Surface aggregate morphology of chiral porphyrins as a function of constitution and amphiphilic nature

Article abstract of DOI:10.1039/b815177f

The deposition of molecules onto surfaces from dilute solutions can lead to a variety of layer morphologies depending on the balance of interactions between solvent and molecule, molecules themselves, and these two components and the surface. Here we expl

Full text of DOI:10.1039/b815177f

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/njc | New Journal of Chemistry
Surface aggregate morphology of chiral porphyrins as a function
of constitution and amphiphilic naturew
´
Patrizia Iavicoli, Maite Simon-Sorbed and David B. Amabilino*
Received (in Montpellier, France) 2nd September 2008, Accepted 27th October 2008
First published as an Advance Article on the web 16th December 2008
DOI: 10.1039/b815177f
The deposition of molecules onto surfaces from dilute solutions can lead to a variety of layer
morphologies depending on the balance of interactions between solvent and molecule, molecules
themselves, and these two components and the surface. Here we explore the behaviour of a set of
chiral tetra meso-amidophenyl-substituted porphyrins—containing long hydrophobic tails at the
periphery of the conjugated p-electron system—after depositing a drop of each compound from
different solutions onto graphite. The synthesis of the new compounds is detailed and the
morphology of the aggregates they form on the substrate has been investigated by atomic force
microscopy (AFM). Depending on the solvent used and composition and constitution of the
compound the structures formed are very different. Round shape aggregates and larger dewetting
type patterns were formed from solutions of the compounds in methanol—in which all the
molecules exhibit non-specific aggregation—and when chloroform and toluene are used fibril-like
structures appear, whose alignment with the graphite axes depends on the length of the alkyl
chains attached to the amide moiety in the molecules.
As part of an ongoing project to investigate the role of
Introduction
hydrogen bonds in the aggregation of aromatic systems at
surfaces, we chose to prepare and study the tetra-meso-
amidophenyl-substituted porphyrin derivative 1 (Fig. 1). This
compound gives a variety of different superstructures at the
surface depending on the solvent used upon casting the
molecule on the substrate, as shown by acoustic mode atomic
force microscopy (AFM), after depositing a drop of a solution
of the compound on the freshly cleaved substrate (either
graphite or mica) and allowing the solvent to evaporate.30 It
was demonstrated how different solvents can modify the
interactions of the molecule with itself and with the surface.
Porphyrins are attractive components in molecular materials for
a number of reasons, including the transfer of charge where a
number of groups, notably including that of Jean-Pierre
Sauvage, have made important discoveries concerning electron
transfer.1–10 These studies, inspired by the photosynthetic reac-
tion centre,11 have helped towards understanding the pheno-
menon within relatively large molecules, but another important
area is that of the transport of charge in much larger aggre-
gates.12–15 In this sense, the preparation of synthetic assem-
blies on surfaces16,17 and the study of properties such as
photoconductivity are important areas of activity.18,19
While many of the subtle mechanisms governing the aggrega-
tion of molecular species in solution have been unravelled,20–25
the understanding of the way molecules come together at
surfaces is still very limited:26–27 The formation of self-ordered
nanostructures at surfaces is more complicated than in solution
as it requires the additional control over interactions of either
molecules or their aggregates with the surface. In addition,
the packing of the first layer can be different from that of the
subsequent layers because of the interaction of the molecule with
the surface.28,29 A deeper understanding of the assembly of
different compounds at various surfaces under different condi-
tions is crucial to achieve full control over the growth of
aggregates across multiple length scales of functional architectures
with desired structure and properties.26
`
Institut de Ciencia de Materials de Barcelona (CSIC), Campus
Universitari de Bellaterra, 08193 Cerdanyola del Valles Catalonia,
`
Spain. E-mail: amabilino@icmab.es; Fax: +34 93 5805729;
Tel: +34 93 5801853
w Dedicated to Prof. Jean-Pierre Sauvage on the occasion of his 65th
birthday.
Fig. 1 Chemical structures of the compounds prepared in this work.
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
358 | New J. Chem., 2009, 33, 358–365

View Article Online
However, it is clear that non-covalent interactions are playing
a very important role in the morphology of the films, which are
new and intriguing. In an attempt to shed light on the key
factors influencing the aggregate morphology, we have varied
the molecular composition and constitution in order to
explore the origins of these effects, and here we report our
findings. Specifically, the series of novel porphyrin derivatives
2–4 (Fig. 1) was synthesized, where the number of carbon
atoms in the alkyl chain and their position on the phenyl ring
affect the self-assembly and the organization onto a surface.
