Engineering a remarkably low HOMO-LUMO gap by covalent linkage of a strong π-donor and a π-acceptor - Tetrathiafulvalene-σ-polynitrofluorene diads: Their amphoteric redox behavior, electron transfer and spectroscopic properties

Article abstract of DOI:10.1002/1521-3765(20021018)8:20<4656::AID-CHEM4656>3.0.CO;2-1

Novel R₃TTF-σ-A compounds 14, 16 and 19 (R₃TTF=trial-kyltetrathiafulvalene, σ = saturated spacer, A = polynitrofluoren-9-dicyanomethylene acceptor) incorporating very strong donor and acceptor moieties have been synthesized by conden

Full text of DOI:10.1002/1521-3765(20021018)8:20<4656::AID-CHEM4656>3.0.CO;2-1

FULL PAPER
Engineering a Remarkably Low HOMO LUMO Gap by Covalent Linkage
of a Strong p-Donor and a p-Acceptor–Tetrathiafulvalene-
s-Polynitrofluorene Diads: Their Amphoteric Redox Behavior,
Electron Transfer and Spectroscopic Properties
Dmitrii F. Perepichka,[a] Martin R. Bryce,*[a] Andrei S. Batsanov,[a] Eric J. L. McInnes,[b]
Jing P. Zhao,[b] and Robert D. Farley[c]
Abstract: Novel R3TTF
pounds 14, 16 and 19 (R3TTF ˆ trial-
kyltetrathiafulvalene,
s ˆ saturated
s
A
com-
For compound 14 a strongEPR signal
is observed in the solid state, ascribed to
intermolecular complexation: a less in-
tense signal is seen in solution, corre-
spondingto ca. 2% of the molecules
existingin a radical form at room
temperature. Intramolecular charge
transfer in diads 14 and 16 is manifested
in strongabsorption bands in the near-
IR region of their electronic spectra.
Spectroelectrochemical data reveal
marked electrochromic behavior in the
visible and near-IR region of both com-
pounds. The first X-ray crystal structure
of a fluorene radical-anion salt is re-
ported, namely the copper salt of 2,4,5,7-
tetranitro-9-dicyanomethylenefluorene
(1:1 stoichiometry).
spacer, A ˆ polynitrofluoren-9-dicyano-
methylene acceptor) incorporatingvery
strongdonor and acceptor moieties have
been synthesized by condensation of the
correspondingR 3TTF s-fluoren-9-one
diads with malononitrile. Reversible
five-step amphoteric redox behavior
has been observed with an extremely
low HOMO LUMO gap (ꢀ0.3 eV).
Keywords: donor acceptor systems
¥
electrochromism
¥
electron
transfer ¥ HOMO LUMO gap ¥
tetrathiafulvalene
character of a conjugated system, its rigidification into a
planar conformation, and the alternation of p-donor and p-
acceptor fragments in the polymer chain. However, much less
is known about monomeric organic compounds with a low
HOMO LUMO gap, which can be engineered by linkage of
an electron donor (introducinga high-lyingHOMO) and an
electron acceptor (introducinga low-lyingLUMO) by a
spacer unit which precludes mixingof HOMO and LUMO
orbitals. These systems represent novel charge transfer
materials with predefined D/A stoichiometries for molecular
electronics applications, e.g. molecular conductors[2] and
molecular switches.[3] This type of molecule, specifically a
TTF s-TCNQ diad (TTF is tetrathiafulvalene; TCNQ is
7,7',8,8'-tetracyano-p-quinodimethane) was proposed by Avir-
am and Ratner as a candidate for unimolecular rectification.[4]
Since then, TTF derivatives bearingan electron acceptor
substituent have been prime targets.[5] Different acceptor
groups have been covalently attached to TTF: namely full-
erene,[5a c] phthalocyanines,[5a] pyromellitic diimide,[5d,e] quino-
nes,[5a,f,g] 11,11,12,12-tetracyano-9,10-anthraquinodimethane
(TCNAQ),[5a] thioindigo,[5h] viologen and related acceptor-
s,[3a, 5a,d] but these possess only moderate electron affinity
(EA). TTFs linked to a strongelectron acceptor moiety (i.e.,
of similar EA to TCNQ) are very difficult to obtain.[6] The
only example[6a] of couplingTTF with a substituted TCNQ
Introduction
There is continuing interest in low band gap organic materials
due to the advanced electronic and electrooptic properties
which they display.[1] The main principles for constructinglow
band-gap polymers include tailoring the aromatic/quinoid
[a] Prof. Dr. M. R. Bryce, Dr. D. F. Perepichka, Dr. A. S. Batsanov
Department of Chemistry, University of Durham
Durham DH1 3LE (UK)
Fax : (‡44)191-384-4737
E-mail: m.r.bryce@durham.ac.uk
[b] Dr. E. J. L. McInnes, Dr. J. P. Zhao
EPSRC c.w. EPR Service Centre, Department of Chemistry
The University of Manchester, Manchester M13 9PL (UK)
E-mail: eric.mcinnes@man.ac.uk
[c] Dr. R. D. Farley
EPSRC ENDOR Service Centre, Department of Chemistry
Cardiff University, Cardiff CF10 3TB (UK)
E-mail: rdfarley@cf.ac.uk
Supportinginformation for this article is available on the WWW under
http://www.chemeurj.orgor from the author: Experimental details of
the preparation of the TTF analogues of 13a and 13b and of the
reaction of TTFCH2OH with 17; 1H NMR spectra of compounds 5b, 6,
18, 19 and a mixture of 6 ‡ 11; COSY NMR spectra of compounds 9
and 15; spectroelectrochemical data for compounds 3b, 6 and 11; UV/
Vis-near-IR spectrum of 24; an ORTEP diagram for 18 and a diagram
of the disorder in 25 (from X-ray data).
4656
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4656 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 20

4656 4669
(which required an eight-step synthesis) gave EPR-active
products, which were difficult to purify and they were not
investigated in detail. While many TTF benzoquinone diads
have been reported,[5a,f,g] all attempts to increase their accept-
or ability by conversion to the correspondingTCNQ or N,N'-
dicyanoquinodiimine derivatives have failed due to the
incompatibility of TTF with the strongly acidic conditions
(TiCl4) of these reactions. On the other hand, it is known that
condensation of polynitrofluoren-9-ones with malononitrile
takes place under milder conditions[7] and the resulting
dicyanomethylene derivatives have similar electron affinity
to TCNQ. With this in mind we now report[8] the first TTF
fluorene conjugates which posses both strong electron donor
and strongacceptor properties.
The donor synthons were obtained from TTF derivative 7[9]
containingalkyl substituents to lower the oxidation potential
and pentyl chains to improve solubility, as shown in Scheme 2.
Me
OHC
Me
Ph
N
OHC
Me
S
S
S
S
i
S
S
S
S
S
S
S
S
C5H11
C5H11
C5H11
C5H11
C5H11
C5H11
7
8
9
ii
iii
Me
RO
Ph
Ph
N
S
S
Me
Me
N
H
S
S
S
S
S
S
v
S
S
Results and Discussion
C5H11
C5H11
S
S
Synthesis: The covalent linkage of a TTF fragment to a
fluorene acceptor was first achieved through the formation of
an ester or amide bond. Contrary to the previously used
C5H11
12
C5H11
C5H11
C5H11
10: R = H
11: R = C(0)Me
iv
methodology for TTF
s
TCNAQ diads,[9] the carbonyl
Scheme 2. i) LDA/Et2O, À788C, 2 h, then PhN(Me)CHO À788C ! 208C,
12 h; ii) NaBH4/EtOH, 208C, 1 h; iii) PhCH2NH2 ‡ 4 ä MS/cyclohexane,
reflux, 15 h; iv) PhCOCl ‡ Py/MeCN, 208C, 2 h; v) LiAlH4/Et2O, 20 8C,
3.5 h.
group was placed on the acceptor (fluorene) component,
because when attached to the TTF system, it raises its oxidation
potential. The synthesis of the fluorene carbonyl chlorides 5a,b
with different length s-bridges is presented in Scheme 1.
The reaction of the lithium salt of 7 with N-methylformanilide
afforded aldehyde 8 (66% yield) together with compound 9
(5% yield) as a product of a base-catalyzed condensation of 8
with a second molecule of N-methylformanilide. Aldehyde 8
was reduced with NaBH4 to give hydroxymethyl-TTF 10. The
synthesis of aminomethyl-TTF by amination of (unsubstitut-
ed) TTF-carbaldehyde followed by reduction of the Schiff
base has been reported and the best yield (35%) was achieved
for the N-benzyl derivative.[11] A slightly modified procedure
in our case gave a significantly higher yield of amine 12 (88%
from 8) which might be a useful synthon for the incorporation
of a TTF moiety into other systems.
The TTF fluorene conjugates (Scheme 3) were synthe-
sized by couplingof the acid chlorides 5a,b with the alcohol
10 usingpyridine as a nucleophilic catalyst (basic catalysis, e.g.
Et3N, is not applicable due to the high sensitivity of
polynitrofluorenes to bases). Alternatively, diad 13b was
synthesized by direct esterification of acid 4b with alcohol 10
usingdicyclohexylcarbodiimide and p-(dimethylamino)pyri-
dine catalysis. The ester bond in compounds 13a,b and 14
under certain conditions might be sensitive to hydrolysis;
therefore, the amide derivatives 15 and 16 were synthesized
from amine 12.
NO2 NO2
NO2 NO2
i
X
O
O2N
NO2
O2N
S
OMe
O
O
2a: X = CH2
2b: X = (CH2)2
1
ii
NO2 NO2
NO2 NO2
OMe
X
O
O
O2N
S
O2N
S
O
O
R
O
O
v
NC
CN
O
3a,b: R = OMe
4a,b: R = OH
5a,b: R = Cl
6
iii
iv
Scheme 1. i) HS-X-CO2Me‡NaHCO3/MeCN, 208C,
2 6 h; ii) H2O2/
AcOH, 60 708C, 3 h; iii) CF3CO2H/H2O, reflux, 4 6 h; iv) (COCl)2/
CH2Cl2, 208C, 20 40 h; v) CH2(CN)2/DMF, 208C, 6 h.
The 2-nitrogroup in compound 1 was selectively substituted
with 2-mercaptoacetic or 3-mercaptopropionic ester in ace-
tonitrile solution in the presence of NaHCO3 (as a base
catalyst and as a trap for the nitronic acid formed duringthe
reaction). These conditions were superior to those described
earlier for butylmetcaptan where aprotic dipolar solvents and
no catalyst were used.[10] The resultingsulfides 2a,b were
oxidized to sulfones 3a,b with hydrogen peroxide in acetic
acid and the ester group was then converted to the acids 4a,b
and acid chlorides 5a,b by treatment with aqueous trifluoro-
acetic acid and oxalyl chloride, respectively. The overall yield
for the four steps was 33% and 72% for 5a and 5b,
respectively.
The D
s
A diads 13 16 possess flexible s-bridges which
p complexation
are longenough to allow intramolecular
p
(see below). Usingfluorene-4-carbonyl chloride derivative 17
as an acceptor synthon would provide a shorter s-bridge
precludingthe formation of an intramolecular complex.
However, in a model reaction, attempted couplingof acid
chloride 17 with TTFCH2OH under the conditions used for 5
(pyridine catalysis) did not afford the target diad. Instead, the
.
‡
radical cation salt (TTFCH2OH )ClÀ was isolated in 90%
yield, probably as the result of an electron transfer reaction
Chem. Eur. J. 2002, 8, No. 20
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4657 $ 20.00+.50/0
4657

