3.67 eV; for 10b, HOMO ) -4.90 eV,

LUMO) -3.69 eV) with an estimated gap of 1.37 eV for

10a and 1.21 eV for 10b.

(dashed line), 568 nm excitation. The arrows indicate the

position of the CdO and CdC stretchings in the Raman

spectra of neutral p-benzoquinone and TTF crystals, respec-

tively.

All spectroscopic data (¹H and ¹³C NMR, MS, IR,

Raman) were in agreement with the described structures

of 9 and 10a . Particularly, these compounds appeared

to be especially stable. As suggested first by the presence

of the molecular peak as the base peak in mass spec-

trometry, this stability was confirmed by the thermal

gravimetric analysis (TGA) study, which showed the

beginning of the decomposition at 240 and 290 °C for 9

and 10a , respectively. The Raman spectrum of D-A 10a

(Figure 2) showed a clear downward shift of both carbonyl

(∼1630 cm^-1) and central CdC (1446 cm^-1) stretching of

the quinone and TTF units, respectively, with respect to

the corresponding values (∼1665 and 1518 cm^-1) of

neutral p-benzoquinone²⁴and neutral TTF.²⁵A less

pronounced downward shift was observed for the CdO

stretching of A-D-A 9, whereas the TTF CdC stretching

is practically unshifted in this case (Figure 2; the

frequencies are at ∼1655²⁴and 1522 cm^-1). The same

trend was found in the IR spectra, where the carbonyl

antisymmetric stretch is located at 1650 and at 1648 cm^-1

for 9 and 10a , respectively, to be compared to about 1665

cm^-1for p-benzoquinone.²⁴This behavior indicated a

partial charge transfer from the TTF core to the carbonyl

groups of the quinone moiety. The charge transfer was

rather small for 9 but increased in the asymmetric unit

10a and, in the solid state, could have both intra- and

intermolecular character (see below).

(22) Phosphonate 17 was synthesized according to well-established

procedures from corresponding substituted 1,3-dithiole-2-thione: Moore,

A. J .; Bryce, M. R. Synthesis 1991, 26.

(23) 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.; 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.; Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen,

W.; Wong, M. W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.;

Pople, J . A. Gaussian 98, revision A.9; Gaussian, Inc.: Pittsburgh, PA,

1998.

(24) Liu, R.; Zhou, X.; Pulay, P. J . Phys. Chem. 1993, 96, 4255 and

references therein. Notice that in both Raman and IR, the carbonyl

stretching bands are affected by Fermi resonance. We believe that the

doublet structure seen in the Raman spectra of 9 and 10a (Figure 2)

share the same origin. Accordingly, in the text we report as an

approximate frequency the corresponding average.

(25) Bozio, R.; Zanon, I.; Girlando, A.; Pecile, C. J . Chem. Phys. 1979,

71, 2282.

J . Org. Chem, Vol. 69, No. 6, 2004 2167

Dumur et al.

SCHEME 2. P ola r iza tion of th e S-CdC-CdO Con ju ga ted System of Tr ia d 9 Su p p or ted by th e Ch a r ge

Distr ibu tion Obta in ed by Th eor etica l Ca lcu la tion s a n d in Agr eem en t w ith th e P ola r iza tion Su ggested for

Com p ou n d 19²⁶

On the other hand, this influence of TTF on the

benzoquinone moiety was shown in solution by comparing

the ¹³C spectra of 9 and 10a with that of p-benzoquinone

itself. Although the ¹³C chemical shift of the carbonyl

functionality appeared at 187.1 ppm (CDCl₃as the

reference) for p-benzoquinone, the upfield shift to 177.9

and 177.7 ppm for the corresponding carbon of 9 and 10a ,

respectively, should result from the displacement of the

electron density caused by the push-pull S-CdC-Cd

O system, suggesting the mesomeric form shown in

Scheme 2. This resonance form was previously proposed

for the bis(p-benzoquinone) 19, which showed a maxi-

mum absorption at 508 nm in acetonitrile.²⁶The charge

distribution calculated by DFT methods on the neutral

compound 9 was in complete agreement with a strong

F IGURE 3. Electronic absorption spectra of 9 and 10a in CS₂.

polarization of the S-CdC-CdO conjugated system and

strongly supported the partial zwitterionic nature of the

ground state (Scheme 2).

TABLE 1. Wa velen gth of th e Ch a r ge Tr a n sfer UV-vis

Absor p tion Ma xim a of A-D-A 9 a n d D-A 10a in Solven ts

of Va r yin g P ola r ity^a

The electronic absorption spectrum of 9 confirmed the

existence of the electronic interaction between both D and

A moieties, and comparatively, the effect of the strong

donor tetrathiafulvalene became evident. The UV-visible

spectra of 9 showed the presence of a broad absorption

band in the 500-1100 nm region, with the strongest

absorption evidenced in CS₂and centered at ca. 808 nm,

which clearly indicates a weak charge-transfer interac-

tion resulting from the conjugation involving both donor

and acceptor moieties (Figure 3).

solvent

A-D-A 9 (λ nm)

D-A 10a (λ nm)

DMSO

DMF

acetonitrile

toluene

dichloromethane

CCl₄

670

735

738

773

782

804

808

762

758

776

820

847

863

892

CS₂

a

Extinction molar coefficient of this charge transfer band was

determined for 9 and 10a in toluene to be 780 and 425 M^-1cm^-1

,

The measurement at different concentrations proved

the intramolecular nature of this charge transfer from

donor to acceptor moiety. A red-shift effect was observed

for 10a , which presented a broad absorption band be-

tween 600 and 1300 nm centered at ca. 892 nm in CS₂.

For both 9 and 10a , the position of the band just

corresponds to the HOMO-LUMO gap calculated as

described above. These D-A and A-D-A compounds

exhibited strong solvatochromism of the charge-transfer

band depending on the polarity of solvents (Table 1).

Electr och em ica l P r op er ties of F u sed TTF -Qu i-

n on e(s) 9 a n d 10a . The cyclic voltammogram of D-A

respectively.

to the successive generation of the cation radical and

dication of the TTF moiety. Two reduction processes were

shown for the p-benzoquinone moiety, including the first

0

one-electron reversible reduction wave at E_red1) -0.21

V (Figure 4) and the second reduction wave E⁰

at

red2

approximately -1.20 V, which was not reversible in these

experimental conditions. Concerning the A-D-A com-

pound 9, the oxidation potentials were clearly shifted to

more positive values (E_ox1⁰) +0.99 and E_ox2⁰) +1.36 V,

vs Ag/AgCl), the electron-withdrawing effect of the

quinone group being responsible for this phenomenon.

The p-benzoquinone moiety was characterized by a two-

10a (n-Bu₄NPF₆0.1 M in CH₂Cl₂/acetonitrile 9/1) showed

0

two one-electron reversible oxidation waves at E_ox1

)

+0.74 V and E_ox2⁰) +1.11 V (vs Ag/AgCl) corresponding

0

electron reversible reduction wave E_red1approximately

at -0.25 V. In fact, a splitting of this first reduction wave

(26) Hu¨nig, S.; Siunzger, K.; Bau, R.; Metzenthin, T.; Salbeck, J .

Chem. Ber. 1993, 126, 465.

0

(E_red1) -0.20 V and E_red1′) -0.28 V) was observed by

2168 J . Org. Chem., Vol. 69, No. 6, 2004

Novel Fused D-A Dyad and A-D-A Triad

F IGURE 4. Cyclic voltammograms (top) and their corre-

sponding deconvolution (bottom) of D-A 10a and triad 9; Pt

electrode vs Ag/AgCl, nBu₄NPF₆0.1 M in CH₂Cl₂/CH₃CN 9/1,

10^-3M, v ) 500 mV/s. The second reduction waves are not

presented on this figure.

