Donor-substituted 1,1,4,4-tetracyanobutadienes (TCBDs): New chromophores with efficient intramolecular charge-transfer interactions by atom-economic synthesis

Article abstract of DOI:10.1002/chem.200501113

A wide variety of monomeric and oligomeric, donor-substituted 1,1,4,4-tetracyanobutadienes (TCBDs) have been synthesized by [2+2] cycloaddition between tetracyanoethylene (TNCE) and donor-substituted alkynes, followed by electrocyclic ring opening of the

Full text of DOI:10.1002/chem.200501113

FULL PAPER
DOI: 10.1002/chem.200501113
Donor-Substituted 1,1,4,4-Tetracyanobutadienes (TCBDs): New
Chromophores with Efficient Intramolecular Charge-Transfer Interactions by
Atom-Economic Synthesis
Tsuyoshi Michinobu,[a] Corinne Boudon,[b] Jean-Paul Gisselbrecht,[b] Paul Seiler,[a]
Brian Frank,[a] Nicolle N. P. Moonen,[a] Maurice Gross,[b] and FranÅois Diederich*[a]
Abstract: A wide variety of monomeric
and oligomeric, donor-substituted
crystal structures demonstrate a high
quinoid character in strong donor sub-
stituents, such as N,N-dimethylanilino
(DMA) rings.The maxima of the CT
bands shift bathochromically upon re-
duction of the amount of conjugative
coupling between strong donor and ac-
ceptor moieties.Each TCBD moiety
undergoes two reversible, one-electron
reduction steps.Thus, a tri-TCBD de-
rivative with a 1,3,5-trisubstituted ben-
zene core shows six reversible reduc-
tion steps within an exceptionally
narrow potential range of 1.0 V. The
first reduction potential Ered,1 is strong-
ly influenced by the donor substitution:
introduction of more donor moieties
causes an increasingly twisted TCBD
structure, a fact that results in the ele-
vation of the LUMO level and, conse-
quently, a more difficult first reduction.
The potentials are also strongly influ-
enced by the nature of the donor resi-
dues and the extent of donor–acceptor
coupling.A careful comparison of elec-
trochemical data and the correlation
with UV-visible spectra made it possi-
ble to estimate unknown physical pa-
rameters such as the Ered,1 of unsubsti-
tuted TCBD (ꢀ0.31 V vs Fc+/Fc) as
well as the maxima of highly broad-
ened CT bands.Donor-substituted
TCBDs are stable molecules and can
be sublimed without decomposition.
With their high third-order optical non-
linearities, as revealed in preliminary
measurements, they should become in-
teresting chromophores for ultra-thin
film formation by vapor deposition
techniques and have applications in
opto-electronic devices.
1,1,4,4-tetracyanobutadienes (TCBDs)
have been synthesized by [2+2] cyclo-
addition between tetracyanoethylene
(TNCE) and donor-substituted alkynes,
followed by electrocyclic ring opening
of the initially formed cyclobutenes.
Reaction yields are often nearly quan-
titative but can be affected by the elec-
tron-donating power and steric de-
mands of the alkyne substituents.The
intramolecular charge-transfer (CT) in-
teractions between the donor and
TCBD acceptor moieties were compre-
hensively investigated by X-ray crystal-
lography, electrochemistry, UV-visible
spectroscopy, and theoretical calcula-
tions.Despite the nonplanarity of the
new chromophores, which have a sub-
stantial twist between the two dicyano-
vinyl planes, efficient intramolecular
CT interactions are observed, and the
Keywords: charge transfer · conju-
gation · cycloaddition · donor–ac-
ceptor systems · electrochemistry
Introduction
Donor–acceptor (D–A)-substituted conjugated organic mol-
ecules have attracted much attention for their highly polar-
izable structures and the resulting efficient second- and
third-order nonlinear optical (NLO) effects.[1] One of the
most noticeable advantages of using organic chromophores
is the ability to tune the physical properties and to enhance
a specific NLO effect by simply modifying the chemical
structure.In the past decade, a number of structure–NLO
property relationships were established for various classes of
conjugated organic molecules by changing conjugation
length, as well as donor and acceptor strength and substitu-
[a] Dr.T.Michinobu, P.Seiler, B.Frank, Dr.N.N.P.Moonen,
Prof.Dr.F.Diederich
Laboratorium für Organische Chemie, ETH-Hçnggerberg
HCI, 8093 Zürich (Switzerland)
Fax : (+41)1-632-1109
E-mail: diederich@org.chem.ethz.ch
[b] Dr.C.Boudon, Dr.J-.P.Gisselbrecht, Prof.Dr.M.Gross
Laboratoire dꢀElectrochimie et de Chimie Physique du Corps Solide
UMR 7512, C.N.R.S, UniversitØ Louis Pasteur
4, rue Blaise Pascal, 67000 Strasbourg (France)
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2006, 12, 1889 – 1905
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tion pattern.[2] Well-defined guidelines to enhance the mo-
lecular first-order hyperpolarizability b were established,
but definite principles for achieving high molecular second-
order hyperpolarizability g and high bulk NLO susceptibili-
ties are still being pursued.
A variety of organic and organometallic TCBD-containing
molecules have been reported before,[9,10] and some of them
have been investigated as second-order NLO materials,
taking into account the nonplanar structure of the TCBD
moieties.However, there has been no systematic study on
their synthesis and electronic properties.Here, we describe
the reactivity of a series of electron-rich alkynes towards
TCNE and also report the synthesis of donor-substituted
TCBD oligomers.Their electronic properties are character-
ized by X-ray crystallography, electrochemistry, optical ab-
sorption spectroscopy, and theoretical calculations.The data
confirm that donor-substituted TCBDs, despite their nonpla-
narity, are powerful charge-transfer (CT) compounds with
physical properties suitable for nonlinear optical applica-
tions[7] and device fabrication.
We have in the past shown that tetraethynylethenes (3,4-
diethynylhex-3-ene-1,5-diynes, TEEs) substituted with N,N-
dimethylanilino (DMA) donor and p-nitrophenyl acceptor
groups feature high third-order optical nonlinearities, in par-
ticular in the case of low molecular symmetry.[3] More re-
cently, cyanoethynylethenes (CEEs), hybrid structures be-
tween TEEs and tetracyanoethylene (TCNE),[4a,b] were
proven to function as efficient acceptor groups for NLO ap-
plications if substituted with DMA donor groups.[4c] As a
distinct advantage over the corresponding TEE chromo-
phores, DMA-substituted CEEs are more compact and can
be sublimed without decomposition, thereby opening per-
spectives for opto-electronic device fabrication by ultra-thin
film deposition.
Results and Discussion
TCNE is known as one of the strongest organic electron
acceptors, and its high chemical reactivity towards nucleo-
philes or electron-rich reagents is frequently used to intro-
duce strong acceptor moieties into organic molecules.[5] For
example, DMA-substituted tricyanomonoethynylethene 1
Synthesis of monomeric donor-substituted tetracyanobuta-
dienes: A variety of electron-rich alkynes (22–42) were pre-
pared by Sonogashira cross-coupling or Hay coupling reac-
tions (see Supporting Information) and subsequently sub-
jected to the reaction with TCNE to give products 2–21
(Tables 1 and 2).
In the preparation of monomeric TCBDs, we first com-
pared the reactivity of o-, m-, and p-N,N-dimethylanilino
(DMA) derivatives 22–27 towards TCNE (entries 1–6,
Table 1).Whereas the p-DMA-substituted, terminally de-
protected alkyne 22 reacted at 208C to give TCBD 2 in
nearly quantitative yield (97%), the yield of the iPr3Si-pro-
tected product 3 was lower (78%), reflecting the steric hin-
drance from the iPr3Si group.Starting from Me Si derivative
3
23, TCBD 2 was isolated in only 48% yield after chroma-
tography, with silyl deprotection taking place on the weakly
acidic SiO2 support, as a result of the Si activation by the at-
tached dicyanovinyl moiety.In contrast, the reactions of the
o- and m-DMA-substituted alkynes with TCNE did not pro-
ceed at room temperature due to sterically reduced (ortho)
or lacking (meta) electron-donating ability.Rather, heating
to 708C in the absence of solvent and in the presence of an
excess of TCNE was necessary to accomplish transforma-
tion.Solvents such as CH 2Cl2 are sometimes found to
reduce the reaction yield, whereas an excess of TCNE does
not induce undesired side reactions and is easily removed by
sublimation and chromatography.The TCBD product from
2-ethynyl-N,N-dimethylaniline was too unstable to be isolat-
ed, but iPr3Si-protected TCBD 4 was obtained from the cor-
responding alkyne 25 in a yield of 27% (entry 4, Table 1).The
low yield is derived from the limited chemical stability of
the product which, in sharp contrast to highly stable 2 and 3,
completely decomposed after one day in the solid state at
room temperature. m-DMA-substituted alkynes 26 and 27
did not undergo cycloaddition to TCNE; rather, tricyanovi-
nylation occurred in para position of the aniline ring yield-
ing the stable donor-substituted tricyanoethenes 5 and 6, re-
spectively, in good yield (68–69%; entries 5 and 6, Table 1).
was synthesized by nucleophilic addition–elimination reac-
tion of TCNE with the corresponding copper(i) arylacety-
lide, prepared from 4-ethynyl-N,N-dimethylaniline and
CuOAc.[6] We have recently found that the same combina-
tion of initial starting materials, 4-ethynyl-N,N-dimethylani-
line and TCNE, can also furnish a member of a new class of
D–A chromophores, that is, DMA donor-substituted 1,1,4,4-
tetracyanobuta-1,3-diene (TCBD) 2.[7] This atom-econom-
ic,[8] one-step transformation proceeds in nearly quantitative
yield by means of [2+2] cycloaddition between TCNE and
the electron-rich alkyne followed by electrocyclic ring open-
ing of the intermediately formed cyclobutene ring to give
the TCBD framework (Scheme 1).
Scheme 1.Reaction between TCNE and an alkyne substituted with an
electron-donating group (EDG) to yield the corresponding donor-substi-
tuted TCBD derivative.
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Chem. Eur. J. 2006, 12, 1889 – 1905

Donor–Acceptor Systems
FULL PAPER
Table 1.Summary of the reactions of monomeric electron-rich alkynes with TCNE.The
s-cis or s-trans conformation of the TCBDs is shown according to X-ray crystal structure
analysis.
Next, we studied the difference in reac-
ꢁ
tivity between the two C C bonds in p-
DMA-substituted buta-1,3-diynes 28–30
(entries 7–9, Table 1).All butadiynes pref-
erentially reacted with TCNE at the more
Alkyne
Product
Yield Condi-
[%]
tions
ꢁ
electron-rich C C bond directly attached
to the p-DMA donor moiety, resulting in
ethynyl-substituted TCBDs.Thus, buta-
diynes 29 and 30 selectively gave 8 and 9,
respectively, at room temperature.The
Me3Si group of 8 was partially cleaved
during column chromatography on SiO2,
leading to decomposition, whereas the
iPr3Si group of 9 was unaffected.The iso-
lated yields (8: 15%; 9: 77%) clearly re-
flect this difference in stability between
the two silyl protecting groups.On the
other hand, only the 4-(dimethylamino)-
phenylethynyl-substituted TCBD 7, result-
ing from addition to the sterically more ac-
[a]
1
2
97
[b]
48
78
[b]
3
4
ꢁ
cessible terminal C C bond, was isolated
in a low yield of 8% from the addition of
unprotected 28 to TNCE.We believe,
however, that the major product results
from addition to the more electron-rich,
[c]
27
ꢁ
DMA-substituted C C bond of 28, leading
to Me3Si-deprotected 8, which decomposes
during chromatographic workup.A second
[c]
5
6
69
68
ꢁ
addition to the residual C C bond in 7–9
was not observed, even in the presence of
a large excess of TCNE.
Gratifyingly, bis-DMA-substituted al-
kynes 31–33 provided TCBD molecules
10–12 in almost quantitative yields at
room temperature (entries 10–12, Table 1).
This result is particularly remarkable for
the transformation of 33, featuring one o-
and one m-DMA moiety.
The comparison between o-, m-, and p-
DMA-substituted alkynes (entries 1–6,
Table 1) had clearly shown that their reac-
tivity in the cycloaddition with TNCE de-
pends strongly on the electron-donating
power of the anilino residue.Correspond-
ingly, alkynes bearing weaker electron-do-
nating substituents, such as p-anisyl and 2-
thienyl rings, required heating in order to
[c]
[b]
7
8
9
8
15
77
[b]
[b]
reach
a
transformation (entries 13–17,
Table 1).In particular, the transformations
of p-anisyl-substituted alkynes were sensi-
tive to the applied temperature.The reac-
tion of 34 in boiling benzene for 5 h af-
forded the corresponding TCBD 13 in a
yield of 32% (entry 13, Table 1), whereas
di-p-anisyl-substituted alkynes 35 and 36
did not react with TCNE at 808C.By
changing the solvent to boiling toluene
[d]
10
100
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F.Diederich et al.