M. R. Bryce et al.
FULL PAPER
The acceptor ability of the fluorene moiety in 13b, 15 and
18 was increased by conversion to the dicyanomethylene
derivatives 14, 16 and 19, respectively, by treatment with
malononitrile in DMF solution (Schemes 3 and 4). As the
separation of the dicyanomethylene derivatives from the
startingfluorenones was difficult, a large excess of malononi-
trile was employed to complete the conversion. Under these
conditions a deep-blue by-product was obtained, the yield of
which increased in the presence of silica gel.[12] To elucidate its
structure, the reaction between fluorenone 1 and the excess of
malononitrile was performed in DMF and DMSO (the
reaction goes faster in DMSO) in the presence of silica gel.
A second molecule of malononitrile substitutes the cyano
group[13] in the initially formed 9-dicyanomethylenefluorene
(22) to give a tricyanovinyl derivative which being an excep-
tionally strongC-H acid exists in its carbanion form 23
(Scheme 5); the structure of 23 was established by X-ray
analysis of a potassium complex. The source of potassium is
believed to be potassium salts present in the silica gel.[14]
5a(b) + 10 4b + 10
NO2
NO2
i
ii
O
O
S
NO2
X
C5H11
S
S
O
S
S
O
O
C5H11
Me
13a: X = CH2
13b: X = (CH2)2
iii
NO2
NO2
O
S
O
C5H11
C5H11
NO2
S
S
O
O
S
S
Me
NC
CN
14
5 + 12
i
NO2
NO2
O
S
O
C5H11
C5H11
NO2
S
S
S
S
N
O
Ph
O
Me
15
NO2 NO2
NO2 NO2
iii
NO2
NO2
CN
1
O2N
NO2
O
S
O2N
NO2
O
i
C5H11
C5H11
NO2
S
S
S
N
CN
CN
O
NC
NC
CN
Ph
S
Me
NC
22
23
16
Scheme 5. i) CH2(CN)2, SiO2/DMSO, 208C, 12 h.
Scheme 3. i) Pyridine/MeCN, 208C, 6 h; ii) dicyclohexylcarbodiimide ‡
4-dimethylaminopyridine/CH2Cl2, 208C, 15 h; iii) CH2(CN)2/DMF, 208C,
6 h.
The anion radical salts of 22 were synthesized as model
compounds with complete charge transfer. Lithium and
copper salts 24 and 25 were prepared by the electron transfer
reaction of 22 with lithium
between the TTF-methanol and a strongly electron accepting
intermediate, such as 2,5,7-trinitrofluorene-9-one-4-carbonyl-
N-pyridinium. Compound 10 similarly gave a cation radical
salt. Diad 18 was, however, synthesized in 78% yield by
couplingof the acid chloride 17 with the lithium alkoxide
derivative of 10 at À1008C. The electron transfer reaction
also did not occur when a milder acceptor was employed,
namely the acid chloride 20 for which the pyridine-catalyzed
iodide and copper wire, respec-
tively, and a single crystal of
NO2 NO2
25 ¥ MeCN was grown for X-ray
analysis.
M+
NO2
O2N
NC
CN
IR Spectra: The high sensitivity
of the nitrile stretchingfre-
quency to the charge accumu-
reaction with TTFCH2OH gave D
yield (Scheme 4).
s A diad 21 in 86%
24: M = Li
25: M = Cu
Me
C5H11
C5H11
Me
C5H11
C5H11
S
S
S
S
S
S
S
S
O
O
O
Cl
i
O
O
NO2
NO2
NO2
ii
O2N
NO2
O2N
NO2
O2N
NO2
O
O
NC
CN
17
18
19
S
S
S
COCl
O
S
O
O2N
NO2
iii
O2N
NO2
O
O
20
21
Scheme 4. i) 10 ‡ BuLi, THF, À1008C ! 208C, 1 h, then ‡ 17, À1008C !À 158C, 3 h, then À158C, 12 h; ii) CH2(CN)2/DMF, 208C, 8 h; iii) TTFCH2OH ‡
pyridine/MeCN, 208C, 12 h.
4658
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4658 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 20

Tetrathiafulvalene-Polynitrofluorene Diads
4656 4669
lated on the molecule can be utilized to monitor charge-
transfer interactions involvingcyano-substituted acceptors.
than that of SO2CH2
(
(
EÀZDd ˆ 0.036 ppm) and CH2CON
EÀZDd ˆ 0.040 ppm) protons (which are much closer to the
For example, for TCNQ nÄCꢁ ˆ 2225 and 2180 cmÀ1 for the
isomerized bond), but no observable difference in the shift for
the isomers (EÀZDd <0.005 ppm) was found for 6-H and
8-H protons. This is very unlikely to be a ™through-bond∫
transmitted effect, and we explain it by a contribution of a
head-to-tail folded, p p intramolecularly complexed con-
formation of these diads where a ™through-space∫ interaction
can take place. The remarkable difference in the behavior of
the 1,3-H and 6,8-H protons could be a result of the ICT
complex topology where the p p interaction occurs mostly
between the TTF unit and the sulfonyl substituted benzene
ringof the fluorene nuclei. A similar trend was observed for a
stronger acceptor 19: EÀZDd ˆ 0.171 ppm for 1-H and ˆ
0.01 ppm for 8-H protons (the shifts of 3-H and 6-H protons
could not be determined due to PMB effect, Figure S3 in the
SupportingInformation).
N
neutral and anion radical species, respectively.[15] The nÄCꢁ of
N
the diads 14, 16 and 19 (ca. 2203 cmÀ1 in KBr pellets[16]) is
substantially lower than that of similar fluorene acceptors
without a TTF moiety, e.g. 6 and 22 (2235 cmÀ1). We attribute
this to significant charge transfer in the solid state of 14, 16
and 19. The value of nÄCꢁN for the anion radical salt 24 is further
lowered to 2185 cmÀ1[17] and, therefore a degree of CT (dCT
)
ꢀ0.65 electrons can be calculated for 14, 16 and 19.[18]
A
similar value of dCT (0.6 0.7 electrons) could be also pre-
dicted[18] from the difference in oxidation and reduction
potentials of the donor and acceptor moieties (see the
Electrochemistry Section). Only small variations (within
À1
ˆ
5 cm ) in the ketone C O stretchingfrequency were found
in fluorenones 3, 13, 15 and 18 in accord with the significantly
reduced charge transfer in these diads.
EPR Spectra: The high donor and acceptor ability of the TTF
and fluorene moieties, respectively, in 14 results in facile
electron transfer in this compound, which is manifested in a
strong EPR signal in the solid state and a less intense signal in
solution (Figure 1). Dichloromethane and acetone fluid
1
1H NMR spectra: H NMR spectra of compounds 14, 16 and
19 in [D6]acetone solution feature broadened signals of the
protons adjacent to both the TTF and fluorene fragments
which indicates a significant spin concentration (see the EPR
section) on the D and A moieties (paramagnetic broadening,
PMB). The extent of this broadeningis inversely proportional
to the distance of the resonant group to the radical center (i.e.,
fluorene or TTF) and it was not observed in diads 13, 15 and
18 which possess a weaker acceptor moiety. The broader
signals of 3-H and 6-H compared with 1-H and 8-H[19] indicate
a higher spin concentration in the former positions of the
fluorene nuclei.[7] A weaker PMB in acetone solution was
previously reported for other strongfluorene acceptors (as a
result of interaction with basic impurities)[7] but it is not
observed in this solvent for TTF molecules alone. In the case
of fluorene acceptors without a TTF substituent the PMB
could be completely suppressed by addition of traces of
CF3COOH. For the D A diads addition of CF3COOH results
in only partial restoration of the resolution of the protons
adjacent to fluorene (and further enhances the PMB of
protons adjacent to TTF[20]). Pure fluorene 6 (representingthe
A part of diads 14 and 19) gave a clear sharp 1H NMR
spectrum, but on mixture with the TTF derivative 11
(representingthe D part) in [D 6]acetone solution in 4 Â
10À2 m concentration, a very similar PMB is observed (see
Supporting Information). Based on these data we suggest that
PMB for 14, 16 and 19 is due to electron transfer from the TTF
moiety onto the fluorene nucleus.
Figure 1. X-band EPR spectra of compound 14 in acetone solution at
293 K (a) and frozen CH2Cl2 solution at 110 K (b).
solutions of 14 reveal a broad (2.6 G in CH2Cl2 at 2988C)
single line, centered at giso ˆ 2.007 (Figure 1a).[21] Frozen
CH2Cl2 solutions and powdered samples give rise to a rhombic
spectrum with g values: g1 ˆ 2.014, g2 ˆ 2.006 and g3 ˆ 2.002
(Figure 1b). The anisotropic g values average well to the
isotropic value giso ˆ 2.007, and are almost the same as those
reported for substituted TTF radical cations.[22] Therefore, we
assign these EPR signals to the radical cation of the TTF
moiety. However, there is no indication of a second radical
species (correspondingto the fluorene radical anion), even at
Q-band frequency, although the PMB effect in the NMR
spectra suggests significant spin concentration is present on
the fluorene moiety. It is possible that this second signal is
quenched by formation of head-to-head dimers; a similar
process has been observed for the radical anion of TCNQ.[23]
Spin countingexperiments in 3 Â 10À3 m solution in CH2Cl2
show that only ꢀ2% of the molecules exist in a radical form
at room temperature. Takinginto account this low concen-
tration of the radical species we were careful to ensure that
Another special feature in the NMR spectra resultingfrom
a donor acceptor interaction is seen for the amide-linked
diads 15 and 16. The known slow rotation around a C(O) N
À
amide bond results in two sets of signals in a ꢀ1:2 ratio
correspondingto the E and Z isomers (see Figure S2 in
SupportingInformation). The difference in the chemical shifts
of both isomers (EÀZDd) should normally rapidly decrease
with the distance between the amide bond and a resonant
group. However, in the case of 15 quite high EÀZDd values
(0.117 and 0.058 ppm) were found for the fluorene protons in
the 1- and 3-positions.[19] This value is close to that of both
N-CH2 groups (EÀZDd ˆ 0.151 and 0.101 ppm) and even higher
Chem. Eur. J. 2002, 8, No. 20
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4659 $ 20.00+.50/0
4659

M. R. Bryce et al.
FULL PAPER
the signal does not originate from impurities. One can
speculate that in spite of mildly basic conditions in the
synthesis of 14 and 16, certain acidic impurities could cause
the appearance of the signal of the TTF radical cation,[20] but
this is incompatible with any basic impurity which would need
to be present to form the radical anion of the fluorene nucleus.
Model compounds, 6 and 11, do not give any significant signal,
although they were synthesized under the same conditions
(and might, therefore, be expected to contain the same
impurities, if any). Finally, the intensity of the signal from 14
did not change upon exposure to sunlight for 1 h, thus ruling
out the possibility of a photoinduced electron transfer.
The intensity of the signal from the powdered samples of 14
increases as the temperature decreases (Figure 2) and no
maxima were found down to 10 K. It is noteworthy that the
Figure 3. X-band EPR spectrum (a) and ENDOR spectrum (static field
correspondingto the middle of the EPR multiplet) (b) of 24 in MeCN/
toluene (3:2 v/v) solution at 285 K.
Figure 2. Temperature dependence of the intensity of EPR signal for a
powdered sample of 14.
intermolecular complex TTF:22, which was shown by X-ray
analysis to form alternatingDADA stacks and to have only
partial charge transfer,[7] gives rise to a very similar EPR
signal with the same g values in the solid state.
larger of the 1H couplings (3.25 MHz) to the 3-, 6-positions of
the fluorene ring, in accord with the PMB observed for similar
fluorene compounds (see above). The 0.14 MHz coupling
belongs to the protons at the 1-, 8-ring positions. According to
the McConnell equation,[25] the unpaired electron density in
the C 2pz orbitals contributingto the p-system was calculated
from the aH values to be ꢀ5% of the unpaired electron
density on each of the C3 and C6 positions and ꢀ0.2% on
each of C1 and C8. The crude estimation[26] of the unpaired p-
electron density at the two sets of two 14N nuclei gives ꢀ4 and
0.1%, but we cannot unambiguously assign these.
The observed paramagnetism of 14 prompted us to measure
the electrical conductivity. Earlier, metallic conductivity was
found in a 2:1 CTC of fluorene 22 with bis(ethylenedioxy)-
TTF (srt ˆ 18 ScmÀ1, in compressed pellets), but when a 1:1
complex was formed (with fluorene 1), only weak semi-
conductivity was observed (srt ꢀ10À10 ScmÀ1).[27] For the diads
14 and 16 with 1:1 stoichiometry no observable conductivity
was found from their compressed pellets (srt < 10À8 ScmÀ1,
two-probe method).
From these data we conclude that the origin of the EPR
signal of 14 is the ground (not thermoexcited) state. Most
probably, the intense signal in the solid state results from an
intermolecular self-complex [e.g. (14)2], whereas in solution
this kind of complex would readily dissociate, so only 2% spin
concentration is found.[24] Therefore, in the absence of the
intermolecular complexation, the ground state of compound
14 is neutral.
‡
The Li salt of the fluorene radical anion, 24, gives a well
resolved EPR spectrum in MeCN/toluene solution at room
temperature, centered at g ˆ 2.0030, and the best resolution
was achieved at 285 K (Figure 3a). In frozen solution, and as a
powdered sample, 24 gives rise to an axial spectrum with g1,2
ˆ
2.0030 and g3 ˆ 2.0026. Copper salt 25 gives a broad signal
with g ˆ 2.003; no evidence was found for the presence of a
paramagnetic CuII ions in the sample. The solution ENDOR
1
spectrum of 24 (Figure 3b) reveals two distinct H couplings
of 3.38 and 0.14 MHz (1.21 and 0.05 G, respectively); 14N
couplingwas not observed in the ENDOR spectra. The EPR
spectrum could be simulated well with hyperfine couplings of
(number of equivalent nuclei in parentheses) aH (2) ˆ
3.38 MHz, aH (2) ˆ 0.14 MHz, aN (2) ˆ 3.25 MHz, aN (2) ˆ
0.51 MHz, and a Lorentzian linewidth of 0.1 G. A third set
of two equivalent 14N nuclei is present in 24, however, these
were not resolved due to a very weak coupling. We assign the
Consistent with the X-ray data (see below) which shows no
long-range stacking, the copper salt 25 is an electrical
insulator (srt <10À8 ScmÀ1). In contrast to 25, semiconductive
behavior was shown by the lithium salt 24 (srt ˆ 1 Â
10À3 ScmÀ1, s200K ˆ 3  10À5 ScmÀ1). Such relatively high con-
ductivity is unexpected for a 1:1 salt with complete charge
transfer,[28] and is, probably, an effect of dopingby traces of
neutral fluorene 22.
4660
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4660 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 20