F IGURE 5. Cyclic voltammogram (top) and its deconvolution

(bottom) of triad 9; Pt electrode vs Ag/AgCl, nBu₄NPF₆0.1 M

in o-dichlorobenzene/CH₃CN 19/1, 5 × 10^-4M, v ) 200 mV/s.

using a slowest scan rate or cyclic voltammogram decon-

volution. Thus, the successive generation of Q-TTF-Q^-•

and Q^-•-TTF-Q^-•species was observed. This phenom-

enon of splitting showed that the electrochemical behav-

ior of both p-benzoquinone moieties is resulting from

modifications on the electronic interaction between TTF

and p-benzoquinone moieties at the Q-TTF-Q^-•stage

and from Coulombic repulsion between reduced species

at the Q^-•-TTF-Q^-•stage. The values corresponding to

the difference between the oxidation potential and the

electron affinity were experimentally determined to be

1.19 eV for triad A-D-A 9 and 0.95 eV for dyad D-A

10a , by calculating the difference between the first

oxidation peak of TTF (Ep_a) and the first reduction peak

of p-benzoquinone (Ep_c).

As the bis(1,4-benzoquinone)TTF 9 was clearly char-

acterized in terms of cyclic voltammetry, we were inter-

ested in the problem resulting from the bis(1,4-naphtho-

quinone)TTF 8 and the absence of electroactive species

of this compound upon oxidation as noted by W. H.

Watson et al.¹⁶We therefore applied our synthetic

methodology to synthesize the bis(1,4-naphthoquinone)-

TTF (Scheme 3). Thus, the reaction of 2,3-dichloronaph-

thoquinone with potassium sulfide and carbon disulfide

in DMF, followed by treatment with sodium dithionite,

afforded the 2-thioxo-1,3-dithiole derivative 20 as de-

scribed.¹⁶Precursor 22 was obtained by acetylation using

acetic anhydride in the presence of triethylamine in 79%

yield and transchalcogenation by treatment with mer-

curic acetate in glacial acetic acid in 96% yield. Triethyl

phosphite coupling reaction was performed, affording the

tetrathiafulvalene derivative 23 in 53% yield. The con-

version into quinone functionality described herein was

successfully carried out using DDQ, affording in 68%

yield the bis(1,4-naphthoquinone)TTF 8 as a light green

powder, this characteristic being in agreement with the

compound previously reported.¹⁶

To clearly observe the second two-electron reduction

waves of the p-benzoquinone moiety, we performed

experiments using o-dichlorobenzene/acetonitrile (19/1)

as the mixture of solvents. The cyclic voltammogram of

triad 9 exhibited two reversible one-electron oxidation

0

processes with redox potentials E_ox1and E_ox2at +0.97

and +1.34 V (vs Ag/AgCl), respectively, and two inde-

pendent reduction processes. After deconvolution, the

first reversible system was shown as two successive

reductive steps corresponding to the generation of

Q-TTF-Q^-•and Q^-•-TTF-Q^-•species with redox po-

Despite its very low solubility, this compound 8 was

studied by cyclic voltammetry using n-Bu₄NPF₆0.1 M

as a supporting electrolyte and o-dichlorobenzene/aceto-

nitrile (19/1) as the mixture of solvents (2 × 10^-4M, v )

200 mV/s). In contradiction with previous observation,¹⁶

compound 8 was characterized by two reversible oxida-

tion and two reduction waves attributed to the TTF and

naphthoquinone moieties, respectively, this cyclic voltam-

0

tentials E_ed1and E_red1′at -0.33 and -0.40 V, respec-

tively. The second quasi-reversible system showed

one broad wave corresponding to the reduction into

Q^2--TTF-Q^-•and Q^2--TTF-Q^2-species at -1.16 V

(Figure 5).

J . Org. Chem, Vol. 69, No. 6, 2004 2169

Dumur et al.

SCHEME 3^a

a

Reagents: (a) K₂S, CS₂, DMF, 65% (lit.^16a63%). (b) Na₂S₂O₄, 75% (lit.^16a97%). (c) Ac₂O, Et₃N, 79%. (d) Hg(OAc)₂, CH₂Cl₂/glacial

AcOH, 96%. (e) ∆ P(OEt)₃, 53%. (f) (i) MeONa/MeOH; (ii) PTSA, H₂O; (iii) DDQ, 68%

mogram being similar to that obtained for 9 (Figure 5).

Thus, the two oxidation waves corresponding to the

formation of the cation radical and dication of the TTF

were shown at +0.96 and +1.35 V (vs Ag/AgCl), respec-

tively. The first reduction process appeared as a split

system with two different waves at -0.56 and -0.61 V

and the second reduction process as a broad wave at

-1.20 V.

P r op er ties of Oxid ized a n d Red u ced Sp ecies

fr om Tr ia d 9 a n d Dya d 10a . The optical properties of

the cation radical and dication of bis(1,4-benzoquinone)-

TTF 9 were investigated by in situ UV-vis-NIR spec-

troscopy, by addition of increasing amounts of NOBF₄.

Chemical oxidation led to the rapid disappearance of

bands attributed to the neutral TTF derivative (broad

band from 600 to 1100 nm centered at 782 nm) and to

the development of new bands characteristic for the

cation radical (434, 580 nm) and the dication (566 nm)

F IGURE 6. Evolution of the optical spectrum for the neutral

(Figure 6).²⁷The values of the HOMO-LUMO difference

triad 9 (3 × 10^-4M in CH₂Cl₂) upon oxidation using NOBF₄

calculated by DFT methods followed the same trend as

the UV-visible data and were estimated to be 1.50 eV

for 9^+•(HOMO ) -9.65 eV, LUMO ) -8.15 eV) and 1.82

eV for 9²⁺(HOMO ) -14.46 eV, LUMO ) -12.54 eV).

As for the neutral molecule 9, the optimized geometry

found for the cation radical 9^+•was almost planar, while

the dication 9²⁺presented distortion from planarity of

14°.²⁸This torsion angle in the geometry of 9²⁺may be

related to increasing σ-character in the C-C central bond

between the two 1,3-dithiolium moieties. This is sup-

ported by the optimized central bond lengths, computed

as 1.35 Å for the neutral molecule 9, 1.40 Å for the cation

in CH₃CN solution.

presence of triflic acid according to a synthetic approach

recently reported for the efficient stoichiometric control

of TTF-derived cation radicals.²⁹The IR spectrum of

9^+•‚CF ₃SO₃clearly showed the appearance of strong

-

bands at 1255, 1027, and 636 cm^-1characteristic of the

-

SO₃anion.²⁹The most evident change in the Raman

spectrum is the downward shift of the TTF central

double-band stretch from 1519 to 1399 cm^-1. The ESR

signal of an acetone solution of the cation radical salt

9^+•‚CF ₃SO₃^-exhibited the expected quintet (g ) 2.0071),

showing a small coupling of the electronic spin with the

four equivalent hydrogen atoms of the quinone moieties

(a_H) 0.36 G). Moreover, the ³³S hyperfine coupling

constant was also observed upon amplification of the

spectrum (a_S) 4.1 G).

radical 9^+•, and 1.44 Å for the dication 9²⁺

.

