Directing the Self-Assembly Behaviour of Porphyrin-Based Supramolecular Systems

Article abstract of DOI:10.1002/chem.201605872

The self-assembly behaviour of a library of tetra-amidated porphyrin molecules decorated with a variety of solubilizing wedges is investigated as dilute solutions in methylcyclohexane. Small changes in the solubilising wedge of the porphyrins resulted in

Full text of DOI:10.1002/chem.201605872

A Journal of
Accepted Article
Title: Directing the self-assembly behaviour of porphyrin-based
supramolecular systems
Authors: Bert Meijer, Rob Weegen, and Abraham Teunissen
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Directing the Self-assembly Behaviour of Porphyrin-based
Supramolecular Systems
Rob van der Weegen, Abraham J.P. Teunissen and E.W. Meijer*[a]
Abstract: The self-assembly behaviour of a library of tetra-
amidated porphyrin molecules decorated with a variety of
solubilizing wedges is investigated as dilute solutions in
methylcyclohexane. Small changes in the solubilising wedge of
the porphyrins resulted in different aggregated states, as
evidenced by CD and UV-Visible absorption spectroscopy. The
porphyrins form either co-facially stacked H-aggregates or slip-
of porphyrins is easily modified on both the core and the periphery,
giving rise to easily adjustable (supra)molecular properties.16–19
Another key feature is the metal binding centre which allows a
versatile use of porphyrins in catalysis and metal-ligand based
supramolecular chemistry.6
,7,11,20
In supramolecular chemistry the formation of non-discrete
porphyrin aggregates has been studied in great detail, taking
advantage of π-stacking, hydrogen bonding, metal–ligand and
hydrophobic interactions to create functional multi-chromophoric
aggregates. For example, the group of Wasielewski reported on
the self-assembly of Zn-porphyrins appended with four perylene
bisimides into either one-dimensional or two-dimensional
aggregates depending on the perylene bay substituents.5
Nolte and co-workers investigated the self-assembly of porphyrin-
functionalized benzene-1,3,5-tricarboxamides, in which three
non-symmetrical porphyrins were connected by amide linkages to
a benzene core.21–23 Different types of aggregates were obtained
depending on the solvent, as evidenced by the excitonic coupling
of the porphyrin chromophores, highlighting the delicate interplay
between hydrogen bonding and π-stacking in such discotics. The
strategy of combining hydrogen bonding and π-stacking
interactions has also been pursued by Shinkai and co-
workers.2 Here, solubilizing chains were appended to either the
stacked J-aggregates or
a
mixture of both. Detailed
thermodynamic and kinetic analysis showed that in all cases the
formation of J-aggregates proceeds via an isodesmic mechanism
while H-aggregates are formed via a cooperative mechanism. It
is shown that these aggregates assemble in a parallel pathway,
in which both compete for the monomer, compared to a sequential
pathway, in which one of the aggregates interconverts into the
other. Interestingly, kinetic analysis of porphyrins that only form
H-aggregates in thermodynamic equilibrium revealed that the
competing pathway towards J-aggregates is operational in these
systems as well. Our findings show that the balance between H-
and J-aggregates depends on remarkably small changes in the
architecture of the solubilising wedges.
,21–23
Introduction
4,25
3
- or 4-positions on the phenyl rings of tetraphenylporphyrins via
Porphyrins are heterocyclic aromatic macrocycles that occur
ubiquitously in nature and play a crucial role in oxygen transport,
enzymes and various photosynthetic systems. In photosystem II
and chlorosomes, extensive arrays of porphyrins feature in light-
harvesting, exciton splitting and funnelling of excitonic energy to
reaction centres. Of paramount importance for the functionality of
porphyrins in these systems is their mutual geometric orientation
which results from specific non-covalent interactions between the
phenoxyacetamide linkers. The resulting porphyrins were shown
to be efficient organogelators. Remarkably, the different
connectivity of the amides to the porphyrin gave rise to either H-
or J-type aggregates as evidenced by absorbance studies.
Furthermore, considerable differences in gelator efficiency and
thermal stability of the assemblies were found.
Supramolecular polymers based on porphyrins have also
been studied in our group.26–29 In these studies tetra-amidated
porphyrins were appended with solubilizing wedges and their self-
assembly in apolar solvents was investigated. The porphyrins
were found to assemble predominantly into long co-facial H-
aggregated stacks, although in specific cases depending on the
preparation method of the self-assembled architectures, J-
aggregates could also be obtained. These results suggest that
minor variations in the porphyrin structure can give rise to different
types of aggregates. Furthermore, selection of the preparation
method might be used as a tool to guide the self-assembly
process to the desired aggregated state.30–32 In two recent
examples of supramolecular polymerization, careful molecular
design was shown to allow the creation of seeded supramolecular
porphyrins (chlorosomes) or
a
non-covalent framework of
1
proteins that organizes the porphyrins in a specific manner.
Inspired by the functional versatility of porphyrins in nature,
chemists have used synthetic porphyrin derivatives for a myriad
of applications, these including artificial photosynthetic systems,
organic photovoltaics, molecular rotors, supramolecular
chemistry, templated non-covalent synthesis, catalysis, artificial
enzymes and photodynamic therapy.2–15 The molecular structure
[a]
R. van der Weegen, A.J.P. Teunissen, Prof. Dr. E.W. Meijer
Laboratory of Macromolecular and Organic Chemistry
Institute for Complex Molecular Systems
Eindhoven University of Technology
P.O. Box 513, 5600 MB, Eindhoven (The Netherlands)
E-mail: e.w.meijer@tue.nl
processes33,34
polymerization
polymerization3
and living supramolecular
In the latter example, porphyrins bearing
5,36
.
hydrogen-bond moieties and solubilizing groups on two of the
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Chemistry - A European Journal
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meso-phenyl positions were shown to assemble into J- Results and Discussion
aggregates via an isodesmic mechanism. These aggregates then
spontaneously converted into H-aggregates via
a
strongly
In our design, the tetraphenylporphyrin cores are functionalized
with solubilizing aliphatic wedges via amide linkages to provide
solubility in apolar organic solvents and aggregation through four-
fold hydrogen bonding between porphyrins. To study the effects
cooperative mechanism. The authors exploited this meta-stability
by seeding solutions of J-aggregates with small aliquots of
porphyrin H-aggregates and observed a selective elongation of
the existing H-aggregates, instead of the nucleation of new stacks. of the aliphatic wedges on the aggregation behaviour of such
This was explained by the porphyrins in the J-aggregate
depolymerized into monomers which, due to the large nucleation
barrier for the H-aggregates, preferentially grew on existing
stacks. Repetitive seeding experiments resulted in the formation
of supramolecular fibres of predetermined and controlled size,
thereby resembling a living polymerization. In a subsequent
publication by the same authors, the steric bulk on the porphyrin
periphery was used to influence the balance between H- and J-
porphyrins, we designed porphyrins 1-Zn - 5-Zn. The self-
assembly behaviour of porphyrins 1-Zn and 2-Zn has been
studied before in our group.28,29 The solubilizing wedge for
porphyrin 3-Zn resembles that of porphyrin 1-Zn, but lacks the
para-substituent on the phenyl ring. Porphyrins 4-Zn and 5-Zn
bear alkyl chains directly attached to the phenyl ring instead of an
alkoxy linkage as in porphyrins 1-Zn - 3-Zn. In comparison with
porphyrin 4-Zn, again the para-substituent on the solubilizing
wedge is omitted in porphyrin 5-Zn.
3
7
aggregation pathways.