The thermal stability of selected donor-
substituted TCBDs was investigated by
thermogravimetric analysis (TGA) (see
Supporting Information).For some chro-
mophores, decomposition proceeded in
two or three steps.The first noticeable de-
composition temperatures determined by
derivative thermogravimetry ranged from
210 to 4508C, comparable to those report-
ed for other TCBD derivatives.[9c] All
monomeric TCBDs measured did not
show any significant decomposition at
least up to the melting points.
Table 1.(Continued)
Alkyne
Product
Yield Condi-
[%]
tions
[a]
11
12
96
[b]
100
Synthesis of oligomeric donor-substituted
tetracyanobutadienes: p-DMA donors
have the highest alkyne-activating power,
and TCBDs bearing aryl groups at both 2-
and 3-positions are particularly stable.
With these results from the preparation of
monomeric systems in mind, we targeted
novel oligomeric TCBD molecules.To im-
prove the solubility of the molecules, p-
N,N-dihexylanilino (DHA) instead of
DMA groups were introduced as donor
residues.The DHA-substituted oligoal-
kyne precursors 39–42, prepared by Sono-
gashira cross-coupling of 4-ethynyl-N,N-di-
hexylaniline with di- or trihalobenzenes,
immediately reacted with TCNE in
CH2Cl2 at room temperature, yielding the
DHA-substituted TCBDs 18–21 (Table 2).
p-Phenylene-linked dialkyne 39 furnished
the corresponding di-TCBD molecule 18
in a quantitative yield (entry 1, Table 2),
whereas m-phenylene-linked dialkyne 41
afforded 20 in 86% yield (entry 3,
Table 2).The same yield was obtained in
the conversion of 42 to the tri-TCBD de-
rivative 21 with a 1,3,5-trisubstituted ben-
zene core (entry 4, Table 2).The products
were stable in the presence of an excess of
TCNE and could readily be isolated.The
difference in the yields between the p- and
[e]
13
14
15
16
32
42
12
80
[f]
[g]
[h]
[h]
17
80
[a] In C6H6, 208C, 2–3 h.[b] In CH Cl2, 208C, 0.5–1 h. [c] 708C, 0.5 h. [d] In THF, 208C, 1 h.
2
[e] In C6H6, 808C, 5 h.[f] In toluene, 110 8C, 12 h.[g] 170 8C, 10 min.[h] 150 8C, 8–14 h.
(1108C), di-p-anisyl-substituted TCBD 14 was obtained
from 35 in a yield of 42% (entry 14, Table 1).An even
higher temperature was necessary for 36, and the reaction
was very slow below 1608C, especially in solution, while de-
composition of the product dominated above 1808C.Thus,
15 was obtained in poor yield (12%) by heating 36 with
TCNE in the absence of solvent to 1708C for only 10 min
(entry 15, Table 1).The optimization of the reaction condi-
tions for 2-thienyl-substituted alkynes was facilitated by the
higher thermal stability of the products.Thus, 2-thienyl-sub-
stituted TCBDs 16 and 17 were obtained in high yield
(80%) from transformations at 1508C in the absence of sol-
vent (entries 16 and 17, Table 1).
m-phenylene derivatives reflects the differences in the steric
accessibility of the alkyne moieties in 39 and 42.Quadrupo-
lar (e.g., 18) and octupolar (e.g., 21) D–A molecules have
been shown to feature large two-photon absorption (TPA)
cross sections associated with NLO processes.[11]
In contrast to the p- and m-phenylene-linked dialkynes,
the o-phenylene derivative 40 did not produce the expected
di-TCBD molecule, but only mono-adduct 19 was isolated
in 39% yield (entry 2, Table 2).In this case, an unidentified
side reaction between 19 and TCNE in addition to steric
hindrance prevented the cycloaddition of the second alkyne
under formation of the targeted di-TCBD molecule.
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Donor–Acceptor Systems
FULL PAPER
[a]
Table 2.Summary of the reactions of the oligomeric electron-rich alkynes with TCNE.
the planes of the dicyanovinyl
moieties and the directly at-
tached donor rings vary be-
tween ꢂ18 (11, see Supporting
Information) and ꢂ448 (13,
Figure 1).Despite these distor-
tions, nearly all donor-substi-
tuted TCBDs undergo efficient
intramolecular CT interactions
(vide infra).
The crystal packings show
several interesting short inter-
molecular contacts (Figure 2).
For example, the DMA resi-
dues of two neighboring mole-
cules in the crystal of 3 under-
go antiparallel stacking at in-
termolecular C···C distances
around 3.80 Š (Figure 2a).
More interesting are the inter-
molecular interactions of the
strong CN dipoles.[13] A favora-
ble antiparallel dipolar align-
ment of two CN moieties is ob-
served in the crystal structures
of 12 (d(C···N)=3.28 Š) and
17 (d(C···N)=3.21 Š), shown
in Figure 2b and e, respective-
ly.Additionally, the crystal
packing of 17 features two
nearly orthogonal, symmetry
related CN···CN interactions
Alkyne
Product
Yield [%]
1
2
99
39
86
3
4
86
[a] In CH2Cl2, 208C, 3 h.
with
a
sub van der Waals
distance (d(N(17’)···C(21’’))=
ꢁ
3.15 Š, N···C N angle=958).
X-ray structures and bond length alternation: All donor-sub-
stituted TCBDs are colored solids.Many of the monomeric
chromophores furnished single crystals suitable for X-ray
crystallographic analysis by slow diffusion of hexane into a
solution of the molecule in CH2Cl2 at ꢀ158C.The crystal
structures of 3, 12, 13, 14, and 17 are shown in Figure 1 (for
the crystal structures of 2, 10, and 11, see reference [7] and
Supporting Information).
All TCBD moieties are highly distorted.Distortion from
planarity occurs mainly by rotation around the central single
bond of the TCBD moiety.For example, the twist between
the two dicyanovinyl planes in 3 is expressed by the torsion
angle q(C(11)-C(1)-C(16)-C(17))=85.58.If the absolute
value of this torsion angle is less than 908, the TCBD adopts
the s-cis conformation.This is the case for compounds 3, 10,
12, 14, and 17 (Table 3).In contrast, if the absolute value is
larger than 908, the s-trans conformation is preferred in the
solid state, and this geometry is seen in the crystal structures
of compounds 2, 11, and 13.Thus, TCBD derivatives substi-
tuted with aryl groups at both 2- and 3-positions prefer the
s-cis conformation, presumably due to additional favorable
intramolecular aryl–aryl interactions.[12] The angle between
Interestingly, previously unknown nearly orthogonal multi-
polar contacts are observed in the crystal packings of 13, 14,
and 17.The CN groups of one molecule interact with the
C(CN)2 moieties of its neighbor.In 13 (Figure 2c) the short-
est contact is observed between N18 and the central vinylic
C atom C16’ (d(N···C)=3.17 Š, N···C=C angle=1038).It is
unclear at present whether this contact is favorable or not.
However, in this specific alignment, the CN group can form
two rather than only one (nearly orthogonal) CN···CN con-
ꢁ
tact (d(N(18)···C(17’))=3.24 Š, N···C N angle=1078 and d-
(N(18)···C(19’))=3.41 Š, N···C N angle=688).In the crystal
packing of 14, two neighboring molecules feature two sym-
metry-related C N···C(CN)2 interactions, with the N atom
pointing in both cases in a near orthogonal fashion onto the
three C atoms of the dicyanomethylene fragment (Figure
2d).Two similar C N···C(CN)2 contacts are seen in the crys-
tal packing of 17 (Figure 2e).Thus, the crystal structures of
donor-substituted TCBDs visualize once more the important
role of multipolar interactions, and in particular orthogonal
ones, in stabilizing organic crystal lattices.A better under-
standing of such interactions is only just now emerging as an
important target of computational and experimental work.[13]
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F.Diederich et al.
Figure 1.ORTEP plots of a) 3, b) 12, c) 13, d) 14, and e) 17 with vibrational ellipsoids shown at the 30% probability level.Arbitrary numbering.Selected
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
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bond lengths (Š) and angles (8): 3: C1 C11 1.374(5), C1 C2 1.445(4), C1 C16 1.505(4), C2 C7 1.407(4), C2 C3 1.411(5), C3 C4 1.362(5), C4 C5
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1.420(5), C5 N8 1.351(4), C5 C6 1.413(5), C6 C7 1.374(5), C16 C17 1.348(4), C16 Si22 1.948(3); C11-C1-C16 115.0(3), C12-C11-C14 112.6(3), C17-
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
C16-C1 115.3(3), C17-C16-Si22 126.6(2), C18-C17-C20 114.1(3); 12: C1 C11 1.356(2), C1 C2 1.477(2), C1 C16 1.4942(19), C2 C3 1.402(2), C2 C7
1.404(2), C3 C4 1.377(2), C4 C5 1.375(3), C5 C6 1.381(3), C6 C7 1.402(2), C7 N8 1.409(2); C11-C1-C2 122.21(13), C1-C11-C12 124.05(14), C23-C16-
C17 122.29(13), C16-C23-C24 122.81(14); 13: C1 C16 1.356(4), C1 C2 1.466(3), C1 C10 1.468(4), C2 C3 1.395(4), C2 C7 1.407(3), C3 C4 1.384(4),
C4 C5 1.391(4), C5 O8 1.360(3), C5 C6 1.387(4), C6 C7 1.369(4), C10 C11 1.340(4); C2-C1-C10 118.9(2), C11-C10-C1 124.7(2), C12-C11-C14 114.7(2),
C19-C16-C17 115.1(2); 14 for one of the two different molecules in the unit cell: C1 C10 1.3658(16), C1 C2 1.4653(16), C2 C7 1.4016(16), C2 C3
1.4102(16), C3 C4 1.3722(17), C4 C5 1.3974(18), C5 O8 1.3500(16), C5 C6 1.3866(19), C6 C7 1.3831(18); C10-C1-C2 127.82(10), C1-C10-C11
121.03(11); 17: C1 C18 1.3675(19), C1 C2 1.4395(19), C1 C7 1.5121(16), C2 C3 1.4014(19), C2 S6 1.7330(13), C3 C4 1.407(2), C4 C5 1.364(2), C5 S6
1.6951(16); C18-C1-C2 127.45(12), C19-C18-C21 115.77(12). Selected torsion angles (8): 3: C11-C1-C2-C7=19.5(5); 12: C11-C1-C2-C3=ꢀ41.0(2); C23-
C16-C17-C22=ꢀ55.5(2); 13: C16-C1-C2-C3=44.1(4); 14: C10-C1-C2-C7=11.47(19); 17: C13-C7-C8-S9=9.9(2).
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Donor–Acceptor Systems
FULL PAPER
Table 3.Correlation of the quinoid character of donor-substituted
TCBDs with spectral properties to estimate the efficiency of intermolecu-
lar D–A p-conjugation.
the CT conjugation from the donor to the TCBD acceptor
moieties, and can be expressed by the quinoid character (dr)
of the ring [Eq.(1)]. [14]
ꢀ1
ꢁ
dr [Š]
q [8][a]
dmeta [ppm][b]
n(C N) [cm
]
dr ¼ f½ða þ a0Þꢀðb þ b0ފ=2 þ ½ðc þ c0Þꢀðb þ b0ފ=2g=2
ð1Þ
2
0.036
ꢀ144.3
146.5
85.5
62.3
ꢀ96.7
7.51
2212
3
10
11
0.045
7.53
7.79
7.48
7.82
2212
2206
2217
In benzene, the dr value equals 0, whereas values between
0.08 and 0.10 are found in fully quinoid rings (see Fig-
ure 1a,b for the definition of bonds a, a’, b, b’, c, and c’).Cal-
culated from the X-ray crystal structures (Figure 1 and refer-
ence [7]), TCBD 2 with two different molecules in the unit
cell exhibits an average dr of 0.036 (Table 3). TCBDs 3 and
10 show higher values of 0.045 and 0.050, respectively. As a
comparison, the dr values for p-DMA rings in D–A substi-
tuted TEEs, calculated from several X-ray structures, gener-
ally do not exceed 0.025.[2c] Recently reported DMA-substi-
tuted CEEs, which were proven to have stronger D–A inter-
actions, display dr values of 0.033–0.037.[15] Taking into ac-
count these results, DMA-substituted TCBDs clearly feature
efficient intramolecular CT interactions.Even 12, with a
0.050
[c]
12
13
14
0.034[d]
0.019
0.020
ꢀ53.9
ꢀ144.5
75.1
2223
2224
2224
7.45
7.77
ꢀ121.9
17
88.5
2224
[a] The torsion angle between the two dicyanovinyl planes in the TCBD
moieties.[b] 1H NMR chemical shifts (300 MHz) in CDCl3.[c] The data
are not reliable, see reference [7].[d] Determined from the o-DMA ring.
