Soluble poly(diacetylene)s using the perfluorophenyl-phenyl motif as a supramolecular synthon

Article abstract of DOI:10.1021/ja802964a

A series of diacetylene monomers with benzoyl, 4-hexylbenzoyl, 4-dodecylbenzoyl, and perfluorobenzoyl substituents were synthesized and investigated with respect to their crystal structures and polymerizability. In the absence of perfluorophenyl-phenyl interactions, the crystal structures of related alkylated and nonalkylated derivatives were substantially different and dominated by the phase segregation between the alkylated side chains and the diaryl-substituted diacetylene cores. By contrast, the perfluorophenyl-phenyl interactions served as a reliable supramolecular synthon in that they persisted in the crystal structures of different alkylated and nonalkylated derivatives. The packing of the diacetylene functions was appropriate for a topochemical polymerization in these cases, and the perfluorophenyl-phenyl interaction determined the polymerization direction. As a result, soluble alternating diacetylene copolymers were obtained which were further characterized with solution phase methods.

Full text of DOI:10.1021/ja802964a

Published on Web 07/25/2008
Soluble Poly(diacetylene)s Using the Perfluorophenyl-Phenyl
Motif as a Supramolecular Synthon
Rui Xu,† W. Bernd Schweizer,‡ and Holger Frauenrath*,†
Department of Materials and Laboratory of Organic Chemistry, ETH Zu¨rich,
Wolfgang-Pauli-Strasse 10, HCI H515, CH-8093 Zu¨rich, Switzerland
Received April 22, 2008; E-mail: frauenrath@mat.ethz.ch
Abstract: A series of diacetylene monomers with benzoyl, 4-hexylbenzoyl, 4-dodecylbenzoyl, and perfluo-
robenzoyl substituents were synthesized and investigated with respect to their crystal structures and
polymerizability. In the absence of perfluorophenyl-phenyl interactions, the crystal structures of related
alkylated and nonalkylated derivatives were substantially different and dominated by the phase segregation
between the alkylated side chains and the diaryl-substituted diacetylene cores. By contrast, the perfluo-
rophenyl-phenyl interactions served as a reliable supramolecular synthon in that they persisted in the
crystal structures of different alkylated and nonalkylated derivatives. The packing of the diacetylene functions
was appropriate for a topochemical polymerization in these cases, and the perfluorophenyl-phenyl
interaction determined the polymerization direction. As a result, soluble alternating diacetylene copolymers
were obtained which were further characterized with solution phase methods.
Introduction
features, however, is still a matter of debate. While it has been
attributed to the quadrupolar moments of arene and perfluoro-
Noncovalent interactions between aromatic residues are an
important factor controlling the structures and properties of
molecular assemblies in biological systems and have, therefore,
attracted increasing interest in recent years as design elements
in drug design, solution phase supramolecular chemistry, and
crystal engineering, as well as materials science.1,2 In most cases,
the interacting arene residues avoid π-π stacking in favor of
edge-to-face interactions, or they prefer a parallel-displaced π-π
stacking. The latter appears to be a viable compromise between
a maximum surface contact and a favorable arrangement of the
residues’ quadrupolar moments and, hence, the energetic
optimum in terms of dispersive and electrostatic contributions.
With an interplanar distance of about 3.6 Å and a parallel
displacement of up to 1.8 Å, centroid distances significantly
larger than 4 Å are typically observed. By contrast, arene-per-
fluoroarene interactions most often result in an eclipsed or
staggered face-to-face π-π stacking with only minimal parallel
displacement, an interplanar distance of 3.4 Å, a centroid
distance of around 3.7 Å, and only little deviation from a parallel
packing of the interacting residues.2,3 Experimental and calcu-
lated binding energies in the range 15 to 30 kJ mol-1 have been
reported,4–7 and arene-perfluoroarene interactions may be
favored by up to 10 kJ mol-1 per phenyl ring compared to
conventional arene-arene interactions.8 The exact origin of the
comparably strong interaction and the peculiar geometric
arene residues9–12 which are similar in magnitude but opposite
in sign,13 recent investigations indicate that dispersive interac-
tions may still be the most important contribution.14–16 Equally
controversial is the actual relevance of the C-H· · ·F short
contacts observed in many crystal structures as an additional
stabilizing element.3,14,17,18 Nevertheless, it is probably safe to
say that the electrostatic contribution makes the difference in
comparison to normal arene interactions, in particular, with
respect to the reliable and peculiar packing properties.8,15,16 It
is this feature that make arene-perfluoroarene interactions an
interesting “supramolecular synthon”19 both in crystal engineer-
ing and solution phase supramolecular chemistry. They were,
(5) Hernandez-Trujillo, J.; Colmenares, F.; Cuevas, G.; Costas, M. Chem.
Phys. Lett. 1997, 265, 503–507.
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1997, 10, 347–350.
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304.
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Gavezzotti, A. Chem.sEur. J. 2006, 12, 3538–3546.
(9) Williams, J. H. Acc. Chem. Res. 1993, 26, 593–598.
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Engl. 1992, 31, 1655–1657.
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5534.
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775–776.
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Lett. 1981, 78, 421–423.
† Department of Materials.