From these examples it becomes clear that porphyrins are
highly interesting molecules for the generation of supramolecular
architectures. However, their complex assembly behaviour can
give rise to a variety of self-assembled architectures from the
same molecular structure.30,38–40 Furthermore, small changes in
the molecular architecture or coordinated metal frequently result
in the formation of different types of aggregates.41,42 While various
observations on these phenomena have been reported,
systematic studies have rarely been performed. Based on
previous investigations in our group, we here investigate a library
of tetra-amidated porphyrins that self-assemble by a combination
of hydrogen bonding and π-stacking interactions (Figure 1).
The syntheses of porphyrins 1-Zn - 5-Zn are shown in
Scheme 1. The key aniline precursors that were reacted with
meso-tetra(4-carboxyphenyl)porphyrin in the final step of the
synthesis were prepared according to two different routes. Aniline
derivatives 6 and 7 were prepared according to reported
procedures.28,29 For aniline derivative 13, a similar route was
followed starting from methyl 3,5-dihydroxybenzoate (8). Double
Williamson ether synthesis with tosylate 9 afforded methyl ester
10 in 92% yield. Subsequently, methyl ester 10 was converted to
acyl azide derivative 12. A Curtius rearrangement of 12 afforded
the corresponding isocyanate in situ, which was hydrolysed to the
amine to afford aniline 13 in 32% yield after column
chromatography. For the synthesis of aniline 18 a reported
procedure was used.43,44 For the synthesis of aniline 21, the same
procedure as for 18 was applied but slightly modified. 1,2,3-
Triiodo-5-nitrobenzene (15) was obtained by a Sandmeyer
reaction and subsequent iodination on 2,6-diiodo-4-nitroaniline 14.
For the synthesis of 19, the Sandmeyer reaction on 14 was
performed in ethanol, resulting in the thermolysis of the diazonium
salt.45–48 Both 15 and 19 were then reacted with 1-dodecyne (16)
under Sonogashira conditions to afford alkynes 17 and 20 which
were subsequently reduced to yield aniline derivatives 18 and 21
in 98% and 89% yield, respectively. The library of porphyrins 1-
Figure 1. Library of porphyrin tetra-amides 1-Zn - 5-Zn that bear a variety of
solubilizing wedges on the periphery.
Zn
- 5-Zn was generated by reaction of meso-tetra(4-
carboxyphenyl)porphyrin with the various anilines under standard
conditions for amide bond formation. In the final step, the
porphyrins were treated with zinc acetate in dichloromethane to
yield zinc metallated porphyrins 1-Zn - 5-Zn. The end products
were thoroughly purified by column chromatography and
characterized by NMR spectroscopy and MALDI-ToF
spectrometry.
Our aim is to get insights into the pathway complexity and
sensitivity of porphyrin supramolecular systems towards changes
in the molecular architecture of the solubilizing periphery. Such
insights will play vital role in the reproducible generation of
porphyrin based supramolecular architectures.
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Scheme 1. Synthesis of porphyrins 1-Zn - 5-Zn. Reagents and conditions: i) K
2
3
CO , TBAB, MIBK, reflux; ii) NaOH, EtOH, reflux; iii) ethyl chloroformate, TEA, THF;
NaN
EtOAc, EtOH; viii) NaNO
Zn(OAc) , DCM, RT.
3
, H
2
O, THF, RT; iv) dioxane, 90 °C, tetrabutylammonium hydroxide; v) NaNO
2
, H
2
SO
4
, KI, acetic acid, H
2
O; vi) Pd(PPh
3
)
2
Cl
2
, CuI, Et
3
N, 80 °C; vii) Pd/C, H
2
,
2
, H SO , ethanol, reflux; ix) Pd(PPh Cl , CuI, Et N, 60 °C; x) Pd/C, H
2
4
3
)
2
2
3
2
EtOAc, EtOH; xi) C
2
Cl , DMF, CHCl
O
2 2
3
; xii) Et
3
N, CHCl , 0 °C; xiii)
3
2
Figure 2. UV–Visible absorption spectroscopy spectra recorded for porphyrins 1-Zn - 5-Zn after different sample preparation methods (red lines: molecularly
dissolved, black lines: injection method, blue lines: quenching method, pink lines: slow cooling method, MCH, c = 2.5×10-6 M, l = 1 cm). From left to right:
porphyrins 1-Zn to 5-Zn.
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The self-assembly behaviour of zinc porphyrins 1-Zn - 5-Zn
as dilute solutions in methylcyclohexane (MCH) was investigated
by UV-Visible absorption spectroscopy (Figure 2). Three different
methods for aggregate preparation were evaluated: 1) injection of
a small aliquot of a concentrated porphyrin solution (c = 1×10-3 M)
of a non-aggregating solvent (chloroform) into an aggregating
spectroscopy cooling curves display non-sigmoidal shapes
characterized by a critical temperature below which aggregation
takes place, typical for a nucleation-elongation mechanism. In
contrast, cooling curves measured for porphyrins 4-Zn and 5-Zn
(Figure 3 A) are sigmoidal in shape and lack a critical temperature,
which is indicative of an isodesmic self-assembly mechanism.49
Apparently, the two different aggregate types formed by
porphyrins 1-Zn - 5-Zn are formed via different mechanisms.
solvent (MCH), resulting in a final concentration of c = 2.5×10-6
M
followed by equilibration of the sample for five hours at room
temperature; 2) rapidly cooling (quenching) of a porphyrin solution
in MCH (c = 2.5×10-6 M) from the molecularly dissolved state at
high temperature (T = 363 K) to the assembled state at low
temperature (T = 293 K); 3) slow cooling (rate = 0.5 K/min) of a
porphyrin solution (c = 2.5×10-6 M) from the molecularly dissolved
A
B
1
.0
1.0
4-Zn 0.5 K/min
-Zn 0.5 K/min
3-Zn
0.2 K/min
0.5 K/min
5
0.8
0.8
0.6
0.4
0.6
0.4
state (T = 363 K) to the assembled state (T = 293 K) and
equilibration of the sample for 12 hours. The UV-Visible
absorption spectroscopy spectra recorded for all sample-
preparation methods as well as the molecularly dissolved state at
T = 363 K are depicted in Figure 2. At elevated temperatures in
MCH (T = 363 K, c = 2.5×10-6 M) all porphyrins show sharp Soret
absorption bands indicative of molecularly dissolved species in
solution with λmax = 419 nm. As expected, the molecular structure
of the wedge architectures does not influence the ground state
electronic properties of the porphyrin cores. However, significant
differences in aggregation behaviour are observed in the series of
porphyrins. Furthermore, the aggregation behaviour varies
strongly with the preparation method. Porphyrin 1-Zn shows an
identical outcome independent of the method of preparation
0
.2
0.2
0.0
0.0
2
80
290
300
310
320
330
340
350
300
310
320
330
340
350
360
Temperature (K)
Temperature (K)
C
D
0
0
0
.77
1.15
-20
40
-5
0.76
-
-10
15
20
25
30
1.10
3-Zn
CD
OD
3
-Zn
CD
OD
0.75
-60
-80
-
1.05
-
0.74
0.73
-100
-
1
.00
-
120
-
0.72
-140
295
280
285
290
295
300
305
310
300
305
310
315
Temperature (K)
Temperature (K)
Figure 3. UV–Visible absorption spectroscopy cooling curves of porphyrins 4-
Zn and 5-Zn in MCH solution (λ = 419 nm, c = 2.5×10 M, l = 1 cm, rate = 0.5
K/min) (A). UV–Visible absorption spectroscopy cooling curves for 3-Zn MCH
solution (λ = 419 nm, c = 2.5×10 M, l = 1 cm, rate = 0.5 K/min and 0.2 K/min)
-6
29
(
Figure 2 A). One-dimensional stacks of co-facially aggregated
-
6
porphyrins are formed (H-aggregates), as indicated by the
hypsochromic shift of the Soret absorption to λmax = 390 nm with
respect to the molecularly dissolved state. Porphyrins 4-Zn and
(
B). UV–Visible absorption spectroscopy and CD cooling (C) and heating (D)
curves of porphyrin 3-Zn (λ = 390 nm, c = 2.5×10-6 M, l = 1 cm, rate = 0.1 K/min).
