Electron acceptors of the fluorene series. 9. Derivatives of 9-(1,2- dithiol-3-ylidene)-, 9-(1,3-dithiol-2-ylidene)-, and 9-(1,3-selenathiol-2- ylidene)fluorenes: Synthesis, intramolecular charge transfer, and redox properties

Article abstract of DOI:10.1021/jo990100r

The synthesis and physical properties of four series of novel fluorene push-pull compounds (4-7) of the D-π-A type with intramolecular charge transfer (from 1,3- and 1,2-dithiole and 1,3-selenathiole donor (D) moieties) are described. The nature of the heteroatom (S or Se) in the donor fragment has no effect on the maxima of intramolecular absorption bands (λ(ICT)), whereas a change of position of the heteroatoms in the dithiole moiety from 1,3 to 1,2 leads to a substantial bathochromic shift in λ(ICT). Solvatochromism, thermochromism, and negative halochromism in these compounds are demonstrated. Cyclic voltammograms of 4-7 exhibit two, separate, single- electron reversible redox waves, the potentials of which (as well as the ICT energies in the molecules) are quantitatively described by σ(p)^- constants of the substituents in the fluorene ring. Compounds 4-7 exhibit reversible salt formation in sulfuric acid, and for compound 5g in diluted sulfuric acid an additional absorption in the near-IR region has been observed that we attribute to radical species formation from the equilibrium [5g-H]⁺ + 5g ? 5g·⁺ + [Sg-H]·.

Full text of DOI:10.1021/jo990100r

VOLUME 64, NUMBER 19
SEPTEMBER 17, 1999
© Copyright 1999 by the American Chemical Society
Electr on Accep tor s of th e F lu or en e Ser ies. 9.1 Der iva tives of
9-(1,2-Dith iol-3-ylid en e)-, 9-(1,3-Dith iol-2-ylid en e)-, a n d
9-(1,3-Selen a th iol-2-ylid en e)flu or en es: Syn th esis, In tr a m olecu la r
Ch a r ge Tr a n sfer , a n d Red ox P r op er ties
Dmitrii D. Mysyk,† Igor F. Perepichka,*,‡ Dmitrii F. Perepichka,‡ Martin R. Bryce,*,§
Anatolii F. Popov,‡ Leonid M. Goldenberg,§,|, and Adrian J . Moore§
Department of Chemistry, Donetsk Technical University, Donetsk 340000, Ukraine, L. M. Litvinenko
Institute of Physical Organic & Coal Chemistry, National Academy of Sciences of Ukraine,
Donetsk 340114, Ukraine, Department of Chemistry, University of Durham, Durham DH1 3LE, U.K., and
School of Engineering, University of Durham, Durham DH1 3LE, U.K.
Received J anuary 20, 1999
The synthesis and physical properties of four series of novel fluorene push-pull compounds (4-7)
of the D-π-A type with intramolecular charge transfer (from 1,3- and 1,2-dithiole and 1,3-
selenathiole donor (D) moieties) are described. The nature of the heteroatom (S or Se) in the donor
fragment has no effect on the maxima of intramolecular absorption bands (λICT), whereas a change
of position of the heteroatoms in the dithiole moiety from 1,3 to 1,2 leads to a substantial
bathochromic shift in λICT. Solvatochromism, thermochromism, and negative halochromism in these
compounds are demonstrated. Cyclic voltammograms of 4-7 exhibit two, separate, single-electron
reversible redox waves, the potentials of which (as well as the ICT energies in the molecules) are
quantitatively described by σp- constants of the substituents in the fluorene ring. Compounds 4-7
exhibit reversible salt formation in sulfuric acid, and for compound 5g in diluted sulfuric acid an
additional absorption in the near-IR region has been observed that we attribute to radical species
formation from the equilibrium [5g-H]+ + 5g a 5g•+ + [5g-H]•.
In tr od u ction
plexes (CTC).3,4 Polynitro-9-fluorenones and polynitro-9-
dicyanomethylenefluorenes2c,5 whose ability to form CTC
is widely used to sensitize the photoconductivity of poly-
9-Substituted polynitrofluorenes combining high elec-
tron affinity2 and an extended π-electron system are of
considerable interest for studies on charge-transfer com-
(3) (a) Mysyk, D. D.; Perepichka, I. F.; Sokolov, N. I. J . Chem. Soc.,
Perkin Trans. 2 1997, 537. (b) Mysyk, D. D.; Sivchenkova, N. M.;
Kampars, V. E.; Neilands, O. Ya. Izv. Akad. Nauk Latv. SSR, Ser.
Khim. 1987, 621; Chem. Abstr. 1988, 109, 92406q. (c) Mysyk, D. D.;
Sivchenkova, N. M.; Kampars, V. E.; Neilands, O. Ya. Izv. Akad. Nauk
Latv. SSR, Ser. Khim. 1984, 332. (d) Mysyk, D. D.; Perepichka, I. F.;
Sivchenkova, N. M.; Kampars, V. E.; Neilands, O. Ya.; Kampare, R.
B. Izv. Akad. Nauk Latv. SSR, Ser. Khim. 1984, 328; Chem. Abstr.
1984, 101, 210699q.
(4) (a) Sirotkina, E. E.; Poleschuk, O. Kh.; Pirogova, I. D. Izv. SO
AN SSSR, Ser. Khim. Nauk 1990, 56. (b) Sirotkina, E. E.; Filimonov,
I. L.; Trushnikov, V. N.; Filimonov, V. D. Izv AN SSSR, Ser. Khim.
1985, 90. (c) Cherkasov, Yu. A.; Piryatinskii, Yu. P.; Kirpach, Yu. N.;
Alexandrova, E. L. Opt. Spektrosk. 1989, 67, 352.
† Department of Chemistry, Donetsk Technical University.
‡ Institute of Physical Organic & Coal Chemistry, Donetsk.
§ Department of Chemistry, University of Durham.
School of Engineering, Univeristy of Durham.
| On leave from the Institute for Chemical Physics Research,
Russian Academy of Sciences, Chernogolovka, Moscow Region 142432,
Russian Federation.
(1) (a) Part 8: Skabara, P. J .; Serebryakov, I. M.; Perepichka, I. F.
J . Chem. Soc., Perkin Trans. 2 1999, 505. (b) Mysyk, D. D.; Perepichka,
I. F. Presented in part at the 16th International Symposium on Organic
Chemistry of Sulfur (ISOCS-16), Merseburg, J uly 10-15, 1994;
Phosphorus, Sulfur, Silicon 1994, 95-96, 527.
(2) (a) Kampars, V. E.; Neilands, O. Ya. Usp. Khimii 1977, 46, 945;
Chem. Abstr. 1977, 87, 101429y. (b) Chen, E. C. M.; Wentworth, W.
E. J . Chem. Phys. 1975, 63, 3183. (c) Mukherjee, T. K. Tetrahedron
1968, 24, 721.
(5) (a) Mukherjee, T. K.; Levasseur, L. A. J . Org. Chem. 1965, 30,
644. (b) Kuder, J .; Pochan, J . M.; Turner, S. R.; Hinman, D. F. J .
Electrochem. Soc.: Electrochem. Sci. Technol. 1978, 125, 1750.
10.1021/jo990100r CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/25/1999

6938 J . Org. Chem., Vol. 64, No. 19, 1999
Mysyk et al.
Ch a r t 1
N-vinylcarbazole (PVK) and related carbazole-containing
polymers6 are the most widely known fluorene acceptors.
The attachment of electron-donating groups to electron-
acceptor compounds of the fluorene series results in
intramolecular charge transfer (ICT) from the donor
moiety into the acceptor fluorene ring1,7-10 that is mani-
fested in the appearance of long-wavelength bands in the
visible or even in the near-IR region of their electron
absorption spectra. Recently, it has been shown that
fluorene acceptors with ICT can efficiently sensitize the
photoconductivity of carbazole-containing polymers in
their ICT spectral region,7-9,11-14 offering applications for
photoconductive materials with selective spectral zones
of photosensitivity, and control their charge (electron and
hole) generation and transport properties. Especially
interesting results were obtained on fluorene acceptors
with ICT from a 1,3-dithiole9,12 donor moiety. Sensitiza-
tion of the photoconductivity of poly-N-(2,3-epoxypropyl)-
carbazole (PEPC) films by acceptors 1a -d (R1 ) R2
)
NO2) increased the holographic sensitivity (He-Ne laser,
λ ) 632.9 nm) of photothermoplastic materials by 10-
20 times as compared to the widely used sensitizer 2,4,7-
trinitro-9-fluorenone (2). Redox and ICT investigations
of this class of acceptors (1d , 3)9 established that they
are very promising candidates for electron or hole trans-
port materials with high photosensitivity in long-
wavelength and near-IR regions of the spectrum (Chart
1).
Other promising applications of such push-pull com-
pounds are the design of single-component organic semi-
conductors,15,16 nonlinear optical materials,10,17,18 and
(6) (a) Hoegl, H.; Barchietto, G.; Tar, D. Photochem. Photobiol. 1972,
16, 335. (b) Enomoto, T.; Hatano, M. Die Makromol. Chem. 1974, 175,
57. (c) Perepichka, I. F.; Mysyk D. D.; Sokolov, N. I. In Current Trends
in Polymer Photochemistry; Allen, N. S., Edge, M., Bellobono I. R., Selli,
E., Eds.; Ellis Horwood: New York, London, 1995; p 318. (d) Getman-
chuk, Yu. P.; Sokolov, N. I. In Fundamentals of Optical Memory and
Medium; Vyshcha Shkola: Kiev, 1983; Vol. 14; p 11 (in Russian).
(7) Semenenko, N. M.; Abramov, V. N.; Kravchenko, N. V.; Trushina,
V. S.; Buyanovskaya, P. G.; Kashina, V. L.; Mashkevich, I. V. Zh. Org.
Khim. 1985, 55, 324.
(8) Perepichka, I. F.; Popov, A. F.; Orekhova, T. V.; Bryce, M. R.;
Vdovichenko, A. N.; Batsanov, A. S.; Goldenberg, L. M.; Howard, J . A.
K.; Sokolov, N. I.; Megson, J . L. J . Chem. Soc., Perkin Trans. 2 1996,
2453.
(9) Perepichka, I. F.; Perepichka, D. F.; Bryce, M. R.; Goldenberg,
L. M.; Kuz’mina, L. G.; Popov, A. F.; Chesney, A.; Moore, A. J .; Howard,
J . A. K.; Sokolov, N. I. Chem. Commun. 1998, 819.
(10) Perepichka, I. F.; Perepichka, D. F.; Bryce, M. R.; Chesney, A.;
Popov, A. F.; Khodorkovsky, V.; Meshulam, G.; Kotler, Z. Synth. Metals
1999, 102, 1158.
(11) Abramov, V. N.; Andrievskii, A. M.; Bodrova, N. A.; Borodkina,
M. S.; Kravchenko, N. V.; Kostenko, L. I.; Malakhova, I. A.; Nikitina,
E. G.; Orlov, I. G.; Perepichka, I. F.; Pototskii, I. S.; Semenenko, N.
M.; Trushina, V. S. USSR Patent 1,343,760, 1987.
(12) (a) Mysyk, D. D.; Neilands, O. Ya.; Kuvshinsky, N. G.; Sokolov,
N. I.; Kostenko, L. I. USSR Patent 1,443,366, 1987. (b) Belonozhko,
A. M.; Davidenko, N. A.; Kuvshinsky, N. G.; Neilands, O. Ya.; Mysyk,
D. D.; Prizva G. I. USSR Patent 1,499,553, 1989. (c) Mysyk, D. D.;
Neilands, O. Ya.; Khodorkovsky, V. Yu.; Kuvshinsky, N. G.; Be-
lonozhko, A. M.; Davidenko, N. A. USSR Patent 1,665,678, 1991.
(13) Kuvshinskii, N. G.; Nakhodkin, N. G.; Davidenko, N. A.;
Belonozhko A. M.; Mysyk, D. D. Ukr. Fiz. Zh. 1989, 34, 1100.
(14) Perepichka, I. F.; Mysyk, D. D.; Sokolov, N. I. Synth. Met. 1999,
101, 9.
(15) (a) Mart´ın N.; Seoane, C. In Handbook of Organic Conductive
Molecules and Polymers; Nalwa, H. S., Ed.; Wiley: Chichester, 1997;
Vol. 1, pp 1-86. (b) Mart´ın N.; Segura, J . L.; Seoane, C. J . Mater. Chem.
1997, 7, 1661.
(16) Tsubata, Y.; Suzuki, T.; Miyashi, T. J . Org. Chem. 1992, 57,
6749.
conductive polymers with a low band-gap.19 Surprisingly,
although 1,3-dithiole donor moieties are widely exploited
as building blocks in conductive charge-transfer salts
based on tetrathiafulvalenes (more than 3000 TTF
derivatives, the CTCs and radical salts are known to the
date), their incorporation as donor components of π-con-
jugated push-pull compounds is relatively limited.1,9,12,19-25
In continuation of our recent report on the role of the
conjugated bridge in the (1,3-dithiole)-π-fluorene sys-
tems,9 in the present paper we study the effect of varying
the heteroatoms in the heterocyclic donor unit (S or Se,
compounds 4 and 5) and their location (1,3 or 1,2,
compounds 4 and 6) on the ICT process in push-pull-
type fluorene acceptors.
(19) Skabara, P. J .; Serebryakov, I. M.; Perepichka, I. F. Synth. Met.
1999, 102, 1336.
(20) Blanchard-Desce, M.; Ledoux, I.; Lehn, J .-M.; Malthete J .; Zyss,
J . J . Chem. Soc., Chem. Commun. 1988, 737. (b) Inoue, S.; Aso, Y.;
Otsubo, T. Chem. Commun. 1997, 1105 and references therein.
(21) Gotthardt, H.; Oppermann, M. Tetrahedron Lett. 1985, 26, 1627.
(22) (a) Gompper, R.; Kutter, E.; Wagner, H.-U. Angew. Chem. 1966,
78, 545. (b) Gompper, R.; Wagner, H.-U. Tetrahedron Lett. 1968, 165.
(c) Wagner, H.-U.; Gompper, R. Angew. Chem. 1969, 81, 1004. (d)
Gompper, R.; Wagner, H.-U.; Kutter, E. Chem. Ber. 1968, 101, 4123.
(e) Gompper, R.; Wagner, H.-U.; Kutter, E. Chem. Ber. 1968, 101, 4145.
(23) Neidlein, R.; Zeiner, H. Arch. Pharm. 1982, 315, 1013.
(24) 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.; Viruela, P. M.; Tarbit, B. J . Mater. Chem. 1998, 8, 1173.
(25) 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.
(17) Verbiest, T.; Houbrechts, S.; Kauranen, M.; Clays, K.; Persoons,
A. J . Mater. Chem. 1997, 7, 2175.
(18) Moore, A. J .; Chesney, A.; Bryce, M. R.; Batsanov, A. S.;
Howard, J . A. K.; Perepichka, I. F.; Perepichka, D. F.; Khodorkovsky,
V.; Meshulam, G.; Kotler, Z. Manuscript in preparation.