‡ Laboratory of Organic Chemistry.
(14) Dunitz, J. D.; Schweizer, W. B. Chem.sEur. J. 2006, 12, 6804–6815.
(15) Dunitz, J. D.; Gavezzotti, A.; Schweizer, W. B. HelV. Chim. Acta 2003,
86, 4073–4092.
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Perkin Trans. 2 2001, 651–669.
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Ed. 2003, 42, 1210–1250.
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Desiraju, G. R. J. Am. Chem. Soc. 1998, 120, 8702–8710.
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2008 American Chemical Society
J. AM. CHEM. SOC. 2008, 130, 11437–11445 11437

A R T I C L E S
Xu et al.
Chart 1. Diacetylene Monomers with 4-Alkylbenzoyl, Benzoyl, and Perfluorobenzoyl Substituents
for example, utilized in 2 + 2 cycloadditions of cinnamic acid
or stilbene derivatives,20 in an attempted topochemical diacety-
lene polymerization of diarylbutadiyne derivatives,21 in crystal
engineering investigations on (arylethynyl)benzene, 1,4-bis(aryl-
ethynyl)benzene, as well as 1,3,5-tris(arylethynyl)benzene
derivatives,22–25 and in the stacking of diaryl-ꢀ-diketonate
complexes.26 Furthermore, the role of perfluoroarene-arene
interactions on the formation of thermotropic LC phases,27,28
the gelation of octafluoronaphthalene and pyrene-endcapped
PEG in aqueous solution,29 or the conformational stability of
oligopeptides containing perfluorophenylalanine residues was
investigated.30,31
We recently reported the utilization of perfluorophenyl-phenyl
interactions in the topochemical diacetylene polymerization32,33
which led to the first unambiguously proven example of a strictly
alternating diacetylene copolymer.34 Unfortunately, the obtained
copolymer turned out to be only poorly soluble in organic
solvents, which hampered its characterization and limited its
potential applications. This problem would be conveniently
addressed with alkyl decoration, as it has been done in other
examples of soluble poly(diacetylene)s.35 However, the prepara-
tion of a corresponding alkylated alternating copolymer would
require that the stacking motif established by the perfluorophe-
nyl-phenyl interactions persisted in spite of alkylation. Only
few investigations to date have dealt with functional molecules
where the perfluoroarene-arene interaction competed with other
typesofsupramolecularinteractionssuchashydrogenbonding4,36–38
or van der Waals interactions between alkyl residues.23 In the
latter example, the perfluoroarene-arene interactions were
shown to become less of a determining factor with increasing
steric demand of the alkyl substituent.
In the present paper, we prepared and investigated a series
of 2,4-hexadiyne-1,6-diol derivatives with benzoyl, 4-hexyl-
benzoyl, 4-dodecylbenzoyl, and perfluorobenzoyl substituents
(Chart 1) with respect to their crystal structures and polymer-
izability. We wish to demonstrate that perfluorophenyl-phenyl
interactions indeed deserve to be regarded as a reliable su-
pramolecular synthon because they persist when combined with
another type of supramolecular interaction. Thus, the crystal
structures of related alkylated and nonalkylated derivatives were
substantially different in the absence of perfluorophenyl-phenyl
interactions, and the phase segregation between the alkylated
side chains and the diacetylene cores appeared to be the
dominating factor in this case. By contrast, the crystal structures
of different alkylated and nonalkylated diacetylene monomers
which exhibited perfluorophenyl-phenyl interactions were
strikingly similar and appeared to complement the requirements
of both the aromatic interactions and the packing of the alkyl
substituents. Moreover, the packing of the diacetylene functions
was found to be appropriate for a topochemical polymerization
in these cases, and the perfluorophenyl-phenyl interaction
(20) Coates, G. W.; Dunn, A. R.; Henling, L. M.; Ziller, J. W.; Lobkovsky,
E. B.; Grubbs, R. H. J. Am. Chem. Soc. 1998, 120, 3641–3649.
(21) Coates, G. W.; Dunn, A. R.; Henling, L. M.; Dougherty, D. A.; Grubbs,
R. H. Angew. Chem., Int. Ed. Engl. 1997, 36, 248–251.
(22) Ponzini, F.; Zagha, R.; Hardcastle, K.; Siegel, J. S. Angew. Chem.,
Int. Ed. 2000, 39, 2323–2325.
(23) Smith, C. E.; Smith, P. S.; Thomas, R. L.; Robins, E. G.; Collings,
J. C.; Dai, C.; Scott, A. J.; Borwick, S.; Batsanov, A. S.; Watt, S. W.;
Clark, S. J.; Viney, C.; Howard, J. A. K.; Clegg, W.; Marder, T. B. J.
Mater. Chem. 2004, 14, 413–420.
(24) Dai, C.; Nguyen, P.; Marder, T. B.; Scott, A. J.; Clegg, W.; Viney, C.
Chem. Commun. 1999, 2493–2494.
(25) Watt, S. W.; Dai, C.; Scott, A. J.; Burke, J. M.; Thomas, R. L.;
Collings, J. C.; Viney, C.; Clegg, W.; Marder, T. B. Angew. Chem.,
Int. Ed. 2004, 43, 3061–3063.