We chose to study the molecules on a graphite surface, because
the amide’s ability to self-assemble functional units in fibre-like
aggregates is disturbed on a hydrophilic surface, because of the
possible interaction between the amide groups of the molecules
with it, as seen for other amide derivatives.31,32 The studies are
distinct from those carried out under equilibrium conditions in
solvent at the graphite surface33,34 because kinetics and solvent
evaporation play an important role in the formation of the
nanostructures.27 The alkyl chain can modify the morphology
of aggregates because it changes the solubility, and the porphyrins
substituted at the 3-position might be expected to hinder the
formation of well defined aggregates because of the multiple
conformers that exist for these compounds.
lactate in the presence of triphenylphosphine and diisopropyl-
azodicarboxylate, as reported previously.35,36 The resulting alde-
hydes 5 and 6 were then used in the condensation with pyrrole in
refluxing propionic acid in air37 to give the new corresponding
porphyrin derivatives 7 and 8. These compounds showed the
characteristic spectroscopic data of tetraphenylporphyrin deriva-
tives. The condensations of the esters with dodecylamine and
octadecylamine were performed by heating the esters 7 and 8 at
80 1C using the amines as solvent. This procedure afforded the
chiral amides 1–4 in respectable yields after thorough purifica-
tion by column chromatography. Their structures were con-
firmed by all the habitual spectroscopic techniques and elemental
analysis.
2. Atomic force microscopy measurements
The morphologies of the aliphatic porphyrin aggregates at the
air–substrate interface were studied by acoustic mode AFM
after depositing a drop of a solution of the compounds on a
freshly cleaved piece of highly oriented pyrolytic graphite
(HOPG) substrate and allowing the solvent to evaporate.
The technique is particularly appropriate for the study of this
kind of aggregate because no treatment of the surface is
necessary prior to imaging, which was always performed in
ambient conditions.
Results and discussion
Topographic AFM images of films of (R,R,R,R)-2—which
has four dodecyl chains substituted at the 3-position of the
phenyl groups—drop cast from different solvents onto HOPG
are shown in Fig. 2–5. When the solution of the compound in
methanol is cast onto the graphite surface, a typical dewetting
phenomenon is observed whereby worm-like islands of mate-
rial with no internal structure are formed (Fig. 2). A shattered
monolayer around 2 nm thick can be observed with small
layers a further 2 nm thick growing on top of it in places. In
this solvent, it seems that the interactions between the surface
and the molecules are not strong enough to dominate a specific
film forming process. The diameter of a tetraphenylporphyrin
is estimated to be 1.4 nm, the chain length 1.7 nm in this case,
and the thickness is 0.4 nm. Therefore the total length of the
porphyrin molecule core and the two opposite tails is 4.8 nm.
If we assume the molecule to be perpendicular to the substrate
with the chains extended away following the plane of the
porphyrin ring, the distance between the methyl groups at
the ends of two opposite chains is less than 4.8 nm. It therefore
appears that the layers contain molecules with the porphyrin
core oriented quasi-perpendicularly to the surface with the
alkyl chains folded in an approximately parallel orientation to
the surface.
1. Synthesis and characterisation
The porphyrins 1–4 were prepared by the synthetic route
described in Scheme 1. In the first step 3- and 4-hydroxy-
benzaldehyde were condensed stereoselectively with (S)-methyl
When the solvent used is changed to chloroform (Fig. 2 and
Fig. 3) the formation of needle like structures of between 6 and
10 nm thick (as judged from the z—vertical with respect to the
flat surface—scale in the AFM image), around 40 nm wide and
approximately 150 to 300 nm in length are formed. In this less
polar solvent, well defined structures are formed partially
thanks to the better interaction between molecules themselves
and the substrate, as indicated upon Fourier transform of
the images which reveals a clear preference for alignment of
the acicular structures along the symmetry axes of the graphite
(not shown). The image showing the smaller area (Fig. 3)
Scheme 1
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
New J. Chem., 2009, 33, 358–365 | 359

View Article Online
Fig. 2 Topographic AFM images of films of (R,R,R,R)-2 drop cast onto HOPG from a 1 Â 10À5 M solution in MeOH (left), chloroform (centre)
and toluene (right). The contours in the frames below the images correspond to the line in the image.