Tetrathiafulvalene-Polynitrofluorene Diads
4656 4669
Table 1. Data from CV measurements.[a]
Compound E1ox0/V E2ox0/V E1red0/V E2red0/V E3red0/V logKdispr
Electrochemistry: The cyclic voltammetry (CV) of the diads
13 16, 18 and 19 in CH2Cl2 is characterized by clear
multiredox amphoteric behavior (Figure 4) consisting of two
DE/ eV[c]
[b]
3a
3b
6
À 0.64
À 0.68
À 0.31
À 1.01
À 1.05
À 0.91
À 1.50
À 1.87
À 6.3
À 6.3
À 1.57[d] À 9.8
7
À 0.15 0.32
0.52
8
0
9
10
11
12
13a
13b
14
15
16
À 0.05 0.41
À 0.23 0.24
À 0.13 0.40
À 0.22 0.30
À 0.07 0.40
À 0.13 0.37
À 0.09 0.35
À 0.17 0.31
À 0.10 0.32
À 0.11 0.40
À 0.10 0.41
À 0.66
À 0.68
À 0.39
À 0.69
À 0.38
À 0.72
À 0.39
À 1.01
À 1.04
À 0.90
À 1.06
À 0.90
À 1.00
À 0.93
À 1.58[e] À 5.9
0.59
0.55
0.30
0.52
0.28
0.66
0.29
À 1.86
À 1.57
À 1.84
À 1.56
À 1.81
À 1.62
À 6.1
À 8.6
À 6.3
À 8.8
À 4.7
À 9.2
18
19
[a] 0.2m Bu4NPF6 in CH2Cl2, vs. Fc/Fc ; [b] log Kdispr ˆ À(E1red À E2red0)/0.059;
‡
0
Figure 4. CV of compounds 15 and 16 measured in CH2Cl2 at 50 mVsÀ1
.
[c] ref. [30]; [d] this compound in MeCN showed four reversible reduction waves:
0
0
0
0
E1red ˆ À0.24 V, E2red ˆ À0.85 V, E3red ˆ À1.48 V, E4red ˆ À1.97 V; [e] this wave
was irreversible due to rapid degradation of the derived radical trianion.
reversible single-electron oxidation waves yielding a radical
cation and dication state of the TTF moiety, and three
reversible single-electron reductions of the fluorene fragment,
which afford a radical anion, dianion and radical trianion
species:
0
0
shift of E1ox and E1red as compared to the model donor/
acceptor compounds 3a and 11 (see also the following
Section). As the ICT p p interaction is not possible in the
shortest-bridge diads 18 and 19, the donor ability of the TTF
fragment in these compounds is not perturbed (within 10 mV)
by the keto ! dicyanomethylene transformation. In accord-
ance with the fact that this charge-transfer interaction should
disappear with reduction of the acceptor fragment to the
radical anion, the presence of the TTF moiety has no
influence on the second and third reduction waves of the
fluorene nuclei.
.
.
‡
D2‡
s
A > D
s
A > D
s
A > D
> D
s
A À
.
s
A
2À > D A 3À
s
The thermodynamic potentials E0 are given in Table 1,
together with data for compounds 3, 6 8, 10 and 12 to show
the mutual influence of the TTF and fluorene fragments. As
expected,[7] the conversion of the keto group into the
dicyanomethylene group (3b ! 6, 13b ! 14, 15 ! 16, 18 !
19) results in a significant positive shift in the reduction
0
It is remarkable that the difference between the oxidation
potentials with larger shifts being observed for E1red (290
and reduction potentials (E1ox À E1red0) for compounds 14, 16
0
0
0
370 mV) and E3red (190 310 mV) than for E2red (70
160 mV). Also, the thermodynamic stability of the derived
radical anions of the dicyanomethylene derivatives (which
and 19 is as small as 280 300 mV, which represents the
smallest solution HOMO LUMO gap (ꢀ0.3 eV[30]) so far
reached for closed-shell organic compounds.
.
relates to the disproportionation equilibrium 2A À > A‡A2À)
is consistently higher than that of the fluorenone precursors
(Table 1). As for the TTF moiety, a very predictable decrease
or increase in its donor ability was found upon the attachment
of the electron withdrawingCHO ( 7 ! 8) or electron releas-
Electronic absorption spectra: Charge transfer interactions in
the diads are also manifested in broad absorption bands in
their visible and near-IR electronic spectra, with the maxima
and intensities strongly dependant on the solvent used. These
bands were not observed in solutions of either the separate
donor (11) or acceptor (4 or 6) components, or their radical
ingCH OH (7 ! 10) groups. Less predictably, an increase in
2
0
the E1ox values followed the acylation of alcohol 10 to yield
11, possibly as a result of a ™through-space∫ effect of the
CH2OC(O)R substituent. This kind of behavior was noted
earlier for TTFCH2OC(O)Ph.[29]
Table 2. ICT bands in electronic absorption spectra of the diads.
For the ™b∫ series possessingthe lonegr
s-bridge, the
Compound
Solvent
lCT-1/ nm (e/mÀ1 cmÀ1
)
lCT-2/ nm (e/mÀ1 cmÀ1
)
attachment of the TTF moiety to the fluorenone (3b ! 13b,
3b ! 15) has no apparent influence on the acceptor ability of
the fluorene unit, whereas the same change for the dicyano-
methylene analogues (6 ! 14, 6 ! 16) results in a 60 70 mV
negative shift of the first reduction potential; this indicates an
interaction between the donor and acceptor moieties in
compounds 14 and 16. There is a concomitant 40 70 mV
positive shift in the E1ox0 value of TTF due to the presence of
the fluorenedicyanomethylene fragment (11 ! 14, 15 ! 16).
In the shorter-bridge series ™a∫ the D/A interaction is also
observable in fluorenone 13b manifested in the 20/60 mV
13a
CH2Cl2
acetone
CH2Cl2
acetone
CH2Cl2
acetone
acetone
CS2
CH2Cl2
acetone
CH2Cl2
CH2Cl2
1045 (550)
920sh (440)
990 (260)
900sh (130)
975sh (240)
920sh (150)
900sh
765 (700)
715 (550)
750 (300)
705 (150)
775 (260)
725 (170)
630sh
13b
15
18
14
1230 (4200)
1230 (4700)
800
800 (2000)
790 (850)
800 (1350)
785 825
16
1260 (3400)
1200 1330
19[33]
Chem. Eur. J. 2002, 8, No. 20
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4661 $ 20.00+.50/0
4661

M. R. Bryce et al.
FULL PAPER
ions (see the spectroelectrochemical experiments below), but
a very similar spectrum was obtained for an intermolecular
complex TTF:22 (Figure 5). The increase in the acceptor
character on conversion from the fluorenone (13, 15 and 18)
to the dicyanomethylene derivatives (14, 16 and 19) results in
a bathochromic shift and a substantial increase in the intensity
of the CT bands indicatinga much stronger donor acceptor
interaction in the latter series, in accordance with the CV
results.
which can be modulated by variations in the diad concen-
tration and the flexibility of the s-bridge.
The apparent discrepancy between the electrochemical
HOMO LUMO gap and hnÄ(ICT) (ca. 1 eV) arises from the
fact that ICT occurs solely in a CT complex, whereas CV data
characterise uncomplexed or equilibrium states; the HO-
MO LUMO orbital interactions in the former should
increase the gap proportionally to the degree of interaction.
The concentration dependence of the intensity of the CT
bands confirmed their intramolecular nature. A linear de-
pendence (r >0.999) was established for compounds 13 16 in
acetone and CH2Cl2 over a wide range of concentrations
Spectroelectrochemistry: Compounds for which color and
transparency in the visible/near-IR regions can be changed by
applyingvarious potentials (electrochromic materials) are of
great current interest.[34] Some of them have found commer-
cial applications, for example in information displays and self-
[35]
darkeningrear-view mirrors for cars.
For 14 and 16 the
relatively high intensity of the ICT band at lmax 1200 nm
tailingto beyond 2000 nm, which was expected to vanish with
oxidation/reduction of the D/A fragments, led us to study
their electrochromism. Applyinga potential stepwise up to
‡0.6 V (vs Pt wire quasireference electrode), to generate the
radical cation, resulted in the complete disappearance of the
near-IR ICT bands; instead, two bands characteristic of the
TTF radical cation (lmax 460 and 645 nm) arose (Figure 6a)
and the solution changed its color from brown to green.[36] At
more positive potentials (0.95 V) the longwavelength bands
(460 and 645 nm) disappeared and the solution turned yellow
indicatingthe formation of the dication species ( lmax 428 nm,
Figure 5. Electronic spectra of compounds 13b, 14 (in CH2Cl2) and CTC
22:TTF (in PhCN).
Figure 6b). Analogously, switching to À0.6 V gave rise to the
[37]
radical anion and the correspondingspectral change
(new
(10À3 10À5 m), but little deviation was seen in the high
concentration (ꢂ10À3 m) region, especially in a less polar
solvent (CS2).[31] This suggests that, even though the intra-
molecular charge transfer process dominates in these mole-
cules, intermolecular complexation giving rise to a similar CT
absorption can also take place at high concentrations. We
bands at lmax 315, 515 and 780 nm and a low intensity broad
band at l 900 1900 nm) made the solution violet (Figure 6c).
The formation of the dianion species while scanningdown to
À1.5 V was monitored by loss of the characteristic vibronic
band at 515 nm, an increase in the intensity of the near-IR
band and the appearance of two new bands at lmax 360
(shoulder) and 440 nm, although the radical trianion species
can contribute to the spectrum at this potential (Figure 6d).
The two oxidation and the first two reduction processes
were completely reversible for compound 16, that is the initial
spectra returned after re-settingthe potential to ‡0.2 V and
the system can be cycled between these five redox states for at
least a few hours. The radical trianion state and also the
dication and dianion states for 14 were partly irreversible
(presumably, due to the lower stability of the linkingester
compared with the amide bond): the prolonged exposure to
redox potentials generating those states lead to partial
decomposition of the compounds manifested in the reduced
intensity of the ICT band on a reverse scan. The intensities of
the bands belonging to the ionic states did not change,
however, which indicates that the linkingbonds (ester or
amide) and not the donor/acceptor moieties were the sites of
decomposition. We believe that compound 16 is a very
promisingelectrochromic material by virtue of havingfive
suggest that these low energy bands arise from a p
p
through-space charge transfer process involving an intra-
molecularly ™head-to-tail∫ complexed state of the molecules.
Geometry optimization usingsemiempirical PM3 methods for
14 shows that a folded ™head-to-tail∫ conformation where the
ICT interaction can take place is not only geometrically
allowed but also is almost equal in energy to the linear
conformation (DH ˆ 23.0 and 22.4 kcalmolÀ1, respectively[32]).
Interestingly, the ICT bands of fluorenone 13a with the
shorter s-bridge are more than twice as intense as those of
13b, which suggests a more efficient CT interaction in the
former, in agreement with the CV results. The behavior of the
shortest s-bridge diads 18 and 19 (the geometry of which
preclude intramolecular complexation) further corroborates
the p p ™through-space∫ origin of the CT bands: the change
in solution absorbance as a function of concentration (order
>1)[33] and almost no absorption at concentrations below
10À4 m indicates that only the intermolecular CT complex is
responsible for the long-wavelength absorption in these diads.
It appears, therefore, that beingseparated by a s-bridge the
donor and acceptor moieties in these TTF fluorene diads
behave essentially as independent molecules giving rise to
very similar manifestations of inter- and intramolecular
interactions. In many cases these are concurrent processes
.
.
redox states (2 À , À , 0, ‡, 2‡) each with distinctive visible/
near-IR absorption spectra.
X-Ray analysis: TTF fluorene-9-one derivative 18 was the
only diad molecule to afford crystals suitable for X-ray
analysis. The fluorenone moiety in 18 adopts a slightly twisted
4662
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4662 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 20