(26) Hori, A.; Shinohe, A.; Yamasaki, M.; Nishibori, E.; Aoyagi, S.; Sakata,
M. Angew. Chem., Int. Ed. 2007, 46, 7617–7620.
(27) Weck, M.; Dunn, A. R.; Matsumoto, K.; Coates, G. W.; Lobkovsky,
E. B.; Grubbs, R. H. Angew. Chem., Int. Ed. 1999, 38, 2741–2745.
(28) Kishikawa, K.; Oda, K.; Aikyo, S.; Kohmoto, S. Angew. Chem., Int.
Ed. 2007, 46, 764–768.
(29) Kilbinger, A. F. M.; Grubbs, R. H. Angew. Chem., Int. Ed. 2002, 41,
1563–1566.
(35) Most investigations on soluble poly(diacetylene)s to date have been
carried out with dodeca-5,7-diyne bis(toluenesulfonate) (PTS-12),
dodeca-5,7-diyne bis(butylcarboxymethyl carbamate) (P4BCMU), or
closely related monomers; for the original investigations, see: Wenz,
G.; Mu¨ller, M. A.; Schmidt, M.; Wegner, G. Macromolecules 1984,
17, 837. Patel, G. N.; Chance, R. R.; Witt, J. D. J. Polym. Sci., Polym.
Lett. Ed. 1978, 16, 607. Chance, R. R. Macromolecules 1980, 13, 396.
(36) Reddy, L. S.; Nangia, A.; Lynch, V. M. Cryst. Growth Des. 2004, 4,
89–94.
(30) Butterfield, S. M.; Patel, P. R.; Waters, M. L. J. Am. Chem. Soc. 2002,
124, 9751–9755.
(31) Gorske, B. C.; Blackwell, H. E. J. Am. Chem. Soc. 2006, 128, 14378–
14387.
(32) Wegner, G. Z. Naturforsch., B 1969, 24, 824–832.
(33) Zuilhof, H.; Barentsen, H. M.; van Dijk, M.; Sudho¨lter, E. J. R.;
Hoofman, R. J. O. M.; Siebbeles, L. D. A.; de Haas, M. P.; Warman,
J. M. In Supramolecular and PhotosensitiVe ElectroactiVe Materials;
Nalwa, H. S., Ed.; Academic Press: San Diego, CA, 2001; pp 339-
437.
(37) Meejoo, S.; Kariuki, B. M.; Harris, K. D. M. ChemPhysChem 2003,
4, 766–769.
(34) Xu, R.; Gramlich, V.; Frauenrath, H. J. Am. Chem. Soc. 2006, 128,
5541–5547.
(38) Wojciech, J.; Gdaniec, M.; Polonski, T. Acta Crystallogr., Sect. C
2006, C62, o492–o494.
9
11438 J. AM. CHEM. SOC. VOL. 130, NO. 34, 2008

Soluble Poly(diacetylene)s
A R T I C L E S
Scheme 1. Synthesis of the Monomers 1b, 1c, 2b, and 2ca
a Reaction conditions: (a) for 1b: NEt3, DCM; for 1c: EDCI, DPTS, DCM; (b) C6F5COCl, NEt3, DCM.
Table 1. Crystallographic Data of the Novel Monomers 1b, 1c, 2b, and 2c, as well as the Cocrystal 1b·3 in Comparison to the Previously
Determined Crystal Structures of 1a, 2a, and the Cocrystal 1a·334,40
1a
1b
1c
1a·3
1b·3
2a
2b
2c
formula
C20H14O4
C32H38O6
C44H62O6
C20H4F10O4 ·
C20H14O4
866.35
C20H4F10O4 ·
C32H38O6
508.43
C20H9F5O4
C26H21F5O5
C32H33F5O5
mw
318.31
monoclinic
P21/n
colorless
14.038(2)
4.353(1)
14.864(2)
90.00
117.06(2)
90.00
808.8(3)
Cu KR
1.31
518.64
monoclinic
P21/n
colorless
25.279(5)
7.7559(14)
19.608(3)
90.00
129.618(10)
90.00
2961.37
Mo KR
1.16
686.96
monoclinic
P21/c
colorless
27.6013(7)
7.6701(2)
19.6075(4)
90.00
102.3582(8)
90.00
4054.8(2)
Mo KR
1.125
408.27
monoclinic
P21/c
colorless
16.822(2)
7.1205(7)
15.706(2)
90.0
107.423(8)
90.0
1795.0(3)
Cu KR
1.51
508.44
monoclinic
P21/c
colorless
8.5473(2)
33.5122(7)
8.5937(2)
90.0
98.590(1)
90.0
2434.0(1)
Mo KR
1.39
592.59
crystal system
space group
color
a (Å)
b (Å)
triclinic
triclinic
triclinic
j
j
j
P1
P1
P1
colorless
5.9825(7)
7.576(1)
19.295(2)
96.91(1)
91.74(1)
93.07(1)
866.4(2)
Cu KR
1.56
light orange
5.9343(1)
7.4644(1)
27.3032(5)
97.839(1)
90.534(1)
93.184(1)
1196.10(3)
Mo KR
1.412
light orange
5.9780(1)
7.3408(2)
32.998(1)
87.6
87.610(1)
85.8
1442.18(6)
Mo KR
1.365
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
radiation
Dcalcd (g cm-3
)
mcalcd (mm-1
)
0.091
0.08
0.073
0.144
0.122
0.139
0.12
0.112
F000
T
332
295
1112
295
1496
223
412
295
524
220(2)
824
295
1048
223
620
153
Z
2
4
4
1
1
4
4
2
2
R, Rw
0.067,
0.210
0.0545,
0.124
0.085,
0.234
0.0745,
0.243
0.0732,
0.2069
0.0593,
0.194
0.066,
0.175
0.064,
0.189
GOF
0.94
0.68
1.33
0.948
1.029
0.940
1.28
1.036
appeared to determine the direction of polymerization. Hence,
soluble perfluorophenyl-substituted poly(diacetylene)s were
obtained which could be characterized with solution phase
methods and may, furthermore, be subjected to solution phase
processing into optoelectronically active materials.
