Postfunctionalization of helical polyisocyanopeptides with phthalocyanine chromophores by "click chemistry"

Article abstract of DOI:10.1002/cplu.201200087

Rigid rod polyisocyanopeptides bearing phthalocyanines as pendant groups have been synthesised through CuAAC of polyisocyanopeptides containing acetylene groups with zinc(II) phthalocyanine azide. As confirmed by UV/Vis, fluorescence, and circular dichroi

Full text of DOI:10.1002/cplu.201200087

DOI: 10.1002/cplu.201200087
Postfunctionalization of Helical Polyisocyanopeptides with
Phthalocyanine Chromophores by “Click Chemistry”
Ismael Lꢀpez-Duarte,[a] M. Victoria Martꢁnez-Dꢁaz,[a] Erik Schwartz,[b] Matthieu Koepf,[b]
Paul H. J. Kouwer,[b] Alan E. Rowan,*[b] Roeland J. M. Nolte,*[b] and Tomꢂs Torres*[a, c]
In memory of Rafael Suau
Rigid rod polyisocyanopeptides bearing phthalocyanines as
pendant groups have been synthesised through CuAAC of pol-
yisocyanopeptides containing acetylene groups with zinc(II)
phthalocyanine azide. As confirmed by UV/Vis, fluorescence,
and circular dichroism spectroscopies, the phthalocyanines are
arranged in a helical fashion along the polymer backbone,
forming the longest reported well-defined phthalocyanine as-
sembly described to date.
Introduction
The development of well-defined arrays of chromophoric mol-
ecules inspired by the naturally occurring photosynthetic ma-
chinery has attracted great interest in recent years owing to
their potential application in the fields of molecular photon-
ics.[1] The naturally occurring photosynthetic light-harvesting
antenna complexes exhibit a precise organization and orienta-
tion of the chromophores, thus ensuring an efficient absorp-
tion and transportation of light and its subsequent conversion
into chemical energy.[2]
been constructed which exhibit excellent exciton and charges
migration properties along the stacked chromophores.[12]
Phthalocyanines (Pcs) are well-known chromophoric com-
pounds characterized by their intense absorption in the red/IR
region (Q-band).[13] The aggregation properties of Pcs, mainly
realized by p–p stacking interactions between the flat aromatic
macrocycles, favor their self-organization into one-dimensional
columnar aggregates,[14] which exhibit high charge mobili-
ties.[15] However, as in the case of other chromophoric mole-
cules, there is a persistent need of controlling the Pc organiza-
tion into well-defined, robust systems to integrate these dye
molecules into materials in which energy transfer between the
units would be possible over large distances.
The self-organization of programmed chromophores by
non-covalent interactions such as hydrogen bonding, p–p
stacking, and metal–ligand coordination has been used as
a tool for the construction of well-defined chromophoric archi-
tectures with interesting photophysical and (opto)electronic
properties as a result of excitonic interactions between the
chromophores.[3] Certain applications, however, require more
robust assemblies that cannot be obtained by non-covalent
synthesis, that is applications in which a full control of the final
structure is needed, which until now can only be afforded by
covalent synthesis.[4]
Several strategies for the incorporation of phthalocyanines
into polymers have been described.[16] Poly(phthalocyaninate
siloxane)s[17] and the so-called “Shish-kebab polymers”[18] are
examples of polymers in which the main backbone consists of
a cofacial arrangement of the Pc molecules, leading to materi-
als with electrical conductivity owing to the overlap of the
p orbitals. Furthermore, ordered stacked phthalocyanine poly-
mers based on long-chain octa-substituted phthalocyanines
bearing terminal olefin groups have also been prepared by
a photostimulated [2+2] cycloaddition reaction[19] or a metathe-
Nolte, Rowan, and co-workers have developed a covalent
strategy to prepare long and well-ordered arrays of chromo-
phore molecules by grafting them onto a rigid and well-de-
fined helical polyisocyanide backbone.[5] Polyisocyanides are
stable helical polymers that do not unfold if bulky side chains
are present.[6] The polyisocyanide helical structure can also be
stabilized and rigidified if chiral amino acid or peptide residues
are attached close to the polymeric backbone to promote the
formation of hydrogen bonding interactions between the side
chains of the resulting polymer.[7]
[a] Dr. I. Lꢀpez-Duarte, Dr. M. V. Martꢁnez-Dꢁaz, Prof. T. Torres
Department of Organic Chemistry, Autonoma University of Madrid
28049-Madrid (Spain)
E-mail: tomas.torres@uam.es
[b] Dr. E. Schwartz, Dr. M. Koepf, Dr. P. H. J. Kouwer, Prof. A. E. Rowan,
Prof. R. J. M. Nolte
Radboud University Nijmegen, Institute for Molecules and Materials
6525 ED Nijmegen (The Netherlands)
E-mail: r.nolte@science.ru.nl
Polyisocyanopeptides exhibit a 154-helical conformation with
an average spacing between the side chains n and (n+4) of
4.6 ꢃ.[8] In addition, the chiral centers of the amino acid or pep-
tide units control the handedness (left or right) of the helix.[9]
By making use of the well-defined nature of polyisocyanides,
long arrays of porphyrin[10] and perylenediimide[11] dyes have
a.rowan@science.ru.nl
[c] Prof. T. Torres
IMDEA-Nanociencia
c/Faraday 9, Campus de Cantoblanco, 28049 Madrid (Spain)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201200087.
