Electron Acceptors of the Fluorene Series. 7.1 2,7-Dicyano-4,5-dinitro-9-X-fluorenes: Synthesis, Cyclic Voltammetry, Charge Transfer Complexation with N-Propylcarbazole in Solution, and X-ray Crystal Structures of Two Tetrathiafulvalene Complexes

Article abstract of DOI:10.1021/jo9803481

The synthesis and physical properties of a series of novel fluorene π-electron acceptors (7-9) are described. Cyclic voltammograms of 7 and 8 exhibit three separate reversible (or quasi-reversible) one-electron redox waves, characteristic of strong electron acceptors. Spectroelectrochemical experiments show the appearance in the long-wavelength visible region of absorption bands at appropriate potentials which were attributed to the transformations A → A^.- and A^.- → A^2-. Charge-transfer complexation with N-propylcarbazole in dioxane shows the formation of 1:1 complexes with parameters characteristic for other fluorene acceptors. The single-crystal X-ray structures of 1:1 charge-transfer complexes of tetrathiafulvalene with the electron acceptor 8 and with the strongest fluorene acceptor If both show ...A...D...A...D... stacking in the crystal.

Full text of DOI:10.1021/jo9803481

6484
J . Org. Chem. 1998, 63, 6484-6493
Electr on Accep tor s of th e F lu or en e Ser ies. 7.1
2,7-Dicya n o-4,5-d in itr o-9-X-flu or en es: Syn th esis, Cyclic
Volta m m etr y, Ch a r ge Tr a n sfer Com p lexa tion w ith
N-P r op ylca r ba zole 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,*,† Lyudmila G. Kuz’mina,‡ Dmitrii F. Perepichka,† Martin R. Bryce,*,§
Leonid M. Goldenberg,§,|, Anatolii F. Popov,† and J udith A. K. Howard§
L.M.Litvinenko Institute of Physical Organic & Coal Chemistry, National Academy of Sciences of
Ukraine, Donetsk 340114, Ukraine, Kurnakov Institute of General & Inorganic Chemistry,
Russian Academy of Sciences, Moscow 117907, GSP-1, Russian Federation, Department of Chemistry,
University of Durham, Durham DH1 3LE, U.K., and School of Engineering, University of Durham,
Durham DH1 3LE, U.K.
Received February 24, 1998
The synthesis and physical properties of a series of novel fluorene π-electron acceptors (7-9) are
described. Cyclic voltammograms of 7 and 8 exhibit three separate reversible (or quasi-reversible)
one-electron redox waves, characteristic of strong electron acceptors. Spectroelectrochemical
experiments show the appearance in the long-wavelength visible region of absorption bands at
appropriate potentials which were attributed to the transformations A f A•- and A•- f A2-. Charge-
transfer complexation with N-propylcarbazole in dioxane shows the formation of 1:1 complexes
with parameters characteristic for other fluorene acceptors. The single-crystal X-ray structures of
1:1 charge-transfer complexes of tetrathiafulvalene with the electron acceptor 8 and with the
strongest fluorene acceptor 1f both show ‚‚A‚‚‚D‚‚‚A‚‚‚D‚‚ stacking in the crystal.
In tr od u ction
complexing agents for optical resolution,9 and as spray
reagents for nondestructive detection of many classes of
biologically active compounds, polyaromatics and het-
eroaromatics.10
Subsequently, fluorene acceptors containing cyano
substituents in the benzene rings (2-3) were synthe-
sized.4c,11 They have been shown to form semiconducting
CTC with electron donors and to sensitize poly-N-
epoxypropylcarbazole (PEPC). It was also found that
substitution of the nitro group in position 4 of 9-dicya-
nomethylene-2,4,7-trinitrofluorene (1e) by a cyano group
leads to a more effective sensitizer (3c) of PEPC photo-
conductivity.12
Polynitrosubstituted 9-fluorenones (1a -c)2 and 9-di-
cyanomethylenefluorenes (1d -f),3 synthesized some de-
cades ago, are a unique class of electron acceptor mol-
ecules. They have been widely employed as acceptors for
charge-transfer complex (CTC) formation,4 as photosen-
sitizers and electron transport materials,5,6 in the prepa-
ration of π-complexing phases for HPLC7 and TLC,8 as
† Institute of Physical Organic & Coal Chemistry, Donetsk.
‡ Institute of General & Inorganic Chemistry, Moscow.
§ Department of Chemistry, University of Durham.
| School of Engineering, University of Durham.
On leave from the Institute of Chemical Physics in Chernogolovka,
Russian Academy of Sciences, Chernogolovka, Moscow Region 142432,
Russian Federation.
(1) Part 6: Mysyk, D. D.; Perepichka, I. F.; Sokolov, N. I. J . Chem.
Soc., Perkin Trans. 2 1997, 537.
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(b) Orchin, M.; Reggel, L.; Woolfolk, E. O. J . Am. Chem. Soc. 1947, 69,
1225.
For acceptors 1b,c,e,f, and 3b (Chart 1) the structures
were determined by single-crystal X-ray analysis which
revealed significant steric interaction of the substituents
in positions 4 and 5.13-15 However, very little X-ray
(3) (a) Mukherjee, T. K.; Levasseur, L. A. J . Org. Chem. 1965, 30,
644. (b) Mukherjee, T. K. Tetrahedron 1968, 24, 721. (c) Dupuis, P.;
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J . Chem. 1978, 56, 2381. (c) Sbrana, G.; Scotton, M.; Angeloni, L. J .
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(5) (a) 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.
(b) Getmanchuk, Yu. P.; Sokolov, N. I. In Fundamentals of Optical
Memory and Media; Vyshcha Shkola: Kiev, 1983; Issue 14, p 11 (in
Russian).
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101. (b) Heacock R. A.; Forrest, J . E. J . Chromatogr. 1973, 78, 241. (c)
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Mater. Chem. 1996, 6, 1113. (b) Pearson, J . M. Pure Appl. Chem. 1977,
49, 463. (c) Mukherjee, T. K. J . Phys. Chem. 1966, 70, 3648. (d) Kuder,
J . E.; Pochan, J . M.; Turner, S. R.; Hinman, D.-L. F. J . Electrochem.
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Barchietto, G.; Tar, D. Photochem. Photobiol. 1972, 16, 335.
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85. (b) Karger, B. L.; Martin, M.; Loheac, J .; Guiochon, G. Anal. Chem.
1973, 45, 496.
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77,102,734; Chem. Abstr. 1978, 88, 97420q. (b) Mysyk, D. D.; Perepich-
ka, I. F.; Sivchenkova, N. M.; Kampars, V. E.; Neilands, O. Ya.;
Kampare, R. B. Izv. Akad. Nauk Latv. SSR, Ser. Khim. 1984, 328;
Chem. Abst. 1984, 101, 210699q. (c) Mysyk, D. D.; Perepichka, I. F.;
Edzina, A. S.; Neilands, O. Ya. Latvian J . Chem. 1991, 727 (in
Russian).
(12) (a) Mysyk, D. D.; Perepichka, I. F.; Sivchenkova, N. M.;
Kostenko, L. I.; Pototskii I. S.; Baratov, A. G. USSR Patent 1,092,151.
