Click functionalization of a dibenzocyclooctyne-containing conjugated polyimine

Article abstract of DOI:10.1002/anie.201508639

A conjugated poly(phenyl-co-dibenzocyclooctyne) Schiff-base polymer, prepared through polycondensation of dibenzocyclooctyne bisamine (DIBO-(NH₂)₂) with bis(hexadecyloxy)phenyldialdehyde, is reported. The resulting polymer, which has

Full text of DOI:10.1002/anie.201508639

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201508639
German Edition: DOI: 10.1002/ange.201508639
Conjugated Polymers
Click Functionalization of a Dibenzocyclooctyne-Containing
Conjugated Polyimine
Vladimir Kardelis, Ryan C. Chadwick, and Alex Adronov*
Abstract: A conjugated poly(phenyl-co-dibenzocyclooctyne)
Schiff-base polymer, prepared through polycondensation of
dibenzocyclooctyne bisamine (DIBO-(NH2)2) with bis(hexa-
decyloxy)phenyldialdehyde, is reported. The resulting poly-
mer, which has a high molecular weight (Mn > 30 kDa, Mw >
60 kDa), undergoes efficient strain-promoted alkyne–azide
cycloaddition reactions with a series of azides. This enables
quantitative modification of each repeat unit within the
polymer backbone and the rapid synthesis of a conjugated
polymer library with widely different substituents but a con-
sistent degree of polymerization (DP). Kinetic studies show
a second-order reaction rate constant that is consistent with
monomeric dibenzocyclooctynes. Grafting with azide-termi-
nated polystyrene and polyethylene glycol monomethyl ether
chains of varying molecular weight resulted in the efficient
syntheses of a series of graft copolymers with a conjugated
backbone and maximal graft density.
molecular weights, polydispersities, and regiochemistries; all
factors that have an effect on polymer properties.[31] In light of
these limitations, a method for the generation of libraries of
conjugated polymers with different backbone structures but
identical degree of polymerization and polydispersity is
desired. Such a method would require modification of the
backbone structure after polymerization in order to maintain
constant polymer length. This is challenging, since the post-
polymerization modification of conjugated polymer back-
bones is uncommon and often suffers from incomplete
functionalization.[32] Benzannulations have recently been
demonstrated as an efficient method for post-polymerization
modification, but they generally result in a very specific
polymer structure.[33]
We have previously investigated the use of a dibromo
derivative of dibenzoazacyclooctyne (DIBAC) for post-poly-
merization functionalization through strain-promoted azide–
alkyne cycloaddition (SPAAC).[34] The strained cyclooctyne
within the dibromo-DIBAC structure permitted rapid trans-
formation of the alkynes into conjugated triazoles, thereby
altering their electronic and physical properties. Unfortu-
nately, we were unable to introduce the cyclooctyne moiety
into the backbone of a polymer because the metal catalysts
used in most cross-coupling polymerizations (Ni, Pd, Cu)
rapidly underwent cycloaddition reactions with the strained
alkyne of the monomer, rather than the desired oxidative
addition at the carbon–halogen bond.[35–37] This led us to
explore polymerization methods that do not involve the use of
transition-metal catalysts, including reactions such as the
Wittig, Horner–Wadsworth–Emmons,[38–40] Aza-Wittig,[41,42]
and Knoevenagel condensation,[43] as well as Schiff-base
formation.[44,45] Many of these methods have been demon-
strated to yield high-molecular-weight polymers, and a wide
variety of structural diversity has been explored. Amongst
these, Schiff-base formation offers several advantages: it has
been well-explored,[46–48] can produce high-molecular-weight
polymers, and the installation of amine groups is straightfor-
ward to achieve by using Buchwald–Hartwig chemistry.[49]
The structurally most simple parent structure, dibenzocy-
clooctyne (DIBO),[50] is ideal as a monomer for conjugated
polymer synthesis because it has a relatively planar, sym-
metrical structure.[50–54] In our hands, the synthetic approach
based on a Wittig–PrØvost homologation sequence was found
to be compatible with initial introduction of aryl halides (in
