Tunable self-assembly of triazole-linked porphyrin-polymer conjugates

Article abstract of DOI:10.1002/chem.201301133

The convergence of supramolecular chemistry and polymer science offers many powerful approaches for building functional nanostructures with well-defined dynamic behaviour. Herein we report the efficient "click" synthesis and self-assembly of AB₂- and AB₄-type multitopic porphyrin-polymer conjugates (PPCs). PPCs were prepared using the copper(I)-catalysed azide-alkyne cycloaddition (CuAAC) reaction, and consisted of linear polystyrene, poly(butyl acrylate), or poly(tert-butyl acrylate) arms attached to a zinc(II) porphyrin core via triazole linkages. We exploit the presence of the triazole groups obtained from CuAAC coupling to direct the self-assembly of the PPCs into short oligomers (2-6 units in length) via intermolecular porphyrinatozinc-triazole coordination. By altering the length and grafting density of the polymer arms, we demonstrate that the association constant of the porphyrinatozinc-triazole complex can be systematically tuned over two orders of magnitude. Self-assembly of the PPCs also resulted in a 6a K increase in the glass transition temperature of the bulk material compared to a non-assembling PPC. The modular synthesis and tunable self-assembly of the triazole-linked PPCs thus represents a powerful supramolecular platform for building functional nanostructured materials. Tunable building blocks: Triazole-linked porphyrin-polymer conjugates (PPCs) were prepared in high yield using the copper(I)-catalysed azide-alkyne cycloaddition (CuAAC) "click" reaction. The triazole groups were introduced from CuAAC coupling to guide the self-assembly of the PPCs into short oligomers (2-6 units in length) via intermolecular porphyrinatozinc-triazole coordination. Association constants of the PPCs could be tuned by altering the polymer microenvironment around the porphyrin core, thus presenting a modular platform for designing self-assembled porphyrin-polymer materials. Copyright

Full text of DOI:10.1002/chem.201301133

FULL PAPER
DOI: 10.1002/chem.201301133
Tunable Self-Assembly of Triazole-Linked Porphyrin–Polymer Conjugates
Derrick A. Roberts,[a, b] Timothy W. Schmidt,[b] Maxwell J. Crossley,*[b] and
Sꢀbastien Perrier*[a]
Abstract: The convergence of supra-
molecular chemistry and polymer sci-
ence offers many powerful approaches
for building functional nanostructures
with well-defined dynamic behaviour.
Herein we report the efficient “click”
synthesis and self-assembly of AB2-
and AB4-type multitopic porphyrin–
polymer conjugates (PPCs). PPCs were
prepared using the copper(I)-catalysed
azide–alkyne cycloaddition (CuAAC)
reaction, and consisted of linear poly-
styrene, poly(butyl acrylate), or poly(-
tert-butyl acrylate) arms attached to a
zinc(II) porphyrin core via triazole
linkages. We exploit the presence of
the triazole groups obtained from
CuAAC coupling to direct the self-as-
sembly of the PPCs into short oligom-
ers (2–6 units in length) via intermolec-
ular porphyrinatozinc–triazole coordi-
nation. By altering the length and
grafting density of the polymer arms,
we demonstrate that the association
constant of the porphyrinatozinc–tria-
zole complex can be systematically
tuned over two orders of magnitude.
Self-assembly of the PPCs also resulted
in a 6 K increase in the glass transition
temperature of the bulk material com-
pared to a non-assembling PPC. The
modular synthesis and tunable self-as-
sembly of the triazole-linked PPCs thus
represents a powerful supramolecular
platform for building functional nano-
structured materials.
Keywords: click chemistry · cyclo-
addition · porphyrins · polymeriza-
tion · supramolecular chemistry
Introduction
Earlier research efforts on porphyrin–polymer conjugates
have employed microphase separation and solvophobic ag-
gregation of amphiphilic polymers for building micelles, fi-
brils, and nanoparticles.[11] Well-defined porphyrin–polymer
nanostructures have also been prepared by anchoring por-
phyrins to poly(isocyanide)[12] and polyethylene back-
bones.[13] In these systems self-assembly was due to the ag-
gregation behaviour of the polymer chains, with the por-
phyrin moiety playing an unremarkable role in the self-as-
sembly mechanism. Zimmerman and co-workers have re-
ported the sole example of using supramolecular porphyrin
chemistry to induce the self-assembly of a synthetic poly-
mer.[14] At present, this powerful route for building function-
al nanostructures remains relatively unexplored.
Herein we report an efficient “click” synthesis of AB2-
and AB4-type multitopic porphyrin–polymer conjugates
(PPCs) using the copper(I)-catalysed azide–alkyne cycload-
dition (CuAAC) reaction.[15] The PPCs consist of linear pol-
ystyrene, poly(butyl acrylate) or poly(tert-butyl acrylate)
arms, synthesised by reversible addition–fragmentation
chain transfer (RAFT) polymerisation,[16] attached to a
zinc(II) porphyrin core via triazole linkages. We exploit the
presence of the triazole group obtained from CuAAC to
direct the self-assembly of the PPCs into short oligomers via
intermolecular porphyrinatozinc–triazole coordination. We
demonstrate that the association constant of the porphyrina-
tozinc–triazole complex can be tuned by altering the poly-
mer microenvironment around the porphyrin core, and
switched completely to the disassembled state by introduc-
ing pyridine as a competitive ligand. In the solid state, por-
phyrinatozinc–triazole self-assembly caused a 6 K increase
The recent convergence of supramolecular chemistry[1] and
controlled polymerisation techniques[2] offers powerful tools
for designing hierarchically-organised polymer architectures
for nanotechnology and nanomedicine.[3] Synthetic polymers
are promising supramolecular building blocks due to their
low cost, high processability and modular functionality. By
incorporating small-molecule recognition units into polymer
chains, it is possible to target complex and dynamic macro-
molecular aggregates that may eventually mimic the struc-
ture and function of biological entities,[4] from nucleic acids
and proteins up to cells and entire living organisms.
Numerous supramolecular recognition motifs have been
applied to the rapidly expanding field of polymer self-as-
sembly. Hydrogen-bonding has featured prominently,[5] as
have metal–ligand coordination[6], p–p stacking,[7] and host–
guest inclusion complexes.[8] Surprisingly, porphyrin-based
supramolecular complexes have been largely overlooked for
directing polymer self-assembly despite their rich physical
properties[9] and well-studied supramolecular chemistry.[10]
[a] D. A. Roberts, Prof. S. Perrier
Key Centre for Polymers and Colloids, The University of Sydney
Sydney NSW 2006 (Australia)
E-mail: sebastien.perrier@sydney.edu.au
[b] D. A. Roberts, Prof. T. W. Schmidt, Prof. M. J. Crossley
School of Chemistry, The University of Sydney
Sydney NSW 2006 (Australia)
E-mail: maxwell.crossley@sydney.edu.au
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201301133.
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in the glass transition temperature for
to a non-assembled control, which we attribute to coordina-
tion-induced cross-linking of the PPCs.
(PS20)2–Zn compared
place of the alkyne-polymer. These model compounds were
designed to help elucidate the H NMR spectra and self-as-
sembly behaviour of the PPCs.
1
CuAAC coupling was performed under microwave (MW)
irradiation in N,N-dimethylformamide (DMF) using cop-
per(II) sulfate and sodium ascorbate to generate the cop-
per(I) catalyst (Scheme 1). A 5–10 mol% excess of the
alkyne-polymer was required to ensure that the azidopor-
phyrins were functionalised completely. Excess free polymer
was removed by preparative size-exclusion chromatography
(SEC) using Biobeads SX-1 in toluene. Chromatography
was simplified by the characteristic colours of the RAFT
polymer (bright yellow), two-arm PPCs (red) and four-arm
PPCs (purple), which enabled direct collection of the de-
sired bands.
Results and Discussion
Synthesis of porphyrin-polymer conjugates: Triazole-linked
PPCs were prepared from azidopoprhyrin and alkyne–
RAFT polymer precursors, as summarised in Scheme 1.