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 64, No. 19, 1999 6939
Sch em e 1a
To this end, we have synthesized three series of
fluorene acceptors 4-6 (see Scheme 1) with ICT from 1,3-
dithiole, 1,3-selenathiole, and 1,2-dithiole moieties, re-
spectively, and investigated their spectral and redox
properties. We also describe the synthesis and properties
of the series of compounds 7 (Scheme 1) to allow a
comparison of the benzo-1,3-dithiole moiety with phenyl-
substituted analogue 4. Additionally, we report quantita-
tive effects of substitution in the fluorene ring on ICT
energies and redox potentials in compounds 4-7.
4-substituted derivatives (8) with nitric acid or its
mixture with acetic or sulfuric acids, depending on the
target products. Heterocyclic thiones 10-13 were con-
verted into dithiolium or selenathiolium salts 14-17 by
treatment with either methyl iodide, dimethyl sulfate,
or methyl triflate. 2,7-Dinitro-4-R1-5-R2-fluorenes (9) as
strong C-H acids26 reacted readily with chalcogenathio-
lium salts 14-17 in N,N-dimethylformamide (DMF)
solution yielding the corresponding substituted 9-(chal-
cogenathiolylidene)fluorenes (4-7). The reaction condi-
tions depended substantially on the substituents R1 and
R2 in fluorenes 9 and varied from 25 to 100 °C and from
a few minutes to several hours. The reaction rates and
Resu lts a n d Discu ssion
Syn th esis. The synthesis of the novel compounds 4-7
is depicted in Scheme 1. Nitrosubstituted fluorenes 9
were obtained by nitration of fluorene itself or its
(26) Kravchenko, N. V.; Abramov, V. N.; Semenenko, N. M. Zh. Org.
Khim. 1989, 25, 1938.

6940 J . Org. Chem., Vol. 64, No. 19, 1999
Mysyk et al.
X-ray structure for [TTF-H]+BF4 was reported,31 con-
firming covalent bonding of H with the central carbon
atom of one 1,3-dithiole ring and localization of the
positive charge on the other 1,3-dithiole moiety. However,
one should expect a substantial decrease of both Lewis
and Brønsted basicity with electron-withdrawing groups
attached to the 1,3-dithiole unit, so the ability of com-
pounds 4-7 to form salts is not so predictable. Indeed,
in trifluoroacetic acid (H0 ) -3.1, -4.4, -5, -5.0328)
compounds 4-7 do not give salts, although Gompper and
Wagner reported that push-pull compounds 22 and 23
were decolored in trifluoroacetic acid due to salt forma-
tion [CHCl3: λmax ) 645 nm (22), 758 nm (23); CF3-
CO2H: λmax ) 374 nm (22), 382 nm (23)].22b Salt forma-
tion (Scheme 2) is reversible, and on addition of water
to the solution of salts 18-21 in H2SO4, starting com-
pounds 4-7 were quantitatively recovered [except for
derivatives where acid-sensitive substituents on the
fluorene ring (CN, CO2R) were partially hydrolyzed].
-
Sch em e 2a
1H NMR Sp ectr a . The extremely low solubility (some-
times less than ∼0.1 g L-1) of the compounds under
investigation in common organic solvents meant thou-
sands of scans were needed to obtain their NMR spectra.
In some cases, e.g., for the series of fluorenes 7, insolubil-
ity prevented NMR experiments. In the case of unsym-
metrical fluorene moieties (R1 * R2), compounds 4-6 can
exist as E or Z isomers. Due to strong ICT in these
compounds giving rise to zwitterionic resonance struc-
tures 4′-6′ (Chart 2), the rotation barrier around the
formally double C(9)dC(2′) bond is expected to be low,8,32
and NMR spectra show the mixture of E-Z isomers or
broadened signals due to the dynamic process of E-Z
isomerization. Together with the possibility of paramag-
netic broadening of the NMR signals in polar/basic media
due to electron transfer from a solvent, as observed
previously with strong electron acceptors,3a,33 NMR spec-
tra were complicated in some cases, and at increased
temperatures the rotation became faster leading to
further broadening or disappearance of the signals
precluding the use of increased temperatures (to increase
the solubility) for recording NMR spectra. Data on
chemical shifts of all the observed signals for compounds
4-6 are summarized in Table 1. Salts 18-21, which were
formed by dissolution of compounds 4-6 in concentrated
sulfuric acid, are more soluble, and have no isomers to
complicate their spectra, gave finely resolved spectra that
confirm their structures (see the Experimental Section).
yields decreased with the reduction of the electron-
withdrawing abilities of substituents R1 and R2 in the
fluorene ring, and the condensation of fluorenes with poor
C-H acidities (9a -c) demanded pyridine (Py) addition
or even neat Py as a solvent.
Compounds 4-7 are air- and moisture-stable highly
colored solids with high melting points and low solubility
in most organic solvents. Their color depends on the
substituents in the fluorene ring and varies from orange-
red (for R1 ) R2 ) H) to black (for R1 ) R2 ) NO2).
Unfortunately, all our attempts to grow single crystals
of compounds 4-6 for X-ray structure determinations
were unsuccessful, yielding polycrystalline samples or
twinned crystals; the X-ray crystal structure for 7g will
be reported elsewhere.
Electr on ic Absor p tion Sp ectr a in th e ICT Region .
Effect of th e Don or Moiety. The presence in the
compounds under investigation of both electron-donor
and electron-acceptor fragments leads to strong ICT that
is manifested in the appearance of two long-wavelength
absorption bands (ICT bands) in the visible region of their
electronic spectra, which we term ICT-1 (short-wave-
length ICT band) and ICT-2 (long-wavelength ICT band)
(Figure 1, Table 2). Their intramolecular nature was
Compounds 4-7 dissolve in concentrated sulfuric acid
[H0 ) -9.85 (95% H2SO4),27 -8.86 (95% H2SO4),28 -11.1,
-11.0, -10.6 (100% H2SO4)28] to give colorless solutions
due to formation of salts 18-21 (Scheme 2). Protonation
of TTF derivatives by strong acids is known,29,30 and the
(30) Giffard, M.; Alonso, P.; Gar´ın, J .; Gorgues, A.; Nguyen, T. P.;
Richomme, P.; Robert, A.; Roncali, J .; Uriel, S. Adv. Mater. 1994, 6,
298.
(31) Giffard, M.; Fre`re, P.; Gorgues, A.; Riou, A.; Roncali, J .; Toupet,
L. J . Chem. Soc., Chem. Commun. 1993, 944.
(32) Perepichka, I. F.; Popov, A. F.; Artyomova, T. V.; Vdovichenko,
A. N.; Bryce, M. R.; Batsanov, A. S.; Howard, J . A. K.; Megson, J . L. J .
Chem. Soc., Perkin Trans. 2 1995, 3.
(33) Perepichka, I. F.; Kuz’mina, L. G.; Perepichka, D. F.; Bryce,
M. R.; Goldenberg, L. M.; Popov, A. F.; Howard, J . A. K. J . Org. Chem.
1998, 64, 6484.
(27) Gordon, A. J .; Ford, R. A. The Chemist’s Companion.
Handbook of Practical Data, Techniques, and References; Wiley: New
York; 1972.
(28) The Chemist’s Handbook; Nikol’skii, B. P., Ed.; Khimiya:
Moscow-Leningrad, 1963; Vol. 3; p 118 (in Russian).
(29) (a) Souizi, A.; Robert, A.; Batail, P.; Ouahab, L. J . Org. Chem.
1987, 52, 1610. (b) Benahmed-Gasmi, A. S.; Fre`re, P.; Belyasmine, A.;
Malik, K. M. A.; Hursthouse, M. B.; Moore, A. J .; Bryce, M. R.; J ubault,
M.; Gorgues, A. Tetrahedron Lett. 1993, 34, 2131. (c) Ro¨hrich, J .;
Mu¨llen, K. J . Org. Chem. 1992, 57, 2374.
A

