Donor-substituted cyanoethynylethenes: Powerful chromophores for opto-electronic applications

Article abstract of DOI:10.1039/b303879c

A comprehensive series of N,N-dimethylanilino- (DMA) substituted cyanoethynylethenes (CEEs) were considered. The electronic properties of the CEEs were compared with those of donor-(DMA) acceptor-(p-nitrophenyl) substituted tetraethynylethene (TEE) analog

Full text of DOI:10.1039/b303879c

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Donor-substituted cyanoethynylethenes: powerful chromophores for
opto-electronic applications†
a
a
b
b
a
Nicolle N. P. Moonen, Robin Gist, Corinne Boudon, Jean-Paul Gisselbrecht, Paul Seiler,
c
c
b
c
a
Tsuyoshi Kawai, Atsushi Kishioka, Maurice Gross, Masahiro Irie and François Diederich*
Laboratorium für Organische Chemie, ETH-Hönggerberg, HCI, CH-8093 Zürich,
a
Switzerland. E-mail: diederich@org.chem.ethz.ch
b
Laboratoire d’Electrochimie et de Chimie Physique du Corps Solide, UMR 7512, C. N. R. S.,
Université Louis Pasteur, 4, rue Blaise Pascal, F-67000 Strasbourg, France
Department of Chemistry and Biochemistry, Graduate School of Engineering,
Kyushu University, Hakozaki 6-10-1, Higashiku, Fukuoka 812-8581, Japan
c
Received 7th April 2003, Accepted 12th May 2003
First published as an Advance Article on the web 15th May 2003
Donor-substituted cyanoethynylethenes (CEEs) were
synthesised, structurally characterised and investigated
for their electronic and two-photon absorption properties,
revealing exceptionally strong intramolecular charge-
transfer interactions.
Recently, we reported the extension of the family of the
1,2
cyanoethynylethenes (CEEs)
and showed their powerful
electron accepting properties, compared to their isoelectronic
tetraethynylethene (TEE) analogues. In order to enhance their
non-linear optical (NLO) and two-photon absorption (TPA)
properties, we decided to introduce electron-donating groups
into these systems, thereby creating strong donor–acceptor
chromophores. From several structure–property relationship
studies it has been concluded that donor and acceptor substi-
tution of conjugated molecules is essential for the improvement
3
of TPA properties. A similar conclusion was reached for the
enhancement of the NLO properties by a systematic study on
4
the donor-acceptor substituted TEEs, which were found to be
5
6
highly active second- and third-order NLO chromophores.
Here we present a comprehensive series of N,N-dimethyl-
anilino- (DMA) substituted CEEs 1–7 (Fig. 1) and compare
their electronic properties with those of donor–(DMA)
acceptor-(p-nitrophenyl) substituted TEE analogues (for some
TEE structures, see ESI†). Furthermore, a first TPA cross-
section value will be reported.
Donor-substituted CEEs 1–4‡ were synthesised by a Knoe-
venagel reaction from the corresponding ketones 8–10 with
i
Pr SiC᎐C–CH
᎐
–CN or malononitrile, respectively (Scheme 1).
3
2
The Z- and E-isomers 1 and 2 were both obtained in a single
reaction step and could be separated by flash chromatography
Fig. 1 New donor-substituted cyanoethynylethenes (CEEs).
(
SiO , CH Cl –hexane 2 : 1) in the dark. Soft deprotection
2 2 2
1
of 3 in a MeOH–THF solution, in the absence of base, and
be expressed by the quinoid character (δr) of the ring defined
subsequent oxidative coupling under Hay conditions (CuCl,
7
by:
TMEDA, O ) resulted in dimer 7. Compound 5 was synthesised
2
by a Sonogashira cross-coupling of dibromofumaronitrile with
p-Me NC H C᎐CH in a yield of 53%.
2
6
4
1
Single crystals of 5 and 6 suitable for X-ray structure
analysis were grown by slow diffusion of hexane into a CH Cl2
2
In benzene, the δr value equals 0, whereas values between
.08 and 0.10 are found in fully quinoid rings (for the definition
of bonds a,aЈ,b,bЈ,c,cЈ see Fig. 2). CEE 5 exhibits a δr of 0.033
solution (Figs. 2 and 3). Both structures show a planar CEE
core and, in the case of 5, the phenyl rings are twisted out of
the main plane by ca. 14Њ. The bond length alternation in the
DMA rings is a good indication for the charge-transfer (CT)
from the DMA donor to the CEE acceptor moiety, which can
0
and 6 has a value of 0.037. In sharp contrast, the δr values for
8
DMA rings in donor–acceptor substituted TEEs, calculated
from several X-ray structures, generally do not exceed 0.025.