The cation radical 9^+•‚CF ₃SO₃was also chemically

prepared as a pure solid by oxidation of the triad 9 by

using as an oxidizing agent iodobenzene diacetate in the

-

The anion radical 9^-•‚P (C₆H₅)₄⁺, as well as a pure

solid, was prepared by chemical reduction with Cu metal

in CH₂Cl₂containing tetraphenylphosphonium bromide.

This compound is highly insoluble, and a very fine

precipitate is formed almost at the beginning of the

(27) For references on calculated and experimental UV-visible

absorption of cation radical and dication of TTF derivatives, see: (a)

Khodorkovsky, V.; Shapiro, L.; Krief, P.; Shames, A.; Mabon, G.;

Gorgues, A.; Giffard, M. Chem. Commun. 2001, 2736. (b) Andreu, R.;

Gar´ın, J .; Orduna, J . Tetrahedron 2001, 57, 7883.

(28) This distortion from planarity between the two dithiolium rings

was previously observed on the crystal structure of the dication from

the unsymmetrical outer S-position isomer of BEDT-TTF. Hudhomme,

P.; Le Moustarder, S.; Durand, C.; Gallego-Planas, N.; Mercier, N.;

Blanchard, P.; Levillain, E.; Allain, M.; Gorgues, A.; Riou, A. Chem.

Eur. J . 2001, 7, 5070.

(29) Giffard, M.; Mabon, G.; Leclair, E.; Mercier, N.; Allain, M.;

Gorgues, A.; Molinie´, P.; Neilands, O.; Krief, P.; Khodorkovsky, V. J .

Am. Chem. Soc. 2001, 123, 3852.

2170 J . Org. Chem., Vol. 69, No. 6, 2004

Novel Fused D-A Dyad and A-D-A Triad

F IGURE 7. Evolution of the UV-vis-NIR spectrum during

the course of the reduction of D-A 10a , at different times of

reaction. The inset is the enlargement of the vis-NIR part.

F IGURE 8. Evolution of the ESR spectra of dyad 10a upon

in situ electrooxidation (A) and subsequent electroreduction

(B-E) (see text).

reduction process. The IR spectrum of 9^-•‚P (C₆H₅)₄

+

showed important modifications on the band correspond-

ing to carbonyl groups and the appearance of character-

istic P-C bands at 650-750 cm^-1. Isolated pure solid

9^-•‚P (C₆H₅)₄⁺is insoluble in most of the common organic

solvents. A much diluted solution can only be prepared

in ethyl acetate and presents a very weak ESR signal

consisting of five lines. The high degree of insolubility of

+

9^-•‚P (C₆H₅)₄prevents the quantitative study of the

UV-vis-NIR spectra of the compound as well as the

generation of the dianionic derivative 9^2-. An ESR study

of the anion radical species 9^-•‚P (C₆H₅)₄⁺generated “in

situ” is presented below.

DFT calculations were performed for a full geometry

optimization of the anion radical Q-TTF-Q^-•system.

The optimized geometry found for the anion radical 9^-•

was perfectly planar. The calculation performed was

unrestricted, and then each orbital obtained was a spin-

orbital with single occupancy. The molecular orbital

analysis showed that the HOMO orbital (singly occupied

spin-orbital), with a calculated energy of -1.40 eV,

presented the same shape (and coefficients) as the LUMO

orbital of the neutral triad Q-TTF-Q 9. The calculated

energy value for the corresponding LUMO of the anion

radical was -1.02 eV. We observed that the overall

character for the single occupied HOMO and the corre-

sponding LUMO was very similar to the LUMO of the

neutral molecule: the only contributions on the HOMO

and LUMO were located on the outer quinone part of the

molecule.

Chemical reduction of the dyad 10a with Cu metal in

CH₂Cl₂containing tetraphenylphosphonium bromide led

to a decrease in the characteristic charge-transfer broad

band of the neutral derivative and to the appearance and

increase with reaction time of the bands due to the anion

radical (425 and 550 nm)³⁰(Figure 7). The ESR spectrum

of this solution consists of a well-defined triplet (g )

2.0046) arising from the coupling of the unpaired electron

with the two equivalent hydrogen atoms of the quinone

(a_H) 2.50 G).

F IGURE 9. Evolution of the ESR spectra of triad 9 upon in

situ electrooxidation (A) and subsequent electroreduction

(B-D) (see text).

of their cation radical and anion radical derivatives upon

oxidation or reduction, respectively. Thus, the cation

radical 10a ^+•was generated by electrochemical oxidation

performed in an electrochemical cell adapted to the ESR

spectrometer at +0.9 V (vs Ag/AgCl) in CH₂Cl₂using

nBu₄NPF₆as an electrolyte and monitored by ESR

spectroscopy (Figure 8).

The corresponding spectrum consisted of an overlapped

triplet with the typical pattern of a coupling with the two

equivalent quinonic protons (g ) 2.0075, a_H) 0.46 G).

By imposing a reduction potential at -0.40 V (vs Ag/

AgCl), we could observe the slow disappearance of the

signal corresponding to the cation radical and the ap-

pearance of the signal due to the anion radical 10a ^-•. The

corresponding signal was the same as the species ob-

tained by chemical reduction, which is a well-resolved

triplet (g ) 2.0047, a_H) 2.51 G). Using the same

experimental procedure for triad 9 (Figure 9), we ob-

served that the ESR spectrum for the cation radical 9^+•

consisted of a poorly resolved quintet (g ) 2.0074) and,

for the anion radical 9^-•, of a quintet having the second

and fourth lines considerably broader than the other

three. The ESR signal of the anion radical was very

The presence on the same molecule of electron donor

and acceptor(s) moieties allows the successive generation

(30) Zhao, X.; Imahori, H.; Zhan, C.-G.; Sakata, Y.; Iwata, S.;

Kitagawa, T. J . Phys. Chem. 1997, 101, 622.

J . Org. Chem, Vol. 69, No. 6, 2004 2171

Dumur et al.

F IGURE 10. Intramolecular electron transfer proccess using the TTF as a bridge in the purely class II mixed-valence Q-TTF-

Q^-•system.

SCHEME 4. Electr on Exch a n ge th r ou gh th e TTF Br id ge betw een th e Tw o Qu in on ic Cen ter s

similar (although much more intense) to the one obtained

330 to 340 K), the spectra were characterized by cou-

plings with two more equivalent protons (five lines 1:4:

6:4:1, a_H) 1.23 G (4H)).³³As the temperature was

gradually decreased from 340 to 260 K, alternant lines

broadened due to the dynamic electron exchange between

both quinone electrophores through the TTF bridge

(Scheme 4).³⁴The low-temperature spectra of Q-TTF-

Q^-•unequivocally demonstrated that the odd electron

was localized on one quinone unit at the ESR time scale

and the activation energy barrier was overcome by

thermal stimulus to promote an intramolecular electron

transfer (IET) process.¹⁷It is important to indicate that

this IET process can only be studied in all its extension

using a 10:1 mixture of ethyl acetate/tert-butyl alcohol.

Due to the high insolubility of the Q-TTF-Q^-•mixed-

valence species, it was not possible to perform a quan-

titative study of the IET process by vis-NIR spectros-

copy.

+

from the ethyl acetate solution of solid 9^-•‚P (C₆H₅)₄

.

The specific features observed in the ESR spectrum for

the anion radical 9^-•can be considered as the signature

of a dynamic process observed in the ESR time scale.³¹

Taking into account that the cyclic voltammogram of the

Q-TTF-Q triad 9 suggested an effective electronic

coupling between both quinone centers by the presence

of two distinguishable reduction processes (∆E ) 80 mV),

the dynamic process can be attributed to the electron

transfer between both quinones. To characterize this

process, we performed the temperature dependence study

of the ESR spectra of the mixed-valence species 9^-•. For

comparison purposes, the anion radical of dyad 10a was

also investigated in the same way. Both species were

generated by chemical reduction with Cu metal in

different solvents containing tetraphenylphosphonium

bromide.