S0022-3263(98)00348-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 08/20/1998

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 63, No. 19, 1998 6485
Ch a r t 1
Sch em e 1a
a
(i) HNO3/H2SO4, 80-85 °C, 6 h; (ii) SOCl2, reflux, 3-4 h, then
NH4OH; (iii) POCl3/DMF, reflux, 30 min; (iv) CH2(CN)2, DMF, rt,
40 min; (v) NH2OH-HCl, DMF, 60 °C, 2 h.
structural data are known for their CTC. Most donors
which have been used to form CTCs are of little interest
for their solid-state electronic properties. Thus, single-
crystal X-ray structures were determined for CTCs of
1b,e with aromatic donors.16-24 To our knowledge only
one X-ray stucture has been reported25 for a CTC of a
fluorene acceptor and tetrathiafulvalene (TTF) donor:
this is a 1:1 complex of the weak acceptor 1a and TTF.
This is surprising as TTF has been complexed with
a wide range of other acceptors to provide materials with
unusual electronic26 and magnetic27 properties. Recently
it was reported28 that bis(ethylenedioxy)tetrathiaful-
valene (BEDO-TTF) forms with 1e and 1f CTCs of 2:1
composition which showed (as compressed pellets) metal-
lic-type electrical conductivity with σrt of 65 and 18 S cm-1
and σmax of 390 (8 K) and 32 (94 K) S cm-1, respectively
(acceptors 1b and 1c gave semiconductive CTC with TTF
of 1:1 compositions with σrt of ca. 10-10 S cm-1), but no
X-ray data were reported for the crystals. These obser-
vations prompt us to report our studies on CTC and
radical ion salts (RS) of fluorene acceptors and TTF
donors.
Herein we describe the synthesis of novel electron
acceptors of the fluorene series, i.e., 2,7-dicyano-4,5-
dinitro-9-X-fluorenes (7-9), investigations of their redox
and spectroelectrochemical properties, CT complexation
with N-propylcarbazole in solution, and single-crystal
X-ray stuctures for 8:TTF:C6H5Cl and 1f:TTF complexes.
(13) (a) Dorset, D. L.; Hybl, A.; Ammon, H. L. Acta Crystallogr., Sect.
B 1972, 28, 3122. (b) 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. (c) Semidetko,
O. V.; Chetkina, L. A.; Bel’skii, V. K.; Mysyk, D. D.; Perepichka, I. F.;
Andrievskii, A. M. Zh. Obshch. Khim. 1987, 57, 415; Chem. Abstr.
1988, 108, 204311k.
(14) (a) Chetkina, L. A.; Semidetko, O. V.; Bels’kii, V. K.; Sobolev,
A. N.; Andrievskii, A. M. Acta Crystallogr., Sect. C 1987, 43, 933. (b)
Baughman, R. G. Acta Crystallogr., Sect. C 1987, 43, 931.
(15) Silverman, J .; Yannoni, N. F.; Krukonis, A. P. Acta Crystallogr.,
Sect. B 1974, 30, 1474.
(16) Brown, J . N.; Cheung, L. D.; Trefonas, L. M.; Majeste, R. J . J .
Cryst. Mol. Struct. 1974, 4, 361.
(17) Suzuki, T.; Fujii, H.; Mijashi, T.; Yamashita, Y. J . Org. Chem.
1992, 57, 6744.
(18) Groziac, M. P.; Wilson, S. R.; Clauson, G. L.; Leonard, N. J . J .
Am. Chem. Soc. 1986, 108, 8002.
Resu lts a n d Discu ssion
Syn th esis. The synthesis of the acceptors is shown
in Scheme 1. Fluorene-9-one-2,7-dicarboxylic acid 4,
readily accessible from 2,7-diacetylfluorene,29 was ni-
trated by fuming HNO3-concentrated H2SO4 mixture to
yield diacid 5, which was then converted into diamide 6
(19) Diederich, F.; Philp, D.; Seiler, P. J . Chem. Soc., Chem.
Commun. 1994, 205.
(20) Zhaolu, Yu; Naijue, Zhu; Daoben, Zhu Acta Phys.-Chim. Sin.
1987, 3, 663.
(21) Baldwin, S. L.; Baughman, R. G. Acta Crystallogr., Sect. C 1993,
49, 1840.
(22) Shah, M. C.; Baughman, R. G. Acta Crystallogr., Sect. C 1994,
50, 1114.
(23) Grigg, R.; Trocha-Grimshaw, J .; King, T. J . J . Chem. Soc.,
Chem. Commun. 1978, 571.
(24) Bulatov, A. V.; Lobkovskaya, R. M.; Khidekel, M. L.; Chekhlov,
A. N.; Shibaeva, R. P. Isv. Akad. Nauk SSSR, Ser. Khim. 1980, 1203
(in Russian); Chem. Abstr. 1980, 93, 186032k.
(25) Soriano-Garc´ıa, M.; Toscano, R. A.; Robles Mart´ınez, J . G.;
Salmero´n U. A.; Lezama R. R. Acta Crystallogr., Sect. C 1989, 45, 1442.
(26) (a) J . Mater. Chem. (Special Issue on Molecular Conductors)
1995, 5, 1469. (b) Ramos, J .; Yartsev, V. M.; Golhen, S.; Ouahab, L.;
Delhaes, P. J . Mater. Chem. 1997, 7, 1313.
(27) Day, P.; Kurmoo, M. J . Mater. Chem. 1997, 8, 1291.
(28) Horiuchi, S.; Yamochi, H.; Saito, G.; Sakaguchi, K.; Kusunoki,
M. J . Am. Chem. Soc. 1996, 118, 8604.
(29) Sulzberg, T.; Cotter, R. J . J . Org. Chem. 1970, 35, 2762.

6486 J . Org. Chem., Vol. 63, No. 19, 1998
Perepichka et al.
Ta ble 1. Cyclic Volta m m etr y Da ta for F lu or en e
Der iva tives 1c,e,f, 3a ,b, 7, 8, a n d 9 (V vs Ag/AgCl)a
1/2
1/2
1/2
b
E1red
E2red
E3red
Kdispr
(M-1
EA
(eV)
compd
(V)
(V)
(V)
)
1c
1e
1f
3a
3b
7
-0.12
+0.02
+0.23
-0.42
-0.20
-0.27
+0.17
-0.38d
-0.41
-0.57
-0.31
-0.74
-0.49
-0.64
-0.45
-0.73
-1.47
-1.37
-1.13
1.2 × 10-5
1.0 × 10-10
7.0 × 10-10
3.8 × 10-6
1.2 × 10-5
5.4 × 10-7
3.1 × 10-11
2.42
2.56
2.77c
2.12
2.34
2.27
2.71
e
-1.33
-1.04
-0.89
8
9
a
Solvent acetonitrile; electrolyte 0.2 M Et4N+BF4-; scan rate
100 mV s-1. All potentials given in the table were corrected using
the Fc0/Fc+ couple as internal reference and recalculated to Ag/
AgCl scale (Fc0/Fc+ couple showed +0.45 V vs Ag/AgCl in these
conditions). Calculated using equation ∆E1-2 ) E1red1/2 - E2red
b
1/2
d
) -0.059 log Kdispr
This value is for E1red
.
c Reference 11c. Irreversible reduction peak.