Fig. 3 Topographic AFM image of a film of (R,R,R,R)-2 drop cast
onto HOPG from a 1 Â 10À5 M solution in CHCl3.
clearly indicates some interaction between the fibres, as they
are often seen in pairs or threes and have quite uniform width.
When (R,R,R,R)-2 was deposited onto the graphite surface
from toluene a range of different morphologies was observed,
the most representative morphology being needle-like objects
in which the border is higher than the centre (Fig. 2). The
Fig. 4 Topographic AFM image of a film of (R,R,R,R)-2 drop cast
onto HOPG from a 1 Â 10À5 M solution in toluene. The contour in the
lower frame corresponds to the line in the image.
height of these borders is approximately 0.4 nm, and the
longitudinal dimensions of the objects are between 100 and
300 nm and the distance between the rims is around 50 nm
(Fig. 4). We are unaware of any report of such a structure
upon deposition of an organic material on a surface. The
orientation of the molecules is presumably planar to the
surface because of the height. This situation also occurs in
physisorbed monolayers in equilibrium on graphite where
(R,R,R,R)-4 is held to the surface by a combination of
C–HÁ Á Áp interactions,38 When this sample of (R,R,R,R)-2
was heat annealed at about 50 1C for 2 h, the structure
reorganised to give much larger tape-like objects (Fig. 5).
Here, the apparent thickness is an average of 0.5 nm, with a
second layer whose surface is at a height of 1.4 nm above the
graphite. This observation indicates that the layer in contact
with the graphite is laying almost flat upon it, while the second
layer is tilted up quasi-perpendicularly to the surface. This
shows an interesting similarity to monolayers of a distinct
porphyrin derivative which shows both flat and perpendicular
arrangements relative to the surface within the monolayer.39
Again, this low polarity solvent gives well defined structures,
which in this case definitely lie flat on the surface and are
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
360 | New J. Chem., 2009, 33, 358–365

View Article Online
respectively. The orientation of the fibres in this latter case is
along the graphite axes.
The AFM images of films of the porphyrin (R,R,R,R)-1
were reported in a previous correspondence.28 Briefly, from
chloroform the molecule forms very fine fibres on graphite and
from toluene somewhat more well defined ones, very similar to
those formed by (R,R,R,R)-3, while from methanol both these
compounds show globular aggregates.
When compound (R,R,R,R)-4 was deposited from MeOH
solution onto the HOPG surface it showed the formation of
round shaped aggregates of between 6 and 12 nm height
(Fig. 7). Presumably, the methanol—which is a poor solvent
for this highly apolar compound—favours the non-specific
interaction between the molecules and, as a consequence of
the small interaction with the substrate, round non-acicular
aggregates are formed.
When a solution of (R,R,R,R)-4 in toluene was deposited
onto graphite areas of a smooth monolayer of 1.5 nm high
are formed (Fig. 7). It can be observed that within some of
these islands smaller needle shaped aggregates are present,
whose length is between 200 and 300 nm, and the space
between the centres of the well-defined fibres is between 30
and 60 nm. These fibres do seem to be aligned with the
substrate symmetry directions. The length of the fully
extended molecule is approximately 6 nm, and so they must
be composed of several molecules. It is noteworthy, however,
that less well resolved fibres are inferred in areas of the AFM
images, which might correspond to single molecule wide fibres.
When the solution is changed to chloroform, long fibres of
(R,R,R,R)-4 with 1.5 nm height and 20–40 nm width are
observed (Fig. 7). The fibres are very different from those
observed in the previous cases, in that they are apparently
isolated from each other and can be extremely long—up to a
micron—and straight with no specific alignment to the
graphite symmetry directions, indicating that the molecule–
molecule interaction is higher than the molecule–surface inter-
action under these conditions. While the fibres are relatively
straight, they do show definite kink points and more smoothly
bent regions. In addition, there are areas in which bundles of
fibres with multiple kinks are observed, and there are clear
points at which fibres merge or diverge from one another.
These characteristics correspond to a polymer type structure,
and indicate that the molecule has formed a non-covalent
chain of molecules with considerable rigidity, and that chains a
single molecule wide are being imaged (since the convolution
of the AFM tip gives a larger value of the width of the fibres
than the actual one). This molecule and solvent combination is
therefore unique amongst the ones studied in this work.