Zinc(II) di- and tetraazidoporphyrins (DN3PP–Zn and
TN3PP–Zn) were obtained in 7–32% overall yield by react-
ing 4-(bromomethyl)benzaldehyde with either pyrrole or
2,2’-dipyrromethane, followed by azide substitution of the
resulting bromoporphyrins and subsequent zinc metalla-
tion.[17] Alkyne-functionalised polystyrene (PS), poly(butyl
acrylate) (PBA) and poly(tert-butyl acrylate) (PtBA) were
prepared by RAFT polymerisation using an alkyne-func-
tionalised chain transfer agent (CTA) (see Supporting Infor-
mation, Section S1), which has been reported in previous
work.[18]
Alkyne-functionalised RAFT polymers were grafted to
the zinc(II) azidoporphyrins using a convergent CuAAC
coupling strategy previously employed by our research
group (Scheme 1).[19] Model compounds bearing triazolyl
acetate arm groups, (TA)2–Zn and (TA)4–Zn, were also pre-
pared using the same protocol, using propargyl acetate in
Porphyrin–polymer coupling was highly efficient (87–98%
1
conversion by H NMR),[20] yielding conjugates with the tar-
geted number of polymer arms per porphyrin core
(Table 1). Conversion was independent of the length of the
grafted polymer chains, demonstrating the efficacy of the
CuAAC reaction for macromolecular coupling. Average
molar mass (Mn) and dispersity values (ꢀ) of the PPCs were
determined using analytical gel permeation chromatography
(GPC) (Table 1). Measured Mn values of the two-arm conju-
gates agreed to within 7% of the theoretical number-aver-
age molar masses (Mn,theor). Mn,theor values of the four-arm
polystyrene conjugates underestimated the measured Mn by
Scheme 1. Synthesis of porphyrin–polymer conjugates. ia) 2,2’-dipyrromethane, trifluoroacetic acid, CH2Cl2, 2 h then 2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone (DDQ), 10%; ib) pyrrole, trifluoroacetic acid, CH2Cl2, 2 h then DDQ, 38%; ii) NaN3, 508C, THF/H2O 4:1, 16 h, 74–88%; iii) Zn(OAc)2·2H2O,
AHCTUNGTRENNUNG
CHCl3/CH3OH 4:1, 1 h, 90–97%; iv) CuSO4·4H2O, sodium ascorbate, DMF, MW irradiation (100 W, 1008C), 25 min; v) HCl (1m), CHCl3, RT. Pn denotes
a polymer chain with repeating unit RM and number-average degree of polymerisation of “n”; “x” corresponds to the number of polymer or triazolyl ace-
tate (TA) arms attached to the porphyrin core.
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Porphyrin–Polymer Conjugates
FULL PAPER
Table 1. Conversion data for CuAAC coupling and GPC characterisation data of the resulting PPCs. Average molar masses (Mn) and dispersity values
(ꢀ) before and after preparative SEC are compared to the theoretical molar mass Mn,theor (see Supporting Information, Section S3).[a]
NMR Conversion (%)
GPC data (before prep. SEC)
GPC data (after prep. SEC)
[a]
[a]
[a]
[a]
[b]
Conjugate
(PS20)2–Zn[c]
(PS30)2–Zn[c]
(PS40)2–Zn[c]
(PS20)4–Zn[c]
(PS30)4–Zn[c]
(PS40)4–Zn[c]
(PBA15)4–Zn[c]
(PtBA19)4–Zn[c]
HNa
HCa
HTz
Mean
s
Mp
Mn
ꢀ
Mp
Mn
ꢀ
Mn,theor
N
98
93
99
95
91
98
93
98
89
87
83
89
80
87
94
102
88
98
78
100
97
93
86
95
92
93
87
94
89
92
91
98
6
6
11
6
9
5
4
3
5450
7700
3700
6300
8550
4850
9650
15150
5300
8150
1.35
1.22
1.35
2.03
1.38
1.30
1.52
1.45
5400
7700
5170
7150
1.18
1.19
1.25
1.30
1.26
1.25
1.24
1.20
5350
7450
9500
10340
14500
18700
9700
E
N
12400
8500
12500
19650
9050
12400
9450
11300
18800
9800
10200
9400
10800
15250
9200
R
N
G
G
A
12000
12200
11800
11750
[a] Average molar masses [g molꢀ1] and dispersity values were determined by GPC using DRI detection and calibrated against linear polystyrene narrow
standards. [b] Mn,theor was calculated from the average degree of polymerisation of the grafted polymer chains (determined by 1H NMR) and the molar
masses of the porphyrin, CTA and repeating unit. [c] GPC eluent: THF, flow rate 1 mLminꢀ1, 408C with toluene flow rate marker.
9–26%, which is consistent with the reduced hydrodynamic
radius of star polymers compared to linear polymers with
the same degrees of polymerisation.[21,22] Coincidentally, Mn
values of both ACHTUNGTRENNUNG(PBA15)4–Zn and HCAUTNTGREN(NUGN PtBA19)4–Zn agreed to
within 5% of their theoretical values. Overall, the purified
conjugates displayed low to moderate dispersities
(1.18<ꢀ<1.30) consistent with the high efficiency of the
coupling reaction.
1
The H NMR spectra of the PPCs in a coordinating sol-
vent (CDCl3/[D5]pyridine, 98:2 v/v) were well-defined, in
each case showing a single set of resonances consistent with
the fully functionalised two-arm and four-arm structures
(Supporting Information, Section S5). PPC spectra were as-
signed according to the spectra of (TA)2–Zn and (TA)4–Zn,
which were themselves assigned using a combination of
1H–13C heteronuclear single quantum correlation (HSQC)
and heteronuclear multiple bond correlation (HMBC) tech-
niques (Supporting Information, Section S5.1). In the spec-
tra of the PPCs, signals of the methylene protons either side
of the triazole ring were split into complex multiplets. Based
on the HSQC and HMBC data, we attribute this splitting to
a combination of diastereotopic induction from the nearby
stereocentre and partial formation of the 1,5-triazole by-
product (<20% by 1H NMR) as a result of the thermal
Huisgen cycloaddition competing with the CuI-catalysed
pathway (Supporting Information, Section S5.2). Fortunate-
ly, the isomeric mixture of 1,4- and 1,5-triazole products did
not prevent self-assembly of the PPCs, most likely due to
the flexibility of the polymer chains around the porphyrin
core.
Figure 1. 1H NMR spectra (300 MHz) of (TA)4–Zn in CDCl3 (~10 mm)
with and without [D5]pyridine (2% v/v). The spectrum of the assembled
state was assigned using 1H–13C HSQC and HMBC NMR spectroscopy
(Supporting Information, Section S7). Pronounced diamagnetic shifting
and broadening of resonances HTz, Hm, HNa and HCa occur without
[D5]pyridine (~10 equiv). The relatively unchanged chemical shifts of
protons Hb and Ho suggest that these environments lie outside the shield-
ing zones of nearby porphyrin rings. Asterisks indicate residual solvent
peaks.
solved, with sharp peaks and chemical shifts consistent with
a molecularly dissolved D4h-symmetric tetraarylporphyrin.
Without a competitive ligand, however, each proton reso-
nance was broadened and shifted upfield by 0.08–0.83 ppm.
The resonances of Hb and phenyl-Ho shifted only slightly
(<0.15 ppm), and did not broaden noticeably, whereas Hm,
HNa, HCa and HTz broadened significantly and shifted upfield
by 0.3–0.8 ppm with respect to the unimer spectrum. These
changes support an intermolecular porphyrinatozinc–tria-
zole coordination complex, in which Hm, HNa, HCa and HTz
reside within the shielded zone of an adjacent porphyrin
ring (Figure 2). Intramolecular porphyrinatozinc–triazole co-
ordination is not possible in this system due to the rigid
structure of the porphyrin–phenylene–triazolyl arms. By
contrast, compounds that employ a flexible linker between
Spectroscopic analysis of PPC self-assembly behavior: The
1H NMR spectra of the PPCs in their assembled and unime-
ric states were complicated by the broad resonances of the
grafted polymer arms. Therefore, four-arm model compound
(TA)4–Zn was used to help elucidate the self-assembly be-
haviour of the PPCs.[23] 1H NMR spectra of unimeric and as-
sembled (TA)4–Zn are compared in Figure 1. PPC unimers
were obtained by preparing the NMR sample with ten
molar equivalents of pyridine (CDCl3/[D5]pyridine, 98:2 v/
v), which is a competitive ligand for the zinc porphyrin. The
unimer spectrum, shown in Figure 1 (red trace), was well-re-
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M. J. Crossley, S. Perrier et al.
any anomalous long-range interactions. In particular, HCa
showed only a single correlation with HTz, and there were
no cross-peaks between Hb and either HNa or HCa
.