Bond length alternation in the benzene rings of the DMA
and anisyl moieties is a good indication for the efficiency of
Figure 2.Arrangement of neighboring molecules in the crystal packings of a) 3, b) 12, c) 13, d) 14, and e) 17.
Chem. Eur. J. 2006, 12, 1889 – 1905
ꢁ 2006 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
www.chemeurj.org
1895

F.Diederich et al.
substantial twist between the donor and acceptor moieties
(see legend to Figure 1), has a value of 0.034 calculated
from the o-DMA ring. p-Anisyl-substituted TCBD deriva-
tives 13 and 14 exhibit reasonably decreased dr values of
0.019 and 0.020, respectively, due to the weaker electron-do-
nating power.
Table 4.(Continued)
Cyclic Voltammetry
Rotating Disk Voltammetry
E8 [V][b] DEp [mV][c] Ep [V][d] E1/2 [V][e]
Slope [mV][f]
[i]
7
8
9
+0.74
ꢀ0.55
ꢀ1.14
+0.91
ꢀ0.75
ꢀ1.13
+0.90
ꢀ0.70
ꢀ1.07
90
90
90
100
110
120
100
75
ꢀ0.56 (1eꢀ)
75
[j]
[g]
The dr values for p-DMA and p-anisyl rings display a
good correlation with the chemical shifts of the protons in
meta positions relative to the dimethylamino and methoxy
substituents (Table 3).Downfield shifts of the meta-protons
are measured as a result of the CT from the donor to the ac-
ceptor moiety and can be considered as another measure for
the efficiency of ground-state D–A conjugation.[4b] The
downfield shifts (and correspondingly the CT efficiency) de-
crease from 10, to 3, and to 2 for p-DMA rings and from 14
to 13 for p-anisyl rings.This order is consistent with that of
the dr values.Note that the downfield shifts resulting from
intermolecular CT in 10 and 14 might have been slightly
overestimated because of anisotropic through-space effects
of the aryl rings, resulting from the s-cis orientation of the
TCBD moieties.
ꢀ0.75 (1eꢀ)
90
[j]
ꢀ1.20 (1eꢀ)
[g]
100
[k]
10 +0.91
+0.86
+0.89 (2eꢀ)
ꢀ1.08 (1eꢀ)
125
90
90
90
100
90
ꢀ1.06
75
100
ꢀ1.29
ꢀ1.36 (1eꢀ)
[g]
11 +0.90
+0.72
+0.76 (1eꢀ)
ꢀ0.91 (1eꢀ)
75
80
90
ꢀ0.89
90
90
ꢀ1.18
ꢀ1.26 (1eꢀ)
[i]
12
+1.06
+0.78
+0.82 (1eꢀ)
ꢀ0.88 (1eꢀ)
ꢀ1.41 (1eꢀ)
ꢀ0.60 (1eꢀ)
ꢀ1.30 (1eꢀ)
ꢀ0.85 (1eꢀ)
ꢀ1.25 (1eꢀ)
ꢀ0.69 (1eꢀ)
ꢀ1.13 (1eꢀ)
ꢀ0.82 (1eꢀ)
ꢀ1.26 (1eꢀ)
ꢀ0.85 (1eꢀ)
ꢀ1.23 (1eꢀ)
+0.91 (2eꢀ)
ꢀ0.75 (1eꢀ)
ꢀ0.97 (1eꢀ)
ꢀ1.45 (2eꢀ)
85
80
100
70
80
65
65
75
70
110
110
110
110
60
60
65
125
ꢀ0.80
ꢀ1.27
120
130
90
90
90
90
80
80
125
125
125
115
75
70
80
75
80
13
14
15
16
17
ꢀ0.56
ꢀ1.21
ꢀ0.81
ꢀ1.18
ꢀ0.65
ꢀ1.05
ꢀ0.75
ꢀ1.09
ꢀ0.79
ꢀ1.05
ꢁ
The vibrational frequency n(C N) of the TCBD moieties
is also correlated with the dr values (Table 3).The shift of
this frequency to lower energy can be considered as a good
indication for the CT from donor to acceptor moieties.The
ꢁ
value of the n(C N) stretching frequency indeed shifts to
low energy as the dr values increase.Taking together into
account the X-ray, NMR, and IR data, the efficiency of the
CT in the ground state increases in the series 13<14<12<
2<3<10.
18 +0.89
ꢀ0.75
ꢀ0.94
Electrochemistry: The redox properties of the donor-substi-
tuted TCBDs were studied using cyclic voltammetry (CV)
and rotating disk voltammetry (RDV) in CH2Cl2 with
nBu4NPF6 (0.1m) as the supporting electrolyte.The redox
potentials vs.Fc +/Fc (ferricinium/ferrocene couple) are
listed in Table 4.
All monomeric TCBDs show two reversible, well-resolved
1eꢀ reduction steps centered on the two dicyanovinyl units.
Each p-DMA moiety undergoes a reversible 1eꢀ oxidation
step, whereas oxidations of p-anisyl and 2-thienyl moieties
are not observed within the available potential range.The
o- and m-DMA groups of 12 give irreversible oxidations
ꢀ1.26
ꢀ1.39
19 +0.75
+0.52
100
85
+0.87 (1eꢀ)
+0.58 (1eꢀ)
ꢀ0.93 (1eꢀ)
ꢀ1.21 (1eꢀ)
+0.91 (2eꢀ)
ꢀ0.82 (1eꢀ)
ꢀ1.05 (1eꢀ)
ꢀ1.50 (2eꢀ)
75
70
80
75
50
60
70
100
ꢀ0.87
85
85
60
70
80
60
65
80
70
90
120
60
70
ꢀ1.10
20 +0.88
ꢀ0.80
ꢀ1.00
ꢀ1.26
ꢀ1.39
21 +0.89
ꢀ0.69
+0.92 (3eꢀ)
ꢀ0.73 (1eꢀ)
ꢀ0.94 (1eꢀ)
ꢀ1.15 (1eꢀ)
ꢀ1.35
40
65
ꢀ0.82
75
[g]
ꢀ1.06
[g]
[g]
[g]
ꢀ1.27
ꢀ1.44
ꢀ1.51
Table 4.Electrochemistry data of donor-substituted TCBDs in CH 2Cl2
(+ 0.1m nBu4NPF6).[a] For an overview of the compounds, see Tables 1
and 2.
ꢀ1.69
60
ꢂꢀ1.7
[a] Potentials versus the ferricinium/ferrocene couple.Working electrode:
glassy carbon electrode; counter electrode: Pt; reference electrode: Ag/
AgCl.[b] E8=(Epc+Epa)/2, in which Epc and Epa correspond to the catho-
Cyclic Voltammetry
Rotating Disk Voltammetry
E8 [V][b] DEp [mV][c] Ep [V][d] E1/2 [V][e]
Slope [mV][f]
ꢀ
dic and anodic peak potentials, respectively.All reductions are 1e trans-
2
3
6
+0.86
ꢀ0.69
ꢀ1.26
+0.90
ꢀ1.10
ꢀ1.34
+0.97
ꢀ1.11
80
80
90
70
90
100
90
80
+0.87 (1eꢀ)
ꢀ0.70 (1eꢀ)
ꢀ1.38 (1eꢀ)
+0.92 (1eꢀ)
70
70
140
70
fers.[c] DEp =EoxꢀEred, in which the subscripts ox and red refer to the
conjugated oxidation and reduction steps, respectively.[d] Ep =Irreversi-
ble peak potential at sweep rate v=0.1 Vsꢀ1.[e] E1/2 =Half-wave poten-
tial.[f] Slope =Slope of the linearized plot of E versus log [I/(IlimꢀI)]. Ilim
is the limiting current and I the current.[g] Unresolved waves.[h] Small
amplitude signal.[i] Electrode inhibition during oxidation.No plateau-
limiting current could be observed.[j] Spread-out wave due to surface
phenomena (insulating film formation).[k] Could not be determined due
to the presence of a cathodic redissolution peak at scan rates lower than
ꢀ1.14 (1eꢀ)
75
[g]
+1.02 (1eꢀ)
ꢀ1.14 (1eꢀ)
90
75
ꢀ1.74[h]
ꢀ1.79 (1eꢀ)[h] 100
1 Vsꢀ1
.
1896
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Chem. Eur. J. 2006, 12, 1889 – 1905

Donor–Acceptor Systems
FULL PAPER
due to the absence of substituents in para position to the di-
methylamino functions: dimerization via the electrogenerat-
ed radical cations has been shown to usually occur at such
positions.[16]
Whereas 2 and 3 do not differ much in the first oxidation
potential (+0.86 vs +0.90 V), the introduction of the addi-
tional iPr3Si substituent in 3 causes a dramatic cathodic shift
of the first reduction potential by 410 mV (ꢀ0.69 (2) vs
ꢀ1.10 V (3)).On the other hand, compounds 8 and 9, with
less efficient coupling between the DMA donor and the
TCBD acceptor in 7 because of the ethynediyl spacer.
Interestingly, the comparison of the CV data of p-DMA-
and p-anisyl-substituted TCBDs allows the extrapolation of
the yet unknown first reduction potential of the unsubstitut-
ed TCBD chromophore.Plotting the first reduction poten-
tials as a function of the number of the donor substituents
(n) affords two lines with different slopes (Figure 3).Defini-
ꢁ ꢀ
ꢁ ꢀ
Me3SiC C and iPr3SiC C substituents, respectively, ex-
hibit only a slight cathodic shift by 60 mV (8) and 10 mV (9)
in their respective first reduction potentials as compared to
2.These cathodic shifts are a consequence of the greater
twist and the resulting enforced deconjugation between the
two dicyanovinyl residues of the TCBD moieties upon intro-
duction of the second substituent.These steric effects are
evidently larger when the bulky silyl substituent is directly
attached to the TCBD skeleton.The X-ray crystal structures
of
2 and 3 nicely support this explanation (Table 3,
Figure 1); the TCBD chromophore in 2 is more planar than
in 3.
The presence of a second DMA donor also brings about a
remarkable cathodic shift of the first reduction potentials.
From 10 (two p-DMA), to 11 (two p-DMA), and to 12 (one
o-, one m-DMA) the observed shifts are ꢀ370 mV,
ꢀ200 mV, and ꢀ110 mV, respectively, relative to the first re-
duction potential of 2 (Ered,1 =ꢀ0.69 V). The same tendency,
with less pronounced differences in the cathodic shifts, is ob-
served for p-anisyl- or 2-thienyl-donor-substituted TCBDs.
The values shift by ꢀ250 mV and ꢀ90 mV for 14 and 15, re-
spectively, relative to the first reduction potential of p-
anisyl-substituted TCBD 13 (Ered,1 =ꢀ0.56 V). The potential
of 17 shifts cathodically by only 40 mV relative to that of
thienyl-substituted 16 (Ered,1 =ꢀ0.75 V).
Figure 3.Linear correlation between the number of donor substituents
*
: p-
(n) on the TCBD moiety and the first reduction potential Ered,1
.
&
DMA donors, : p-anisyl donors.
tively, the p-DMA moiety is a more powerful electron-do-
nating group than the p-anisyl moiety, shifting the first re-
duction potential to more negative potentials by 130 mV (2
against 13; one donor group) and 250 mV (10 against 14;
two donor groups).The latter value is about twice as large
as the former one, which is a good indication of the additivi-
ty of the substituent effects (Hammett correlation)[18] on the
TCBD chromophore.This additivity is the overlap of both
the electronic effect and the enforced deconjugation of the
TCBD moiety, sterically induced by the second donor
group.The two lines are crossing each other at n=0, indi-
cating that the unsubstituted TCBD will probably be re-
duced at ꢀ0.31Æ0.01 V. This value is comparable to that of
TCNE (ꢀ0.32 V).[19]
Some of these measured potential shifts result from differ-
ences in the twist between the two dicyanovinyl residues of
the TCBD acceptor as well as from sterically enforced devi-
ations from planarity of individual donor-substituted dicya-
novinyl moieties, thereby reducing the extension of p conju-
gation.But another significant part of the observed shifts is
a direct consequence of the extent of D–A coupling.[4b,17] In
a p-conjugated system, the presence of an electron-donating
group hinders the electron reduction and an electron-with-
drawing group makes the oxidation more difficult.In other
words, efficient D–A conjugation leads to a lowering and an
elevation of the HOMO and LUMO levels, respectively,
and weaker D–A coupling, in contrast, brings about an ele-
vation and a lowering of the HOMO and LUMO levels, re-
spectively.As an example, the structure of TCBD 7 is an ex-
panded version of 2, with an ethynediyl spacer inserted be-
tween the DMA donor and the TCBD acceptor.The first
reduction potential of 7 is anodically shifted by 140 mV rela-
tive to that of 2, and the first oxidation potential is, in con-
trast, cathodically shifted by 120 mV.Thus, the electrochem-
ical HOMO–LUMO gap of 7 (1.29 eV) is much smaller
than that of 2 (1.55 eV). The value of 1.29 V is the lowest in
the entire series.This result clearly shows that there is much
The dimeric TCBD derivatives 18 and 20 exhibit four
TCBD-centered reduction steps and one DMA-centered ox-
ꢀ
idation wave.The first two 1e reduction potentials reflect
the difference in the connector (p- or m-phenylene) between
the two TCBD moieties.The oxidation peak shape is indica-
tive of two overlapping one-electron transfers, which means
that the two DMA groups are far away from each other,
avoiding any electrostatic repulsion between the oxidized
sites.RDV confirmed the exchange of two electrons for the
oxidative process by comparing the wave amplitudes of the
oxidation and reduction processes.Whereas the first two re-
Chem. Eur. J. 2006, 12, 1889 – 1905
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www.chemeurj.org
1897

F.Diederich et al.
ductions are well resolved, the third and fourth reductions
give rise to a unique spread-out wave, due to the formation
of insulating films with potentials more negative than those
observed by CV (for CV traces, see Supporting Informa-
tion).
