Quadruple hydrogen bonded oligo(p-phenylene vinylene) dimers

Article abstract of DOI:10.1039/b005903j

Direct self-assembly of π-conjugated oligomers via self-complementary quadruple hydrogen bonding is achieved and the first steps towards supramolecular polymers with functional side chains are described.

Full text of DOI:10.1039/b005903j

Quadruple hydrogen bonded oligo(p-phenylene vinylene) dimers
Abdelkrim El-ghayoury, Emiel Peeters, Albertus P. H. J. Schenning and E. W. Meijer*
Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB
Eindhoven, The Netherlands
Received (in Cambridge, UK) 21st July 2000, Accepted 23rd August 2000
First published as an Advance Article on the web
Direct self-assembly of p-conjugated oligomers via self-
complementary quadruple hydrogen bonding is achieved
and the first steps towards supramolecular polymers with
functional side chains are described.
Conjugated polymers are investigated for a manifold of
electronic semiconductor applications.1 It is also widely
accepted that well-defined oligomers will play a crucial role in
the future advancement of p-conjugated materials, since their
precise chemical structure and conjugation length stand for
defined functional properties and facilitate enhanced control
over their supramolecular architecture.2,3 Synthetic efforts have
been mainly directed towards the synthesis of extended linear
conjugated oligomers of length of 5–10 nm, but cyclic,4
bicyclic,5 spiro6 and dendritic7 structures have also been
reported. Further, different p-conjugated functionalities have
been combined in a large number of well-defined donor–
acceptor molecules. The major challenge is now to obtain
control of the supramolecular ordering over length scales
extending into the macroscopic regime.8 Only a few examples
have been reported on spatial organization of functional p-
conjugated entities by making use of hydrogen bonding motifs.
Self-assembled fibers of mono and bisthiophene bisurea
compounds have been reported and showed efficient charge
transport within these fibers.9 Superstructure formation of p-
conjugated materials has also been obtained by hydrogen
bonding complexation of perylene bisimide derivatives with a
ditopic melamine compound10 and with chlorine singlet
excited-state electron donor and a naphthalene bisimide
acceptor.11
Scheme 1 Synthesis of OPV3UP. (a) di-tert-butyl tricarbonate, CH2Cl2,
100%; (b) 6-tridecylisocytosine, pyridine, 90 °C, 26%.
pyrimidinone units. These recent developments pave the way to
combine the specific electronic and optical properties of
conjugated oligomers with the material properties of polymers,
by incorporating well-defined p-conjugated moieties in these
supramolecular polymeric assemblies. Here we report on the
synthesis of the ureidopyrimidinone derivatives OPV3UP,
OPV4UP1 and OPV4UP2 (depicted in Schemes 1 and 2) and
on their supramolecular ordering.
Compound OPV3UP was prepared starting from the amino
functionalized oligomer. Using di-tert-butyl tricarbonate the
amine functionality was quantitatively converted to the iso-
cyanate 2.13 Reaction of 2 with 1.5 eq. of 6-tridecylisocytosine
Recently, we have reported supramolecular polymers which
exhibit real macroscopic polymeric properties.12 These poly-
meric systems are based on the strong dimerization of quadruple
hydrogen-bonding self-complementary 2-ureido-4[1H]-ureido-
Scheme 2 Synthesis of OPV4UP1 and OPV4UP2. (a) diethyl 4-cyanobenzylphosphonate, t-BuOK, DMF, 91%; (b) LiAlH4, Et2O, 93%; (c) COCl2, toluene,
100 °C, 100%; (d) 6-tridecylisocytosine, pyridine, 90 °C, 52%; (e) diethyl 4-(methylbenzoate)phosphonate, t-BuOK, DMF, THF; (f) KOH, EtOH, 80 °C,
100%; (g) (COCl)2, CH2Cl2, DMF, 100%; (h) MgCl2, Et3N, EtOAc, HCl aq., 30%; (i) (NH2)2CNNH·HCO3, EtOH, 90%; (j) n-C4H9NCO, pyridine,
90 °C.
DOI: 10.1039/b005903j
Chem. Commun., 2000, 1969–1970
This journal is © The Royal Society of Chemistry 2000
1969