this case, iodides), which could subsequently be converted
into the required amines in the target monomer 6 (DIBO-
(NH2)2). As illustrated in Scheme 1, starting with dibenzosu-
berone, standard iodination conditions generated diiodosu-
berone 1 in modest yield.[55] No ortho/para selectivity was
observed for the halogenation, and the ortho,ortho-, para,
C
onjugated polymers have attracted tremendous attention
in both academia and industry as a consequence of their
unique properties.[1–3] A wide range of conjugated macro-
molecules have been investigated, including derivatives of
polyacetylene,[4,5] polyphenylene,[6] polyarylenevinylene,[7,8]
polypyrrole,[9] polythiophene,[10] and polyfluorene back-
bones,[11,12] as well as numerous more complex structures.[13]
This structural variability, combined with post-polymerization
modification (i.e., doping), allows manipulation of the
optoelectronic and physical properties, including absorption/
emission wavelengths, band gap, HOMO/LUMO levels,
conjugation length, and solubility.[14–18] These parameters
have made numerous commercial applications possible,
including light-emitting diodes (LEDs),[19–23] field-effect tran-
sistors (FETs),[24] organic solar cells,[25] and chemical sen-
sors.[26] Conjugated polymers have also been investigated as
components in printed electronics.[1] A more recent and
rapidly growing area of application involves the selective
dispersion of single-walled carbon nanotubes.[27–30] In all of
these cases, investigation of structure–activity relationships,
where the backbone or side-chain structure of conjugated
polymers is varied, requires de novo synthesis of each
conjugated polymer. In addition, differences in monomer
ratios within iterative syntheses can result in a range of
[*] V. Kardelis, R. C. Chadwick, A. Adronov
Department of Chemistry, McMaster University
1280 Main St. W. , Hamilton, ON L8S 4m1 (Canada)
E-mail: adronov@mcmaster.ca
Supporting information and ORCID(s) from the author(s) for this
article are available on the WWW under http://dx.doi.org/10.1002/
anie.201508639.
Angew. Chem. Int. Ed. 2016, 55, 945 –949
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
945

Angewandte
Communications
Chemie
achieved by varying the catalyst amount and
stopping the polymerization before oligomer cou-
pling becomes significant. Addition of 2 mol%
PTSA resulted in uniform polymerization, pro-
ducing polymer with molecular weight on the
order of 30 kDa within 3–4 hours (P0, Table 1).
The product polymer P0 was characterized by 1H-
and 13C-NMR, Raman, UV/Vis, and fluorescence
spectroscopy , as well as gel-permeation chroma-
tography (GPC). The presence of alkyne moieties
in P0 was confirmed through observation of the
alkyne stretch at 2160 cmÀ1 by Raman spectrosco-
py, and the position of the bridgehead signals in
1
the H-NMR spectra (Figure 1a,b, respectively).
Addition of larger quantities of PTSA resulted in
higher polymerization rates, but initial formation
of lower-molecular-weight oligomers. Over the
course of several days, these oligomers undergo
coupling reactions, thereby resulting in a polymer
fraction with much higher molecular weight
(> 100 kDa). However, a bimodal distribution
containing a significant amount of the initially
Scheme 1. Synthesis of the DIBO-(NH2)2 monomer 6 (a), and the bis(alkoxy)phenyl
dialdehyde comonomer 9 (b).
para-, and ortho,para- derivatives were each isolated in
approximately equal amounts. Ring expansion of 1 using the
Table 1: Physical and electronic properties of polyimine polymer P0 and
Wittig–PrØvost homologation was carried out in good yield to
generate the 8-membered cyclooctanone 3.[56] Subsequently,
standard Buchwald–Hartwig amination conditions using
benzophenone imine generated the diimine-protected
ketone 4 (Scheme 1).[49] In situ generation of the enol triflate
followed by elimination using KHMDS formed the cyclo-
octyne 5,[54,57] and finally deprotection under aqueous acidic
conditions allowed the isolation of monomer 6. The co-
monomer, an alkoxybenzene dialdehyde (9), was synthesized
from bis(hexadecyloxy)diiodobenzene through a modified
Bouveault aldehyde synthesis (Scheme 1b).[58–60]
its clicked derivatives.
