Electron acceptors of the fluorene series. 10. Novel acceptors containing butylsulfanyl, butylsulfinyl, and butylsulfonyl substituents: Synthesis, cyclic voltammetry, charge-transfer complexation with anthracene in solution, and X-ray crystal structures of two tetrathiafulvalene complexes

Article abstract of DOI:10.1021/jo991796r

2,4,5,7-Tetranitro-9-fluorenone (1b) reacts readily with n-butanethiol in dipolar aprotic solvents with selective substitution of nitro groups by butylsulfanyl groups in positions 2 and 7 (2, 3); the 2,5-isomer 4 was formed only as a minor product (<1%). Condensation of fluorenones 2-4 with malononitrile yielded 9-dicyanomethylene derivatives 5-7, which showed strong intramolecular charge transfer (λ ? 510-560 nm) and were found to sensitize the photoconductivity of carbazole-containing polymer films. Oxidation of sulfides 2-4 gave sulfoxide 8 or sulfones 9-11, which then were converted into their corresponding dicyanomethylene derivatives 12-15. All these novel acceptors showed three reversible single-electron reduction waves (cyclic voltammetry) yielding radical anion, dianion, and radical trianion; moreover, acceptors 13-15 showed also a fourth reduction wave, representing reversible tetraanion formation. Substitution of the oxygen of the carbonyl group in the fluorenones by a dicyanomethylene group increased the thermodynamic stability (K(SEM) growth) of the radical anion; K(SEM) ranged from 3 x 10⁵ to 3 x 10⁹ M^-1. CV measurements characterize compounds 3, 4 (EA = 1.86-1.89 eV) as poor acceptors, 2, 6-11 (EA = 2.13-2.31 eV) as moderate acceptors, and 5, 12- 15 (EA = 2.53-2.66 eV) as strong electron acceptors. Charge-transfer complex (CTC) formation between acceptors 9, 10, 13, 14, and anthracene as a donor was monitored by the appearance of additional low-energy bands in the visible region (CTC bands) of their electron absorption spectra. Increasing the EA of the acceptors from 9-fluorenones to the corresponding 9- dicyanomethylenefluorenes increases the complexation constants K(CTC) by 2.5- 3 times, while sulfonyl substituents present substantial steric hindrance for complexation (as compared to the nitro group), decreasing K(CTC) values. Two CTCs for acceptors 14 and 17 with tetrathiafulvalene (TTF) were obtained, and their structures were solved by single-crystal X-ray diffractometry, giving the stoichometries 14:TTF, 2:3, and 17:TTF:PhCl, 1:1:0.5. In the former complex the packing motif is a mixed ... DDAD'A ... stack; in the latter complex the D and A moieties form unusually close CT pairs, which pack in a herringbone motif.

Full text of DOI:10.1021/jo991796r

J . Org. Chem. 2000, 65, 3053-3063
3053
Electr on Accep tor s of th e F lu or en e Ser ies. 10.1 Novel Accep tor s
Con ta in in g Bu tylsu lfa n yl, Bu tylsu lfin yl, a n d Bu tylsu lfon yl
Su bstitu en ts: Syn th esis, Cyclic Volta m m etr y, Ch a r ge-Tr a n sfer
Com p lexa tion w ith An th r a cen e in Solu tion , a n d X-r a y Cr ysta l
Str u ctu r es of Tw o Tetr a th ia fu lva len e Com p lexes
Igor F. Perepichka,*,† Anatolii F. Popov,† Tatyana V. Orekhova,† Martin R. Bryce,*,‡
Alexander M. Andrievskii,§ Andrei S. Batsanov,‡ J udith A. K. Howard,‡ and
Nikolai I. Sokolov|
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., Stock Company “Center of International Cooperation and Service”
(SC “CMESS”) Moscow 123100, Russian Federation, and Laboratory of Holography,
Natural Faculty, University “Kievo-Mogilyanskaya Academy”, Kiev 254145, Ukraine
Received November 19, 1999
2,4,5,7-Tetranitro-9-fluorenone (1b) reacts readily with n-butanethiol in dipolar aprotic solvents
with selective substitution of nitro groups by butylsulfanyl groups in positions 2 and 7 (2, 3); the
2,5-isomer 4 was formed only as a minor product (<1%). Condensation of fluorenones 2-4 with
malononitrile yielded 9-dicyanomethylene derivatives 5-7, which showed strong intramolecular
charge transfer (λ ≈ 510-560 nm) and were found to sensitize the photoconductivity of carbazole-
containing polymer films. Oxidation of sulfides 2-4 gave sulfoxide 8 or sulfones 9-11, which then
were converted into their corresponding dicyanomethylene derivatives 12-15. All these novel
acceptors showed three reversible single-electron reduction waves (cyclic voltammetry) yielding
radical anion, dianion, and radical trianion; moreover, acceptors 13-15 showed also a fourth
reduction wave, representing reversible tetraanion formation. Substitution of the oxygen of the
carbonyl group in the fluorenones by a dicyanomethylene group increased the thermodynamic
stability (KSEM growth) of the radical anion; KSEM ranged from 3 × 105 to 3 × 109 M-1. CV
measurements characterize compounds 3, 4 (EA ) 1.86-1.89 eV) as poor acceptors, 2, 6-11 (EA
) 2.13-2.31 eV) as moderate acceptors, and 5, 12-15 (EA ) 2.53-2.66 eV) as strong electron
acceptors. Charge-transfer complex (CTC) formation between acceptors 9, 10, 13, 14, and anthracene
as a donor was monitored by the appearance of additional low-energy bands in the visible region
(CTC bands) of their electron absorption spectra. Increasing the EA of the acceptors from
9-fluorenones to the corresponding 9-dicyanomethylenefluorenes increases the complexation
constants KCTC by 2.5-3 times, while sulfonyl substituents present substantial steric hindrance
for complexation (as compared to the nitro group), decreasing KCTC values. Two CTCs for acceptors
14 and 17 with tetrathiafulvalene (TTF) were obtained, and their structures were solved by single-
crystal X-ray diffractometry, giving the stoichometries 14:TTF, 2:3, and 17:TTF:PhCl, 1:1:0.5. In
the former complex the packing motif is a mixed ...DDAD′A... stack; in the latter complex the D
and A moieties form unusually close CT pairs, which pack in a herringbone motif.
In tr od u ction
acceptors fluorene derivatives are the most effective
photoconductivity sensitizers for poly-N-vinylcarbazole
(PVK), poly-N-(2,3-epoxypropyl)carbazole (PEPC), and
related carbazole-containing polymers.4,5 Recently, other
applications of this class of electron acceptors in advanced
materials have been demonstrated: (i) polynitro-9-dicya-
nomethylenefluorenes were found to form 1:2 CTCs with
bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) with
metallic-type electrical conductivity;6 (ii) the polynitro-
Electron acceptors of the fluorene series are of consid-
erable interest in the study of charge-transfer complexes
(CTC) with semiconducting and photoconducting proper-
ties and as electron transport materials.2,3 An extended
π-system structurally similar to that in carbazole deter-
mines the fact that among different classes of electron
* Corresponding author. E-mail: M.R.Bryce@durham.ac.uk.
† Institute of Physical Organic & Coal Chemistry, Donetsk.
‡ Department of Chemistry, University of Durham.
§ SC "CMESS”, Moscow.
(4) Strohriegl, P.; Grazulevicius, J . V. In Handbook of Organic
Conductive Molecules and Polymers; Nalwa, H. S., Ed.; Wiley: Chich-
ester, 1997; Vol. 1, p 553, and references therein.
(5) Getmanchuk, Yu. P.; Sokolov, N. I. In Fundamentals of Optical
Memory and Medium; Vyshcha Shkola: Kiev, 1983; Issue 14, p 11 (in
Russian). (b) 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, 1995; p 318. (c)
Perepichka, I. F.; Mysyk, D. D.; Sokolov, N. I. Synth. Met. 1999, 101,
9.
| University “Kievo-Mogilyanskaya Academy”, Kiev.
(1) Part 9: Mysyk, D. D.; Perepichka, I. F.; Perepichka, D. F.; Bryce,
M. R.; Popov, A. F.; Goldenberg, L. M.; Moore, A. J . J . Org. Chem.
1999, 64, 6937.
(2) Sbrana, G.; Scotton, M.; Angeloni, L. J . Chem. Soc., Perkin Trans.
2 1982, 1611.
(3) Matsui, M.; Fukuyasu, K.; Shibata, K.; Muramatsu, H. J . Chem.
Soc., Perkin Trans.
2 1993, 1107. (b) Matsui, M.; Shibata, K.;
Muramatsu, H.; Nakazumi, H. J . Mater. Chem. 1996, 6, 1113. (c) Hoegl,
H.; Barchietto, G.; Tar, D. Photochem. Photobiol. 1972, 16, 335.
(6) Horiuchi, S.; Yamochi, H.; Saito, G.; Sakaguchi, K.; Kusunoki,
M. J . Am. Chem. Soc. 1996, 118, 8604.
10.1021/jo991796r CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/26/2000

3054 J . Org. Chem., Vol. 65, No. 10, 2000
Perepichka et al.
Ch a r t 1
fluoren-9-ylidene fragment was used as a terminal ac-
ceptor unit in push-pull D-π-A chromophores with
high second-order nonlinear optical (NLO) susceptibility7
and as a side group in an electroactive polythiophene sys-
tem.8 Our recent X-ray crystallographic investigations of
CTC of fluorene acceptors with TTF donors have dem-
onstrated the possibility of various stoichometries (D:A
) 1:1 and 2:1), different motifs of crystal packing within
the stacks (DADA, DDADDA), and supramolecular ar-
chitectures for the CTC depending on the structures of
the components, offering an approach to crystal engi-
neering and the design of CTC with predictable electronic
properties.9-12 These studies are motivating increased
interest in fluorene acceptors within the field of materials
chemistry.