5-Zn also display aggregation behaviour that is independent of
aggregate preparation method but a different type of aggregate is
obtained (Figure 2 D and E). Here, λmax of the Soret absorption
peak remains roughly constant but the Soret band appears
broadened and diminishes in intensity. These spectral features
corroborate the formation of J-aggregates where the porphyrin
central cores are laterally displaced with respect to each other,
instead of the co-facial arrangement as observed for porphyrin 1-
Zn. Interestingly, porphyrins 2-Zn and 3-Zn form a mixture of J-
and H-aggregates, as indicated by the hypsochromic shift in the
band at λ = 390 nm and the diminished band at λ = 419 nm (Figure
As porphyrin 3-Zn possesses stereogenic centres, H-
aggregates formed by porphyrin 3-Zn are supramolecularly chiral
and show a Cotton effect in CD spectroscopy (no Cotton effect is
observed for J-aggregated states of 1-Zn and 3-Zn). Therefore,
the Cotton effect observed for porphyrin 3-Zn functions as a
selective tool to probe the aggregation mechanism of the H-
aggregates. Variable temperature experiments were carried out
to study the formation mechanisms of both type of aggregates in
porphyrin 3-Zn. Cooling a dilute solution of 3-Zn (T = 360 K, c =
2.5×10-6 M, MCH) at a rate of 0.5 K/min to T = 305 K resulted in
the selective formation of porphyrin J-aggregates as evident from
CD and UV-Visible absorption spectroscopy spectra. The self-
assembly process is monitored at λ = 419 nm and the resulting
curve is sigmoidal in shape, suggesting an isodesmic self-
assembly mechanism (Figure 3 B). Further cooling of the solution
below T = 305 K results in the formation of co-facial porphyrin H-
aggregates as evidenced by the appearance of a hypsochromic
shift in absorption and the concomitant appearance of a Cotton
effect at λ = 390 nm (Figure 3 C). The resulting cooling curve is
non-sigmoidal in shape and a clear critical temperature Te is
observed, indicative of a cooperative assembly mechanism.
However, the resulting solution appears not to be under
thermodynamic equilibrium, as a Cotton effect of only -33 mdeg
is obtained in the cooling curve instead of the maximal Cotton
effect at c = 2.5×10-6 M of -145 mdeg that was found in the
2
B and C). Furthermore, the ratio between both states depends
strongly on the preparation method. Summarizing, porphyrins 1-
Zn - 5-Zn can be classified into three different types according to
the aggregates they form. Porphyrin 1-Zn displays co-facial H-
aggregation, porphyrins 4-Zn and 5-Zn display slipped stack J-
aggregation while porphyrins 2-Zn and 3-Zn show the
coexistence of both type of aggregates.
Next, we compared the self-assembly mechanism of
porphyrins 1-Zn - 5-Zn by monitoring the CD and UV-Visible
absorption spectroscopy signals as a function of temperature
under thermodynamically controlled conditions by slow cooling
(
rate = 0.5 K/min). The H-aggregates formed by porphyrin 1-Zn
were previously shown to form via a cooperative mechanism in
29
dilute solutions in MCH. The CD and UV-Visible absorption
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Chemistry - A European Journal
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FULL PAPER
equilibrium experiment described in Figure 2. Apparently, the
formation of H-aggregates of porphyrin 3-Zn is slow with respect
to the cooling rate applied. Indeed, after equilibration of the
resulting solution at room temperature for 12 hours, the Cotton
effect further develops to its maximum value of -145 mdeg,
indicating that the assembly curve was not measured at
equilibrium conditions. To overcome the kinetic issues observed
in the formation of aggregates of porphyrin 3-Zn, a disassembly
curve is measured instead. A solution of porphyrin 3-Zn (c =
second aggregate, as is for example the case in a nucleation-
elongation
mechanism.
In
the
case
of
porphyrin
3-Zn, the presence of two distinct aggregates may therefore be
explained by the cooperative self-assembly mechanism of the co-
facial H-aggregates instead of being an independent aggregate.
In this case, the observed J-aggregate would be the nucleus for
the formation of the H-aggregates. In order to discern the relation
between the two states observed in porphyrin 3-Zn, we turned our
attention to kinetic experiments on the self-assembly process. We
hypothesized that in the parallel scheme conversion from J- to H-
aggregates proceeds via the monomeric state and should
therefore be slower than the direct formation of H-aggregates
from the monomer. In contrast, the sequential pathway requires
the preformation of J-aggregates in order to form H-aggregates.
Therefore, the conversion of J- to H-aggregates should proceed
equally fast or faster (not slower) than the assembly from the
monomeric state. In this manner, the rates with which J-
aggregates and monomer are converted into H-aggregates
should allow us to discriminate between the two types of
assembly pathways. Solutions of 3-Zn in MCH (c = 2.5×10-6 M)
were prepared at different temperatures by injection from a
concentrated solution of 3-Zn in chloroform and allowed to reach
equilibrium (Figure 5 A). At equilibrium, all porphyrins are
aggregated in either H- or J-aggregates, where the magnitude of
the Cotton effect at λ = 390 nm corresponds to the amount of H-
aggregate present at the various temperatures. The equilibrated
solutions are then cooled to T = 293 K and again the Cotton effect
at λ = 390 nm is monitored as a function of time. The resulting
kinetic curves are compared to the kinetic curves obtained from
the experiment where the monomeric stock solution is injected
into MCH at T = 293 K (Figure 5B). All solutions should over time
reach the same equilibrium ratio between H- and J-aggregates
and thus the same Cotton effect.
2
.5×10-6 M, MCH) is equilibrated at room temperature for a period
of 72 hours (maximum Cotton effect of -145 mdeg stable after 24
hours). Next, the co-facial porphyrin aggregates are
disassembled by heating from room temperature (0.1 K/min,
Figure 3 D). Gratifyingly, they reveal a strongly non-sigmoidal
disassembly curve with a sharp transition at a critical temperature
e
T = 309 K. These results indicate that the co-facial H-stacks
formed by porphyrin 3-Zn assemble via a highly cooperative self-
assembly mechanism. The results suggest that the two different
aggregated states present in porphyrin 3-Zn are formed by the
same self-assembly mechanisms that govern the assembly of the
corresponding porphyrins that form a single aggregate (1-Zn and
4-Zn/5-Zn). Additionally, the results indicate a significant
hysteresis effect in the assembly and disassembly of H-
aggregates of porphyrin 3-Zn as the assembly and disassembly
curves are strongly dissimilar for similar experimental conditions
(
Figure 3 C,D). The observed hysteresis is probably rate-
dependent hysteresis, as cooled solutions of 3-Zn develop a
Cotton effect over time upon equilibration at low temperatures.