When the NOESY spectrum of (TA)4–Zn was recorded in
neat CDCl3, additional cross-peaks due to intermolecular
correlations between HCa–Hb, HCa–Ho and HNa–Hb were ob-
served (Figure 4b). These correlations are consistent with
the intermolecular porphyrinatozinc–triazole assembly ge-
ometry illustrated in Figures 2 and 4b. Interestingly, the
cross-peak between HCa and HTz observed in the control ex-
periment was absent in the assembled state. We propose
that conformational restriction within the assembled com-
plex turns these protons away from each other, eliminating
cross-relaxation.
Under the same conditions, the PPCs showed very similar
self-assembly behaviour to (TA)4–Zn. 1H NMR spectra of
Figure 2. The Dd values of protons in Subunit A correlate with their posi-
tion from the centre of the porphyrin ring in Subunit B. Dd (ppm) values
are shown next to each proton environment. Only one of the two shield-
ing cones of the porphyrin ring is shown.
AHCTUNGTREN(GUNN PtBA19)4–Zn have been selected as representative examples
(Figure 3). 1H NMR spectra of other assembled PPCs are
shown in the Supporting Information (Section S8). In
CDCl3/[D5]pyridine (98:2 v/v), the spectrum displays sharp
signals for the porphyrin–phenylene–triazolyl spin systems,
which supports a unimeric D4h symmetric porphyrin core. In
the absence of [D5]pyridine, however, resonances of the por-
phyrin, phenyl and triazole spin systems were broadened
and shifted upfield with respect to the unimer spectrum, in a
the porphyrinatozinc and triazole subunits display intramo-
lecular coordination.[24] Peak broadening and the apparent
D4h symmetry of the porphyrin signals is consistent with en-
semble averaging due to dynamic exchange between the un-
imeric and assembled species at a fast rate compared to the
NMR timescale.[25]
1
similar fashion to the behaviour of (TA)4–Zn. The H NMR
The proposed porphyrinatozinc–triazole assembly mode
can be used to rationalise the change in chemical shift (Dd)
of each proton resonance upon self-assembly of (TA)4–Zn.
The value of Dd is taken as the difference between the as-
sembled and unimeric chemical shifts:
spectrum of freebase PPC
ACHTNUGTRNEUN(GN PS20)2-H2, prepared by acidic de-
metallation of (PS20)2–Zn (Scheme 1), demonstrates the im-
AHCTUNGTRENNUNG
portance of the porphyrinatozinc moiety for PPC self-assem-
bly: the spectrum recorded in CDCl3 (Supporting Informa-
tion, Figure S15) did not display the peak broadening and
shifting observed in the zinc-PPC samples. The PPCs, there-
fore, do not self-assemble if the centrally-bound zinc ion is
removed from the porphyrin macrocycle.
Dd ¼ dassembled ꢀ dunimer
ð1Þ
The Dd values observed in the 1H NMR spectra of the
two-arm and four-arm PPCs showed similar trends to those
of (TA)4–Zn (Table 2). The spectral changes upon aggrega-
tion of the four-arm conjugates were nearly identical to
those observed for (TA)4–Zn. The two-arm conjugates also
behaved similarly; however, the proton resonances of the as-
sembled two-arm PPCs were much sharper than the analo-
gous peaks of their four-arm counterparts, and Dd values
were larger, suggesting that higher grafting densities destabi-
lise the supramolecular assemblies.
Figure 2 shows that the Dd values of protons in subunit A
correlate with their positions from the centre of the porphyr-
in ring in subunit B. Protons situated above subunit B coin-
cide with the shielding zone of the porphyrinꢁs ring current
field, causing diamagnetic shifting of the signals.[26,27] The
closer a proton is to the centre of the porphyrin ring, the
greater the shielding effect.[28] Values of Dd are lower than
those observed for other porphyrin-based host–guest com-
plexes,[29] which is consistent with the labile nature of the
porphyrinatozinc–triazole interaction. The pattern of the Dd
values suggests that (TA)4–Zn assembles into open acyclic
structures, whereby the porphyrin rings are oriented in an
approximately T-shaped geometry as shown in Figure 2. The
design of the PPCs prevents the formation of closed cyclic
dimers,[30–33] which would cause a steric clash between the
phenyl ring and porphyrin macrocycle on adjacent PPCs.
NOESY was attempted on the smallest PPC, ACTHNUGTRNEUNG(PS20)2–Zn
(Figure S21). The expected intramolecular correlations were
present in the control sample; however the key intermolecu-
lar correlations observed in the NOESY spectrum of assem-
bled (TA)4–Zn (i.e., HCa–Hb, etc.) were absent (Figure 4).
Surprisingly, HCa did not display any cross-peaks, which sug-
gests that NOESY is not sufficiently sensitive for detecting
Two-dimensional nuclear Overhauser effect spectroscopy
(NOESY) was used to probe the structure of the porphyri-
natozinc–triazole complex in solution. A control 1H–1H
NOESY experiment of (TA)4–Zn in CDCl3/[D5]pyridine
(98:2 v/v) was performed to establish the intramolecular cor-
relations within the unimeric species (Figure 4a). The ex-
pected nearest-neighbor correlations were observed without
1
the through-space H–1H correlations within the PPCs. We
attribute this limitation to the lability of the self-assembled
oligomers, the low intensity of the porphyrin resonances
compared to those of the polymer, and rapid exchange be-
tween the assembled and unimeric species. Attempts to en-
hance the NOE for HNa and HCa by deoxygenation of the
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Porphyrin–Polymer Conjugates
FULL PAPER
Table 2. Values of Dd for various zinc(II) PPCs. 1H NMR spectra recorded at 500 MHz, 300 K, in CDCl3 with sample concentrations ranging from 2–
10 mm.
Dd [ppm]
Compound
Hmeso
Hb1
Hb2
Ho
Hm
HNa
HTz
HCa
(TA)4–Zn
A
–
–
–
–
–
–
–
–
–
–
–
ꢀ0.14
ꢀ0.03
ꢀ0.04
ꢀ0.04
+0.01
+0.02
ꢀ0.09
ꢀ0.05
ꢀ0.02
ꢀ0.08
ꢀ0.03
ꢀ0.05
ꢀ0.05
0.00
ꢀ0.27
ꢀ0.35
ꢀ0.23
ꢀ0.26
ꢀ0.26
ꢀ0.22
ꢀ0.16
ꢀ0.79
ꢀ0.51
ꢀ0.42
ꢀ0.39
ꢀ0.83
ꢀ0.56
ꢀ0.58
ꢀ0.64
ꢀ0.60
ꢀ0.54
ꢀ1.80
ꢀ1.26
ꢀ1.05
ꢀ0.17[a]
ꢀ0.20[a]
ꢀ0.19[a]
ꢀ0.16
ꢀ0.31[a]
ꢀ0.36[a]
ꢀ0.22[a]
ꢀ0.23
E
R
N
R
–
0.00
ꢀ0.12
ꢀ0.16
A
+0.10
+0.11
+0.12
ꢀ0.02
0.04
0.06
ꢀ0.15
ꢀ0.12
ꢀ0.07
ꢀ0.31[a]
ꢀ0.36[a]
ꢀ0.30[a]
ꢀ0.41[a]
ꢀ0.37[a]
ꢀ0.41[a]
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
total concentration of the PPC was varied, the relative pro-
portions of these two populations changed (Figure 6), indi-
cating an equilibrium between unimers and self-assembled
oligomers in solution.
To demonstrate that the red-shifted shoulder bands were
indeed due to axial coordination of a basic ligand to the zinc
porphyrin, the UV/Vis spectrum of ACHTUNRTGNE(UNG PS20)4–Zn was re-re-
corded in chloroform with 5 equiv of pyridine (Figure 5). A
complete shift of the original Soret band from 421 to
430 nm indicates quantitative formation of the porphyrinato-
zinc–pyridine complex. Both the Soret and Q-bands shifted
by approximately 500 cmꢀ1 without any associated spectral
broadening. Good agreement between the position of the
shoulder feature and the peak wavelength of the porphyri-
natozinc-pyridine complex suggests that the shoulder band
in Figure 5 is due to self-association of the PPCs via por-
phyrinatozinc–triazole coordination.