Nitro derivatives of 9-fluorenone and 9-dicyanometh-
ylenefluorene are the best known in this series of electron
acceptors. Among other electron-withdrawing substitu-
ents on the benzene rings, derivatives containing CO2H,
CO2R, CONH2, CONHR, CONR2, CN, Cl, Br, and I have
been synthesized.2,13-15
Recently, proceeding from the readily accessible fluo-
rene-2,7-disulfonyl chloride, we synthesized a series of
derivatives containing sulfonyl groups, i.e., 4,5-dinitro-
9-X-fluorene-2,7-disulfonic acids derivatives, and dem-
onstrated their ability to form CTC and to sensitize PEPC
photoconductivity.16 In the framework of our interest in
nucleophilic substitution reactions in fluorene acceptors17
we have now synthesized new polynitro fluorene deriva-
tives with substituents BuS, BuSO, and BuSO2 and
studied their electrochemical behavior, intramolecular
charge transfer (ICT) for derivatives with donor butyl-
sulfanyl substituents, and the formation of intermolecular
charge-transfer complexes (CTC) with anthracene in
solution and with tetrathiafulvalene (TTF) in the solid
state. We have also evaluated two derivatives as sensitiz-
ers of photoconductivity in hole transport materials.
Resu lts a n d Discu ssion
Syn th esis. Polynitro-9-fluorenones are known to react
with various proton-containing nucleophiles with sub-
stitution of the nitro group by a nucleophile.18-20 Thus,
2,4,5,7-tetranitro-9-fluorenone (1b) reacts with secondary
aliphatic amines with the selective substitution of the
nitro group at position 2 by the amino group.17,18 Reaction
of 1b with water in hexamethylphosphoric triamide
(HMPA) yields a mixture of products from substitution
of the nitro groups by OH at positions 2 and 4, the ratio
of which depends on the reaction conditions.19 Nitro group
substitution by the hydroxy group in 2,4,7-trinitro-9-
fluorenone (1a )19 and 2,5,7-trinitro-4-cyano-9-fluorenone
(1c)20 occurs selectively at position 4 under the action of
water in HMPA. On the other hand, Ong showed21 that
polynitro-9-fluorenones react with 1-butanethiol in the
presence of equimolar quantities of AlCl3 to yield the
corresponding polynitrofluorene-9-thioacetals. We now
report that in bipolar aprotic solvents, i.e. dimethyl
sulfoxide (DMSO), N,N-dimethylformamide (DMF), and
HMPA, the reaction occurs by another route, namely,
with the substitution of nitro groups similarly to other
nucleophiles considered above. Depending on the reaction
conditions, substitution of one or two nitro groups by
butylsulfanyl groups was observed. The reaction pro-
ceeded selectively in positions 2 and 7 of the fluorene
nucleus, and 4(5)-isomers were formed only in trace
amounts (Scheme 1). Thus, when the reaction was carried
out in HMPA, in addition to the 2,7-isomer 3 as the major
product, the 2,5-isomer 4 was isolated as a minor product
in ca. 1% yield.
(7) Perepichka, I. F.; Perepichka, D. F.; Bryce, M. R.; Chesney, A.;
Popov, A. F.; Khodorkovsky, V.; Meshulam, G.; Kotler, Z. Synth. Met.
1999, 102, 1558. (b) Moore, A. J .; Chesney, A.; Bryce, M. R.; Batsanov,
A. S.; Howard, J . A. K.; Perepichka, I. F.; Perepichka, D. F.; Khodor-
kovsky, V.; Meshulam, G.; Kotler, Z.; Kelly, J . F.; Berkovic, G.; Mazor,
R. Manuscript in preparation.
(8) Skabara, P. J .; Serebryakov, I. M.; Perepichka, I. F. Synth. Met.
1999, 101, 1336.
(9) 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, 63, 6484.
(10) Moore, A. J .; Bryce, M. R.; Batsanov, A. S.; Heaton, J . N.;
Lehmann, C. W.; Howard, J . A. K.; Robertson, N.; Underhill, A. E.;
Perepichka, I. F. J . Mater. Chem. 1998, 8, 1541.
(11) Bryce, M. R.; Moore, A. J .; Batsanov, A. S.; Howard, J . A. K.;
Robertson, N. R.; Perepichka, I. F. In Supramolecular Engineering of
Synthetic Metallic Materials: Conductors and Magnets; Veciana, J .,
Rovira, C., Amabilino, D. B., Eds.; NATO ASI Series, Vol. 518; Kluwer
Publishers: Dordrecht, 1999; p 437.
(12) Kuz’mina, L. G.; Perepichka, I. F.; Perepichka, D. F.; Howard,
J . A. K.; Bryce, M. R.; Alexandrov, G. G.; Kuz’min, V. S. Izv. RAN,
Ser. Khim., submitted.
(13) Sulzberg, T.; Cotter, R. J . J . Org. Chem. 1970, 35, 2762. (b)
Bloom, M. S.; Groner, C. F. Res. Disclosure 1977, 32. (c) Mysyk, D. D.;
Sivchenkova, N. M.; Kampars, V. E.; Neilands, O. Ya. Izv. Akad. Nauk
Latv. SSR, Ser. Khim. 1987, 621 (in Russian).
(14) Mysyk, D. D.; Perepichka, I. F.; Edgina, A. S.; Neilands, O. Ya.
Latvian J . Chem. 1991, 727 (in Russian). (b) 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). (c) Miyamura, M.; Tsori, K.; Kato, H.; Tomii, M.
J apan Kokai 77,102,734 (Chem. Abstr. 1978, 88, 97420q).
(15) Newman, M. S.; Blum, J . J . Am. Chem. Soc. 1964, 86, 5600.
(16) Mysyk, D. D.; Perepichka, I. F.; Sokolov, N. I. J . Chem. Soc.,
Perkin Trans. 2 1997, 537.
(17) 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. (b) 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.
Acceptors 2-4 are orange crystalline compounds, their
color being due to intramolecular charge transfer (ICT)
(18) Chetkina, L. A.; Povetyeva, Z. P.; Bel’skii, V. K.; Bespalov, B.
P. Kristallografiya 1985, 30, 910 (Chem. Abstr. 1985, 103, 204122w).
(19) Andrievskii, A. M.; Grekhova, N. G.; Andronova, N. A.; Shifrina,
R. R.; Alexandrov, V. N.; Dyumaev, K. M. Zh. Org. Khim. 1982, 18,
1961 (Chem. Abstr. 1983, 98, 106926v).
(20) Semidetko, O. V.; Chetkina, L. A.; Bel’skii, V. K.; Mysyk, D.
D.; Perepichka, I. F.; Andrievskii, A. M. Zh. Obsch. Khim. 1987, 57,
415 (Chem. Abstr. 1988, 108, 204311k).
(21) Ong, B. S. J . Chem. Soc., Chem. Commun. 1984, 266.

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 65, No. 10, 2000 3055
Sch em e 1a
a
(i) 4.4 equiv BuSH, HMPA, rt, 2 days; or 2.8 equiv BuSH, DMSO, 80 °C, 30-60 min; (ii) 4.4 equiv BuSH, DMSO, 80 °C, 1 h; or 3.4
equiv BuSH, HMPA, rt, 4 days; (iii) CH2(CN)2, DMF, rt, 2 h; (iv) CH2(CN)2, DMF, 60-65 °C, 2 h; (v) 27% H2O2, AcOH, 65 °C, 2.5 h; (vi)
27% H2O2, AcOH, 60-65 °C, 24 h; (vii) 27% H2O2, AcOH, 100-108 °C, 6 h; (viii) CH2(CN)2, DMF, rt, 4 h; (ix) CH2(CN)2, DMF, rt, 1 h; (x)
CH2(CN)2, DMF, 40-45 °C, 4 h; (xi) CH2(CN)2, DMF, 50 °C, 25 h.
from the donor sulfur atom to the acceptor fluorene
moiety. Still more intensive ICT (dark-violet color) is ob-
served in their 9-dicyanomethylene derivatives 5-7 ob-
tained by condensation of fluorenones 2-4 with malono-
nitrile in DMF. Oxidation of the sulfides 2-4 with 27%
aqueous hydrogen peroxide in acetic acid gave the cor-
responding sulfoxide (8) and sulfones (9-11). Their con-
densation with malononitrile in DMF yielded 9-dicya-
nomethylenefluorenes 12-15, respectively (Scheme 1).
1H NMR Sp ectr a . Chemical shifts and coupling
constants in the 1H NMR spectra confirm their struc-
tures. The aromatic proton signals were assigned in the
light of previous chemical shift data.1,9,16,17,22 The C4H9S
and C4H9SO2 fragments in compounds 2-7 and 9-11,
13-15 result in a group of signals typical for the butyl
substituent. In the case of sulfoxides 8 and 12 the
asymmetrical sulfur atom leads to two sets of signals
(corresponding to two isomers) from the methylene group
directly linked to the sulfur atom with chemical shifts of
δ 3.25 and 3.04 ppm.
For the strong acceptors 12-15 paramagnetic broad-
ening of the aromatic proton signals was observed and
their interaction with the polar solvent (and/or with trace
amounts of donor compounds) can result in radical ion
species in the solution. Such behavior of strong electron
acceptors of the fluorene series was previously observed,
and it was shown that the addition of a small amount of
an acid resulted in reduction of the fine structure of the
spectrum without changing the chemical shifts of the
protons.9,16 The considerably greater broadening of C(3)-H
and C(6)-H signals, as compared to C(1)-H and C(8)-
H, indicates significant localization of the spin density
on the C-3 and C-6 atoms in the radical anion rather then
on the C-1 and C-8 atoms.