Fig. 5 Topographic AFM image of a film of (R,R,R,R)-2 drop cast
onto HOPG from a 1 Â 10À5 M solution in toluene and heat annealed.
The contour in the lower frame corresponds to the line in the image.
formed partially thanks to the better interaction between mole-
cules themselves and the substrate, as indicated upon Fourier
transform of the images, which reveals a clear preference for
alignment along the symmetry axes of the graphite.
When (R,R,R,R)-3—which is identical to 2 with the excep-
tion that octadecyl chains are present instead of dodecyl
chains—was deposited onto graphite from a methanol solu-
tion a complex morphology resulted (Fig. 6). At first sight, it
appears that a dewetting pattern is the only one present, as for
the shorter chain analogue. Yet closer inspection reveals that
these areas of material are not uniform, but are pitted, and
that in between them a much thinner layer of material is
present. This situation can best be appreciated in the profiles
of the layers shown in Fig. 6. The thinner layer has a
maximum thickness of approximately 1 nm—consequent with
a monolayer forming a very slight angle with the surface—
while the dewetting shapes are approximately 8 nm thick
(much larger than mono- or bilayer thickness), with pits going
down to the monolayer height.
When (R,R,R,R)-3 was deposited onto graphite from a
chloroform solution, a complex web of short fibres of up to
1.5 nm high was formed (Fig. 6). The fact that the fibres
overlapped each other and that they are oriented randomly
strongly suggests that they are formed in solution and
deposited as such onto graphite. A tilted orientation of the
molecules with respect to the surface is thought to dominate in
these objects. When the same molecule is deposited from a
toluene solution, needles are formed (Fig. 6). The height of the
objects is approximately 1.5 nm, which corresponds to the
width of the tetraphenylporphyrin core, and the width
and length of the fibres are 130–160 nm and 200–350 nm,
Discussion
A wide variety of surface morphologies have been observed for
the four porphyrins and for the different conditions under
which they were deposited onto the graphite surface. The
solvent certainly plays a role in the aggregation of all the
porphyrins which have been studied here, as has been observed
in different systems, although the trends are different, pre-
sumably because of the different chemical composition and
flexibility of the molecules. The more polar solvent—methanol,
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
New J. Chem., 2009, 33, 358–365 | 361

View Article Online
Fig. 6 Topographic AFM images of films of (R,R,R,R)-3 drop cast onto HOPG from a 1 Â 10À5 M solution in methanol (left), chloroform
(centre) and toluene (right). The contours correspond to the lines in the images above them.
Fig. 7 Topographic AFM images of films of (R,R,R,R)-4 drop cast onto HOPG from a 1 Â 10À5 M solution in methanol (left), chloroform
(centre) and toluene (right). The contours correspond to the lines in the images above them.
which is a poor solvent for the molecules and also a better
hydrogen bond donor than the others—promotes non-specific
molecule–molecule interactions with a consequent dewetting
phenomenon being dominant in the layer formation, as
observed in the AFM topography images of the samples. This
aggregation in methanol was confirmed by UV-visible absorp-
tion spectroscopy, where a clear shift in the absorption bands is
observed for methanol solutions (Fig. 8 for (R,R,R,R)-3, the
other compounds show essentially the same difference in
methanol) when compared with the spectra in either chloroform
or toluene. Besides, methanol scarcely possesses an affinity for
the apolar graphite surface compared with the other solvents,
which presumably aids in favouring the adsorption of the
porphyrin molecules into poorly ordered assemblies, such as
the amorphous thin dewetting we observed. The longer alkyl
chains seem to favour the formation of smaller structures at the
surface, evidenced by the smaller globular type structures seen
for 3 (in part) and 4.
The less polar solvents, with a lower ability to form hydrogen
bonds but greater ability to solvate the apolar parts of the
molecules, apparently induce more specific intermolecular
interactions between the amide groups in the molecules,
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
362 | New J. Chem., 2009, 33, 358–365

View Article Online
chains which can overcome unfavourable conformations and
ensure aggregation, the octadecyl chain being particularly
useful.
The compounds can form quite well ordered linear struc-
tures on graphite along the symmetry axes of the substrate,
indicating that both molecule–molecule and molecule–
substrate interactions are involved.40 This situation arises only
when non-polar solvents are used. The only case where align-
ment with the surface symmetry directions is not observed is
when strong molecule–molecule interactions arise, in the case
of 4, where long fibril architectures are observed. It is hoped
that these architectures and those derived from them can be
exploited as active components for applications in various
fields including (opto)electronics, photovoltaics, magnetism,
and catalysis.