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 64, No. 19, 1999 6941
Ch a r t 2
corroborated by the concentration dependence of their
intensities showing good linear dependence (with an
accuracy of ca. 3%) of an absorbance (A/ l) versus
concentration [e.g., for 5g: AICT-1 ) 1.036, AICT-2 ) 0.491
(C ) 5.53 × 10-4 M-1, l ) 0.10 cm cell), AICT-1 ) 0.994,
AICT-2 ) 0.472 (C ) 2.73 × 10-5 M-1, l ) 2.00 cm cell)].
In some solvents, the shape of both the ICT bands are
unsymmetrical (nonGaussian in shape), which can be
explained by overlapping of some bands with close ICT
transition energies, partly arising from closely lying ICT
bands for the E and Z isomers.
The absorption maxima of the ICT bands, which
depend on the structure of the acceptor and the donor
moieties, and the solvent properties, lie in the range of
400-510 nm for ICT-1 and 490-640 nm for ICT-2 (Table
2).
As seen from Table 2 and Figure 1, the heteroatom (S
or Se, compounds 4 or 5) in the donor moiety has no
apparent influence on the location of both ICT bands
(λICT-1 and λICT-2) on the difference in their energies
(hνICT-1 - hνICT-2 ≈ 0.70-0.72 eV) and on the ratio of
their intensities (AICT-1/AICT-2 ≈ 2). However, a change
in the position of sulfur atoms in the heterocycle from
1,3 to 1,2 (compounds 4 and 6, respectively) causes a
substantial bathochromic shift of both ICT bands, with
the shift of a short wavelength band (ICT-1) being more

6942 J . Org. Chem., Vol. 64, No. 19, 1999
Mysyk et al.
a
Ta ble 2. λm a x (n m ) of ICT-1 a n d ICT-2 Ba n d s for Com p ou n d s 4-7 in Va r iou s Solven ts a t 25 °C
dioxane
(2.209)b
chlorobenzene
(5.62)b
C2H4Cl2
(10.36)b
acetone
(20.74)b
DMF
acetonitrile
(37.5)b
DMSO
(48.9)b
(36.7)b
-
compd Σσp
λICT-1 λICT-2
λICT-1
λICT-2
λICT-2
λICT-1
λICT-2 λICT-1 λICT-2 λICT-1 λICT-2
λICT-1
λICT-2
4a
4b
4c
4d
4e
4f
2.54
406.5
412.7
419.3
420.3
429.7
432
491.7
515.3
3.176
3.54
3.81
4.446 426.4
4.81
5.08
418.2
419.6
514.9 423.7
525.3 427.2
556.2 434
552.5 435.5
570.8 444.2
524.3
539.4
577.4
580.6
596.9
520.1
530.3
563.6
563.6
584.7
419
421
431
432
433
508
535
568
571
575
426.7
426.7
436.9
439.2
449.5
538
545
582.1
580.8
604.4
543
567
569
599
426.4
434.2
4g
441.4
447.5
446.5
599
602
(22400) (10500)
5a
5b
5c
5d
5e
5f
2.54
3.176
3.54
3.81
4.446 424.8
4.81
5.08
403.7
410
417.9
422
429.4
431.2
440.6
489.9
513.8
520.2
538.6
564.3
564.3
585.1
415.8
420.2
515.9 422.3
531 428.9
555.6 433.3
554.4 437
525.8
548
573.5
579.2
596.9
419
427
430
432
433
521
548
568
571
575
425.6
425.6
436.1
438.4
449.5
537.1
551
583.5
583.5
608.5
425.5
433.1
5g
571.5 443.4
(18500) (8700)
(17500) (8200)
6a
6b
6c
6d
6e
6f
2.54
3.176
3.54
3.81
4.446 490.4
4.81
5.08
460sh
470sh
480sh
485sh
495sh
490.3
498.7
527.3
557.4
564.9
573.1
588.5
601.2
616.2
470sh 565
480sh 572.2 490sh
480sh
577.2
584.7
599.2
608
470sh
492
565
595
490
582.4
590.5
613.9
620.4
639.8
500sh 587
490sh
504.1
501
591.7 499.7
593.1 493.8
605.8 502.4
498
509
492
613
486.1
492.3
6g
621.1
633
512.8
(11500) (20000)
6h
7b
7d
7e
7f
4.538
3.176
3.81
4.446
4.81
604
498
513.5
542.5
549.5
569
7g
5.08
425.5
428
577
(21300) (10700)
a
b
Molar extinction coefficients, ꢀ/M-1 cm-1, are given in parentheses. Relative permittivity, ꢀs, is given in parentheses.
F igu r e 2. Electronic absorption spectra of compounds 4c, 4f,
and 6f in the visible region.
F igu r e 1. Intramolecular charge-transfer bands in the elec-
tronic absorption spectra of compounds 4g-7g in chloroben-
zene (4g-6g) and DMSO (7g).
1,3-dithiole moiety from terminal (phenyl substituent,
compounds 4) to annelated benzene ring (compounds 7)
drastically effects the ICT energies, resulting in a hypso-
chromic shift of both ICT bands. However, the ratio of
the intensities of ICT-1 and ICT-2 and the difference in
their energies remain about the same as in compounds
4.
As follows from Table 3, the ICT from 1,2-dithiole
moieties (compounds 23 and 25, Chart 3) is of lower
energy than from 1,3-dithiole isomers (compounds 22 and
24): bathochromic shifts of the longest wavelength ICT
absorption for a transition 22 f 25 are ∼105-112 nm22a-c
pronounced than that of the long wavelength band (ICT-
2) (ca. 60 and 30 nm, respectively) causing a decrease in
the difference in their electron transition energies: hνICT-1
- hνICT-2 ≈ 0.46-0.48 eV. Moreover, the ratio of their
intensities also changes dramatically (Figures 1 and 2).
Thus, in compounds 4 and 5 it is the short wavelength
absorption band, λICT-1, which is more intense (AICT-1
/
AICT-2 ≈ 2), whereas in compounds 6 the situation is
reversed (AICT-1/AICT-2 ≈ 0.7).
The change in the mode of benzene ring linkage to the

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 64, No. 19, 1999 6943
Ta ble 3. Electr on ic Absor p tion Ma xim a for Com p ou n d s
22, 23, 24, a n d 25 in Ch lor ofor m
parameter of the sensitivity of ICT energies to the
structure of the acceptor moiety. The parameters of
correlations are collected in Table 4.
compd
λ
max/nm (log ꢀ)
ref
As seen from Table 4, the values of FICT lie in the range
-0.064 to -0.096 eV for ICT-1 and -0.091 to -0.190 eV
for ICT-2, which is comparable to those for other push-
pull fluorene systems reported by us recently:8 9-[bis-
(dimethylamino)methylene]fluorenes (26), FICT ) -(0.050-
0.086) eV, 9-[cyano(dimethylamino)methylene]fluorenes
(27), and FICT ) -(0.13-0.18) eV (one ICT band only was
observed for these series of compounds).
22
638 (4.75), 590 (4.79), 547 (4.57)
645 (4.75)
22a
22b
22c
20b
22c
22b
22c
22c
640
641 (4.97), 589 (4.93), 548 (4.68)a
23
700
758 (3.98), 633 (3.90), 500 (4.42)
660, 610
750
24
25
a
In dichloromethane.
For compounds 4 and 5, the sensitivity parameter (FICT
)
for the ICT-2 band is ca. 1.7-2.3 times higher than that
for the ICT-1 band (Table 4). In the case of compounds 6
and 7, the first ICT band maxima could not always be
determined accurately, and no good correlations of hνICT-1
Ch a r t 3
-
vs Σσ were observed due to overlapping of λICT-1 by
other bands. Values of FICT-2 vary only slightly within
the change of the heteroatom from S to Se (from 4 to 5)
and for compounds 4, 5, and 7 lie in the range of -(0.14-
0.19) eV, whereas the change in the location of the sulfur
atom from 1,3 (4) to 1,2 (6) leads to a decrease in FICT-2
values, which are ca. 1.5 times lower than those for
compounds 4, 5, and 7 and lie in the range of -(0.09-
0.12) eV depending on the solvent (Table 4).
It should be mentioned that regularities in changes of
energies and intensities for the ICT-2 bands, and also
their sensitivity to the substituents on the fluorene ring,
are more important than for the ICT-1 band from the
viewpoint of the design of new electronic materials based
on this class of push-pull compounds (e.g., in regard to
increasing the photoconductivity in the long-wavelength
and near-IR region of the spectra). From this point of
view, the bathochromic shift and increase in intensities
of ICT-2 bands for the series of acceptors 6 provides a
very promising approach for designing highly sensitive
photoconductive materials for the spectral region g600-
800 nm.
In some cases, correlation coefficients (r ) 0.956-0.989
for ICT-1 and 0.968-0.994 for ICT-2) and the accuracy
of FICT determination are lower than that observed
previously for fluorene acceptors with ICT, 26, and 27.8
The reason for this is the above-mentioned complication
of both ICT-1 and ICT-2 bands due to overlapping ICT
transitions. The observed maxima, λICT, depend on their
relative positions and intensities, which vary with a
change of substituents on the fluorene ring (cf. com-
pounds 4c and 4f in Figure 2) and with a change of
solvent (cf. compound 6f or 4f in chlorobenzene and in
DMSO, Figure 2).
Solven t Effects. All the compounds investigated
display solvatochromic behavior (Table 2). The maximum
observed shift in λICT with a change of solvent (from
dioxane to DMSO) was about 20 nm for ICT-1 and 35
nm for ICT-2. However, for these systems a single
parameter, i.e., the medium polarity, is insufficient to
explain the effect of solvents upon ICT energies, since
most of the solvents used have pronounced electrophilic
or basic properties that cannot be neglected. As men-
tioned above, the observed first and second ICT bands
reflect different electron transitions with close energies,
whose solvatochromic behavior is not the same, bringing
about a change in the shape of ICT bands and complicat-
ing a quantitative evaluation of the influence of solvent
properties on ICT energy.
and for 24 f 23 are 4022c or 98 nm.22b Changing the type
of link of the aromatic substituent in the 1,3-dithiole
derivatives from phenyl (24) to annelated benzene ring
(22) is accompanied by a hypsochromic shift of 15-22
nm. In contrast, for 1,2 dithiole derivatives such a change
[23 (λmax ) 700 nm) f 25 (λmax ) 750 nm)]22c is ac-
companied by a substantial bathochromic shift of 50 nm,
although in an earlier paper by the same authors a
different value, λmax ) 758 nm, for compound 23 was
reported.22b
Effect of th e Accep tor Moiety. Increasing the ac-
ceptor character of the fluorene fragment by introduction
of electron-withdrawing substituents in the fluorene ring
results in a bathochromic shift of both ICT bands. To
estimate quantitatively the effect of the substituents
upon the energies of the ICT bands (hνICT corresponding
to λICT) we used eq 18
hνICT ) hν0ICT + FICTΣσ-p
(1)
-
-
where Σσp is the sum of the nucleophilic σp constants
of the substituents34 in the fluorene ring and FICT is a
(34) Hansch, C.; Leo, A. Substituent Constants for Correlation
Analysis in Chemistry and Biology; Wiley: New York, 1979; 339 p.
This also explains the fact that, in contrast to the