This clearly demonstrates the highly enhanced intramolecular
CT in the CEEs, as compared to the TEEs. The δr values calcu-
†
Electronic supplementary information (ESI) available: Crystal pack-
ing of 5, UV/Vis spectra of donor-acceptor-substituted TEEs in com-
parison to those of CEEs, full electrochemical data for the donor-
substituted CEEs and structure of the AF-50 standard for two-photon
absorption. See http://www.rsc.org/suppdata/ob/b3/b303879c/
9
lated at the B3LYP/6-31G** level of theory for 5 (0.032) and 6
(
0.038) are in good agreement with those determined from the
X-ray crystal structure data.
2
032
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 2 0 3 2 – 2 0 3 4
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3

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Table 1 Longest-wavelength absorption maxima from UV/Vis spectra
and potential difference Eox,1 Ϫ Ered,1 (HOMO–LUMO gap) measured
by cyclic voltammetry
a
Ϫ1
Ϫ1
b
λmax/nm (eV)
ε/M cm
Eox,1 Ϫ Ered,1/V
1
2
3
4
5
6
7
468 (2.65)
464 (2.67)
520 (2.38)
524 (2.37)
563 (2.20)
591 (2.10)
600 (2.07)
25000
24400
36700
47300
65900
43800
30700
2.20
2.20
1.91
1.94
1.88
1.65
1.43
a
b
Solvent: CHCl3. Cyclic voltammetry data in CH Cl (ϩ0.1 M
2
2
n-Bu NPF ); working electrode: glassy carbon electrode; counter elec-
4
6
Ϫ1
trode: Pt; reference electrode: Ag/AgCl. Scan rate: 0.1 V s . Potentials
vs. the ferrocene–ferricenium couple.
Fig. 3 a) ORTEP representation of 6 with vibrational ellipsoids
obtained at 243 K and shown at the 30% probability level. Selected
bond lengths (Å) and angles (Њ): C1–C2 1.392(2), C1–C6 1.401(2), C2–
C3 1.366(2), C3–C4 1.415(2), C4–C5 1.410(3), C4–N7 1.356(2), C5–C6
1
.370(2), C10–C11 1.209(2), C1–C10 1.410(2), C12–C15 1.365(3), C15–
C16 1.432(2), C16–N17 1.139(2), C1–C10–C11 179.17(18), C10–C11–
C12 177.93(19), C11–C12–C13 118.79(16), C16–C15–C18 119.90(16).
b) Crystal packing of 6, showing the donor–acceptor stacking of the
CEE core with the DMA donor.
i
Scheme 1 Synthesis of donor-substituted CEEs: i, Pr SiC᎐C–CH –
3
2
i
CN, Pr EtN, EtOH, 20 ЊC, 50% (1) and 30% (2); ii, CH (CN) , Al O
2
2
2
2
3
(
act. –), CH Cl , 40 ЊC, 77% (3), 65% (4); iii, MeOH–THF 1 : 1,
2 2
2
0 ЊC, then CuCl, TMEDA, CH Cl , O , 20 ЊC, 19%; iv) Me NC -
2 2 2 2 6
i
H C᎐CH, [PdCl (PPh ) ], CuI, Pr NH, THF, 52%.
4
2
3
2
2
Fig. 4 UV/Vis spectra of 1–7 in CHCl3.
longest-wavelength absorption bands was obtained by the
disappearance of the band upon protonation of the DMA
moieties with TFA and the reappearance upon deprotonation
Fig. 2 ORTEP representation of 5 with vibrational ellipsoids obtained
at 120 K and shown at the 30% probability level. Selected bond lengths
(
Å) and angles (Њ): C1–C1Ј 1.372(4), C1–C2 1.441(3), C2–N3 1.146(3),
with Et N. Increasing the number of cyano groups upon chang-
3
C1–C4 1.417(3), C4–C5 1.207(3), C6–C7 1.397(3), C6–C11 1.401(3),
C7–C8 1.370(3), C8–C9 1.410(3), C9–C10 1.411(3), C9–N12 1.368(2),
C10–C11 1.374(3), C2–C1–C4 118.51(18), C1–C4–C5 176.1(2), C4–
C5–C6 177.6(2).