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sis.[20] Other approaches consist of incorporating phthalocya-
nines as pending groups linked to the main backbone. For ex-
ample, [60]fullerene–phthalocyanine-based copolymers have
been prepared by metathesis copolymerization of fullerene–
and phthalocyanine–norbornene monomers for application in
organic solar cells.[21] The possible contact between the elec-
tron-donor phthalocyanine and the electron-acceptor fullerene
accounts for an efficient photoinduced charge separation.
Other examples of polymers incorporating phthalocyanines as
pendant groups for photovoltaic applications make use of
modified poly-3-hexylthiophene (P3HT) and poly(2-methoxy-5-
(3’,7’-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV).[22]
The copper(I)-catalyzed 1,3-dipolar cycloaddition of alkynes
and azides (CuAAC) to give substituted 1,2,3-triazoles has
emerged as a powerful tool to link molecules together.[23] In
materials science, this reaction has proven to be a successful
synthetic tool for the quantitative functionalization of single-
wall carbon nanotubes (SWNTs),[24] polymers, and surfaces.[25]
By using the CuAAC approach, the research groups of Nolte
and Rowan have overcome the classical difficulties encoun-
tered in the synthesis of polyisocyanides with pendant chro-
mophoric moieties, that is in fact the synthesis of the chromo-
phore-containing isocyanide monomer is tedious and consider-
able problems are often encountered in the dehydration step
of the formamide into the isocyanide. The CuAAC approach
makes use of terminal alkyne-containing[26a,b] or terminal azide-
containing[26c] polyisocyanopeptides, which can be used as
a modular scaffold to which a variety of derivatized azides or
acetylenes can be attached.
Despite the interest in the field of molecular electronics to
organize phthalocyanines with the help of a rigid macromolec-
ular skeleton, polyisocyanides bearing phthalocyanine units as
side groups have never been reported. Herein, we describe the
synthesis and characterization of the polyisocyanide l,l-PIAA-
PEZnPc 1 (Scheme 1) prepared by postfunctionalization by
CuAAC between the rigid rod alkynyl-terminated polyisocya-
nide l,l-PIAAPE 2 and ZnPcN3 3, which contains three solubiliz-
ing tert-butyl groups and one azide functional group.
Results and Discussion
When planning the synthesis of a new unsymmetrically substi-
tuted Pc derivative, the choice of the peripheral substituents
can be crucial to successfully carry out the final isolation of the
desired compound from the statistical mixture of Pcs formed
by cross-condensation of two differently substituted phthaloni-
trile precursors. The separation of the mixture of Pcs by
column chromatography can be facilitated by using peripheral
substituents of rather different polarity and/or bulky groups
that reduce the strong tendency of Pcs towards aggregation.
Our research group has reported an efficient synthesis (38%
yield) of the hydroxymethyl-substituted Pc derivative 5,[27]
which is carried out by statistical cross-condensation of a 3:1
mixture of tert-butylphthalonitrile and 4-hydroxyphthalonitrile
(6; Scheme 2).