1b·3 were obtained by recrystallization from DCM/hexanes.
The crystal structure observed in the case of the 2,4-hexadiyne-
1,6-diyl dibenzoate 1a (Table 1) corresponded to one of the
two known polymorphs.34,40 While, in this particular case, the
geometric parameters are not appropriate for a topochemical
diacetylene polymerization, the typical parallel-displaced π-π
stacking of the aryl substituents in 1a is representative for
various literature examples of polymerizable and nonpolymer-
izable diacetylene derivatives.41–44 By contrast, the crystal
structures of both the bis(p-hexyloxybenzoate) 1b and the bis(4-
dodecyloxybenzoate) 1c were remarkably different from 1a
(Figure 1).
In contrast to the centrosymmetric arrangement of 1a, the
molecules in crystals of 1b and 1c adopted an approximate,
noncrystallographic twofold axis. The two dodecyloxybenzoate
substituents showed a dihedral angle of 110°, forming a “twisted
U-shape” packed into layers with a mean plane distance of 6.5
Å by lattice translation along the [0 1 0] axis. For both 1b and
1c, two diacetylenes from layers across an inversion center
exhibited C · · ·C short contacts,45 but the closest packing of two
Results and Discussion
Monomer Synthesis. The nonalkylated monomers 1a, 2a, and
3 were prepared as described previously.34 For the synthesis of
monomer 1b and 2b, 4-(hexyloxy)benzoyl chloride was reacted
with an approximately stoichiometric amount of hexa-2,4-diyne-
1,6-diol, affording a mixture of the monosubstituted intermediate
4b and the disubstituted diacetylene 1b (Scheme 1). The two
compounds were separated by column chromatography, and 4b
was subsequently esterified with perfluorobenzoic chloride,
yielding the unsymmetrically substituted diacetylene monomer
2b. Similarly, the dodecylated monomers 1c and 2c were
prepared by reacting roughly equimolar amounts of 4-(dode-
cyloxy)benzoic acid and hexa-2,4-diyne-1,6-diol, using 4-(N,N-
dimethylamino)-pyridinium 4-toluenesulfonate (DPTS) and N-eth-
yl-(N′-dimethylaminopropyl)-carbodiimide hydrochloride (EDCI ·
HCl) as the catalyst system,39 followed by esterification of the
monosubstituted compound 4c with perfluorobenozic chloride.
Comparison of the Monomer Crystal Structures. Single-
crystalline samples of 1a-c, 2b, and 2c as well as a cocrystal
(40) Hanson, A. W. Acta Crystallogr., Sect. B 1975, B31, 831–834.
(41) Enkelmann, V.; Wegner, G. Angew. Chem., Int. Ed. 1977, 89, 416.
(42) Enkelmann, V.; Leyrer, R. J.; Wegner, G. Makromol. Chem. 1979,
180, 1787–1795.
(43) Patel, G. N.; Duesler, E. N.; Curtin, D. Y.; Paul, I. C. J. Am. Chem.
Soc. 1980, 102, 461–466.
(39) Moore, J. S.; Stupp, S. I. Macromolecules 1990, 23, 65–70.
(44) Enkelmann, V. AdV. Polym. Sci. 1984, 63, 91–136.
9
J. AM. CHEM. SOC. VOL. 130, NO. 34, 2008 11439

A R T I C L E S
Xu et al.
Figure 1. A comparison of the crystal structures of (A) the hexyloxy-substituted monomer 1b and (B) the dodecyloxy-substituted monomer 1c with (C) the
previously determined crystal structure of the unsubstituted derivative 1a34,40 revealed that the alkyl substituents exerted a major influence. Whereas 1a
exhibited the typical parallel-displaced π-π stacking of the phenyl groups, no aromatic interaction was observed in 1b and 1c at all which, instead, were
packed in “bilayer”-like arrangements of the “twisted U-shaped” molecules.
diacetylenes within one layer occurred along the [0 1 0] direction
with lattice periods of 7.756 Å (1b) and 7.670 Å (1c),
respectively, which is incompatible with the requirements for a
topochemical polymerization. The same distances were observed
between the phenyl groups, which is obviously too large to be
considered as a π-π stacking interaction.45 Instead, the
molecules were arranged such that the phenyl groups gave rise
to a C-H· · ·π short contact with the alkyl residue of one
neighboring molecule and a π-π interaction with the diacety-
lene group of the other neighbor. Hence, the introduction of
the alkoxy substituents significantly altered the molecular
symmetry and the crystal structures of 1b and 1c as compared
to 1a. Looking at these differences with the eyes of a polymer
chemist, one might say that, by analogy with ABA triblock
copolymers, phase segregation occurred between the aliphatic
side chains and the diacetylene cores of the molecules, leading
to a “lamellar bilayer packing” of the “U-shaped” molecules.45
The dense packing of the alkoxy substituents appeared to be
the dominating factor in the crystal structure and outperformed
π-π stacking interaction of the phenyl groups which, in this
sense, cannot be regarded as a reliable supramolecular synthon.