TCBD 19 shows reversible electron transfers, namely two
oxidation and two reduction steps.The first reduction poten-
tial is attributed to the TCBD moiety.The first oxidation
potential is derived from the ethynylated DMA moiety, be-
cause the other DMA moiety, which is directly attached to
the TCBD acceptor, is more difficult to oxidize.Thus, the
interaction between HOMO and LUMO levels is weak,
leading to the low electrochemical HOMO–LUMO gap of
1.39 V.
group results in a hypsochromic shift of the longest wave-
length absorption maximum of 3 (lmax: 454 nm (2.73 eV)),
reflecting sterically enforced deconjugation.This deconjuga-
tion of the TCBD moiety elevates the LUMO level, thereby
resulting in a larger band gap.The spectra of 8 and 9 feature
a distinct band at nearly the same energy as 3, with an addi-
tional broad shoulder at about 550 nm (2.25 eV). In con-
trast, the CT band of the expanded TCBD 7 is composed of
a single, rather intense absorption, significantly shifted to
lower energy (698 nm (1.78 eV), Table 5). The single CT
Table 5.Summary of the UV-visible spectra of donor-substituted TCBDs
in CH2Cl2 and electrochemical band gaps determined by CV in CH2Cl2.[a]
lmax [nm (eV)]
lend [nm (eV)]
D(Eox,1ꢀEred,1) [V]
Remarkably, one large oxidation peak and six reversible
reduction steps are detected in the CV of the trimeric
TCBD molecule 21 (Supporting Information).The limiting
current for the six reduction steps observed by RDV at
ꢀ1.8 V is twice as large as the limiting oxidation current.
Since the oxidation involves three-electron transfers derived
from three DMA groups, it is reasonable to conclude that
each reduction step occurs as a 1eꢀ transfer.A conjugated
organic molecule that shows six successive and reversible
1eꢀ reduction steps within a narrow potential range of 1.0 V
(from ꢀ0.69 V to ꢀ1.69 V in this case) is, to our knowledge,
unprecedented.Careful examination of the oxidation wave
shape provided the wave slope of 40 mV, indicating that
structural change might have occurred after the first oxida-
tion.[20]
2
3
7
8
9
10
11
18
19
20
21
570 (2.18)
454 (2.73)
960 (1.29)
630 (1.97)
990 (1.25)
760 (1.63)
790 (1.57)
660 (1.88)
780 (1.59)
810 (1.53)
980 (1.27)
765 (1.62)
800 (1.55)
1.55
2.00
1.29
1.66
1.60
1.92
1.61
1.64
1.39
1.68
1.58
698 (1.78)
[b]
550[c] (2.25)
470 (2.64)
526 (2.36)
[b]
[b]
[b]
590[c] (2.10)
[a] The optical band gap is either determined from lmax of the CT band
or from the optical end-absorption lend.[b] Could not be determined due
to strong peak broadening.[c] Shoulder.
band indicates that the DMA donor in 7 senses the TCBD
moiety as a single acceptor in 7, presumably due to the ab-
sence of a substantial twist between the two dicyanovinyl
moieties.The lower energy of the CT band of 7, relative to
that found for 2, clearly reflects the weaker D–A coupling
as a result of the insertion of the ethynediyl spacer (vide
supra).As previously observed in the study of donor-substi-
tuted CEEs,[4b] the acetylenic spacer serves as an “insulator”
between donor and acceptor moieties and this decoupling
leads to a decrease in both optical and electrochemical
HOMO–LUMO gaps.
UV-visible spectroscopy: Most of the donor-substituted
TCBDs show multiple CT bands, resulting from different
D–A transitions.For example, 2 displays two rather weak
CT bands at 481 and 570 nm (2.58 and 2.18 eV, respectively;
Figure 4).These bands are derived from two different D–A
transitions, involving different donor-located orbitals (vide
infra).The weaker D–A interaction reasonably shifts the
CT band to lower energy.Substitution of 2 with the iPr3Si
Introduction of a second p-DMA donor group dramatical-
ly increases the intensity of the CT bands (Figure 5).The
longest wavelength CT bands of 10 and 11 feature a lmax of
470 nm (2.64 eV) with a molar extinction coefficient (e) of
55000mꢀ1 cmꢀ1 and a lmax of 526 nm (2.36 eV) with e of
38100mꢀ1 cmꢀ1, respectively.In contrast, 12 with o- and m-
DMA donors exhibits a much weaker, nearly vanishing CT
absorption.Upon protonation of the DMA moieties with
trifluoroacetic acid (TFA), the solutions of 10 and 11 turn
from purple to colorless and the longest wavelength absorp-
tion bands disappear almost completely.The CT bands can
be fully regenerated upon neutralization with Et3N.
The spectral behavior of the p-anisyl donor-substituted
TCBDs 13–15 is similar to that of the corresponding p-
DMA-substituted analogues 2, 10, and 11 (Supporting Infor-
mation).Di- p-anisyl-substituted TCBDs 14 and 15 exhibit
more intense CT bands than 13, and their absorption
maxima are hypsochromically shifted relative to that of 13
Figure 4.UV-visible spectra of monomeric DMA donor-substituted
TCBDs in CH2Cl2.
1898
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Chem. Eur. J. 2006, 12, 1889 – 1905

Donor–Acceptor Systems
FULL PAPER
Figure 6.Linear correlation between the optical band gap Egap, deter-
Figure 5.UV-visible spectra of bis-DMA donor-substituted TCBDs in
CH2Cl2.
&
*
mined from lmax
(
) for 2, 3, 7, 9, 10, 11, and 21 and lend ( ) for 2, 3, 7, 8,
9, 10, 11, 18, 19, 20, and 21, and D(Eox,1ꢀEred,1).
cal data can also be used to predict the CT band for weakly
coupled D–A interactions.
by 66 nm (0.48 eV) and 21 nm (0.14 eV), respectively. Di-
thienyl-substituted TCBD 17 displays a lmax of 366 nm
(3.39 eV) with double the intensity of 16 (369 nm (3.36 eV)),
again resulting from the double number of donor substitu-
ents.
The CT bands of oligomeric TCBDs feature very large e
values and are accompanied with a long tail or shoulder
reaching into the near infrared (Supporting Information,
Table 5).Thus, the spectrum of dimeric 18 displays a CT
Fluorescence and solvatochromism: Donor-substituted
TCBD molecules do not fluoresce in CHCl3, but some of
them show a very weak emission in hexane (see Supporting
Information).The highest quantum yield determined is
0.015 for 16.However, some species show very large Stokes
shifts of ~7000 cmꢀ1, indicating a large transition dipole
moment.
band with
a
lmax of 476 nm (2.61 eV) and
e
of
A distinct solvatochromism is observed for all donor-sub-
stituted TCBDs in various hexane/CHCl3 mixtures (see Sup-
porting Information).Noncentrosymmetric bis-DMA-substi-
tuted TCBD 11 exhibits the largest solvent effect.From
CHCl3 (lmax =526 nm, 2.36 eV) to hexane (lmax =477 nm,
2.60 eV), a shift of 0.24 eV is observed. It is generally
known that solvatochromism is a characteristic behavior of
dipolar molecules.[21] However, centrosymmetric molecules
such as 10, 14, 17, and 18 as well as the octupolar-type mole-
cule 21 also display solvatochromic effects similar to those
measured for the noncentrosymmetric dipolar donor-substi-
tuted TCBDs.As an example, the absorption maximum of
14 shifts from 379 nm (3.27 eV) in CHCl3 to 358 nm
(3.46 eV) in hexane. A strong CT from the ground to the ex-
cited state would produce a partially positive charge on the
donors and a negative charge on the acceptors, which forms
a quadrupole for 10, 14, 17, and 18 and an octupole for 21.
We therefore propose that the increase in electric moment
from the ground to the excited state through a change in the
quadrupole or octupole moment is the most likely explana-
tion for the solvatochromic effects observed for these mole-
cules.[4b,22]
99900mꢀ1 cmꢀ1.This e value is almost twice as large as that
of m-phenylene-linked analogue 20 (e=54200mꢀ1 cmꢀ1) and
exceeds even that of trimeric 21 (e=90700mꢀ1 cmꢀ1).As ex-
pected, the CT band of 18, with a p-phenylene connector, is
bathochromically shifted from the band in 20, with a m-
phenylene connector.
A plot of the optical band gap, calculated from the lmax of
the CT band or the end-absorption lend in the UV-visible/
NIR spectrum, against the difference between the first oxi-
dation potential and the first reduction potential in the CV
(the electrochemical band gap, Table 5) shows a linear cor-
relation (R=0.978 for lmax and R=0.954 for lend) between
the two quantities (Figure 6).This suggests that the same or-
bitals are involved in both optical and electrochemical band
gaps.
Some optical band gaps, especially of oligomeric TCBDs,
could not be determined from lmax, due to broad and weak
lowest energy transitions.Weak D–A interactions usually
result in an obscure CT band with a relatively low e.[4b]
However, most of these D–A molecules are gratifyingly
redox active species, yielding the electrochemical band gaps.
By applying the electrochemical band gaps to the correla-
tion, the optical band gaps from lmax were estimated to be
546 nm (2.27 eV, 18), 636 nm (1.95 eV, 19), and 532 nm
(2.33 eV, 20).These values are reasonably located on the
broad CT bands.This result suggests that the electrochemi-
Computational studies: We recently performed B3LYP/6–
31G** calculations[23] using the Gaussian 98 program[24] on
donor-substituted CEEs, such as 1, and found good correla-
tions of the results of geometry optimizations with the ex-
Chem. Eur. J. 2006, 12, 1889 – 1905
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www.chemeurj.org
1899

F.Diederich et al.
perimental data from X-ray crystal structures.[15] These re-
sults were nicely reproduced in the present study in which
the B3LYP/6–31G** method implemented in Spartanꢀ04[25]
was used.Geometry optimizations were subsequently per-
formed on TCBDs 2 and 10, producing good agreement
with the X-ray structure data (see Supporting Information).
Thus, calculated and experimental bond lengths and torsion
angles were in good agreement except for the calculated tor-
sion angle (78.818) about the central single bond in the
TCBD moiety of 10, which deviated by more than 158 from
the experimental value (62.298).The experimental torsion
angle seems to be influenced by crystal packing forces,
which are absent in theoretical (gas-phase) geometry deter-
mination.For 2, the calculated quinoid character (dr=
0.035) was in good agreement with the experimental value
(0.036, Table 3), whereas a substantial deviation between ex-
perimental (0.050) and calculated value (0.036) was found
for 10.
Table 6.Experimental electronic transitions for TCBDs 2 and 10, derived
from the UV-visible spectra in CH2Cl2, and computed values, based on
the TD-B3LYP/6–31G*//B3LYP/6–31G* method.[a]
Experimental
Computed Values
Composition of band/
CI coefficients
l [nm] e [Mꢀ1 cmꢀ1
]
l [nm]
f
2
343
10200
347
0.29
Hꢀ3!L
0.11
0.11
0.57
0.22
0.69
Hꢀ2!L
Hꢀ1!L
H!L+1
481
570
7000
4900
403
659
0.0005 Hꢀ2!L
Hꢀ1!L
ꢀ0.14
0.13
H!L
0.64
H!L+1
ꢀ0.11
10 390
17900[b]
384
457
473
0.58
0.03
0.08
Hꢀ1!L
H!L+1
Hꢀ1!L
H!L+1
Hꢀ1!L+1
H!L
ꢀ0.27
0.57
0.