.
e This value could not be reliably calculated
as E1 is an irreversible wave.
F igu r e 1. 250 MHz 1H NMR spectra of acceptor 8 in acetone-
d6 at 25 °C: (a) original spectrum; (b) after 1 drop of CF3COOD
was added to solution a.
by subsequent action of thionyl chloride and ammonia.
Dehydration of diamide 6 by POCl3 gave 2,7-dicyano-4,5-
dinitro-9-fluorenone (7) which was transformed into
9-dicyanomethylene derivative 8 and oxime 9 by reaction
with malononitrile or hydroxylamine hydrochloride, re-
spectively, in DMF.
1H and 13C NMR spectra were entirely consistent with
their structures, by comparison with data for previous
tetrasubstituted fluorenes.1 We note one peculiarity in
the spectra for acceptor 8. Because of its strong electron
acceptor nature, significant paramagnetic broadening of
1
the aromatic protons is observed in the H NMR spec-
trum (Figure 1a) as a result of possible interaction with
donor solvent (acetone) or with traces of donor impurities.
The protons in positions 3 and 6 are broadened much
more than those in positions 1 and 8, confirming a higher
spin density on C-3,6 atoms in the radical anion of 8. In
the 13C NMR spectra of the compound, only C-1,8, CN,
and C-3,6 signals are observable. Addition of trifluoro-
acetic acid completely restores the fine resolution of both
the 1H NMR (Figure 1b) and 13C NMR (see Experimental
Section) spectra of compound 8. Broadening of the
F igu r e 2. Cyclic voltammograms of compounds 7-9 (under
the conditions stated in Table 1).
lost (to the electrode or by reaction with neutral oxime
9) and the second and third waves (at E1/2 -0.73 and
-0.89 V) are tentatively assigned to the first and second
single-electron reductions of this reaction product, for
which possible structures are the nitroso isomer of 9 or
an azo compound containing two fluorene groups. Fur-
ther studies on the electrochemistry of oxime 9 are
planned. The results are summarized in Table 1 together
with data for known acceptors 1c,e,f and 3a ,b measured
under the same conditions. The CVs of compounds 7-9
are shown in Figure 2.
1
signals in the H NMR spectra was previously observed
for other strong electron acceptors of the fluorene series1
in the presence of dipolar solvents.
Electr och em istr y. To study the redox properties of
the novel acceptors 7-9, we carried out cyclic voltam-
metry (CV) measurements in acetonitrile solution at room
Electron affinities (EA) were estimated (Table 1) by eq
1:
temperature with Et4N+BF4 as supporting electrolyte.
-
By analogy with nitrofluorenes 1a -f, acceptors 7 and 8
show two, reversible, single-electron reduction waves
resulting in radical anion and dianion species, respec-
tively, followed at a considerably more negative potential
by a third, quasi-reversible, single-electron reduction
wave resulting in the radical trianion. The CV behavior
of oxime 9 is anomalous: an irreversible reduction wave
is followed by two reversible reduction waves. This
suggests that the radical anion of 9 is converted into
another compound which is a poorer electron acceptor
than 9. At this potential (-0.38 V) an electron could be
1/2
1/2
EA(ref) - EA ) E1red (ref) - E1red
(1)
indicating that compound 8 is a rather strong acceptor
(EA ) 2.71 eV), comparable to the strongest known
acceptor of the fluorene series, i.e., 1f, which was used
as the reference acceptor [EA(ref) ) 2.77 eV11c]. More-
over, acceptor 8 is much more soluble than 1f, especially
in low polarity solvents, thereby making 8 more useful
for CTC and RS preparation.

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 63, No. 19, 1998 6487
F igu r e 4. Electronic absorption spectra in visible and near-
IR region for compound 8 at various applied potentials; solvent
acetonitrile, electrolyte Et4N+BF4- (0.2 M); potentials are given
vs Ag/AgCl.
F igu r e 3. Electronic absorption spectra in visible and near-
IR region for compound 7 at various applied potentials; solvent
acetonitrile, electrolyte Et4N+BF4- (0.2 M); potentials are given
vs Ag/AgCl.
Disproportionation constants (Kdispr) in the equilibrium
2:
Kdispr
{
2A•-
} A + A2-
(2)
determined from the difference in potentials of the
corresponding radical anion and dianion by the known
equation30 ∆E1-2 ) E1red - E2red ) -0.059 log Kdispr
indicate thermodynamic stability of the radical anions
from 7 and 8, which is even higher than that for the
corresponding tetranitrosubstituted fluorenes 1c,f.
Sp ectr oelectr och em istr y. To study the effect of the
transformations A f A•- f A2- on the electronic absorp-
tion spectra, we performed spectroelectrochemical experi-
ments for acceptors 7 and 8. (The stability of the
electrode system was established in the 0 to -1.5 V
potential range.) As seen from Figure 3, compound 7 has
no absorption at λ g 400 nm. At a potential of -0.4 V vs
Ag/AgCl an additional band at ca. 450 nm and a low-
intensity broad band at 800-900 nm appear, as a result
of the formation of the A•- species in the solution. At
more negative potentials of -0.8 and -1.5 V, when the
formation of A2- and A•3- species are expected, the short
wavelength band does not change its position or intensity,
whereas a hypsochromic shift and an increase in the
intensity is observed for the long wavelength band.
If the potential is switched off (to open the circuit) after
scanning to -0.8 V, the starting spectrum is fully
restored, confirming the reversibility of the processes of
radical anion and dianion formation. Turning off the
potential after scanning to -1.5 V does not restore the
original spectrum; instead absorption spectra of decom-
position products are observed in the visible region.
We mentioned above that broadening of the aromatic
protons in the NMR spectrum of compound 8 can be
attributed to the formation of paramagnetic species A•-
due to electron transfer from donor solvent to acceptor
molecule. Figure 4 reveals that acceptor 8 in acetonitrile
at open circuit vs Ag/AgCl has a low-intensity broad band
at ca. 800 nm which can be attributed to the existence of
A•- in solution. This agrees with the CV data (A f A•-
1/2
1/2
F igu r e 5. Electronic absorption spectra for CTC of acceptors
7 and 8 with N-propylcarbazole in dioxane, 25 °C.
for 8 occurs at E1red ) -0.28 V vs Fc/Fc+ ≡ +0.17 V vs
1/2
Ag/AgCl). When a negative potential of -0.1 V is applied
to the solution of 8, this band increases in intensity,
confirming its assignment to the radical anion species,
and at -0.8 V the absorption at 800 nm almost disap-
peared due to the transformation A•- f A2-
. (This
spectrum was essentially unchanged when obtained at
-1.5 V.)
CTC in Solu tion . The ability of fluorene acceptors
to form molecular CTC with electron donors is well-
known.1-3,5,10,16-25 We investigated the formation of CTC
of acceptors 7 and 8 with N-propylcarbazole in dioxane.