In a system consisting of a monomer and two different self-
assembled species, two principal mechanism can be
differentiated; a parallel and a sequential pathway (Figure 4). In
the parallel pathway, the monomer is in equilibrium with both
aggregated states, and the aggregated states do not interconvert
directly (Figure 4 A). In the sequential pathway, monomers first
form one type of aggregate which subsequently converts to a
second, different type of aggregate (Figure 4 B). Here, the first
aggregate can be interpreted as intermediate for forming the
A
B
0
-
20
40
60
80
100
120
2
83 K
293 K
93 K
303 K
03 K
-
2
-
3
-
313 K
-
-
0
25 50 75 100 125 150 175 200 225 250
Time (min)
Figure 5. Kinetic experiments on H-aggregate formation of 3-Zn in MCH (A)
-
3
(
c = 2.5×10 M, l = 1 cm) by injection from chloroform into MCH at different
temperatures. Kinetic experiments on aggregate conversion of 3-Zn after a
temperature jump from T = 303 K (green curve) or T = 313 K (blue curve) to
T = 293 K, compared to injection form CHCl
B).
3
into MCH at T = 293 K (red curve)
(
Interestingly, we observe that the formation of H-aggregates
proceeds at a lower rate when J-aggregates are present (cool to
T = 293 K, Figure 5B green and blue curves) compared to when
the self-assembly process is carried out from a molecularly
dissolved solution (direct injection at T = 293 K, Figure 5 red
curves). Hence it appears that the presence of J-aggregates of 3-
Zn slows down the formation of H-aggregates in MCH solution.
Furthermore, this inhibition appears stronger when more of the J-
Figure 4. Schematic illustration of parallel versus sequential self-assembly
pathways of a monomer and two aggregated states.
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Chemistry - A European Journal
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aggregate is present in the pre-aggregated solution (Figure 5 B,
blue versus green curves). As a result, the H- and J-aggregated
states observed in porphyrin 3-Zn must follow a parallel self-
assembly pathway where both aggregated states are in
competition for the monomer (Figure 4 A).
the ones observed for porphyrins 3-Zn, 4-Zn and 5-Zn and
suggest the formation of offset-stacked porphyrin J-aggregates.
Upon further cooling the solution, the absorption band
corresponding to H-aggregates at
λ = 390 nm appears,
concomitant with a characteristic Cotton effect (Figure 6 D).
Intrigued by the self-assembly behaviour observed in
porphyrin 3-Zn, we wondered whether similar assembly pathways
could also be observed in the other porphyrins. Porphyrin 2-Zn
also shows the coexistence of J- and H-aggregates in MCH
solution and a cooling curve measured at the monomer band λ =
The results described above indicate that porphyrin 1-Zn
aggregates into two distinct aggregates, although only one type
of aggregate is obtained after equilibration at room temperature
in MCH, independent of the aggregate preparation method (vide
infra). Apparently, the co-facial H-aggregates formed by 1-Zn are
more stable than its J-aggregates and conversion between the
two aggregates is fast enough to allow the exclusive formation of
H-stacks. This is in contrast with the structurally similar porphyrin
3-Zn, where both aggregate types coexist at room temperature
and aggregate conversion is much slower.
4
19 nm (c = 2.5×10-5 M, rate = 0.5 K/min) showed the occurrence
of two aggregation steps (Figure 6 A). The first aggregation
process starts at T = 360 K, while the second commences around
T = 337 K. This observation suggests the occurrence of similar
pathway complexity in porphyrin 2-Zn as in porphyrin 3-Zn. In
porphyrin 2-Zn, the formation of J-aggregates occurs before the
formation of H-aggregates and therefore we also investigated the
self-assembly process of exclusively H-aggregating porphyrin 1-
Zn. We recorded assembly curves at specific wavelengths and
full Cd and UV-Visible absorption spectroscopy spectra for 1-Zn
as a function of temperature (Figure 6 B-D). Interestingly, a
cooling curve recorded at the monomer absorption band (λ = 419
nm) shows the presence of two distinct aggregation processes for
Nevertheless, porphyrin 1-Zn probably possesses similar
pathway complexity as displayed by porphyrin 3-Zn. The group of
Takeuchi has recently reported on the supramolecular assembly
of structurally related porphyrins into J- and H-aggregates3
Their finding show the J-aggregates to be a metastable state that
converts into H-aggregates via the free monomer in a highly
cooperative manner. Our results confirm the formation of multiple
aggregated states in porphyrin supramolecular polymers that
polymerize and depolymerize in a parallel pathway via the free
3,34
1-Zn (Figure 6 B). The first transition, starting at T = 360 K,
appears as an isodesmic self-assembly process in view of the
absence of a critical temperature. The second process occurs at
T = 335 K and is characteristic of a cooperative supramolecular
polymerization. Moreover, when a cooling curve is measured at a
wavelength specific for the H-aggregate (λ = 390 nm), a single
cooperative transition is observed in both the optical density and
the Cotton effect, which overlaps with the second transition
observed in the assembly curve measured at λ = 419 nm. In the
CD and UV-Visible absorption spectroscopy spectra we observed
that starting from the molecularly dissolved state (T = 80 °C), the
Soret band is diminished in intensity and slightly broadened upon
cooling (Figure 6 C). These spectral characteristics are similar to
monomer. In contrast, some of our compounds show
coexistence of J- and H-aggregates.
a
Combined, the results indicate that both the kinetics and
thermodynamics of porphyrin aggregation is highly dependent on
the peripheral substituents of the porphyrin molecules. For
porphyrins 1-Zn - 5-Zn, the alkoxy linkage on the solubilizing
wedge appears to influence the equilibrium between H- and
J-aggregates. Porphyrins 1-Zn - 3-Zn (alkoxy linkage) form
H-aggregates while porphyrins 4-Zn and 5-Zn exclusively form J-
aggregates. The phenyl group of the solubilizing wedge is more
electron rich for 1-Zn - 3-Zn, possibly resulting in a more acidic
amide NH and a stronger hydrogen bond. FT-IR analysis of 1-Zn
-
5-Zn as solutions in MCH however, proved inconclusive in
judging the hydrogen bonds in 1-Zn - 5-Zn. Alternatively, weak
electrostatic interactions between alkoxy linkages has been
shown to lead to stronger binding interactions in
5
0
perylenebisimides, similar interactions might favour co-facial
H-aggregation over slip-stacked J-aggregation in our system.
For porphyrin 2-Zn it was previously found that by changing
the porphyrin central metal atom from zinc to copper, the
formation of co-facial H-aggregates was promoted with respect to
the formation of J-aggregates.29 To investigate the influence of
the central metal atom on our findings, we synthesize copper
variants of porphyrins 1-Zn - 5-Zn. Similar as for the zinc
porphyrins, copper porphyrin aggregates were prepared by three
different methods and their UV-Visible absorption spectroscopy
spectra were recorded (Figure 7).
Figure 6. Cooling curves of porphyrins 2-Zn (A) and 1-Zn (B) (λ = 419 or 390
nm, c = 2.5×10-6 M, rate = 0.5 K/min, l = 1 cm) and the corresponding CD and
UV-Visible absorption spectroscopy spectra for 1-Zn as a function of
temperature (C) and (D).