Electr och em istr y. The electrochemical behavior of
these novel electron acceptor compounds was studied by
cyclic voltammetry (CV) in acetonitrile at room temper-
ature, using tetraethylammonium tetrafluoroborate as
the supporting electrolyte. The redox potentials are
summarized in Table 1.
The cyclic voltammograms of the compounds 2-15
exhibit three or four reversible (the last reduction waves
were electrochemically reversible or quasi-reversible)
single-electron reduction waves. It should be noted that
the reversible two-step, single-electron, reduction to yield
sequentially the radical anion and dianion is character-
istic of 9-X-fluorene nitro derivatives.1,9,14a,17,22,23 In our
earlier investigation14a by CV at a graphite electrode only
two first stages of the single-electron reduction were
found to be reversible for compounds 1, 16, and related
acceptors; further reduction processes were highly ir-
reversible and involved three or four electrons. In some
cases a third reduction wave resulting in radical trianion
formation is also observed that is reversible, quasi-
reversible, or irreversible.1,9,17,22 However, when the
potential is further increased, reduction of the nitro
groups and subsequent reactions are observed; that is,
(22) Skabara, P. J .; Serebryakov, I. M.; Perepichka, I. F. J . Chem.
Soc., Perkin Trans. 2 1999, 505.

3056 J . Org. Chem., Vol. 65, No. 10, 2000
Ta ble 1. CV Da ta for Com p ou n d s 1-16a
Perepichka et al.
EA (eV)
1/2
1/2
1/2
1/2
1/2
b
compd
E1 (V)
E2 (V)
E3 (V)
E4 (V)
∆E1-2 (V)
KSEM (M-1
)
1bc
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16a c
16bc
-0.12
-0.41
-0.68
-0.65
-0.01
-0.23
-0.22
-0.32
-0.24
-0.30
-0.32
+0.07
+0.12
+0.05
+0.04
+0.02
+0.23
-0.41
-0.70
-0.96
-0.92
-0.57
-0.77
-0.75
-0.64
-0.57
-0.70
-0.71
-0.53
-0.43
-0.47
-0.47
-0.57
-0.31
-1.47
-1.44
-1.61
-1.60
-1.28
-1.35
-1.41
-1.42
-1.08
-1.25
-1.26
-1.25
-1.09
-1.07
-1.05
-1.37
-1.13
0.29
0.29
0.28
0.27
0.56
0.54
0.53
0.32
0.33
0.40
0.39
0.56
0.55
0.52
0.51
0.59
0.54
8.2 × 105
8.2 × 105
5.6 × 105
3.8 × 105
3.1 × 109
1.4 × 109
9.6 × 108
2.7 × 105
3.9 × 105
6.0 × 106
4.1 × 106
3.1 × 109
2.1 × 109
6.5 × 108
4.4 × 108
1.0 × 1010
1.4 × 109
2.42
2.13
1.86
1.89
2.53
2.31
2.32
2.22
2.30
2.24
2.22
2.61
2.66
2.59
2.58
2.56
2.77
-1.49
-1.39
-1.41
Solvent acetonitrile, electrolyte 0.1 M Et4N+BF4-, scan rate 100 mV s-1; all potentials are given vs Ag/AgCl, An error appeared in
a
b
refs 28a,c: the sign “minus” was omitted when the disproportionation constants for the radical anion were calculated (Kdispr ) 1/KSEM);
this resulted in wrong values of Kdispr tabulated in the papers which, in fact, are KSEM
.
c From ref 9.
slightly weaker (i.e., by 0.09 to 0.16 V) than the strongest
known electron acceptor of the fluorene series, i.e.,
2,4,5,7-tetranitro-9-dicyanomethylenefluorene (16b). Elec-
tron affinities (EAs) of the acceptors 2-15 were estimated
(Table 1) by eq 19,14a using known acceptors 16a ,b as
reference acceptors:
1/2
EA(ref) - EA ) E11/2(ref) - E1
(1)
As seen from Table 1, compounds 2, 6-11 can be
characterized as moderate acceptors (EA ≈ 2.1-2.3 eV),
and the 9-dicyanomethylene derivatives 5, 12-15 are
rather strong acceptors (EA > 2.5 eV), comparable to
strong fluorene acceptors 16a ,b.
The thermodynamic stability of the radical anions was
determined from the difference in potentials of the
corresponding radical anion and dianion using the equa-
tion ∆E ) E11/2 - E21/2 ) 0.059 log KSEM24 (Table 1), where
KSEM is the equilibrium constant in eq 2:
F igu r e 1. Cyclic voltammogram of compound 13 (under the
conditions stated in Table 1).
the system becomes electrochemically irreversible. It is
of interest, therefore, that fluorene derivatives 2-15 are
capable of yielding not only radical anions and dianions
but also fairly stable, reversibly formed radical trianions,
and for compounds 13-15 even tetraanion formation is
observed (Table 1, Figure 1).
KSEM
A + A2- y z 2A•-
(2)
For electron acceptor compounds of the p-benzoquinone
series, and substituted and π-extended analogues, the
degree of charge delocalization in the radical anions
increases in the following order: quinones < dicyano-
quinodiimines < tetracyanoquinodimethanes, and the
thermodynamic stability of the radical anions diminishes
(due to a decrease in intramolecular Coulombic repulsion)
in the same order.25 This results in a decrease in the
9-Fluorenones with butylsulfanyl substituents (2-4)
are relatively weak acceptors with reduction potentials
1/2
E1 ranging from -0.41 to -0.68 V vs Ag/AgCl. Oxida-
tion of the sulfanyl group into the sulfinyl and sulfonyl
analogues decreases the reduction potential by 0.09 and
0.17-0.19 V, respectively. Substitution of oxygen in the
carbonyl group in 9-fluorenones (2-4, 8-11) by the
dicyanomethylene group (5-7, 12-15) significantly in-
creases the acceptor properties of the molecules, which
result in an anodic shift in their reduction potentials by
0.35-0.45 V. Comparison of the reduction potentials for
compounds 3,4 and 6,7 shows that the location of the BuS
substituent on the fluorene nucleus (positions 2 or 4) does
not exert a notable effect upon the electrochemical
behavior of these compounds. This is in agreement with
the approximate equivalence of positions 2 and 4 in
fluorene derivatives in terms of their electronic effect
upon the properties of the molecule, based upon UV and
NMR studies of other derivatives.17
1/2
1/2
difference in the reduction potentials E1 and E2 and,
hence, to a decrease in the equilibrium constant KSEM in
the range of the substituents CdO > CdN-CN >
CdC(CN)2.26-28 The characteristic feature of the least
stable radical anion is represented by the observation
(23) Kuder, J . E.; Pochan, J . M.; Turner, S. R.; Hinman, D.-L. F. J .
Electrochem. Soc.: Electrochem. Sci., Technol. 1978, 125, 1750. (b)
Ramaley, L.; Gaul, S. Can. J . Chem. 1978, 56, 2381.
(24) J ensen, B. S.; Parker, V. D. J . Am. Chem. Soc. 1975, 97, 5211.
(b) Hu¨nig, S. Pure Appl. Chem. 1990, 62, 395.
(25) 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.
(26) Czekanski, T.; Hanack, M.; Becker, J . Y.; Bernstein, J .; Bittner,
S.; Kaufman-Orenstein, L.; Peleg, D. J . Org. Chem. 1991, 56, 1569.
(b) Aumu¨ller, A.; Hu¨nig, S. Liebigs. Ann. Chem. 1986, 165.
Compounds 13 and 14 are rather strong electron
acceptors whose reduction to the radical anion is observed
at positive potential values vs Ag/AgCl. They are only

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 65, No. 10, 2000 3057
that the first and second reduction waves coalesce into a
single two-electron reduction wave.25,28,29
In the acceptors of the fluorene series the opposite
tendency is observed; that is, in the transition from
substituted 9-fluorenones to the corresponding 9-dicya-
nomethylenefluorenes the difference in the potentials for
the first and second reduction waves increases and KSEM
grows from 4 × 105 to 6 × 106 for compounds 2-4, 8-11
up to 4 × 108 to 3 × 109 for 5-7, 12-15, i.e., by 3 orders
of magnitude (Table 1). Thus, in the fluorene acceptors,
substitution of oxygen of the carbonyl group by a dicya-
nomethylene group does not decrease (as in benzoquino-
nes and TCNQ derivatives) but, instead, increases the
thermodynamic stability of the radical anion.
In tr a m olecu la r Ch a r ge Tr a n sfer (ICT). Intramo-
lecular donor-acceptor interaction in compounds 2-4
was manifested in their electron absorption spectra: in
the short-wave visible region additional bands corre-
sponding to ICT from the donor sulfur atom onto the
acceptor fluorene unit appeared {the ICT nature of the
transition was corroborated by studies of concentration
dependencies of its intensity, which showed good linearity
A ) f([C])}. Increasing the acceptor ability of the fluorene
moiety by substitution of the carbonyl oxygen atom by
the dicyanomethylene group (by 0.35-0.40 eV, according
to CV data; Table 1) leads to an enhancement of ICT,
which is manifested in a significant bathochromic shift
of the ICT bands (from ∼420-430 nm for 2, 3 to ∼510-
560 nm for 5-7; see Experimental Section).
In ter m olecu la r CTC in Solu tion . The ability of the
sulfonyl-containing acceptors 9, 10, 13, and 14 to form
intermolecular CTC with donors was studied in 1,2-
dichloroethane (DCE) solution using anthracene as the
π-donor. CTC formation is accompanied by the appear-
ance of two additional bands in the visible region (CT
bands), which are absent in the initial components
(Figure 2). Isomolar series experiments gave A:D ) 1:1
stoichometries for all CTC:
F igu r e 2. Electronic absorption spectra for CTC of accep-
tors 9, 10, 13, and 14 with anthracene in 1,2-dichloroethane,
25 °C.