Polymer lmax,ab [nm] lmax,em [nm] mn [kgmolÀ1
]
mw [kgmolÀ1
]
PDI[a]
P0
P1
P2
P3
P4
P5
313, 412
300, 409
297, 409
298, 409
295, 409
288, 409
545 (weak) 30.8
62.6
44.1
41.3
42.5
38.3
49.5
2.03
2.15
2.16
2.25
2.55
2.06
–
–
–
–
–
20.6
19.1
18.9
15.0
24.0
[a] PDI=Polydispersity index.
Polymerization was performed by heating monomers 6
and 9 in toluene with p-toluenesulfonic acid (PTSA) as
a catalyst (Scheme 2). This polymerization proceeds rapidly
until all of the amines either react or become protonated by
the acid catalyst. After this point, the polymerization
continues at a much slower rate, since the remaining
ammonium ions must undergo deprotonation in order to
react. Thus, a degree of molecular-weight control can be
formed oligomers could not be avoided. The best results were
thus achieved when low catalyst loadings were used.
Polymer P0 was then reacted with a series of aryl azides at
room temperature in toluene at an alkyne concentration of
approximately 35 mm by using a 1.5-fold excess of azide
(Scheme 2). In all cases, complete functionalization was
observed in 30 min, and the 1H-NMR spectra showed no
trace of unreacted cyclooctyne (see the Supporting Informa-
tion). Varying the substituents on the aromatic
ring from electron withdrawing (p-, m-, and o-
nitro) to electron donating (tert-butyl and
OTIPS) had no observable effect on the rate
of cycloaddition. To our surprise, changing the
electron-withdrawing/donating nature of the
cycloadduct had little effect on the photophys-
ical properties of the polymer backbone, as
evidenced by UV/Vis absorption spectroscopy
(see Table 1 and Figure S5 in the Supporting
Information). Interestingly, whereas the
alkyne-containing polymer was weakly fluores-
cent, none of the “clicked” derivatives P1–P5
exhibited any fluorescence.
GPC data for the clicked polymers
(Table 1) suggested that a decrease in molec-
Scheme 2. Synthesis of cyclooctyne-containing polymer P0 and its cycloadducts P1–P5.
946
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 945 –949

Angewandte
Communications
Chemie
literature value for DIBO derivatives (0.057mÀ1 sÀ1),[65] but is
unsurprising when taking into account the decreased avail-
ability and mobility of the cyclooctyne functionality within
the polymer chain.
To further test the cycloaddition, we performed a series of
reactions with azide-terminated polymers (Scheme 2, P6–
P10). Initially we used polystyrene azides with molecular
weights of 4, 9, and 24 kDa (Table 2).[66,67] Polymer P0 was
Table 2: Graft copolymer properties (P6--P10).
Graft
Graft copolymer
Graft
mn
PDI
mn
Theor. Weight %
Composition
(GPC,
kDa)
(GPC)
(GPC,
kDa)
mn
(kDa)
Graft
N3-PS-4k (P6)
N3-PS-9k (P7)
N3-PS-24k (P8)
N3-PEG-OMe-2k 2.0
(P9)
3.9
8.7
24
1.12
1.09
1.13
–
140
270
182
330
980
106
83
91
97
71
790
N/A[a]
Figure 1. a) Raman spectrum of P0 and 6 at 785 nm excitation.
b) 1H NMR spectra of P0 and 6. Note the preservation of ethylene
bridge proton signals at 2.5 and 3.4 ppm.
N3-PEG-OMe-5k 5.0
–
N/A[a]
220
86
(P10)
Da
[a] Values not measured due to poor solubility in THF.
ular weight occurred upon alkyne–azide cycloaddition. How-
1
ever, H-NMR indicated no evidence of backbone degrada-
tion, since the amount of residual aldehyde, arising from the
end groups, remained constant relative to backbone signals.