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Chemistry - A European Journal
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FULL PAPER
1-Cu
2-Cu
3-Cu
4-Cu
5-Cu
O
O
O
O
O
O
=
R
=
=
R
=
R
O
=
R
R
O
D
1.0A
1.0B
C
1.2E
1.0
0
.8
1.0
0.8
0.8
0.6
0.4
0.2
0.0
0.8
0
.6
0.8
0.6
0.6
0.6
0.4
0.2
0
.4
0.4
0.4
0
.2
0.2
0.2
0.0
0.0
0.0
350
0.0
350
350
400
λ (nm)
450
350
400
λ (nm)
450
400
λ (nm)
450
350
400
λ (nm)
450
400
450
λ(nm)
Figure 7. UV–Visible absorption spectroscopy spectra recorded for copper metallated variants of porphyrins 1-Cu - 5-Cu after different sample preparation (red
-
6
lines: molecularly dissolved, black lines: injection method, blue lines: quenching method, purple lines: slow cooling method, MCH, c = 2.5×10 M, l = 1 cm).
more stable and conversion between the two aggregates is fast
Interestingly, copper porphyrins 1-Cu - 5-Cu show similar
behaviour when compared to the zinc variants. Porphyrin 1-Cu
forms co-facial H-aggregates and porphyrins 4-Cu and 5-Cu form
offset stacked J-aggregates, all independent of the aggregate
preparation method. For porphyrin 2-Cu the J-aggregate is only
observed when the aggregates are prepared by quenching a
solution from the molecularly dissolved state at elevated
on the time scale of the cooling experiment (rate = 0.5 K/min). The
results for porphyrins 1-Cu - 5-Cu suggest that a similar
competition between J- and H-aggregate formations exist as in
their zinc counterparts. Overall, the Cu functionalized porphyrins
seem to have a slightly greater tendency to form H-aggregates.
temperatures. Porphyrin 3-Cu is able to exclusively form either Conclusions
types of aggregate depending on preparation method. Similar to
our observations for porphyrins 1-Zn and 2-Zn, two assembly
processes could be identified for porphyrins 1-Cu and 2-Cu by
slow cooling solutions from the molecularly dissolved state to
The assembly process of a library of structurally similar tetra-
amidated zinc porphyrins has been investigated. Intriguingly,
small changes in the solubilizing wedge architecture of the
porphyrins are shown to have a dramatic effect on the nature of
the obtained aggregate. Depending on the molecular structure, H-
or J-aggregates are formed which are shown to assembly via
cooperative and isodesmic mechanism, respectively. Kinetic
experiments reveal that these aggregates are formed via a
parallel assembly pathway and thus interconvert via
depolymerisation to the free monomer. Variable temperature
spectroscopy suggests that the pathway of J-type aggregation is
also present in porphyrins that exclusively form H-aggregates
under thermodynamic equilibrium. In addition to the molecular
architecture, the aggregate preparation method is shown to have
a significant influence on the self-assembly process. To test the
generality of these phenomena, we also investigated the copper
metallated variants of the porphyrin library. Here, similar results
were obtained, with a slightly higher preferences for the formation
of H-aggregates in the Cu functionalized variants. The generation
of porphyrin arrays with control over aggregate size and
morphology can be used as a tool to control their organization in
supramolecular architectures. On the other hand, the pathway
complexity that is displayed also shows limitations to their use as
supramolecular motifs.
room temperature and measuring their assembly curves
6
(
λ = 416 nm, c = 2.5×10- M, Figure 8).
Figure 8. UV–Visible absorption spectroscopy cooling curves for porphyrins 1-
Cu and 2-Cu in methylcyclohexane (c = 2.5×10-6 M, l = 1 cm, λ = 416 nm).
Again, the first assembly process appears isodesmic while
the second process appears to be cooperative. For both
porphyrins, the H-aggregated state appears thermodynamically
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Chemistry - A European Journal
10.1002/chem.201605872
FULL PAPER
Synthesis of 3,5-Bis[(S)-3,7-dimethyloctyloxy]benzoyl azide 12: 3,5-
Bis[(S)-3,7-dimethyloctyloxy]benzoic acid 11 (3.9 g, 8.98 mmol), and
triethylamine (1.7 mL) where dissolved in THF (60 mL) and cooled to 0 °C.
A solution of ethyl chloroformate (1.09 mL, 11.4 mmol) in THF (15 mL) was
added dropwise. The solution was stirred for 45 minutes at 0 ˚C, the
Experimental Section
Instrumentation, materials and methods: Unless specifically mentioned,
reagents and solvents were obtained from commercial suppliers and used
without further purification. All solvents were of AR quality. Deuterated
chloroform for NMR analyses was provided with TMS as the 0 ppm
reference. The methylcyclohexane used in all spectroscopic experiments
was of spectroscopic grade. Column chromatography was performed on a
Biotage Isolera One using SNAP KP-SNAP columns and solvent gradients.
1H-NMR and 13C-NMR spectra were recorded on a Varian Mercury Vx 400
MHz instrument (100 MHz for 13C) and all chemical shifts are reported in
parts per million relative to tetramethylsilane (TMS). MALDI-ToF MS
analyses were performed in reflector mode on a PerSeptive Biosystems
Voyager-DE Pro using α-cyano-4-hydroxycinnamic acid (CHCA) and 2-
resulting ethyl chloroformate ester was not isolated. A solution of NaN
3
(1.8 g, 27.7 mmol) in water (15 mL) was added; afterwards the solution
was stirred for 2 hours while being allowed to warm to room temperature.
Water (150 mL) and diethyl ether (150 mL) were added and the layers
were separated. The aqueous layer was extracted with diethyl ether (2 x
2 4
75 mL) and the combined organic layers were dried with Na SO . The
suspension was filtered and the filtrate was concentration in vacuo to yield
1
a yellow oil. Yield = 4.03 g. η = 94 %. H-NMR (400 MHz, CDCl
3
) δ = 7.15
-O), 1.81 (m, 2H, CH
), 1.27-1.12 (m, 12H, CH ), 0.92 (d, 6H, CH
). 13C-NMR (100 MHz, CDCl
) δ = 160.2, 108.1, 107.1,
7.0, 39.5, 37.4, 36.3, 30.1, 28.4, 24.7, 22.7, 20.0.
(
s, 2H, Ar-H), 6.69 (s, 1H, Ar-H), 4.00 (m, 4H, CH
2
3
-
CH), 1.59 (m, 4H, O-CH -CH
2
2
2
3
),
[
(
(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile
DCTB) as matrices. Ultraviolet-visible (UV-Visible) absorbance spectra
0
.85 (d, 12H, CH
3
3
6
were recorded on a Jasco V-650 UV–Visible spectrometer with a Jasco
ETCR-762 temperature controller. Circular dichroism (CD) spectra were
recorded on a JASCO J-815 CD spectrometer with a JASCO PTC-348
temperature controller. Solid state infrared (IR) spectra were recorded on
a Perkin Elmer Spectrum One spectrometer equipped with an ATR
universal sampler accessory and in dilute solution using 1 mm NaCl cells.
Synthesis of 3,5-Bis[(S)-3,7-dimethyloctyloxy]aniline 13: 3,5-Bis[(S)-
,7-dimethyloctyloxy]benzoyl azide 12 (4.02 g, 8.75 mmol) was dissolved
3
in dioxane (50 mL) and heated under reflux conditions for 30 minutes. After
reflux the solution was cooled to 70 ˚C and slowly added to a solution of
tetrabutylammonium hydroxide (40 wt % in water, 8 mL) in dioxane (200
mL) at 90 ˚C via a cannula. The solution was stirred for another 15 minutes
at 90 ˚C, allowed to cool to room temperature and dried under vacuum.
The residue was partitioned between water (150 mL) and diethyl ether
The syntheses of (S)-3,7-Dimethyloctyl 4-methylbenzenesulfonate 9 and
3
,4,5-tris[(S)-3,7-dimethyloctyloxy]aniline 6 were performed according to
28,29
reference literature.