6944 J . Org. Chem., Vol. 64, No. 19, 1999
Ta ble 4. Cor r ela tion sa of ICT En er gies of Com p ou n d s 4-7 by Eq 1
Mysyk et al.
4
5
6
7
solvent
ꢀs
ICT-1
ICT-2
ICT-1
ICT-2
ICT-1
ICT-2
ICT-2
dioxane 2.209 hν0ICT/eV
3.20 ( 0.05
2.91 ( 0.10 3.21 ( 0.05
2.88 ( 0.09 2.58 ( 0.04
2.51 ( 0.04
-9.1 ( 0.9
0.985
102 × FICT/eV -6.4 ( 1.1
-14.5 ( 2.2
-6.5 ( 1.2
0.956
-13.8 ( 2.0
-1.1 ( 5.1
r
s0
n
0.956
0.968
0.970
0.214b
1.5 × 10-2
2.8 × 10-2
1.5 × 10-2
2.6 × 10-2
2.3 × 10-2
3
1.2 × 10-2
5
5
5
5
5
PhCl
5.62 hν0ICT/eV
3.20 ( 0.05
3.00 ( 0.09 3.21 ( 0.04
2.92 ( 0.09 2.56 ( 0.32
2.48 ( 0.03
-9.3 ( 0.6
0.994
102 × FICT/eV -7.8 ( 1.1
-18.3 ( 1.9
0.983
-7.9 ( 1.0
0.976
-16.6 ( 2.0
0.979
-1.5 ( 6.7
r
0.971
0.221b
s0
n
1.4 × 10-2
2.6 × 10-2
1.3 × 10-2
2.6 × 10-2
3.0 × 10-2
3
0.8 × 10-2
5
5
5
5
5
C2H4Cl2 10.28 hν0ICT/eV
2.86 ( 0.17
-15.0 ( 3.7
0.944
102 × FICT/eV
r
s0
n
3.5 × 10-2
4
acetonec 20.74 hν0ICT/eV
3.28 ( 0.02
2.91 ( 0.04 3.32 ( 0.03
2.92 ( 0.04
-15.7 ( 1.0
0.990
2.64 ( 0.03
102 × FICT/eV -9.0 ( 0.6
-15.3 ( 1.0
0.990
-9.6 ( 0.6
0.989
-12.2 ( 0.8
0.989
r
s0
n
0.989
1.3 × 10-2
1.0 × 10-2
1.5 × 10-2
2.3 × 10-2
1.9 × 10-2
7
7
7
7
7
DMF
36.7
hν0ICT/eV
2.54 ( 0.12
-11.2 ( 2.6
0.975
3.15 ( 0.06
-19.0 ( 1.5
0.991
102 × FICT/eV
r
s0
n
2.4 × 10-2
1.9 × 10-2
3
5
CH3CN 37.1
DMSO 48.9
hν0ICT/eV
3.20 ( 0.04
3.02 ( 0.16 3.13 ( 0.06
2.80 ( 0.14
-13.2 ( 3.1
0.924
102 × FICT/eV -6.7 ( 1.0
-17.7 ( 3.7
0.942
-5.4 ( 1.4
0.918
r
s0
n
0.968
1.3 × 10-2
4.8 × 10-2
1.8 × 10-2
3.1 × 10-2
5
5
5
5
hν0ICT/eV
3.24 ( 0.06
2.87 ( 0.09 3.27 ( 0.07
2.88 ( 0.09 2.76 ( 0.09
2.55 ( 0.04
-11.8 ( 0.9
0.990
102 × FICT/eV -9.2 ( 1.5
-16.0 ( 2.1
0.976
-9.6 ( 1.6
0.960
-16.3 ( 2.0
0.979
-6.4 ( 1.9
0.918
r
0.963
s0
n
1.9 × 10-2
2.7 × 10-2
2.1 × 10-2
2.6 × 10-2
2.3 × 10-2
1.2 × 10-2
5
5
5
5
4
5
a
b
Calculated by five points (4-6c-g and 7b,d -g) of the data in Table 2. No satisfactory correlations obtained due to overlapping of
ICT-1 bands by other bands. c Calculated by seven points (a -g) of the data in Table 2.
Ta ble 5. Effect of th e Tem p er a tu r e on th e λICT for Com p ou n d s 4g-6g in Va r iou s Solven ts a n d Cor r ela tion s of h νICT
Accor d in g to Eq 2
4g
5g
6g
solvent
PhCl
ꢀs
ICT-1
ICT-2
ICT-1
443.5
442
440
ICT-2
597
587
580
ICT-1
502.5
500
499
ICT-2
5.62 λmax3°C/nm
λmax25°C/nm
λmax55°C/nm
λmax92°C/nm
hνT ICT/eV
R/eV K
446
444
442
439
601
597
586
576
621
616
611
2.96 ( 0.01
2.40 ( 0.02
2.92 ( 0.01
2.41 ( 0.03
2.56 ( 0.02
2.17 ( 0.00
-49.32 ( 3.15 -94.39 ( 6.68 -36.1 ( 2.97
-98.81 ( 9.47 -28.08 ( 6.96 -53.05 ( 0.14
r
s0
0.996
0.995
0.997
0.995
0.971
1.000
2.1 × 10-3
4.4 × 10-3
1.3 × 10-3
4.1 × 10-3
3.0 × 10-3
6.2 × 10-5
acetone 20.74 λmax25°C/nm
441.5
585
440.5
585
499
616
λmax50°C/nm
440
582
-42a
583
R/eV K
CH3CN
37.5
λmax25°C/nm
λmax50°C/nm
575
441
440
582
a
Estimated by two points.
previous compounds 26 and 27 that showed good cor-
relations using polarity and basicity functions of the
solvents in the Koppel-Palm equation,35 we could not
obtain quantitative relationships between the FICT or λICT
values and any solvent parameters for compounds 4-7
with the series of solvents used. Correlations of ICT
The compounds under investigation also display ther-
mochromism, which is characteristic for solvatochromic
substances due to a change in the solute/solvent interac-
tions within the change of the temperature.36,37 Hypso-
chromic shifts were observed for both the ICT-1 and
ICT-2 bands with increasing the temperature (Figure 3,
Table 5). In all cases, the ICT-2 band displays a much
greater temperature dependence than ICT-1. Thus, the
ICT-2 band of 1,3-dithiole derivative 4g in chlorobenzene
energies versus ET(30) or ET values36 were also unsat-
N
isfactory.
(35) (a) Koppel, I. A.; Palm, V. A. In Advances in Linear Free Energy
Relationships; Chapman, N. B., Shorter, J ., Eds.; Plenum Press:
London, 1972; Chapter 5, p 203. (b) Palm, V. A. Fundamentals of
Quantitative Theory of Organic Reactions; Khimiya: Leningrad, 1977;
p 109 (in Russian).
(36) Reichardt, C. Solvents and Solvent Effects in Organic Chemistry,
2nd ed.; VCH: Weinheim; 1990; pp 363-371.
(37) (a) Ray, A. J . Am. Chem. Soc. 1971, 93, 7146. (b) Kiprianov, A.
I.; Timoshenko, E. S. Zh. Obsch. Khim. 1947, 17, 1468.

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 64, No. 19, 1999 6945
Ta ble 6. Cyclic Volta m m etr y Da ta for F lu or en e
Der iva tives 4-7 (vs F c0/F c+ Cou p le)a ,b
1/2
1/2
1/2
1/2
c
Eox
(V)
E1red
(V)
E2red
E3red
∆E1-2
(V)
Kdispr
(M-1
)
compd
(V)
(V)
4a
4b
4c
4d
4e
4f
4g
5a
5b
5c
5d
5e
5f
5g
6a
6b
6c
6d
6e
6f
6g
7e
7g
+0.64d -1.37
+0.67d -1.29
-1.17
-1.54
-1.49
-1.35
-1.27
-1.19
-1.12
-1.01
-1.54
-1.49
-1.33
-1.30
-1.17
-1.09
-1.02
0.17
0.20
0.18
0.19
0.23
0.21
0.22
0.18
0.20
0.18
0.21
0.22
0.18
0.22
1.3 × 10-3
4.1 × 10-4
8.9 × 10-4
6.0 × 10-4
1.3 × 10-4
2.8 × 10-4
1.9 × 10-4
8.9 × 10-4
4.1 × 10-4
8.9 × 10-4
2.8 × 10-4
1.9 × 10-4
8.9 × 10-4
1.9 × 10-4
-1.08
-0.96
-0.91
-0.79
+0.69d -1.36
-1.29
-1.15
-1.09
-0.95
-2.00
-1.99
-0.91
-0.80
-1.35
F igu r e 3. Effect of temperature on the position of ICT bands
in compound 4g in chlorobenzene (no correction for expansion
of the solvent with temperature was made, leading to a minor
decrease in observed ꢀ values with increasing temperature).
-1.25
-1.14
-1.09
-1.01
-1.12
-1.09
-1.02
-1.17
-1.00
0.11
0.12
0.16
0.23
0.22
1.4 × 10-2
9.2 × 10-3
1.9 × 10-3
1.3 × 10-4
1.9 × 10-4
-0.97
-0.86
-0.94
-0.78
a
For compounds 7b-d ,f, cyclic voltammograms were not
b
obtained due to the very low solubility of the compounds. Solvent
DMA; electrolyte 0.2 M Bu4N+PF6
.
c Calculated using equation
-
1/2
1/2
d
∆E1-2 ) E1red
oxidation peak.
- E2red
) -0.059 log Kdispr
.
Irreversible
dithiole moiety, removing its donor properties. The
longest wavelength absorptions in the resulting spectra
are in the 350-400 nm region, similar to the correspond-
ing polynitrofluorenes 1.1b Decreasing the acidity of the
solvent by gradual dilution with water resulted in reap-
pearance of the color, followed by precipitation of the
starting compounds, which were isolated in high yield.
It should also be mentioned that in dilute sulfuric acid,
in a certain range of concentrations, we observed in the
electronic absorption spectra of 4g and 5g additional
bands in the near-IR region that are characteristic of
radical ion species. Thus, Figure 5 demonstrates that
dilution with water of a colorless solution of compound
21 in H2SO4 leads progressively to the appearance of the
absorption of starting compound 5g at ca. 600 nm due to
reverse reaction (Scheme 2) and also to the development
of a new absorption band in the 800-1000 nm region
with a peak at λmax ) 940 nm in 48% H2SO4. This can be
explained by the electron-transfer interaction of neutral
compound 5g (formed upon dilution) with its salt 21 (i.e.,
[5g-H]+HSO4-) yielding radical and radical cation species:
F igu r e 4. Plots of hνICT-2 versus 1/T for compounds 4g-6g.
is blue shifted by 25 nm upon increasing the temperature
from 3 to 92 °C, whereas the ICT-1 band is shifted by
only 7 nm. The effect of temperture on λICT appears to be
much more pronounced in low polarity media than in
high-polarity media, as follows from a comparison of λICT
shifts for 5g in chlorobenzene (ꢀs 5.62) with those in
acetone (ꢀs 20.74) or acetonitrile (ꢀs 37.5) (Table 5). The
hνICT energies display good linear dependence with
inverse temperature (Figure 4). To estimate quantita-
tively the temperature effect on the energies of ICT
transitions we used eq 2:
5g + [5g-H]+ a 5g•+ + [5g-H]•
(3)
A similar type of electron exchange interaction between
1
T
hνICT ) hνTIC∞T + R
(2)
-
TTF and [TTF-H]+BF4 yielding TTF• and TTF•+ was
proved earlier,30 demonstrating the generation of radicals
and the formation of electrically conducting materials by
protic doping of TTF. More detailed electronic absorption
and ESR spectral investigations of this equilibrium in
4-6 will be reported elsewhere.
Electr och em istr y. To study the redox properties of
the novel compounds 4-7, we carried out cyclic voltam-
metry (CV) measurements in N,N-dimethylacetamide
(DMA) solution at room temperature with tetrabutylam-
monium hexafluorophosphate as the supporting electro-
lyte.
Parameters of correlations for compounds 4g-6g in
chlorobenzene are summarized in Table 5 confirming an
excellent correlation in all the cases. The sensitivity
parameters R for compounds 4g and 5g are very close,
whereas compound 6g shows ca. 2 times lower sensitivity
of hνICT-2 to the temperature.
Compounds 4-7 display negative halochromism: their
dissolution in concentrated sulfuric acid results in disap-
pearance of both ICT bands due to protonation of the
molecule and localization of the positive charge on the