We hypothesized that the change in apparent molecular
weight could be due to a change in the conformation of the
polymer in solution, rather than chain scission. To investigate
this hypothesis, modeling studies using both density func-
tional theory (DFT) and semi-empirical methods were used
to determine any changes in conformation upon cycloaddi-
tion. Using DFT (M06 Functional, Popleꢀs 6-31 basis set),[61,62]
we modeled the structure of the DIBO unit before and after
cycloaddition (see the Supporting Information). We then
constructed oligomers (4 repeat units) using this structure and
geometry-optimized them using semi-empirical methods
(Parametric Method 3).[63] These studies suggest that cyclo-
addition results in an accordion-like contraction of the
polymer chain, which is congruent with the decreased
molecular volume exhibited by the “clicked” polymers as
measured by GPC (Figure 2).
stirred with 1.5 equivalents of azide-terminated polymer (per
alkyne) at 608C for 12 hours in deuterated toluene. Alkyne
conversion was found to be quantitative, even when employ-
ing 24 kDa polystyrene grafts, as Raman and 1H-NMR
spectroscopy showed no evidence of residual alkyne in the
high-molecular-weight products (Figure 3a,b, and Table 2).
The quantitative grafting of polymer chains also provides
a method for modifying the solution properties of the
polyimine. By grafting with azide-terminated polyethylene
glycol monomethyl ether (N3-PEG-OMe), we were able to
alter the solubility of this polymer. As expected, the starting
polyimine and its small-molecule cycloadducts (P0–P5) are
highly soluble in nonpolar solvents such as chloroform,
toluene, and tetrahydrofuran. These structures show only
slight solubility in N,N-dimethylformamide and dimethylsulf-
oxide, and essentially no solubility in other polar solvents.
After grafting with 2 kDa N3-PEG-OMe, the graft copolymer
remained soluble in toluene but also exhibited high solubility
in methanol. However, grafting with 5 kDa N3-PEG-OMe
resulted in a graft copolymer that exhibited marked solubility
in water (Figure 4d). As in the case of polystyrene, 1H-NMR
and Raman data show quantitative conversion of the back-
bone alkynes to the resulting triazole rings (Figure 4a,b).
By using tapping-mode atomic force microscopy (AFM),
we were able to image individual graft-copolymer structures
(Figure 3c and Figure 4c). Samples for AFM measurements
were prepared by spin-coating dilute solutions of the graft
copolymers onto freshly cleaved mica. These AFM images
show individual graft copolymers on the mica surface with
sizes and aspect ratios that are consistent with the expected
features of the graft copolymers. For example, polymer P8,
which has 24 kDa PS grafts, exhibits a rigid, cylindrical shape
with a width on the order of 30 nm, and a length on the order
of 80 nm (Figure 3c), while polymers P9 and P10, which have
An NMR kinetics study to determine cyclooctyne reac-
tivity within the polymer backbone indicated a second-order
rate constant of 0.031mÀ1 sÀ1 in chloroform (for full details, see
the Supporting Information).[64] This is slightly lower than the
Figure 2. Optimized geometry of short polymer chain (PM3) before (a)
and after (b) reaction with phenyl azide. Note the accordion-like
contraction of the polymer backbone.
Angew. Chem. Int. Ed. 2016, 55, 945 –949
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
947

Angewandte
Communications
Chemie
Figure 3. a) Raman spectra measured with 785 nm excitation confirm
the complete reaction of all alkyne moieties (2160 cmÀ1, see inset for
magnification) of P0 for each polystyrene graft (P6–P8). b) 1H-NMR of
P0 and P8 (24 kDa graft) in [D8]toluene, showing complete disappear-
ance of the ethylene bridge protons (d=3.27 and 2.66 ppm, magnified
in the inset). c) Amplitude mode AFM images showing individual graft
copolymers for the polystyrene 24k graft (P8). Note: dashed boxes
indicate the area of magnification in the subsequent image to the
right; the inset shows the height profile along the indicated dotted
line.
PEO grafts, exhibit a more spherical shape, with diameters on
the order of 20–30 nm (Figure 4c). The greater flexibility and
lower molecular weight of the PEO grafts allowed the
polymer to adopt a more coiled, globular structure, rather
than the extended cylindrical shape of P8.