The electron affinities of acceptors 9, 10, 13, and 14
were also estimated from the energies of their CTC by
eq 4:
EA - EA(ref) ) hνCTC(ref) - hνCTC
(4)
where hνCTC(ref) and hνCTC denote charge-transfer ener-
gies in CTC of the reference acceptor and the acceptor
under analysis in the same conditions. EACTC values
(Table 2) for fluorene derivatives 9 and 10 are in good
agreement with EACV values (Table 1), whereas for the
dicyanomethylene derivatives 13 and 14 the CTC method
gives somewhat higher electron affinities (by 0.08-0.12
eV) than CV. This can be explained by an accuracy in
the estimation of the maximum of the longest-wavelength
CT absorption, which can represent two or more overlap-
ping CT bands.
X-r a y Cr ysta l Str u ctu r es of CTCs 14:TTF , 2:3
Stoich iom etr y (I) a n d 17:TTF :P h Cl, 1:1:0.5 Stoich i-
om etr y (II). The asymmetric unit of crystal I comprises
one acceptor molecule 14 (A) and one complete TTF
molecule (D) in general positions and a half of another
TTF molecule (D′) located at a crystallographic inversion
center (Figure 3). Thus the donor:acceptor ratio of 3:2 is
the first example of this stoichiometry in TTF-fluorene
complexes. Molecule D′ is rigorosly planar, whereas D is
slightly puckered ((0.07 Å); their mean planes form a
dihedral angle of 7° between them and are inclined,
respectively, by 4° and 5° to the fluorene mean plane.
The long axes of the D and D′ molecules are nearly
perpendicular (88°) to each other. The packing motif is a
mixed stack with ...DDAD′A... succession (Figure 4) with
interplanar separations D-D ca. 3.6 Å, D-A 3.3 Å, and
A-D′ 3.5 Å.
The acceptor molecule shows extensive disorder. Each
nitro group is disordered over two positions, tilted out of
the fluorene plane in opposite directions. The nitrogen
atom [N(4) or N(5)] and one oxygen atom [O(42) or O(52)]
of each nitro group are disordered, while the other oxygen
atom [O(41) or O(51)] remains in the same position. In
each single molecule the nitro groups can only be tilted
in opposite directions from the fluorene plane, as the cis-
disposition would cause improbably short O‚‚‚O contacts.
The observed planarity of the fluorene system is probably
spurious, masking the overlap of two opposite-sense
puckerings. Both n-butyl chains are also disordered.
The asymmetric unit of II (Figure 5) comprises one
acceptor (17)16 and one donor (TTF) molecule in general
A + D {K } [Aδ-,Dδ+
]
(3)
CTC
Complexation constants, KCTC, and molar extinction
coefficients, ꢀCTC, are summarized in Table 2, together
with literature data for related acceptors. The sulfonyl
substituent is more bulky than the NO2 group, which
leads to some hindrance for CTC formation and, hence,
a decrease in KCTC and ꢀCTC values (cf. 9 f 10, 13 f 14
and also data for 17 and 18; Table 2).
(27) Gonza´lez, M.; de Miguel, P.; Mart´ın, N.; Segura, J . L.; Seoane,
C.; Ort´ı, E.; Viruela, R.; Viruela, P. M. Adv. Mater. 1994, 6, 765. (b)
Mart´ın, N.; Segura, J . L.; Seoane, C.; Tor´ıo, C.; Gonza´lez, A.; Pingarro´n,
J . M. Synth. Met. 1994, 64, 83. (c) Barranco, E.; Gonza´lez, A.; Mart´ın,
N.; Pingarro´n, J . M.; Segura, J . L.; Seoane, C.; de la Cruz, P.; Langa,
F. Synth. Met. 1993, 55-57, 1717. (d) Mart´ın, N.; Segura, J . L.; Seoane,
C.; Albert, A.; Cano, F. H. J . Chem. Soc., Perkin Trans. 2 1993, 2363.
(e) Barranco, E.; Mart´ın, N.; Segura, J . L.; Seoane, C.; de la Cruz, P.;
Langa, F.; Gonza´lez, A.; Pingarro´n, J . M. Tetrahedron 1993, 49, 4881.
(f) de la Cruz, P.; Mart´ın, N.; Miguel, F.; Seoane, C.; Albert, A.; Cano,
F. H.; Leverenz, A.; Hanack, M. Synth. Met. 1992, 48, 59.
(28) Bando, P.; Mart´ın, N.; Segura, J . L.; Seoane, C.; Ort´ı, E.;
Viruela, P. M.; Viruela, R.; Albert, A.; Cano, F. H. J . Org. Chem. 1994,
59, 4618. (b) Bando, P.; Davidkov, K.; Mart´ın, N.; Segura, J . L.; Seoane,
C.; Gonza´lez, A.; Pingarron, J . M. Synth. Met. 1993, 55-57, 1721. (c)
de la Cruz, P.; Mart´ın, N.; Miguel, F.; Seoane, C.; Albert, A.; Cano, F.
H.; Gonza´lez, A.; Pingarron, J . M. J . Org. Chem. 1992, 57, 6192.
(29) Batsanov, A. S.; Bryce, M. R.; Coffin, M. A.; Green, A.; Hester,
R. E.; Howard, J . A. K.; Lednev, I. K.; Mart´ın, N.; Moore, A. J .; Moore,
J . N.; Ort´ı, E.; Sa´nchez, L.; Saviro´n, M.; Viruela, P. M.; Viruela, R.;
Ye, T.-Q. Chem. Eur. J . 1998, 4, 2580. (b) Kini, A. M.; Cowan, D. O.;
Gerson, F.; Mo¨ckel, R. J . Am. Chem. Soc. 1985, 107, 556.

3058 J . Org. Chem., Vol. 65, No. 10, 2000
Perepichka et al.
Ta ble 2. CTC F or m a tion betw een Accep tor s 9, 10, 13, 14, 17, 18, a n d An th r a cen e in Dich lor oeth a n e, 25 °C
variation range of concentrations
CT
a
a
compd
λmax (nm)
CA × 103 (M)
5.75-46.0
0.98-5.38
0.61-4.91
0.28-3.64
CD × 102 (M)
0.25-4.03
1.00-5.52
0.25-4.00
0.84-5.52
KCTC (M-1
)
ꢀCTC (M-1 cm-1
)
na
R0
Rf
EA (eV)
9
10
13
14
581,b 495
550sh,b 502
716,b 515sh
705,b 500sh
648
4.98 ( 0.34
1.94 ( 0.22
14.05 ( 0.63
5.22 ( 0.34
709 ( 42
544 ( 58
1127 ( 38
926 ( 53
23
32
26
22
0.9996
0.9995
0.9996
0.9992
1.04
1.26
1.74
0.47
2.34
2.22
2.74
2.71
2.56
16a c
17c
18c
725
685
1.26-7.57
1.98-3.95
0.32-5.07
1.28-5.12
8.17 ( 0.43
3.60 ( 0.71
989 ( 42
878 ( 150
33
15
0.9994
0.9992
1.90
2.05
a
n is a number of measurements: R0 is multiple correlation coefficient; Rf is the misalignment factor between an experimental datum
and a fit, Rf ) [∑(ACTC(i) - ACTC(i)calc)2/∑ACTC(i)exp] × 100%, where ACTC(i) and ACTC(i)
are experimental and calculated values of a
exp
exp
calc
b
CTC absorbance for ith point, respectively. These λmax were used for measurements ACTC to estimate KCTC and ꢀCTC values (see
Experimental Section). c From ref 16.
F igu r e 3. Molecules in structure I (showing the disorder).
Primed atoms are related via the inversion center; butyl
hydrogens are omitted for clarity.
F igu r e 5. Molecular structure of II showing disorder of the
chlorobenzene molecule (H atoms omitted).
F igu r e 4. Crystal packing of I (disorder is not shown).
positions and a half of a chlorobenzene molecule, which
is situated about an inversion center and disordered over
two positions, related via this center. Molecule 17 is
distorted in the usual way:9,17,30 the nitro groups in
positions 4 and 5 are tilted to opposite sides of the
F igu r e 6. Crystal packing of II.
fluorene plane to avoid short O‚‚‚O contacts, and the
These CT pairs are packed in a herringbone motif (Figure
fluorene moiety itself is bent to follow the tilt. Both rings
6), forming a layer parallel to the (0 0 1) plane. Chlo-
of the TTF molecule are planar, with a 6° twist around
the central C(1T)dC(4T) bond. The donor and acceptor
robenzene molecules and phenyl groups of 17 are ap-
proximately perpendicular to the donor/acceptor moieties
molecules lie approximately parallel, with extremely
and parallel to the layers that they separate from each
short contacts S(1T)‚‚‚C(14) 3.18 Å, S(1T)‚‚‚C(16) 3.26 Å,
other.
S(2T)‚‚‚C(8) 3.20 Å, and S(3T)‚‚‚C(1) 3.32 Å, cf. the
Certain bond distances in the 14 and 17 moieties of I
normal van der Waals S‚‚‚C contact distance31 of 3.61 Å.
and II (Table 3) differ appreciably from neutral molecules
with a similar core.30,32 Thus the C(9)dC(14) bond [1.374-
(30) Silverman, J .; Yannoni, N. F.; Krukonis, A. P. Acta Crystallogr.
Sect. B 1974, 30, 1474.
(31) Rowland, R. S.; Taylor, R. J . Phys. Chem. 1996, 100, 7384.