The situation was fundamentally different in the case of the
cocrystals 1a·3 and 1b·3 as well as the crystals of 2a and 2c
(Figures 2 and 3).34,46 The remarkably similar crystal structures
proved that the perfluorophenyl-phenyl interactions remained
the dominating factor despite the presence of the alkyloxy
(45) See Supporting Information for additional figures and detailed
discussion.
(46) It should be acknowledged that the hexyl-substituted 2b constituted a
notable exception; see Supporting Information.
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11440 J. AM. CHEM. SOC. VOL. 130, NO. 34, 2008

Soluble Poly(diacetylene)s
A R T I C L E S
Figure 2. (A) Crystal structure of the cocrystal 1b·3 and, for comparison, (B) the related crystal structure of the cocrystal 1a·3;34 in both cases, the
characteristic packing of the molecules into a “zigzag chain” pattern along the [1 0 0] axis and the almost perfectly eclipsed perfluorophenyl-phenyl
stacking were preserved in spite of the presence of the alkyl substituents in 1b; the diacetylene functions of adjacent molecules in the [0 1 0] direction were
not placed in the same plane so that identity periods of 7.46 and 7.58 Å were observed, respectively.
Figure 3. The crystal structure of both (A) 2c and, for comparison, (B) 2a34 exhibited “tubular arrays” obtained via stacking dimers connected with
perfluorophenyl-phenyl interactions along the [0 1 0] axis; the relative orientation of these “tubular arrays” was different, however; the perfluorophenyl-phenyl
interaction not only was preserved in the dodecylated derivative 2c but also showed an almost perfectly eclipsed stacking; the diacetylene functions of
adjacent molecules in the [0 1 0] direction were not placed in the same plane so that identity periods of 7.34 and 7.12 Å were observed, respectively.
substituents. In all cases, the alternating perfluorophenyl and
phenyl groups exhibited an almost perfectly eclipsed stacking
with only a minimal parallel displacement and centroid-centroid
distances close to the closest contact distances (Table 2). The
alkoxy chains of adjacent stacks in 1b·3 and 2c were inter-
digitated in order to accommodate the perfluorophe-
nyl-phenyl stacking, and even the details of the diacetylene
packing were virtually identical as compared to the respective
nonalkylated siblings 1a·3 and 2a. Thus, the molecular packing
in the cocrystals 1a·3 and 1b·3 gave rise to a characteristic
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J. AM. CHEM. SOC. VOL. 130, NO. 34, 2008 11441

A R T I C L E S
Xu et al.
Table 2. Comparison of Diacetylene Packing Parameters and Side Group Interactions in the Case of 1a-c and 2a-c, as well as 1a·3 and
1b·3
diacetylene packing parameters
side group interaction
reactive
carbon
distancec
(Å)
close
contact
distanced
(Å)
diacetylene
distance da
(Å)
centroid
distancee
(Å)
lattice
direction
inclination
angle φb
mode
1a
[0 1 0]
4.35
59°
4.02
3.60
4.35
parallel
displaced
1b
1c
[0 1 0]
[0 1 0]
[0 1 0]
[1 1 0]
[1 -1 0]
[0 1 0]
[1 1 0]
[1 -1 0]
[0 1 0]
7.756
7.670
57°
58°
-
4.356
4.345
-
7.756
7.670
-
-
-
-
h
h
h
1a·3
1a·3
1a·3
1b·3
1b·3
1b·3
2a
7.56
35°, 38°f
51°, 54°f
46°, 53°f
35°, 38°
52°, 53°f
48°, 51°f
38°
-
-
4.62, 4.78f
4.80, 5.10f
7.464
3.84
3.79
-
3.48
3.44
3.82
3.76
eclipsed
eclipsed
h
h
h
-
-
-
4.59, 4.69f
4.76, 5.03f
7.12
3.80
3.77
-
3.385
3.402
3.25
3.75
eclipsed
3.72
3.78, 3.69
eclipsed
staggered,
eclipsedi
2b
2c
2c
2c
[1 0 0]
[0 1 0]
[1 1 0]
[1 -1 0]
8.54
49°
-
-
n.a.