Figure 4. a) Raman spectra at 785 nm excitation confirm complete
reaction of all of the alkyne groups (2160 cmÀ1) of P0 for each PEG-
OMe graft (P9 and P10). b) 1H-NMR spectra for P0, P9, and P10 in
[D8]toluene, showing complete disappearance of the ethylene bridge
protons (d=3.27 and 2.66 ppm). A shift in the imine protons is also
observed (d=9.5 ppm). c) Amplitude-mode AFM images showing
individual PEG-OMe graft copolymers (P9 and P10). Note: dashed
boxes indicate the area of magnification in the subsequent image to
the right. d) 2 kDa PEG-OMe graft copolymer exhibits no solubility in
water (i), but shows solubility in methanol (ii); 5 kDa PEG-OMe graft
copolymer exhibits solubility in both water (iii) and methanol (iv).
In summary, we have demonstrated the synthesis of
a
high-molecular-weight (> 30 kDa) polymer containing
strained dibenzocyclooctyne moieties. Each cyclooctyne
within the polymer backbone reacts with aliphatic and aryl
azides at a rate that is consistent with similar small-molecule
cyclooctynes. We prepared a library of homologous triazole-
containing polymers (P1–P5) from the single progenitor poly-
alkyne (P0) through SPAAC. We also demonstrated the high-
efficiency of these reactions though coupling with azide-
terminated polystyrene and polyethylene glycol monomethyl
ether chains. These polymer grafting reactions were rapid and
quantitative, producing samples with compositions containing
up to 97% graft in under 12 hours at modest temperatures
(608C). Further studies to investigate more diverse modifi-
cation of these polymers and their applications are now in
progress.
(NSERC), and the NSERC CREATE program on the
Integrated Development of Extracellular Matrices (IDEM).
R.C. and V.K. are grateful for support through the Ontario
Graduate Scholarships (OGS) program.
Keywords: click chemistry · conjugated polymers ·
graft copolymers · polymer modification · polymers
How to cite: Angew. Chem. Int. Ed. 2016, 55, 945–949
Angew. Chem. 2016, 128, 957–961
Acknowledgements
[1] A. Facchetti, Chem. Mater. 2011, 23, 733 – 758.
[2] Conjugated Polymer Processing and Applications (Eds.: T. A.
Skotheim, J. R. Reynolds), CRC, Boca Raton, 2007.
Financial support for this work was provided by the Natural
Science and Engineering Research Council of Canada
948
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 945 –949

Angewandte
Communications
Chemie
[3] Conjugated Polymers: Theory, Synthesis Properties, and Char-
[34] R. C. Chadwick, V. Kardelis, S. Liogier, A. Adronov, Macro-
acterization (Eds.: T. A. Skotheim, J. Reynolds), CRC, Boca
Raton, 2006.
molecules 2013, 46, 9593 – 9598.
[35] G. Wittig, S. Fischer, Chem. Ber. 1972, 105, 3542 – 3552.
[36] M. A. Bennett, H. P. Schwemlein, Angew. Chem. Int. Ed. Engl.
1989, 28, 1296 – 1320; Angew. Chem. 1989, 101, 1349 – 1373.
[37] G. Grçger, U. Behrens, F. Olbrich, Organometallics 2000, 19,
3354 – 3360.
[38] G. A. Lapitskii, S. M. Makin, A. A. Berlin, Polym. Sci. U.S.S.R.
1967, 9, 1423 – 1430.
[39] B. J. Laughlin, R. C. Smith, Macromolecules 2010, 43, 3744 –
3749.
[4] H. Shirakawa, E. J. Louis, A. G. MacDiarmid, C. K. Chiang, A. J.
Heeger, J. Chem. Soc. Chem. Commun. 1977, 578.
[5] C. Chiang, C. Fincher, Y. Park, A. Heeger, H. Shirakawa, E.
Louis, S. Gau, A. MacDiarmid, Phys. Rev. Lett. 1977, 39, 1098 –
1101.
[6] M. Rehahn, A.-D. Schlüter, G. Wegner, W. J. Feast, Polymer
1989, 30, 1060 – 1062.
[7] J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks,
K. Mackay, R. H. Friend, P. L. Burns, A. B. Holmes, Nature 1990,
347, 539 – 541.
[40] D. A. M. Egbe, H. Tillmann, E. Birckner, E. Klemm, Macromol.