(4) Å in I, 1.379(4) in II] is longer than in 16b,30 16b.-
PhCl,32 and 18′(R ) NH2)32 [1.354(15), 1.357(2), and

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 65, No. 10, 2000 3059
Ta ble 3. Selected Bon d Dista n ces (Å) a n d Tor sion
An gles a r ou n d C(9)dC(14) Bon d (τ, d eg)
I
II
C(9)-C(10)
C(9)-C(13)
C(9)-C(14)
C(14)-CN, av
τ
1.461(4)
1.459(5)
1.374(4)
1.426(5)
5.3
1.467(4)
1.448(4)
1.379(4)
1.426(4)
2.9
1.355(7) Å, respectively]. The C(9)-C(10) bond and C(9)-
C(13) bonds are shorter, averaging 1.460(5) Å in I and
1.458(4) in II, vs 1.470(9), 1.480(2), and 1.474(7) Å in the
neutral species 16a , 16b, and 18′, respectively. The
C(14)-CN bonds [mean 1.426(5) Å in both I and II] are
also shorter than in the neutral species [1.436(9), 1.444-
(2), and 1.440(7) Å]. These differences can be attributed
to an accumulation of negative charge on the acceptors
in I and II. To envisage this, one can refer to metal
π-complexes with the η5-fluorenyl ligand,33 wherein all
C-C bonds of the five-membered ring are of similar
length (1.43-1.44 Å). On the other hand, in II the central
C(1T)dC(4T) bond of the TTF molecule [1.361(4) Å] is
longer than in the crystal of pure TTF [1.349(3) Å]34 and
the adjacent C-S bonds are shorter [mean 1.740(3) vs
1.757(2) Å], indicating35 a positive charge of 0.4-0.5e.
Thus a considerable CT interaction takes place in II and
probably in I, although intense thermal libration (or
disorder) of the TTF molecules in I precluded determining
their bond lengths with sufficient precision.
F igu r e 7. Spectral response of electrophotographic sensitivity
(S∆V, m2 J -1) for PEPC films sensitized by 2 mol % of acceptors
5, 6, 1a , and 16a .
Ch a r t 2
Sen sitization of P EP C P h otocon du ctivity by Elec-
tr on Accep tor s 5 a n d 6. 2,7-Bis(butylsulfonyl)-9-dicya-
nomethylenefluorene has previously been used as a
sensitizer in electrophotographic materials,36 and re-
cently, we showed that derivatives of 4,5-dinitro-9-X-
fluorene-2,7-disulfonic acid can sensitize the PEPC pho-
toconductivity and be used in photothermoplastic storage
media (PTSM).16 However, in both these cases the sulfur
substituents in the acceptors were in the form of electron-
withdrawing SO2 groups.
We have now studied analogues containing electron-
donating butylsulfanyl substituents, i.e., 5 and 6, as
sensitizers of photoconductivity in PTSM. Figure 7
demonstrates the spectral response of electrophoto-
graphic sensitivity (S∆, m2 J -1) of PTSM based on PEPC
films sensitized by acceptors 5 and 6, as well as by the
known fluorene acceptors 1a and 16a , widely used as
sensitizers of the photoconductivity of carbazole-contain-
ing polymers.4,5a In the short-wavelength visible region,
both 5 and 6 show a lower level of electrophotosensitivity
than sensitizer 1a (the latter was the first fluorene
acceptor introduced by IBM in its Copier 1 series in
19704), although their electron affinities are higher than
for 1a (EA ) 2.2 eV). However, the spectral responses
for 5 and 6 have no such sharp decrease of S∆ with
increasing λ; thus in the long-wavelength region (>600
nm for 5 and >650 nm for 6), these new acceptors show
higher S∆ values than 1a , and in the near-infrared region
(>750 nm) acceptor 5 shows even higher S∆ values than
an effective sensitizer 16a . Despite ICT observed in these
novel acceptors (see above) the spectral response of S∆
does not show an increase of the photosensitivity in the
ICT region of the acceptors, as was observed for other
fluorene ICT acceptors (19, 20,5c,17a 21,37 and 2238,39). This
can be explained by the low intensity of the ICT bands
in acceptors 5 and 6 (ꢀICT 2600 and 1500 M-1 cm-1
respectively), whereas acceptors 19-22 showed ꢀICT
,
≈
(32) Perepichka, I. F.; Batsanov, A. S.; Bryce, M. R. Unpublished
data.
(33) Atwood, J . L.; Shakir, R.; Malito, J . T.; Herberhold, M.;
Kremnitz, W.; Bernhagen, W. P. E.; Alt, H. G. J . Organomet. Chem.
1979, 165, 65. (b) Schmid, H. G.; Alt, H. G.; Milius, W. J . Organomet.
Chem. 1996, 525, 15, and references therein.
(37) Semenenko, N. M.; Abramov, V. N.; Kravchenko, N, V.;
Trushina, V. S.; Buyanovskaya P. G.; Kashina, V. L.; Mashkevich, I.
V. Zh. Obsch. Khim. 1985, 55, 324. (b) 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.
(34) Cooper, W. F.; Edmonds, J . W.; Wudl, F.; Coppens, P. Cryst.
Struct. Commun. 1974, 3, 23.
(35) Clemente, D. A.; Marzotto, A. J . Mater. Chem. 1996, 6, 941.
(36) Bugner, D. E.; Kung, T.-M., Rossl, L. US Patent 4,948,911,
1990.
(38) 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.

3060 J . Org. Chem., Vol. 65, No. 10, 2000
Perepichka et al.
fitting based on a complete solution of eq 5:9,16,40
9000-10000 M-1 cm-1 or more. Nevertheless, acceptors
5 and 6 showed good rheological properties in PTSM
films: the maximal diffraction efficiency, ηmax, for planar
light wave holograms was 16% and 18% for 5 and 6,
respectively, which allowed the attainment of real holo-
graphic sensitivity of PTSM by a visualized image Sη ≈
60-90 m2 J -1 (He-Ne laser, λ ) 632.9 nm). This level of
photosensitivity Sη makes these derivatives suitable for
using in practice as sensitizers in PTSM for hologram
recording.
ꢀCTC
1
ACTC
)
CA + CD
+
-
[
(
)
2
KCTC
2
1
CA + CD
+
- 4CACD (5)
(
)
]
KCTC
x
where ACTC is an absorbance of CTC (at λmaxCT) for given
concentrations of donor and acceptor, CA and CD.
X-r a y Cr ysta llogr a p h y. The single-crystal X-ray diffrac-
tion experiment for I was carried out on a Siemens P4 four-
circle diffractometer, using graphite-monochromated Mo KR
radiation; for II with
a SMART 1K CCD area detector
Con clu sion s
(mounted on a three-circle diffractometer) using Si-monochro-
mated synchrotron radiation (Daresbury, station 9.8) and an
Oxford Cryosystems open-flow N2 gas cryostat. Analytical
absorption correction was applied for I (six crystal faces
indexed, ABSPSI program,41 min. and max. transmission
factors 0.79 and 0.87). For II, intensities were corrected for
absorption and decline of the primary beam intensity, by
semiempirical methods based on Laue equivalents and mul-
tiple measurements (SADABS program,42 min./max. correction
factors 0.72/1.00). The structures were solved by direct meth-
ods and refined by full-matrix least-squares against F2 of all
data, using SHELXTL software.43 In I, non-hydrogen atoms
were refined with anisotropic displacement parameters (dis-
ordered carbon atoms in isotropic approximation), with all H
atoms in a “riding” model. In II, non-hydrogen atoms were
refined in anisotropic and H atoms in isotropic approximation,
except for the disordered benzene ring (therein, non-hydrogen
atoms isotropic, H atoms ”riding”). Crystal data and experi-
mental details are listed in Table 4; atomic coordinates,
thermal parameters, and bond distances and angles have been
deposited at the Cambridge Crystallographic Data Centre.44
P h ot op h ysica l Mea su r em en t s of Sen sit ized P E P C
F ilm s. PTSM were prepared in the following way: anionic
PEPC (0.5 g)45 and a corresponding amount of the acceptor
were dissolved separately in methyl ethyl ketone (both in 5
mL), and then the solutions were combined and filtered. The
resulting solution was supported on an ITO-coated glass base.
The final thickness of the photoconductive films was 1.2 ( 0.1
µm. The surface of the film was charged by a positive corona
discharge grid, with the final potentials were V0 ≈ 120-160
V µm-1 (measured by the dynamic sonde method). The relative
dark decay of the surface potential (∆V × 100/V0) was
estimated for the time of 30 s (∆V ) V0 - Vτ, where Vτ is the
charge potential of the surface in the dark after τ ) 30 s) and
lies in the range 10-15%. The electrophotographic sensitivity
(S∆V, m2 J -1) was estimated on the level of 20% decay of the
initial potential under illumination with wavelengths of 400-
900 nm and an intensity of 0.1 µWt cm-1. Real holographic
sensitivity (Sη, m2 J -1) was estimated at the level of 1%
diffraction efficiency (η ) 1%) of the visualized image by
recording holograms of the planar light wave at the spatial
frequency of ν ) 450 mm-1 with irradiation of a He-Ne laser
(λ ) 632.9 nm). The maximal diffraction efficiency, achieved
without amplification of the hologram recording (ηmax, %), was
found as the ratio of the beam intensity diffracted into the
first order of a diffraction to the intensity of the beam grazed
on the hologram, when the ratio of the intensities of the
integrated beams was 1:3.
New fluorene acceptors (2-15) containing BuS, BuSO,
and BuSO2 substituents have been synthesized. Nucleo-
philic substitution of the nitro groups in 2,4,5,7-tetrani-
tro-9-fluorenone (1b) by butylsulfanyl groups proceeds
selectively, giving 2- and 2,7-substitution (with the 2,5-
isomer as a minor product, <1%). ICT observed in 3 and
4, and more pronounced in 5-7, is manifested in the
appearance of the corresponding ICT bands in the visible
region of the electronic absorption spectra. Cyclic volta-
mmetry showed three or four reversible single-electron
reduction waves for acceptors 2-15 (compounds 13-15
gave electrochemically stable tetraanions). The new
acceptors readily formed charge-transfer complexes with
electron donors, as demonstrated by the complexation of
9, 10, 13, and 14 with anthracene in solution (dichloro-
ethane) and by CTC of 14 and 17 with TTF in the solid
state. Single-crystal X-ray analysis for two complexes, 14:
TTF (2:3 stoichiometry) and 17:TTF:PhCl (1:1:0.5 stoi-
chiometry), showed interesting packing motifs. Further
studies on the electronic and optical properties of fluorene
acceptors, with particular emphasis on inter- and in-
tramolecular CT processes of relevance to optoelectronic
devices, will be reported in due course.