Figure 3. 1H NMR spectra (500 MHz) of
ACTHUNRGTNEGN(U PtBA19)4–Zn in CDCl3 with
and without [D5]pyridine (2% v/v). Assembly-induced shifting of signals
C–F agree closely with the shifts observed for (TA)4–Zn. Complex split-
ting of F is most likely due to diastereotopic induction by the nearby
chiral center (see Supporting Information, Section S5.2). Assignments:
A=Hb, B=Ho, C=Hm, D=HNa, E=HTz, F=HCa. Asterisks indicate re-
sidual solvent peaks.
Measurement of PPC association constant: Since the PPCs
are multitopic subcomponents, self-assembly can yield step-
growth supramolecular oligomers of the type shown in
Scheme 2. We have modeled the self-assembly behaviour as
an isodesmic oligomerisation process, whereby short linear
structures are formed. The system illustrated in Scheme 1 is
described by the addition of a single unimer unit to a supra-
molecular chain of length n, extending it to length n+1:
samples (freeze-pump-thaw) did not improve the quality of
the spectrum, while increasing the mixing time above
500 ms introduced spin-diffusion artifacts (Supporting Infor-
mation, Figure S22), which are typical of high molecular
weight compounds.[34] We were unable to identify a set of
NOESY parameters that provided readable intensity for the
peaks undergoing chemical exchange (HCa and HNa) while
also preventing macromolecular spin-diffusion. Despite the
limitations of the NOESY experiment, good agreement be-
tween the one-dimensional 1H NMR spectra of the PPCs
supports self-assembly via porphyrinatozinc–triazole coordi-
nation in each instance.
The Soret and Q-bands in the UV/Vis spectra of the
PPCs were split into two populations when recorded in
chloroform. The absorption spectrum of ACTHNUGTRNEUNG(PS20)4–Zn in
chloroform is shown as an example (Figure 5). The domi-
nant contributions to the broadened Soret band and Q-
bands are typical of a zinc porphyrin without an axial sub-
stituent,[35,36] whereas the red-shifted shoulder features are
attributed to the porphyrinatozinc–triazole complex. As the
PnþP1 Ð Pnþ1
ð2Þ
which has the following equilibrium constant expression:
½Pnþ1
ꢁ
ð3Þ
K ¼
½P1ꢁ½Pnꢁ
We do not expect any desolvation or pre-organisational ef-
fects to drive self-assembly in this system. The association
constant is therefore assumed to be the same for the addi-
tion of each subunit. This “Equal-K” or isodesmic self-as-
sembly behaviour is in direct contrast to cooperative self-as-
sembly, which involves the initial unfavourable association
of monomer units (nucleation) followed by favourable elon-
gation to form large assemblies.[37]
The concentration-dependent self-assembly of the PPCs
was monitored by UV/Vis spectroscopy, observing character-
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M. J. Crossley, S. Perrier et al.
absorbance of the Qa-band was
too weak at low concentrations.
Splitting of the Qb-band re-
sults from a superposition of
the spectra of porphyrinatozinc
subunits with (“bound”) and
without (“non-bound”) an ax-
ially-coordinated triazole unit.
Bound porphyrins, indicated by
unshaded porphyrin rings in
Scheme 2, will invariably be
constituents of the assembled
structures; unbound porphyrins,
shaded in grey in Scheme 2, can
be either the chain-ends of the
oligomers or free unimers.
Since the UV/Vis spectra do
not exhibit any excitonic cou-
pling effects—evidenced by the
narrow widths of the absorb-
ance bands at the high and
low
concentration
limits
(Figure 6)—the observed spec-
trum is the sum of the compo-
nent spectra.[38] By applying a
Gaussian multiple peak-fitting
procedure to these spectra,[39]
the double-humped absorption
feature was resolved into the
Qb-bands of the non-bound
(high energy) and bound (low
energy) zinc porphyrin chromo-
phores (Supporting Informa-
tion, Section S10). The peaks
Figure 4. a) Partial NOESY spectrum of unimeric (TA)4–Zn (10 mm in CDCl3/[D5]pyridine, 98:2 v/v),
500 MHz, 500 ms mixing time). Key correlations along the porphyrin-phenylene-triazole arm are highlighted
with arrows. Nearest-neighbour correlations, including an Ho-Hm COSY artifact, were observed. b) Partial
NOESY spectrum of assembled (TA)4–Zn (10 mm in CDCl3, 500 MHz, 500 ms mixing time). For clarity, only
substituents involved in monotopic binding are shown. Key intermolecular NOE correlations (closed circles)
support the proposed porphyrinatozinc–triazole complex. The HCa–Hb correlation along the vertical axis was
obscured by t1 noise. The intramolecular HCa–HTz correlation (dashed circle) was not observed.
and width of the fitted spectra were optimised to achieve a
global fit at all concentrations.
Association constants were calculated by fitting the iso-
desmic model described by Equation 4 to the concentration-
dependent assembly data:
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ð2CTK þ 1Þ ꢀ 4CTK þ 1
Vbound
¼
ð4Þ
2CTK
where Vbound is the fraction of porphyrin moieties that have
a bound triazole ligand, CT is the total concentration of
PPC (calculated using Mn,theor from Table 1) and K is the as-
sociation constant. The self-assembly model is derived in
full in the Supporting Information (Section S11).[40]
Figure 5. UV/Vis spectra of ACHTNUGRTNEUNG
(PS20)4–Zn (ca. 5ꢂ10ꢀ5 m) in: CHCl3 (solid
line); and CHCl3 + 5 equiv pyridine (dashed line). The spectrum in neat
chloroform displays shoulder peaks at 420 and 560 nm, indicating partial
self-assembly at this concentration.
Influence of polymer chains on PPC association constant:
UV/Vis spectra of PPCs in chloroform at various concentra-
tions were recorded and Vbound was plotted as a function of
total conjugate concentration (CT) (Figure 7). Measured as-
sociation constants are summarised in Table 3, with uncer-
tainties estimated from non-linear regression analysis of the
fitted model. Approximate degrees of supramolecular poly-
merisation (DPN) were estimated from association constants
istic changes in the lineshape of the Qb absorption band due
to zinc–triazole coordination. The UV/Vis spectra of
ACHTUNGTRENNUNG(PS20)2–Zn in chloroform at different concentrations is
shown as an example in Figure 6. The Qb-band was ana-
lysed, rather than the Qa or Soret bands, because the ab-
sorbance of the Soret band exceeded the saturation limit of
the spectrophotometer at high concentrations, whereas the
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Porphyrin–Polymer Conjugates
FULL PAPER
Figure 6. Q-band region of the ACHTUNTRGENUNG(PS20)2–Zn UV/Vis spectra in CHCl3 at
various concentrations. Absorption data was converted to molar absorp-
tivity [mꢀ1 cmꢀ1] in order to negate the effect of using cuvettes with differ-
ent path lengths.
Table 3. Association constants (K) of PPCs, and indicative values of the
degree of supramolecular polymerisation (DPN) at the maximum concen-
trations studied by UV/Vis.
Conjugate
K [mꢀ1
]
CT [mm]
DPN
(TA)4–Zn
AHCTUNGTRENNUNG
3.4ꢂ0.3ꢂ104
4.5ꢂ0.6ꢂ103
8.2ꢂ0.3ꢂ102
3.5ꢂ0.1ꢂ102
1.1ꢂ0.1ꢂ103
6.3ꢂ0.9ꢂ102
9.7ꢂ1.9ꢂ102
0.3
7.5
10
6.8
4.0
3.2
3.2
3.7
6.3
3.4
2.1
2.6
2.0
2.3
AHCTUNGTRENNUNG
G
AHCTUNGTRENNUNG
Scheme 2. Schematic representation of a linear supramolecular oligomer-
isation process via porphyrinatozinc–triazole coordination. Only the coor-
dinating substituents are shown for clarity. Subunits are shaded according
to the UV/Vis spectra that they will exhibit: grey subunits are the non-
coordinated chromophores, and white (unshaded) subunits are those with
an axially-coordinated triazole ligand.