Tetrathiafulvalene-Polynitrofluorene Diads
4656 4669
.
.
‡
Figure 6. Spectroelectrochemical data for 16: the formation of 16 (a), 162‡ (b), 16 À (c), 162À (d).
conformation, due to the repulsion between the carboxy and
nitro groups in positions 4 and 5, respectively, typical for 4,5-
disubstituted fluorene derivatives (Figure 7). The TTF moiety
is folded alongthe S(1) ¥¥¥ S(2) and S(3) ¥¥¥ S(4) vectors by 2.48
and 10.88 and twisted by 2.68 around the central C(15) ˆ C(18)
bond. As suggested from the electronic spectra in solution,
there are no intramolecular contacts between donor and
acceptor moieties: the TTF fluorenone part of the molecule
is roughly planar. These parts of two molecules contact face-
to-face: in the resultingdimer the donor (TTF) unit of one
molecule overlaps with the acceptor (fluorenone) unit of
another giving rise to a CT band, responsible for the black
color of the crystals. The dimers pack in a herringbone (edge-
to-face) manner, without any continuous stacks. The packing
leaves vast cavities, occupied by n-pentyl chains, which are
disordered between different orientations, partially super-
imposed with similar chains of
adjacent molecules and with
acetone molecules of crystalli-
zation (in a non-stoichiometric
occupancy). In the TTF moiety,
À
all the C S bonds are essential-
ly equal (average 1.760(4) ä)
ˆ
and so are all the C C bonds
(average 1.347(5) ä); their
lengths are characteristic for
neutral TTF, indicatingvery
little (or no) charge transfer in
this diad.
The asymmetric unit of 25 ¥
2MeCN contains two anion
Figure 7. Dimer of compound 18 showingan overlap of TTFand fluorene moieties in the crystal (minor positions
of the disordered n-pentyl chains are not shown).
Chem. Eur. J. 2002, 8, No. 20
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4663 $ 20.00+.50/0
4663

M. R. Bryce et al.
FULL PAPER
Table 3. Average bond lengths [ä].
radicals of 22 (i and ii), each of them bridging two copper
atoms through both cyano groups. Anion radicals of type i
link Cu(1) and its equivalents, related through a 21 axis, into
an infinite chain (Figure 8); anion radicals of type ii link Cu(2)
Bonds[a]
22[b]
22 ¥ PhCl[c]
23a
25 ¥ 2MeCN
À
C(9) C(14)
1.354(15)
1.470(9)
1.411(12)
1.478(6)
1.436(9)
1.357(2)
1.480(2)
1.419(2)
1.483(2)
1.444(2)
1.405(5)
1.447(5)
1.435(5)
1.454(4)
1.457(5)
1.411(5)
1.426(5)
1.145(5)
1.413(2)
1.450(3)
1.445(3)
1.449(3)
1.423(3)
À
C(9) C(10)
À
C(10) C(11)
À
C(11) C(12)
À
C(14) CN
À
C(14) C(16)
À
C(16) CN
C N
ꢁ
1.140(10)
1.147(2)
1.153(3)
[a] Averaged with all chemically equivalent bonds; [b] at room temper-
ature;[38]; [c] at 150 K.[39]
ˆ
À
C(9) C(14) bond and c) strengthening of the adjacent C CN
bonds in 25, similar to that observed in the TCNQ anion
.
radical.[40] The fluorene nucleus in 22 À is more planar than in
neutral 22 (the deviation of thirteen fluorene carbon atoms
from their mean plane averages 0.078 ä in moiety i and
0.055 ä in ii, versus 0.115 ä in 22 ¥ PhCl), but the twist around
ˆ
the C(9) C(14) bond (3.28 in i, 8.08 in ii) is slightly higher than
Figure 8. Chains in the structure of 25 ¥ 2MeCN. Primed atoms are
in 22 or 22 ¥ PhCl (ca. 28). The anion radical i is disordered:
two conformers with opposite tilts of the nitro groups occupy
the same site with a ca. 9:1 ratio (Figure S11). The coordina-
tion of the cyano groups is nearly linear, the Cu-N-C angles
are wider in the chain than in the dimer [average 172.9(2) and
165.3(2)8]. In both cases, the anion radical and the two
coordinated copper atoms are approximately coplanar. Thus,
in the dimer the Cu2(22)2 system is planar, but in the chain
each two adjacent anion radicals are nearly perpendicular to
each other. It is instructive to compare 25 ¥ 2MeCN with two
recently studied polymorphs of [TCNQ]Cu salt,[41] where the
distorted tetrahedral coordination of copper(i) comprises four
cyano groups of TCNQ with no additional ligands, while each
TCNQ bridges four Cu atoms, giving rise to a three-dimen-
sional framework. In the tetragonal polymorph (a good
semiconductor, srt ˆ 0.25 ScmÀ1, band gap 0.137 eV) TCNQ
anion radicals of both frameworks form infinite stacks with
interplanar separation of 3.24 ä. In the monoclinic form
(poor semiconductor, 1.3 Â 10À5 ScmÀ1, band gap 0.332 eV)
these moieties pack in a brickwork mode–parallel but poorly
overlapping. The structure of 25 ¥ 2MeCN contains face-to-
face pairs of anion-radicals 22 (one of type i and another of
type ii, see above) contactingeach other in an edge-to-face
(herringbone) fashion, but no continuous stacks exist, which
explains the absence of conductivity.
À
À
generated by a 21 axis. Bond lengths [ä]: Cu(1) N(1) 2.003(2), Cu(1) N(3)
À
À
1.991(2), Cu(1) N(6) and Cu(1) N(8') 1.990(2).
and its inversion equivalent into a closed dimer (Figure 9).
The coordination of each copper atom in 25 is completed by
two linear acetonitrile ligands forming a distorted tetrahedron
(Cu-N-Me angles 170.2(2) to 176.8(2)8). The shortest Cu ¥¥¥ Cu
distances are 7.369(1) ä in the chain and 6.967(1) ä in the
dimer.
The asymmetric unit of K[23] ¥ H2O ¥ 1³2Me2CO (23a) com-
prises two potassium cations, one terminal and one m2-aqua
ligand, one m2-acetone ligand and two anions 23, both m2-
bridging in the same manner, via two cyano groups (Fig-
ure 10). The primary structural unit is a dimer, in which K(1)
and K(2) atoms are bridged by two anion radicals, one aqua
ligand [O(9)] and the acetone oxygen O(19), with K(1)
coordinatingalso one terminal aqua liagnd [O(10)]. The
environment of K(2) is completed to form a distorted
octahedron by two nitro oxygen atoms, O(7) and O(11),
belonging to different dimers but strongly coordinated. The
coordination of K(1) can be described as a tetragonal pyramid
with O(9) in the apical position, completed to a distorted
Figure 9. Dimers in the structure of 25 ¥ 2MeCN. Primed atoms are
À
generated by an inversion centre. Bond lengths [ä]: Cu(2) N(11)
À
À
À
2.002(2), Cu(2) N(13) 1.993(2), Cu(2) N(16) 1.987(2), Cu(2) N(18')
1.994(2).
The bond lengths in both anion radicals are essentially
equal; a comparison with the neutral molecule in pure 22[38]
and in its PhCl solvate[39] (Table 3) shows a) increased p-
conjugation in the five-membered ring; b) weakening of the
4664
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4664 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 20

Tetrathiafulvalene-Polynitrofluorene Diads
4656 4669
organic compounds. Significant charge-transfer (ca. 0.6 elec-
trons in the solid state) in compound 14, 16 and 19 is
ꢁ
manifested in a loweringof the C N stretchingin the IR
spectra, a strongEPR signal (in the solid state) and intense
ICT bands in the near-IR region of their electronic spectra (in
solution). Although the ground state of these diads in dilute
solution is essentially neutral, intermolecular self-complex-
ation in the solid state (and in concentrated solutions) gives
rise to a strong ground-state EPR signal. Compounds 14 and
16 show distinctive electrochromism; the remarkable stability
.
.
of five differently colored redox states of 16 (0, ‡, 2‡, À ,
and 2 À ) makes it a promisingelectrochromic material for the
near-IR spectral region. As shown by X-ray (for 18) and
spectroscopic analyses, in the shortest-bridge diads (18 and
19) no ™through space∫ intramolecular donor acceptor
interaction is possible, which is an advantage for molecular
rectification applications.[4]
Figure 10. Crystal structure of K[23] ¥ H2O ¥ 1³2Me2CO (23a). Bond lengths
Experimental Section
À
À
À
[ä]: K(1) N(8) 2.398(4), K(1) N(16) 2.409(4), K(1) O(9) 2.446(3),
À
À
À
K(1) O(10) 2.262(3), K(1) O(19) 2.405(3), K(1) O(1''') 2.728(3),
General methods: EPR spectra were recorded on Bruker ESP 300E
Q-band or EMX X-band spectrometers. Solid state variable temperature
(300 10 K) studies on 14 were performed at Q-band under non-saturating
conditions determined at 10 K (0.1 mW microwave power; 100 kHz and
5 G modulation frequency and amplitude, respectively). Spin counting
experiments on 14 in CH2Cl2 were performed at X-band and room
temperature by calibration against a range of concentrations of standard
dpph solutions in benzene measured under identical, non-saturating
conditions. The experimental protocol was tested for accuracy against
solutions of known concentration of other radical species. ENDOR spectra
were measured usinga Bruker ER 200 ENB ENDOR cavity with a field
modulation frequency of 12.5 kHz. The spectrometer was fitted with a
Bruker VT 2000 variable temperature system; an ER033M field frequency
lock, which was used for multiple EPR acquisitions and ENDOR experi-
ments. Accurate field measurements were made usinga single sweep with a
Bruker 035 NMR Gaussmeter (corrected usinga sample of the perylene
radical cation in conc. H2SO4, g ˆ 2.002569 Æ 0.000006). ENDOR spectra
were obtained with the above system fitted with a Bruker ESP 360 DICE
ENDOR system usingRF modulation (again with frequency 12.5 kHz) and
an ENI A-300 RF power amplifier operatingat an attenuation of 8 dB (ca.
200 400 W). Concentrations of ꢀ 10À3 m were used for all solution EPR
and ENDOR measurements.
À
À
À
K(2) N(6) 2.497(4), K(2) -N(18) 2.481(4), K(2) O(9) 2.391(3),
K(2) O(19) 2.335(3), K(2) O(7') 2.429(3), K(2) O(11'') 2.423(3). The
disorder of the nitro groups at C(24) and C(25) is not shown.
À
À
À
octahedron by a much weaker interaction with a nitro oxygen
atom O(1) of another dimer.
One of the fluorene anions displays the same disorder of the
nitro groups as observed in 25 ¥ 2MeCN, also in a 9:1 ratio.
Puckeringof the fluorene moieties in 23a is similar in
magnitude and kind to that in 25 ¥ 2MeCN, the deviation of
the carbon atoms from the mean plane averaging 0.07 ä.
However, steric demands of the additional cyano group cause
ˆ
a substantial twist around the C(9) C(14) bond (24 and 258)
À
and the C(14) C(16) bond (20 and 158). In spite of the twist,
there is p-delocalization through the C(9)-C(14)-C(16)(CN)2
moiety, which does not involve the C(15)N(6) cyano group.
Similar delocalization was observed in donor-tricyanoethy-
lene systems, for example N-substituted 1-amino-1,2,2-tricya-
noethylene,[42] or 1-(N-pyridino)benzoylmethylene-1,2,2-tri-
cyanoethylene.[43] In 23a, as in 25 ¥ 2MeCN, the five-mem-
bered fluorene ringacquires almost aromatic character. Thus,
in both complexes, negative charge is extensively delocalized
between the fluorene nucleus and the cyano-containing
substituent in the 9-position.
Cyclic voltammetry experiments were performed at ambient temperature
with a BAS CV50 electrochemical analyzer, in a three-electrode cell (Ag/
AgNO3 in MeCN reference) using1.6 mm diameter platinum disk as a
workingelectrode. 0.2 m Bu4NPF6 in CH2Cl2 was used as the electrolyte. All
the potentials (except in the spectroelectrochemical section) are quoted vs.
‡
the ferrocene/ferrocenium (Fc/Fc ) couple, which was used as the internal
standard except when it overlapped with the oxidation peaks of the sample.
The Fc/Fc couple showed 0.21 V (vs Ag/AgNO3) and 0.50 V (vs Ag/
‡
AgCl).
Spectroelectrochemical data were recorded for compounds 3b, 6, 11, 14
and 16 (ca. 10À4 m) in MeCN and CH2Cl2 with Bu4NPF6 (0.1m) as supporting
electrolyte on a Varian Cary5 spectrophotometer between 250 2300 nm at
ambient temperature. Spectra were corrected for background absorption
arisingfrom the cell, the electrolyte and the workingelectrode. The
OTTLE cell used a Pt gauze working electrode, Pt wire counter and pseudo
reference electrodes. The solutions were analyzed in situ: the working
electrode was held at a potential at which no electrochemical work was
beingdone in the cell and the spectrum of the neutral compound was
recorded, which was identical to the spectrum recorded for open-circuit
conditions. The potential was then increased in 50 200 mV increments and
held until equilibrium had been obtained, as evidenced by a sharp drop in
the cell current. The cell was based upon that described elsewhere,[44] and
was driven by a home-built potentiostat.
Conclusion
We have synthesized TTF
s fluorene compounds possess-
ingboth strong p-electron donor and acceptor moieties which
provide rare examples of non-photoinduced electron transfer
in donor acceptor diads.[3d] Their redox behavior is fully
reversible and comprises two single-electron oxidation and
three single-electron reduction waves. Compounds 14, 16 and
19 possess a HOMO LUMO gap (ꢀ0.3 eV in solution)
which is the lowest reported for closed-shell monomeric
Chem. Eur. J. 2002, 8, No. 20
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4665 $ 20.00+.50/0
4665