The synthesis of 4-hydroxyphthalonitrile (6)[28] was carried
out by reduction of the corresponding formyl derivative 7 by
NaBH4 in 85% yield after purification by column chromatogra-
phy. Although the synthesis of the 4-formylphthalonitrile (7)
was first carried out from oxidative cleavage of 4-vinylphthalo-
nitrile by ozonolysis,[29] a simpler synthetic route has been de-
veloped by starting from the commercially available 4-methyl-
Scheme 1. Molecular structure of l,l-PIAAPEZnPc 1.
Scheme 2. Synthesis of phthalocyanine ZnPcN3 3. 1) NBS, AIBN, CCl4, reflux; 2) aqueous Me2NH, 608C; 3) NaBH4, EtOH; 4) Zn(OAc)2, DMAE, 1408C; 5) PPh3, I2,
CH2Cl2; 6) NaN3, THF/H2O (10:1 v/v), reflux. AIBN=azobisisobutyronitrile, DMAE=N,N-dimethylaminoethanol, THF=tetrahydrofuran.
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Helical Structures
phthalonitrile, which was subjected to benzylic bromination
using N-bromosuccinimide (NBS) to yield 4-dibromophthaloni-
trile (8). According to Bankston,[30] compound 8 was further
transformed into the corresponding 4-formylphthalonitrile (7)
in 80% yield by reaction with aqueous dimethylamine (40%)
for 1 hour at 608C.
frequency corresponding to the acetylene moieties gave us an
indication that polyisocyanopeptide 2 underwent almost com-
plete grafting by the azide derivative ZnPcN3 3. In addition,
the characteristic band of the azide stretch was no longer pres-
ent, thus indicating that the removal of excess azide was suc-
cessful during the purification process. Figure 1a shows the
Classic routes for preparing organic azides imply a two-step
transformation of the corresponding alcohol into a sulfonate
or halide derivative and subsequent displacement of the leav-
ing group by the azide ion.[31] Thus, hydroxymethyl derivative
ZnPcOH 5 was reacted with triphenylphospine and resublimed
iodine at room temperature, and afforded iodide compound
ZnPcI 4 in 80% yield. Then, ZnPcI 4 was converted into the
azide derivative 3 by heating a solution of 4 in a THF/H2O mix-
ture in the presence of sodium azide (Scheme 2). The azido
1
compound ZnPcN3 3 was characterized by H and 13C NMR, FT-
IR, UV/Vis, and fluorescence spectroscopies as well as by mass
spectrometry. The characteristic intense band of the azide
stretch at n=2100 cmꢀ1 in the IR spectrum confirmed the pres-
ence of the azide functionality in 3 (see the Supporting Infor-
mation).
The introduction of the Pcs side groups onto the polyisocya-
nide scaffold of l,l-PIAAPE 2, which was synthesized according
to published procedures,[26] was accomplished by CuAAC using
1.6 equivalents of ZnPcN3 3 (with respect to the number of
acetylene units in the polymer), copper bromide (0.17 equiv)
as catalyst, and an excess of N,N,N’,N’,N”-pentamethyldiethyle-
netriamine (PMDETA) as ligand at room temperature
(Scheme 3). After 12 hours of reaction, the polymer was
Figure 1. a) UV/Vis spectra of ZnPcN3 3 (dotted line) and polymer l,l-PIAA-
PEZnPc 1 (solid line) in CHCl3. b) Emission spectra of ZnPcN3 3 (dotted line)
and polymer l,l-PIAAPEZnPc 1 (solid line) in CHCl3.
UV/Vis spectra of azide 3 and polymer 1 in CHCl3. The broad
and blue-shifted absorption centered at about 630 nm indi-
cates the presence of exciton-coupled stacks of phthalocya-
nines forming H-type aggregates along the polymeric back-
bone. In addition, the fluorescence of polymer l,l-PIAAPEZnPc
1 is significantly quenched in comparison to that of the com-
pound ZnPcN3 3 (Figure 1b), which confirms the presence of
excited-state–chromophoric interactions between neighboring
phthalocyanine compounds.
Scheme 3. Synthesis of polyisocyanopeptide 1.
washed several times with diethyl ether to remove any starting
azide and further purified by size-exclusion chromatography.