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
was increased to PS30 (K=8.2ꢂ0.3ꢂ102 mꢀ1) and PS40 (K=
3.5ꢂ0.1ꢂ102 mꢀ1), respectively. The effect of increasing
chain length exhibited a diminishing influence on the associ-
ation constant as the polymer length was increased, suggest-
ing that the polymer repeating units nearest to the porphyr-
in core have the greatest influence on steric shielding. Simi-
lar core shielding effects have been observed with porphyr-
in-cored star polymers.[21,44]
The effect of changing grafting density (i.e., two or four
grafted polymer arms) showed a similar trend to the arm
length series, with the association constant decreasing as the
degree of steric crowding around the porphyrin core in-
creased (Figure 7b). Increasing the grafting density involves
two competing factors: greater steric crowding around the
porphyrin core, but also a larger number of triazole ligands
within the PPC framework. The observed decrease in associ-
ation constant with increasing grafting density implies that
steric hindrance around the porphyrin core is the dominant
factor. In similar work on steric protection of porphyrin-
cored star polymers, Hecht et al. concluded that the number
of arms grafted to the porphyrin core has little influence on
the degree of steric shielding.[44] In this instance, the authors
were investigating porphyrin-cored stars with eight and six-
teen grafted polymer arms, as opposed to the two- and four-
arm conjugates presented herein. Since we observe a differ-
ence in association constant for grafting densities of two and
four, the optimal grafting density for shielding the porphyrin
using the method of Smulders et al.[41] Supramolecular as-
semblies ranged in size from the dimer to the hexamer at
the concentrations investigated in this study. Concentrations
higher than 10 mm were not studied because the optical den-
sity of the porphyrin solutions exceeded the detection limit
of the spectrophotometer. Fortunately, we were able to
obtain assembly data over a sufficiently wide concentration
rage to measure the association constants.
Figure 7a shows the concentration-dependent assembly
behaviour of (TA)4–Zn and the set of two-arm polystyrene
conjugates with different arm lengths. (TA)4–Zn represents
a PPC with a chain length of zero. While (TA)2–Zn would
have provided an ideal comparison to the two-arm conju-
gates, its concentration-dependent behaviour could not be
analysed due to its very low solubility in chloroform. Excel-
lent agreement between the experimental data and the
model described by Equation (4) supports an isodesmic self-
assembly mechanism. The association constant of (TA)4–Zn
(K=3.4ꢂ0.3ꢂ104 mꢀ1) is of the same order of magnitude as
other non-stabilised supramolecular porphyrin complexes
based on zinc–triazole and zinc–pyridine coordination.[32,42,43]
The association constant decreased by 87% upon attach-
ment of two PS20 chains (K=4.5ꢂ0.6ꢂ103 mꢀ1), and contin-
ued to decrease by a further 82 and 59% as the chain length
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M. J. Crossley, S. Perrier et al.
properties—such as the polymers selected herein—are com-
patible with sterically-controlled self-assembly. It is impor-
tant to note, also, that the isodesmic model fails to describe
the assembly behaviour of the four-arm conjugates in Fig-
ure 7c at low concentrations (CT <10ꢀ4 m). The persistence
of bound chromophores at low CT suggests that there may
be a barrier to disaggregation for the four-arm conjugates.
The origin of this barrier is presently unknown, but could
arise from steric shielding of the zinc–triazole interaction
from solvent molecules in small (dimeric) PPC assemblies.
Effect of self-assembly on solid-state properties: The degree
of supramolecular polymerisation is only appreciable at very
high concentrations for an isodesmic assembly process.[41]
Since the highest concentration obtainable for a typical sub-
stance is that of the bulk material, we anticipated that self-
assembly of the PPCs would manifest as a change in glass
transition temperature (Tg) in the solid state.
Differential scanning calorimetry (DSC) was performed
on
ACHTUTGNREN(UNG PS20)2–Zn and the freebase CAHTUNGTRENNNUG
freebase conjugate was prepared directly from ACHTUNGTRENNUNG
by acidic demetallation under mild conditions (Supporting
Information, Section S6). Figure 8 shows that the Tg of the
zinc conjugate was ~6 K higher than the freebase. We attrib-
ute the increase in Tg to self-assembly via the zinc–triazole
assembly mode, which most likely cross-links the material in
the bulk state
Conclusion
The marriage of molecular self-assembly and polymer chem-
istry offers numerous routes for building nanostructured soft
materials with interesting dynamic behaviour. We have pre-
sented a modular strategy for synthesising triazole-linked
porphyrin–polymer conjugates, which assemble into supra-
molecular assemblies via porphyrinatozinc–triazole coordi-
nation. By altering the polymer microenvironment around
the porphyrin core we are able to systematically tune the as-
Figure 7. Concentration-dependent assembly curves of the PPCs. The
fraction of bound chromophores (Vbound) is plotted against the total con-
jugate concentration (CT). Experimental data are fitted to Equation (4).
a) Arm length dependence. (TA)4–Zn represents an effective chain
length of zero. Shaded markers represent repetitions within a dataset. b)
Grafting density dependence. c) Polymer repeating unit dependence.
core most probably lies between four and eight polymer
arms. This is an important consideration when designing
PPCs as supramolecular building blocks, as it is important to
maintain steric access to the porphyrin core while also maxi-
mising the number of polymer chains that can be organised
by a single supramolecular recognition motif. It is also
useful to know the minimum number of polymer chains
needed to sterically protect a porphyrin or other chromo-
phore from excited-state quenching in solution.[45]
We observed no significant difference between the associ-
ation constants of PPCs with different polymer repeating
units, suggesting that self-assembly is relatively insensitive to
the steric bulk of the repeating unit (Figure 7c). Conse-
quently, chemically-similar polymers with different bulk
Figure 8. DSC traces of ACTHUNRGTENNUG(PS20)2–Zn and CAHTUNTGRENN(UGN PS20)2-H2, with Tg values of 88
and 948C, respectively.
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Porphyrin–Polymer Conjugates
FULL PAPER
lytical gel permeation chromatography (GPC) on a Shimadzu LC-10AT
liquid chromatography system fitted with a PLgel 5 mm MiniMIX-C (50ꢂ
4.6 mm) guard column and two PLgel 5 mm MIXED-C (300ꢂ7.5 mm)
columns. The system was equipped with a Shimadzu RID-10A differen-
tial refractive index detector and a Shimadzu SPD-10 A UV-visible ab-
sociation constant of the porphyrinatozinc–triazole coordi-
nation complex, or switch it completely to the disassembled
state by introducing a competitive ligand. Porphyrinatozinc–
triazole coordination was shown to alter the properties of
the bulk material, manifesting in a 6 K increase in the glass
sorption detector. THF containing 1,4-hydroquinone (0.04 gLꢀ1
) was
used as the mobile phase, eluting at 1.0 mLminꢀ1 at 408C. Analyte sam-
ples were dissolved in THF spiked with 0.5 vol% toluene as the flow rate
marker and filtered through a polytetrafluoroethylene filter (0.45 mm
pore size) prior to injection (100 mL loop volume). Chromatograms were
calibrated using linear polystyrene standards. Experimental molecular
weight (Mn) and dispersity (ꢀ) values of the synthesised polymers were
determined by conventional calibration using Cirrus software. 1D
1H NMR spectra were recorded at 300 K on a Bruker Avance DPX 200
(200 MHz), DPX 300 (300 MHz) or DPX 500 MHz NMR spectrometer
using tetramethylsilane (TMS) as the internal reference. Signals are re-
corded in terms of chemical shift (in ppm), relative integral, multiplicity,
coupling constants (in Hz) and assignment, in that order. The following
abbreviations for multiplicity are used: s, singlet; d, doublet; t, triplet; m,
multiplet; br, broad. Deuterated solvents were purchased from Cam-
bridge Isotope Laboratories, Inc., and stored away from light at room
temperature. Deuterated chloroform was de-acidified by passage through
basic alumina (Brockmann Grade I) immediately prior to use. Samples
were filtered through a plug of dry cotton wool directly into NMR tubes
prior to analysis to remove any suspended solids. Two-dimensional
1H NMR spectra were recorded at 300 K on a Bruker Avance DPX
500 MHz NMR spectrometer, using a BBO two-channel probe that was
automatically tuned and matched to the correct operating frequencies
(1H and 13C). Pulse calibration (908) was routinely performed for 1H ex-
periments (typically ~12.3 ms at 15.488 W), and T1 values were estimated
by the inversion-recovery method using the standard Bruker pulse pro-
gram t1ir1d. Spectra were processed using Varian Topspin 3 and Mestre-
nova Lite software. Two-dimensional NOESY spectra were recorded on
a Bruker Avance DPX 500 MHz spectrometer using the standard Bruker
program noesygptp. At least three different mixing times ranging from
100 to 500 ms were tested to ensure optimal discrimination between
direct cross-relaxation and spin-diffusion and to estimate the mixing time
range where the initial rate approximation holds. Spectra were acquired
at 300 K with 2048 data points in f2. Typically 8 scans were accumulated
for 512 increments in f1. Phase and baseline corrections were applied
along both axes, and excessive t1 noise was removed by subtracting 1D
projections of the random noise from a correlation-free region of the 2D
spectra. All data processing was performed using Bruker Topspin 3.0
software. Differential scanning calorimetry (DSC) was performed using a
TA Instruments DSC 2920 modulated calorimeter, calibrated using an
indium metal standard. Samples (5–10 mg) were heated in a tared alumi-
nium pan from 25 to 3008C under a nitrogen atmosphere (60 cm3 minꢀ1).