6946 J . Org. Chem., Vol. 64, No. 19, 1999
Mysyk et al.
Ta ble 7. Cor r ela tion s of th e Electr och em ica l Red u ction
P oten tia ls for Com p ou n d s 4-7 Accor d in g to Eq 4
compd CV wave
E01/2/V
F- × 102/V
ra
nb
1/2
4
E1red
E2red
E1red
E2red
E1red
E2red
E1red
E2red
-1.970 ( 0.030
-2.094 ( 0.037
-1.947 ( 0.030
-2.106 ( 0.031
-1.806 ( 0.027
-1.810 ( 0.022
-2.06
22.7 ( 1.4
20.7 ( 1.6
22.2 ( 1.3
21.2 ( 1.4
18.1 ( 1.2
15.3 ( 5.0
25.2
0.991
0.985
0.991
0.989
0.989
7
7
7
7
7
1/2
1/2
1/2
1/2
1/2
1/2
1/2
4
5
5
6
6
0.952 3c
7d
7d
2
2
-2.36
26.8
a
b
Correlation coefficient. Number of points. c By three points,
d
6e,f,g. Estimated by two points, 7e,g.
electron affinities can be estimated as ca. 2.1-2.2 eV38
[EoxFc/Fc+ was reported to be + 0.45 V vs Ag/AgCl in CH3-
CN;8 + 0.44 V vs SCE in CH2Cl2 and DMF;16 +0.40 V
39
(in H2O and MeOH), +0.34 V (CH3CN), +0.39 V (DMF)
vs SCE;40 +0.31 V vs SCE in CH3CN.41].
For compounds 4 and 5 the number of electron-
withdrawing substituents on the fluorene ring does not
effect the ∆E1-2 value (within experimental error). De-
creasing the electron-withdrawing ability of the fluorene
moiety in acceptors 6 leads to a decrease in the difference
F igu r e 5. Electronic absorption spectra of compound 5g in
sulfuric acid of various concentrations: (a) 94% H2SO4 (H0
)
-9.7), (b) 87% H2SO4 (H0 ) -8.4), (c) 84% H2SO4 (H0 ) -7.95),
(d) 73% H2SO4 (H0 ) -6.25), (e) 48% H2SO4 (H0 ) -3.1); (H0
values were found from the plot “H0 - %H2SO4” by data from
ref 27).
1/2
1/2
between the reduction potentials E1red
and E2red
[∆E1-2 ) 0.16 eV (6g), 0.12 (6f), 0.11 (6e)], and for
acceptors 6a -d only one, two-electron reduction peak is
observed (Table 6). For compounds 5, in some cases, a
third single-electron reduction wave at a considerably
more negative potential (-2 V vs Fc0/Fc+) resulting in a
radical trianion species was observed (Figure 6). All three
reduction waves are reversible or quasireversible. For
poor electron acceptors 4a ,b and 5a , cyclic voltammetry
showed an additional single-electron oxidation wave to
yield the radical cation at ca. +0.64-0.69 V that was
irreversible.
For a quantitative estimation of the effect of substit-
uents in compounds 4-6 upon their electrochemical
behavior we used eq 4
E1/2 ) E10/2 + FCVΣσ-p
(4)
where Σσp is the same as in eq 1, E1/2 is the half-wave
potential for the reduction of a compound, E01/2 is E1/2 for
the reference compound (unsubstituted benzene rings in
fluorenes, Σσp- ) 0), and FCV is a parameter showing the
sensitivity of the electrochemical potential to substitu-
ents.
-
The results are summarized in Table 7. For the series
of compounds 4 and 5, both reduction processes, i.e., A
f A•- and A•- f A2-, are characterized by similar
F igu r e 6. Cyclic voltammogram of compound 5f: electrolyte
Bu4N+PF6 (0.2 M); solvent DMA; scan rate 200 mV s-1
potentials are represented versus Fc0/Fc+.
;
-
1red
2red
sensitivities: FCV
≈ FCV
≈ 0.21-0.23 V. Compounds
1red
6 show a slightly smaller sensitivity parameter FCV
)
0.18 ( 0.01 V. For the series of compounds 26 and 27
close parameters of the sensitivity FCV were observed [25:
All four series of compounds, i.e. 4-7, showed similar
electrochemical behavior: two closely spaced single-
electron reduction waves were observed resulting in
radical anion and dianion species, respectively [Figure
1red
2red
1red
FCV
) 0.20 V, FCV
) 0.18 V; 27: FCV
) 0.17 V,
2red
FCV
) 0.14 V].8
1/2
1/2
The thermodynamic stability of radical anion was
estimated from the differences in the potentials of the
corresponding radical anion and dianion by the equation
6, Table 6; ∆E1-2 ) E1red - E2red ) 0.17-0.23 V (4),
0.18-0.22 V (5), e 0.16 V (6), ≈ 0.23 V (7)]. The first
reduction waves, E1red1/2, for compounds 4-7 lie in the
range -(1.37-0.78) V (vs Fc0/Fc+) and the second reduc-
tion waves, E2red1/2, lie in the range of -(1.54-1.00) V
depending on the substituents in the fluorene ring
(increasing the electron affinity of the fluorene moiety
(38) Mysyk, D. D.; Perepichka, I. F.; Edzina, A. S.; Neilands, O. Ya.
Latvian J . Chem. 1991, 727.
(39) Zanello, P.; Opromolla, G.; Giorgi, G.; Sasso, G.; Togni, A. J .
Organomet. Chem. 1996, 506, 61.
(40) Mann, C. K.; Barnes, K. K. Electrochemical Reactions in
Nonaqueous Systems; Marcel Dekker: New York, 1970; pp 421, 427.
(41) Bard, A. J .; Faulkner, L. R. Electrochemical Methods. Funda-
mentals and Applications; Wiley: New York, 1980; p 701.
1/2
leads to a positive shift in the potentials). E1red poten-
tials of ca. -0.78-0.86 V vs Fc/Fc+ for acceptors 4g-7g
characterize them as moderate electron acceptors whose