The circular dichroism (CD) spectrum of polymer 1 in CHCl3
is shown in Figure 2. The positive Cotton effect at l=310 nm
can be assigned to the n–p* transition of the helically arranged
imine groups present in the polymer backbone, indicating that
the right-handed (P) helix of the polymer scaffold[26] is not af-
fected by the click reaction. The positive Cotton effects found
at l=350 and 690 nm are assigned, respectively, to the Soret-
and Q-bands of the phthalocyanine moieties, thus showing
1
Polymer l,l-PIAAPEZnPc 1 was characterized by H NMR, UV/
Vis, FT-IR, and fluorescence spectroscopies as well as by atomic
1
force microscopy (AFM). The H NMR spectrum of 1 in CDCl3
led to poorly resolved resonance signals, indicating aggrega-
tion of the phthalocyanines. The FT-IR measurements allowed
us to determine the scope of the CuAAC reaction (see the Sup-
porting Information). The absence of any residual stretching
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T. Torres, A. E. Rowan, R. J. M. Nolte et al.
Figure 3. AFM image of polymer l,l-PIAAPEZnPc 1 (1 mgLꢀ1 in CHCl3 spin
coated on mica).
Figure 2. a) CD spectrum of polymer l,l-PIAAPEZnPc 1 in CHCl3 indicating
that the Pcs are in a chiral environment. b) CD spectrum of polymer 2 in
CHCl3.
that these dyes are in a chiral environment created by the
inner core of the helix. This result is in sharp contrast to previ-
ous results on dye-functionalized polyisocyanopeptides synthe-
sized using CuAAC. When a perylene azide was clicked to the
polymer scaffold 2, no signals were observed in the perylene-
diimide region (i.e., l=450–650 nm).[26b] The observed differen-
ces might be attributed to a small change of the helical pitch
induced by the bulky phthalocyanine. However, (empirically)
this would be accompanied by a change in the Cotton effect
at l=310 nm, as observed for polymers to which dodecylazide
or 1-azido-11-methoxy-3,6,9-trioxaundecane were clicked.[26]
Therefore, the presence of the additional CD signals, besides
the signals corresponding to the n–p* transition of the polyi-
mine, might be attributed to the properties of the azido com-
pounds that are clicked to the polyisocyanide.
Figure 4. Histogram of the length distribution of polymer l,l-PIAAPEZnPc 1,
as calculated from the AFM images of 1.
lar weight and polydispersity parameters can be reliably calcu-
lated.[32,33] Hence, the analysis of AFM images such as the one
shown in Figure 3, summarized in the histogram depicted in
Figure 4, allowed us to determine the weight-average (Lw) and
number-average (Ln) apparent lengths as well as the length
polydispersity (PD) by using the Equations (1)–(3):
P
i Ni ꢁ L2i
P
ð1Þ
ð2Þ
ð3Þ
Lw ¼
Ln ¼
PD ¼
i Ni ꢁ Li
P
i Ni ꢁ Li
P
Polymer l,l-PIAAPEZnPc 1 could be visualized by atomic
force microscopy (AFM) after spin-coating dilute solutions
(ca. 1 mgLꢀ1) of 1 in CHCl3 on mica samples. As seen in
Figure 3, individual polymer strands of 1 are visible, highlight-
ing the rodlike character of the well-folded polyisocyanopepti-
des. As in previous examples, the molecular weight and poly-
dispersity of these materials could not be determined by
MALDI-MS or GPC techniques owing to the rod-like nature of
the polymers.[9] However, it has been reported that by measur-
ing the contours of rigid polymers in AFM images the molecu-
i Ni
Lw
Ln
The former two values amounted to Lw ꢂ79 nm and Ln
ꢂ68 nm, respectively, giving a PDꢂ1.15. Assuming a helical
pitch of 0.46 nm (i.e., every monomer segment adds 1.15 ꢃ to
the polymer chain) as measured by powder X-ray diffraction of
poly(l-isocyanoalanyl-l-alanine methyl ester),[8] these values
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Helical Structures
the organic solvent was evaporated and the resulting crude reac-
tion mixture was dissolved in 40% aqueous dimethylamine
(100 mL) and heated to 608C under argon for 1 h. The brown solu-
tion was cooled to room temperature and poured into CH2Cl2
(100 mL). The layers were separated and the organic layer was
washed consecutively with brine (2ꢅ50 mL), aqueous HCl (1 N)
(2ꢅ50 mL) and water. The organic layer was dried over anhydrous
Na2SO4 and purified by column chromatography using CH2Cl2 as
eluent to give 4-formylphthalonitrile (7) (2.4 g, 45%). 1H NMR
(300 MHz, CDCl3, 208C): d=10.12 (s, 1H, CHO), 8.31 (d, J(H,H)=
2 Hz, 1H), 8.23 (dd, J(H,H)=8 Hz, 2 Hz, 1H), 8.03 ppm (d, J(H,H)=
8 Hz); 13C NMR (75 MHz, CDCl3, 208C): d=188.21 (CHO), 138.82,
134.50, 133.73, 133.21, 120.26, 117.25, 114.51 (CN), 114.31 ppm
(CN); FTIR (KBr): n=3106, 3071, 3047, 2878, 2233 (CN), 1709, (C=O),
1567, 1381, 1149, 1096, 850, 752 cmꢀ1; MS (EI): m/z (%): 156 (61)
[M+].