Samples were then cooled to 08C before being heated to 3008C at a rate
of 108Cminꢀ1. This cycle of cooling and reheating was performed 3
times. An empty aluminium pan was used as a reference. The glass transi-
tion temperature (Tg) was determined at the stationary point on the first
derivative curve of the heating cycle data.
transition temperature of ACTHNUTRGEN(UNG PS20)2–Zn. We envisage that the
multitopic design of the PPCs may stabilise the tertiary
structure of larger supramolecular assemblies due to poten-
tial preorganisational effects. Furthermore, the inter-chro-
mophore distances between the porphyrin subunits may be
sufficiently small to enable light-mediated energy-transfer
processes along the porphyrinatozinc–triazole backbone.
Consequently, PPCs containing ruthenium and cobalt metal-
loporphyrin cores are currently being investigated for con-
structing larger, more stable PPC arrays with potentially in-
teresting photophysical properties.
Experimental Section
Additional experimental information, characterisation data, assignment
of 1H, 13C, HSQC, HMBC and NOESY NMR spectra, analytical GPC
traces, UV/Vis spectra, model derivation and self-assembly analysis are
included in the Supporting Information.
Materials: Commercial solvents and reagents were used without further
purification unless specified otherwise. 2-(Butylthiocarbonothioylthio)-
propanoic acid (PABTC) and 2,2’-azobisisobutyronitrile were received
from DuluxGroup Australia. (Prop-2-ynyl propanoate)yl butyl trithiocar-
bonate (PYPBTC) RAFT agent was synthesised by Dr. Raphael Barbey
(KCPC, The University of Sydney, Australia) using a procedure based on
that of Konkolewicz et al.[18] Tetrahydrofuran (THF) was distilled from
the sodium/benzophenone ketyl under N2 to remove water and the inhib-
itor (4-hydroxy-3,5-di-tert-butyltoluene). Liquid styrene was passed over
basic alumina prior to polymerisation to remove the inhibitor. 2,3-Di-
chloro-5,6-dicyano-1,4-benzoquinone (DDQ) was recrystallised from
CHCl3 and dried under vacuum prior to use.[46] Pyrrole was distilled from
calcium hydride under reduced pressure and stored under nitrogen; dis-
tilled pyrrole was passed through alumina immediately prior to use.
Chlorobenzene was distilled from CaCl2 under reduced pressure and can-
nulated directly into the reaction vessel under N2.
Methods: Microwave syntheses were performed on an A.I. Scientific
CEM Discover S-Class synthesis microwave using 5 mL borosilicate seal-
able microwave tubes. Preparative size-exclusion chromatography (SEC)
was conducted using a gravity fed column (3 cm internal diameter ꢂ
40 cm) containing Bio-Rad Biobeads S-X1 cross-linked polystyrene size-
exclusion matrix using toluene as the eluent (flow rate 0.5 mLminꢀ1).
Optical absorption spectroscopy was performed at 295 K on a Varian
Cary 4000 UV-visible spectrophotometer operating in double beam mode
with air in the reference path. Temperature of the samples was controlled
using an Agilent Technologies Cary Peltier-type temperature controller.
Samples were analysed using quartz cuvettes with optical path lengths of
1 cm, 2 mm, 1 mm or 0.1 mm (demountable), depending on the concen-
tration of the porphyrin solution. Electrospray ionisation (ESI) mass
spectra were recorded on a ThermoQuest Finnigan LCQ ion trap mass
spectrometer. High resolution ESI and matrix-assisted laser desorption/
ionisation Fourier transform ion cyclotron resonance (MALDI-FTICR)
mass spectra were recorded on a Bruker Daltonics 7T FTICR Mass Spec-
trometer. No additional matrix was required for porphyrin-containing
samples. Attenuated Total Reflection (ATR) infrared spectra were re-
corded on a Bruker Alpha-E ATR spectrometer fitted with a zinc–sele-
nide crystal. Diffuse Reflectance Infrared Fourier Transform Spectrosco-
py (DRIFTS) was performed on a Varian 800 Scimitar Series FT-IR spec-
trometer. Spectra were recorded with a resolution of 4 cmꢀ1 for 16 repeti-
tions. Molecular weight distributions of polymers were measured by ana-
Zinc(II) tetra(triazolyl acetate)porphyrin, (TA)4–Zn: A 5 mL microwave
tube was charged with TN3PP–Zn (10 mg, 11 mmol), sodium ascorbate
(4.4 mg, 22 mmol), propargyl acetate (1.48 mL, 60 mm solution in THF),
copper(II) sulfate (1.1 mg, 4.5 mmol), and DMF (2 mL). The contents of
the tube were sonicated briefly to obtain a homogeneous purple solution,
then a magnetic stirrer bar was added and the tube sealed. The reaction
was heated under microwave irradiation (100 W, 1008C) for 25 min, then
allowed to cool to room temperature. The solvent was removed by rotary
evaporation and the purple residue was redissolved in a minimal amount
of CH2Cl2 with 5% v/v pyridine and passed through a short alumina
column to remove any remaining copper salts. After removal of the sol-
vents, the product was obtained as shiny purple microcrystals (14.1 mg,
98%). M.p. >3008C; 1H NMR (500 MHz, CDCl3/TMS
+ 2% v/v
[D5]pyridine): d = 8.84 (s, 8H, b-pyrrolic H), 8.18 (d, J=8.0 Hz, 8H,
phenyl Ho), 7.85 (s, 4H, triazole H), 7.60 (d, J=8.0 Hz, 8H, phenyl Hm),
5.86 (s, 8H, Na-triazole CH2), 5.31 (s, 8H, Ca-triazole CH2), 2.12 ppm (s,
12H, acetate CH3); 13C NMR (125 MHz, CDCl3/TMS
+ 2% v/v
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M. J. Crossley, S. Perrier et al.
[D5]pyridine): d = 171.1 (acetate C=O), 150.0 (a-pyrrole), 144.1 (phenyl
ipso), 143.6 (triazole C4), 135.3 (phenyl Cortho), 133.6 (phenyl Cpara), 131.8
(b-pyrrole), 126.1 (phenyl Cmeta), 124.1 (triazole C5), 119.8 (porphyrin
meso), 57.8 (triazole-HCa), 54.3 (triazole-HNa), 21.0 ppm (acetate CH3).;
ACHTUNGTRENNUNG
C
C
IR (ATR, solid film): nmax = 2923, 2852, 2246, 1736, 1223, 993, 906, 796,
782, 720, 646 cmꢀ1; UV/Vis (0.124m pyridine in CHCl3): lmax (log10(e)) =
409 (4.64), 430 (5.71), 563 (4.29), 603 nm (4.02); UV/Vis (CHCl3): lmax
(log10(e)) = 400 (4.57), 420 (5.66), 548 (4.30), 586 nm (3.68); HRMS
(MALDI-FTICR): m/z: calcd for: 1311.36507; found: 1311.36537
[M+Na]+; MS (MALDI-FTICR): m/z (%): 1311.37 [M+Na]+ (20),
1249.45 [M+HꢀC2H3O]+ (100), 1227.47 [MꢀZn]+ (40).
358H, backbone -CH2CH- and -S-CH
2ACHTUGNTREN[UNGN CH2]CH3), 0.92 ppm (brm, 24H,
-S(CH2)3-CH3 and -O(C=O)CHCH3); IR (DRIFTS, KBr matrix): nmax =
A
U
3077, 3060, 3025, 2924, 2852, 1944, 1874, 1804, 1734, 1601, 1493, 1452,
1157, 1028, 908, 756, 698 cmꢀ1; UV/Vis (THF): lmax (log10(e)) = 312
(4.75), 404 (4.56), 425 (5.67), 484 (3.26), 518 (3.47), 557 (4.24), 596 nm
(3.81).