In conclusion, directed self-assembly of p-conjugated oligo-
mers via self-complementary quadruple hydrogen bonding has
been achieved. It opens new possibilities for the design of
electronically active supramolecular materials in which the
specific properties of well-defined oligomers can be combined
with the material properties of polymers.
We thank Michel Fransen for the synthesis of the starting
materials, Joost van Dongen for MALDI-TOF MS measure-
ments, and Dr Rint Sijbesma for fruitful and helpful discus-
sions. This work has been supported by Netherlands Organiza-
tion for Scientific Research (NWO) and the Royal Netherlands
Academy of Arts and Sciences.
Notes and references
Fig. 1 1H-NMR spectra of OPV4UP1 recorded in CDCl3.
† Full synthetic details will be given elsewhere. All new compounds were
authenticated by 1H and 13C NMR, FT-IR, MALDI-TOF MS and elemental
analyses. Selected data: for OPV3UP: dN–H (CDCl3) 12.91, 12.35, 12.11,
MALDI-TOF MS (MW = 974.68) m/z = 974.77 [M]+, elemental analyses
C, 74.46 (75.11), H, 9.28 (9.30), N, 5.96 (5.74%); OPV4UP1: dN–H
(CDCl3) 13.06, 12.07, 10.89, MALDI-TOF MS (MW = 1629.28) m/z =
1629.89 [M]+, elemental analyses C, 77.68 (77.35), H, 10.77 (10.39), N,
3.26 (3.44%); OPV4UP2: dN–H (CDCl3) 13.91, 12.03, 10.29, MALDI-TOF
MS (MW = 1490.24) m/z = 1490.09 [M]+, elemental analyses C, 75.99
(76.60), H, 9.58 (10.00), N, 3.45 (3.80%); calculated values in parenthe-
sis.
in anhydrous pyridine at 90 °C afforded OPV3UP in 26% yield
after column chromatography. The low yield of OPV3UP is
probably due to the relatively low reactivity of aromatic
isocyanates. Therefore, benzylic isocyanates were used for the
preparation of OPV4UP1. To obtain the benzylic isocyanate,
aldehyde 3 was allowed to react with diethyl 4-cyanobenzyl-
phosphonate in a Wittig–Horner reaction to give the nitrile
compound in 91% yield. The nitrile functionality was subse-
quently reduced using LAH to afford the benzylic amine. The
pure compound was isolated after work-up and precipitation in
93% yield. The amine derivative was reacted with phosgene in
refluxing toluene to give the isocyanate. Reaction of the latter
with 6-tridecylisocytosine in anhydrous pyridine at 90 °C gave
OPV4UP1 in 52% yield. In order to obtain full conjugation
between the OPV and hydrogen bonding unit, OPV4UP2 was
synthesized. Reaction of aldehyde 3 with diethyl 4-(me-
thylbenzoate)phosphonate in a Wittig–Horner reaction afforded
a mixture of esters 5. Saponification of these esters gave
quantitatively the acid, which was quantitatively converted to
the acid chloride using oxalylchloride in DCM and DMF. The
b-ketoester was obtained in 30% yield by reaction of the acid
chloride with potassium ethylmalonate in presence of triethyla-
mine and magnesium chloride. Reaction of the b-ketoester with
guanidinium carbonate yielded quantitatively the isocytosine.
The desired compound OPV4UP2 was finally obtained in 90%
yield by reaction of the isocytosine and n-butylisocyanate in
anhydrous pyridine at 90 °C.
All the compounds OPV3UP, OPV4UP1 and OPV4UP2
were fully characterized.† These p-conjugated oligomers form
quadruple hydrogen bonded DDAA-dimers in solution as is
evident from the 1H-NMR spectra (Fig. 1). The large downfield
shift for the N–H protons gives direct evidence for the
involvement of these protons in strong hydrogen bonding.14 The
electronic absorption spectra recorded in CHCl3 solution
display a weak band in the visible spectral region (lmax = 409
nm) for the less extended p-conjugated OPV3UP. In the case of
tetrameric oligophenylene vinylene, OPV4UP1 and
OPV4UP2, the absorption maxima are located at lmax = 431