(
150 mL) and the layers were separated. The combined organic layers
were washed with brine (50 mL), dried using Na
SO , filtered and dried
under vacuum. The crude product was purified by column chromatography
gradient of 0 % to 15 % ethyl acetate in heptane). Yield = 1.14 g. η = 32 %.
2
4
Synthesis of Methyl 3,5-bis[(S)-3,7-dimethyloctyloxy]benzoate 10:
S)-3,7-Dimethyloctyl 4-methylbenzenesulfonate 9 (8.355 g, 26.7 mmol)
was dissolved in MIBK (30 mL). To this solution methyl 3,5-
dihydroxybenzoate 8 (2.040 g, 12.136 mmol), K CO (8.30 g, 60 mmol)
(
(
1
H-NMR (400 MHz, CDCl
m, 4H, CH -O), 1.76 (m, 2H, CH
.17 (m, 12H, CH ), 0.93 (d, 6H, CH
) δ = 161.2, 148.2, 94.3, 92.1, 66.2, 39.2, 37.3, 36.2, 29.9, 28.0,
4.6, 22.7, 22.6, 19.6.
3
) δ = 5.91 (s, 2H, Ar-H), 5.84 (s, 1H, Ar-H), 3.93
-CH), 1.49 (m, 4H, O-CH -CH ), 1.30-
). 13C-NMR (100
), 0.87 (d, 12H, CH
2
3
(
1
2
3
2
2
and TBAB (0.64 g, 2 mmol) where added and the solution was heated
under reflux conditions for 24 hours. MIBK was removed under vacuum
and the residue was taken up in DCM (50 mL) and 3 N HCl (50 mL). The
product was further extracted from the aqueous layer with DCM (3 x 70
mL) and the combined organic fractions were washed with water (100 mL)
2
3
3
MHz, CDCl
2
3
Synthesis of 1,2,3-Triiodo-5-nitrobenzene 15: Glacial acetic acid (60
mL) was cooled in an ice bath and 2,6-diiodo-4-nitroaniline (10.3 g, 26.4
mmol) was slowly added. Then a solution of sodium nitrite (3 g, 0.043
mmol) in sulphuric acid (15 mL) was added dropwise and subsequently
the mixture was allowed to warm to room temperature. The mixture was
stirred until everything was dissolved (90 minutes) and poured into ice
water (200 mL) while stirring. Urea (4.0 g, 66.6 mmol) was added and the
mixture was filtered. Potassium iodide (6.0 g, 36.2 mmol) in water (30 mL)
was added while stirring. The yellow/brown reaction mixture was then
heated to 95 °C for 2 hours. After cooling, sodium bisulphate (5.0 g, 41.6
mmol) was added to quench the excess iodide. The precipitate was filtered
of, the crude product was dried under vacuum and purified by column
2 4
and brine (100 mL) and then dried with Na SO . The suspension was
filtered and the filtrate was concentration in vacuo. The residue was
purified by column chromatography (gradient of 0 % to 10 % ethyl acetate
1
in heptane). Yield = 5.03 g. η = 92 %. H-NMR (400 MHz, CDCl
3
) δ = 7.16
-O), 3.90 (s, 3H, O-CH ),
), 1.16 (m, 12H, CH ), 0.95
). 13C-NMR (100 MHz, CDCl
) δ = 167.1,
60.0, 131.7, 107.6, 106.8, 66.8, 52.3, 39.5, 37.6, 36.0, 29.6, 27.7, 24.5,
2.2, 19.5. MALDI-ToF-MS (m/z) calc. for C28 448.36 found 448.40
(
s, 2H, Ar-H), 6.63 (s, 1H, Ar-H), 3.99 (m, 4H, CH
.81 (m, 2H, CH -CH), 1.55 (m, 4H, O-CH -CH
d, 6H, CH ), 0.88, (d, 12H, CH
2
3
1
3
2
2
2
(
3
3
3
1
2
48 4
H O
·
+
(M ) .
Synthesis of 3,5-Bis[(S)-3,7-dimethyloctyloxy}benzoic acid 11:
Methyl-3,5-bis{(S)-3,7-dimethyloctyloxy}benzoate 10 (5.02 g, 11.2 mmol)
was dissolved in ethanol (50 mL) and a solution of NaOH (2.24 g, 53.8
chromatography (gradient of 0 % to 30 % chloroform in heptane) to afford
the product as yellow crystals. Yield = 11.69 g. η = 88 %. 1H-NMR (400
MHz, CDCl ): δ = 8.62 (s, 2H, Ar-H).
3
mmol) in H
The solvent was evaporated and the residue was partitioned between H
and DCM (each 100 mL). The organic layer was neutralized with 1 M HCl
50 mL), washed with H O (2 x 50 mL) and brine (50 mL) and then dried
2
O (10 mL) was added. The mixture was refluxed for 72 hours.
2
O
Synthesis of 1,2,3-Tri(dodecynyl)-5-nitrobenzene 17: 1,2,3-Triiodo-5-
nitrobenzene 15 (3 g, 6 mmol), TEA (100 mL), CuI (112 mg, 0.6 mmol) and
bis(triphenylphosphine)-palladium(II) dichloride (256 mg, 0.3 mmol) were
charged in a Schlenk tube and the reaction mixture was subjected to five
freeze-pump-thaw cycles. The resulting mixture was heated to 80 °C and
then 1-dodecyne (3.54 g, 20.9 mmol) was added dropwise under argon
counterflow. The resulting mixture was stirred for 4 hours at 80 °C after
which the solvent was removed in vacuo. The crude material was purified
(
2
with Na
2
SO
4
.
The suspension was filtered and the filtrate was
1
concentration in vacuo to yield a yellow oil. Yield = 3.97 g. η = 82 %. H-
NMR (400 MHz, CDCl
3
) δ = 7.22 (s, 2H, Ar-H), 6.69 (s, 1H, Ar-H), 4.01 (m,
-O), 1.78 (m, 2H, CH -CH), 1.52 (m, 4H, O-CH -CH ), 1.19 (m,
2H, CH ), 0.96 (d, 6H, CH ), 0.89 (d, 12H, CH
). 13C-NMR (100 MHz,
) δ = 160.2, 130.9, 108.1, 107.6, 66.6, 39.7, 37.6, 36.3, 29.8, 28.2,
4.5, 22.5, 19.7.
4
H, CH
2
3
2
2
1
2
3
3
CDCl
3
by column chromatography (gradient of 0% to 10% dichloromethane in
2
1
heptane). Yield = 3.0 g. η = 82 %. H-NMR (400 MHz, CDCl
3
) δ = 8.08 (s,
2 2
2H, Ar-H), 2.55 (t, 2H, CΞC-CH ), 2.45 (t, 4H, CΞC-CH , 1.8-1.0 (m, 48H,
aliphatic), 1.90 (t, 9H, CH ).