The characteristic ESR spectrum of the anion radical

TTF-Q^-•10a ^-•that consists of three lines with 1:2:1

intensities was singularly invariant over a wide temper-

ature range between 270 and 325 K in CH₂Cl₂and

between 260 and 340 K in a 10:1 mixture of ethyl acetate/

tert-butyl alcohol. On the contrary, the ESR spectrum of

the anion radical Q-TTF-Q^-•, prepared under the same

conditions, changed upon cooling from 340 to 260 K.³²

Thus, whereas the spectrum at 260 K was essentially

identical with that of the analogue TTF-Q^-•(three 1:2:1

lines, a_H) 2.47 G (2H)), at higher temperatures (from

We have clearly demonstrated for the first time that

TTF can be used as a bridge promoting electron conduc-

tion between two redox centers and that the triad 9 is

therefore the prototype of mixed-valence compound able

to undergo fast intramolecular electron transfer through

this bridge (Figure 10).³⁵

With the aim of developing devices using the direct

electronic conduction through single molecules,³⁶our

interest was then focused on the study of the role of

various parameters governing the IET rates. The dynam-

(33) As the coupling constant a_His dependent on the spin density,

the delocalization of the electron over both quinones requires that this

(31) Weil, J . A.; Bolton, J . R.; Wertz, J . E. Electron Paramagnetic

Resonance; J ohn Wiley & Sons: New York, 1994.

coupling constant is two times less for compound 9 than for 10a : a_H

)

(32) Spectra were recorded at the very beginning of the reduction

process. At this stage, the major species present in the solution is the

ESR silent neutral compound 9. The observed ESR signal is due to

the anion radical, since for statistical reasons dianion radical must

have a negligible concentration.

(8πg_e/3g_o)γ_Hâ_HF_H(r_H). g_e/g_ois the ratio of the isotropic g value for the

radical to that of the free electron; γ_Hand â_Hare the gyromagnetic

nuclear ratio and the nuclear magneton, respectively, and F_S(r_H) is the

spin density on the nucleus of the hydrogen atom.

(34) Hudson, A.; Luckhurst, G. R. Chem. Rev. 1969, 69, 1961.

2172 J . Org. Chem., Vol. 69, No. 6, 2004

Novel Fused D-A Dyad and A-D-A Triad

F IGURE 12. Segregated stacks of D-A-D or A-D-A

systems.

SCHEME 5. Cr ysta llogr a p h ic a n d Sin gle-Cr ysta l

IR Stu d ies

F IGURE 11. ESR spectra of Q-TTF-Q^-•P(C₆H₅)₄⁺at 300 K,

generated “in situ” in different solvents. (A) Dichloromethane,

(B) ethyl acetate, (C) ethyl acetate/ tert-butyl alcohol 10:1, and

(D) tert-butyl alcohol.

ics of the intramolecular exchange process was simulated

using the Heinzer program,³⁷and first-order rate con-

stants were extracted by fitting the experimental spectra.

The values obtained by simulation of all spectra obtained

in a 10:1 mixture of ethyl acetate/tert-butyl alcohol led

to a linear Arrhenius plot over the range 340-260 K,

giving the following activation parameters: E_act) 7.96

coupled redox centers as indicated by cyclic voltammetry

results. This system can be compared with polyacene

diquinones 24-26 as fused weak donors and acceptors

previously reported (Scheme 5). It was also demonstrated

that the odd electron of the anion radical of 24 was

delocalized,³⁹and on the contrary, the anion radicals

derived from 25 and 26 were not delocalized and could

then formally be considered as mixed-valence species.⁴⁰

Indeed, the optical spectra suggested that the unpaired

electron on these anion radicals were localized on each

subunit and was hopping from one side to another. Such

an interpretation was confirmed by temperature-variable

ESR spectra, and it would be interesting to note that the

activation parameters previously reported for the anion

radical of anthracene-diquinone 26⁴¹were close to those

determined for the anion radical Q-TTF-Q^-•.

Cr ysta llogr a p h ic a n d Sin gle-Cr ysta l IR Stu d ies.

The packing mode in the crystals of these materials is a

crucial parameter of their potential ability to reach

conductivity.¹⁸To obtain such conducting-linked donor-

acceptor complexes, the most important architectural

requirement was the aggregation in the solid state of both

donors (D) and acceptors (A) in segregated stacks, as

extended in the approach of D-A-D⁴²and A-D-A⁴³

systems for which the tendency to produce the corre-

sponding stacking motifs was observed (Figure 12).

Although the weak donor and acceptor character of

both moieties usually implies mixed stacks, diquinone

derivatives can serve as an example of the A-D-A motif

characterized by segregated stacking, showing an almost

ideal one-dimensional array of quinone and phenyl

kcal/mol; log A ) 13.9 (∆G^q

) 6.4 kcal/mol, ∆H^q

)

298K

7.4 kcal/mol, and ∆S^q) 3.1 eu). As expected, the rate

constant of the IET process varied with the solvent used

due to the energy variation resulting from solvent

reorganization.³²In Figure 11, the differences in the rate

constant at 300 K in dichloromethane, ethyl acetate, tert-

butyl alcohol, and a 10:1 mixture of ethyl acetate/tert-

butyl alcohol were clearly observed by the variation of

the ESR spectra.

The Q-TTF-Q^-•species is therefore a prototypical

class II mixed-valence system³⁸involving moderately

(35) Other organic systems presenting IET between redox centers

have been previously reported: (a) Nelsen, F. S.; Thomson-Colon, J .

A.; Katfory, M. J . Am. Chem. Soc. 1994, 116, 1589. (b) Bonvoisin, J .;

Launay, J .-P.; Rovira, C.; Veciana, J . Angew. Chem., Int. Ed. Engl.

1994, 33, 2106. (c) Lahlil, K.; Moradpour, A.; Bowlas, C.; Menou, F.;

Cassoux, P.; Bonvoisin, J .; Launay, J .-P.; Dive, G.; Dehareng, D. J .

Am. Chem. Soc. 1995, 117, 9995. (d) Nelsen, F. S.; Ismagilov, R. F.;

Trieber, D. A. Science 1997, 278, 846. (e) Lambert, C.; No¨ll, G. Angew.

Chem., Int. Ed. 1998, 37, 2107. (f) Lambert, C.; No¨ll, G. J . Am. Chem.

Soc. 1999, 121, 8434. (g) Ruiz-Molina, D.; Sedo´, J .; Rovira, C.; Veciana,

J . In Handbook of Advanced Electronic and Photonic Materials and

Devices; Nalwa, H. S., Ed.: Academic Press: San Diego, 2001; Vol. 3,

p 303. (h) Launay, J . P. Chem. Soc. Rev. 2001, 30, 386. (i) Rovira, C.;

Ruiz-Molina, D.; Elsner, O.; Vidal-Gancedo, J .; Bonvoisin, J .; Launay,

J .-P.; Veciana, J . Chem.sEur. J . 2001, 7, 240. (j) Mayor, M.; Bu¨schel,

M.; Fromm, K. M.; Lehn, J .-M.; Daub, J . Chem. Eur. J . 2001, 7, 1266.

(k) Lambert, C.; No¨ll, G.; Schelter, J . Nat. Mater. 2002, 1, 69. (l)

Lindeman, S. V.; Rosokha, S. V.; Sun, D.; Kochi, J . K. J . Am. Chem.