amount to a degree of polymerization of approximately 750,
a Mw of 694 kgmolꢀ1, and a Mn of 598 kgmolꢀ1. To our knowl-
edge, this is the longest well-defined phthalocyanine assembly
described so far. Identical results were obtained using the
starting material polyisocyanide l,l-PIAAPE 2, further confirm-
ing that “postfunctionalization” does not affect the rod-like
starting polymer.[26a]
Conclusion
The preparation and characterization of a polyisocyanide bear-
ing phthalocyanines as pendant groups has been achieved
through CuAAC of polyisocyanopeptides containing acetylene
groups with zinc(II) phthalocyanine azide, forming the longest
reported well-defined phthalocyanine assembly described to
date.
4-Hydroxymethylphthalonitrile (6): 4-Formylphthalonitrile (1.7 g,
10.8 mmol) was dissolved in EtOH (100 mL) and the mixture was
cooled to 08C. Then, NaBH4 (104 mg, 27.5 mmol) was added por-
tionwise. The reaction mixture was stirred for 2 h at RT, and then
water was added dropwise to neutralize the excess NaBH4. The sol-
vent was evaporated under vacuum, and then the crude reaction
mixture was dissolved in EtOAc (100 mL), and further washed with
water (2ꢅ100 mL). The organic layer was dried over anhydrous
Na2SO4, filtered, and the solvent was removed under vacuum. The
product was purified by column chromatography on silica gel
using CH2Cl2/EtOAc (5:1) to afford the 4-hydroxymethylphthaloni-
trile (6; 1.4 g, 85%). 1H NMR (300 MHz, CDCl3, 208C): d=7.9 (m,
2H), 7.81 (d, J(H,H)=6 Hz, 1H), 4.73 ppm (s, 2H); 13C NMR (75 MHz,
CDCl3, 208C): d=150.48, 134.86, 132.36, 132.27, 116.78, 116.67,
114.88 (CN), 63.38 ppm (CH2-O); FT-IR (KBr): n=3356, 3106, 3071,
3047, 2230 (CꢃN), 1567, 1381, 1163,1097, 852, 749 cmꢀ1; MS (EI):
m/z (%): 158 (16) [M+].
The polymer has a rigid chiral core to which the phthalocya-
nine dyes have been attached in a helical arrangement as con-
firmed by UV/Vis, fluorescence, and CD spectroscopies. It was
found that in the postfunctionalized polymer, electronic inter-
actions between the phthalocyanine units take place, as
shown by UV/Vis and fluorescence spectroscopies.