0.34
0.27
0.63
6
470
55000
The HOMOs and LUMOs resulting from the calculations
are depicted in Figure 7.For both 2 and 10, the density in
[a] f=oscillator strength; CI=configuration interaction; H=HOMO;
L=LUMO.[b] Shoulder.
sorption is mainly a HOMO–LUMO transition (Figure 7),
whereas the second band at higher energy is a transition
from the DMA-located HOMOꢀ2 to the LUMO level.Sim-
ilarly, the lowest energy transition of 10 is a HOMO–
LUMO transition.Overall, the calculations reproduce well
the geometric and electronic properties of TCBDs 2 and 10.
Conclusion
A series of monomeric, donor-substituted TCBD molecules
was synthesized in a remarkable one-step synthesis consist-
ing of the [2+2] cycloaddition between TCNE and electron-
rich alkynes, followed by electrocyclic ring opening of the
initially formed cyclobutene.Reaction yields are largely de-
pendent on the strength of the donor attached to the al-
kynes and steric factors.Based on the findings in the synthe-
sis of monomeric TCBDs, oligomeric TCBDs were also pre-
pared in good yields from DMA donor-substituted alkynes
attached to m- and p-phenylene or 1,3,5-benzenetriyl cores.
The opportunity for future extension to polymeric structures
such as 43 and 44 is indicated by the successful preparation
of TCBDs 12 and 17.Reaction between the corresponding
oligo- and poly(arylene ethynylene)s[26] and an excess of
TCNE should yield these novel, alternate D–A polymers.
As an advantage, the excess of TCNE will not lead to unde-
sirable side reactions and should be readily removable by
vacuum sublimation.These polymers could serve not only
as efficient NLO materials, but also as low-band-gap-conju-
gated polymers, which are interesting because of high intrin-
sic conductivity in the neutral state and tunable electroac-
tive properties upon doping.[27]
Figure 7.Orbital plots of a) 2 and b) 10.
the HOMO is concentrated on the DMA moiety and the
density in the LUMO on the TCBD part.The HOMOs
show a partial CT from the DMA to the TCBD fragment.
Electronic transition analysis for TCBDs 2 and 10 (TD-
B3LYP/6–31G*//B3LYP/6–31G*) was performed by using
Gaussian 98[24] (Table 6).The electronic transition analysis
of compound 2 suggests that both weak absorption bands
result from a D–A transition.The longer wavelength ab-
Despite considerable twists of the two dicyanovinyl moiet-
ies around the connecting single bond, as well as deviations
of dicyanovinyl moieties and attached donor rings from co-
1900
www.chemeurj.org
ꢁ 2006 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
Chem. Eur. J. 2006, 12, 1889 – 1905

Donor–Acceptor Systems
FULL PAPER
given in Hz.The resonance multiplicity is described as s (singlet), brs
(broad singlet), d (doublet), t (triplet), q (quintet), sept (septet), and m
(multiplet).Infrared spectra (IR) were recorded on a Perkin–Elmer
FT1600 spectrometer.UV-visible spectra were recorded on a Varian
CARY-5 spectrophotometer.The spectra were measured in a quartz cuv-
ette of 1 cm.The absorption wavelengths are reported in nm with the ex-
tinction coefficient in mꢀ1 cmꢀ1 in brackets.Shoulders are indicated as sh.
Fluorescence spectra were measured on a Jobin Yvon Horiba Spex Fluo-
rolog 3 spectrophotometer.Quantum yields were determined versus rho-
damine 6G (fF =0.95)[39] or anthracene (fF =0.32).[40] EI-MS and ESI-MS
spectra were measured on a Hitachi–Perkin–Elmer VG-TRIBID spec-
trometer and a Finnigan Mat TSQ 7000 spectrometer, respectively.High-
resolution (HR) FT-MALDI spectra were measured on an Ionspec Fouri-
er transform instrument with 2,5-dihydroxybenzoic acid (DHB), trans-2-
[3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB),
or 3-hydroxypicolinic acid (3-HPA) in MeOH/H2O as matrix, and the
compound in CH2Cl2 (two-layer technique).The most important signals
are reported in m/z units with M as the molecular ion.Elemental analy-
ses were performed by the Mikrolabor at the Laboratorium für Organi-
sche Chemie, ETH Zürich.
planarity, donor-substituted TCBDs feature strong intramo-
lecular CT bands in their UV-visible spectra.The efficiency
of the intramolecular CT interactions and the D–A coupling
is readily deduced from ground-state properties such as
bond length alternation determined from the X-ray crystal
1
structures, H NMR chemical shifts, shifts in the frequency
of the CN stretching vibration, and electrochemical redox
potentials.As discussed previously for donor-substituted
CEEs, the position of the longest wavelength CT absorption
in the UV-visible spectra is not a good measure for the effi-
ciency of D–A conjugation: stronger D–A coupling leads to
higher energy absorptions, whereas weaker coupling be-
tween strong donor and acceptor moieties results in lower
HOMO–LUMO gaps.The present study confirms that this
concept is of general utility to predict the band gap of conju-
gated D–A molecules.[28]
Lastly, but not least, the monomeric donor-substituted
TCBDs were revealed to be thermally stable up to their
high melting points.They are small enough to be sublimed
without decomposition under laboratory conditions, which
offers the potential for ultra-thin film preparation by vapor
deposition techniques.[29] Applications of this readily avail-
able new class of D–A compounds in NLO[7] and other op-
toelectronic devices represent a worthwhile objective for
future work.
Electrochemistry: Electrochemistry measurements were carried out at
208C in CH2Cl2 containing 0.1m nBu4NPF6 in a classical three-electrode
cell.CH 2Cl2 was purchased in spectroscopic grade from Merck, dried
over molecular sieves (4 Š), and stored under Ar prior to use. nBu4NPF6
was purchased in electrochemical grade from Fluka and used as received.
The working electrode was a glassy carbon disk electrode (2 mm in diam-
eter) used either motionless for CV (0.1 to 10 Vsꢀ1) or as rotating disk
electrode for rotating disk voltammetry (RDV).The auxiliary electrode
was a platinum wire, and the reference electrode was an aqueous Ag/
AgCl electrode.All potentials are referenced to the ferricinium/ferrocene
(Fc+/Fc) couple, used as an internal standard, and are uncorrected from
ohmic drop.The accessible range of potentials on the glassy carbon elec-
trode was +1.4 to ꢀ2.4 V versus Fc+/Fc in CH2Cl2.The electrochemical
cell was connected to
a computerized multipurpose electrochemical
device AUTOLAB (Eco Chemie BV, Utrecht, The Netherlands), and
controlled by the GPSE software, running on a personal computer.
X-ray analysis: The structures were solved by direct methods (SIR97)[41]
and refined by full-matrix least-squares analysis (SHELXL-97),[42] using
an isotropic extinction correction.All heavy atoms were refined aniso-
tropically; H atoms were refined isotropically, whereby H-positions are
based on stereochemical considerations.
X-ray crystalstructure of
3: Crystal data at 220(2) K for
Experimental Section
C25H31N5Si·CH2Cl2, Mr =514.56, monoclinic, space group P21/n (no.14),
1calcd =1.216 gcmꢀ3, Z=4, a=13.2717(4), b=14.2125(4), c=15.8651(5) Š,
b=110.061(1)8, V=2810.98(15) Š3; Bruker-Nonius Kappa-CCD diffrac-
Materials and general methods: Chemicals were purchased from Acros,
Aldrich, and Fluka, and used as received.THF was distilled from Na/
benzophenone and iPr2NH from CaH2.Hay catalyst refers to a freshly
prepared solution of CuCl (100 mg, 1.0 mmol) and N,N,N’,N’-tetramethyl-
ethylenediamine (TMEDA; 0.15 mL, 1.0 mmol) in acetone (25 mL).
TCNE was purified by sublimation, followed by recrystallization from
CH2Cl2.The reactions with TCNE and Pd catalysts were carried out
under an inert atmosphere by applying a positive pressure of Ar.Com-
pounds 2,[7] 10,[7] 11,[7] 22,[30] 23,[31] 26,[32] 31,[33] 32,[32] 35,[34] 36,[35] 37,[36]
38,[37] and 4-ethynyl-N,N-dihexylaniline[38] were prepared according to lit-
erature procedures.Column chromatography (CC) and plug filtrations
were carried out with Fluka SiO2 60 (particle size 40–63 mm, 230–400
mesh) or Fluka Al2O3 (particle size 50–150 mm) and distilled technical
solvents.Size-exclusion chromatography (GPC) was carried out with Bio-
beads S-X3 from the company Bio-Rad and distilled technical solvents.
Melting points (M.p.) were measured in open capillaries with a Büchi
Melting Point B540 apparatus and are uncorrected.“Decomp” refers to
decomposition.Some melting/decomposition points could not be deter-
mined due to the low stability of the compounds.Thermogravimetric
analysis (TGA) was carried out on a Mettler Toledo TGA/SDTA851e
under nitrogen flow, at a heating rate of 108C minꢀ1 between 208C and
7508C. 1H NMR and 13C NMR spectra were measured on a Varian
Gemini 300 MHz or a Varian Gemini 500 MHz spectrometer at 208C.
Chemical shifts are reported in ppm downfield from SiMe4, with the sol-
ventꢀs residual signal as an internal reference.Coupling constants ( J) are
tometer, MoKa radiation, l=0.7107 Š, m=0.296 mmꢀ1.A red crystal of
3
(linear dimensions ca. 0.18”0.16”0.13 mm) was obtained by slow diffu-
sion of hexane into a solution of compound 3 in CH2Cl2 at ꢀ158C.Num-
bers of measured and unique reflections were 9190 and 4925, respectively
(Rint =0.035). The iPr3Si group exhibited static disorder, which was re-
solved for C23, C25, C26, and C28 (not shown in Figure 1).Final R(F)=
0.082, wR(F2)=0.228 for 343 parameters and 3689 reflections with I>
2s(I) and 2.85<q<25.058 (corresponding R-values based on all 4925 re-
flections are 0.105 and 0.253, respectively).
X-ray crystalstructure of 12: Crystal data at 223(2) K for C24H20N6, Mr =
392.46, triclinic, space group P1 (no.2), 1calcd =1.214 gcmꢀ3, Z=2, a=
¯
8.8810(5), b=9.8950(7), c=13.6052(12) Š, a=82.105(4), b=86.857(3),
g=65.047(3)8, V=1073.71(14) Š3.Bruker-Nonius Kappa-CCD diffrac-
tometer, MoKa radiation, l=0.7107 Š, m=0.076 mmꢀ1.A black crystal of
12 (linear dimensions ca. 0.26”0.23”0.20 mm) was obtained by slow dif-
fusion of hexane into a solution of compound 12 in CH2Cl2 at ꢀ158C.
Numbers of measured and unique reflections were 6809 and 4124, respec-
tively (Rint =0.022). Final R(F)=0.050, wR(F2)=0.121 for 296 parameters
and 3348 reflections with I>2s(I) and 2.53<q<26.018 (corresponding R
values based on all 4124 reflections are 0.064 and 0.130, respectively).
X-ray crystalstructure of 13.Crystal data at 223(2) K for C 15H8N4O, Mr =
260.25, monoclinic, space group P21/c (no.14), 1cald =1.316 gcmꢀ3, Z=4,
a=13.4460(7), b=13.3106(5), c=7.4402(3) Š, b=99.396(1)8, V=
Chem. Eur. J. 2006, 12, 1889 – 1905
ꢁ 2006 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
www.chemeurj.org
1901

F.Diederich et al.
1313.74(10) Š3.Bruker-Nonius Kappa-CCD diffractometer, Mo
radia-
(300 MHz, CDCl3): d=0.93 (d, J=8 Hz, 9H), 1.10 (d, J=8 Hz, 9H), 1.45
(sept, J=8 Hz, 3H), 2.65 (s, 6H), 7.31–7.62 ppm (m, 4H); IR (neat): n˜ =
2941, 2891, 2864, 2187, 2154, 1593, 1580, 1496, 1467, 1363, 1339, 1298,
1268, 1186, 1103, 1067, 995, 883, 814 cmꢀ1; HR-FT-MALDI-MS (3-HPA):
m/z calcd for C25H32N5Si+: 430.2427; found: 430.2430 [M+H]+.
Ka
tion, l=0.7107 Š, m=0.088 mmꢀ1.A red crystal of 13 (linear dimensions
ca. 0.21”0.13”0.04 mm) was obtained by slow diffusion of hexane into a
solution of compound 13 in CH2Cl2 at ꢀ158C.Numbers of measured and
unique reflections are 4005 and 2359, respectively (Rint =0.044). Final
R(F)=0.060, wR(F2)=0.150 for 191 parameters and 1797 reflections with
I>2s(I) and 3.07 < q < 25.408 (corresponding R-values based on all
2359 reflections are 0.080 and 0.160, respectively).