Soc. 2002, 124, 842.

(36) (a) Bumm, L. A.; Arnold, J .; Cygan, M. T.; Dunbar, T. D.;

Burgin, T. P.; J ones, L. II; Allara, D. L.; Tour, J . M.; Weiss, P. S. Science

1996 271, 1705. (b) Reed, M. A.; Zhou, C.; Muller, C. J .; Burgin, T. P.;

Tour, J . M. Science 1997, 278, 252. (c) Metzger, R. M. Acc. Chem. Res.

1999, 32, 950. (d) Collier, C. P. Wong, E. W.; Belohradsky, M.; Raymo,

F. M.; Stoddart, J . F.; Kuekes, P. J .; Williams, R. S.; Heath, J . R.

Science 1999, 285, 391. (e) J oachim, C.; Gimzewski, J . K.; Aviram, A.

Nature 2000, 408, 541. (f) Tour, J . M. Acc. Chem. Res. 2000, 33, 791.

(g) Batchtold, A.; Hadley, P.; Nakanishi, T.; Dekker, C. Science 2001,

294, 1317. (h) Scandola, F., Chiorboli, C., Indelli, M. T., Rampi, M. A.,

Eds.; Electron Transfer in Chemistry; Wiley-VCH: New York, 2001;

Vol. 3.

(38) Robin, M. B.; Day, P. Adv. Inorg. Chem. Radiochem. 1967, 10,

247. Mixed-valence compounds are classified in three categories: (a)

the redox centers are completely localized and behave as separated

entities (class I), (b) intermediate coupling between the mixed-valence

centers exists (class II), or (c) the system is completely delocalized and

the intermediate redox states are attributed to the redox centers (class

III).

(39) J ozefiak, T. H.; Miller L. L. J . Am. Chem. Soc. 1987, 109, 6560.

(40) J ozefiak, T. H.; Almlo¨f, J . E.; Feyereisen, M. W.; Miller, L. L.

J . Am. Chem. Soc. 1989, 111, 4105.

(41) Rak, S. F.; Miller, L. L. J . Am. Chem. Soc. 1992, 114, 1388.

(42) Becker, J . Y.; Bernstein, J .; Bittner, S.; Levi, N.; Shaik, S. S.;

Zer-Zion, N. J . Org. Chem. 1988, 53, 1689 and references therein.

(43) Le Paillard, M. P.; Robert, A.; Garrigou-Lagrange, C.; Delhaes,

P.; Le Maguere`s, P.; Ouahab, L.; Toupet, L. Synth. Met. 1993, 58, 233.

(37) Heinzer, J . Mol. Phys. 1971, 22, 167; Quantum Chemistry

Program Exchange 1972, No. 209. We thank Prof. A. Lund for a copy

of this program.

J . Org. Chem, Vol. 69, No. 6, 2004 2173

Dumur et al.

SCHEME 6

TABLE 2. Bon d Len gth s a n d In tr a m olecu la r

In ter a ction s in th e Tr ia d 9 Deter m in ed by th e X-r a y

Cr ysta llogr a p h ic Str u ctu r e a n d DF T Ca lcu la tion s

a

b

C₁-C₁

C₁-S

S-C₃

crystallographic 3.01(2) 3.22(3) 1.340(9) 1.769(4) 1.739(5)

distance (Å)

F IGURE 13. Regular stacking mode of TTF-diquinone

molecules in the structure of 9‚CH₂Cl₂.

calculated

distance (Å)

3.030

3.277

1.349

1.792

1.751

In fact, two consecutive molecules in stacks were

shifted one from each other along the main molecular

axis leading to a bond over cycle-type overlap between

the central CdC bond of the TTF core and the benzene

cycle of the acceptor (Figure 14a). Moreover, the bis(1,4-

benzoquinone)TTF intermolecular distance between the

face-to-face planes of the donor and acceptor moieties

(d ) 3.60 Å) showed a significant overlap and may be

compared to the plane-to-plane distances between donor

and acceptor molecules in crystal packings of mixed-stack

intermolecular charge transfer complexes.⁴⁷For example,

the interplanar distance between donor and acceptor

molecules in the charge-transfer complex octamethylene-

TTF-TCNQ is 3.53 Å. However, compared to the D...A

interactions, compound 9 did not exhibit the infinite

mixed stacking ...A..D..A..D.. motif: as a consequence of

the shift mode of molecules, only [A...D...A]-type “triplets”

were encountered in stacks along the direction perpen-

dicular to the molecular plane (Figure 14b).

C₃-C₂

C₃-C₄

C₄-O

C₄-C₅

C₅-C₆

crystallographic 1.349(6) 1.471(6) 1.227(6) 1.462(7) 1.342(7)

distance (Å)

calculated

distance (Å)

1.356

1.480

1.224

1.489

1.342

moieties for 27 and two-dimensional stacking for 28

(Scheme 6).⁴⁴

Fine blue needles were obtained by slow evaporation

of a solution containing the fused A-D-A system 9 in

CH₂Cl₂/petroleum ether as a mixture of solvents. The

X-ray crystallographic analysis revealed that the mol-

ecule is nearly planar, and only the carbonyl groups

protruded from the molecular plane by 4°. This could be

compared with the repulsion of the sulfur and oxygen

lone pairs suggested in the case of 19, for which the

crystal structure showed that the carbonyl group pro-

truded from the molecule plane by 2-10°.²⁶Intramolecu-

lar S...O interactions were also shown [3.01(2) Å] between

the oxygen atom of the quinone and the sulfur atom of

TTF, this distance being shorter than the sum of the van

der Waals radii of both atoms (d ) 3.25 Å).⁴⁵Moreover,

calculated bond lengths and intramolecular interactions

were in good agreement with the corresponding distances

determined from the crystallographic structure (Table

2).⁴⁶

It must be noted that in the prototypical D-A-D

system previously reported,^40,48i.e., the dibenzylTCNQ

compound involving a strong acceptor (TCNQ) and weak

donors (benzyl), isolated triplets D...A...D formed by the

central TCNQ ring of a molecule and two phenyl rings

of two neighboring molecules were clearly observed.

However, in this last structure, X-ray analysis also

revealed a segregated mode of stacking for TCNQ parts,¹⁷

which differed from the observed situation in 9 where

TTF moieties did not form segregated stacks. The inter-

stack CH(benzene cycle)...O(quinone) hydrogen bond

interactions were of particular interest and seemed to

strongly influence the crystal packing of triad 9, leading

The packing arrangement of A-D-A molecules, in-

volving a strong donor (TTF) and a weak acceptor

(benzoquinone), was characterized by regular stacks

along the a axis (Figure 13), as encountered in the vast

majority of weak charge transfer complexes.

2

to cyclic R₂(8) motifs, according to Etter’s representa-

tion,⁴⁹and cavities in which disordered solvent molecules

(CH₂Cl₂) were inserted (Figure 15).

(44) (a) Becker, J . Y.; Bernstein, J .; Bittner, S.; Shaik, S. S. Pure

Appl. Chem. 1990, 62, 467. (b) Becker, J . Y.; Bernstein, J .; Bittner, S.;

Giron, Y.; Harlev, E.; Kaufman-Orenstein, L.; Peleg, D.; Shahal, L.;

Shaik, S. S. Synth. Met. 1991, 41-42, 2523.

(45) Bondi, A. J . Phys. Chem. 1964, 68, 441.