6.06j
edge-to-face j
h
h
h
7.341
36°
-
-
-
4.840, 4.984g
4.757, 4.380g
53°, 45°g
51°, 57°g
3.929, 3.535
3.792, 3.910
3.320
3.284
3.684
3.660
eclipsed
eclipsed
a Identity period d along the [0 1 0] axis; in the case of 1a·3, 1b·3, and 2c in the [1 1 0] and [1 -1 0] direction, the two different end-to-end
distances between adjacent diacetylenes were given. b Inclination angle between the diacetylene axis and the respective crystallographic axis. c Distance
between the two reactive carbon centers in adjacent diacetylenes. d Shortest contact distance between two carbons in the aromatic side groups of two
adjacent molecules. e Distance between the centroids of the aromatic rings of two adjacent molecules. f The diacetylene moieties of 1 and 3 in the 1a·3
cocrystal and 1b and 3 in the 1b·3 cocrystal were not aligned exactly parallel with respect to one another. g Both ends of each diacetylene of 2 have the
same distance to the respective diacetylene ends adjacent, but the distance to the diacetylene above was different from the distance to the diacetylene
below; accordingly, there were also two inclination angles. h The phenyl-perfluorophenyl pairs stacked along the [0 1 0] axis connected adjacent
molecules in 1a·3, 1b·3, and 2c in the [1 1 0] and [1 -1 0] directions, respectively; therefore, they were listed in the rows below. i There were two
groups of disordered perfluorobenzoate groups in 2, showing a staggered and an eclipsed face-to-face packing, respectively. j The edge-to-face
interaction of a phenyl ring pointing toward the center of a perfluorophenyl ring in 2 did not involve adjacent molecules along the [1 0 0] axis.
“zigzag” chain of the molecules along the [1 0 0] axis for
symmetry reasons, whereas they were arranged into “tubular
arrays” along the [0 1 0] axis in the case of 2a and 2c.45 As a
result, the diacetylene moieties of adjacent monomers in the [0
1 0] direction were placed in different layers in all cases, so
that the identity periods of the diacetylenes were twice the
perfluorophenyl-phenyl stacking distance (Table 2) and, hence,
inappropriate for a topochemical polymerization.
Due to the “lamellar packing” of the molecules and the
interdigitation of the dodecyloxy chains in 2c, however, the
relative orientation of the “tubular arrays” was different from
that in 2a. In the crystal structure of 2a, the diacetylene moieties
in adjacent “tubular arrays” related by the glide-plane were
not parallel to one another, and the “tubular arrays” were
laterally offset. By contrast, all diacetylene functions had to be
parallel by symmetry (inversion center) in 2c, and additionally,
adjacent “tubular arrays” were stacked on top of each other.
As a consequence of this difference, 2c featured continuous two-
dimensional arrays of parallel diacetylene groups and geometries
appropriate for topochemical polymerizations along the [1 1 0]
and [1 -1 0] directions, as did 1a·3 and 1b·3 (Table 2).
From all of these experimental observations, one may
conclude that, similar to the case of the alkoxy substituted
derivatives 1b and 1c and by analogy with ABA triblock
copolymers, the dodecyloxy chains in both 1b·3 and 2c added
an element of phase segregation between the aliphatic segments
and the diacetylene cores.45 However, this appeared to be rather
an additional factor controlling the overall crystal structure
which, at the same time, accommodated and preserved the
perfluorophenyl-phenyl stacking. In fact, the crystallization of
the dodecyl chains even appeared to improVe the overall order
in the perfluorophenyl-phenyl stacks and also induced a
different packing of the stacks relative to one another. The most
important consequence was that 2c, similar to 1a·3 and 1b·3
but contrary to its nonalkylated sibling 2a, featured two-
dimensional (“lamellar”) arrays of the diacetylene moieties and
a diacetylene packing with an appropriate geometry for a
topochemical polymerization diagonal to the lattice axes.
Topochemical Polymerization and Characterization of the
Soluble Poly(diacetylene)s. The above analysis of the monomer
crystal structures helped to identify both 1b·3 and 2c as possible
candidates for topochemical diacetylene polymerizations, ex-
hibiting essentially the same geometric features as the poly-
merizable cocrystal 1a·3.34 Surprisingly, however, only the
unsymmetrically substituted monomer 2c was experimentally
found to undergo a clean topochemical polymerization, produc-
ing the novel soluble poly(diacetylene) P2c (Scheme 2) in
preparatively useful yields.47 Thus, UV irradiation of the
acetone-soluble, colorless monomer 2c led to an instantaneous
color change to bright red-orange. The material turned partially
insoluble in acetone but remained soluble in DCM or chloro-
form. These solubility properties allowed separation of the
polymer from the residual monomer by extraction with acetone
and characterization of both the reaction mixture and the
obtained pure poly(diacetylene) P2c in solution.
(47) The other monomers (1a-c as well as 2a and 2b) were not poly-
merizable, in agreement with the geometric features inappropriate for
a topochemical polymerization. In the case of 1b·3, UV irradiation
caused a significant color change to bright orange. However, acetone
extraction of the sample after 3 h of irradiation only yielded 3% of
insoluble material; longer irradiation generated more material, but only
1
in total isolated yields of below 5%. Nevertheless, the H NMR and
Raman spectra of the obtained material were consistent with poly(di-
acetylene) formation and resembled those of polymer P2c. As the
crystal structure of 1b·3 was found to be similar to those of 1a·3 and
2c and, in particular, the geometric parameters of the diacetylene
packing were almost identical, the surprising lack of bulk polymer-
izability may tentatively be attributed to the overall poor crystal quality.