M. R. Bryce et al.
FULL PAPER
Table 4. Crystal data and experimental details.
(8 mL) was added and the reaction mixture was refluxed for 6 h. Then it
was evaporated in vacuo, the residue was triturated with chloroform (3 mL)
and the precipitate was filtered off and dried in vacuo to give acid 4a
(48 mg, 68%) as a solvate 4a ¥ 1³2CF3CO2H. M.p. >1508C (decomp);
1H NMR (300 MHz, [D6]acetone): d ˆ 9.05 (d, J ˆ 2 Hz, 1H), 8.86 (d, J ˆ
2 Hz, 1H), 8.80 (d, J ˆ 2 Hz, 1H), 8.67 (d, J ˆ 2 Hz, 1H), 4.81 (s, 2H); MS
Compound
18[a]
23a
25 ¥ 2MeCN
formula
Fw
T [K]
C32H31N3O9S4 ¥ 1³4C3H6O C39H18K2N14O19 C40H20CuN16O16
744.36
120
1064.87
120
1107.80
110
‡
‡
(CI): m/z (%): 411 (30) [M‡NH4 À CO2] , 397 (10) [M‡NH4 À CH2CO2] ,
381 (100); elemental analysis calcd (%) for C15H4N3O11S ¥ 1³2CF3CO2H: C
37.66, H 1.48, N 8.23; found: C 37.31, H 1.57, N 8.46.
symmetry
space group
a [ä]
b [ä]
c [ä]
a [8]
b [8]
g [8]
V [ä3]
Z
monoclinic
I2/a (no. 15)
15.719(5)
12.586(4)
37.231(13)
90
95.49(1)
90
7332(4)
8
triclinic
P1 (no. 2)
monoclinic
P21/c (no. 14)
14.2240(7)
10.2424(6)
29.7103(15)
90
96.270(3)
90
4302.5(4)
4
39493
8895
0.048
7167
0.038
0.094
≈
8.714(3)
15.364(4)
17.161(5)
78.57(1)
76.74(1)
74.80(1)
2134.6(11)
2
5-Methyl-4',5'-dipentyltetrathiafulvalene-4-carbaldehyde (8): LDA (3 mL
of a 1.6m solution in THF/heptane, 4.8 mmol) was added at À788C to a
solution of TTF derivative 7[9] (1.44 g, 4.0 mmol) in anhydrous diethyl ether
(50 mL), the reaction solution was stirred for 2 h at À788C followed by
addition of N-methylformanilide (0.55 mL, 4.5 mmol). The reaction
mixture was allowed to reach 208C overnight, then quenched with ice-
water and neutralized with AcOH (ca. 0.9 mL). The organic layer was
separated, washed with water and brine, dried over MgSO4 and, after
evaporation, was purified by chromatography on silica gel, eluting with
ethyl acetate/petroleum ether (1:3 v/v). The red-violet fraction was
evaporated and dried in vacuo to give aldehyde 8 (1.03 g, 66%) as a dark
red solid. M.p. 54 578C; 1H NMR (300 MHz, [D6]acetone): d ˆ 9.77 (s,
1H), 2.54 (s, 3H), 2.44 (t, J ˆ 7.5 Hz, 4H), 1.58 1.45 (m, 4H), 1.40 1.26 (m,
8H), 0.89 (t, J ˆ 6 Hz, 6H); 13C NMR (75 MHz; [D6]acetone): d ˆ 180.4,
refls collected
unique refls
43576
9722
26957
11157
Rint
.
0.050
0.035
8075
0.084
0.299
refls F2 > 2s(F2) 6646
R[F2 > 2s(F2)] 0.070
wR(F2), all data 0.238
[a] Complex disorder of both n-pentyl chains. Atoms C(24) to C(27):
occupancies 75% in positions A, 25% in B. Position A is superimposed
with an acetone molecule (occupancy 25%), in which C and O atoms are
statistically mixed in positions O/C(1S) and O/C(3S). Atoms C(29) to C(32)
in positions A have occupancies of 50%, C(29B) and C(30B) have
153.9, 134.3, 130.1, 129.7, 113.1, 103.7, 31.9, 30.20, 30.18, 29.2 (2C), 23.1
À1
ˆ
(2C), 14.27 (2C), 14.19; IR (nujol): nÄ ˆ 1664 (C O), 1461, 1376, 722 cm
;
UV/Vis (CH2Cl2): lmax (e) ˆ 296 (12200), 495 nm (2000mÀ1 cmÀ1); MS (EI):
‡
m/z (%): 386 (100) [M] ; elemental analysis calcd (%) for C18H26OS4: C
55.92, H 6.78; found: C 55.78, H 6.79.
occupancies of 50%; C(31) and C(32) in positions
occupancies of 25%. C(26B) lies on axis 2.
B and C have
The by-product 9 (105 mg, 5%) was isolated from the last chromatography
fraction as a dark red tar. 1H NMR (500 MHz; [D6]acetone): d ˆ 9.94 (s,
1H), 7.42 (t, J ˆ 8 Hz, 2H), 7.33 (d, J ˆ 13 Hz, 1H), 7.29 (dd, J ˆ 1, 8 Hz,
2H), 7.16 (t, J ˆ 8 Hz, 1H), 6.54 (d, J ˆ 13 Hz, 1H), 3.42 (s, 3H), 2.42 (t, J ˆ
7.5 Hz, 4H), 1.58 1.45 (m, 4H), 1.40 1.26 (m, 8H), 0.89 (t, J ˆ 6 Hz, 6H);
13C NMR (75 MHz; [D6]acetone): d ˆ 179.1, 155.1, 147.3, 144.2, 130.4, 129.9,
129.5, 126.9, 125.0, 120.5, 114.0, 103.0, 94.1, 37.0, 31.9 (2C), 30.18, 30.16, 29.2
X-ray crystallography: X-ray diffraction experiments (coveringfull sphere
of reciprocal space) were carried out on a SMART 3-circle diffractometer
with a 1 K CCD area detector, usingrgaphite-monochromated Mo
radiation (l ˆ 0.71073 ä) and a Cryostream (Oxford Cryosystems) open-
flow N2 gas cryostat. The structures were solved by direct methods and
refined by full-matrix least squares against F2 of all data, usingSHELXTL
software.[45] Crystal data and experimental details are summarized in
Table 2, full structural information has been deposited with the Cambridge
Crystallographic Data Centre as supplementary publications nos. CCDC-
172395 (18), CCDC-168417 (23a) and CCDC-168416 (25 ¥ 2MeCN).
Ka
ˆ
(2C), 23.0 (2C), 14.3 (2C); IR (KBr): nÄ ˆ 1649 (C O), 1611, 1591, 1461,
1377, 1130, 722 cmÀ1; lmax (e) ˆ 259 (5900), 307 (7000), 336 (6000), 405 nm
‡
(10500), 495 (1800mÀ1 cmÀ1); MS (EI): m/z (%): 503 (100) [M] ; elemental
analysis calcd (%) for C26H33NOS4: C 61.98, H 6.60, N 2.78; found: C 61.75,
H 6.65, N 2.76.
Compounds 2b 5b and 6 were prepared as described.[46]
4-Hydroxymethyl-5-methyl-4',5'-dipentyltetrathiafulvalene (10): Sodium
borohydride (70 mg, 1.84 mmol) was added to a solution of aldehyde 8
(0.56 g, 1.44 mmol) in dry EtOH and the reaction mixture was stirred at
208C for 1 h (the red color of 8 vanished within 10 min). Then ethyl acetate
(20 mL) was added, the organic layer was washed with water and brine,
2-(Methoxycarbonylmethylsulfanyl)-4,5,7-trinitrofluorene-9-one
(2a):
Methyl 2-mercaptoacetate (0.50 mL, 5.6 mmol) followed by NaHCO3
(0.50 g, 5.9 mmol) were added to a solution of fluorenone 1 (0.71 g,
2.0 mmol) in MeCN (20 mL). The red-brown reaction mixture was stirred
at 208C for 2 h and the solvent was removed in vacuo. The residue was
purified by chromatography on silica gel eluting with CH2Cl2 to give pure
sulfide 2a (0.45 g, 54%[47]). M.p. 182 1838C; 1H NMR (300 MHz, CDCl3):
d ˆ 8.93 (d, J ˆ 2 Hz, 1H), 8.76 (d, J ˆ 2 Hz, 1H), 8.05 (d, J ˆ 2 Hz, 1H),
8.00 (d, J ˆ 2 Hz, 1H), 3.89 (s, 2H), 3.82 (s, 3H); 13C NMR (75 MHz,
[D6]acetone): d ˆ 185.5, 168.3, 148.7, 146.8, 145.8, 145.7, 139.3, 137.62,
137.60, 129.1, 127.4, 125.9, 125.5, 122.4, 53.3, 34.3; MS (EI): m/z (%): 419
dried over MgSO4, and filtered through
a 1 cm pad of silica gel.
Evaporation of the filtrate gave alcohol 10 (0.52 g, 92%) as an amorphous
solid. M.p. 59 628C; 1H NMR (200 MHz; [D6]acetone): d ˆ 4.42 4.30 (m,
3H), 2.41 (t, J ˆ 7.5 Hz, 4H), 1.99 (s, 3H), 1.60 1.42 (m, 4H), 1.42 1.24 (m,
8H), 0.90 (t, J ˆ 6 Hz, 6H); 13C NMR (50 MHz; [D6]acetone): d ˆ 131.2,
129.75, 129.68, 125.7, 108.1, 107.7, 58.1, 31.9, 30.2 (2C), 29.2 (2C), 23.1 (2C),
‡
14.3 (2C), 13.6; MS (EI): m/z (%): 388 (100) [M] ; elemental analysis calcd
(%) for C18H28OS4: C 55.92, H 7.26; found: C 55.79, H 7.25.
‡
(100) [M] ; elemental analysis calcd (%) for C16H9N3O9S: C 45.83, H 2.16,
N 10.02; found: C 45.39, H 2.10, N 9.73.
4-Acetoxymethyl-5-methyl-4',5'-dipentyltetrathiafulvalene (11): Pyridine
(0.08 mL, 0.10 mmol), followed by acetyl chloride (0.05 mL, 0.088 mmol)
was added to a solution of alcohol 10 (65 mg, 0.0167 mmol) in dry MeCN
(10 mL) and the reaction mixture was stirred at 208C for 2 h. After
evaporation of the solvent in vacuo the residue was purified by
chromatography on silica gel eluting with ethyl acetate/petroleum ether
(2:5 v/v) affording 11 (64 mg, 89%) as an orange oil. 1H NMR (200 MHz;
[D6]acetone): d ˆ 4.82 (s, 2H), 2.42 (t, J ˆ 7 Hz, 4H), 2.09 (s, 3H), 2.04 (s,
3H), 1.60 1.42 (m, 4H), 1.42 1.25 (m, 8H), 0.90 (t, J ˆ 6 Hz, 6H); IR
2-(Methoxycarbonylmethylsulfonyl)-4,5,7-trinitrofluorene-9-one
(3a):
33% Aqueous H2O2 (1 mL, excess) was added to a solution of sulfide 2a
(0.42 g, 1.0 mmol) in hot AcOH (20 mL) and the reaction mixture was
stirred at 708C for 3 h. Two thirds of the solvent was evaporated in vacuo,
then water (1.5 mL) was added and the solution was cooled to 58C. The
precipitate was filtered off, washed with 80% AcOH, hot water and
methanol giving a pale-yellow powder of 3a (0.40 g, 89%). M.p. 176
1
1778C; H NMR (300 MHz, [D6]acetone): d ˆ 9.06 (d, J ˆ 2 Hz, 1H), 8.87
(nujol): nÄ ˆ 1750 (C O), 1462, 1377, 1219, 722 cmÀ1; MS (EI): m/z (%): 430
ˆ
(d, J ˆ 2 Hz, 1H), 8.79 (d, J ˆ 2 Hz, 1H), 8.66 (d, J ˆ 2 Hz, 1H), 4.85 (s,
2H), 3.72 (s, 3H); 13C NMR (75 MHz, [D6]acetone): d ˆ 185.5, 163.7, 151.2,
147.3, 147.2, 145.0, 139.9, 139.6, 138.4, 138.0, 131.9, 128.9, 126.7, 123.4, 59.9,
‡
(100) [M] ; elemental analysis calcd (%) for C20H30O2S4: C 55.77, H 7.02;
found: C 55.47, H 6.78.
‡
‡
53. 4; MS (EI): m/z (%): 451 (4) [M] , 421 (22) [M À NO] , 405 (18) [M À
4-(N-Benzylaminomethyl)-5-methyl-4',5'-dipentyltetrathiafulvalene (12):
Aldehyde 8 (83 mg, 0.214 mmol), benzylamine (27 mL, 0.248 mmol) and
molecular sieves 4 ä (300 mg) were refluxed in dry cyclohexane (5 mL) for
15 h, until TLC showed a complete conversion of the aldehyde. The
reaction mixture was filtered and evaporated in vacuo. The residue was
‡
NO2] , 329 (100); elemental analysis calcd (%) for C16H9N3O11S: C 42.58,
H 2.01, N 9.31; found: C 42.40, H 1.96, N 9.32.
2-(Hydroxycarbonylmethylsulfonyl)-4,5,7-trinitrofluorene-9-one (4a): Es-
ter 3a (74 mg, 0.164 mmol) was dissolved in TFA (5 mL) at reflux, water
4666
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4666 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 20