Zinc(II) di(triazolyl acetate)porphyrin, (TA)2–Zn: A 5 mL microwave
tube was charged with DN3PP–Zn (10.0 mg, 15.7 mmol), sodium ascor-
bate (5.5 mg, 28 mmol), propargyl acetate (0.37 mL, 95 mm solution in
THF), copper(II) sulfate (1.2 mg, 4.7 mmol), and DMF (2 mL). The con-
tent of the tube was sonicated briefly to obtain a homogeneous purple
solution, then a magnetic stirrer bar was added and the tube sealed. The
reaction was heated under microwave irradiation (100 W, 1008C) for
25 min, then allowed to cool to room temperature. Work-up was per-
formed as for (TA)4–Zn to yield the product as a dark purple solid resi-
due (12.5 mg, 97%). M.p. >3008C; 1H NMR (500 MHz, CDCl3/TMS +
15% v/v [D5]pyridine): d = 10.23 (s, 2H, meso-H), 9.38 (d, J=4.5 Hz,
4H, b-pyrrolic H), meso-H), 9.03 (d, J=4.5 Hz, 4H, b-pyrrolic H), 8.24
(d, J=8.0 Hz, 4H, phenyl Ho), 7.93 (s, 2H, triazole H), 7.65 (d, J=
8.0 Hz, 4H, phenyl Hm), 5.88 (s, 4H, Na-triazole CH2), 5.35 (s, 4H, Ca-tri-
azole CH2), 2.13 ppm (s, 6H, acetate CH3); 13C NMR (125 MHz, CDCl3/
TMS + 15% v/v [D5]pyridine): d = 170.9 (acetate C=O), 149.7 (pyrrole),
149.5 (pyrrole), 144.0 (phenyl Cipso), 143.5 (triazole C4), 133.5 (phenyl
AHCTUNGTRENNUNG
(PS40)4–Zn: Mn,GPC (THF)=15250 gmolꢀ1; ꢀ=1.25; 1H NMR (300 MHz,
CDCl3/TMS + 2% v/v [D5]pyridine): d = 8.77 (brs, 8H, b-pyrrolic H),
8.13 (brs, 8H, phenyl Ho), 7.67 (brm, 4H, triazole Ar-H), 7.51 (brs, 8H,
phenyl Hm), 7.25–6.25 (brm, 800H, polystyrene Ar-H), 5.76 (brm, 8H,
triazole-HNa), 5.11–5.00 (brm, 8H, triazole-HCa), 4.87–4.73 (brm, 4H,
-CH-SCS2), 3.24 (brs, 8H, -SCH2CH2-), 1.86–1.08 (brm, 478H, backbone
-CH2CH- and -S-CH
2ACHTUNGTRNE[UNG CH2]CH3), 0.90 ppm (brm, 24H, -SCAHUTGNTREN(NUGN CH2)3-CH3 and
-O(C=O)CHCH3); IR (DRIFTS, KBr matrix): nmax = 3077, 3060, 3025,
AHCTUNGTRENNUNG
2924, 2852, 1944, 1874, 1805, 1734, 1601, 1493, 1452, 1157, 1028, 756,
698 cmꢀ1; UV/Vis (THF): lmax (log10(e)) = 312 (4.74), 404 (4.56), 425
(5.67), 485 (3.27), 517 (3.48), 557 (4.24), 596 (3.81), 642 nm (2.48).
(PS20)2–Zn: Mn,GPC (THF)=5170 gmolꢀ1; ꢀ=1.18; 1H NMR (500 MHz,
AHCTUNGTRENNUNG
CDCl3/TMS + 2% v/v [D5]pyridine): d = 10.23 (s, 2H, porphyrin meso-
H), 9.37 (brs, 4H, b-pyrrolic H), 9.01 (brm, 4H, b-pyrrolic H), 8.24
(brm, 4H, phenyl Ho), 7.71 (brm, 2H, triazole Ar-H), 7.61 (brs, 4H,
phenyl Hm), 7.45–6.30 (brm, 200H, polystyrene Ar-H), 5.84 (brm, 4H,
triazole-HNa), 5.18 (brm, 4H, triazole-HCa), 4.97–4.72 (brm, 2H, -CH-
SCS2), 3.27 (brs, 4H, -SCH2CH2-), 2.58–1.16 (brm, 124H, backbone
C
ortho), 132.0 (phenyl Cpara), 131.8 (pyrrole), 126.1 (phenyl Cmeta), 124.0
(triazole C5), 118.4 (porphyrin Cmeso), 106.0 (pyrrole), 57.8 (triazole-HCa),
54.3 (triazole-HNa), 20.9 ppm (acetate CH3); IR (DRIFTS, KBr matrix):
nmax = 2923, 2852, 1739, 1518, 1439, 1394, 1366, 1236, 1146, 1119, 1058,
996, 850, 823, 781, 729, 702 cmꢀ1; UV/Vis (THF): lmax (log10(e)) = 313
(4.25), 353 (4.05), 393, (4.63), 413 (5.72), 451 (3.19), 504 (3.45), 543
(4.31), 581 nm (3.54); HRMS (MALDI-FTICR): m/z: calcd for:
831.21287; found: 831.21236 [M+H]+; MS (MALDI-FTICR): m/z (%):
831.21 [M+H]+ (10), 747.53 [M+Hꢀ2ꢂCOCH3]+ (100).
-CH2CH- and -S-CH
2ACHTUNGTRNE[UNG CH2]CH3), 0.92 ppm (brm, 12H, -SCAHUTGNTREN(NUGN CH2)3-CH3 and
-O(C=O)CHCH3); IR (DRIFTS, KBr matrix): nmax = 3080, 3061, 3025,
AHCTUNGTRENNUNG
2926, 1944, 1870, 1804, 1735, 1600, 1493, 1453, 1370, 1157, 1066, 1027,
999, 907, 757, 699 cmꢀ1; UV/Vis (THF): lmax (log10(e)) = 312 (4.37), 392
(4.42), 413 (5.47), 451 (3.57), 505 (3.40), 543 (4.12), 580 (3.40), 633 nm
(2.73).
AHCTUNGTRENNUNG
(PS30)2–Zn: Mn,GPC (THF)=7150 gmolꢀ1; ꢀ=1.19; 1H NMR (500 MHz,
CDCl3/TMS + 2% v/v [D5]pyridine): d = 10.13 (s, 2H, porphyrin meso-
H), 9.27 (brs, 4H, b-pyrrolic H), 8.91 (brm, 4H, b-pyrrolic H), 8.15
(brm, 4H, phenyl Hi), 7.63 (brm, 2H, triazole Ar-H), 7.52 (brs, 4H,
phenyl Hn), 7.17–6.30 (brm, 300H, polystyrene Ar-H), 5.75 (brm, 4H, tri-
azole-HNa), 5.07 (brm, 4H, triazole-HCa), 4.97–4.72 (brm, 2H, -CH-SCS2-
), 3.17 (brs, 4H, -SCH2CH2-), 2.58–1.16 (brm, 184H, backbone -CH2CH-
General Procedure for PPC synthesis: Synthesis of ACTHNUGTRNEUNG(PS30)4–Zn is descri-
bed. Azidoporphyrin TN3PP–Zn (10 mg, 11 mmol), alkyne-functionalised
RAFT polystyrene (DP=30, 147 mg, 49.0 mmol), copper(II) sulfate pen-
tahydrate (1.7 mg, 6.7 mmol) and sodium ascorbate (7.7 mg, 39 mmol)
were weighed into a 5 mL sealable microwave tube. DMF (3 mL) and a
magnetic stirrer bar was added and the vessel sealed. The reaction mix-
ture was sonicated briefly, then heated under microwave irradiation
(100 W, 1008C) for 25 min then allowed to cool. Work-up procedure con-
sisted of passing the crude reaction mixture directly through a short alu-
mina column (Brockmann grade I), then diluting with ethyl acetate (ca.