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 64, No. 19, 1999 6947
9c: 1H NMR (400 MHz, DMSO-d6) δ 8.836 (1H, s), 8.827
(1H, s), 8.61 (1H, s), 8.47 (1H, d, J 5,6 ) 9 Hz), 8.44 (1H, dd),
4.29 (2H, s).
∆E1-2 ) E1red1/2 - E2red1/2 ) -0.059 log Kdispr 42 where Kdispr
,
is the disproportionation constant in the equilibrium (5):
9d : 1H NMR (400 MHz, DMSO-d6) δ 8.89 (1H, br), 8.82 (1H,
d, J 3,1 ) 1.5 Hz), 8.62 (1H, br), 8.35 (1H, dd, J 6,5 ) 9 Hz, J 6,8
) 2 Hz,), 8.12 (1H, d, J 5,6 ) 9 Hz), 4.39 (2H, s).
Kdispr.
{
2A•+
} A + A2-
(5)
As seen from Table 6, compounds 4, 5, and 7 show
9f: 1H NMR (400 MHz, DMSO-d6) δ 8.98 (1H, m), 8.96 (1H,
m), 8.87 (1H, d, J 3,1 ) 1.5 Hz), 8.79 (1H, d, J 6,8 ) 1.5 Hz), 4.52
(2H, s).
similar thermodynamic stabilities of the radical anions,
with Kdispr values in the range of 10-3-10-4 L mol-1
,
9g: 1H NMR (400 MHz, DMSO-d6) δ 9.05 (2H, br), 8.79 (2H,
d, J 3,1 ) 2 Hz), 4.60 (2H, s).
whereas the thermodynamic stabilities of the radical
anions derived from compounds 6 are somewhat lower.
2,7-Din itr o-4-m eth oxyca r bon ylflu or en e 9b. 4-Methoxy-
carbonylfluorene 8b (3.60 g, 20.0 mmol) was gradually added
to a well-stirred mixture of fuming nitric acid (30 mL) and
glacial acetic acid (20 mL) at 10-15 °C, the resulting solution
was stored for 24 h at room temperature and then diluted with
acetic acid (35 mL), and after 2-3 h the resulting solid was
filtered off and washed with acetic acid and then with water,
yielding a pale yellow crude product 9b (2.55 g, 47%): mp 223-
228 °C. After two recrystallizations from dioxane pure 9b (2.00
Con clu sion s
In summary, we have synthesized four series of fluo-
rene push-pull compounds 4-7 that show strong ICT
from the donor chalcogenathiole moiety to the acceptor
fluorene ring. The influence of the nature of heteroatoms
(S or Se) and their location in the donor moiety, the mode
of linking the benzene ring to the 1,3-dithiole moiety, and
the effects of the substituents in the fluorene ring on the
energies of ICT and the redox properties in these
compounds establish the following. (i) The replacement
of S (1,3-dithiole) by Se (1,3-selenathiole) has no apparent
effect on the maxima and the extinction coefficients of
the ICT bands whereas a change in the location of S in
the dithiole ring from 1,3 to 1,2 leads to a substantial
bathochromic shift in the long-wavelength ICT band and
an increase in its intensity. In view of the great impor-
tance of materials that possess long-wavelength ICT
absorption for the design of photothermoplastic storage
media, particularly in holography using He-Ne lasers
(λ ) 632.9 nm) or solid-state near-IR lasers, this observa-
tion is very significant as a basis for the development of
new sensitizers for photoconductive materials with high
holographic sensitivity in long-wavelength and near-IR
regions of the spectrum. (ii) Effects of substituents in the
fluorene ring on both ICT energies and reduction poten-
tials E1/2 in compounds 4-7 can be quantitatively de-
scribed by Hammett-type equations. The reversible for-
mation of salts 18-21 from compounds 4-7 by the action
of sulfuric acid has been demonstrated; a new absorption
band in the near-IR region (ca. 940 nm) in dilute H2SO4
can be attributed to the formation of radical ion species
in the solution.
1
g, 37%) was obtained: mp 233-236 °C; H NMR (400 MHz,
DMSO-d6) δ 8.67 (1H, br), 8.53 (1H, br), 8.49 (1H, br), 8.42
(1H, d, J 5,6 ) 9 Hz), 8.24 (1H, dd), 4.21 (2H, s), 4.03 (3H, s).
2,5,7-Tr in itr o-4-m eth oxyca r bon ylflu or en e 9e. To a well-
stirred mixture containing 90% HNO3 and 7.5% H2SO4 (45 mL)
was added 4-methoxycarbonylfluorene 8b (2.24 g, 10.0 mmol)
in portions, keeping the temperature below -10 °C. The
reaction mixture was stirred at this temperature for 1 h and
stored overnight at room temperature. It was diluted with 30%
aqueous acetic acid (60 mL) and cooled at 0 °C for 2-3 h, and
the resulting precipitate was filtered off and washed with
acetic acid (10 mL) and then with water (200-300 mL),
yielding crude fluorene derivative 9e (2.85 g, 79%), mp 195-
197 °C dec. Recrystallization from a dioxane- 2-propanol
mixture gave a yellow crystalline product: mp 204 °C dec: 1H
NMR (400 MHz, DMSO-d6) δ 8.97 (1H, m), 8.85 (1H, m), 8.73
(1H, d, J 3,1 ) 2 Hz), 8.52 (1H, d, J 6,8 ) 2 Hz), 4.52 (2H, s), 3.84
(3H, s). Anal. Calcd for C15H9N3O8: C, 50.15; H, 2.53; N, 11.70.
Found: C, 50.23; H, 2.61; N, 11.78%.
2,5,7-Tr in itr o-4-ca r boxyflu or en e 9h . To a well-stirred
mixture containing 90% HNO3 and 7.5% H2SO4 (50 mL) was
added fluorene-4-carboxylic acid 8h (5.00 g, 23.8 mmol) in
portions, keeping the temperature below -10 °C. The reaction
mixture was stirred at this temperature for 1 h, and then H2-
SO4 (25 mL) was added dropwise and the mixture was stored
for 1 day at room temperature. The reaction mixture was then
poured into ice-water (300 mL), and the solid was filtered off,
washed with water, and dried, yielding acid 9h (7.6 g, 92.5%):
mp 238 °C dec (lit.46 mp 245 °C dec). Anal. Calcd for
C
14H7N3O8: C, 48.71; H, 2.04; N, 12.17. Found: C, 48.46; H,
2.12; N, 12.33. The compound was used without further
purification.
Exp er im en ta l Section
2,5,7-Tr in itr oflu or en e-4-ca r boxylic Acid (Tr ieth ylen e-
glycol Mon om eth yl Eth er ) Ester 9i. A mixture of fluorene-
4-carbonyl chloride (2.44 g, 10.6 mmol), triethyleneglycol
monomethyl ether (3.5 mL, 22 mmol), and DMF (one drop)
was stirred at 80-85 °C for 15 h, and the resulting yellow
solution was evaporated in vacuo. After cooling, the residue
was dissolved in carbon tetrachloride (25 mL), thoroughly
washed with dilute sodium bicarbonate solution, and dried
over calcium chloride. After the solvent was removed in vacuo,
the crude fluorene-4-carboxylic acid (triethyleneglycol mono-
methyl ether) ester 8i (3.02 g, 80%) was obtained as a yellow
oil. Without further purification, this ester (1.8 g, 3.7 mmol)
was added slowly to a mixture of fuming nitric acid (25 mL, d
) 1.5 g mL-1) and concentrated sulfuric acid (2 mL) at -(6-
8) °C with vigorous stirring. The resulting red solution was
stirred at this temperature for 40 min and was then allowed
to stand at room temperature for 6 h. The reaction mixture
Gen er a l Meth od s. Dioxane, acetone, DMF, and dimethyl
sulfoxide were purified as described previously.27 Chloroben-
zene and 1,2-dichloroethane were stirred with sulfuric acid,
washed with water, dried over CaCl2, and distilled from P4O10
and then from CaO. For cyclic voltammetry experiments,
platinum wire, platinum disk diameter 1.6 mm, and Ag/Ag+
(AgNO3 in acetonitrile) were used as counter, working, and
reference electrodes, respectively. All potentials were corrected
using ferrocene-ferrocenium couple (Fc0/Fc+) as internal
reference. In all cases, CV experiments were performed in dry
DMA (Fluka, anhydrous) with Bu4N+PF6 (Fluka, puriss) as
-
supporting electrolyte (0.2 M) under N2 flow; concentrations
of acceptors were ca. 10-4 M-1. The scan rate was 200 mV s-1
.
4-Methoxycarbonylfluorene 8b was obtained as described
previously.43
Nitrosubstituted fluorenes 9c,38 9d ,44 9f,38 and 9g45 were
obtained as described previously (for 9g see also ref 7 and 44).
(42) (a) J ensen, B. S.; Parker, V. D. J . Am. Chem. Soc. 1975, 97,
5211. (b) Rainis, A.; Szwarc, M. J . Am. Chem. Soc. 1974, 96, 3008.
(43) Graebe, C. Ann. Chem. 1888, 247, 257.
(44) Yoshira, A.; Nippon Kagaku Kaishi (J . Chem. Soc. J pn., Chem.
Ind. Chem.) 1981, 1966.
(45) (a) Perepichka, I. F.; Mysyk, D. D. USSR Patent 862,561, 1981.
(b) Mysyk, D. D.; Perepichka, I. F.; Kostenko, L. I. USSR Patent
1,050,249, 1983.
(46) Migachyov, G. I. Zh. Vses. Khim. Ova im. D. I. Mendeleeva 1979,
24, 395.

6948 J . Org. Chem., Vol. 64, No. 19, 1999
Mysyk et al.
was poured onto an ice-water mixture (200 mL) and allowed
to stand at 0-5 °C for 2-3 h. After the aqueous layer was
decanted, a new portion of water was added to the residual
oil; it was stored under the water overnight, decanted again,
and dissolved in chloroform (25 mL), and the organic layer
was dried over CaCl2. Flash column chromatography on silica
gel [eluent: chloroform containing EtOH (0.3% v/v) and
acidified with concentrated aqueous HCl (0.1 g L-1)] gave
fluorene 9i as a yellow oil (1.59 g, 51% overall) that crystallized
over several weeks: EIMS (M+) 491; 1H NMR (200 MHz,
CDCl3) δ 8.85 (1H, d, J 1,3 ) 2 Hz), 8.78 (1H, d, J 8,6 ) 2 Hz),
8.71 (1H, d, J 3,1 ) 2 Hz), 8.64 (1H, d, J 6,8 ) 2 Hz), 4.54 (2H, t,
J ) 5 Hz), 4.36 (2H, s), 3.89 (2H, t, J ) 5 Hz), 3.77-3.53 (8H,
m), 3.37 (3H, s); νmax/cm-1 (KBr) 3093, 2923, 2876, 1723(Cd
O), 1532 (NO2), 1344 (NO2), 1290, 1097, and 738.
9-(4-P h en yl-1,3-d it h iol-2-ylid en e)-2,7-d in it r o-4-m et h -
oxyca r bon ylflu or en e 4b. A solution of fluorene 9b (0.11 g,
0.35 mmol) in Py (5 mL) was added to dithiolium salt 14,
prepared from thione 10 (0.10 g, 0.48 mmol), and the reaction
mixture was heated with stirring until dissolution of the
starting salt was completed. After the mixture was cooled to
room temperature during 2-3 h and diluted with acetone (10
mL), the precipitate was filtered off and thoroughly washed
with acetone and water, giving brick-red needles of fluorene
4b (0.11 g, 71%). Recrystallization from DMF (25 mL) gave
pure compound 4b (0.08 g, 50%): mp 283 °C; λmax (acetone)
364, 387, 413, 515 nm; MS (CI) 490 (M+); MW (calcd)
490.02933. Anal. Calcd for C24H14N2O6S2: C, 58.77; H, 2.88;
N, 5.71. Found: C, 58.97; H, 2.73; N, 5.86.
9-(4-P h en yl-1,3-d ith iol-2-ylid en e)-2,7-d in itr o-4-cya n o-
flu or en e 4c. A solution of fluorene 9c (0.15 g, 0.53 mmol) in
a mixture of DMF (5 mL) and Py (2 mL) was added to
dithiolium salt 14, prepared from thione 10 (0.10 g, 0.48 mmol)
and stirred for 3-4 h. The deposition of a dark product soon
began. The precipitate was filtered off and thoroughly washed
with ethyl acetate, yielding 4c (0.09 g, 55%). After recrystal-
lization from DMF (40 mL), pure compound 4c (0.08 g, 49%)
was obtained: mp > 360 °C; λmax (acetone) 359, 380sh, 419,
520 nm; HRMS 457.01800 (M+); MW (calcd) 457.01910. Anal.
Calcd for C23H11N3O4S2: C, 60.38; H, 2.42; N, 9.18. Found: C,
60.22; H, 2.35; N, 9.26.
9-(4-P h en yl-1,3-d it h iol-2-ylid en e)-2,5,7-t r in it r oflu o-
r en e 4d . Fluorene 9d (0.31 g, 1.02 mmol) and DMF (4 mL)
were added to dithiolium salt 14, prepared from thione 10 (0.21
g, 1.00 mmol), and the reaction mixture was heated to 100 °C
and then stored overnight at room temperature. The precipi-
tate was filtered off, washed with DMF (5 mL), and thoroughly
with acetone, giving 4d (0.20 g, 42%). After recrystallization
from DMF (40 mL), pure compound 4d (0.13 g, 26%) was
obtained: mp 332-334 °C; λmax (acetone) 360, 380sh, 420, 530
nm; HRMS 477.00899 (M+); MW (calcd) 477.00893. Anal. Calcd
for C22H11N3O6S2: C, 55.34; H, 2.32; N, 8.80. Found: C, 55.30;
H, 2.36; N, 8.87.
4-Phenyl-1,3-dithiole-2-thione (10)47 and 5-phenyl-1,2-dithi-
ole-3-thione (12)48 were obtained as described previously.
4-P h en yl-1,3-selen a t h iole-2-t h ion e 11. This compound
was prepared by a modified procedure.49 4-Phenyl-1,2,3-
selenadiazole50 (2.09 g, 10.0 mmol) was added to a stirred
solution of KOH (0.80 g, 14 mmol) in 2-propanol at room
temperature. The reaction mixture was stirred until nitrogen
evolution ceased, and carbon disulfide (1.5 mL) was added.
After 5 min, the product began to crystallize. The reaction
mixture was stirred for 1 h and then left for ca. 8 h while the
product crystallized. The precipitate was filtered and washed
with 2-propanol (20 mL) and water yielding thione 11 (1.85 g,
72%) as a yellow powder, mp 114-117 °C. Recrystallization
from ethyl acetate gave analytically pure thione 11 (1.48 g,
58%), mp 116-117 °C (lit.49 mp 115 °C).
4-P h en yl-2-m et h ylt h io-1,3-selen a t h ioliu m iod id e 15.
4-Phenyl-1,3-selenathiole-2-thione 11 (1.28 g, 4.98 mmol) and
methyl iodide (5 mL) in n-butyl acetate (5 mL) were refluxed
for 1.5 h. After cooling, the resulting solid was filtered off and
washed with butyl acetate (5 mL) and dry benzene (10 mL),
yielding orange plates of selenathiolium salt 15 (1.48 g, 74%),
mp 111-112 °C dec.
2-Meth ylth io-ben zo[d ]-1,3-d ith ioliu m tr ifla te 17. Meth-
yl triflate (0.40 mL, 3.5 mmol) was added to a hot solution of
benzo[d]-1,3-dithiole-2-thione (13) (0.50 g, 2.7 mmol) in dry
chloroform (10 mL), and the reaction mixture was kept at 50-
55 °C for 1 h; a yellow-brownish oil formed and crystallized
during this period. The reaction mixture was diluted with dry
ether (3 mL) and kept at 0 °C for ca. 8 h, and the product was
filtered off, washed with ether, and dried in vacuo, yielding
salt 17 (0.88 g, 94%) as yellow crystals.
4-P h en yl-2-m eth ylth io-1,3-d ith ioliu m m eth yl Su lfa te
14 a n d 5-P h en yl-3-m eth ylth io-1,2-d ith ioliu m m eth yl Su l-
fa te 16. Gen er a l P r oced u r e. The corresponding thione, 10
or 12 (5 mmol), was refluxed with dimethyl sulfate (2.0 mL,
19 mmol) in n-butyl acetate (20 mL) for 5 min (for 10) or 20
min (12) and cooled to room temperature, and the solvent was
decanted from the solid. The residue of the resulting salt, 14
or 16, in a small amount of the solvent was used for condensa-
tion with fluorenes 9 without further isolation and purification.
9-(4-P h en yl-1,3-d it h iol-2-ylid en e)-2,7-d in it r oflu or en e
4a . A solution of fluorene 9a (0.12 g, 0.47 mmol) in pyridine
(Py, 4.5 mL) was added to dithiolium salt 14, prepared from
thione 10 (0.12 g, 0.57 mmol), and the reaction mixture was
heated to 100 °C for 3 min. After the mixture was cooled to
room temperature during 2-3 h and diluted with acetone (10
mL), the resulting precipitate was filtered off and thoroughly
washed with acetone and water, yielding compound 4a (0.11
g, 50%). Recrystallization from DMF (25 mL) gave compound
4a as red needles (0.10 g, 46%): mp > 360 °C; λmax (acetone)
363, 383, 407, 492 nm; MS (CI) 432 (M+); MW (calcd)
432.02385. Anal. Calcd for C22H12N2O4S2: C, 61.10; H, 2.80;
N, 6.48. Found: C, 61.26; H, 2.88; N, 6.33%.
9-(4-P h en yl-1,3-d ith iol-2-ylid en e)-2,5,7-tr in itr o-4-m eth -
oxyca r bon ylflu or en e 4e. Fluorene 9e (0.20 g, 0.56 mmol),
DMF (4 mL), and Py (5 drops) were added to dithiolium salt
14, prepared from thione 10 (0.15 g, 0.71 mmol) and stirred
for 2-3 h. The deposition of a dark product soon began. The
solid was filtered off and washed with DMF (5 mL) and
thoroughly with ethyl acetate, giving product 4e (0.15 g, 67%).
After recrystallization from DMF (25 mL), pure compound 4e
(0.11 g, 49%) was obtained: mp 329-333 °C; λmax (acetone)
370, 390sh, 430, 564 nm; HRMS 535.01299 (M+); MW (calcd)
535.01441. Anal. Calcd for C24H13N3O8S2: C, 53.83; H, 2.45;
N, 7.85. Found: C, 54.03; H, 2.51; N, 7.78.
9-(4-P h en yl-1,3-d it h iol-2-ylid en e)-2,5,7-t r in it r o-4-cy-
a n oflu or en e 4f. This was obtained similarly to 4e from
fluorene 9f and dithiolium salt 14 in 60% yield: mp 337-340
°C; λmax (acetone) 361, 385sh, 432, 564 nm; HRMS 502.00301
(M+); MW (calcd) 502.00418. Anal. Calcd for C23H10N4O6S2: C,
54.98; H, 2.01; N, 11.15. Found: C, 54.80; H, 2.00; N, 11.22.
9-(4-P h en yl-1,3-d ith iol-2-ylid en e)-2,4,5,7-tetr a n itr oflu -
or en e 4g. Fluorene 9g (0.35 g, 1.0 mmol) and DMF (4 mL)
were added to dithiolium salt 14, prepared from thione 10 (0.21
g, 1.0 mmol), and the reaction mixture was heated to 100 °C.
After the mixture was cooled to room temperature, the
precipitate was filtered off and washed with DMF (5 mL) and
thoroughly with acetone, giving black-violet crystalline product
4g (0.37 g, 71%). After recrystallization from DMF, pure
compound 4g (0.32 g, 62%) was obtained: mp 357-360 °C;
λmax (acetone) 362, 441, 585 nm; HRMS 521.99288 (M+); MW
(calcd) 521.99401. Anal. Calcd for C22H10N4O8S2: C, 50.58; H,
1.93; N, 10.72. Found: C, 50.64; H, 1.91; N, 10.81.
9-(4-P h en yl-1,3-selen a th iol-2-ylid en e)-2,7-d in itr oflu o-
r en e 5a . Salt 15 (0.120 g, 0.30 mmol) was added to a hot
solution of fluorene 9a (0.077 g, 0.30 mmol) in Py (2.5 mL)
and stirred for a few minutes. The precipitation of a dark solid
soon began. The reaction mixture was stored for 0.5 h and then
diluted with acetone (10 mL), and dark red crystals were
filtered off and washed with acetone (15 mL) and water, giving
(47) Haley, N. F.; Fichtner, M. W. J . Org. Chem. 1980, 45, 175.
(48) Thuillier, A.; Vialle, J . Bull. Soc. Chim. Fr. 1959, 1398.
(49) Shafiee, A.; Lalezari, I.; Savabi, F. Synthesis 1977, 764.
(50) Lalezari, I.; Shafiee, A.; Yalpani, M. Tetrahedron Lett. 1969,
5105.