ing from 1 to 3 to 6 results in a bathochromic shift of this
band. Interestingly, the CT band in the geminally bis-DMA-
substituted 4 is hypsochromically shifted by 43 nm (0.18 eV)
with respect to the corresponding absorption in the trans
derivative 5. A similar behaviour was observed in a series of
The crystal packing of 5 shows a slipped parallel stacking of
the chromophores, with a DMA ring centre-to-centre distance
of 3.95 Å (see ESI†), whereas 6 exhibits a favourable anti-
parallel dipolar alignment in the stacks, with the DMA donor
and the CEE acceptor moieties placed at a distance of 3.44 Å
8
DMA- p-nitrophenyl-substituted TEEs (see ESI†). Extension
of the conjugation from 3 to 7 results in a large red-shift of
80 nm (0.31 eV).
Interestingly, the DMA–CEE conjugates 3,4,6 and 7 are not
or only very weakly fluorescent, whereas 5 is highly fluorescent
(
Fig. 3b).
Further evidence for the pronounced CT-character of the
with a quantum yield of 0.58 in hexane–CHCl 95 : 5 (but not in
3
CEEs was obtained from their UV/Vis spectra (Fig. 4, Table 1).
Compared to the DMA- p-nitrophenyl-substituted TEEs, the
maximum of the lowest-energy band λmax of 4 and 5 is
bathochromically shifted by 30–38 nm (0.13–0.18 eV). Fur-
thermore, the CT-bands are much more dominant and the
molar absorption coefficients higher for the CEEs then for their
TEE analogues (see ESI†). Proof for the CT-character of the
pure CHCl or CH Cl ). The fluorescence quantum yields of 1
and 2 could not be accurately determined due to fast cis–trans
isomerisation of these compounds in hexane.
The difference between first oxidation potential and first
reduction potential, Eox,1 Ϫ Ered,1, determined by cyclic
voltammetry (Table 1) can be regarded as a measure for the
HOMO–LUMO gap. There exists a strong linear correlation
3
2
2
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 2 0 3 2 – 2 0 3 4
2033

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(
R = 0.97) between the Eox,1 Ϫ Ered,1 (V) and λmax values (in eV)
2 Previously reported CEEs: (a) H. Hopf and M. Kreutzer,
Angew. Chem., 1990, 102, 425–426 (Angew. Chem. Int. Ed., 1990,
of 1–6, indicating that both quantities represent the same
physical effect.
In order to obtain a first impression of the two-photon
absorption (TPA) properties of the new chromophores, the
TPA cross-section of CEE 4 was measured. A value of 8.8 ×
2
9, 393–395); (b) L. Yu. Ukhin, A. M. Sladkov and Zh. I.
Orlova, Bull. Acad. Sci. USSR, Div. Chem. Sci., 1969, 637–638;
c) L. Dulog, B. Körner, J. Heinze and J. Yang, Liebigs Ann., 1995,
663–1671.
(
1
3 (a) M. Albota, D. Beljonne, J. -L. Brédas, J. E. Ehrlich, J.-Y. Fu,
A. A. Heikal, S. E. Hess, T. Kogej, M. D. Levin, S. R. Marder,
D. McCord-Maughon, J. W. Perry, H. Röckel, M. Rumi, G. Subra-
maniam, W. W. Webb, X.-L. Wu and C. Xu, Science, 1998, 281,
Ϫ49
4
Ϫ1
1
0
cm s photon at 900 nm in 1,1,2,2-tetrachloroethane
was found, which is about three times higher than the value for
the AF-50 standard (3.0 × 10 cm s photon at 796 nm in
Ϫ49
4
Ϫ1
1
653–1656; (b) M. Rumi, J. E. Ehrlich, A. A. Heikal, J. W. Perry,
10
benzene, see ESI†), indicating the enormous potential of the
small CEE molecules for opto-electronic applications. In this
context of potential technological applications, it should be
noted that the new chromophores 5 and 6 can be sublimed
without decomposition under laboratory conditions (100–160
ЊC, 0.1 Torr), which is not possible with the corresponding
TEEs and could pave the way for the preparation of ultra-thin
films by vapor deposition.
S. Barlow, Z.-Y. Hu, D. McCord-Maughon, T. C. Parker, H. Röckel,
S. Thayumanavan, S. R. Marder, D. Beljonne and J.-L. Brédas,
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L. Yuan, G. S. He and P. N. Prasad, Chem. Mater., 1998, 10, 1863–
1
874.