This donor was chosen because it can be considered as a
low-molecular-weight model of poly-N-vinylcarbazole (PVC)
and poly-N-(2,3-epoxypropyl)carbazole (PEPC) which are
both widely used as polymer photoconductors for optical
storage media.5 The formation of CTC between 7 or 8
and N-propylcarbazole was evident from the appearance
of additional absorbance bands (CTC bands) in the visible
region of the electronic spectra (Figure 5) which are
absent in the spectra of both acceptors and donor.
Isomolar series experiments (Figure 6) indicated the
formation of CTC of 1:1 composition only.
Recently, we estimated equilibrium constants K for 1:1
CTC (eq 3) of a number of fluorene acceptors with
N-propylcarbazole in dioxane5a,31 and with anthracene in
1,2-dichloroethane1 by nonlinear fitting of eq 4:
(30) J ensen, B. S.; Parker, V. D. J . Am. Chem. Soc. 1975, 97, 5211;
Rainis, A.; Szwarc, M. J . Am. Chem. Soc. 1974, 96, 3008.

6488 J . Org. Chem., Vol. 63, No. 19, 1998
Perepichka et al.
Ta ble 2. Equ ilibr iu m Con sta n ts (K ) a n d Mola r Extin ction Coefficien ts (E) for CTC of F lu or en e Accep tor s 7 a n d 8 w ith
N-P r op ylca r ba zole in Dioxa n e, 25 °C, Eva lu a ted by Non lin ea r F ittin g (4) a n d Ben esi-Hild ebr a n d Meth od (5), a n d Th eir
Com p a r ison w ith Liter a tu r e Da ta for 1b,c,e,f
variation range of concntrtns
d
compd λ (nm)a concn condtns
CA × 103 (M)
0.86-18.4
0.86-5.1
0.86-5.1
6.10-18.4
1.47-2.35
1.47-2.35
1.47-2.35
1.47-2.35
CD × 102 (M)
K (M-1
)
ꢀ (M cm-1
)
Nb R or rc
Rf or s0
methode
7
448
all data
0.48-32.8
5.8-32.8
5.8-32.8
0.48-7.7
1.12-9.58
1.11-2.31
1.63-8.27
1.63-8.27
1.07 ( 0.07 1930 ( 120 37 0.9996 1.33
1.00 ( 0.09 2070 ( 160 20 0.9993 1.12
0.96 ( 0.09 2130 ( 190 20 0.9994 7.2 × 10-5
0.99 ( 0.10 2080 ( 190 17 0.9991 1.19
6.65 ( 0.90 1110 ( 110 26 0.9941 3.33
(4)
(4)
(5)
(4)
(4)
(4)
(4)
(5)
(4)
(4)
(4)
(4)
CD g 10CA
CD g 10CA
CD < 10CA
all data
8
525
CD < 10CA
CD g 10CA
CD g 10CA
7.45 ( 5.86 1020 ( 700
6.66 ( 1.23 1120 ( 150 20 0.9914 3.48
6
0.9917 1.88
7.13 ( 0.80 1060 ( 100 20 0.9952 1.8 × 10-4
1b
1c
1e
1f
588
596
633
704
1.68 ( 0.08
1.74 ( 0.07
6.11 ( 0.26 1120 ( 40
8.38 ( 0.28 1430 ( 40
810 ( 30
860 ( 30
20
22
21
10
a
b
Wavelength at which measurements were made. N is quantity of points used in optimization procedure (4) or in correlation (5).
c Multiple correlation coefficient (R) or correlation coefficient (r) is given for nonlinear (4) and linear (5) methods, respectively. The
d
misalignment factor (Rf) between experimental data and fitting is given for nonlinear method which is described as Rf ) [∑(Aiexp
-
Aicalc)2/∑Aiexp] × 100% (where Aiexp and Aicalc are experimental and calculated values of a CTC absorbance for ith point, respectively) and
indicates a mean percentage deviation of experimental ACTC values from the fit according to eq 4. Standard deviation (s0) is given for
linear methods (5). e Enumeration of the methods corresponds to the number of an equation in the text.
it is similar to that for 1e,f within experimental error.
These data, together with E1red1/2 and E2red1/2 values for 7
and 8, show that there are no significant changes in the
electron acceptor and complexation abilities of the mol-
ecules, resulting from changing the nitro groups into
cyano groups in positions 2 and 7. Treatment of the set
of experimental data corresponding to a high excess of
the donor [CD . CA (or CA . CD) is a condition to
transform eq 4 into approximation 5: in practice, usually
a limitation of CD g 10CA or CA g 10CD is used] by the
Benesi-Hildebrand method32 (5):
CA
1
1
1
=
+
(5)
ACTC ꢀCTC KꢀCTC CD
F igu r e 6. Effect of donor-acceptor ratio on absorbance of
solution of CTC of 2,7-dicyano-4,5-dinitro-9-dicyanomethyl-
enefluorene (8) with N-propylcarbazole in dioxane, 25 °C, at
two CTC bands (λ ) 670 and 525 nm); CA + CD ) 9.94 × 10-3
M (method of isomolar series).
gave K and ꢀ values comparable within error with those
obtained by eq 4 for both CD g 10CA conditions and for
the full set data we obtained (Table 2).
Sin gle-Cr ysta l X-r a y An a lysis for CTCs 1f:TTF , 1:1
(I) a n d 8:TTF :C6H5Cl, 1:1:1 (II). Single crystals of both
complexes were grown from chlorobenzene solutions of
equimolar amounts of TTF and the corresponding accep-
tors, i.e., 1f or 8. The unit cell of I is composed of TTF
and fluorenone 1f molecules in a 1:1 ratio; the unit cell
of II is composed of TTF, acceptor 8, and C6H5Cl
molecules in the ratio of 1:1:1. Figure 7 shows the
packing diagrams for I and II. It is seen that the donor
and acceptor molecules alternate in stacks which is a
characteristic motif for semiconducting CTC.33
Inclusion of the third component (solvent) in II does
not significantly change the mode of stacking. In both
complexes each TTF molecule in the stack is situated
between the two translation-related (c in I and a in II)
acceptor molecules; hence the mean planes of the acceptor
molecules in the stack are rigorously parallel. In I and
II, these stacks run along the a and c axes, respectively.
Within the stacks, the dihedral angle between the TTF
and the acceptor molecules is 2.9° in I and 4.1° in II. The
A + D {K
\
}[Aδ-, Dδ+
]
(3)
ꢀCTC
1
K
ACTC
)
C + C +
-
(
[
)
A
D
2
2
1
K
C + C +
- 4CACD (4)
(
x
)
A
D
]
where CA and CB are starting concentrations of a donor
and an acceptor, ꢀCTC is the molar extinction coefficient
for CTC [Aδ-, Dδ+], and ACTC is the equilibrium absor-
bance of the solution of the mixture of CA and CD.
Using this approach we estimated K values for 1:1 CTC
of acceptors 7 and 8 with N-propylcarbazole in dioxane
under the same conditions as in the previous study31
(Table 2). Complexation constants for 7 and 8 (Table 2)
are comparable with those for acceptors 1b,c,e,f; the K
value for 7 is ca. 1.6 times less than that for tri- and
tetranitrosubstituted 9-fluorenones (1b,c) whereas for 8
(32) Benesi, S. A.; Hildebrand, J . H. J . Am. Chem. Soc. 1949, 71,
2703.