Chem. Phys. 2001, 202, 2712 – 2726.
[8] R. A. Wessling, R. G. Zimmermann, No Title, 1972, U.S. Pat.
3,401,152.
[41] J. Miyake, Y. Tsuji, A. Nagai, Y. Chujo, Macromolecules 2009,
42, 3463 – 3468.
[9] R. McNeill, R. Siudak, J. Wardlaw, D. Weiss, Aust. J. Chem. 1963,
16, 1056.
[10] T. Yamamoto, K. Sanechika, A. Yamamoto, J. Polym. Sci.
Polym. Lett. Ed. 1980, 18, 9 – 12.
[11] M. Leclerc, J. Polym. Sci. Part A 2001, 39, 2867 – 2873.
[12] V. V. Prey, H. Schindlbauer, D. Cmelka, Angew. Makromol.
Chemie 1973, 28, 137 – 143.
[13] P. M. Beaujuge, J. R. Reynolds, Chem. Rev. 2010, 110, 268 – 320.
[14] Design and Synthesis of Conjugated Polymers (Eds.: M. Leclerc,
J.-F. Morin), Wiley-VCH, Weinheim, 2010.
[42] J. Miyake, Y. Chujo, Macromolecules 2008, 41, 9677 – 9682.
[43] S. Kim, C.-K. Lim, J. Na, Y.-D. Lee, K. Kim, K. Choi, J. F. Leary,
I. C. Kwon, Chem. Commun. 2010, 46, 1617 – 1619.
[44] J. H. Hodgkin, J. Heller, J. Polym. Sci. Part C 2007, 29, 37 – 46.
[45] C.-J. Yang, S. A. Jenekhe, Macromolecules 1995, 28, 1180 – 1196.
[46] C. S. Marvel, N. Tarkoy, J. Am. Chem. Soc. 1958, 80, 832 – 835.
[47] H. A. Goodwin, J. C. Bailar, J. Am. Chem. Soc. 1961, 83, 2467 –
2471.
[48] A. Iwan, D. Sek, Prog. Polym. Sci. 2008, 33, 289 – 345.
[49] J. P. Wolfe, J. Šhman, J. P. Sadighi, R. A. Singer, S. L. Buchwald,
Tetrahedron Lett. 1997, 38, 6367 – 6370.
[50] G. Seitz, L. Pohl, R. Pohlke, Angew. Chem. Int. Ed. Engl. 1969, 8,
447 – 448; Angew. Chem. 1969, 81, 427 – 428.
[15] P. Zalar, Z. B. Henson, G. C. Welch, G. C. Bazan, T. Q. Nguyen,
Angew. Chem. Int. Ed. 2012, 51, 7495 – 7498; Angew. Chem.
2012, 124, 7613 – 7616.
[16] G. C. Welch, G. C. Bazan, J. Am. Chem. Soc. 2011, 133, 4632 –
4644.
[51] N. E. Mbua, J. Guo, M. A. Wolfert, R. Steet, G.-J. Boons,
ChemBioChem 2011, 12, 1912 – 1921.
[17] J. a E. H. Van Haare, E. E. Havinga, J. L. J. Van Dongen, R. a J.
Janssen, J. Cornil, J. L. BrØdas, Chem. Eur. J. 1998, 4, 1509 – 1522.
[18] H. Sirringhaus, P. J. Brown, R. H. Friend, M. M. Nielsen, K.
Bechgaard, B. M. W. Langeveld-Voss, A. J. H. Spiering, R. A. J.
Janssen, E. W. Meijer, P. Herwig, et al., Nature 1999, 401, 685 –
688.
[52] H. Meier, H. Gugel, Synthesis 1976, 338 – 339.
[53] S. Kornmayer, F. Rominger, R. Gleiter, Synthesis 2009, 2547 –
2552.
[54] H. Bühl, H. Gugel, H. Kolshorn, H. Meier, Synthesis 1978, 536 –
537.
´
ˇ
[55] L. Leseticky, S. Smrcek, V. Svµta, J. Podlahovµ, J. Podlaha, I.