Experimental section
Fig. 8 UV-Vis absorption spectra of (R,R,R,R)-3 in 5 Â 10À6
M
solutions in methanol, chloroform and toluene.
General details
The starting materials were purchased commercially and were
used without further purification. Thin-layer chromatography
(TLC) was performed on aluminium plates coated with Merck
silica gel 60 F254. Developed plates were air-dried and
scrutinized under a UV lamp. Silica gel 60 (35–70 mesh, SDS)
was used for column chromatography. Melting points were
determined by differential scanning calorimetry (DSC) using a
Perkin Elmer DSC 7 instrument. LDI-TOF-MS were obtained
using a Kratos Kompact Maldi 2 K-probe (Kratos Analytical)
operating with pulsed extraction of the ions in linear high power
mode. The samples were deposited directly onto a non-polished
leading to the formation of fibril-like structures. In addition
they seem to lead to a favourable interaction of the molecules
with the apolar graphite surface, as revealed by the alignment
of the fibres with the axes of the substrate, and avoid the
kinetically driven (trapped) adsorption of porphyrins into the
amorphous layer on the surface. The one exception in which
the fibres do not follow the graphite axes is that of 4, and here
the porphyrins presumably preorganise in solution phase by
hydrogen bonds and p–p interactions and produce columnar
oligomers of molecules, which make the edge-on stacking style
favourable when assembled on a solid substrate. Thus the
planes of the porphyrins could be tilted from or perpendicular
to the substrate. When the alkyl chain is longer, a better
interaction with the surface stabilizes the structures and a
tilted orientation of the porphyrin with respect to the surface
plane is favoured.
1
stainless steel sample plate from dichloromethane solution. H
and 13C NMR spectra were recorded using the deuterated
solvent as lock and tetramethylsilane as internal reference.
Coupling constants are in Hertz. Compounds (R)-5,29 (R)-6,30
(R,R,R,R)-4 and (R,R,R,R)-834 were prepared as described
previously.
Conclusions
Synthesis
The series of chiral tetra(alkylamidophenyl)-substituted
porphyrins described here can be synthesized readily, and their
self-assembly on graphite shows the dramatic role that solvent
and composition can have on the film morphology, as revealed
by the AFM studies. There is no evidence that the chirality of
the molecule is expressed in the aggregates that are formed at
the surface of the graphite, although it should be stated that
any helicity within single fibres would be below the resolution
limit of the AFM tips used in the experiments performed by
us. The results do not rule out the utility of the porphyrins
described here as chiral materials.41
5,10,15,20-Tetra[3-(R,R,R,R)-methyl 2-phenoxypropanoate]-
porphyrin ((R,R,R,R)-7). Freshly distilled pyrrole (266 mL,
3.84 mmol) and (R)-methyl 2-(3-formylphenoxy)propanoate
(800 mg, 3.84 mmol) were added to refluxing propionic acid
(14 mL) in air. After refluxing for 90 min, the solution was
cooled to room temperature and the propionic acid was
removed by careful evaporation in vacuo. The dark viscous
material remaining was then washed thrice with hot water to
remove remaining propionic acid and other undesired tar. The
crude product was subjected to column chromatography on
silica gel with CH2Cl2–MeOH (100 : 0.5) giving (R,R,R,R)-7 as
a purple solid (600 mg, 15% yield). MF: C60H54N4O12; MW:
1022.37; LDI-TOF/MS m/z (%): 1022.65 (100) [M]+;
1H NMR (250 MHz, CDCl3): 8.84 (dd, J = 3.9, 8H, pyrrole
CH), 7.82 (d, J = 7.3, 4H, ArH), 7.71 (s, 4H, ArH), 7.63 (t, J =
7.5, 4H, ArH), 7.31 (d, J = 7.9, 4H, ArH), 4.97 (q, J = 6.9, 4H,
ArOCHCH3COOMe), 3.78 (s, 12H, ArOCHCH3COOMe), 1.71
(d, J = 6.7, 12H, ArOCHCH3COOMe), À2.87 (s, 8H, pyrrole
NH) ppm; FT-IR (KBr): 2992 (w, CH3), 2949 (w, CH3), 1756
(s, CO), 1736 (s, CO), 1597 (m, phenyl), 1506 (m, phenyl),
The octadecyl chains favour greatly the formation of fibril-
like structures when compared with the dodecyl counterparts.