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 64, No. 19, 1999 6949
5a (0.08 g, 62%). After recrystallization from DMF (18 mL),
pure compound 5a (0.07 g, 54%) was obtained: mp > 360 °C;
λmax (acetone) 360, 380, 404, 490 nm; MS (CI) 480 (M+); MW
(calcd) 479.96830. Anal. Calcd for C22H12N2O4SSe: C, 55.12;
H, 2.52; N, 5.84. Found: C, 54.84; H, 2.43; N, 6.07.
for C22H10N4O8SSe: C, 46.41; H, 1.77; N, 9.84. Found: C, 46.33;
H, 1.78; N, 9.93.
9-(5-P h en yl-1,2-d it h iol-3-ylid en e)-2,7-d in it r oflu or en e
6a . Fluorene 9a (0.10 g, 0.39 mmol) and Py (4.5 mL) were
added to dithiolium salt 16, prepared from thione 12 (0.1 g,
0.48 mmol), and the reaction mixture was heated to reflux.
The reaction mixture was left to cool for 30 min and diluted
with acetone (10 mL), and the precipitate was filtered off,
washed with acetone and then with water, giving fluorene 6a
(0.07 g, 40%). Recrystallization from DMF (25 mL) yielded
dark red needles (0.06 g, 34%): mp > 360 °C; MS (CI) 432
(M+); MW (calcd) 432.02385. Anal. Calcd for C22H12N2O4S2: C,
61.10; H, 2.80; N, 6.48. Found: C, 61.10; H, 3.00; N, 6.30.
9-(5-P h en yl-1,2-d it h iol-3-ylid en e)-2,7-d in it r o-4-m et h -
oxyca r bon ylflu or en e 6b. Fluorene 9b (0.15 g, 0.48 mmol)
and Py (5 mL) were added to dithiolium salt 16, prepared from
thione 12 (0.12 g, 0.57 mmol), and the reaction mixture was
heated until full dissolution of staring salt and deposition of
product. The reaction mixture was stored for 0.5 h, diluted
with acetone (5 mL), and cooled to room temperature, and the
precipitate was filtered off and washed with acetone and water,
giving 6b (0.11 g, 44%). Recrystallization from DMF (15 mL)
yielded dark red crystals (0.10 g, 40%): mp 326 °C; MS (CI)
9-(4-P h en yl-1,3-selen a t h iol-2-ylid en e)-2,7-d in it r o-4-
m eth oxyca r bon ylflu or en e 5b. Salt 15 (0.120 g, 0.30 mmol)
was added to a hot solution of fluorene 9b (0.094 g, 0.30 mmol)
in Py (2.5 mL) and stirred for a few minutes until the reaction
mixture became a thick paste. The reaction mixture was left
for 0.5 h and then diluted with acetone (10 mL), and the solid
was filtered off and washed with acetone (15 mL), yielding 5b
(0.15 g, 93%). The crude compound was dissolved in hot DMF
(8 mL) and diluted with acetone (10 mL). Pure compound 5b
(0.145 g, 90%) crystallized on cooling the solution: mp 280-
282 °C; λmax (acetone) 361, 384, 410, 514 nm; MS (CI) 538 (M+);
MW (calcd) 537.97378. Anal. Calcd for C24H14N2O6SSe: C,
53.64; H, 2.63; N, 5.21. Found: C, 53.52; H, 2.54; N, 5.04.
9-(4-P h en yl-1,3-selen a th iol-2-ylid en e)-2,7-d in itr o-4-cy-
a n oflu or en e 5c. Salt 15 (0.20 g, 0.50 mmol) was added to a
hot solution of fluorene 9c (0.15 g, 0.53 mmol) in a mixture of
DMF (5 mL) and Py (2 mL). After the mixture was cooled to
room temperature, the precipitate was filtered off and washed
with DMF (10 mL) and ethyl acetate (20 mL), giving 5c (0.22
g, 86%). After recrystallization from DMF (50 mL), pure
compound 5c (0.20 g, 78%) was obtained: mp > 360 °C; λmax
(acetone) 358, 375sh, 418, 520 nm; HRMS 504.96299 (M+); MW
(calcd) 504.96355. Anal. Calcd for C23H11N3O4SSe: C, 54.77;
H, 2.20; N, 8.33. Found: C, 54.60; H, 2.12; N, 8.38.
9-(4-P h en yl-1,3-selen a t h iol-2-ylid en e)-2,4,7-t r in it r o-
flu or en e 5d . Salt 15 (0.20 g, 0.50 mmol) was added to a hot
solution of fluorene 9e (0.17 g, 0.56 mmol) in a mixture of DMF
(5 mL) and Py (1 mL) followed by dilution with ethyl acetate
(10 mL). After the mixture was cooled to room temperature,
the precipitate was filtered off and washed with ethyl acetate,
yielding 5d (0.25 g, 94%). After recrystallization from DMF
(40 mL), pure compound 5d (0.15 g, 56%) was obtained: mp
291-293 °C; λmax (acetone) 360, 380sh, 422, 539 nm; HRMS
524.95499 (M+); MW (calcd) 524.95338. Anal. Calcd for
490 (M+); MW (calcd) 490.02933. Anal. Calcd for C24H14
-
N2O6S2: C, 58.77; H, 2.88; N, 5.71. Found: C, 58.50; H, 2.90;
N, 5.90.
9-(5-P h en yl-1,2-d it h iol-3-ylid en e)-2,5,7-t r in it r oflu o-
r en e 6d . Fluorene 9d (1.50 g, 5.0 mmol) and DMF (20 mL)
were added to dithiolium salt 16, prepared from thione 12 (1.05
g, 5.0 mmol), and the reaction mixture was heated to 100 °C.
After the mixture was cooled to room temperature during a
few hours, the precipitate was filtered off and washed with
DMF (10 mL) and acetone (50 mL), giving black crystals of
product 6d (1.55 g, 65%). Recrystallization from DMF (170 mL)
yielded pure 6d (1.20 g, 50%): mp 315-317 °C; HRMS
477.00945 (M+); MW (calcd) 477.00893. Anal. Calcd for
C
22H11N3O6S2: C, 55.34; H, 2.32; N, 8.80; S, 13.42. Found: C,
55.36; H, 2.48; N, 9.07; S, 13.34.
9-(5-P h en yl-1,2-d ith iol-3-ylid en e)-2,7-d in itr o-4-cya n o-
flu or en e 6c. This was prepared similarly to 6d in 70% yield:
mp 347-348 °C; HRMS 457.01898 (M+); MW (calcd) 457.01910.
Anal. Calcd for C23H11N3O4S2: C, 60.38; H, 2.42; N, 9.18.
Found: C, 60.16; H, 2.33; N, 9.29.
9-(5-P h en yl-1,2-d ith iol-3-ylid en e)-2,5,7-tr in itr o-4-m eth -
oxyca r bon ylflu or en e 6e. This was prepared similarly to 6d
in 69% yield: mp 348-350 °C; HRMS 535.01439 (M+); MW
(calcd) 535.01441. Anal. Calcd for C24H13N3O8S2: C, 53.83; H,
2.45; N, 7.85; S, 11.97. Found: C, 53.98; H, 2.66; N, 7.85; S,
11.59.
9-(5-P h en yl-1,2-d it h iol-3-ylid en e)-2,5,7-t r in it r o-4-cy-
a n oflu or en e 6f. This was prepared similarly to 6d in 75%
yield: mp 350-353 °C; HRMS 502.00338 (M+); MW (calcd)
502.00418. Anal. Calcd for C23H10N4O6S2: C, 54.98; H, 2.01;
N, 11.15. Found: C, 54.86; H, 2.04; N, 11.20.
C
22H11N3O6SSe: C, 50.39; H, 2.11; N, 8.01. Found: C, 50.31;
H, 2.07; N, 8.08.
9-(4-P h en yl-1,3-selen a th iol-2-ylid en e)-2,4,7-tr in itr o-4-
m eth oxyca r bon ylflu or en e 5e. Salt 15 (0.20 g, 0.5 mmol)
was added to a solution of fluorene 9e (0.17 g, 0.47 mmol) in
DMF (5 mL) with Py (5 drops) and stirred for 2-3 h. The
deposition of a dark product soon began. The precipitate was
filtered off, washed with DMF (5 mL) and thoroughly with
ethyl acetate, giving 5e (0.25 g, 88%). For purification, crude
product was dissolved in hot DMF (40 mL) and diluted with
2-propanol (50 mL), giving pure fluorene 5e (0.18 g, 63%): mp
304-305 °C; λmax (acetone) 360, 385sh, 429, 564 nm; HRMS
582.95656 (M+); MW (calcd) 582.95886. Anal. Calcd for
C
24H13N3O8SSe: C, 49.50; H, 2.25; N, 7.21. Found: C, 49.62;
H, 2.32; N, 7.25.
9-(4-P h en yl-1,3-selen a th iol-2-ylid en e)-2,4,7-tr in itr o-4-
cya n oflu or en e 5f. Salt 15 (0.10 g, 0.25 mmol) was added to
a solution of fluorene 9f (0.09 g, 0.27 mmol) in DMF (5 mL)
and stirred for 2-3 h. The precipitation of a dark product soon
began. The precipitate was filtered off and washed with DMF
(5 mL) and thoroughly with ethyl acetate, giving 5f (0.16 g,
79%). After recrystallization from DMF (30 mL), pure com-
pound (0.12 g, 59%) was obtained: mp 325-326 °C; λmax
(acetone) 360sh, 385sh, 431, 564 nm; HRMS 549.94582 (M+);
MW (calcd) 549.94863. Anal. Calcd for C23H11N3O4SSe: C,
50.28; H, 1.83; N, 10.20. Found: C, 50.12; H, 1.80; N, 10.26.
9-(4-P h en yl-1,3-selen a t h iol-2-ylid en e)-2,4,5,7-t et r a n i-
tr oflu or en e 5g. Salt 15 (0.40 g, 1.0 mmol) was added to a
solution of fluorene 9g (0.35 g, 1.0 mmol) in DMF (10 mL) and
stirred for 2-3 h. The precipitation of dark product soon began.
The reaction mixture was diluted with acetone (20 mL), and
the precipitate was filtered off and thoroughly washed with
acetone, giving desired 5g (0.58 g, ∼100%). After recrystalli-
zation from DMF (45 mL), pure compound (0.50 g, 88%) was
obtained: mp 340-342 °C; λmax (acetone) 360, 385sh, 441, 585
nm; HRMS 569.93690 (M+). MW (calcd) 569.93846. Anal. Calcd
9-(5-P h en yl-1,2-d ith iol-3-ylid en e)-2,4,5,7-tetr a n itr oflu -
or en e 6g. This was prepared similarly to 6d in 88% yield:
mp > 360 °C; HRMS 521.99444 (M+); MW (calcd) 521.99401.
Anal. Calcd for C22H10N4O8S2: C, 50.58; H, 1.93; N, 10.72; S
12.27. Found: C, 50.64; H, 1.91; N, 10.81; S 12.07.
9-(5-P h en yl-1,2-d ith iol-3-ylid en e)-2,5,7-tr in itr o-4-ca r -
boxyflu or en e 6h . This was prepared similarly to 6d in 88%
yield. For purification, 6e was recrystallized from a large
amount of dioxane: mp > 300 °C; IR (KBr) ν/cm-1 1700 (Cd
O), 1570 (NO2), 1345 (NO2), 1320, 1240, 1160, 1100, 860. Anal.
Calcd for C23H11N3O8S2: C, 52.97; H, 2.13; N, 8.06; S 11.74.
Found: C, 53.14; H, 2.01; N, 7.98; S 11.53.
9-(5-P h en yl-1,2-dith iol-3-yliden e)-2,5,7-tr in itr o-4-[(3,6,9-
tr ioxa d ecyl)oxyca r bon yl]flu or en e 6i. To a solution of
thione 12 (0.30 g, 1.4 mmol) in dry dichloromethane (2.5 mL)
was added methyl triflate (0.2 mL, 1.8 mmol), resulting in an
exothermic reaction. The reaction mixture was stirred at 35-
40 °C for 1 h, then two-thirds of the solvent was removed in
vacuo and the residue was diluted with dry ether (2 mL). The
precipitated dithiolium salt was filtered off, washed with ether,