Exp er im en ta l Section
Gen er a l P r oced u r es. Acetonitrile for CV and UV-vis
spectral measurements was twice distilled from P4O10, then
from CaH2. 1,2-Dichloroethane for CTC measurements was
twice treated with concentrated sulfuric acid, washed with
water, dried over CaCl2, and twice distilled from P4O10
.
TLC analyses were performed using Chemapol “Silufol UV
254” precoated silica aluminum backed sheets; eluents were
benzene, benzene/dioxane, (4-8):1, or toluene/dioxane/heptane,
(4-8):(1-3):1, mixtures. For column chromatography, Che-
mapol Silicagel (100-160 mesh or 40-100 mesh) was em-
ployed, with benzene or benzene/acetone, (2-5):1, as eluents.
Electr och em ica l Mesu r em en ts. Cyclic voltammetry ex-
periments were performed on a BAS CV50W voltammetric
analyzer and on a EG&G PARC Model 263A potentiostat, both
with iR compensation and PC-controlled. Platinum wire,
platinum disk [Ø 1.6 mm (BAS), Ø 2.0 mm (PARC)], and Ag/
AgCl were used as counter, working, and reference electrodes,
respectively. In all cases, CV experiments were performed in
-
dry MeCN with EtN4+BF4 as supporting electrolyte (0.1 M)
2-Bu tylsu lfan yl-4,5,7-tr in itr oflu or en -9-on e (2). (a) 2,4,5,7-
Tetranitrofluoren-9-one (1) (3.0 g, 8.4 mmol) was dissolved in
under N2 flow; concentrations of acceptors were ca. 10-4 M-1
.
The scan rate was 100 mV s-1
.
CTC Sp ectr a l Mea su r em en ts. Measurements of isomolar
series and also absorption of CTCs for estimations of equilib-
rium constants were made at the maxima of CTC absorptions.
Evaluation of KCTC and ꢀCTC values was performed by nonlinear
(40) Grebenyuk, S. A. Dissertation, Inst. Phys. Org., & Coal Chem.,
Donetsk, 1994.
(41) Alcock, N. W.; Marks, P. J . J . Appl. Crystallogr. 1994, 26, 200.
(42) Sheldrick, G. M. SADABS, Program for scaling and correction
of area detector data; University of Gottingen: Germany, 1996.
(43) Sheldrick, G. M. SHELXTL Version 5/VMS; Bruker axs,
Analytical X-ray Systems: Madison, WI, 1995.
(44) The coordinates for I and II can be obtained on request from
the Director, Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge, CB2 1EZ, U.K.
(45) Inaki, J .; Sheibeni, G.; Takemoto, K. Technol. Rep. Osaka Univ.
1975, 25, 249.
(39) 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.

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 65, No. 10, 2000 3061
Ta ble 4. Cr ysta l Da ta a n Da ta Collection for I a n d II
I
II
formula
M
C
865.1
24H22N4O8S2‚3/2C6H4S4
C28H14N4O10S2‚C6H4S4‚1/2C6H5Cl
891.2
cryst size (mm)
T (K)
0.4 × 0.35 × 0.32
0.16 × 0.04 × 0.02
293
150
symmetry
unit cell dimensions
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
U (Å3)
space group
Z
triclinic
monoclinic
10.089(1)
13.954(1)
15.732(1)
108.72(1)
98.44(1)
108.05(1)
1918.2(3)
P1h
14.370(3)
10.772(2)
24.156(5)
90
98.38(1)
90
3699(1)
P21/c
4
2
λ (Å)
0.71073
5.2
1.50
0.6849
4.7
1.60
µ (cm-1
)
Dx (g cm-3
)
scan mode
2θmax (deg)
no. of total data
no. of unique data
no. of data obsd, I > 2σ(I)
Rint
2θ/ω
ω (0.15° frames)
50
54
6873
6474
4551
0.010
20 499
7958
5137
0.069
no. of variables
wR(F 2), all data
R(F), obsd data
511
0.173
0.058
0.59, -0.93
591
0.120
0.049
0.49, -0.56
∆Fmax,min (e Å-3
)
HMPA (10 mL) at room temperature, n-butanethiol (4 mL, 37
mmol) was added dropwise, and the mixture was kept at room
temperature for 2 days. Then it was poured onto 5% HCl (50
mL) and ice (50 g). The brown oil was separated from the
aqueous solution and twice recrystallized from 50% acetic acid,
yielding 2 (2.76 g, 82%) as orange crystals, mp 153-155 °C.
(200 MHz, acetone-d6): δ 7.92 (2H, d, J 1,3 ) 1.8 Hz), 7.85 (2H,
d, J 1,3 ) 1.8 Hz), 3.28 (4H, t, J ) 7.2 Hz), 1.75 (4H, m), 1.56
(4H, m), 0.97 (6H, t, J ) 7.2 Hz). UV-vis (MeCN), λmax/nm:
428. IR (KBr): ν/cm-1 3440, 3080, 2950, 2930, 2870, 2850, 1725
(CdO), 1600, 1535 (NO2), 1460, 1430, 1410, 1360 (NO2), 1320,
1270, 1250, 1230, 1195, 1100, 1070, 900, 880, 780, 765, 750,
740, 715. Anal. Calcd for C21H22N2O5S2: C, 56.44; H, 5.05; N,
6.34; S, 14.29. Found: C, 56.50; H, 4.93; N, 6.28; S, 14.35.
2,5-Bis(bu tylsu lfa n yl)-4,7-d in itr oflu or en -9-on e (4). The
HMPA mother liquor from the synthesis of sulfide 3 (method
“b”) was combined with the dioxane/propan-2-ol solution from
its recrystallization; the solvents were evaporated under
reduced pressure, and the residue was TLC-analyzed (benzene/
acetone, 4:1), showing a minor orange spot running faster than
the main orange spot of 3. Flash chromatography on silica
100-160 mesh (benzene; 3 × 40 cm column) gave the crude
product, which was then purified by repeated chromatography
on silica 40-100 mesh (the same conditions), yielding sulfide
4 (0.11 g, 0.9%), mp 122-123 °C. 1H NMR (200 MHz, acetone-
d6): δ 8.56 (1H, d, J 6,8 ) 2.1 Hz), 8.24 (1H, d, J 6,8 ) 2.1 Hz),
7.94 (1H, d, J 1,3 ) 1.8 Hz), 7.91 (1H, d, J 1,3 ) 1.8 Hz) 3.30 (2H,
t, J ) 7.3 Hz), 3.17 (2H, t, J ) 7.3 Hz), 1.76 (2H, m), 1.56 (2H,
m), 1.3-1.6 (4H, m), 0.97 (3H, t, J ) 7.2 Hz), 0.86 (3H, t, J )
7.2 Hz). m/z: 446 (M+, 100), 416 (7), 390 (13), 370 (9), 334 (12),
301 (55), 257 (11), 229 (9), 201 (9), 169 (9), 57 (63). Anal. Calcd
for C21H22N2O5S2: C, 56.61; H, 4.99; N, 6.30; S, 14.22. Found:
C, 56.50; H, 4.93; N, 6.28; S, 14.35.
(b) 2,4,5,7-Tetranitrofluoren-9-one (1) (6.0 g, 16.7 mmol) was
dissolved in DMSO (60 mL) at room temperature, n-butane-
thiol (5 mL, 47 mmol) was added, and the reaction mixture
was heated with stirring at 80 °C for 30-60 min (TLC
monitoring). After cooling to room temperature it was poured
onto 5% HCl (200 mL) and ice (50 g). The solid was filtered
off, washed with water and propan-2-ol, and dried, yielding
compound 2 (4.8 g, 71%), mp 152-157 °C. This crude product
was dissolved in hot dioxane (10 mL) and diluted with hot
propan-2-ol (50 mL), yielding 2 (4.5 g, 67%) as orange crystals,
mp 155-157 °C. Rf: 0.56 (benzene). 1H NMR (200 MHz,
acetone-d6): δ 8.01 (1H, d, J 1,3 ) 1.8 Hz), 8.06 (1H, d, J 1,3
)
1.8 Hz), 8.92 (1H, d, J 6,8 ) 2.1 Hz), 8.68 (1H, d, J 6,8 ) 2.1 Hz),
3.37 (2H, t, J ) 7.3 Hz), 1.80 (2H, m), 1.58 (2H,m), 1.00 (3H,
t, J ) 7.2 Hz). UV-vis (MeCN), λmax/nm: 423. IR (KBr): ν/cm-1
3450, 3080, 2960, 2930, 2870, 1740 (CdO), 1605, 1590, 1540,
1530 (NO2), 1460, 1420, 1360, 1340 (NO2), 1290, 1250, 1220,
1185, 1070, 925, 915, 880, 805, 785, 775, 745, 730, 710. Anal.
Calcd for C17H13N3O7S: C, 50.51; H, 3.34; N, 10.20; S, 7.94.
Found: C, 50.62; H, 3.23; N, 10.42; S, 7.94.