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11442 J. AM. CHEM. SOC. VOL. 130, NO. 34, 2008

Soluble Poly(diacetylene)s
A R T I C L E S
Scheme 2. Preparation of the Soluble Poly(diacetylene) P2c by Topochemical Polymerization of 2c upon UV Irradiation
After acetone extraction, the pure poly(diacetylene) P2c was
obtained as a deep red-orange powder. The polymer formed
yellow solutions in DCM or chloroform, and the corresponding
UV spectra45 showed a maximum at λmax ) 465 nm with a
molar extinction coefficient of ε ) 9.4 × 106 cm2 mol-1. Solid
films obtained via dropcasting from DCM solution were red
and exhibited two absorption maxima at λmax ) 525 nm as well
as 485 nm. The solid state Raman spectrum obtained from 2c
after UV irradiation also showed that the monomer diacetylene
absorption at 2264 cm-1 was replaced by the typical bands of
poly(diacetylene) backbone double and triple bonds at 1509 and
2106 cm-1 (Figure 4A). A comparison of the solution-phase
13C NMR spectra (Figure 4B) of 2c and the corresponding
poly(diacetylene) P2c proved that the four acetylene peaks at
71.8, 71.6, 69.9, and 68.2 ppm in the monomer spectrum had
completely disappeared in the spectrum of the polymer, and
the methylene groups attached to the diacetylene moieties were
shifted from 54.1 and 52.3 ppm to 65.1 and 63.6 ppm, similar
to what had been observed in the solid-state NMR spectra of
1a·3.34 Additionally, the new polymer backbone carbons could
be observed as small, broad peaks at 128.5 and 127.4 as well
as 99.8 and 98.4 ppm.
relative integration of the aromatic protons at 8.0 and 7.8
ppm in the 1H NMR spectra of the reaction mixture obtained
from the dissolved irradiated crystalline material. Therefore,
the polymerization kinetics could conveniently be followed
by irradiating crystalline powders of 2c, dissolving samples
after different time intervals in CDCl3, and determining the
1
conversion via integration in the H NMR spectra (Figure
5B). Thus, in representative polymerization experiments, a
maximum conversion of about 40% was already reached after
around 360 min of UV irradiation. The reaction kinetics could
be reasonably well described with a fitting function xp(t) )
x∞ · t/(a + t) which had previously been used in the literature48
as well as, even better, a second-order exponential function.
Both types of functions, however, are unfortunately devoid
of any mechanistic meaning. The limiting factor for a higher
conversion appeared to be mainly the crystal quality, as was
confirmed by irradiating larger single crystals in a separate
experiment, resulting in 51% yield after 20 h of UV
irradiation (Figure 5B).
GPC measurements of polymer P2c in chloroform at 35 °C
suggested a molecular weight of Mn ) 2 × 106 (PDI ) 4.5).
However, the very broad multimodal elution peak near the upper
exclusion limit may as well suggest (partial) aggregation and
shear-induced degradation of the polymer on the column.
Therefore, the molecular weight of polymer P2c was also
evaluated by static light scattering. Polymer P2c exhibited a
radius of gyration Rg ) 80 nm. Comparing this value with the
radius of gyration and molecular weight of poly(diacetylene)s
reported in the literature49 resulted in an estimated molecular
weight of Mw ) 9 × 105 which may be a more reliable
approximation than the value derived from GPC.
1
Furthermore, a comparison of the H NMR spectra of the
monomer 2c with both the reaction mixtures during UV
irradiation of the single crystals (after dissolution of the latter
in CDCl3) and the final polymer P2c (after acetone extraction)
revealed several new or shifted peaks (Figure 5A). The
aromatic proton signals were shifted from 8.0 to 7.7 ppm
and from 6.9 to 6.7 ppm; the two signals of the CH2 groups
adjacent to the diacetylenes at around 5 ppm experienced a
slight downfield shift; the dodecyloxy CH2O group signal
was shifted from 4.0 to 3.9 ppm; and all polymer peaks
appeared broadened. The isolated yield of the pure polymer
P2c after acetone extraction was determined to be 37%
gravimetrically, which turned out to be acceptably consistent
with the conversion of around 38% determined from the
(48) Tieke, B.; Wegner, G. Makromol. Chem. 1978, 179, 1639–1642.
(49) Wenz, G.; Mu¨ller, M. A.; Schmidt, M.; Wegner, G. Macromolecules
1984, 17, 837–850.
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J. AM. CHEM. SOC. VOL. 130, NO. 34, 2008 11443

A R T I C L E S
Xu et al.
Figure 5. (A) Relative integration of the polymer and the monomer peaks
1
in the H NMR spectra of 2c after different periods of UV irradiation and
dissolution in CDCl3 allowed following the polymerization kinetics; (B) in
representative experiments (0), a maximum conversion was reached after
about 360 min of irradiation, and the kinetics were reasonably well described
by the function xp(t) ) x∞ ·t/(a + t) (solid line); however, irradiation of
larger single crystals led to higher conversion (b), indicating that the crystal
quality was the limiting factor for conversion.