While the 4-substituted phenyl group might be expected to
favour greatly the formation of ordered structures compared
with the 3-phenyl compound (because of the multiple con-
formational isomers that exist for the latter), the effect here is
not dramatic, although the 4-phenyl derivatives in general
seem to organise better. These observations underline the
importance of the dispersion interactions between the alkyl
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
New J. Chem., 2009, 33, 358–365 | 363

View Article Online
1471 (m), 1282 (m), 1204 (s), 1177 (m), 1133 (s, OCH3), 1098 (m),
806 (m) cmÀ1; UV-Vis (CHCl3) lmax/nm (e/mol LÀ1 cmÀ1): 420
(33579), 515 (1748), 550 (624), 589 (532), 645 (286); elemental
analysis (%) calculated: C 70.44, H 5.32, N 5.48, found: C 70.51 H
5.45, N 5.56.
after purification. MF:
C
104H146N8O8; MW: 1635.13;
LDI-TOF/MS m/z (%): 1635.61 (100) [M]+; 1H NMR
(250 MHz, CDCl3): 8.84 (s, 8H, pyrrole CH), 8.14 (d, J =
8.5, 8H, ArH), 7.30 (d, J = 8.7, 8H, ArH), 6.69 (t, J =
6.2, 4H, CONH), 4.99 (q, J = 6.8, 4H, –OCHCH3CONH–),
3.47–3.38
(d,
8H, –CONHCH2CH2(CH2)9CH3), 1.36–1.16 (m, 72H,
–CONHCH2CH2(CH2)9CH3), 0.79 (t, 6.0, 12H,
(m,
8H,
–CONHCH2(CH2)10CH3),
1.80
10,15,20-Tetra[3-(R,R,R,R)-2-N-dodecylamidoethyloxyphenyl]-
porphyrin ((R,R,R,R)-2). Porphyrin (R,R,R,R)-7 (100 mg,
98 mmol) was mixed with an excess of dodecylamine and the
mixture heated to 80 1C. The mixture was allowed to react for
about 16 h until no trace of starting material was left (control
was done using TLC). The mixture was cooled and the dark
red residue obtained was purified by column chromatography,
obtaining 130 mg of (R,R,R,R)-2 (79% yield) as a purple solid.
Chromatography was carried out on silica gel with
CH2Cl2–MeOH (100 : 1) mixture. MF: C104H146N8O8; MW:
1635.13; LDI-TOF/MS m/z (%): 1635.47 (100) [M+]; 1H
NMR (250 MHz, CDCl3): 8.84 (s, 8H, pyrrole CH), 7.88
(d, J = 7.0, 4H, ArH), 7.79 (s, 4H, ArH), 7.67 (t, J = 7.2,
4H, ArH), 7.33 (d, J = 7.9, 4H, ArH), 6.64 (s, 4H, –CONH–),
J
= 6.8, 12H, –OCHCH3CONH–), 1.66–1.63 (m,
J
=
–CONHCH2CH2(CH2)15CH3), À2.8 (s, 4H, pyrrole NH)
ppm; FT-IR (KBr): 3286 (w, NH), 2924 (s, CH2), 2853 (s,
CH2), 1656 (s, CO), 1606 (m, phenyl), 1505 (m, phenyl), 1468
(m), 1277 (w), 1236 (s), 1176 (m), 1082 (m), 801 (m) cmÀ1
;
UV-Vis (CHCl3) lmax/nm (e/mol LÀ1 cmÀ1): 419 (34618), 515
(1290), 549 (818), 590 (418), 645 (436); elemental analysis (%)
calculated: C 76.34, H 8.99, N 6.85, found: C 76.25, H 9.17,
N 6.93.
AFM experiments
Solutions of the porphyrins in the different solvents were
prepared by gentle warming prior to deposition of a drop on
freshly cleaved graphite (ZYB grade). The AFM images were
recorded on a PicoSPM (Molecular Imaging). The acoustic
mode was used with resonance frequencies of the silicon tips
(Nanosensors, FM type force constant 1.2–3.5 N mÀ1 and
diameter 5 nm) of around 60–70 kHz. All the images were
recorded under atmospheric conditions.