4
5
U. Gubler and C. Bosshard, Adv. Polym. Sci., 2002, 158, 123–191.
R. Spreiter, C. Bosshard, G. Knöpfle, P. Günter, R. R. Tykwinski,
M. Schreiber and F. Diederich, J. Phys. Chem. B, 1998, 102,
2
9–32.
6
(a) R. R. Tykwinski, U. Gubler, R. E. Martin, F. Diederich,
C. Bosshard and P. Günter, J. Phys. Chem. B, 1998, 102, 4451–4465;
Acknowledgements
(
b) M. B. Nielsen, M. Schreiber, Y. G. Baek, P. Seiler, S. Lecomte,
Support by the ETH Research Council, the ERASMUS
exchange program (R. G.) and the German Fonds der
Chemischen Industrie is gratefully acknowledged.
C. Boudon, R. R. Tykwinski, J.-P. Gisselbrecht, V. Gramlich,
P. J. Skinner, C. Bosshard, P. Günter, M. Gross and F. Diederich,
Chem. Eur. J., 2001, 7, 3263–3280.
7
8
(a) A. Hilger, J.-P. Gisselbrecht, R. R. Tykwinski, C. Boudon,
M. Schreiber, R. E. Martin, H. P. Lüthi, M. Gross and F. Diederich,
J. Am. Chem. Soc., 1997, 119, 2069–2078; (b) C. Dehu, F. Meyers
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Tykwinski, M. Schreiber, V. Gramlich, P. Seiler and F. Diederich,
Adv. Mater., 1996, 8, 226–231.
Notes and references
1
13
‡
All new compounds were characterised by IR, UV/Vis, H and
NMR, elemental analysis or HR-MS. Crystal data of 5 at 120 K:
C H N , [M = 364.44]: monoclinic, space group P2 /n (no. 14),
C
2
4
20
4
r
1
Ϫ3
D = 1.237 g cm , Z = 2, a = 3.9477(2), b = 11.1064(4), c = 22.3725(9) Å,
β = 93.769(2)Њ, V = 978.79(7) Å . Bruker-Nonius Kappa-CCD, MoK
c
3
α
9 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery,
Jr., R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam,
A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi,
V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli,
C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala,
Q. Cui, K. Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavach-
ari, J. B. Foresman, J. Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
C. Gonzalez, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon,
E. S. Replogle and J. A. Pople, Gaussian 98, Revision A.7, Gaussian,
Inc., Pittsburgh PA, 1998 .
2
radiation, λ = 0.7107 Å. Final R(F) = 0.053, wR(F ) = 0.108 for 128
parameters and 2232 reflections with I > 2σ(I ) and 2.05 < θ < 27.52Њ
(
0
corresponding R-values based on all 4186 reflections are 0.108 and
.158, respectively). Crystal data of 6 at 243 K (C H N , M = 246.27):
1
5
10
4
r
Ϫ3
¯
triclinic, space group P1, D = 1.220 g cm , Z = 2, a = 7.014(1),
c
b = 7.085(1), c = 14.149(2) Å, α = 77.79 (2)Њ, β = 89.21(1)Њ, γ = 77.40(2)Њ,
3
V = 670.28(16) Å . Nonius CAD4 diffractometer, CuK radiation,
α
2
λ = 1.5418 Å. Final R(F) = 0.058, wR(F ) = 0.172 for 183 parameters
and 2631 reflections with I > 2σ(I ) and 3.20 < θ < 74.87Њ (corre-
sponding R-values based on all 2922 reflections are 0.064 and 0.179,
respectively). CCDC reference numbers 207516 and 207517. See http://
www.rsc.org/suppdata/ob/b3/b303879c/ for crystallographic data in .cif
or other electronic format.
1
0 The values vary depending on the monitoring wavelength and the
solvent used, see: O.-K. Kim, K.-S. Lee, H. Y. Woo, K.-S. Kim,
G. S. He, J. Swiatkiewicz and P. N. Prasad, Chem. Mater., 2000, 12,
284–286.
1
N. N. P. Moonen, C. Boudon, J.-P. Gisselbrecht, P. Seiler,
M. Gross and F. Diederich, Angew. Chem., 2002, 114, 3170–3173
(
Angew. Chem., Int. Ed., 2002, 41, 3044–3047).
2
034
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 2 0 3 2 – 2 0 3 4