6950 J . Org. Chem., Vol. 64, No. 19, 1999
Mysyk et al.
and dried in vacuo, giving pure 5-phenyl-3-methylthio-1,2-
dithiolium triflate 16 (Y ) CF3SO3; Scheme 1) (0.43 g, 81%).
This dithiolium salt (93 mg, 0.249 mmol) was added to a
solution of fluorene 9i (114 mg, 0.23 mmol) in DMF (1 mL),
and the resulting mixture was stirred at room temperature
and left for 20 h (TLC analysis showed full conversation of
the starting fluorene). The reaction mixture was diluted with
acetone (2 mL) and stored for 2 h at 0-5 °C. The precipitate
was filtered off, washed with acetone-2-propanol mixture (1:1
v/v), and recrystallized from toluene (3 mL), yielding pure
product 6i (100 mg, 65%): mp 210 °C. Anal. Calcd for
7f: ∼100% (89%); mp >360 °C; MS (CI) 494 (M+ + 18), 476
(M+); MW (calcd) 475.98853. Anal. Calcd for C21H8N4O6S2: C,
52.94; H, 1.69; N, 11.76. Found: C, 53.12; H, 1.77; N, 11.70.
7g: 87% (83%); mp >360 °C; λmax (DMF) 369, 426, 569 nm;
MS (CI) 514 (M+ + 18), 496 (M+); MW (calcd) 495.97836. Anal.
Calcd for C20H8N4O8S2: C, 48.39; H, 1.62; N, 11.29. Found:
C, 48.52; H, 1.65; N, 11.40.
Rever sible F or m a tion of Sa lts 18-21. The 9-chalcogena-
thiolylidenefluorene derivatives 4-7 (5-20 mg) were stirred
in concentrated sulfuric acid (1-5 mL) at room temperature
until complete dissolution and decoloration was observed (from
10 to 20 min to 2-4 h). The resulting solutions of salts 18-21
in H2SO4 are colorless or pale yellow and stable at ambient
temperature for some days (partial hydrolysis of CN and CO2-
Me groups was observed for compounds b,c,e,f). When water
was added dropwise to these solutions, the initial color of 4-7
reappeared (from red to dark blue depending on substituents
R1 and R2) followed by essentially quantitative precipitation
of compounds 4-7.
C
30H25N3O11S2: C, 53.97; H, 3.77; N, 6.29. Found: C, 54.21;
H, 3.91; N, 6.23.
9-(Ben zo[d ]-1,3-d ith iol-2-ylid en e)-2,7-d in itr o-4-R1-5-R2-
flu or en es 7. Gen er a l P r oced u r e. 2-Methylthio-1,3-ben-
zodithiolium triflate 17 (164 mg, 0.47 mmol) was added to a
solution of the corresponding fluorene 9 (0.40 mmol) in DMF
(3 mL), and the reaction mixture was stored for several hours
at 20-70 °C with monitoring of the reaction by TLC (by
conversion of the starting fluorene). The reaction conditions
were as follows: 7b, 70 °C, 25 h; 7d , 60 °C, 17 h; 7e, 25 °C, 25
h; 7f, 25 °C, 20 h; 7g, 20 °C, 2 h. After the reaction was
complete, the precipitate was filtered off and washed with
DMF and then with acetone. The crude product was then
recrystallized from DMF (yields after recrystallization are
given in parentheses).
18g: δH [500 MHz, 98% D2SO4 (99.5 at. %)] 10.9s (H2SO4),
9.75s (1H), 9.29d (2H, J ) 2.0 Hz), 9.07d (2H, J ) 2.0 Hz),
7.80d (2H, J ) 7.0 Hz), 7.75t (1H, J ) 6.5 Hz), 7.69dd (2H, J
) 7.0, 6.5 Hz).
19g: δH [500 MHz, 98% D2SO4 (99.5 at. %)] 10.9s (H2SO4),
9.28d (2H, J ) 2.0 Hz), 9.04s (2H), 8.64s (1H), 8.05d (2H, J )
8.0 Hz), 7.96t (1H, J ) 7.5 Hz), 7.80dd (2H, J ) 8.0, 7.5 Hz).
7b: 27% (25%); mp ≈ 330 °C; MS (CI) 464 (M+); MW (calcd)
464.01368. Anal. Calcd for C22H12N2O6S2: C, 56.89; H, 2.60;
N, 6.03. Found: C, 56.76; H, 2.56; N, 6.10.
7d : 70% (58%); mp >360 °C; MS (CI) 451 (M+); MW (calcd)
450.99328. Anal. Calcd for C20H9N3O6S2: C, 53.21; H, 2.01;
N, 9.31. Found: C, 53.25; H, 2.07; N, 9.30.
Ack n ow led gm en t. We thank EPSRC for funding
(A.J .M.) and the Royal Society for funding visits to
Durham (I.F.P. and L.M.G.).
7e: 84% (77%); mp >360 °C; MS (CI) 527 (M+ + 18), 509
(M+); MW (calcd) 508.99876. Anal. Calcd for C22H11N3O8S2: C,
51.87; H, 2.18; N, 8.25. Found: C, 51.81; H, 2.25; N, 8.29.
J O990100R