20 mL) and washing the organic phase with deionised water (5ꢂ50 mL)
to remove the DMF. The organic layer was dried over Na2SO4, filtered
and the solvents removed on a rotary evaporator. The resulting amor-
phous purple solid was dissolved in minimal CH2Cl2 and precipitated by
dropwise addition into methanol at ꢀ788C to afford the purified polymer
as a pale purple powder. For two-arm conjugates, the amount of polymer,
catalyst and reducing agent was halved, but reaction volume remained
constant.
and -S-CH2ACHTUNGTERN[NGUN CH2]CH3), 0.80 ppm (brm, 12H, -SAHCTNURTGEGN(NNU CH2)3-CH3 and -OACHTUNGTRENNUNG(C=
O)CHCH3); IR (DRIFTS, KBr matrix): nmax = 3080, 3061, 3025, 2926,
1944, 1870, 1804, 1735, 1600, 1493, 1453, 1370, 1157, 1066, 1027, 999, 907,
757, 699 cmꢀ1; UV/Vis (THF): lmax (log10(e)) = 312 (4.37), 393 (4.31), 413
(5.38), 451 (3.41), 505 (3.34), 543 (4.02), 580 (3.35), 634 nm (2.89).
AHCTUNGTRENNUNG
(PS40)2–Zn: Mn,GPC (THF)=10200 gmolꢀ1; ꢀ=1.25; 1H NMR (500 MHz,
CDCl3/TMS + 2% v/v [D5]pyridine): d = 10.13 (s, 2H, porphyrin meso-
H), 9.27 (brs, 4H, b-pyrrolic H), 8.91 (brm, 4H, b-pyrrolic H), 8.15 (brd,
J=6.7 Hz, 4H, phenyl Ho), 7.63 (brm, 2H, triazole Ar-H), 7.53 (brd, J=
7.0 Hz, 4H, phenyl Hm), 7.24–6.16 (brm, 400H, polystyrene Ar-H), 5.75
(brm, 4H, triazole-HNa), 5.07 (brm, 4H, triazole-HCa), 4.97–4.72 (brm,
2H, -CH-SCS2), 3.17 (brs, 4H, -SCH2CH2-), 2.58–1.16 (brm, 184H, back-
bone -CH2CH- and -S-CH
2ACHTUNGTREN[UNG CH2]CH3), 0.80 ppm (brm, 12H, -SACHTUNGTRENNUNG(CH2)3-
ACHTUNGTRENNUNG
(PS20)4–Zn: Mn,GPC (THF)=9400 gmolꢀ1; ꢀ=1.30; 1H NMR (500 MHz,
CH3 and -O(C=O)CHCH3); IR (DRIFTS, KBr matrix): nmax = 3082,
AHCTUNGTRENNUNG
CDCl3/TMS + 2% v/v [D5]pyridine): d = 8.77 (brs, 8H, b-pyrrolic H),
8.14 (d, J=7.5 Hz, 8H, phenyl Ho), 7.67 (brm, 4H, triazole Ar-H), 7.53
(d, J=7.5 Hz, phenyl 8H, Hm), 7.25–6.25 (brm, 400H, polystyrene Ar-
H), 5.78 (brm, 8H, triazole-HNa), 5.12 (brm, 8H, triazole-HCa), 4.90–4.71
(brm, 4H, -CH-SCS2-), 3.25 (brs, 8H, -SCH2CH2-), 1.86–1.08 (brm,
3060, 3024, 2924, 1945, 1866, 1803, 1735, 1601, 1493, 1452, 1369, 1154,
1068, 1028, 998, 905, 758, 698 cmꢀ1; UV/Vis (THF): lmax (log10(e)) = 312
(4.36), 393 (4.30), 413 (5.37), 451 (3.40), 506 (3.34), 543 (4.02), 580 (3.34),
633 nm (2.89).
(PBA15)4–Zn:
Mn,GPC
(THF)=9190 gmolꢀ1
;
ꢀ=1.24;
1H NMR
238H, backbone -CH2CH- and -S-CH
2ACHTUGNTREN[UNGN CH2]CH3), 0.90 ppm (brm, 24H,
(500 MHz, CDCl3/TMS + 2% v/v [D5]pyridine): d = 8.72 (s, 8H, b-pyr-
rolic H), 8.10 (d, J=7.0 Hz, 8H, phenyl Ho), 7.84 (brm, 4H, triazole Ar-
H), 7.54 (d, J=7.4 Hz, 8H, phenyl, Hm), 5.82 (d, J=6.15 Hz, 8H, tria-
zole-HNa), 5.25 (brm, 8H, triazole-HCa), 4.75 (brm, 4H, -CH-SCS2), 3.97
(brs, 120H, butyl acrylate a-CH2), 3.27 (t, J=7.5 Hz, 8H, -SCH2CH2-),
-S(CH2)3-CH3 and -O(C=O)CHCH3); IR (DRIFTS, KBr matrix): nmax =
A
U
3079, 3061, 3025, 2924, 2852, 1944, 1873, 1804, 1734, 1601, 1493, 1450,
1157, 1028, 906, 756, 698, 540 cmꢀ1; UV/Vis (THF): lmax (log10(e)) = 311
(4.76), 404 (4.57), 425 (5.66), 486 (3.26), 517 (3.50), 557 (4.25), 595 (3.82),
643 nm (2.6).
2.54–1.17 (brm, 436H, backbone -CH2CH- and -S-CH2ACHTNUGTRNEUNG[CH2]CH3 and
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Porphyrin–Polymer Conjugates
FULL PAPER
butyl acrylate b,g-CH2), 1.09 (t, J=6.9 Hz, 12H, -O
0.93 ppm (brs, 192H, -SACHTUNTRGNEUN(G CH2)3-CH3 and butyl acrylate -CH3); IR
(DRIFTS, KBr matrix): nmax = 2960, 2880, 1736, 1730, 1460, 1395, 1380,
1241, 1166, 1117, 1064, 943, 906, 837, 737 cmꢀ1; UV/Vis (THF): lmax
(log10(e)) = 310 (4.75), 404 (4.59), 425 (5.66), 486 (3.48), 517 (3.56), 557
(4.26), 596 (3.86), 644 nm (2.98).
(C=O)CHCH3),
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A
;
ꢀ=1.20; 1H NMR
(500 MHz, CDCl3/TMS + 2% v/v [D5]pyridine): d = 8.72 (s, 8H, b-pyr-
rolic H), 8.10 (d, J=7.5 Hz, 8H, phenyl Ho), 7.84 (brm, 4H, triazole Ar-
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12H, -S
2ACHTUGNTRENN[GNU CH2]CH3), 2.17 (brs, 152H,
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG(CH2)3-CH3); IR (DRIFTS, KBr matrix): nmax = 2920, 2880, 1736,
1722, 1480, 1460, 1366, 1250, 1150, 906, 840 cmꢀ1; UV/Vis (THF): lmax
(log10(e)) = 310 (4.73), 404 (4.58), 425 (5.66), 486 (3.48), 517 (3.55), 557
(4.26), 596 nm (3.86).
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Acknowledgements
The authors acknowledge Dr. Algi Serelis of DuluxGroup for providing
the RAFT agent, and Dr. Robert Chapman, Dr. Maarten Danial and Dr.
Raphael Barbey for providing alkyne-functionalised polymers. D.A.R. ac-
knowledges the Australian Government for an Australian Postgraduate
Award and the University of Sydney for the Vice Chancellorꢁs Research
Scholarship. M.J.C. acknowledges the Australian Research Council Dis-
covery Project grant DP1092560 for funding. S.P. acknowledges funding
from the Australian Research Council Future Fellowship and Discovery
programs.
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M. J. Crossley, S. Perrier et al.
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Received: March 25, 2013
Published online: && &&, 0000
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Chem. Eur. J. 0000, 00, 0 – 0
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These are not the final page numbers!

Porphyrin–Polymer Conjugates
FULL PAPER
Porphyrins
D. A. Roberts, T. W. Schmidt,
M. J. Crossley,* S. Perrier* . &&&& — &&&&
Tunable Self-Assembly of Triazole-
Linked Porphyrin–Polymer Conjugates
Tunable building blocks: Triazole-
linked porphyrin–polymer conjugates
(PPCs) were prepared in high yield
using the copper(I)-catalysed azide–
alkyne cycloaddition (CuAAC) “click”
reaction. The triazole groups were
introduced from CuAAC coupling to
guide the self-assembly of the PPCs
into short oligomers (2–6 units in
length) via intermolecular porphyrina-
tozinc–triazole coordination. Associa-
tion constants of the PPCs could be
tuned by altering the polymer micro-
environment around the porphyrin
core, thus presenting a modular plat-
form for designing self-assembled por-
phyrin–polymer materials.
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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These are not the final page numbers!