2-[4-(Dimethylamino)-2-ethynylphenyl]ethylene-1,1,2-tricarbonitrile (5):
A mixture of 26 (60 mg, 0.41 mmol) and TCNE (106 mg, 0.826 mmol)
was stirred for 30 min at 708C.After cooling to 20 8C, CC (CH2Cl2) af-
forded 5 (70 mg, 69%) as a purple solid.Mp..195–196
8C; 1H NMR
X-ray crystalstructure of 14: Crystal data at 223(2) K for C22H14N4O2,
Mr =366.37, monoclinic, space group C2/c (no.15), 1calcd =1.302 gcmꢀ3
,
(300 MHz, CDCl3): d=3.15 (s, 6H), 3.57 (s, 1H), 6.72 (dd, J=3, 9 Hz,
1H), 6.92 (d, J=3 Hz, 1H), 7.58 ppm (d, J=9 Hz, 1H); 13C NMR
(75 MHz, CDCl3): d=40.36, 80.48, 87.12, 89.42, 112.16, 112.40, 112.49,
113.83, 117.77, 117.85, 124.72, 132.53, 140.13, 153.51 ppm; IR (neat): n˜ =
3238, 2916, 2226, 2218, 2104, 1593, 1519, 1494, 1438, 1372, 1321, 1271,
1229, 1201, 1109, 1062, 956, 899, 863, 844, 807 cmꢀ1; UV/Vis (CH2Cl2): l
(e)=273 (12000), 333 (sh, 6000), 529 nm (22500); EI-MS (70 eV): m/z:
246 [M]+; elemental analysis calcd (%) for C15H10N4 (246.27): C 73.16, H
4.09, N 22.75; found: C 72.15, H 4.07, N 22.37.
Z=8, a=14.9643(3), b=12.8404(3), c=19.4643(4) Š, b=92.113(1)8, V=
3737.48(14) Š3.Bruker-Nonius Kappa-CCD diffractometer, Mo
radia-
Ka
tion, l=0.7107 Š, m=0.087 mmꢀ1.A yellow crystal of 14 (linear dimen-
sions ca. 0.21”0.18”0.17 mm) was obtained by slow diffusion of hexane
into a solution of compound 14 in CH2Cl2 at ꢀ158C.Numbers of mea-
sured and unique reflections are 6835 and 3796, respectively (Rint
=
0.016). Final R(F)=0.042, wR(F2)=0.112 for 270 parameters and 3259
reflections with I>2s(I) and 2.09<q<26.398 (corresponding R values
based on all 3796 reflections are 0.050 and 0.120, respectively).
2-{4-(Dimethylamino)-2-[(triisopropylsilyl)ethynyl]phenyl}ethylene-1,1,2-
tricarbonitrile (6): A mixture of 27 (113 mg, 0.375 mmol) and TCNE
(95 mg, 0.74 mmol) was stirred for 30 min at 708C.After cooling to 20 8C,
CC (CH2Cl2) afforded 6 (103 mg, 68%) as a purple solid.Mp. .70–71 8C;
1H NMR (300 MHz, CDCl3): d=1.13–1.18 (m, 21H), 3.14 (s, 6H), 6.69
(dd, J=3, 9 Hz, 1H), 6.86 (d, J=3 Hz, 1H), 7.51 ppm (d, J=9 Hz, 1H);
13C NMR (75 MHz, CDCl3): d=11.42, 18.85, 40.33, 89.55, 102.72, 103.18,
111.78, 112.32, 112.51, 113.95, 117.55, 117.91, 126.09, 132.26, 140.52,
153.50 ppm; IR (neat): n˜ =2944, 2864, 2226, 2216, 1592, 1486, 1376, 1323,
1269, 1218, 1201, 1119, 1064, 1017, 998, 970, 905, 882, 851, 805 cmꢀ1; UV/
Vis (CH2Cl2): l (e)=260 (17200), 275 (sh, 8000), 340 (sh, 3400), 384
(1300), 533 nm (15900); EI-MS (70 eV): m/z: 402 [M]+; HR-FT-MALDI-
MS (3-HPA): m/z calcd for C24H31N4Si+: 403.2318; found: 403.2320
[M+H]+; elemental analysis calcd (%) for C24H30N4Si (402.61): C 71.60,
H 7.51, N 13.92; found: C 71.89, H 7.61, N 13.67.
X-ray crystalstructure of 17: Crystal data at 203(2) K for C16H6N4S2, Mr =
318.37, triclinic, space group P1 (no.2), 1calcd =1.429 gcmꢀ3, Z=2, a=
¯
8.4001(2), b=8.5650(2), c=10.8960(3) Š, a=81.033(2), b=81.365(1), g=
74.127(1)8, V=740.04(3) Š3.Bruker-Nonius Kappa-CCD diffractometer,
MoKa radiation, l=0.7107 Š, m=0.359 mmꢀ1.A yellow crystal of 17
(linear dimensions ca. 0.25”0.23”0.19 mm) was obtained by slow diffu-
sion of hexane into a solution of compound 17 in CH2Cl2 at ꢀ158C.
Numbers of measured and unique reflections are 5773 and 3367, respec-
tively (Rint =0.018). Final R(F)=0.033, wR(F2)=0.094 for 208 parameters
and 2996 reflections with I>2s(I) and 2.54<q<27.478 (corresponding
R-values based on all 3367 reflections are 0.038 and 0.098, respectively).
CCDC-274233 (3), CCDC-274235 (12), CCDC-274231 (13), CCDC-
274232 (14), and CCDC-274234 (17) contain the supplementary crystallo-
graphic data for this paper.These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif. The crystal structures of 2, 10, and 11 are described
in reference [7].
2-{[4-(Dimethylamino)phenyl]ethynyl}buta-1,3-diene-1,1,4,4-tetracarboni-
trile (7): TCNE (76 mg, 0.59 mmol) was added to a solution of 28
(100 mg, 0.591 mmol) in CH2Cl2 (3 mL).The mixture was stirred for 1 h
at 208C.Evaporation and CC (CH 2Cl2) afforded 7 (15 mg, 8.4%) as a
blue solid. 1H NMR (300 MHz, C2D2Cl4): d=3.13 (s, 6H), 6.70 (d, J=
9 Hz, 2H), 7.64 (d, J=9 Hz, 2H), 7.70 ppm (s, 1H); 13C NMR (75 MHz,
C2D2Cl4): d=40.38, 88.43, 88.80, 94.03, 105.11, 109.95, 112.04, 112.24,
112.41, 113.24, 128.05, 136.16, 139.76, 148.49, 153.33 ppm; IR (neat): n˜ =
2921, 2851, 2151, 1740, 1598, 1534, 1465, 1391, 1372, 1257, 1193, 1166,
1136, 972, 820 cmꢀ1; UV/Vis (CH2Cl2): l (e)=290 (11800), 299 (12000),
367 (22000), 698 nm (12600); HR-FT-MALDI-MS (3-HPA): m/z calcd
for C18H10N5+: 296.0936; found: 296.0935 [MꢀH]+.
2-[4-(Dimethylamino)phenyl]buta-1,3-diene-1,1,4,4-tetracarbonitrile (2):
A solution of TCNE (176 mg, 1.37 mmol) in C6H6 (15 mL) was added to
22 (200 mg, 1.38 mmol). The mixture was stirred for 2.5 h at 208C.Evap-
oration and CC (CH2Cl2) afforded 2 (364 mg, 97%) as a purple solid.
M.p. 144–1458C; 1H NMR (300 MHz, CDCl3): d=3.16 (s, 6H), 6.75 (d,
J=9 Hz, 2H), 7.51 (d, J=9 Hz, 2H), 8.02 ppm (s, 1H); 13C NMR
(75 MHz, CDCl3): d=40.26, 77.98, 97.19, 109.06, 111.51, 112.10, 113.13,
113.74, 117.66, 132.11, 154.32, 156.67, 158.81 ppm; IR (neat): n˜ =3028,
2921, 2212, 1600, 1486, 1435, 1379, 1346, 1294, 1212, 1172, 942, 821 cmꢀ1
;
UV/Vis (CH2Cl2): l (e)=343 (10200), 481 (7000), 570 nm (4900); EI-MS
(70 eV): m/z: 273 [M]+; elemental analysis calcd (%) for C16H11N5
(273.29): C 70.32, H 4.06, N 25.63; found: C 70.13, H 4.08, N 25.35.
2-[4-(Dimethylamino)phenyl]-3-[(trimethylsilyl)ethynyl]buta-1,3-diene-
1,1,4,4-tetracarbonitrile (8): TCNE (62 mg, 0.48 mmol) was added to a so-
lution of 29 (116 mg, 0.481 mmol) in CH2Cl2 (5 mL).The mixture was
stirred for 1 h at 208C.Evaporation and CC (CH Cl2) afforded 8 (26 mg,
2-[4-(Dimethylamino)phenyl]-3-(triisopropylsilyl)buta-1,3-diene-1,1,4,4-
tetracarbonitrile (3): TCNE (45 mg, 0.35 mmol) was added to a solution
of 24 (105 mg, 0.348 mmol) in CH2Cl2 (3 mL).The mixture was stirred
2
15%) as a brown solid.Mp..150–151 8C (decomp); 1H NMR (300 MHz,
CDCl3): d=0.31 (s, 9H), 3.18 (s, 6H), 6.74 (d, J=10 Hz, 2H), 7.72 ppm
(d, J=10 Hz, 2H); 13C NMR (75 MHz, CDCl3): d=ꢀ0.76, 40.43, 74.43,
97.29, 97.83, 110.09, 111.15, 112.31, 113.27, 114.43, 117.55, 128.06, 132.60,
150.94, 154.73, 159.87 ppm; IR (neat): n˜ =2901, 2214, 1607, 1552, 1494,
for 1 h at 208C.Evaporation and CC (CH Cl2) afforded 3 (117 mg, 78%)
2
as a red solid.Mp. .175–177 8C; 1H NMR (300 MHz, CDCl3): d=1.10 (d,
J=7 Hz, 9H), 1.13 (d, J=7 Hz, 9H), 1.47 (sept, J=7 Hz, 3H), 3.13 (s,
6H), 6.72 (d, J=9 Hz, 2H), 7.53 ppm (d, J=9 Hz, 2H); 13C NMR
(75 MHz, CDCl3): d=12.42, 18.92, 18.95, 40.27, 74.85, 99.92, 110.94,
111.99, 112.98, 113.88, 114.14, 115.25, 131.67, 154.33, 169.58, 180.88 ppm;
IR (neat): n˜ =2959, 2874, 2212, 1769, 1740, 1698, 1592, 1486, 1431, 1391,
1336, 1294, 1239, 1209, 1167, 1086, 1069, 1038, 1006, 945, 929, 902, 872,
813 cmꢀ1; UV/Vis (CH2Cl2): l (e)=252 (13500), 415 (sh, 15800), 454 nm
(19700); HR-FT-MALDI-MS (DHB): m/z: calcd for C25H32N5Si+:
430.2427; found: 430.2423 [M+H]+; elemental analysis calcd (%) for
C25H31N5Si (429.63): C 69.89, H 7.27, N 16.30; found: C 69.67, H 7.19, N
16.05.
1439, 1385, 1349, 1307, 1249, 1214, 1174, 1064, 1023, 943, 845, 821 cmꢀ1
;
UV/Vis (CH2Cl2): l (e)=302 (18700), 438 (23100), 457 nm (22900); ESI-
MS: m/z: 370.2 [M+H]+; elemental analysis calcd (%) for C21H19N5Si
(369.49): C 68.26, H 5.18, N 18.95; found: C 68.62, H 4.72, N 18.96.
2-[4-(Dimethylamino)phenyl]-3-[(triisopropylsilyl)ethynyl]buta-1,3-
diene-1,1,4,4-tetracarbonitrile (9): TCNE (118 mg, 0.921 mmol) was
added to a solution of 30 (300 mg, 0.921 mmol) in CH2Cl2 (10 mL).The
mixture was stirred for 1 h at 208C.Evaporation and CC (CH 2Cl2) af-
forded 9 (323 mg, 77%) as a black solid. M.p. 134.9–135.68C; 1H NMR
(300 MHz, CDCl3): d=1.07–1.22 (m, 21H), 3.17 (s, 6H), 6.73 (d, J=
9 Hz, 2H), 7.73 ppm (d, J=9 Hz, 2H); 13C NMR (75 MHz, CDCl3): d=
11.25, 18.71, 40.44, 74.02, 96.82, 100.06, 110.20, 111.24, 112.32, 113.32,
114.43, 117.43, 126.74, 132.55, 150.97, 154.77, 160.22 ppm; IR (neat): n˜ =
2943, 2865, 2216, 2129, 1608, 1538, 1498, 1462, 1441, 1385, 1349, 1310,
2-[2-(Dimethylamino)phenyl]-3-(triisopropylsilyl)buta-1,3-diene-1,1,4,4-
tetracarbonitrile (4): A mixture of 25 (100 mg, 0.332 mmol) and TCNE
(44 mg, 0.34 mmol) was stirred for 30 min at 708C.After cooling to 20 8C,
CC (CH2Cl2) afforded
4 (39 mg, 27%) as a
red solid. 1H NMR
1902
www.chemeurj.org
ꢁ 2006 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
Chem. Eur. J. 2006, 12, 1889 – 1905

Donor–Acceptor Systems
FULL PAPER
1253, 1213, 1175, 1158, 1064, 1018, 997, 947, 918, 880, 817 cmꢀ1; UV/Vis
(CH2Cl2): l (e)=263 (14800), 312 (15500), 434 (22800), 469 (sh, 19600),
550 nm (sh, 6400); HR-FT-MALDI-MS (3-HPA): m/z calcd for
C27H31N5Si+: 453.2349; found: 453.2319 [M]+; elemental analysis calcd
(%) for C27H31N5Si (453.65): C 71.48, H 6.89, N 15.44; found: C 71.72, H
6.98, N 15.39.