(33) (a) Gutman, F. E.; Lyons, L. E. Organic Semiconductors; J ohn
Wiley & Sons: New York, 1967. (b) Mayoh, B.; Prout, C. K. J . Chem.
Soc., Faraday Trans. 2 1972, 68, 1072. (c) Torrance, J . B. Acc. Chem.
Res. 1979, 12, 79.
(31) Grebenyuk, S. A. Dissertation, Inst. Phys. Org. & Coal Chem-
istry, Donetsk, 1994. Grebenyuk, S. A.; Perepichka, I. F.; Popov, A. F.
Manuscript in preparation.

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 63, No. 19, 1998 6489
F igu r e 7. Packing diagram for I (a) and II (b) in the crystals.
mutual arrangement of the donors and acceptors in the
stacks of I and II is qualitatively similar (Figure 8). In
both cases, the central CdC bond of TTF is almost
parallel to a bond of the C(9) atom with a benzene ring
of an acceptor [C(9)-C(13) in 1f and C(9)-C(10) in 8].
One dithiole ring of TTF is packed between the cyclo-
pentadiene rings of the two adjacent fluorene molecules,
whereas the other dithiole ring is situated in the vicinity
of a cyano group at C(14).
There are a number of short interatomic contacts
between the donor and adjacent acceptors (A and B) in a
stack of both I and II (Table 3) indicating dimerized
stacks. The contacts between TTF and acceptor A in I
and acceptor B in II (see Table 3) are shorter than
contacts with the other acceptor molecule (i.e., B in I and
A in II).
The single principal distinction in the stacking geom-
etry in I and II is the occurrence of a very short interstack
contact of 3.12 Å between S(2) and O(4) atoms in the
dimer in I, which is not seen in II, due to a different
rotation of the corresponding nitro group in the two
structures.
The mutual arrangement of the stacks in crystals of I
and II is different (Figure 9). Each acceptor molecule
within a stack in I is connected with two translation b
related TTF molecules from two adjacent stacks via
specific S‚‚‚O [atoms S(1) and O(3)] interactions and N‚
‚‚H-C (atoms N(2) and C(3′)) hydrogen bonds (Figure 9a).
The S‚‚‚O distance (3.10 Å) is rather short. The geometry
of the C(1′)-S(1)‚‚‚O(3)-N(4) contact [angle O(3)‚‚‚S(1)-
F igu r e 8. Mutual arrangement of two acceptor molecules and
one TTF molecule in a stack of I (acceptor 1f) (a) and in a stack
of II (acceptor 8) (b).
C(1′) is 162.3°] fills the σ-n orbital interaction between
the S-C bond σ* orbital and the oxygen atom lone pair
on an sp2 orbital as well as the π-n interaction of S(1)
atom lone pair on the p orbital with the π* orbital of the
O-N bond.
The packing of stacks in the crystal of II is more
complicated due to the included solvent molecules. Two
types of specific interactions between TTF and acceptor
molecules in adjacent stacks are observed. The interac-
tion C(1′)-S(2)‚‚‚N(3) and C(4′)-S(3)‚‚‚O(2) have the
following parameters: S(2)‚‚‚N(3) 3.08 Å, C(1′)-S(2)‚‚‚N(3)
168°, S(2)‚‚‚N(3)-C(17) 174° and S(3)‚‚‚O(2) 3.04 Å,
C(4′)-S(3)‚‚‚O(2) 173° (Figure 9b). In the first case, the
stacks related by translation b are considered. In the
second case, the stacks are related by a symmetry center.
In addition, the solvent molecules are involved in weak
specific interactions with both TTF and the acceptor.
Atom Cl(1) interacts with atom S(4) (Cl‚‚‚S 3.69 Å) and
atom Cl(2) interacts with atom O(2) (Cl‚‚‚O 3.36 Å). The
corresponding distances are rather long, although in both
cases a lone pair of chlorine is oriented toward the
corresponding heteroatom; C-Cl‚‚‚S and C-Cl‚‚‚O angles
(98.1 and 97.5°, respectively) are close to 90°.
In I and II, TTF molecules manifest different types of
out-of-plane deformations. In I, the most significant one

6490 J . Org. Chem., Vol. 63, No. 19, 1998
Perepichka et al.
Ta ble 3. In tr a sta ck Sh or t Con ta cts (Å) betw een TTF a n d Tw o Above (A) a n d Un d er (B) Molecu les of Accep tor s 1f a n d 8
in Str u ctu r es I a n d IIa
structure I
structure II
molecule A
S(1)‚‚C(8)
S(2)‚‚C(11)
S(2)‚‚C(12)
S(2)‚‚O(4)
S(4)‚‚C(14)
S(4)‚‚C(16)
S(4)‚‚C(15)
C(1′)‚‚C(9)
C(1′)‚‚C(13)
C(1′)‚‚C(10)
C(2′)‚‚C(7)
C(2′)‚‚C(6)
C(3′)‚‚C(5)
C(3′)‚‚C(12)
C(4′)‚‚C(9)
C(4′)‚‚C(14)
C(6′)‚‚N(1)
molecule B
molecule A
molecule B
3.32
S(1)‚‚C(9)
3.63
3.60
3.67
3.66
3.64
3.44
3.64
3.78
3.66
3.63
3.59
3.54
3.59
3.76
3.52
3.50
S(1)‚‚C(4)
S(2)‚‚C(2)
S(2)‚‚C(17)
S(3)‚‚C(10)
S(3)‚‚C(1)
3.61
S(1)‚‚C(11)
3.37
3.42
3.45
3.40
3.73
3.22
3.25
3.25
3.60
3.26
3.38
3.48
3.45
3.63
3.68
3.63
3.39
3.29
3.48
3.39
3.22
3.39
3.12
3.20
3.42
3.36
3.29
3.31
3.60
3.52
3.67
3.51
3.45
3.27
3.42
3.38
S(1)‚‚C(13)
S(2)‚‚C(10)
S(2)‚‚C(11)
S(3)‚‚C(1)
3.47
3.55
3.86
3.87
3.72
3.46
3.65
3.75
3.74
3.79
3.84
3.55
3.82
3.72
3.64
3.69
3.62
S(1)‚‚C(12)
S(2)‚‚C(10)
S(2)‚‚C(1)
S(2)‚‚C(9)
S(3)‚‚O(1)
S(4)‚‚C(15)
S(4)‚‚N(1)
S(4)‚‚C(11)
S(4)‚‚C(12)
S(4)‚‚C(13)
C(1′)‚‚C(2)
C(1′)‚‚C(3)
C(1′)‚‚C(4)
C(1′)‚‚C(11)
C(4′)‚‚C(10)
C(4′)‚‚C(1)
C(4′)‚‚C(11)
C(5)‚‚C(14)
C(6′)‚‚C(9)
C(6′)-C(13)
S(3)‚‚C(14)
S(3)‚‚C(15)
S(4)‚‚C(8)
C(1′)‚‚C(9)
C(1′)‚‚C(10)
C(2′)‚‚C(13)
C(2′)‚‚C(12)
C(2′)‚‚C(13)
C(3′)‚‚C(11)
C(3′)‚‚C(12)
C(6′)‚‚N(1)
S(4)‚‚C(13)
C(1′)‚‚C(9)
C(1′)‚‚C(10)
C(1′)‚‚C(13)
C(2′)‚‚C(4)
C(2′)‚‚C(11)
C(3′)‚‚C(1)
C(3′)‚‚C(2)
C(4′)‚‚C(13)
C(4′)‚‚C(9)
C(4′)‚‚C(14)
C(5′)‚‚C(15)
a
Enumeration of the atoms corresponds to Figures 8a and 8b for structures I and II, respectively.
is a twist of 7.1° around the central CdC bond. In II,
the two dithiole rings are bent toward one another by
an angle of 7.3° giving TTF a boat conformation. Such
small distortions of planarity (within the range of 0-8°)
are typical for TTF molecules included in the Cambridge
Crystallographic Database (CCD).34 In the two crystal
modifications of TTF, no similar distortions have been
observed.35,36 Apparently, the distortions in I and II are
determined by a compromise between tendencies to
provide optimum molecular overlap and close packing in
the crystals.