(47) Chasseau, D.; Gaultier, J .; Fabre, J . M.; Giral, L. Acta Crys-

tallogr. 1982, B38, 1632.

(48) Becker, J . Y.; Bernstein, J .; Bittner, S.; Levi, N.; Shaik, S. S.

J . Am. Chem. Soc. 1983, 105, 4468.

(46) Bond distances suggest a weak intramolecular charge transfer

from TTF to benzoquinone moiety; see: Guionneau, P.; Kepert, C. J .;

Bravic, D.; Chasseau, D.; Truter, M. R.; Kurmoo, M., Day, P. Synth.

Met. 1997, 86, 1973.

(49) Etter, M. C.; MacDonald, J . C. Acta Crystallogr. 1990, B46, 256.

2174 J . Org. Chem., Vol. 69, No. 6, 2004

Novel Fused D-A Dyad and A-D-A Triad

F IGURE 14. (left) Bond over cycle overlap type between two consecutive molecules in stacks and (right) schematic representation

of the packing arrangement showing the A..D..A triplets.

F IGURE 15. View of the crystal structure of 9‚CH₂Cl₂along the stack axis showing intermolecular hydrogen bonding (dashed

lines) and disordered CH₂Cl₂molecules.

chosen the light polarizations to maximize the differences

between the intensities of the IR bands. The electric

vector of the radiation made an angle of approximately

45 and 135 degrees with respect to the needle axis. In

addition to the IR features, the spectra displayed an

electronic broad absorption centered around 13 000 cm^-1

(1.6 eV, 770 nm). The band was clearly associated with

the intramolecular charge transfer transition identified

above in the solution spectra. However, the band was not

polarized, and a closer inspection of the spectra revealed

a slightly different position of the band maxima in the

two polarizations (the difference was about 500 cm^-1

;

notice the logarithmic scale in the wavenumber axis).

Given the mixed stack motif of the crystal structure, we

speculated that we observed two overlapping charge

transfer transitions, one intra- and the other intermo-

lecular. The two were orthogonal each other. If the above

supposition was correct, A-D-A would represent a good

example of a two-dimensional, “intra-inter” charge

transfer crystal.

F IGURE 16. Polarized absorption spectra of A-D-A 9 from

600 to 21 000 cm^-1. Notice the logarithmic wavenumber scale.

Beyond 4000 cm^-1, different beam splitters and polarizers have

been used. No cosmetic changes have been made to reduce the

noise or join the different spectral regions.

In any case, we have clearly shown that this fused and

perfectly planar A-D-A assembly involving a strong

donor (TTF) and a weak acceptor (quinone) had a high

propensity to crystallize in the crystallographic arrange-

ment characterized by the nonideal packing to reach

conductivity, in contrast to nonfused A-D-A or D-A-D

We have also obtained polarized IR and NIR-visible

(from 600 to 21 000 cm^-1) absorption spectra of A-D-A

crystal, as shown in Figure 16. The crystal plane was

not identified, but it is likely ac (Figure 13). We have

J . Org. Chem, Vol. 69, No. 6, 2004 2175

Dumur et al.

4,7-Dih yd r oxy-1,3-ben zod ith iole-2-th ion e 13. To a sus-

pension of the iminium salt 12 (9.80 g, 31 mmol) in 130 mL of

methanol was added by fractions sodium sulfide nonahydrate

(59.3 g, 0.246 mol) with vigorous stirring. After stirring at room

temperature for 3 h, the red solution was poured into a mixture

of glacial acetic acid (80 mL) and water (2 L). The solution

was stored in a refridgerator for 48 h, and then filtration

yielded 6.67 g (yield ) 98%) of pale yellow crystals. Mp )

239 °C (AcOH/MeOH) (lit.^19a238 °C).

systems 27 and 28, respectively. In fact, the electrical

conductivity measured on pellets using the four-probe

technique was estimated to be 10^-9and 2 × 10^-9S/cm

for fused D-A 10 and A-D-A 9 systems, respectively,

confirming the low degree of charge transfer in the

undoped state.

Con clu sion

4,7-Dia cetyloxy-1,3-ben zod ith iole-2-th ion e 14a . To a

suspension of hydroquinone 13 (7.12 g, 33 mmol) in 30 mL of

CH₂Cl₂were successively added 37 mL of triethylamine (0.263

mol) and 12.4 mL (0.132 mol) of acetic anhydride. After stirring

for 1 h, the mixture was partially concentrated. After addition

of 50 mL of petroleum ether, the precipitate was filtered and

washed with methanol, affording 7.9 g (yield ) 80%) of yellow

crystals. Mp ) 154 °C (CH₂Cl₂) (lit.^19a148-149 °C).

To control the stoichiometry between D and A, we have

developed an interesting approach consisting of synthe-

sizing TTF fused to acceptors such as p-benzoquinone.

The quinone moiety of 9 and 10 can be used as a

precursor for stronger acceptor moieties, e.g., DCNQI or

TCNQ.⁵⁰Consequently, work is in progress to improve

this acceptor ability of the quinone moiety in order to

reach unprecedented fused TTF-TCNQ (D-A) deriva-

tives and TCNQ-TTF-TCNQ (A-D-A). Quinone- or

TCNQ-based intramolecular donor-acceptor systems

constitute a promising field of applications due to the

interesting optoelectronic properties they can exhibit.

Moreover, with the aim of controlling the stacking of the

D-A system, the preparation of LB films⁵¹of bisdodecyl-

substituted derivative, as well as their possible rectifying

behavior, is also under study.

In addition, we have obtained a purely mixed-valence

compound 9^-•in which the existence of a temperature-

dependent intramolecular electron transfer has clearly

been established. The results we have just presented

unambiguously show that TTF is a suitable bridge for

promoting intramolecular electron transfer between two

redox centers. Such a system is of particular interest for

understanding electron-transfer processes for the design

of molecular wires.⁵²

4,7-Bis(ter t-bu tyld ip h en ylsilyloxy)-1,3-ben zod ith iole-

2-th ion e 14b. To a solution of hydroquinone 13 (6.48 g, 30

mmol) in 120 mL of DMF were successively added tert-

butyldiphenylchlorosilane (20.4 mL, 78 mmol) and imidazole

(10.2 g, 150 mmol). The mixture was stirred overnight at room

temperature. After addition of methanol (300 mL), the pre-

cipitate was filtered, and recrystallization furnished 17.68 g

(yield ) 86%) of yellow crystals. Mp ) 176 °C (CH₂Cl₂/

petroleum ether). Anal. Calcd for C₃₉H₄₀O₂S₃Si₂(693.10): C,

67.58; H, 5.82; S, 13.88. Found: C, 67.52; H, 5.84; S, 13.99.

4,7-Dia cetyloxy-1,3-ben zod ith iole-2-on e 15a . To a solu-

tion of compound 14a (4.95 g, 16.5 mmol) in CH₂Cl₂(150 mL)

and glacial acetic acid (110 mL) was added mercuric acetate

(13.09 g, 41.1 mmol). After stirring at room temperature for

15 min, the solution was filtered on Celite. The solution was

successively washed with water (3 × 150 mL), a saturated

solution of NaHCO₃(4 × 50 mL), and water (50 mL). The

organic layer was dried (MgSO₄) and concentrated. The residue

was purified by chromatography on silica gel (CH₂Cl₂).

Recrystallization using CH₂Cl₂/petroleum ether afforded

4.10 g of white crystals (yield ) 88%). Mp ) 164 °C (lit.^19a

163-164 °C).