3
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Chemistry - A European Journal
10.1002/chem.201605872
FULL PAPER
Synthesis of 3,4,5-Triidodecylaniline 18: 1,2,3-Tri(1-dodecynyl)-5-
nitrobenzene 17 (3 g, 4.92 mmol) was dissolved in a mixture of ethyl
acetate (45 mL) and ethanol (5 mL). Argon was bubbled through the
solution for 15 minutes after which Pd/C (300 mg) was carefully added and
Synthesis of Porphyrin 3: Tetrakis(4-carboxyphenyl)porphyrin 22 (113
mg, 0.14 mmol) in CHCl
3
(15 mL), 3,5-bis[(S)-3,7-dimethyloctyloxy]aniline
(426 mg, 1.05 mmol) and N,N-diisopropylethylamine (0.28 mL) in CHCl
3
(15 mL). Column conditions: gradient of 0 % to 15 % MeOH in CHCl
3
. Yield
1
the mixture was subsequently subjected to H
2
in a Parr hydrogenation
= 0.26 g. η = 85 %. H-NMR (400 MHz, CDCl
3
) δ = 8.84 (s, 8H, ß-pyrrolic
apparatus. Upon completion of the reaction, the suspension was filtered
and the solution was evaporated to dryness. The crude product was
protons), 8.32 (d, 8H, Ar-H), 8.24 (d, 8H, Ar-H), 8.08 (s, 4H, NH), 7.04 (s,
8H, Ar-H), 6.37 (s, 4H, Ar-H), 4.08 (m, 16H, CH -O), 1.85 (m, 2H, CH -CH),
1.59 (m, 16H, O-CH -CH ), 1.42-1.10 (m, 48H, CH ), 1.01 (d, 24H, CH ),
0.88 (d, 48H, CH ) δ = 165.6,
), -2.79 (s, 2H,). 13C-NMR (100 MHz, CDCl
160.8, 145.6, 139.6, 134.8, 134.6, 125.5, 119.2, 98.9, 66.6, 39.3, 37.3,
6.2, 29.9, 28.0, 24.7, 22.7, 22.6, 19.7. MALDI-ToF-MS (m/z) calc for
12 2340.61 found 2341.34 (M+H)+.
2
3
purified by column chromatography using heptane as eluent. Yield = 3 g.
2
2
2
3
1
η = 98 %. H-NMR (400 MHz, CDCl
3
) δ = 6.4 (s, 2H, Ar-H), 2.47 (t, 6H, Ar-
3
3
CH
2
), 1.6-1.0 (m, 60H, aliphatic), 0.88 (t, 9H, CH
3
).
3
C
152 210 8
H N O
Synthesis of 1,3-Diiodo-5-nitrobenzene 19: 2,6-Diiodo-4-nitroaniline
10.24 g, 26.67 mmol) was dissolved in ethanol (167 mL) and the solution
(
was cooled to 0 ˚C. Sulphuric acid (14 mL) was added dropwise and the
mixture was heated to 60 ˚C. Sodium nitrite (5.29 g, 77.0 mmol) was slowly
added and the mixture was heated under reflux for 3 hours after which the
mixture was allowed to cool to room temperature and poured into ice water
Synthesis of Porphyrin 4: Tetrakis(4-carboxyphenyl)porphyrin 22 (100
mg, 0.13 mmol) in CHCl (20 mL, 3,4,5-tridodecylaniline (430 mg, 0.72
mmol) and N,N-diisopropylethylamine (218 mg, 1.7 mmol) in CHCl (20
mL). Column chromatography conditions: heptane:dichloromethane:ethyl
acetate 9:9:1. Yield = 0.30 g. η = 73 %. 1H-NMR (400 MHz, CDCl
) δ =
3
3
(200 mL). The resulting solids where filtered of and dried under vacuum.
3
The crude material was recrystallized from iso-propanol to afford greenish
8.87 (s, 8H, ß-pyrrolic protons), 8.35 (d, J = 8.4 Hz, 8H, Ar-H), 8.28 (d, J =
8.4 Hz, 8H, Ar-H), 8.04 (s, 4H, NH), 7.47 (s, 8H, Ar-H), 2.67 (m, 24H), 1.66
1
needles. Yield = 3.53 g. η = 36 %. H-NMR (400 MHz, CDCl
3
) δ = 8.52 (s,
2
H, Ar-H), 8.37 (s, 1H, Ar-H).
(m, 24H), 1.5-1.2 (m, 216H, aliphatic), 0.9 (m, 36H, CH
13C-NMR (100 MHz, CDCl
) δ = 165.4, 145.4, 142.1, 135.5, 135.3, 134.9,
34.8, 125.5, 119.1, 118.8, 35.4, 33.4, 31.9, 31.9, 31.8, 31.7, 31.2, 30.3,
0.0, 29.7, 29.7, 29.6, 29.5, 29.4, 29.3, 29.0, 26.4, 26.3, 22.8, 22.7, 22.6,
3
), -2.81 (s, 2H).
3
1
3
2
Synthesis of 1,3-Di(1-dodecynyl)-5-nitrobenzene 20: 1,3-Diiodo-5-
nitrobenzene 19 (600 mg, 1.6 mmol), TEA (20 mL), CuI (20 mg, 0.11 mmol)
and bis(triphenylphosphine)-palladium(II) dichloride (40 mg, 0.057 mmol)
were charged in a Schlenk tube and the reaction mixture was subjected to
five freeze-pump-thaw cycles. The resulting mixture was heated to 60 °C
and 1-dodecyne (532 mg, 3.2 mmol) was added dropwise under argon
counterflow. The resulting mixture was stirred for 24 hours at 60 °C after
which the solvent was removed in vacuo. The crude material was purified
2.6, 14.1, 14.1. MALDI-ToF MS (m/z) calc for C216
found 3111.68 (M+H) .
H N O
338 8 4
3110.66
+
Synthesis of Porphyrin 5: Tetrakis(4-carboxyphenyl)porphyrin 22 (110
mg, 0.14 mmol) in CHCl (20 mL, 3,5-didodecylaniline (343 mg, 0.75
mmol) and N,N-diisopropylethylamine (222 mg, 1.7 mmol) in CHCl (20
mL). Column chromatography conditions: heptane:chloroform:ethyl
acetate 4:3:1. Yield = 0.23 g. η = 57 %. 1H-NMR (400 MHz, CDCl
) δ =
8.87 (s, 8H, ß-pyrrolic protons) 8.35 (d, 8H, Ar-H), 8.29 (d, 8H, Ar-H), 8.10
(s, 4H, NH), 7.47 (s, 8H, Ar-H), 6.89 (s, 4H, Ar-H), 2.67 (t, 16H Ar-CH ),
1.70 (m, 16H, Ar-CH -CH ), 1.28 (d, 144H, aliphatic protons), 0.88 (t, 24H,
CH ) δ = 165.5, 145.3, 144.3,
), -2.78 (s, 2H). 13C-NMR (100 MHz, CDCl
37.7, 134.7, 127.9, 125.5, 119.1, 117.7, 64.2, 36.3, 31.9, 31.4, 29.6, 22.5,
4.5. MALDI-ToF-MS (m/z) calc. for C168 2436.90 found 2437.96
3
3
by column chromatography (gradient of 0 % to 25 % dichloromethane in
heptane). Yield = 0.68 g. η = 95 %. H-NMR (400 MHz, CDCl
1
3
) δ = 8.08 (s,
), 1.68 –
), 1.39 – 1.19 (m, 24H, CH ),
3
2H, Ar-H), 7.66 (s, 1H, Ar-H), 2.41 (t, 4H, J = 7.1 Hz, CΞC-CH
1.55 (m, 4H, CH ), 1.50 – 1.39 (m, 4H, CH
0.97 – 0.79 (m, 6H, CH ).