The double bonds of TTF are essentially localized. In
I the central CdC bond length is 1.364(9) Å and the
peripheral bonds are both 1.34(1) Å; in II these bonds
are 1.359(6), 1.324(7), and 1.323(7) Å, respectively. These
values are similar to but systematically longer (by
approximately 2 esd) than the corresponding distances
[1.337(4), 1.309(4), and 1.309(4) Å] in the structure of
pure TTF where no plane-to-plane stacking occurs.35 This
effect can be attributed to charge transfer in I and II.
The S-C bond lengths vary within 1.725-1.747(6) Å
in I and 1.731(5) -1.757(4) Å in II, whereas these bond
lengths are 1.731(4) - 1.755(3) Å in the structure of
TTF.35 The molecules of unsubstituted TTF included in
CCD (62 entries) reveal a wide variation of C-C and S-C
bond lengths. The central CdC bond varies within the
range 1.298-1.418 Å, the cyclic CdC bond within 1.260-
1.404 Å, and S-C bonds within 1.626-1.798 Å.
rene (10),37 where such distortion was attributed to steric
hindrance and electrostatic repulsion between the two
adjacent nitro groups in positions 4 and 5. In the
complexes I and II, these nitro groups in 1f and 8 are
rotated from the planes of the corresponding benzene
rings by 32-33° and 40-39°, respectively, whereas
rotations of ca. 35° for 1f 15 and 34° and 40° for 1037 were
observed. For a number of other 4,5-dinitrosubstituted
fluorenes, similar values (26.4-41.7°) were obtained.13,14,38
It should be noted for comparison that for the nonhin-
dered nitro groups in positions 2 and 7 the dihedral
angles with the corresponding benzene rings in acceptor
1f of complex I are only 13.5-14.9°, which is comparable
with literature data for other 2,7-dinitrosubstituted
fluorenes (7.4-20°).39 In addition, out-of-plane displace-
ments of nitrogens in positions 4 and 5 by 0.33 and -0.33
Å in I and 0.22 and -0.31 Å in II, respectively, and
specific distortions of exocyclic angles at C(4) and C(5)
atoms are observed.
The bond lengths in the acceptor molecules of I and II
are basically similar to those in previously studied
derivatives.15,37 The exocyclic double bonds C(9)dC(14)
of 1f in complex I [1.389(8) Å] and of 8 in complex II
[1.379(6) Å] are somewhat longer than that in the
acceptor molecule 1f [1.372(15) and 1.336(14) Å for two
independent molecules15] and are close to that for accep-
tor 10 [1.388(4) Å] in which this bond is involved in
intramolecular charge transfer (10′) which leads to
decreasing bond order (Chart 2).
The acceptor molecules 1f and 8 have a boatlike
distortion in both structures I and II, although each ring
of the tricyclic system is planar. In I, the dihedral angle
between the two benzene rings of 1f is 11.2° and the
angles between each benzene ring and the five-membered
ring are 5.8 and 5.6°; in II these angles for 8 are 7.6, 3.2,
(36) Cooper, W. F.; Edmonds, J . W.; Wudl, F.; Coppens, P. Cryst.
Struct. Commun. 1974, 3, 23.
(37) 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.
(38) (a) Chetkina, L. A.; Povetyeva, Z. P.; Bel’skii, V. K.; Bespalov,
B. P. Kristallografiya 1985, 30, 910; Chem. Abstr. 1985, 103, 204122w.
(b) Semidetko, O. V.; Chetkina, L. A.; Bel’skii, V. K.; Poplavskii, A.
N.; Andrievskii, A. M.; Dyumaev, K. M. Zh. Strukt. Khim. 1988, 29,
187; (Chem. Abstr. 1988, 109, 139617u. (c) Semidetko, O. V.; Chetkina,
L. A.; Bel’skii, V. K.; Poplavskii, A. N.; Andrievskii, A. M.; Dyumaev,
K. M. Dokl. Akad. Nauk SSSR 1988, 299, 375; Chem. Abstr. 1989,
111, 96782r.
and 4.4°, respectively. Such distortion was also observed
15
in the structure of pure 1f
and also in a fluorene
acceptor with intramolecular charge transfer, viz. 2,4,5,7-
tetranitro-9-(R-cyano-R-dimethylaminomethylene)fluo-
(34) Allen, F. H.; Kennard, O. Chem. Design Autom. News 1993,
8(1), 1 and 31-37.
(35) Ellern, A.; Bernstein, J .; Becker, J . Y.; Zamir, Sh.; Shahal, L.
Chem. Mater. 1994, 6, 1378.
(39) Silverman, J .; Yannoni, N. F. J . Phys. Chem. 1967, 71, 1381.

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 63, No. 19, 1998 6491
(or quasi-reversible) single-electron reduction processes.
Single-crystal X-ray structures for two complexes of TTF
with the aceptors 1f and 8 have been obtained: they are
characterized by mixed ‚‚A‚‚‚D‚‚‚A‚‚‚D‚‚ stacking motifs
and there is weak interplanar charge transfer. CTC
formation of 7 and 8 with N-propylcarbazole has been
demonstrated in solution. These studies establish that
new fluorene derivatives are promising acceptor mol-
ecules for the development of organic semiconductors,
conductors, and photoconductors.
Exp er im en ta l Section
Electr och em ica l Mea su r em en ts. Cyclic voltammetry
experiments were performed on a EG&G PARC model 273
potentiostat with an Advanced Bryans XY recorder with iR
compensation. Platinum wire, platinum disk (diameter 1.6
mm, BAS), and Ag/Ag+ (AgNO3 in acetonitrile) were used as
counter, working, and reference electrodes, respectively. All
potentials were corrected using the ferrocene-ferrocenium
couple as internal reference and represented versus Ag/AgCl
which showed in these conditions a potential of -0.45 V
against the Fc0/Fc+ couple. CV experiments were performed
in dry acetonitrile (Fluka, anhydrous) with Et4N+BF4- (Fluka,
puriss.) as supporting electrolyte (0.2 mol dm-3) under N2 flow;
concentrations of acceptors were ca. 10-4 mol dm-3. The scan
rate was 100 mV s-1
.