Experimental Section
All click reactions were performed under Schlenk conditions using
distilled solvents. Sodium azide and PMDETA were purchased from
ACROS chemicals. Copper bromide was purchased from Sigma Al-
drich. All purchased chemicals were used as received. Polymer l,l-
PIAAPE 2 was prepared by literature procedures.[26] Column chro-
matography was performed using silica gel (40–60 mm) purchased
from Merck. The TLC analyses were carried out using glass coated
with silica 60F254 obtained from Merck. Size-exclusion chromatogra-
phy was performed by using a column packed with Bio Bead S-X1
2(3),9(10),16(17)-Tri-tert-butyl-23-(iodomethyl)phthalocyaninato
zinc(II) (4): A solution of PPh3 (175 mg, 0.66 mmol) and resublimed
iodine (178 mg, 0.67 mmol) in CH2Cl2 (5 mL) was stirred at RT for
5 min. Subsequently, a solution of ZnPcOH 5 (100 mg, 0.13 mmol)
in CH2Cl2 (10 mL) was added and the mixture was further stirred
for 3 h at RT. Then, it was diluted with diethyl ether (50 mL) and
successively washed with aqueous 5% NaHCO3 (2ꢅ25 mL) and
brine (2ꢅ25 mL), dried over anhydrous MgSO4, and evaporated to
give a crude product which was purified by column chromatogra-
phy on silica gel using a mixture of hexanes/THF (4:1) to afford the
corresponding ZnPcI 4 (92 mg, 80%). 1H NMR (300 MHz, [D8]THF,
208C): d=9.0 (m, 8H), 8.3 (m, 3H), 7.8 (m, 1H), 5.1 (m, 2H),
1.8 ppm (m, 27H). 13C NMR (75 MHz, [D8]THF, 208C): d=149.26,
138.51, 138.45, 138.27, 137.16, 137.04, 136.90, 136.73, 135.18,
134.76, 134.68, 134.35, 127.51, 127.22, 125.04, 124.92, 124.79,
120.47, 120.21, 117.03, 116.78, 33.75 (C(CH3)), 29.68 ppm (C(CH3)).
UV/Vis (THF): lmax (e)=341 (80000), 642 (sh), 700 nm
(148000 molꢀ1 m3 cmꢀ1); FT-IR (KBr): n=3443, 3075, 2956, 2901,
2858, 1613, 1502, 1482, 1462, 1427, 1392, 1363, 1317, 1281, 1258,
1112, 1089, 1008, 893, 828, 749, 702, 674 cmꢀ1; EM (MALDI-TOF, di-
thranol): m/z: 757–761 [MꢀI]+.
1
using CHCl3 as eluent. The H NMR spectra were recorded, at 208C,
on a Bruker AC-300 spectrometer operating at 300 MHz. The
13C NMR spectra were recorded on a Bruker AC-300 spectrometer
operating at 75 MHz. The FT-IR spectra were recorded on a Thermo-
Mattson IR300 spectrometer equipped with a Harrick ATR unit;
compounds were measured as solids. Mass spectrometry measure-
ments were performed on a VG 7070E instrument (EI/CI). The CD
spectra were recorded on a Jasco 810 instrument equipped with
a Peltier temperature control unit and were measured at 208C. The
AFM experiments were performed by using a Nanoscope IV instru-
ment from Digital Instruments. Solutions of the samples were spin
coated onto freshly cleaved Muscovite mica. All images were re-
corded with the AFM operating in tapping mode in air at room
temperature with a resolution of 512ꢅ512 pixels using moderate
scan rates (1–2 linessꢀ1). Commercial tapping-mode tips (NT-MDT)
were used with a typical resonance frequency around 300 kHz. The
UV/Vis absorption spectra were obtained with a Varian 4000 UV/Vis
spectrophotometer or a Varian Cary 50 spectrometer and fluores-
cence spectra on a PerkinElmer Luminescence spectrometer LS50B.
The MALDI-TOF spectra were measured on a Bruker Biflex III spec-
trometer using dithranol as the matrix.