Tetrathiafulvalene-Polynitrofluorene Diads
4656 4669
ꢁ
dissolved in dry diethyl ether (5 mL) and LiAlH4 (12 mg, 0.31 mmol) was
added. The reaction mixture was stirred at 208C for 3.5 h (full conversion
within 3 h was confirmed by TLC) and wet ethyl acetate was added slowly
to quench the excess of LiAlH4. After evaporation, the mixture was
purified by chromatography on silica gel, eluting with petroleum ether/
ethyl acetate mixture (5:1 v/v) to give amine 12 (88 mg, 88%) as a pink
solid. M.p. 67 688C; 1H NMR (300 MHz, [D6]acetone): d ˆ 7.40 7.27 (m,
4H), 7.22 (tt, J ˆ 7, 2 Hz, 1H), 3.77 (s, 2H), 3.52 (d, J ˆ 0.6 Hz, 2H), 2.41 (t,
J ˆ 7.5 Hz, 4H), 2.2 (brs, NH2), 1.91 (s, 3H), 1.58 1.45 (m, 4H), 1.40 1.27
(m, 8H), 0.90 (t, J ˆ 6.5 Hz, 6H); 13C NMR (75 MHz; [D6]acetone): d ˆ
141.2, 130.9, 129.7, 129.6, 129.0, 128.9, 127.6, 124.7, 108.5, 107.4, 53.0, 46.5,
31.9, 30.1 (2C), 29.15, 29.14, 23.0 (2C), 14.2 (2C), 13.7; IR (nujol): nÄ ˆ 1461,
adjacent to the TTF moiety were not observed; IR (KBr): nÄ ˆ 2203 (C N),
‡
1742 (C O), 1543, 1340, 1133 cmÀ1; MS (FAB): m/z (%): 869 (27) [M] , 371
ˆ
(87), 243 (100); elemental analysis calcd (%) for C37H35N5O10S5: C 51.08, H
4.05, N 8.05; found: C 50.64, H 4.11, N 7.86.
Compound 15: Pyridine (14 mL, 0.17 mmol) followed by a solution of
amine 12 (80 mg, 0.17 mmol) in dry MeCN (4 mL) were added at À308C to
a suspension of acid chloride 5b (80 mg, 0.17 mmol) in dry MeCN (5 mL)
and the reaction mixture was stirred for 1 h at À308C and left to warm up
to 208C overnight. The thick precipitate was filtered off, washed with
MeCN and MeOH, and then purified by chromatography on silica gel
elutingwith ethyl acetate/petroleum ether (1:2 v/v) to yield compound 15
(75 mg, 55%). M.p. 110 1158C (decomp); 1H NMR (300 MHz, [D6]ace-
tone): d ˆ 9.04 (d, J ˆ 2 Hz, 1H), 8.82 (d, J ˆ 2 Hz, 1H), [E: 8.80 brs, Z: 8.75
brs (1H)], [E: 8.67 brs, Z: 8.56 brs (1H)], 7.37 (t, J ˆ 7 Hz, 1H), 7.33 7.21
(m, 4H), [Z: 4.67 brs, E: 4.52 brs (2H)], [E: 4.29 brs, Z: 4.19 brs (2H)],
3.98 3.86 (m, 2H), 3.11 2.98 (m, 2H), 2.46 2.33 (m, 4H), [E: 1.89 brs, Z:
1.81 brs (3H)], 1.58 1.42 (m, 4H), 1.41 1.25 (m, 8H), 0.96 0.84 (m, 6H);
13C NMR (75 MHz; [D6]acetone): d (E, Z) ˆ 185.2, 185.0, 169.9, 169.4,
150.8, 150.7, 147.4, 147.3, 147.2, 145.3, 145.0, 138.9, 139.5, 138.2, 138.2, 137.8,
137.5, 137.4, 137.3, 131.6, 131.5, 129.7, 129.3, 128.8, 128.4, 128.2, 127.3, 126.5,
126.4, 123.3, 123.2, 52.0, 51.3, 49.2, 31.3, 28.1, 27.6, 23.0, 14.25, 14.23; some of
‡
1376, 722 cmÀ1; MS (EI): m/z (%): 477 (100) [M] , 372 (100) [M À
‡
PhCH2N] ; elemental analysis calcd (%) for C25H35NS4: C 62.85, H 7.38,
N 2.93; found: C 62.44, H 7.36, N 2.69.
Compound 13a: Acid 4a (0.13 g, 0.30 mmol) was stirred in oxalyl chloride
(1 mL) with DMF (1 mL) as a catalyst for 20 h. Then the volatile materials
were removed in vacuo and the residual acid chloride 5a was used
immediately in the next step. A solution of alcohol 10 (117 mg, 0.30 mmol)
and pyridine (70 mL, 0.87 mmol) in dry MeCN (15 mL) was added to acid
chloride 5a and the reaction mixture was stirred at 208C for 6 h. After
removingthe solvent in vacuo, the residue was triturated with methanol
(3 mL), filtered and purified by chromatography on silica gel eluting with
ethyl acetate/petroleum ether (1:3 v/v) to give product 13a (72 mg, 30%).
ˆ
TTF carbons are not observable; IR (KBr): nÄ ˆ 1732 (C O), 1651, 1539,
1462, 1455, 1377, 1131, 732 cmÀ1; MS (ES‡): m/z (%): 910 (100) [M] , 911
‡
‡
(85) [M‡H] ; elemental analysis calcd (%) for C41H42N4O10S5: C 54.05, H
1
M.p. 1608C (decomp); H NMR (300 MHz, [D6]acetone): d ˆ 8.99 (d, J ˆ
4.65, N 6.15; found: C 53.78, H 4.64, N 6.01.
2 Hz, 1H), 8.86 (d, J ˆ 2 Hz, 1H), 8.77 (d, J ˆ 2 Hz, 1H), 8.54 (d, J ˆ 2 Hz,
1H), 4.95 (s, 2H), 4.81 (s, 2H), 2.45 2.24 (m, 4H), 2.03 (s, 3H), 1.57 1.39
(m, 4H), 1.39 1.25 (m, 8H), 0.97 0.84 (m, 6H); IR (nujol): nÄ ˆ 1731
Compound 16: Fluorenone 15 (25 mg, 0.028 mmol) and malononitrile
(25 mg, 0.38 mmol) were stirred in dry DMF (1 mL) at 208C for 6 h then
stored at 08C for 12 h. The solution volume was reduced in vacuo to ca.
0.1 mL, diluted with methanol (2 mL) and the dark brown precipitate was
filtered off, washed with methanol, then dissolved in CH2Cl2 and filtered
through silica gel to give 16 (23 mg, 72%). M.p. 137 1428C (decomp);
1H NMR (300 MHz; [D6]acetone): d ˆ [E: 9.44 d, Z: 9.26 (d, J ˆ 2 Hz,
1H)], 9.11 (brs, 1H), 8.98 (br, 1H), 8.83 (brs, 1H), 7.37 (t, J ˆ 7 Hz, 1H),
7.36 7.21 (m, 4H), [Z: 4.77 brs, E: 4.49 brs (2H)], [E: 4.05 brm, Z: 3.82
brm (2H)], 3.16 3.04 (m, 2H), 1.7 1.2 (brm, 8H), 1.00 0.84 (m, 6H);
CH3 and 5CH2 groups closest to the TTF nucleus are not observable due to
(C O), 1615, 1541, 1343, 1192, 1119, 780 cmÀ1; MS (ES‡): m/z (%): 808
ˆ
‡
‡
(30) [M‡H] , 807 (25) [M] , 564 (100); elemental analysis calcd (%) for
C33H33N3O11S5: C 49.06, H 4.12, N 5.20; found: C 48.91, H 4.09, N 5.17.
Compound 13b: A solution of alcohol 10 (0.18 g, 0.46 mmol) and pyridine
(0.10 mL, 1.2 mmol) in dry MeCN (15 mL) was added to acid chloride 5b
(0.225 g, 0.48 mmol), the reaction mixture was stirred at 208C for 6 h and
the resulting gray-green precipitate was filtered off and thoroughly washed
with acetonitrile, NaHCO3/water, then water and, finally, methanol to give
fluorenone 13b (0.235 g, 62%). M.p. 1458C (decomp). The mother liquor
was evaporated, the residue washed with methanol, hot hexane and
purified by chromatography on silica gel, eluting with diethyl ether to give
an additional portion of 12b (0.03 g, 8%). M.p. 1458C (decomp); 1H NMR
([D6]acetone): d ˆ 9.04 (d, J ˆ 2 Hz, 1H), 8.82 (d, J ˆ 2 Hz, 1H), 8.79 (brs,
1H), 8.63 (brs, 1H), 4.79 (s, 2H), 3.92 (t, J ˆ 7 Hz, 2H), 2.96 (t, J ˆ 7 Hz,
2H), 2.41 (m, 4H), 2.03 (s, 3H), 1.57 1.45 (m, 4H), 1.39 1.28 (m, 8H),
ꢁ
ˆ
ˆ
PMB; IR (KBr) nÄ ˆ 2202 (C N), 1653 (C O), 1647 (C O), 1610, 1540,
1340, 1132 cmÀ1; MS (FAB): m/z (%): 958.2 (86) [M] , 371.2 (100);
‡
elemental analysis calcd (%) for C44H42N6O9S5: C 55.10, H 4.41, N 8.76;
found: C 54.91, H 4.50, N 8.39.
2,5,7-Trinitro-4-chlorocarbonylfluorene-9-one (17) was obtained as descri-
bed.[13] 1H NMR (200 MHz; CDCl3): d ˆ 9.20 (d, J ˆ 2 Hz, 1H), 8.81 (d, J ˆ
2 Hz, 1H), 8.65 (d, J ˆ 2 Hz, 1H), 8.54 (dd, J ˆ 8, 2 Hz, 1H), 8.42 (d, J ˆ
8 Hz, 1H).
ˆ
0.94 0.86 (m, 6H); IR (KBr): nÄ ˆ 1735 (C O), 1617, 1542, 1343, 1192,
‡
1139 cmÀ1; MS (ES‡): m/z (%): 821 (100) [M] ; elemental analysis calcd
(%) for C34H35N3O11S5: C 49.70, H 4.26, N 5.12; found: C 49.67, H 4.28, N
4.90.
Compound 18: BuLi (1.6m; 80 mL, 0.128 mmol) was added at 08C to a
solution of compound 10 (50 mg, 0.128 mmol) in dry THF (2 mL). The
reaction mixture was then cooled to À1008C, a solution of acid chloride 17
(55 mg, 0.142 mmol) in dry THF (1.5 mL) was added dropwise and it was
stirred for 1 h at À1008C, then allowed to warm up to ca. À208C during2 h
and left overnight in a freezer (À158C). The solvent was removed in vacuo
and the residue was taken up in ethyl acetate. The organic layer was
subsequently washed with water, NaHCO3 solution and brine, dried over
MgSO4 and evaporated. Flash chromatography on silica gel eluting with
cyclohexane/ethyl acetate (3:1 v/v) gave a green fraction which was
evaporated, the residue washed with methanol and hexane yielding 18
(70 mg, 75%). M.p. 1408C; 1H NMR (300 MHz, [D6]acetone): d ˆ 9.02 (d,
J ˆ 2 Hz, 1H), 8.84 (d, J ˆ 2 Hz, 1H), 8.80 (d, J ˆ 2 Hz, 1H), 8.71 (d, J ˆ
2 Hz, 1H), 5.13 (s, 2H), 2.40 (m, 4H), 2.19 (s, 3H), 1.50 (m, 4H), 1.32 (m,
8H), 0.89 (m, 6H); 13C NMR (75 MHz; [D6]acetone, 508C): d ˆ 186.0,
165.1, 150.9, 150.8, 147.4, 144.4, 140.4, 140.2, 139.4, 133.8, 132.3, 131.3, 130.0,
126.5, 123.1, 122.7, 122.4, 61.6, 32.05, 32.03, 30.2 (2C), 23.1 (2C), 14.3 (2C),
14.2; [the two central carbons of TTF were not observed (expected as low
intensity peaks at 100 115 ppm), two of CH2 carbons were hidden under
the solvent signal and one signal must be overlapping with another in the
Compound 13b (alternative synthesis): Dicyclohexylcarbodiimide (17 mg,
0.083 mmol) was added to a suspension of acid 4b (27 mg, 0.060 mmol) in
dry CH2Cl2 (2.5 mL), the reaction mixture was stirred at 08C for 40 min.
Alcohol 10 (27 mg, 0.069 mmol) followed by 4-dimethylaminopyridine
(1 mg, 0.01 mmol) were added to this mixture which was stirred at 208C for
15 h. After filtering, the filtrate was purified by chromatography on silica
gel, eluting with CH2Cl2/ethyl acetate (20:1 v/v). The green fraction was
evaporated, the residue was triturated with MeCN (2 mL), filtered off,
subsequently washed with MeCN, methanol and hexane to give 13b
(17 mg, 34%) with spectral characteristics identical to those of the above
sample.
Compound 14: Fluorenone 13b (59 mg, 0.068 mmol) and malononitrile
(59 mg, 0.89 mmol) were stirred in DMF (1 mL) for 6 h at 208C; the
solution volume was reduced in vacuo to ꢀ0.3 mL, diluted with methanol
(3 mL) and the precipitate was filtered off and washed with methanol
yieldinga brown powder (54 mg) which was purified by flash chromatog-
raphy on silica gel eluting with ethyl acetate/petroleum ether (1:1 v/v) to
give 14 (47 mg, 80%). M.p. 1508C (decomp); 1H NMR (300 MHz;
[D6]acetone): d ˆ 9.5 9.0 (brm, 4H), 4.73 (brm, 2H), 4.02 (brm, 2H),
3.07 (t, J ˆ 6 Hz, 2H), 2.53 (brm, 4H), 2.1 1.8 (brm, 3H), 1.57 1.34 (m,
4H), 1.34 1.15 (m, 8H), 0.88 0.70 (m, 6H); 1H NMR (300 MHz;
[D6]acetone ‡ CF3COOH): d ˆ 9.28 (s, 1H), 9.21 (s, 1H), 8.98 (brs, 1H),
8.69 (brs, 1H), 4.02 (t, J ˆ 6 Hz, 2H), 3.08 (t, J ˆ 6 Hz, 2H), 1.79 1.49
(brm, 4H), 1.38 (brm, 8H), 0.99 0.86 (m, 6H); CH2 and CH3 protons
ˆ
aromatic region]; IR (KBr): nÄ ˆ 1731 (C O), 1614, 1593, 1537, 1465, 1342,
1174, 739 cmÀ1; MS (EI): m/z (%): 729 (100); elemental analysis calcd (%)
for C32H31N3O9S4: C 52.66, H 4.28, N 5.76; found: C 52.38, H 4.24, N 5.73. A
single crystal for X-ray analysis was grown by slow cooling of an acetone
solution.
Chem. Eur. J. 2002, 8, No. 20
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4667 $ 20.00+.50/0
4667