ˇ
[19] J.-F. Morin, M. Leclerc, Macromolecules 2002, 35, 8413 – 8417.
[20] A. Donat-Bouillud, I. LØvesque, Y. Tao, M. D’Iorio, S. BeauprØ,
P. Blondin, M. Ranger, J. Bouchard, M. Leclerc, Chem. Mater.
2000, 12, 1931 – 1936.
Císarovµ, Collect. Czechoslov. Chem. Commun. 1990, 55, 2677 –
2684.
[56] M. S. Hossini, K. J. McCulloug, R. McKay, G. R. Proctor,
Tetrahedron Lett. 1986, 27, 3783 – 3786.
[21] S. BeauprØ, P. -L. T. Boudreault, M. Leclerc, Adv. Mater. 2010, 22,
E6 – E27.
[57] C. S. McKay, J. Moran, J. P. Pezacki, Chem. Commun. 2010, 46,
931 – 933.
[22] N. Blouin, M. Leclerc, Acc. Chem. Res. 2008, 41, 1110 – 1119.
[23] I. F. Perepichka, D. F. Perepichka, H. Meng, F. Wudl, Adv. Mater.
2005, 17, 2281 – 2305.
[24] H. Sirringhaus, Science 1998, 280, 1741 – 1744.
[25] A. J. Heeger, Chem. Soc. Rev. 2010, 39, 2354 – 2371.
[26] D. Tyler McQuade, A. E. Pullen, T. M. Swager, Chem. Rev. 2000,
100, 2537 – 2574.
[58] L. Bouveault, Bull. Soc. Chim. Fr. 1904, 31, 1306 – 1322.
[59] L. Bouveault, Bull. Soc. Chim. Fr. 1904, 31, 1322 – 1327.
[60] E. A. Braude, E. A. Evans, J. Chem. Soc. 1955, 3334 – 3337.
[61] Y. Zhao, D. G. Truhlar, Theor. Chem. Acc. 2008, 120, 215 – 241.
[62] W. J. Hehre, R. Ditchfield, J. a. Pople, J. Chem. Phys. 1972, 56,
2257 – 2261.
[63] J. J. P. Stewart, J. Comput. Chem. 1989, 10, 209 – 220.
[64] E. M. Sletten, C. R. Bertozzi, Acc. Chem. Res. 2011, 44, 666 –
676.
[27] A. Hirsch, Angew. Chem. Int. Ed. 2002, 41, 1853 – 1859; Angew.
Chem. 2002, 114, 1933 – 1939.
[28] A. Star, Y. Liu, K. Grant, L. Ridvan, J. F. Stoddart, D. W.
Steuerman, M. R. Diehl, A. Boukai, J. R. Heath, Macromole-
cules 2003, 36, 553 – 560.
[29] N. A. Rice, K. Soper, N. Zhou, E. Merschrod, Y. Zhao, Chem.
Commun. 2006, 4937 – 4939.
[65] C. G. Gordon, J. L. MacKey, J. C. Jewett, E. M. Sletten, K. N.
Houk, C. R. Bertozzi, J. Am. Chem. Soc. 2012, 134, 9199 – 9208.
[66] R. C. Chadwick, U. Khan, J. N. Coleman, A. Adronov, Small
2013, 9, 552 – 560.
[67] H. Li, F. Cheng, A. M. Duft, A. Adronov, J. Am. Chem. Soc.
2005, 127, 14518 – 14524.
[30] N. A. Rice, A. Adronov, J. Polym. Sci. Part A 2014, 52, 2738 –
2747.
[31] X. Yang, J. Loos, Macromolecules 2007, 40, 1353 – 1362.
[32] Y. Yuan, T. Michinobu, M. Ashizawa, T. Mori, J. Polym. Sci. Part
A 2011, 49, 1013 – 1020.
[33] H. Arslan, J. D. Saathoff, D. N. Bunck, P. Clancy, W. R. Dichtel,
Angew. Chem. Int. Ed. 2012, 51, 12051 – 12054; Angew. Chem.
2012, 124, 12217 – 12220.
Received: September 15, 2015
Published online: December 8, 2015
Angew. Chem. Int. Ed. 2016, 55, 945 –949
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
949