0.747 mmol) in toluene (10 mL). The mixture was heated to reflux for
12 h.After cooling to 20 8C, the solvent was evaporated.CC (CH Cl2) af-
2
1
forded 14 (116 mg, 42%) as a yellow solid. M.p. 213.4–213.98C; H NMR
(300 MHz, CDCl3): d=3.92 (s, 6H), 7.04 (d, J=9 Hz, 4H), 7.77 ppm (d,
J=9 Hz, 4H); 13C NMR (75 MHz, CDCl3): d=55.97, 82.92, 111.64,
112.48, 115.53, 123.58, 132.02, 164.80, 166.15 ppm; IR (neat): n˜ =2933,
2844, 2224, 1598, 1568, 1532, 1504, 1457, 1438, 1344, 1312, 1272, 1253,
1193, 1173, 1122, 1021, 848, 836 cmꢀ1; UV/Vis (CH2Cl2): l (e)=327 (sh,
18900), 380 nm (29300); EI-MS (70 eV): m/z: 366 [M]+; elemental analy-
sis calcd (%) for C22H14N4O2 (366.37): C 72.12, H 3.85, N 15.29; found: C
69.68, H 3.93, N 14.63.
2,3-Bis[4-(dimethylamino)phenyl]buta-1,3-diene-1,1,4,4-tetracarbonitrile
(10): A solution of TCNE (24 mg, 0.19 mmol) in THF (2.0 mL) was
added to a solution of 31 (50 mg, 0.19 mmol) in THF (5.0 mL). The mix-
ture was stirred for 1 h at 208C.Filtration through a plug (CH 2Cl2) fol-
lowed by removal of the solvent in vacuo afforded 10 (76 mg, 100%) as a
red solid. M.p. 273.5–274.68C; 1H NMR (300 MHz, CDCl3): d=3.14 (s,
12H), 6.69 (d, J=9 Hz, 4H), 7.79 ppm (d, J=9 Hz, 4H); 13C NMR
(75 MHz, CDCl3): d=40.14, 74.81, 111.85, 113.38, 114.59, 118.79, 132.44,
154.01, 165.38 ppm; IR (neat): n˜ =3076, 2921, 2853, 2206, 1597, 1455,
1428, 1377, 1353, 1322, 1286, 1168, 1062, 942, 818 cmꢀ1; UV/Vis (CH2Cl2):
l (e)=278 (10400), 311 (sh, 5100), 323 (sh, 3400), 390 (sh, 17900),
470 nm (55000); HR-ESI-MS: m/z calcd for C24H21N6+: 393.1828; found:
393.1822 [M+H]+, calcd for C24H20N6Na+: 415.1647; found: 415.1635
[M+Na]+; elemental analysis calcd (%) for C24H20N6 (392.46): C 73.45, H
5.14, N 21.41; found: C 70.99, H 5.18, N 20.00.
2-(4-Methoxyphenyl)-3-[(4-methoxyphenyl)ethynyl]buta-1,3-diene-
1,1,4,4-tetracarbonitrile (15): A mixture of 36 (208 mg, 0.792 mmol) and
TCNE (102 mg, 0.796 mmol) was stirred for 10 min at 1708C.After cool-
ing to 208C, CC (CH2Cl2) afforded 15 (36 mg, 12%) as an orange solid.
M.p. 52–548C; 1H NMR (300 MHz, CDCl3): d=3.88 (s, 3H), 3.93 (s,
3H), 6.95 (d, J=9 Hz, 2H), 7.07 (d, J=9 Hz, 2H), 7.59 (d, J=9 Hz, 2H),
7.79 ppm (d, J=9 Hz, 2H); 13C NMR (75 MHz, CDCl3): d=55.79, 56.00,
82.98, 86.62, 92.36, 110.36, 110.96, 111.55, 112.45, 114.95, 115.46, 120.96,
123.01, 132.01, 135.95, 148.96, 162.59, 163.53, 164.88 ppm; IR (neat): n˜ =
2924, 2851, 2228, 2155, 1738, 1598, 1568, 1505, 1462, 1362, 1301, 1256,
1172, 1120, 1021, 833, 802 cmꢀ1; UV/Vis (CH2Cl2): l (e)=332 (17400),
425 nm (25900); EI-MS (70 eV): m/z: 390 [M]+; elemental analysis calcd
(%) for C24H14N4O2 (390.39): C 73.84, H 3.61, N 14.35; found: C 73.84, H
3.56, N 14.07.
2-[4-(Dimethylamino)phenyl]-3-{[4-(dimethylamino)phenyl]ethynyl}buta-
1,3-diene-1,1,4,4-tetracarbonitrile (11): TCNE (114 mg, 0.890 mmol) was
added to a solution of 32 (257 mg, 0.891 mmol) in CH2Cl2 (15 mL).The
mixture was stirred for 2 h at 208C.Evaporation and CC (CH 2Cl2) af-
forded 11 (354 mg, 96%) as a black solid.Mp..191–193
8C; 1H NMR
2-Phenyl-3-(2-thienyl)buta-1,3-diene-1,1,4,4-tetracarbonitrile (16): A mix-
ture of 37 (115 mg, 0.624 mmol) and TCNE (240 mg, 1.87 mmol) was stir-
red for 8 h at 1508C.After cooling to 20 8C, CC (CH2Cl2) afforded 16
(155 mg, 80%) as a red solid. M.p. 207.8–208.38C; 1H NMR (300 MHz,
C2D2Cl4): d=7.35 (dd, J=4, 5 Hz, 1H), 7.58–7.76 (m, 5H), 7.88 (dd, J=
1, 4 Hz, 1H), 8.05 ppm (dd, J=1, 5 Hz, 1H); 13C NMR (75 MHz,
C2D2Cl4): d=73.84, 79.52, 87.08, 110.70, 111.29, 112.11, 128.93, 129.86,
130.04, 130.28, 133.93, 134.85, 137.38, 138.83, 157.45, 166.27 ppm; IR
(neat): n˜ =3097, 2948, 2229, 1592, 1576, 1532, 1493, 1444, 1401, 1364,
(300 MHz, CDCl3): d=3.10 (s, 6H), 3.15 (s, 6H), 6.64 (d, J=9 Hz, 2H),
6.72 (d, J=9 Hz, 2H), 7.48 (d, J=9 Hz, 2H), 7.82 ppm (d, J=9 Hz, 2H);
13C NMR (75 MHz, CDCl3): d=40.29, 40.33, 74.38, 87.80, 90.42, 105.39,
111.71, 111.97, 112.12, 112.87, 113.55, 114.77, 117.93, 125.76, 132.70,
136.28, 150.15, 153.22, 154.53, 161.68 ppm; IR (neat): n˜ =2917, 2217,
2122, 1598, 1538, 1479, 1435, 1372, 1329, 1295, 1210, 1171, 1113, 1063,
941, 808 cmꢀ1; UV/Vis (CH2Cl2): l (e)=279 (13800), 430 (sh, 20800), 464
+
(sh, 25600), 526 nm (38100); HR-ESI-MS: m/z calcd for C26H21N6
:
417.1828; found: 417.1822 [M+H]+; calcd for C26H20N6Na+: 439.1647;
found: 439.1637 [M+Na]+; elemental analysis calcd (%) for C26H20N6
(416.48): C 74.98, H 4.84, N 20.18; found: C 74.98, H 4.90, N 20.12.
1347, 1257, 1236, 1207, 1180, 1110, 1068, 1030, 999, 869, 847, 826 cmꢀ1
;
UV/Vis (CH2Cl2): l (e)=316 (17500), 366 nm (15800); EI-MS (70 eV):
m/z: 312 [M]+; elemental analysis calcd (%) for C18H8N4S (312.35): C
69.22, H 2.58, N 17.94; found: C 66.96, H 2.49, N 16.94.
2-[2-(Dimethylamino)phenyl]-3-[3-(dimethylamino)phenyl]buta-1,3-
diene-1,1,4,4-tetracarbonitrile (12): TCNE (7.0 mg, 0.055 mmol) was
added to a solution of 33 (11.5 mg, 0.0435 mmol) in CH2Cl2 (1 mL).The
2,3-Di-2-thienylbuta-1,3-diene-1,1,4,4-tetracarbonitrile (17): A mixture of
38 (80 mg, 0.42 mmol) and TCNE (162 mg, 1.26 mmol) was stirred for
14 h at 1508C.After cooling to 20 8C, CC (CH2Cl2) afforded 17 (107 mg,
80%) as an orange solid. M.p. 202.4–204.08C; 1H NMR (300 MHz,
CDCl3): d=7.31 (dd, J=4, 5 Hz, 2H), 7.86 (dd, J=1, 4 Hz, 2H),
7.99 ppm (dd, J=1, 5 Hz, 2H); 13C NMR (75 MHz, CDCl3): d=80.62,
111.23, 112.22, 129.97, 134.32, 137.51, 138.56, 156.93 ppm; IR (neat): n˜ =
3081, 2948, 2224, 1523, 1403, 1341, 1240, 1071, 1006, 862 cmꢀ1; UV/Vis
(CH2Cl2): l (e)=315 (16900), 369 nm (30100); EI-MS (70 eV): m/z: 318
[M]+; elemental analysis calcd (%) for C16H6N4S2 (318.38): C 60.36, H
1.90, N 17.60; found: C 60.06, H 1.90, N 17.46.
mixture was stirred for 30 min at 208C.Evaporation and CC (CH Cl2) af-
2
forded 12 (17.0 mg, 100%) as a red-brown solid. M.p. 185.9–186.68C;
1H NMR (300 MHz, CDCl3): d=2.72 (s, 6H), 2.92 (s, 6H), 6.53–7.21 (m,
6H), 7.48 (dt, J=2, 8 Hz, 1H), 7.55 ppm (dd, J=2, 8 Hz, 1H); 13C NMR
(75 MHz, CDCl3): d=40.42, 46.09, 87.65, 89.94, 111.71, 111.80, 112.39,
112.61, 112.89, 116.71, 116.84, 121.35, 124.72, 128.89, 129.93, 132.81,
132.94, 135.22, 150.43, 154.22, 167.24, 169.77 ppm; IR (neat): n˜ =2865,
2223, 1592, 1567, 1549, 1528, 1487, 1454, 1427, 1369, 1326, 1307, 1239,
1183, 1162, 1143, 1071, 1045, 1001, 944, 842 cmꢀ1; UV/Vis (CH2Cl2): l
(e)=260 (29200), 342 (8800), 481 nm (2500); EI-MS (70 eV): m/z: 392
[M]+; elemental analysis calcd (%) for C24H20N6 (392.46): C 73.45, H
5.14, N 21.41; found: C 72.27, H 5.28, N 20.63.