2,7-Bis(bu tylsu lfa n yl)-4,5-d in itr oflu or en -9-on e (3). (a)
2,4,5,7-Tetranitrofluoren-9-one (1) (3.0 g, 8.4 mmol) was dis-
solved in DMSO (30 mL), n-butanethiol (4 mL, 37 mmol) was
added, and the mixture was heated with stirring at 80 °C for
1 h. After cooling to room temperature it was poured onto 5%
HCl (100 mL) and ice (50 g). The solid was filtered off, washed
with water, and twice recrystallized from 50% acetic acid,
yielding 3 (2.64 g, 71%) as orange crystals, mp 162-165 °C.
2-Bu tylsu lfa n yl-4,5,7-tr in itr o-9-d icya n om eth ylen eflu o-
r en e (5). 2-Butylsulfanyl-4,5,7-trinitrofluoren-9-one (2) (0.64
g, 1.6 mmol) was dissolved in DMF (2.5 mL), malononitrile
(0.21 g, 3.2 mmol) was added, and the reaction mixture was
stirred at room temperature for 2 h and diluted with propan-
2-ol (20 mL). The solid was collected by filtration, washed with
propan-2-ol, and dried, yielding compound 5 (0.66 g, 92%), mp
199-202 °C. Purification by dissolution in hot dioxane and
subsequent dilution with 5 times the volume of propan-2-ol
yielded pure 5 (0.65 g, 91%) as black crystals, mp 200-202
(b) 2,4,5,7-Tetranitrofluoren-9-one (1) (10.0 g, 27.8 mmol)
was dissolved in HMPA (30 mL) at room temperature, n-
butanethiol (10 mL, 93 mmol) was added, and the reaction
mixture was left to stand at room temperature for 4 days. The
solution was poured onto 5% HCl (300 mL) and ice (150 g),
and the solid was filtered off, washed with water, and dried,
yielding compound 3 (9.0 g, 73%), mp 160-168 °C. The crude
product was dissolved in hot dioxane (50 mL) and diluted with
hot propan-2-ol (150 mL), yielding 3 (8.1 g, 65%) as bright
1
°C. H NMR (200 MHz, acetone-d6): δ 9.61 (1H, d, J 6,8 ) 2.0
Hz), 8.97 (1H, d, J 6,8 ) 2.0 Hz), 8.77 (1H, d, J 1,3 ) 1.7 Hz),
8.15 (1H, d, J 1,3 ) 1.7 Hz), 3.31 (2H, t, J ) 7.3 Hz), 1.82 (2H,
m), 1.57 (2H, m), 0.97 (3H, t, J ) 7.3 Hz). m/z: 451 (M+, 27),
395 (8), 346 (2.5), 319 (4), 245 (6), 200 (5), 57 (100). UV-vis
(MeCN), λmax/nm (ꢀ/M-1 cm-1): 260 (28 500), 320 (24 800), 420
(10 100), 510sh (2600). Anal. Calcd for C20H13N5O6S (MW
1
orange needles, mp 165-168 °C. Rf: 0.77 (benzene). H NMR

3062 J . Org. Chem., Vol. 65, No. 10, 2000
Perepichka et al.
451.41): C, 53.18; H, 3.00; N, 15.72; S, 7.14. Found: C, 53.21;
H, 2.90; N, 15.51; S, 7.10.
room temperature the solid was filtered off, washed with
water, and dried, yielding sulfone 10 (1.05 g, 92%), mp 291-
294 °C. Recrystallization from benzene gave pure compound
2,7-Bis(bu tylsu lfa n yl)-4,5-d in itr o-9-d icya n om eth ylen e-
flu or en e (6). 2,7-Bis(butylsulfanyl)-4,5-dinitrofluoren-9-one
(3) (0.50 g, 1.1 mmol) was dissolved in DMF (4.0 mL),
malononitrile (0.25 g, 3.8 mmol) was added, and the reaction
mixture was stirred at 60-65 °C for 2 h and diluted with
propan-2-ol (20 mL). The solid was collected by filtration,
washed with propan-2-ol, and dried, yielding compound 6 (0.46
g, 83%), mp 127-129 °C. Purification by dissolution in hot
dioxane (1 mL) and subsequent dilution with propan-2-ol (5
mL) yielded pure 6 (0.42 g, 76%) as long black needles, mp
1
10 (0.81 g, 77%) as yellow needles, mp 292-294 °C. H NMR
(200 MHz, acetone-d6): δ 8.70 (2H, d, J 1,3 ) 1.7 Hz), 8.57 (2H,
d, J 1,3 ) 1.7 Hz), 3.55 (4H, m), 1.75 (4H, m), 1.46 (4H, m), 0.90
(6H, t, J ) 7.4 Hz). Anal. Calcd for C21H22N2O9S2 (MW
510.53): C, 49.23; H, 4.25; N, 5.46; S, 12.60. Found: C, 49.40;
H, 4.34; N, 5.49; S, 12.56.
2,5-Bis(bu tylsu lfon yl)-4,7-din itr oflu or en -9-on e (11). This
compound was obtained by the above procedure for compound
10, from 2,5-bis(butylsulfanyl)-4,7-dinitrofluoren-9-one (4) (46
mg, 0.10 mmol) and 27% hydrogen peroxide (0.2 mL, 1.7 mmol)
in acetic acid (2.50 mL). Reaction time was 3 h (TLC monitor-
ing). Pale yellow crystals of sulfone 11 were isolated (49 mg,
93%), mp 192-194 °C. 1H NMR (300 MHz, acetone-d6): δ 9.02
(1H, d, J 6,8 ) 2.1 Hz), 8.76 (1H, d, J 6,8 ) 2.1 Hz), 8.67 (1H, d,
J 1,3 ) 1.7 Hz), 8.52 (1H, d, J 1,3 ) 1.7 Hz), 3.72 (2H, m), 3.56
(2H, m), 1.86 (2H, m), 1.77 (2H, m), 1.60-1.40 (4H, m), 0.97
(3H, t, J ) 7.3 Hz), 0.91 (3H, t, J ) 7.2 Hz). Anal. Calcd for
C21H22N2O9S2 (MW 510.53): C, 49.45; H, 4.39; N, 5.60; S, 12.47.
Found: C, 49.40; H, 4.34; N, 5.49; S, 12.56.
2-Bu tylsu lfin yl-4,5,7-tr in itr o-9-d icya n om eth ylen eflu o-
r en e (12). 2-Butylsulfinyl-4,5,7-trinitrofluoren-9-one (8) (50
mg, 0.12 mmol) was dissolved in DMF (0.25 mL), malononitrile
(20 mg, 0.30 mol) was added, and the reaction mixture was
stirred at room temperature for 4 h and diluted with methanol
(1.5 mL). After standing at 0 °C for 3 h the solid was collected
by filtration, washed with methanol, and dried, yielding
compound 12 (41 mg, 74%) as pale brown crystals, mp 174-
177 °C. 1H NMR (300 MHz, acetone-d6+1% CF3CO2D): δ 9.70
(1H, d, J 6,8 ) 2.0 Hz), 9.28 (1H, d, J 1,3 ) 1.4 Hz), 9.05 (1H, d,
J 6,8 ) 2.0 Hz), 8.62 (1H, d, J 1,3 ) 1.4 Hz), 3.29 (1H, m), 3.05
(1H, m), 1.85 (1H, m), 1.63 (1H, m), 1.50 (2H, m), 0.92 (3H, t,
J ) 7.3 Hz). Anal. Calcd for C20H13N5O7S (MW 467.41): C,
51.37; H, 2.95; N, 14.99; S, 7.02. Found: C, 51.39; H, 2.80; N,
14.98; S, 6.86.
1
131-133 °C. H NMR (200 MHz, acetone-d6): δ 8.63 (2H, d,
J 1,3 ) 1.7 Hz), 8.00 (2H, d, J 1,3 ) 1.7 Hz), 3.25 (4H, t, J ) 7.3
Hz), 1.78 (4H, m), 1.55 (4H, m), 0.96 (6H, t, J ) 7.2 Hz). m/z:
494 (M+, 63), 446 (7), 438 (5), 418 (6), 306 (10), 277 (5), 245
(4), 57 (100). UV-vis (MeCN), λmax/nm (ꢀ/M-1 cm-1): 275
(29 800), 334 (26 500), 432 (9000), 558 (1500). Anal. Calcd for
C24H22N4O4S2 (MW 494.58): C, 58.25; H, 4.34; N, 11.30; S,
12.84. Found: C, 58.28; H, 4.48; N, 11.33; S, 12.96.
2,5-Bis(bu tylsu lfa n yl)-4,7-d in itr o-9-d icya n om eth ylen e-
flu or en e (7). This was obtained from sulfide 4 (50 mg, 0.11
mmol) similarly to compound 6 as dark red-brown crystals (45
mg, 81%), mp 129-131 °C. 1H NMR (200 MHz, acetone-d6): δ
9.18 (1H, d, J 6,8 ) 1.9 Hz), 8.68 (1H, d, J 1,3 ) 1.6 Hz), 8.59
(1H, d, J 6,8 ) 1.9 Hz), 8.02 (1H, d, J 1,3 ) 1.6 Hz), 3.26 (2H, t,
J ) 7.3 Hz), 3.17 (2H, t, J ) 7.2 Hz), 1.79 (2H, m), 1.55 (2H,
m), 1.3-1.6 (4H, m), 0.97 (3H, t, J ) 7.3 Hz), 0.85 (3H, t, J )
7.2 Hz). UV-vis (MeCN), λmax/nm (ꢀ/M-1 cm-1): 261 (27 200),
278 (25 500), 333 (26 300), 401 (10 300), 529 (2100). Anal.
Calcd for C24H22N4O4S2 (MW 494.58): C, 58.35; H, 4.43; N,
11.41; S, 12.88. Found: C, 58.28; H, 4.48; N, 11.33; S, 12.96.