and 446 nm, respectively. The red shift of the absorption
maxima of OPV4UP2 indicates conjugation between the OPV
segment and the hydrogen bonding unit. In addition, in dilute
CHCl3 solution (ca. 1025 M) these hydrogen bonded species are
present in dimeric form since the association constant of the
ureidopyrimidinone units is extremely high (Kdim = 6 3 107
M21 in CHCl3 solutions).15 In dodecane solution, both the
dimers of OPV4UP1 and OPV4UP2 aggregate into larger
architectures and circular dichroism (CD) spectroscopy shows
an exciton coupling of the p–p* transition in this solvent. In
other words, the side-chain chirality is expressed at the
supramolecular level.16 In the bulk, the two trialkoxybenzene
capped dimers are liquid crystalline, but investigation concern-
ing their detailed structure is in progress.
1 R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes, R. N.
Marks, C. Taliani, D. C. C. Bradley, D. A. Dos Santos, J. L. Brédas, M.
Logdlund and W. R. Salaneck, Nature, 1999, 397, 121.
2 R. E. Martin and F. Diederich, Angew. Chem., Int. Ed., 1999, 38,
1350.
3 J. M. Tour, Chem. Rev., 1996, 84, 303.
4 Z. Hu, J. L. Atwood and M. P. Cava, J. Org. Chem., 1994, 59, 8071;
K. P. Baldwin, R. S. Simons, J. Rose, P. Zimmerman, D. M. Hercules,
C. A. Tessier and W. J. Youngs, J. Chem. Soc., Chem. Commun., 1994,
1257; C. J. Walter and J. K. M. Sanders, Angew. Chem., Int. Ed. Engl.,
1995, 34, 217; J. Zhang, D. J. Pesak, J. L. Ludwick and J. S. Moore,
J. Am. Chem. Soc., 1994, 116, 4227.
5 Z. Wu, S. Lee and J. S. Moore, J. Am. Chem. Soc., 1992, 114, 8730.
6 J. M. Tour, R. Wu and J. S. Schumm, J. Am. Chem. Soc., 1991, 113,
7065; R. Wu, J. S Schumm, D. L. Pearson and J. M. Tour, J. Org. Chem.,
1996, 61, 6906; J. Salbeck, F. Weissörtel and J. Bauer, Macromol.
Symp., 1997, 125, 121.
7 Z. Xu and J. S. Moore, Angew. Chem., Int. Ed., 1993, 32, 1354.
8 D. Goldhaber-Gordon, M. S. Montemerlo, J. C. Love, G. J. Opiteck and
J. C. Ellenbogen, Proceedings of the IEEE, 1997, 85, 521; D. L.
Pearson, L. Jones III, J. S. Schumm and J. M. Tour, Synth. Met., 1997,
84, 303.
9 F. S. Schoonbeek, J. H. van Esch, B. Wegewijs, D. B. A. Rep, M. P. de
Haas, T. M. Klapwijk, R. M. Kellog and B. L. Feringa, Angew. Chem.,
Int. Ed., 1999, 38, 1393.
10 F. Würthner, C. Thalacker and A. Sautter, Adv. Mater., 1999, 11,
754.
11 J. L. Sessler, C. T. Brown, D. O’Conner, S. L. Springs, R. Wang, M.
Sathiosatham and T. Hirose, J. Org. Chem., 1998, 63, 7370.
12 R. P. Sijbesma, F. H. Beijer, L. Brunsveld, B. J. B. Folmer, J. H. K. K.
Hirschberg, R. F. M. Lange, J. K. L. Lowe and E. W. Meijer, Science,
1997, 278, 1601; B. J. B. Folmer, R. P. Sijbesma, R. M. Versteegen,
J. A. J. van der Rijt and E. W. Meijer, Adv. Mater., 2000, 12, 874; L.
Brunsveld, B. J. B. Folmer and E. W. Meijer, MRS Bull., 2000, 25, 49;
J. H. K. K. Hirschberg, F. H. Beijer, H. A. van Aert, P. C. M. M.
Magusin, R. P. Sijbesma and E. W. Meijer, Macromolecules, 1999, 32,
2696.
13 H. W. I. Peerlings and E. W. Meijer, Tetrahedron Lett., 1999, 40,
1021.
14 F. H. Beijer, R. P. Sijbesma, H. Kooijman, A. L. Spek and E. W. Meijer,
J. Am. Chem. Soc., 1998, 120, 6761.
15 S. H. M. Söntjens, R. P. Sijbesma, M. H. P. van Genderen and E. W.
Meijer, J. Am. Chem. Soc., in press.
16 See e.g. E. Peeters, M. P. T. Christiaans, H. F. M. Schoo, H. P. J. M.
Dekkers and E. W. Meijer, J. Am. Chem. Soc., 1997, 119, 9909;
B. M. W. Langeweld-Voss, D. Beljone, Z. Shuai, R. A. J. Janssen,
S. C. J. Meskers, E. W. Meijer and J.-L. Brédas, Adv. Mater., 1998, 10,
1343.
1970
Chem. Commun., 2000, 1969–1970
Typeset and printed by Black Bear Press Limited, Cambridge, England