2-{4-{3,3-Dicyano-1-(dicyanomethylene)-2-[4-(dihexylamino)phenyl]prop-
2-en-1-yl}phenyl}-3-[4-(dihexylamino)phenyl]buta-1,3-diene-1,1,4,4-tetra-
carbonitrile (18): TCNE (30 mg, 0.23 mmol) was added to a solution of
39 (50 mg, 0.078 mmol) in CH2Cl2 (5 mL).The mixture was stirred for
2-(4-Methoxyphenyl)buta-1,3-diene-1,1,4,4-tetracarbonitrile (13): TCNE
(291 mg, 2.27 mmol) was added to a solution of 34 (300 mg, 2.27 mmol)
in C6H6 (11 mL).The mixture was heated to reflux for 5 h.After cooling
to 208C, the solution was passed through a plug (CH2Cl2) and the filtrate
was evaporated.Preparative GPC (CH 2Cl2) afforded 13 (190 mg, 32%)
3 h at 208C.Evaporation and CC (CH Cl2) afforded 18 (70 mg, 99%) as
2
a dark brown solid.Mp..232–234
8C; 1H NMR (300 MHz, CDCl3): d=
0.91 (t, J=7 Hz, 12H), 1.35 (m, 24H), 1.65 (m, 8H), 3.41 (t, J=8 Hz,
8H), 6.72 (d, J=9 Hz, 4H), 7.78 (d, J=9 Hz, 4H), 7.82 ppm (s, 4H);
13C NMR (75 MHz, CDCl3): d=14.22, 22.83, 26.87, 27.54, 31.73, 51.83,
72.15, 90.11, 110.97, 111.57, 112.87, 114.15, 114.55, 116.72, 130.47, 133.01,
136.24, 153.66, 160.87, 167.47 ppm; IR (neat): n˜ =2926, 2856, 2213, 1602,
1532, 1483, 1446, 1415, 1343, 1298, 1260, 1214, 1183, 1118, 1015, 977, 891,
1
as an orange solid. M.p. 181.5–183.48C; H NMR (300 MHz, CDCl3): d=
3.92 (s, 3H), 7.09 (d, J=9 Hz, 2H), 7.45 (d, J=9 Hz, 2H), 8.02 ppm (s,
1H); 13C NMR (75 MHz, CDCl3): d=55.85, 88.91, 98.04, 108.40, 111.13,
111.52, 111.69, 115.64, 122.22, 131.33, 153.21, 161.24, 164.43 ppm; IR
(neat): n˜ =3047, 2851, 2224, 1602, 1534, 1507, 1463, 1348, 1315, 1257,
1181, 1018, 837 cmꢀ1; UV/Vis (CH2Cl2): l (e)=288 (24100), 446 nm
(6200); EI-MS (70 eV): m/z: 260 [M]+; elemental analysis calcd (%) for
C15H8N4O (260.25): C 69.23, H 3.10, N 21.53, O 6.15; found: C 69.08, H
3.27, N 21.51, O 6.32.
819 cmꢀ1
; UV/Vis (CH2Cl2): l (e)=254 (24900), 281 (21600), 346
(31700), 476 nm (99900); HR-FT-MALDI-MS (DHB): m/z: calcd for
C58H65N10+: 901.5394; found: 901.5372 [M+H]+; calcd for C58H64N10Na+:
923.5213; found: 923.5258 [M+Na]+; elemental analysis calcd (%) for
C58H64N10 (901.20): C 77.30, H 7.16, N 15.54; found: C 77.37, H 7.01, N
15.26.
2,3-Bis(4-methoxyphenyl)buta-1,3-diene-1,1,4,4-tetracarbonitrile
(14):
TCNE (96 mg, 0.75 mmol) was added to a solution of 35 (178 mg,
Chem. Eur. J. 2006, 12, 1889 – 1905
ꢁ 2006 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
www.chemeurj.org
1903

F.Diederich et al.
2-[4-(Dihexylamino)phenyl]-3-{2-{[4-(dihexylamino)phenyl]ethynyl}phe-
nyl}buta-1,3-diene-1,1,4,4-tetracarbonitrile (19): TCNE (26 mg,
[2] a) S.R. Marder, J.W. Perry, G. Bourhill, C.B. Gorman, B.G. Tie-
mann, K.Mansour, Science 1993, 261, 186–189; b) F.Meyers, S.R.
0.20 mmol) was added to a solution of 40 (132 mg, 0.21 mmol) in CH2Cl2
(13 mL).The mixture was stirred for 3 h at 20 8C.Evaporation and CC
(CH2Cl2) afforded 19 (61 mg, 39%) as a dark yellow solid.Mp. .43–45 8C;
1H NMR (300 MHz, CD2Cl2): d=0.92 (t, J=7 Hz, 12H), 1.34 (m, 24H),
1.56–1.65 (m, 8H), 3.29 (t, J=8 Hz, 4H), 3.38 (t, J=8 Hz, 4H), 6.61 (brs,
2H), 6.65 (d, J=9 Hz, 2H), 6.84 (dd, J=2, 6 Hz, 1H), 7.06 (brs, 2H),
7.29–7.40 (m, 2H), 7.82 (d, J=9 Hz, 2H), 8.29 ppm (dd, J=2, 6 Hz, 1H);
13C NMR (75 MHz, CD2Cl2): d=14.00, 14.04, 22.85, 22.93, 26.82, 26.99,
27.25, 27.36, 31.80, 31.91, 51.10, 51.41, 73.24, 82.90, 111.29, 111.67, 113.95,
115.10, 115.64, 118.08, 121.82, 126.17, 128.82, 132.21, 132.64, 133.98,
141.30, 143.15, 146.23, 149.65, 152.83, 162.43, 164.60 ppm; IR (neat): n˜ =
2926, 2855, 2214, 1599, 1516, 1486, 1456, 1411, 1354, 1322, 1296, 1257,
Marder, BM. .Pierce, JL. .BrØdas,
J. Am. Chem. Soc. 1994, 116,
10703–10714; c) RR. .Tykwinski, M.Schreiber, V.Gramlich, P.
Seiler, F.Diederich, Adv. Mater. 1996, 8, 226–231; d) R.Spreiter, C.
Bosshard, G.Knçpfle, P.Günter, R.R.Tykwinski, M.Schreiber, F.
Diederich, J. Phys. Chem. B 1998, 102, 29–32; e) R.R. Tykwinski,
U.Gubler, R.E.Martin, F.Diederich, C.Bosshard, P.Günter,
Phys. Chem. B 1998, 102, 4451–4465.
J.
[3] a) C.Bosshard, R.Spreiter, P.Günter, R.R.Tykwinski, M.Schreib-
er, F.Diederich, Adv. Mater. 1996, 8, 231–234; b) U.Gubler, R.
Spreiter, C.Bosshard, P.Günter, RR. .Tykwinski, F.Diederich,
Appl. Phys. Lett. 1998, 73, 2396–2398.
[4] a) N.N.P.Moonen, R.Gist, C.Boudon, J-.P.Gisselbrecht, P.Seiler,
1178, 1105, 816 cmꢀ1; UV/Vis (CH2Cl2): l (e)=278 (21400), 312 (24100),
T.Kawai, A.Kishioka, M.Gross, M.Irie, F.Diederich,
Biomol. Chem. 2003, 1, 2032–2034; b) N.N.P.Moonen, W.C.Pom-
erantz, R.Gist, C.Boudon, J-.P.Gisselbrecht, T.Kawai, A.Kishio-
Org.
+
442 nm (30000); HR-FT-MALDI-MS (3-HPA): m/z: calcd for C52H65N6
:
773.5271; found: 773.5252 [M+H]+; elemental analysis calcd (%) for
C52H64N6 (773.10): C 80.79, H 8.34, N 10.87; found: C 80.68, H 8.46, N
10.57.
ka, M.Gross, M.Irie, F.Diederich,
Chem. Eur. J. 2005, 11, 3325–
3341; c) J.C.May, J.H. Lim, I. Biaggio, N.N.P.Moonen, T. Michi-
nobu, F.Diederich, Opt. Lett. 2005, 30, 3057–3059.
[5] a) A.J. Fatiadi, Synthesis 1986, 249–284; b) A.J. Fatiadi, Synthesis
1987, 749–789; c) O.W. Webster, J. Polym. Sci. Part A 2002, 40,
210–221.
[6] N.N.P.Moonen, C.Boudon, J-.P.Gisselbrecht, P.Seiler, M.Gross,
F.Diederich, Angew. Chem. 2002, 114, 3170–3173; Angew. Chem.
Int. Ed. 2002, 41, 3044–3047.
[7] For a preliminary communication of parts of this work, including
some first NLO data, see: T. Michinobu, J.C. May, J.H. Lim, C.
Boudon, J-.P.Gisselbrecht, P.Seiler, M.Gross, I.Biaggio, F.Dieder-
ich, Chem. Commun. 2005, 737–739.
3,3’-(1,3-Phenylene)bis{2-[4-(dihexylamino)phenyl]buta-1,3-diene-1,1,4,4-
tetracarbonitrile} (20): TCNE (71 mg, 0.55 mmol) was added to a solution
of 41 (118 mg, 0.183 mmol) in CH2Cl2 (12 mL).The mixture was stirred
for 3 h at 208C.Evaporation and CC (CH 2Cl2) afforded 20 (142 mg,
86%) as a dark red solid.Mp..75–79
8C; 1H NMR (300 MHz, CDCl3):
d=0.92 (t, J=7 Hz, 12H), 1.35 (m, 24H), 1.65 (m, 8H), 3.41 (t, J=8 Hz,
8H), 6.70 (d, J=10 Hz, 4H), 7.70–7.76 (m, 6H), 8.01 ppm (d, J=8 Hz,
2H); 13C NMR (75 MHz, CDCl3): d=14.17, 22.70, 26.72, 27.37, 31.58,
51.63, 71.94, 89.66, 110.60, 111.30, 112.56, 112.65, 113.84, 114.25, 116.37,
130.38, 131.08, 132.59, 133.24, 153.27, 160.42, 167.28 ppm; IR (neat): n˜ =
2926, 2856, 2212, 1600, 1483, 1445, 1414, 1341, 1296, 1213, 1182, 1117,
976, 891, 819 cmꢀ1; UV/Vis (CH2Cl2): l (e)=273 (27800), 307 (30400),
[8] B.M.Trost, Science 1991, 254, 1471–1477.
[9] a) C.Cai, I.Liakatas, M-S. .Wong, M.Bçsch, C.Bosshard, P.
460 (54500), 466 nm (54200); HR-FT-MALDI-MS (DHB): m/z: calcd
+
for C58H65N10
:
901.5394; found: 901.5297 [M+H]+; calcd for
C58H64N10Na+: 923.5213; found: 923.5197 [M+Na]+; elemental analysis
calcd (%) for C58H64N10 (901.20): C 77.30, H 7.16, N 15.54; found: C
77.42, H 7.05, N 15.49.
Günter, S.Concilio, N.Tirelli, U.W.Suter,
1849; b) H.Ma, A.K-.Y.Jen, J.Wu, X.Wu, S.Liu, C-.F.Shu, L.R.
Dalton, S.R. Marder, S. Thayumanavan, Chem. Mater. 1999, 11,
2218–2225; c) X.Wu, J.Wu, Y.Liu, A.K-.Y.Jen,
Org. Lett. 1999, 1, 1847–
J. Am. Chem. Soc.
3,3’,3’’-Benzene-1,3,5-triyltris{2-[4-(dihexylamino)phenyl]buta-1,3-diene-
1,1,4,4-tetracarbonitrile} (21): TCNE (50 mg, 0.39 mmol) was added to a
solution of 42 (80 mg, 0.086 mmol) in CH2Cl2 (10 mL).The mixture was
stirred for 3 h at 208C.Evaporation and CC (CH 2Cl2) afforded 21
(97 mg, 86%) as a dark brown solid.Mp. .88–90 8C; 1H NMR (300 MHz,
CDCl3): d=0.92 (t, J=7 Hz, 18H), 1.36 (m, 36H), 1.67 (m, 12H), 3.43 (t,
J=8 Hz, 12H), 6.74 (d, J=9 Hz, 6H), 7.72 (d, J=9 Hz, 6H), 8.01 ppm (s,
3H); 13C NMR (75 MHz, CDCl3): d=14.23, 22.83, 26.87, 27.54, 31.73,
51.90, 72.34, 91.82, 110.37, 111.13, 113.28, 114.21, 114.29, 116.80, 132.97,
133.54, 135.02, 153.87, 159.69, 166.37 ppm; IR (neat): n˜ =2926, 2855,
2212, 1601, 1483, 1445, 1415, 1339, 1296, 1212, 1183, 1103, 979, 888,
1999, 121, 472–473; d) H.Ma, B.Chen, T.Sassa, LR. .Dalton,
A.K-.Y.Jen, J. Am. Chem. Soc. 2001, 123, 986–987; e) A.Galvan-
Gonzalez, G.I.Stegeman, A.K-.Y.Jen, X.Wu, M.Canva, A.C.Ko-
walczyk, X.Q.Zhang, H.S.Lackritz, S.Marder, S.Thayumanavan,
G.Levina, J. Opt. Soc. Am. B 2001, 18, 1846–1853; f) J.Luo, H.Ma,
M.Haller, A.K-.Y.Jen, R.R.Barto,
889; g) Y.V.Pereverzev, O.V.Prezhdo, L.R.Dalton,
Chem. Commun. 2002, 888–
Chem. Phys.
Lett. 2003, 373, 207–212; h) V.Mamane, I.Ledoux-Rak, S.Deveau,
J.Zyss, O.Riant, Synthesis 2003, 455–467; i) Y.Morioka, N.Yoshi-
zawa, J.-i. Nishida, Y. Yamashita, Chem. Lett. 2004, 33, 1190–1191.
822 cmꢀ1
; UV/Vis (CH2Cl2): l (e)=254 (41400), 292 (47100), 463
[10] a) M.I. Bruce, J.R. Rodgers, M.R. Snow, A.G. Swincer,
Soc. Chem. Commun. 1981, 271–272; b) M.I.Bruce, T.W.Hambley,
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Received: September 8, 2005
Published online: January 3, 2006
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1905