M. R. Bryce et al.
FULL PAPER
Compound 19: Fluorenone 18 (20 mg, 0.027 mmol) and malononitrile
(12 mg, 0.18 mmol) were dissolved in DMF (0.5 mL) and stirred at 208C for
8 h. Then the solvent was distilled off in vacuo and the residue was
triturated with methanol (1 mL). The brown precipitate was filtered off and
washed with methanol giving compound 19 (20 mg, 95%). M.p. 1608C;
1H NMR (300 MHz; [D6]acetone): d ˆ 9.9 9.3 (br, 2H, fluorene-H), 5.15
(brs, 2H), 2.40 (brs, 4H), 2.19 (brs, 3H), 1.50 (m, 4H), 1.31 (m, 8H), 0.89
Acknowledgement
We thank EPSRC for funding(D.F.P.), Dr. Igor F. Perepichka (Institute of
Physical Organic and Coal Chemistry, Donetsk, Ukraine) for samples of
compounds 1, 17 and 20, Dr. David Collison (University of Manchester) for
helpful discussions, and Dr. Andres E. Goeta for initial X-ray data
collection for 23a.
(m, 6H); IR (KBr) nÄ ˆ 2204 (C N), 1718 (C O), 1605, 1535, 1340 cmÀ1; MS
ꢁ
ˆ
‡
(FAB): m/z (%): 777 (35) [M] , 371 (100); elemental analysis calcd (%) for
C35H31N5O8S4: C 54.04, H 4.02, N 9.00; found: C 54.24, H 4.37, N 8.55.
2,7-Dinitro-4-chlorocarbonylfluorene-9-one (20) was obtained as descri-
bed.[13] 1H NMR (300 MHz; [D6]acetone): d ˆ 9.11 (d, J ˆ 2 Hz, 1H), 9.04
(d, J ˆ 2 Hz, 1H), 8.84 (d, J ˆ 2 Hz, 1H), 8.83 (d, J ˆ 2 Hz, 1H).
[1] a) J. Roncali, Chem. Rev. 1997, 97, 173 205; b) H. A. M. van Mulle-
kom, J. A. J. M. Vekemans, E. W. Meijer, Chem. Eur. J. 1998, 4, 1235
1243; c) S. Akoudad, J. Roncali, Chem. Commun. 1998, 2081 2082;
d) C. Kitamura, K. Yoshida, Y. Yamashita, Chem. Mater. 1996, 8,
570 578; e) T.-T. Hung, S.-A. Chen, Polymer 1999, 40, 3881 3884;
f) M. Kobayashi, N. Colaneri, M. Boysel, F. Wudl, A. J. Heeger, J.
Chem. Phys. 1985, 82, 5717 5723.
Compound 21: Acid chloride 20 (75 mg, 0.219 mmol) was added to a
solution of TTF-CH2OH (51 mg, 0.218 mmol) in dry MeCN (2 mL)
resultingin the immediate precipitation of a black product. The reaction
mixture was stirred overnight, the precipitate filtered off and thoroughly
washed with boilingMeCN, then with acetone and methanol to igve
compound 21 (101 mg, 86%). M.p. >2208C (decomp); 1H NMR
(200 MHz, [D6]DMSO): d ˆ 8.77 (d, J ˆ 2 Hz, 1H), 8.56 8.48 (m, 3H),
8.38 (d, J ˆ 2 Hz, 1H), 7.07 (s, 1H), 6.71 (s, 2H), 5.31 (s, 2H); IR (KBr): nÄ ˆ
[2] a) M. P. Le Paillard, A. Robert, C. Garrigou-Lagrange, P. Delhaes, P.
¡
Le Magueres, L. Ouahab, L. Toupet, Synth. Met. 1993, 58, 223 232;
b) V. Khodorkovsky, J. Y. Becker in Organic Conductors. Fundamen-
tals and Applications (Ed.: J.-P. Farges), Marcel Dekker, New York,
1994, pp. 75 113; c) Y. Yamashita, M. Tomura, J. Mater. Chem. 1998,
8, 1933 1944.
ˆ
1725 (C O), 1609, 1587, 1523, 1451, 1343, 1267, 1223, 1155, 1087, 798,
‡
736 cmÀ1; MS (EI): m/z (%): 530 (8) [M] , 314 (100); elemental analysis
calcd (%) for C21H10N2O7S4: C 47.54, H 1.90, N 5.28; found: C 47.39, H 1.83,
N 5.29.
[3] a) P. A. Ashton, V. Balzani, J. Becher, A. Credi, M. C. T. Fyfe, G.
Mattersteig, S. Menzer, M. B. Nielsen, F. M. Raymo, J. F. Stoddart, M.
Venturi, D. J. Williams, J. Am. Chem. Soc. 1999, 121, 3951 3957;
b) M. B. Nielsen, S. B. Nielsen, J. Becher, Chem. Commun. 1998, 475
476; c) M. B. Nielsen, J. G. Hansen, J. Becher, Eur. J. Org. Chem. 1999,
2807 2815; d) S. Fuzukumi, K. Okamoto, H. Imahori, Angew. Chem.
2002, 114, 642 644; Angew. Chem. Int. Ed. 2002, 41, 620 622.
[4] a) A. Aviram, M. Ratner, Chem. Phys. Lett. 1974, 29, 277; b) for recent
discussions of this proposal see: R. M. Metzger, J. Mater. Chem. 1999,
9, 2027 2036; R. M. Metzger, J. Mater. Chem. 2000, 10, 55 62.
[5] a) M. R. Bryce, Adv. Mater. 1999, 11, 11 23 and references therein;
Compound 23: Silica gel (supplied by LabPro, 0.40 g) and malononitrile
(53 mg, 0.80 mmol) were added to a solution of compound 1 (108 mg,
0.30 mmol) in DMSO (1 mL) and the resultingdark-green reaction mixture
was stirred at 208C overnight. It was then filtered from silica gel, washed
with DMF and the filtrate, after evaporation in vacuo, was purified by
chromatography on silica gel, eluting initially with neat ethyl acetate to
remove an intermediate 22 and then with ethyl acetate/acetone (v/v 7:1)
mixture. The dark-blue fraction containing 23 was collected and evapo-
rated. The residue was dissolved in acetone (3 mL), diluted with boiling
toluene (5 mL) and left to crystallize overnight in an open flask (the
acetone partly evaporated). The crystalline precipitate was filtered off and
washed with hot toluene affordingcompound 23 (40 mg, 26%) as a
potassium salt. M.p. >3608C; 1H NMR (300 MHz, [D6]acetone) d ˆ 9.30
¬
b) D. M. Guldi, S. Gonzalez, N. MartÌn, J. Org. Chem. 2000, 65, 1978
¬
1983; c) N. MartÌn, L. Sanchez, M. A. Herranz, D. M. Guldi, J. Phys.
Chem. A 2000, 104, 4648 4657; d) M. B. Nielsen, J. G. Hansen, J.
Becher, Eur. J. Org. Chem. 1999, 2807 2815; e) J. G. Hansen, K. S.
Bang, N. Thorup, J. Becher, Eur. J. Org. Chem. 2000, 2135 2144; f) E.
Tsiperman, L. Regev, J. Y. Becker, J. Bernstein, A. Ellern, V.
Khodorkovsky, A. Shames A. L. Shapiro, Chem. Commun. 1999,
1125 1126; g) S. Sheib, M. P. Cava, J. W. Baldwin, R. M. Metzger, J.
Org. Chem. 1998, 63, 1198 1204; h) E. Aqad, A. Ellern, L. Shapiro, V.
Khodorkovsky, Tetrahedron Lett. 2000, 41, 2983 2986; i) M. R. Bryce,
J. Mater. Chem. 2000, 10, 589 598; j) J. L. Segura, N. MartÌn, Angew.
Chem. 2001, 113, 1416 1455; Angew. Chem. Int. Ed. 2001, 40, 1372
1409.
ꢁ
(d, J ˆ 2 Hz, 2H), 8.63 (d, J ˆ 2 Hz, 2H); IR (KBr): nÄ ˆ 2209 (C N), 1625,
1572, 1527, 1494, 1453, 1359, 1314, 1255, 1160, 903, 829, 724 cmÀ1; MS (ES À):
m/z (%): 446 (100) [M À K]À; elemental analysis calcd (%) for
C18H4KN7O8 ¥ H2O: C 42.95, H 1.20, N 19.48; found: C 42.65, H 1.35, N
19.05. A single crystal for X-ray analysis was grown from acetone solution
by slow evaporation.
Salt 24: Anhydrous lithium iodide (4.0 g, 30 mmol) was added to a solution
of compound 22 (200 mg, 0.495 mmol) in dry MeCN (20 mL) and the
resultingdark reaction mixture was left to stand at 0 8C overnight. The
precipitate was filtered in an inert atmosphere, quickly washed with cold
ethyl acetate (2 mL), then with excess CH2Cl2 and, finally, with cold water
(3 mL) to give a black powder of 24 (95 mg, 47%). M.p. >3008C
[6] a) C. A. Panetta, J. Baghdadchi, R. M. Metzger, Mol. Cryst. Liq. Cryst.
1984, 107, 103 113; b) C. A. Panetta, N. E. Heimer, C. L. Hussey,
R. M. Metzger, Synlett 1991, 301 309.
[7] I. F. Perepichka, L. G. Kuz×mina, D. F. Perepichka, M. R. Bryce, L. M.
Goldenberg, A. F. Popov, J. A. K. Howard, J. Org. Chem. 1998, 63,
6484 6493 and references therein.
ꢁ
(exothermic decomp); IR (KBr): nÄ ˆ 2182 (C N), 1590, 1516, 1442, 1398,
1334, 1309, 1248, 1203, 1157, 1083, 981, 827, 779, 729 cmÀ1; MS (ES À ): m/z
(%): 408 (100) [M À Li]À; elemental analysis calcd (%) for C16H4LiN6O8 ¥
2H2O: C 42.59, H 1.79, Li 1.54, N 18.63, I 0.0; found: C 42.55, H 1.33, Li 1.48,
N 18.38, I 0.0.
[8] Preliminary communication: D. F. Perepichka, M. R. Bryce, E. J. L.
McInnes, J. P. Zhao, Org. Lett. 2001, 3, 1431 1434.
[9] D. F. Perepichka, M. R. Bryce, A. S. Batsanov, J. A. K. Howard, A. O.
Cuello, M. Gray, V. M. Rotello, J. Org. Chem. 2001, 66, 4517 4524.
[10] I. F. Perepichka, A. F. Popov, T. V. Orekhova, M. R. Bryce, A. M.
Andrievskii, A. S. Batsanov, J. A. K. Howard, N. I. Sokolov, J. Org.
Chem. 2000, 65, 3053 3063.
[11] J.-M. Fabre, J. GarÌn, S. Uriel, Tetrahedron 1992, 48, 3983 3990.
[12] Even scratches on the glass or a polished surface of a joint could
promote this side reaction, so very smooth glassware or a plastic flask
is recommended to minimize the by-product formation. For the same
reason, it is difficult to use TLC to monitor the reaction (excessive
colorization occurs when the reaction solution is put on a silica gel or
alumina TLC plate).
Salt 25: A copper wire coil (diameter 0.25 mm, 99.999%; 5 cm long) was
dipped in a solution of 22 (22 mg, 0.054 mmol) in dry MeCN (4 mL)
resultingin violet coloration around the wire. After two weeks at 20 8C, the
reaction mixture was cooled to 08C, the black precipitate was scratched
from the wire, filtered off, washed with ethyl acetate, and dried in vacuo
(0.1 mbar, 1008C) affordingsalt 25 (13 mg, 55%). M.p. >3008C (exother-
mic decomp); IR (KBr): nÄ ˆ (cmÀ1) 2199 (C N), 1593, 1526, 1438, 1410,
ꢁ
1334, 1313, 1245, 1211, 1155, 1077, 989, 824, 776 cmÀ1; elemental analysis
calcd (%) for C16H4CuN6O8 ¥ 3³2MeCN: C 42.79, H 1.61, Cu 11.91, N 19.70;
found: C 42.77, H 1.64, Cu 12.08, N 19.82. A single crystal for X-ray analysis
was grown from MeCN solution by slow evaporation.
[13] A detailed investigation of the nucleophilic substitution in 9-dicya-
nomethylenepolynitrofluorenes with amines was described earlier:
I. F. Perepichka, A. F. Popov, T. V. Orekhova, M. R. Bryce, A. N.
Vdovichenko, A. S. Batsanov, L. M. Goldenberg, J. A. K. Howard,
4668
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4668 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 20