Sp ectr oelectr och em ica l Mea su r em en ts. Spectroelec-
trochemistry was undertaken using a Perkin-Elmer Lambda
19 UV-vis-near-IR spectrophotometer with a Ministat (Th-
ompson Electrochem. Ltd, Newcastle upon Tyne, U.K.). The
spectroelectrochemical cell was based on a 1 cm thick cuvette;
Pt wire was used as a counter electrode while Ag wire served
as the quasi-reference electrode (all potentials were corrected
to Ag/AgCl). A thin layer working electrode was constructed
from glass and indium tin oxide conducting glass (sheet
resistance is 30 Ohm cm-2, from Balzers) held together with
0.1 mm thick PTFE spacer (from Goodfellow).
Sin gle-Cr ysta l X-r a y Str u ctu r e Deter m in a tion s. Crys-
tals of complexes of 1f:TTF (1:1 stoichometry) and 8:TTF:C6H5-
Cl (1:1:1 stoichometry) were obtained as long black needles
by addition of a solution of TTF in chlorobenzene to a hot
concentrated solution of the appropriate acceptor, i.e. 1f or 8,
in the same solvent, followed by very slow cooling to room
temperature.
Details of data collection, structure solution, and refinement
are given in Table 4.
In the structure of II, two independent C6H5Cl solvent
molecules were found to occupy the positions around different
symmetry centers, resulting in disordering of the C6H5Cl
molecules. For one of the molecules, the symmetry center
coincides with the center of its benzene ring. As a result, the
Cl substituent appears in two positions [C(1) and C(4)] of the
benzene ring with a half occupancy for each position. For the
second solvent molecule, the center of its benzene ring is
shifted from the symmetry center, so the resultant appearance
of the disordered molecule is more complicated. A pair of
symmetrically related atoms C(5′′) in sites 2 and 6 have the
same coordinates for both disordered positions of the second
solvent (site occupancy factor is 1). The other atoms have
different coordinates (site occupancy factor is 0.5 for each
atom).
F igu r e 9. Specific intermolecular interactions in adjacent
stacks of complexes I (a) and II (b).
Ch a r t 2
The structures were solved and refined using SHELXS8640
and SHELXL9341 software. Software SHELXTL-Plus42 was
used for graphics and preparation of material for publication.
Additional materials containing atomic coordinates, thermal
Con clu sion s
In summary, we have synthesized new strong electron
acceptors 7-9 of the fluorene series. Cyclic voltammetric
and spectroelectrochemical studies on 7 and 8 establish
that these compounds undergo three separate reversible
(40) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(41) Sheldrick, G. M. SHELXL93, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Germany, 1993.
(42) Sheldrick, G. M. SHELXLTL-Plus, Release 4.1; Siemens Ana-
lytical X-ray Instruments Inc.: Madison, WI, 1991.

6492 J . Org. Chem., Vol. 63, No. 19, 1998
Perepichka et al.
Ta ble 4. Cr ysta l Da ta , Da ta Collection , a n d Str u ctu r e Solu tion a n d Refin em en t P a r a m eter s for I a n d II
compd
empirical formula
I (1f:TTF, 1:1)
22H8N6O8S4
C16H4N6O8:C6H4S4
612.58
II (8:TTF:PhCl, 1:1:1)
C30H13ClN6O4S4
C18H4N6O4:C6H4S4:C6H5Cl
685.15
C
form wt
color, habit
crystal size, mm
crystal system
space group
unit cell dimensions
a, Å
black, needle
1.10 × 0.18 × 0.08
orthorhombic
Pna2(1)
black, needle
0.14 × 0.06 × 0.04
triclinic
P1h
21.958(4)
7.204(2)
b, Å
15.447(3)
9.500(2)
c, Å
6.8810(10)
21.660(5)
R, deg
90
90
90
96.25(2)
92.72(2)
95.95(2)
1463.0(6)
â, deg
γ, deg
volume, Å3
Z
2333.9(7)
4
1.743
0.474
2
density (calcd), g cm-3
abs coeff, mm-1
F(000)
1.555
0.466
696
1240
diffractometer
temperature, K
radiation (λ, Å)
Siemens SMART
150.0(2)
graphite monochromatized
Mo KR (0.71073)
ω
0.3
Rigaku AFC-6S
150(2)
graphite monochromatized
Cu KR (1.54184)
scan mode
ω
scan step/width (in ω), deg
time/step (sec); scan rate, deg/min
θ range, deg
1.0 + 0.15tan(θ)
15
8
1.61-25.30
4.11-74.98
index ranges
-24 e h e 21
-8 e h e 8
-17 e k e 17
0 e k e 11
-8 e l e 7
-27 e l e 26
5697
reflectns collected
indep reflectns
data reduction
9469
3721 [R(int) ) 0.1125]
Siemens SAINT (Siemens
Analytical X-ray Instruments, 1995)
empirical (SHELXTL-Plus)
0.6276 and 0.4944
direct methods (SHELX-86)
full-matrix l.s. on F2 (SHELXL-93)
H atoms were found from difference Fourier
synthesis and refined with isotropic thermal
parameters
5367 [R(int) ) 0.0245]
TEXSAN PROCESS
(Molecular Structure Corporation, 1985)
empirical (psi scan)
1.0000 and 0.5472
direct methods (SHELX-86)
full-matrix l.s. on F2 (SHELXL-93)
All H atoms were placed in calculated positions
and refined using riding model [BH ) 1.2BC;
d(C-H) ) 0.93 Å]
5367/15/434
absn corrctn
min and max transmission
solution method
refinement method
hydrogen treatment
data/restraints/parameters
goodness-of-fit on F2
3715/1/362
1.083
1.081
final R indices [I > 2σ(I)]
R1 ) 0.0686, wR2 ) 0.1775
R1 ) 0.0718, wR2 ) 0.1860
0.08(13)
R1 ) 0.0588, wR2 ) 0.1294
R1 ) 0.0982, wR2 ) 0.1520
R indices (all data)
abs structure param
extinction coeff
0.0045(10)
0.938 and -0.444
0.0016(2)
0.546 and -0.558
largest diff peak and hole, e Å-3
parameters, bond lengths and angles are available from the
Cambridge Crystallographic Data Center.43
solid impurities, and the solution was poured into diluted nitric
acid. The solid was filtered off and washed with water,
yielding acid 4 (58.5 g, 92.8%), which can be used in the next
step without purification; mp > 360 °C (lit.29 mp 400 °C dec).
4,5-Din itr oflu or en -9-on e-2,7-dicar boxylic Acid (5). Flu-
oren-9-one-2,7-dicarboxylic acid (4) (40.0 g, 0.149 mol) was
refluxed with a mixture of fuming nitric acid (600 mL, d )
1.51 g cm-3) and concentrated sulfuric acid (400 mL) for 2 h,
cooled to room temperature, and poured into ice water (2 L).
The pale yellow solid was filtered off, washed with water, and
dried yielding crude acid 5. The acid was extracted for 1.5
days in Soxlet apparatus by acetonitrile, yielding acid 5 (40.5
g, 75.8%), mp 357-360 °C (lit.29 mp 285-294 °C). Alterna-
tively, acid 5 can be purified by recrystallization from acetic
acid.