2(3),9(10),16(17)-Tri-tert-butyl-23-(azidomethyl)phthalocyaninato
zinc(II) (3): A solution of ZnPcI 4 (61 mg, 0.068 mmol) and NaN3
(45 mg, 0.68 mmol) in a 10/1 mixture of THF/H2O (11 mL) was
heated at reflux until full conversion of starting material (as deter-
mined by MALDI-TOF analysis; ca. 5 h). The mixture was diluted
with EtOAc (100 mL) and successively washed with water (2ꢅ
100 mL) and brine (2ꢅ100 mL). The organic layer was dried over
4-Formylphthalonitrile (7): A mixture of 4-methylphthalonitrile
(5 g, 34.5 mmol), NBS (31 g, 138 mmol) and AIBN (1 g, 6 mmol) in
CCl4 (400 mL) was refluxed for 24 h. After cooling down to room
temperature, the liquid was filtered through a plug of silica gel
using CH2Cl2 as eluent to remove the succinimide. Subsequently,
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anhydrous Na2SO4, filtered and the solvent was evaporated under
vacuum. The crude product was purified by column chromatogra-
phy on silica gel eluting with hexanes/THF (4:1) to afford the corre-
sponding ZnPcN3 3 (49 mg, 90%). 1H NMR (300 MHz, [D8]THF,
208C): d=9.0 (m, 8H), 8.3 (m, 3H), 7.8 (m, 1H), 4.9 (m, 2H),
1.8 ppm (m, 27H); 13C NMR (75 MHz, [D8]THF, 208C): d=153.44,
153.30, 152.32, 152.25, 152.14, 151.14 151.06, 150.99, 138.68,
138.53, 138.42, 137.76, 137.23, 136.79, 136.17, 135.84, 128.09,
126.51, 126.41, 121.87, 121.67, 121.07, 118.55, 118.50, 118.28, 54.70
(CH2-N3). 35.23 (C(CH3)), 31.11 ppm (C(CH3)). UV/Vis (THF): lmax (e)=
341 (85000), 643 (sh), 700 nm (163000 molꢀ1 m3 cmꢀ1); FT-IR (KBr):
n=3374, 3075, 2956, 2902, 2866, 2100 (N3), 1613, 1487, 1431,
1393, 1363, 1330, 1282, 1256, 1149, 1085, 1047, 831, 753, 693,
674 cmꢀ1; EM (MALDI-TOF, dithranol): m/z: 799–804 [M]+.
Polyisocyanide l,l-PIAAPEZnPc 1: ZnPcN3 3 (50 mg, 0.062 mmol)
was added to a suspension of polymer l,l-PIAAPE 2 (8 mg,
0.038 mmol) in freshly distilled CH2Cl2 (5 mL) under argon. The so-
lution was repeatedly degassed by freeze, pump, and thaw cycles
(3 times). Then PMDETA (1 mL, 4.1 mmol, 47 equiv) and CuBr
(25 mg, 0.17 mmol) were added, and the solution was stirred for
18 h at RT. The precipitated copper salts were removed from the
solution by the repeated addition of a saturated aqueous solution
of EDTA and removal of the water layer from the top. The organic
layer was dried over anhydrous MgSO4, filtered, and the solvent
was removed to give a residue which was subjected to size-exclu-
sion chromatography to remove any starting azides to afford the
desired polymer l,l-PIAAPEZnPc 1 (30 mg). FT-IR (ATR): n=3263
(NH), 2129 (CꢃC), 1746 (C=O ester), 1656 (amide I), 1525 cmꢀ1
(amide II); UV/Vis (CHCl3): lmax =350, 630, 680 nm. For further char-
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Acknowledgements
This study was supported by the Spanish MICINN and MEC (CTQ-
2011–24187/BQU and CONSOLIDER INGENIO 2010, CSD2007–
00010), and by the Comunidad de Madrid (MADRISOLAR-2,
S2009/PPQ/1533). TT also thanks the European Community’s Sev-
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No. 287818 of the X10D project for financial support of this
study.
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Keywords: click
phthalocyanines · polyisocyanopeptides · polymers
chemistry
·
helical
structures
·
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Helical Structures
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Published online on && &&, 0000
ChemPlusChem 2012, 00, 1 – 8
ꢄ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chempluschem.org
&
7
&
ÞÞ
These are not the final page numbers!

FULL PAPERS
I. Lꢀpez-Duarte, M. V. Martꢁnez-Dꢁaz,
E. Schwartz, M. Koepf, P. H. J. Kouwer,
A. E. Rowan,* R. J. M. Nolte,* T. Torres*
&& – &&
Postfunctionalization of Helical
Polyisocyanopeptides with
Phthalocyanine Chromophores by
“Click Chemistry”
Rigid rod polyisocyanopeptides bear-
ing phthalocyanines as pendant groups,
arranged in a helical fashion along the
polymer backbone, have been prepared
by “click chemistry” reaction of polyiso-
cyanopeptides containing acetylene
side-arms with zinc(II) phthalocyanine
azide, resulting in the longest well-de-
fined phthalocyanine assembly reported
to date (see scheme).
&8
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www.chempluschem.org
ꢄ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPlusChem 2012, 00, 1 – 8
ÝÝ
These are not the final page numbers!