Tetrathiafulvalene-Polynitrofluorene Diads
4656 4669
N. I. Sokolov, J. L. Megson, J. Chem. Soc. Perkin Trans. 2 1996, 2453
2470.
[14] Elemental analysis of the silica gel (LabPro, 40/60 for chromatog-
raphy) gave K, 0.64%.
[32] However, the values obtained to estimate the behavior of the
molecule in solution should be used with caution since the solvation
energy was not taken into account.
[33] lmax of these CT bands undergo the red shift as the concentration
increases e.g., for 19 in CH2Cl2: c ˆ 3.34  10À3 m, l ˆ 0.1 cm, D (for
[15] J. S. Chappell, A. N. Bloch, W. A. Bryden, M. Maxfield, T. O. Poehler,
D. O. Cowan, J. Am. Chem. Soc. 1981, 103, 2442 2243.
[16] Unfortunately, the extremely low intensity of the CN peak in solution
precludes a study of the solution IR behavior of this band.
[17] For the copper salt 25 nÄCN was somewhat higher, 2199 cmÀ1, which is
due to overlap with the peak from the solvate molecule of MeCN.
[18] V. Kampar, O. Neilands, Russ. Chem. Rev. 1986, 55, 334 342.
[19] The assignment of the protons has been made by comparison with
previously investigated fluorene derivatives and on the basis of a
COSY experiment (for compound 15).
lmax ˆ 1325 nm) ˆ 0.786
)
e' ˆ 2350mÀ1 cmÀ1; c ˆ 3.34  10À4 m, l ˆ
1 cm, D (for lmax ˆ 1212 nm) ˆ 0.0647 ) e' ˆ 190mÀ1 cmÀ1; (e' was
determined in supposition of the intramolecular absorption).
[34] a) R. J. Mortimer, Chem. Soc. Rev. 1997, 26, 147 156; b) S. H¸nig, M.
Kemmer, H. Wenner, I. F. Perepichka, P. B‰uerle, A. Emge, G.
Gescheit, Chem. Eur. J. 1999, 5, 1969 1973; c) D. R. Rosseinsky, R. J.
Mortimer, Adv. Mater. 2001, 13, 783 793.
[35] M. Mastragostino, in Electrochromic Devices (Ed.: B. Scrosati),
Chapman & Hall, London 1993, Chapter 7, pp. 223 249.
[20] For the formation of radical species from TTF in the presence of acids
see: M. Giffard, P. Alonso, J. CarÌn, A. Gorgues, T. P. Nguyen, P.
Richomme, A. Robert, J. Roncali, S. Uriel, Adv. Mater. 1994, 6, 298
300. For trialkylsubstituted TTFs the PMB was also observed in acidic
solvents (e.g. CDCl3).
[36] Appearance of the same bands was observed by electrochemical
oxidation of TTF derivative 11 (Figure S7).
[37] The assignment of these bands is supported by spectroelectrochemical
experiments on the fluorene derivative
6 (Figure S8) and the
electronic spectra of isolated fluorene ion-radical salt 24.
[38] J. Silverman, N. F. Yannoni, A. P. Krukonis, Acta Crystallogr. Sect. B
1974, 30, 1474 1480.
[21] The same signal was observed for 16.
¬
[22] E. Ribera, C. Rovira, J. Vaciana, J. Tarres, E. Canadell, R. Rousseau,
E. Molins, M. Mas, J-P. Schoeffel, J-P. Pouget, J. Morgado, R. T.
Henriques, M. Almeida, Chem. Eur. J. 1999, 5, 2025 2039.
[39] A. S. Batsanov, I. F. Perepichka, M. R. Bryce, J. A. K. Howard, Acta
Crystallogr. Sect. C 2001, 57, 1299 1302.
[23] R. H. Boyd, W. D. Phillips, J. Phys. Chem. 1965, 43, 2927 2929.
[24] This is also consistent with strongEPR signal from a mixture of model
D and A compounds (6‡7) at high concentration (4  10À2 m). The
intensity of this signal decreased rapidly non-linearly with lowering
the concentration, and no significant signal can be observed at
[40] a) W. Flandrois, D. Chasseau, Acta Crystallogr. Sect. B 1977, 33, 2744
2750; b) T. J. Kistenmacher, T. J. Emge, A. N. Bloch, D. O. Cowan,
Acta Crystallogr. Sect. B 1982, 38, 1193 1199; c) A. S. Batsanov,
M. R. Bryce, A. Chesney, J. A. K. Howard, D. E. John, A. J. Moore,
C. L. Wood, H. Gershtenman, J. Y. Becker, V. Y. Khodorkovsky, A.
Ellern, J. Bernstein, I. F. Perepichka, V. Rotello, M. Gray, A. O.
Cuello, J. Mater. Chem. 2001, 11, 2181 2191.
concentration lower then 10À3 m, indicatingthat
[ 6 ¥ 11] CTC is
responsible for the EPR signal.
[25] H. M. McConnell, J. Chem. Phys. 1956, 24, 764 766.
[41] R. A. Heintz, H, Zhao, X. Ouyang, G. Gandinetti, J. Cowen, K. R.
Dunbar, Inorg. Chem. 1999, 38, 144 156.
[42] J. J. Stezowski, Acta Crystallogr. Sect. B 1977, 33, 2472 2476.
[43] V. N. Nesterov, V. E. Shklover, Yu. T. Struchkov, Yu. A. Sharanin,
A. I. Aitov, A. M. Shestopalov, Acta Crystallogr. Sect. C 1991, 47, 109
112.
[44] C. M. Duff, G. A. Heath, Inorg. Chem. 1991, 30, 2528 2535.
[45] SHELXTL, Version 5.1, Bruker AXS Inc., Madison, Wisconsin, USA,
1998.
[46] D. F. Perepichka, M. R. Bryce, I. F. Perepichka, S. B. Lyubchik, C. A.
Christensen, N. Godbert, A. S. Batsanov, E. Levillain, E. J. L.
McInnes, J. P. Zhao, J. Am. Chem. Soc. in press.
[26] P. H. Rieger, G. K. Fraenkel, J. Chem. Phys. 1963, 39, 609 629.
[27] S. Horiuchi, H. Yamochi, G. Saito, K. Sakaguchi, M. Kusunoki, J. Am.
Chem. Soc. 1996, 118, 8604 8622.
[28] J. B. Torrance, Acc. Chem. Res. 1979, 12, 79 86.
[29] M. R. Bryce, W. Devonport, A. J. Moore, Angew. Chem. 1994, 106,
1862 1864; Angew. Chem. Int. Ed. 1994, 33, 1761 1763.
0
[30] HOMO LUMO gap, DE ˆ e (Ered À Eox0) eV: a) ref. [1a]; b) V. D.
Parker, J. Am. Chem. Soc. 1976, 98, 98 103; c) L. E. Lyons, Aust. J.
Chem. 1980, 33, 1717 1725.
[31] E.g., for 14 in CH2Cl2: c ˆ 2.90  10À3 m, l ˆ 0.1 cm, D ˆ 1.375 ) e ˆ
4800mÀ1 cmÀ1
4920mÀ1 cmÀ1
;
;
c ˆ 2.32  10À4 m, l ˆ 1 cm, D ˆ 1.143
c ˆ 1.66  10À5 m, l ˆ 10 cm, D ˆ 0.823
)
)
e ˆ
e ˆ
[47] The yield could possibly be improved by using5 10 times lower
concentration.
4960mÀ1 cmÀ1; in CS2: c ˆ 5.40  10À3 m, l ˆ 0.1 cm, D (for lmax
ˆ
1260 nm) ˆ 2.80 ) e ˆ 5190mÀ1 cmÀ1; c ˆ 1.325  10À4 m, l ˆ 1 cm, D
(for lmax ˆ 1231 nm) ˆ 0.594
)
e ˆ 4380mÀ1 cmÀ1; c ˆ 1.69  10À5 m,
l ˆ 10 cm, D (for lmax ˆ 1230 nm) ˆ 0.714 ) e ˆ 4230mÀ1 cmÀ1
.
Received: April 9, 2002 [F4009]
Chem. Eur. J. 2002, 8, No. 20
¹ 2002 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4669 $ 20.00+.50/0
4669