4.93 (q,
J = 3.5, 4H, –OCHCH3CONH–), 3.35–3.31
(m, 8H, –CONHCH2(CH2)10CH3), 1.70 (d, J = 6.4, 12H,
OCHCH3CONH), 1.57 (m, 8H, –CONHCH2CH2(CH2)9CH3)
1.20–1.16 (m, 72H, –CONHCH2(CH2)9CH3), 0.85–0.80
(t, J = 6.4, 12H, –CONHCH2(CH2)10CH3), À2.8 (s, 4H,
pyrrole NH) ppm; FT-IR (KBr): 3286 (w, NH), 2923
(s, CH2), 2853 (s, CH2), 1656 (s, CO), 1595 (m, phenyl),
1505 (w, phenyl), 1468 (s), 1237 (m), 1165 (m), 1082 (m),
801 (m) cmÀ1; UV-Vis (CHCl3) lmax/nm (e mol LÀ1 cmÀ1): 420
(31090), 515 (1818), 549 (645), 589 (545), 645 (290) nm;
elemental analysis (%) calculated: C 76.34, H 8.99, N 6.85,
found C 76.18, H 9.52 N 6.64.
Acknowledgements
This work was supported by the European Union Marie Curie
Research Training Network CHEXTAN (MRTN-CT-2004-
512161), the Direccio
Tecnologıa (Spain, under the project CTQ2006-06333/BQU),
and the DGR, Catalonia (Project 2005 SGR-00591). We
warmly thank Amable Bernabe at the ICMAB for recording
n General de Investigacion, Ciencia y
´ ´
5,10,15,20-Tetra[3-(R,R,R,R)-2-N-octadecylamidoethyloxy-
phenyl]porphyrin ((R,R,R,R)-3). Compound (R,R,R,R)-3 was
prepared using the same procedure as for (R,R,R,R)-2, using
octadecylamine, and yielded 81% of the desired material. MF:
C128H194N8O8; MW: 1971.50; LDI-TOF/MS m/z (%): 1971.89
(100) [M+]; UV-Vis (CHCl3) l/nm (e/mol LÀ1 cmÀ1): 419
(28423), 515 (1781), 550 (644), 590 (536), 645 (285); 1H
NMR (250 MHz, CDCl3): 8.88 (s, 8H, pyrrole H), 7.92
(d, J = 7.1, 4H, ArH), 7.83 (s, 4H, ArH), 7.70 (t, J = 7.3,
4H, ArH), 7.40 (d, J = 7.9, 4H, ArH), 6.68 (s, 4H, –CONH–),
´
´
IR and LDI-TOF spectra.
References
1 J. C. Chambron, S. Chardonnoblat, A. Harriman, V. Heitz and
J. P. Sauvage, Pure Appl. Chem., 1993, 65, 2343–2349.
2 A. Harriman and J. P. Sauvage, Chem. Soc. Rev., 1996, 25, 41–48.
3 J. C. Chambron, J. P. Collin, J. O. Dalbavie, C. O. Dietrich-Buchecker,
V. Heitz, F. Odobel, N. Solladie and J. P. Sauvage, Coord. Chem. Rev.,
1998, 178, 1299–1312.
4 M. Andersson, M. Linke, J. C. Chambron, J. Davidsson, V. Heitz,
J. P. Sauvage and L. Hammarstrom, J. Am. Chem. Soc., 2000, 122,
3526–3527.
5 I. M. Dixon, J. P. Collin, J. P. Sauvage and L. Flamigni, Inorg.
Chem., 2001, 40, 5507–5517.
6 L. Flamigni, A. M. Talarico, J. C. Chambron, V. Heitz, M. Linke,
N. Fujita and J. P. Sauvage, Chem.–Eur. J., 2004, 10, 2689–2699.
7 L. Flamigni, V. Heitz and J. P. Sauvage, Struct. Bonding, 2006,
121, 217–261.
8 G. Steinberg-Yfrach, P. A. Lidell, S.-C. Hung, A. L. Moore,
D. Gust and T. A. Moore, Nature, 1997, 385, 239–241.
9 J. A. Hutchison, T. D. M. Bell, T. Ganguly, K. P. Ghiggino,
S. J. Langford, N. R. Lokan and M. N. Paddon-Row,
J. Photochem. Photobiol., A, 2008, 195, 220–225.
10 R. F. Kelley, J. L. Suk, T. M. Wilson, Y. Nakamura, D. M. Tiede,
A. Osuka, J. T. Hupp and M. R. Wasielewski, J. Am. Chem. Soc.,
2008, 130, 4277–4284.