Figure 4. (A) Solid-state Raman spectra and (B) high-resolution solution-
phase 13C NMR spectra of diacetylene 2c and the pure poly(diacetylene)
P2c after UV irradiation of 2c and extraction of residual monomer with
acetone.
Finally, the crystal structure of 2c after 18 h of irradiation
could be solved as a superposition of the monomer 2c (85%)
and the polymer P2c (15%), which helped to unambiguously
confirm the polymer structure (Figure 6C). While P2c may
formally be regarded as an alkylated sibling of the previously
described alternating copolymer P(1a · 3), the polymer mi-
crostructure is noticeably different, featuring an alternating
sequence of two different types of symmetrically substituted
olefin bonds along the backbone, carrying two alkoxyaryl or
two perfluoroaryl residues, respectively. The X-ray structure
analysis of the poly(diacetylene) P2c not only unambiguously
confirmed the polymer structure but also provided more
details about the process of polymer formation. Similar to
what we had previously reported for 1a · 3,34 geometric
parameters approximately in the range of those required for
a topochemical polymerization were observed along both of
the crystallographic [1 1 0] and the [1-1 0] directions in
the crystal structure of 2c (Table 2). The more optimal
aVerage packing parameters were observed in the [1 1 0]
direction (Table 2), and accordingly, the polymerization was
found to proceed along this axis. Interestingly, the polym-
erization direction coincided with the perfluorophe-
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11444 J. AM. CHEM. SOC. VOL. 130, NO. 34, 2008

Soluble Poly(diacetylene)s
A R T I C L E S
persisted almost unchanged between the side groups, al-
though, this time, the phenyl and perfluorophenyl ring planes
were not exactly parallel anymore in the polymer. Neverthe-
less, it appeared as if the perfluorophenyl-phenyl interaction
“stitched together” the polymer so that the “mechanical
properties” of the ester group as the flexible hinge only
allowed the polymerization to proceed along the specified
lattice direction.
Conclusions
Based on the successful synthesis and recrystallization of
different diacetylene monomers and the comparison of their
(co)crystal structures, it may be concluded that the phenyl-per-
fluorophenyl interaction qualifies, in most cases,46 as a
reliable supramolecular motif in the crystalline state, in the
sense that it can be utilized to establish a certain molecular
packing even when combined with other supramolecular
synthons. Thus, the characteristic packing features including
the appropriate arrangement of the diacetylene moieties for
a topochemical polymerization already observed in the
cocrystal of the two mutually complementary, unsubstituted
diacetylenes 1a and 3 were preserved in the case of the
dodecyloxy-substituted self-complementary diacetylene mono-
mer 2c. The latter was successfully polymerized by UV
irradiation, affording the soluble poly(diacetylene) P2c in
preparatively useful yields. According to the crystal structure
of this polymer, the perfluorophenyl-phenyl interactions
appeared to determine the direction of the polymerization
and persisted as a side group interaction in the final polymer.
This fact combined with the solubility profile of P2c makes
it an interesting candidate for processing into oriented thin
films, the optoelectronic properties of which are currently
under investigation.
Acknowledgment. We thank Dr. Heinz Ru¨egger for performing
solid state NMR spectroscopy, Martin Colussi for measuring DSC
and GPC, Prof. Manfred Schmidt and Dr. Karl Fischer for
performing static light scattering experiments, as well as Prof. Dieter
Schlu¨ter for his generous support. Financial support from the
Schweizerischer Nationalfonds (SNF-Projekt 200021-113509) is
gratefully acknowledged.
Figure 6. (A,B) Parameters appropriate for a topochemical polymerization
were observed along both the crystallographic [1-1 0] and the [1 1 0]
direction, but the more optimal parameters were observed in the latter case;
furthermore, the perfluorophenyl-phenyl stacking direction was almost
parallel to the [1 1 0] axis; (C) the crystal structure of the obtained
poly(diacetylene) P2c (solved as a superposition of monomer and polymer
structure from a UV irradiated and partially polymerized crystal of monomer
2c) proved that the polymerization proceeded along [1 1 0] and the
perfluorophenyl-phenyl interaction persisted in the side chains of the
polymer.
Note Added after ASAP Publication. Due to a production error
the version published on the Web July 25, 2008, contained errors.
These errors have been corrected in the version published on the
Web July 31, 2008, and in the print issue.
Supporting Information Available: Detailed experimental
procedures; 1H and 13C NMR spectra of 1b, 1c, 2b, 2c, 4a, and
4b; 19F NMR spectra of 2b and 2c; UV spectra of P2c and
other additional or enlarged figures; complete crystallographic
data (CIF files) of 1b, 1c, 2b, 2c, 1b·3, and P2c. This material
is available free of charge via the Internet at http://pubs.acs.org.
nyl-phenyl stacking direction, as the normal vectors of the
phenyl (perfluorophenyl) ring planes were inclined only 21.9°
(17.8°) against the [1 1 0] axis (Figure 6B) but 60.6° (64.9°)
against the [1-1 0] axis (Figure 6A). As had been the case
for 1a · 3, the perfluorophenyl-phenyl interaction in P2c
JA802964A
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J. AM. CHEM. SOC. VOL. 130, NO. 34, 2008 11445