4,7-Bis(ter t-bu tyld ip h en ylsilyloxy)-1,3-ben zod ith iole-

2-on e 15b. The same experimental procedure that afforded

15a was followed, starting from 2.68 g (8.9 mmol) of compound

14b. The residue was purified by chromatography on silica

gel (CH₂Cl₂/petroleum ether ) 1/4). Recrystallization using

CH₂Cl₂/petroleum afforded 2.16 g of white crystals (yield )

85%). Mp ) 180 °C. Anal. Calcd for C₃₉H₄₀O₃S₂Si₂(676.20):

C, 69.19; H, 5.96; S, 9.47. Found: C, 69.08; H, 5.98; S, 9.77.

Bis(1,4-d ia cetyloxy)d iben zotetr a th ia fu lva len e 16. A

solution of 9.94 g of compound 15a (35 mmol) in freshly

distilled triethyl phosphite (75 mL) was refluxed for 3 h and

30 min. After the solution was cooled, the precipitate was

filtered and the yellow crystals were washed with methanol

(4.20 g; yield ) 45%); mp > 280 °C (lit.^19a> 280 °C).

2,3-Bis(p en tylsu lfa n yl)-6,7-[3,6-bis(ter t-bu tyld ip h en yl-

silyloxy)b en zo]t et r a t h ia fu lva len e 18. To a solution of

0.62 g (1.5 mmol) of phosphonate 17 in 15 mL of anhydrous

THF was added, under an inert atmosphere at -78 °C,

1.0 mL (1.6 mmol) of n-BuLi (1.6 M in hexane). After the

solution was stirred for 10 min, a solution of dithiolone 15b

(0.51 g, 0.75 mmol, 1 equiv) in 15 mL of anhydrous THF was

added dropwise. After stirring for 3 h at room temperature,

the reaction mixture was concentrated and purified by chro-

matography on silica gel (CH₂Cl₂/petroleum ether 1/9 to

eliminate impurities and then 1/4 for the elution of compound

18) affording 0.65 g of yellow crystals (yield ) 90%); mp )

104 °C (CH₂Cl₂/petroleum ether); MS m/z (I%) 966 (M^+•, 100),

864 (8), 534 (9), 457 (26), 135 (15).

Exp er im en ta l Section

The general procedure is listed in Supporting Information.

The melting points are uncorrected. ¹H NMR (200 or 500 MHz)

spectra were measured with Me₄Si as an internal standard;

the δ and J values are given in parts per million and hertz,

respectively. The IR spectra are recorded in units of cm^-1

.

2,5-Dih yd r oxyp h en yl-1-p ip er id in ed ith ioa te 11. To a

solution of p-benzoquinone (5.40 g, 50 mmol) in a solution of

glacial acetic acid (24 mL) and DMF (24 mL) was added rapidly

at 0 °C a solution of the dithiocarbamate salt (12.2 g, 50 mmol)

in a mixture of DMSO (12 mL) and DMF (24 mL). The mixture

was stirred for 1 h before dilution with 500 mL of water.

Filtration of the precipitate yielded 13 g (yield ) 97%) of white

crystals. Mp ) 94-96 °C.

4,7-Dih yd r oxy-1,3-b en zod it h ioylid en -2-N-p ip er id in i-

u m Aceta te 12. p-Benzoquinone (5.22 g, 48 mmol) was added

to a solution of compound 11 (13 g, 48 mmol) dissolved in 250

mL of methanol, immediately yielding a red precipitate. The

mixture was stirred for an additional 30 min and then filtered.

The precipitate was washed with methanol and then dissolved

in 20 mL of glacial acetic acid, and the solution was heated

for 10 min at 80 °C. After the mixture was cooled, the addition

of 150 mL of acetone afforded after filtration 15.16 g (yield )

96%) of pale gray crystals. Mp ) 152-154 °C.

(50) For a review on TCNQ and DCNQI electron acceptors, see:

Mart´ın, N.; Segura, J . L.; Seoane, C. J . Mater. Chem. 1997, 7, 1661.

(51) Nadizadeh, H.; Mattern, D. L.; Singleton, J .; Wu, X.; Metzger,

R. M. Chem. Mater. 1994, 6, 268.

(52) (a) Creager, S.; Yu, C. J .; Bamdad, C.; O’Connor, S.; MacLean,

T.; Lam, E.; Chong, Y.; Olsen, G. T.; Luo, J .; Gozin, M.; Kayyem, J . F.

J . Am. Chem. Soc. 1999, 121, 1059. (b) Caroll, R. L.; Gorman, C. B.

Angew. Chem., Int. Ed. 2003, 41, 4378.

(2,3)-(6,7)-Bis(1,4-d ioxo-1,4-d ih yd r oben zo)tetr a th ia fu l-

va len e 9. To a solution of 106 mg (0.224 mmol) of TTF

derivative 16 in 15 mL on anhydrous THF was added a sodium

methanolate solution prepared by treatment of 50 mg (2.24

mmol) of sodium in 3 mL of anhydrous methanol. The green

2176 J . Org. Chem., Vol. 69, No. 6, 2004

Novel Fused D-A Dyad and A-D-A Triad

solution was stirred for 1 h at 60 °C, and then acidified by

addition of 426 mg (2.24 mmol) of p-toluenesulfonic acid

monohydrate. After the solution was stirred for 5 min, 107

mg of DDQ (0.471 mmol) was added and the solution was

stirred for 2 h at room temperature. After dilution with CH₂-

Cl₂, the organic layer was washed with brine, dried (MgSO₄),

and concentrated in vacuo. The purification on florisil (100-

200 mesh) column chromatography using CH₂Cl₂/EtOAc (99/

1) as a mixture of eluents followed by a recystallization in

CH₂Cl₂/petroleum ether afforded 46 mg of blue crystals (yield

) 57%): thermal gravimetric analysis (TGA) 240 °C (dec.);

IR(KBr) cm^-11656 (CdO), 1544 (CdC); MS m/z (I%) 364

(M^+•, 100), 226 (67), 88 (44).

Cr ysta llogr a p h ic Da ta of Com p ou n d 9. Single crystals

of (0.5 × 0.13 × 0.05 mm) were grown at 293 K by slow

evaporation of a CH₂Cl₂/petroleum ether solution containing

9: C₁₅H₆Cl₂O₄S₄, M ) 449.34 g/mol; monoclinic, P21/c; a )

5.829(1), b ) 10.355(2), c ) 14.429(3) Å, â ) 98.19(2)°, V )

862.0(3) Å³, Z ) 2, F_calcd) 1.731 g/cm³, λ(Mo KR) ) 0.71073 Å,

6445 reflections (2 < θ < 25°) were collected at 293 K, 1626

unique reflections and 842 reflections with I > 2σ(I) used in

refinements, 129 parameters, R ) 0.0537, wR ) 0.0885.

Ca tion Ra d ica l 9^+•‚CF ₃SO₃^-. To a solution of 46.7 mg (0.128

mmol) of Q-TTF-Q 9 in 1.5 mL of CH₃CN was added 20.61

mg (0.064 mmol) of iodobenzene diacetate PhI(OAc)₂and then

22.4 µL (0.256 mmol) of trifluoromethanesulfonic acid. After

the mixture was stirred for 1 h, the resultant black precipitate

was filtered and washed with diethyl ether (10 mL), toluene

(10 mL), and CH₂Cl₂(10 mL) successively. The black precipi-

tate (36 mg) was isolated in 55% yield: IR (KBr) cm^-11658

(CdO), 1255, 1027, 636 (SO₃^-). Anal. Calcd for C₁₅H₄F₃O₇S₅

(514.52): C, 35.02; H, 0.98; S, 31.16. Found: C, 34.88; H, 1.08;

S, 31.39.