4,5-Din itr oflu or en -9-on e-2,7-d ica r boxa m id e (6). Di-
carboxylic acid 5 (11.0 g, 0.0307 mol) was refluxed with thionyl
chloride (50 mL) for 3-4 h giving a dark yellow solution. The
excess thionyl chloride was removed under low pressure, the
residue was dissolved in dry dioxane (100 mL), and ammonia
gas was passed through the stirred solution until pH 8 was
reached (no excess NH3). After cooling, the reaction mixture
was diluted with water (100 mL) and the precipitate was
filtered off, washed with water, and dried yielding crude
diamide (9.5 g, 86.5%). Recrystallization from DMF (250 mL)
gave 6 (8.05 g, 73.5%) as a yellow powder, mp > 300 °C dec:
2,4,5,7-Tet r a n it r o-9-d icya n om et h ylen eflu or en e (1f).
This was prepared according to our modified procedure for
condensation of fluoren-9-ones with malononitrile.1,11c,12,37
2,4,5,7-Tetranitrofluoren-9-one (1c) (1.80 g, 5 mmol) was
dissolved in DMF (10 mL), malononitrile (0.73 g, 11 mmol)
was added, and the reaction mixture was stirred at room
temperature for 1 h and diluted with propan-2-ol (40 mL). The
yellow-green solid was collected by filtration, washed with
propan-2-ol, and dried yielding compound 1f (1.96 g, 96%).
Recrystallization from dioxane gave analytically pure yellow
crystals of 1f (1.30 g, 64%), mp > 360 °C, which were identical
to an authentic sample.3b
F lu or en -9-on e-2,7-d ica r boxylic Acid (4). 2,7-Diacetyl-
fluorene29 (60.0 g, 0.235 mol) was refluxed with 60% nitric acid
(1200 mL) for ca. 5 h with water being distilled off water until
the temperature of the distillate had reached 119 °C. The
reaction mixture was left overnight, and the yellow solid was
filtered off and washed with water. It was dissolved in a
solution of sodium carbonate (ca. 500 mL) and filtered off from
(43) The authors have deposited atomic coordinates for I and II with
the Cambridge Crystallographic Data Centre. The coordinates can be
obtained, on request, from the Director, Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge, CB2 1EZ, U.K.

Electron Acceptors of the Fluorene Series
J . Org. Chem., Vol. 63, No. 19, 1998 6493
1H NMR (250 MHz; DMSO-d6) δ 8.69 (2H, d, J 1,3 ) 1.5 Hz),
8.60 (2H, d, J 1,3 ) 1.5 Hz), 8.58 (2H, s, broad), 7.98 (2H, s,
broad). Anal. Calcd for C15H8N4O7: C, 50.57; H, 2.26; N,
15.73. Found: C, 50.40; H, 2.16; N, 15.65%.
147.57, 139.28, 134.51, 134.26, 133.73, 129.16, 116.93, 116.53,
113.59, 113.16. Anal. Calcd for C18H4N6O4: C, 58.71; H, 1.09;
N, 22.82. Found: C, 58.60; H, 1.10; N, 22.70%.
2,7-Dicya n o-4,5-d in itr oflu or en -9-on e Oxim e (9). Finely
powdered dry hydroxylamine hydrochloride (123 mg, 1.77
mmol) was added to a solution of fluorenone 7 (196 mg, 0.613
mmol) in DMF (1.5 mL), and the reaction mixture was stirred
at 60 °C for 2 h (TLC monitoring of the reaction). The reaction
mixture was cooled to room temperature and diluted with
water (2 mL), and the resulting precipitate was filtered off,
washed with water, and dried yielding crude 8 (161 mg,
78.5%). Recrystallization from a dioxane-propan-2-ol mixture
(1:5 v/v) gave pure oxime (150 mg, 73%), mp >300 °C: 1H NMR
(400 MHz; acetone-d6) δ 9.27 (1H, d, J 1,3 ) 1.5 Hz), 8.68 (1H,
2,7-Dicya n o-4,5-d in itr oflu or en -9-on e (7). A mixture of
diamide 6 (0.56 g, 1.57 mmol), POCl3 (2 mL), and DMF (0.1
mL) was refluxed for 30 min (complete disolution occurred in
5-7 min). The excess POCl3 was removed in vacuo, the
residue was thoroughly mixed with water (10 mL), and the
precipitate was filtered off and washed with a large volume of
water yielding a light-brown powder of crude dinitrile (0.52 g,
≈100%). This product was refluxed in toluene (18 mL), filtered
through a 1 cm layer of Al2O3, and then washed with boiling
toluene (4 mL). Pure 7 (0.16 g, 32%) crystallized on cooling
the combined toluene solutions, mp 278-280 °C. An ad-
ditional portion of the product (0.08 g, 16%) was obtained by
evaporation of two-thirds of the mother liquor: 1H NMR (400
MHz; acetone-d6) δ 8.80 (2H, d, J 1,3 ) 1.4 Hz), 8.60 (2H, d, J 1,3
) 1.4 Hz); 13C NMR (63 MHz; acetone-d6) δ 185.84, 147.27,
138.77, 137.15, 135.35, 132.50, 117.46, 116.43. Anal. Calcd
for C15H4N4O5: C, 56.26; H, 1.26; N, 17.49. Found: C, 56.10;
H, 1.31; N, 17.45%.
2,7-Dicyan o-4,5-din itr o-9-dicyan om eth ylen eflu or en e (8).
Malononitrile (31 mg, 0.47 mmol) was added to a solution of
fluorenone 7 (127 mg, 0.397 mmol) in DMF (1 mL), and the
reaction mixture was stirred for 40 min at room temperature
(TLC monitoring). The reaction mixture was diluted with
propan-2-ol (10 mL) and left to crystallize at 0-5 °C overnight.
The precipitate was filtered off and washed with propan-2-ol
yielding a dark yellow powder of 8 (100 mg, 69%). Recrystal-
lization from toluene-dioxane mixture (3:1 v/v) gave pure
product 8 (94 mg, 64%), mp 285-287 °C: 1H NMR (250 MHz;
acetone-d6; 1 drop of CF3COOD) δ 9.20 (2H, d, J 1,3 ) 1.3 Hz),
8.86 (2H, d, J 1,3 ) 1.3 Hz); 13C NMR (63 MHz; acetone-d6) δ
d, J 1,3 ) 1.3 Hz), 8.63 (1H, d, J 1,3 ) 1.5 Hz), 8.59 (1H, d, J 1,3
)
1.3 Hz); 13C NMR (63 MHz; acetone-d6) δ 147.67, 147.37,
147.20, 141.53, 136.24, 133.95, 132.36, 131.33, 131.09, 130.22,
129.88, 117.03, 116.97, 116.21, 115.65. Anal. Calcd for
C
15H5N5O5: C, 53.74; H, 1.50; N, 20.89. Found: C, 53.90; H,
1.62; N, 20.80.
Ack n ow led gm en t. We thank the Royal Society for
funding visits to Durham (I.F.P., L.G.K., and L.M.G.)
and for a Leverhulme Senior Research Fellowship
(J .A.K.H.).
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic data for structures I and II (7 pages). This material
is contained in libraries on microfiche, immediately follows this
article in the microfilm version of the journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
J O9803481