2-Bu tylsu lfin yl-4,5,7-tr in itr oflu or en -9-on e (8). 2-Butyl-
sulfanyl-4,5,7-trinitrofluoren-9-one (2) (1.40 g, 3.47 mmol) was
dissolved in hot acetic acid (120 mL), 27% hydrogen peroxide
(0.85 mL, 7.4 mmol) was added, and the reaction mixture was
stirred at 60 °C for ca. 2.5 h with TLC monitoring until the
appearance of a spot from sulfone 9. The reaction mixture was
diluted with water (300 mL), and the solid was filtered off and
washed with water. The crude product was purified by flash
chromatography (3.5 × 40 cm column, silica 100/160 mesh).
The first fraction eluted by benzene contained starting sulfide
2; the second fraction eluted by benzene/acetone, 6:1, yielded
pure 8 (0.58 g, 40%) as yellow crystals, mp 164-165 °C. 1H
NMR (200 MHz, acetone-d6): δ 9.00 (1H, d, J 6,8 ) 2.1 Hz),
8.79 (1H, d, J 6,8 ) 2.1 Hz), 8.56 (1H, d, J 1,3 ) 1.5 Hz), 8.49
(1H, d, J 1,3 ) 1.5 Hz), 3.25 (1H, m), 3.04 (1H, m), 1.83 (1H,
m), 1.62 (1H, m), 1.49 (2H, m), 0.92 (3H, t, J ) 7.3 Hz). m/z:
403 (M+ - O, 36), 347 (14), 98 (6), 84 (9), 64 (100). Anal. Calcd
for C17H13N3O8S (MW 419.37): C, 48.89; H, 3.02; N, 10.00; S,
7.72. Found: C, 48.69; H, 3.12; N, 10.02; S, 7.64.
2-Bu tylsu lfon yl-4,5,7-tr in itr o-9-d icya n om eth ylen eflu o-
r en e (13). 2-Butylsulfonyl-4,5,7-trinitrofluoren-9-one (9) (1.00
g, 2.3 mmol) was dissolved in DMF (3.0 mL), malononitrile
(0.35 g, 5.3 mmol) was added, and the reaction mixture was
stirred at room temperature for 1 h and diluted with propan-
2-ol (15 mL). The solid was collected by filtration and washed
with propan-2-ol, yielding compound 13 (1.06 g, 95%), mp 291-
294 °C. Recrystallization from toluene (170 mL) gave pure
1
sulfone 13 (1.00 g, 90%), yellow crystals, mp 294-296 °C. H
NMR (200 MHz, acetone-d6+1% CF3CO2D): δ 9.72 (1H, d, J 6,8
) 1.9 Hz), 9.42 (1H, d, J 1,3 ) 1.4 Hz), 9.08 (1H, d, J 6,8 ) 1.9
Hz), 8.76 (1H, d, J 1,3 ) 1.4 Hz), 3.55 (2H, m), 1.82 (2H, m),
1.51 (2H, m), 0.95 (3H, t, J ) 7.2 Hz). Anal. Calcd for
C
20H13N5O8S (MW 483.41): C, 49.72; H, 2.71; N, 14.41; S, 6.59.
2-Bu tylsu lfon yl-4,5,7-tr in itr oflu or en -9-on e (9). (a) 2-Bu-
tylsulfanyl-4,5,7-trinitrofluoren-9-one (2) (3.0 g, 7.4 mmol) was
dissolved in hot acetic acid (100 mL), 27% hydrogen peroxide
(5.2 mL, 45 mmol) was added, and the reaction mixture was
stirred at 60-65 °C for 24 h. The reaction mixture was diluted
with hot water (100 mL), and the solid was filtered off and
washed with water, yielding sulfone 9 (3.2 g, 99%), mp 213-
215 °C. The product was dissolved in hot dioxane and diluted
with 5 times the volume of propan-2-ol, yielding analytically
pure sulfone 9 (2.9 g, 90%) as pale yellow crystals with the
same melting point.
Found: C, 49.69; H, 2.71; N, 14.49; S, 6.63.
2,7-Bis(bu tylsu lfon yl)-4,5-d in itr o-9-d icya n om eth ylen e-
flu or en e (14). 2,7-Bis(butylsulfonyl)-4,5-dinitrofluoren-9-one
(10) (1.00 g, 1.96 mmol) was dissolved in DMF (15 mL),
malononitrile (0.45 g, 6.8 mmol) was added, and the reaction
mixture was stirred at 40-45 °C for 4 h and diluted with
propan-2-ol (60 mL). The solid was filtered off and washed with
propan-2-ol, yielding compound 14 (0.99 g, 90%), mp 323-326
°C. After two recrystallizations from benzene bright yellow
1
crystals, mp 328-331 °C, were obtained. H NMR (200 MHz,
acetone-d6+1% CF3CO2D): δ 9.39 (2H, d, J 1,3 ) 1.4 Hz), 8.74
(2H, d, J 1,3 ) 1.4 Hz), 3.54 (4H, m), 1.80 (4H, m), 1.49 (4H,
m), 0.92 (6H, d, J ) 7.3 Hz). Anal. Calcd for C24H22N4O8S2
(MW 558.58): C, 51.45; H, 3.85; N, 9.89; S, 11.62. Found: C,
51.61; H, 3.97; N, 10.03; S, 11.48.
(b) Sulfoxide 3 (0.50 g, 1.2 mmol) was oxidized under the
same conditions as above, yielding sulfone 9 (0.51 g, 98%), mp
213.5-215 °C. 1H NMR (200 MHz, acetone-d6): δ 9.04 (1H, d,
J 6,8 ) 2.1 Hz), 8.85 (1H, d, J 6,8 ) 2.1 Hz), 8.71 (1H, d, J 1,3
)
1.6 Hz), 8.59 (1H, d, J 1,3 ) 1.6 Hz), 3.56 (2H, m), 1.76 (2H, m),
1.47 (2H, m), 0.91 (3H, t, J ) 7.5 Hz). Anal. Calcd for
2,5-Bis(bu tylsu lfon yl)-4,7-d in itr o-9-d icya n om eth ylen e-
flu or en e (15). 2,5-Bis(butylsulfonyl)-4,7-dinitrofluoren-9-one
(11) (30 mg, 0.059 mmol) was dissolved in DMF (0.3 mL),
malononitrile (12.5 mg, 0.189 mmol) was added, the reaction
mixture was stirred at 50 °C for 25 h and diluted with
methanol (1.5 mL). After storage at 0 °C for 3 h the solid was
collected by filtration, washed with methanol, and dried,
yielding compound 14 (29 mg, 88%) as yellow crystals, mp
225-228 °C. 1H NMR (300 MHz, acetone-d6+1% CF3CO2D):
C
17H13N3O9S (MW 435.36): C, 46.97; H, 3.05; N, 9.56; S, 7.38.
Found: C, 46.90; H, 3.01; N, 9.65; S, 7.36.
2,7-Bis(bu tylsu lfon yl)-4,5-din itr oflu or en -9-on e (10). 2,7-
Bis(butylsulfanyl)-4,5-dinitrofluoren-9-one (3) (1.00 g, 2,2 mmol)
was dissolved in hot acetic acid (50 mL), 27% hydrogen
peroxide (2.6 mL, 23 mmol) was added, and the reaction
mixture was stirred at 100-108 °C for 6 h. After cooling to

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 65, No. 10, 2000 3063
δ 9.61 (1H, d, J 6,8 ) 1.9 Hz), 9.32 (1H, d, J 1,3 ) 1.4 Hz), 9.04
(1H, d, J 6,8 ) 1.9 Hz), 8.69 (1H, d, J 1,3 ) 1.4 Hz), 3.69 (2H, m),
3.53 (2H, m), 1.78 (4H, m), 1.48 (4H, m), 0.96 (3H, t, J ) 7.3
Hz), 0.91 (3H, t, J ) 7.2 Hz). Anal. Calcd for C24H22N4O8S2
(MW 558.58): C, 51.69; H, 3.95; N, 10.15; S, 11.41. Found: C,
51.61; H, 3.97; N, 10.03; S, 11.48.
Com p lex I: 2,7-Bis(bu tylsu lfon yl)-4,5-d in itr o-9-d icya -
n om eth ylen eflu or en e (14) a n d Tetr a th ia fu lva len e (2:3).
Acceptor 14 was dissolved in hot acetonitrile, TTF was added,
and the reaction mixture was stirred until full dissolution and
left in a flask for slow evaporation at room temperature for
several days, during which time black crystals of the complex
II were formed.
Com p lex II: 2,7-Bis(p h en oxysu lfon yl)-4,5-d in itr o-9-
d icya n om eth ylen eflu or en e (17) a n d Tetr a th ia fu lva len e
(1:1:0.5 P h Cl). Acceptor 1716 (10 mg, 0.016 mmol) was
dissolved in chlorobenzene (2 mL) at 80 °C, TTF (8 mg, 0.039
mmol) was added to this solution, and the mixture was stirred
until full dissolution and left for very slow cooling to room
temperature. Black crystals were collected, washed with a
small portion of chlorobenzene, and dried at room temperature.
Anal. Calcd for C37H20.5Cl0.5N4O10S6 (MW 891.21): C, 49.87;
H, 2.32; N, 6.29; S, 21.59. Found: C, 50.02; H, 2.40; N, 6.20;
S, 21.75.
Ack n ow led gm en t. We thank The Royal Society for
funding visits to Durham (I.F.P.) and The Alexander
von Humboldt Foundation for the donation of EG&G
PARC Model 263A electrochemical equipment (I.F.P.).
We thank Dr. J . N. Heaton for some of the electrochemi-
cal measurements and the synthesis of complex I, and
Prof. W. Clegg and Dr. S. Teat for collecting X-ray
diffraction data of II on the Station 9.8 at Daresbury
Laboratory.
Su p p or t in g In for m a t ion Ava ila b le: Full crystallo-
graphic data for I and II. This material is available free of
charge via the Internet at http://pubs.acs.org.
J O991796R