162 °C); MS m/z (I%) 264 (M^+•, 100), 188 (38), 160 (12), 132

(10), 104 (43), 76 (30).

4,9-Dih yd r oxyn a p h th o[2,3-d ]-1,3-d ith iole-2-on e 20. A

solution of 5 g (18.9 mmol) of compound 19 was shaken in a

separating funnel in 200 mL of an aqueous solution of sodium

dithionite (Na₂S₂O₄) (4% w/w). The initial red solution became

yellow, and the organic layer was washed with water, dried

(MgSO₄), and then concentrated to afford 3.80 g of yellow

powder (yield ) 75%); mp ) 222-224 °C (CH₂Cl₂) (lit.^16a222-

224 °C).

4,9-Dia cetyloxyn a p h th o[2,3-d ]-1,3-d ith iole-2-th ion e 21.

To a suspension of 3.8 g (14.3 mmol) of compound 20 in 40

mL CH₂Cl₂were successively added 17 mL of triethylamine

(121 mmol) and 6 mL (60.5 mmol) of acetic anhydride. After

the mixture was stirred for 1 h, the yellow precipitate was

filtered and 3.92 g of yellow crystals was obtained (yield )

79%); mp ) 240 °C (CH₂Cl₂).

4,9-Dia cetyloxyn a p h th o[2,3-d ]-1,3-d ith iole-2-on e 22. To

a solution of 3.92 g (11.2 mmol) of compound 21 in 100 mL of

CH₂Cl₂and 80 mL of glacial acetic acid was added 9.08 g (28.5

mmol) of mercuric acetate. After stirring for 15 min at room

temperature, the reaction mixture was filtered on Celite. The

filtrate was successively washed with water (2 × 100 mL), a

saturated aqueous NaHCO₃solution (2 × 100 mL), and then

water (50 mL). The organic layer was dried (MgSO₄), and

the solvent was concentrated to afford 3.6 g of white crystals

(yield ) 96%).

Bis(1,4-d ia cet yloxyn a p h t h o)t et r a t h ia fu lva len e 23. A

solution of 3.6 g (10.8 mmol) of compound 4 in 25 mL of freshly

distilled triethyl phosphite was refluxed for 1 h. After the

solution was cooled, the precipitate was filtered and washed

with methanol to afford 2 g of yellow crystals (yield ) 53%):

mp > 300 °C; MS m/z (I%) 636 (M^+•, 100), 622 (17), 600 (30),

558 (15), 506 (25).

An ion Ra d ica l 9^-•‚P (C₆H₅)₄⁺. Q-TTF-Q 9 (5 mg) was

dissolved in 2 mL of a 0.2 M solution of tetraphenylphospho-

nium bromide in anhydrous CH₂Cl₂. A Cu wire was introduced

and led to react at room temperature for 24 h. After removal

of Cu wire, the reaction mixture was centrifuged and the

precipitate washed with CH₂Cl₂several times, giving 6 mg of

greenish powder (62% yield): IR (KBr) cm^-1; 1633, 1615

(CdO), 760, 723, 691 (P-C). UV-vis (ethyl acetate) λ (nm)

421, 516. Anal. Calcd for C₃₈H₂₄O₄PS₆(703.84): C, 64.85; H,

3.44; S, 18.22. Found: C, 65.11; H, 3.00; S, 17.72.

2,3-Bis(p en tylsu lfa n yl)-6,7-(1,4-d ioxo-1,4-d ih yd r oben -

zo)tetr a th ia fu lva len e 10a . To a solution of 100 mg (0.1

mmol) of TTF 18 in 8 mL of anhydrous THF was added 0.26

mL (0.26 mmol) of n-Bu₄NF (1 M in THF). After the solution

was stirred for 30 min at room temperature, 112 mg (0.14

mmol) of p-benzoquinone was added, and stirring was contin-

ued for an additional 5 min. The purification on florisil (100-

200 mesh) column chromatography using CH₂Cl₂/petroleum

ether (1/1) followed by a recystallization in CH₂Cl₂/petroleum

ether afforded 38 mg of green crystals (yield ) 75%): thermal

gravimetric analysis (TGA) 290 °C dec.; IR (KBr) cm^-11650;

MS m/z (I%) 488 (M^+•, 100), 384 (13), 347 (12), 259 (10), 226

(22). Anal. Calcd for C₂₀H₂₄O₂S₆(488.77): C, 49.15; H, 4.95;

S, 39.36. Found: C, 49.11; H, 5.00; S, 37.92.

(2,3)-(6,7)-Bis(1,4-n a p h t h oq u in on e )t e t r a t h ia fu lva -

len e 8. To a suspension of 200 mg (0.31 mmol) of compound

23 in 25 mL of anhydrous THF was added a solution of 170

mg (3.14 mmol) of sodium methoxide in 5 mL of anhydrous

methanol. The green suspension was heated for 4 h at 80 °C.

After the suspension was cooled at 0 °C, 597 mg of p-

toluenesulfonic acid monohydrate (3.14 mmol) and 148 mg

(0.65 mmol) of DDQ were added. After the mixture was stirred

for an additional 2 h at room temperature, the precipitate was

filtered, washed with THF to afford 100 mg of green crystals

(yield ) 68%): mp > 300 °C; MS m/z (I%) MALDI 464 (M^+•);

IR (KBr) cm^-11654 (CdO).

Ack n ow led gm en t. This work was partially sup-

ported by grants from the MENRT for Nicolas Gautier,

the “Ville d’Angers” for Fre´de´ric Dumur, DGI-Spain

BQU2000-1157, and DURSI-Catalunya 2001SGR-00362.

This research was undertaken as part of the European

collaborative COST Program (Action D14/0004/99).

Su p p or t in g In for m a t ion Ava ila b le: ¹H and ¹³C NMR

1

and IR data with assignment of all signals; H and ¹³C NMR

4,9-Dioxo-4,9-d ih yd r on a p h t h o[2,3-d ]-1,3-d it h iole -2-

on e 19. To a suspension of 16.75 g of finely powdered K₂S (152

mmol) in 40 mL of DMF was added 7.5 mL (125 mmol) of CS₂.

After the mixture was stirred for 2 h at room temperature,

14.2 g (62.5 mmol) of 2,3-dichloronaphthoquinone was added.

After stirring for 30 min, the reaction mixture was diluted with

dichloromethane, washed with water, and dried (MgSO₄), and

the solvents were partially concentrated. The product was

precipitated by addition of methanol, and 10.7 g of red crystals

was isolated (yield ) 65%): mp ) 164 °C (CH₂Cl₂) (lit.^16a160-

spectra of dyad 10a ; IR spectra of triad 9 and cation radical

9^+•‚CF ₃SO₃in KBr pellets; ESR spectrum of cation radical

-

9^+•‚CF ₃SO₃^-in acetone solution; IR spectrum of anion radical

9^-•‚P (C₆H₅)₄in KBr pellets; ESR spectrum of the solid

+

9^-•‚P (C₆H₅)₄⁺in ethyl acetate at 300 K; evolution of the UV-

vis-NIR spectrum at the beginning of the reduction of A-D-A

9; and crystallographic data for triad 9. This material is

available free of charge via the Internet at http://pubs.acs.org.

J O035689F

J . Org. Chem, Vol. 69, No. 6, 2004 2177

Article Doi

Novel Fused D-A Dyad and A-D-A Triad Incorporating Tetrathiafulvalene and p-Benzoquinone

DOI: 10.1021/jo035689f

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