Topochemical Polymerization of a Terminal Aryldiacetylene
A R T I C L E S
Figure 1. Topochemical requirements for diacetylene polymerization and
the host-guest strategy of aligning diacetylenes for such requirements.
Figure 2. Two possible mechanisms for the topochemical polymerization
of a diacetylene. (a) Turnstile mechanism. (b) Swinging gate mechanism.
pure substance. Thus, SCSC diacetylene polymerizations are
somewhat a matter of chance and far from common place.
In previous work, we have used a host-guest cocrystal
approach to establish these necessary structural requirements.7
We designed specific host molecules which would self-assemble
via hydrogen bonds establishing a crystalline lattice com-
mensurate with the repeat distance of the desired polymer. The
host molecules would then bind to the guest monomers imposing
upon them the proper spacing and orientation necessary for the
polymerization (Figure 1). Using this methodology we have
prepared in single crystal form several new polydiacetylenes,
including the first examples of a terminal polydiacetylene8 and
poly(diiododiacetylene).9 A similar host-guest approach led us
to the first polytriacetylene10 and the first polytriene11 both via
a SCSC polymerization as well.
There is considerable interest in the preparation of poly(aryl-
diacetylenes), polymers of diacetylenes with aryl groups directly
attached to the acetylene carbon atoms.12 Extending the
conjugation of the polymer backbone on to the aromatic side
groups may significantly enhance the electronic and optical
properties of the modified PDAs. There have been many
reported attempts to bring about a SCSC polymerization of an
aryldiacetylene.13 We have also tried to prepare a crystalline
poly(aryldiacetylene), but have not been successful. Our best
result was obtained by cocrystallizing 4,4′-dipyridyldiacetylene,
with the oxalamide of glycine, H2og, as the host (Figure 3a).14
The cocrystals exhibit very good structural parameters, but the
polymerization does not go SCSC. Instead, the monomer crystals
crumble into a purple powder as the polymerization progresses.
Similar frustrations have been reported by others for different
aryldiacetylene derivatives, sometimes with monomer structures
arranged in a perfect manner. Lee et al.15 investigated the
thermal polymerization of a bisbithazolyldiacetylene. Although
the packing pattern in this work turned out to be excellent, with
a 3.48 Å C1-C4 contact, the monomer crystals showed no
polymerization at all in the solid state.
In an early study, Day and Lando16 polymerized a cyclic
bisphenyldiacetylene to an extent of 35% as confirmed by X-ray
single crystal diffraction. In their work, the diacetylene moiety
seems to follow the “turnstile” pathway (Figure 2) and the
aromatic ring rotates by 19° about its axis. Nakanishi and co-
workers17 studied the solid state polymerization of a different
bisphenyldiacetylene and was able to obtain polymerization of
about 20%. In this case, the authors noticed a swinging motion
of the phenyl ring associated with the polymerization. A
complete topochemical SCSC polymerization was claimed for
1-(N-carbazolyl)-penta-1,3-diyn-5-ol, but no crystallographic
analysis of the resulting polymer was reported.18
In most SCSC polymerizations the structural changes follow
a reaction pathway corresponding to the turnstile mechanism.8,19,20
As illustrated in Figure 2, when energy is applied the monomers
pivot around their centers of mass in a conrotary manner
bringing the neighboring C1 and C4 carbon atoms together to
form a new bond. The required atom movement is just over 1
Å for each reacting atom. This turnstile pathway is particularly
favored for symmetrical diacetylenes.
(7) (a) Fowler, F. W.; Lauher, J. W. J. Phys. Org. Chem. 2000, 13, 850–
857. (b) Lauher, J. W.; Fowler, F. W.; Goroff, N. S. Acc. Chem. Res.
2008, 41, 1215–1229.
The difficulties in SCSC polymerization of aryldiacetylenes
may be attributed to the rigidity of aromatic pedant groups.
When the polymerization occurs, the diacetylene functionality
pivots like a “turnstile” by about 30° bringing the neighboring
C1 and C4 carbon atoms together. The linear sp hybridized
(8) Xi, O. Y.; Fowler, F. W.; Lauher, J. W. J. Am. Chem. Soc. 2003, 125,
12400–12401.
(9) Sun, A. W.; Lauher, J. W.; Goroff, N. S. Science 2006, 312, 1030–
1034.
(10) Xiao, J.; Yang, M.; Lauher, J. W.; Fowler, F. W. Angew. Chem., Int.
Ed. 2000, 39, 2132–2135.
(11) Hoang, T.; Lauher, J. W.; Fowler, F. W. J. Am. Chem. Soc. 2002,
124, 10656–10657.
(15) Lee, J. H.; Curtis, M. D.; Kampf, J. W. Macromolecules 2000, 33,
2136–2144.
(12) (a) Sarkar, A.; Okada, S.; Matsuzawa, H.; Matsuda, H.; Nakanishi,
H. J. Mater.Chem. 2000, 10, 819–828. (b) Chan, Y. H.; Lin, J. T.;
Chen, I. W. P.; Chen, C. H. J. Phys. Chem. B 2005, 109, 19161–
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(16) Day, D.; Lando, J. B. J. Polym. Sci., Part B: Polym. Phys. 1978, 16,
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(17) Nakanishi, H.; Matsuda, H.; Kato, M.; Theocharis, C. R.; Jones, W.
J. Chem. Soc., Perkin Trans. 2 1986, 1965–1967.
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(18) Matsuda, H.; Nakanishi, H.; Hosomi, T.; Kato, M. Macromolecules
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(19) Kane, J. J.; Liao, R. F.; Lauher, J. W.; Fowler, F. W. J. Am. Chem.
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(20) (a) Wilson, R. B.; Duesler, E. N.; Curtin, D. Y.; Paul, I. C.; Baughman,
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