2
2
2
2
2
3
2
2
3
3
1
1
(
Synthesis of 3,5-Didodecylaniline 21: 1,3-Di(1-dodecynyl)-5-
nitrobenzene 20 (0.682 g, 1.51 mmol) was dissolved in a mixture of ethyl
acetate (45 mL) and ethanol (5 mL). Argon was bubbled through the
solution for 15 minutes after which Pd/C (300 mg) was carefully added and
242 8 4
H N O
M+H)+.
the mixture was subsequently subjected to H
apparatus. Upon completion of the reaction, the suspension was filtered
and solution was evaporated to dryness. The crude product was purified
2
in a Parr hydrogenation
General procedure for metal insertion into tetra-amidated porphyrins:
For zinc insertion: The free porphyrin base was dissolved in
dichloromethane and zinc acetate was added. The mixture was stirred for
24 hours at room temperature and afterwards the solvent was removed in
vacuo. The crude mixture was purified using column chromatography.
For copper insertion: The free porphyrin base was dissolved in chloroform
and copper(II) acetate was added. The mixture was stirred under reflux
conditions for 24 hours and afterwards the solvent was removed in vacuo.
The crude mixture was purified using column chromatography.
by column chromatography using heptane as eluent. Yield = 0.58 g. η =
1
8
9 %. H-NMR (200 MHz, CDCl
3
) δ = 6.42 (s, 1H, Ar-H), 6.35 (s, 2H, Ar-
), 2.47 (s, 4H, Ar-CH ), 1.56 (s, 4H, CH ), 1.40-1.14 (d,
), 0.88 (s, 6H, CH ) δ = 144.0, 137.4,
). 13C-NMR (100 MHz, CDCl
19.3, 112.7, 36.0, 32.1, 31.6, 29.8, 29.6, 29.6, 29.6, 29.5, 29.4, 29.3, 22.5,
H), 3.5 (b, 2H, NH
6H, CH
2
2
2
3
1
1
2
3
3
.
+
4.2. MALDI-ToF-MS (m/z) calc for C30H55N 429.43 found 429.46 (M ) .
General procedure for the synthesis of tetra-amide porphyrins:
Tetrakis(4-carboxyphenyl)porphyrin 22 was dissolved in chloroform under
an argon atmosphere. Oxalyl chloride (30 equivalents) and DMF (2 μL)
were added and the mixture was stirred for 3 hours at room temperature.
The solvent and all volatiles were removed in vacuo and the remaining
residue redissolved in chloroform and cooled to 0 °C. A solution of the
aniline derivative and DIPEA in chloroform was added dropwise to the acid
chloride solution under an argon atmosphere, after which the mixture was
stirred for 24 hours at room temperature. Upon completion, the solvent
was removed in vacuo and the residue redissolved in chloroform. The
organic phase was washed with 1 M HCl (3x), 1 M NaOH (3x) and brine
Synthesis of Porphyrin 3-Zn: Porphyrin 3 (262 mg, 0.11 mmol), zinc
acetate (250 mg, 1.34 mmol) and chloroform (10 mL). Column
chromatography conditions: gradient of 0 % to 15 % MeOH in CHCl
3
. Yield
1
= 243 mg. η = 91 %. H-NMR (400 MHz, CDCl
3
) δ = 8.96 (s, 8H, ß- pyrrolic
protons), 8.37 (d, 8H, Ar-H), 8.27 (d, 8H, Ar-H), 8.06 (s, 4H, NH), 7.05 (s,
8H, Ar-H), 6.35 (s, 4H, Ar-H), 4.07 (m, 16H, CH -O), 1.86 (m, 8H, CH -CH),
1.55 (m, 16H, O-CH -CH ), 1.42-1.10 (m, 48H, CH ), 0.99 (d, 24H, CH ),
0.90 (d, 48H, CH ) δ = 165.6, 160.7, 149.9,
). 13C-NMR (100 MHz, CDCl
2
3
2
2
2
3
3
3
146.6, 139.5, 134.9, 134.5, 132.2, 125.3, 98.9, 66.6, 39.3, 37.3, 36.2, 29.9,
28.0, 24.7, 22.7, 22.6, 19.7. MALDI-ToF-MS (m/z) calc for
152 210 8
H N O
12Zn 2402.52 found 2403.55 (M+H)+.
C
(1x) and dried over sodium sulphate. The crude material was further
purified by column chromatography.
Synthesis of Porphyrin 3-Cu: Porphyrin 3 (191 mg, 0.08 mmol),
copper(II) acetate (150 mg, 0.82 mmol) and chloroform (20 mL). Column
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201605872
FULL PAPER
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3
chromatography conditions: gradient of 0 % to 10 % MeOH in CHCl . Yield
=
147 mg. η = 75 %. The paramagnetic nature of the copper ion hinders
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401.52 found 2402.54 (M+H)+.
(
5)
H
210 8
N O12Cu
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(
(
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Yield = 29 mg. η = 86 %. 1H-NMR (400 MHz, CDCl
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3
) δ = 8.96 (s, 8H ß-
pyrrolic protons), 8.34 (d, J = 8 Hz, 8H, aromatic), 8.23 (d, J = 8 Hz, 8H,
aromatic), 8.04 (s, 4H, NH), 7.44 (s, 8H, aromatic), 2.66 (m, 24H), 1.67 (m,
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(12)
(13)
2
4H), 1.5-1.2 (m, 216H, aliphatic), 0.88 (m, 36H, CH
3
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(
(
14)
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CDCl ) δ = 165.4, 145.4, 142.1, 135.5, 135.3, 134.9, 134.8, 125.5, 119.1,
3
1
2
18.8, 35.4, 33.4, 31.9, 31.9, 31.8, 31.7, 31.2, 30.3, 30.0, 29.7, 29.7, 29.6,
9.5, 29.4, 29.3, 29.0, 26.4, 26.3, 22.8, 22.7, 22.6, 22.6, 14.1, 14.1.
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MALDI-ToF-MS (m/z) calc for C216H N O Zn 3172.57 found 3173.61
M+H)+.
(
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(
21)
22)
(
·
+
216 8 4
C H336CuN O 3171.57 found 3171.64 (M ) .
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Synthesis of Porphyrin 5-Zn: Porphyrin 5 (141 mg, 0.06 mmol), zinc
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003, 68 (13), 5037.
1
=
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8
CH
H, Ar-H), 6.86 (s, 4H, Ar-H), 2.63 (t, 16H Ar-CH
2
), 1.66 (m, 16H, Ar-CH
2
-
). 1 C-NMR
3
2
), 1.34-1.28 (d, 144H, aliphatic protons), 0.87 (t, 24H, CH
3
9
819.
(
100 MHz, CDCl
3
) δ = 165.6, 149.8, 146.3, 144.0, 137.8, 134.6, 134.3,
32.1, 125.2, 120.0, 117.5, 45.6, 36.1, 31.9, 31.5, 29.7, 29.7, 29.6, 29.6,
9.5, 29.4, 22.7, 14.1. MALDI-ToF-MS (m/z) calc for C168 Zn
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1
2
2
240 8 4
H N O
.
+
498.81 found 2498.83 (M ) .
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acetate (80 mg, 0.44 mmol) and chloroform (20 mL). Column
3
939.
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3
. Yield
=
66 mg. η = 92 %. The paramagnetic nature of the copper ion hinders
NMR characterization. MALDI-ToF-MS (m/z) calc for C168
2
H
240
N
8
O
4
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This work was supported by the European Research Council
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Ministry of Education, Culture and Science (Gravity program
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Entry for the Table of Contents
FULL PAPER
The supramolecular assembly of
porphyrin tetra-amides is found to be
highly sensitive to variations in the
molecular structure and preparation
Rob van der Weegen, Abraham J.P
Teunissen, Prof. Dr. E.W. Meijer*
Page No. – Page No.
method,
aggregate
modifications to the porphyrin core.
allowing
control
over
without
Directing the self-assembly behaviour
of porphyrin-based supramolecular
systems
architecture
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