4.97 (q,
J = 3.4, 4H, –OCHCH3CONH–), 3.36–3.34
(m, 8H, –CONHCH2(CH2)16CH3), 1.73 (d, J = 6.8, 12H,
OCHCH3CONH), 1.56 (m, 8H, –CONHCH2CH2(CH2)15CH3),
1.24–1.21 (m, 128H, –CONHCH2(CH2)16CH3), 0.91–0.86
(t, J = 6.0, 12H, –CONHCH2(CH2)16CH3), À2.80 (s, 4H,
pyrrole NH) ppm; FT-IR (KBr): 3286 (w, NH), 2923 (s, CH2),
2852 (s, CH2), 1655 (s, CO), 1602 (m, phenyl), 1502 (w, phenyl),
1467 (m), 1237 (m), 1176 (m), 1085 (m), 801 (m) cmÀ1; elemental
analysis (%) calculated: C 77.92, H 9.91, N 5.68, found: C 77.75,
H 9.97, N 5.59.
5,10,15,20-Tetra[4-(R,R,R,R)-2-N-dodecylamidoethyloxyphenyl]-
porphyrin ((R,R,R,R)-1). Compound (R,R,R,R)-1 was prepared
following the same procedure used for the synthesis of
(R,R,R,R)-2. Porphyrin (R,R,R,R)-834 (100 mg, 98 mmol)
was mixed with an excess of dodecylamine. Pure (R,R,R,R)-1
was obtained as a purple solid (135 mg) (81% yield)
11 J. Deisenhofer and H. Michel, Chem. Scr., 1989, 29, 203–220.
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
364 | New J. Chem., 2009, 33, 358–365

View Article Online
12 E. Tsuchida, T. Komatsu and J.-H. Fuhrhop, Polym. Adv.
Technol., 1998, 9, 569–578.
13 M. C. Lensen, S. J. T. van Dingenen, J. A. A. W. Elemans,
H. P. Dijkstra, G. P. M. van Klink, G. van Koten,
J. W. Gerritsen, S. Speller, R. J. M. Nolte and A. E. Rowan,
Chem. Commun., 2004, 762–763.
14 Y. Nakamura, N. Aratani and A. Osuka, Chem. Soc. Rev., 2007,
36, 831–845.
15 R. van Hameren, A. M. van Buul, M. A. Castriciano, V. Villari,
27 E. Gomar-Nadal, J. Puigmartı-Luis and D. B. Amabilino, Chem.
´
Soc. Rev., 2008, 37, 490–504.
28 I. Doudevski and D. K. Schwartz, J. Am. Chem. Soc., 2001, 123,
6867–6872.
29 N. Miyashita, H. Mohwald and D. G. Kurth, Chem. Mater., 2007,
¨
19, 4259–4262.
30 P. Iavicoli, M. Linares, A. Perez del Pino, R. Lazzaroni and
´
D. B. Amabilino, Superlattices Microstruct., 2008, 44,
556–562.
N. Micall, P. Schon, S. Speller, L. M. Scolaro, A. E. Rowan,
¨
J. A. A. W. Elemans and R. J. M. Nolte, Nano Lett., 2008, 8,
253–259.
31 T.-Q. Nguyen, M. L. Bushey, L. E. Brus and C. Nuckolls, J. Am.
Chem. Soc., 2002, 124, 15051–15054.
32 J. Puigmartı
´
´
-Luis, A. Minoia, A. Perez del Pino, G. Ujaque,
s, R. Lazzaroni and D. B. Amabilino,
16 Q. Guo, J. Yin, R. E. Palmer, N. Bampos and J. K. M. Sanders,
J. Phys.: Condens. Matter, 2003, 15, S3127–S3138.
17 A. Huijser, B. M. J. M. Suijkerbuijk, R. J. M. K. Gebbink,
T. J. Savenije and L. D. A. Siebbeles, J. Am. Chem. Soc., 2008,
130, 2485–2492.
18 A. D. Schwab, D. E. Smith, B. Bond-Watts, D. E. Johnston,
J. Hone, A. T. Johnson, J. C. de Paula and W. F. Smith, Nano
Lett., 2004, 4, 1261–1265.
19 A. L. Yeats, A. D. Schwab, B. Massare, D. E. Johnston,
A. T. Johnson, J. C. de Paula and W. F. Smith, J. Phys. Chem.
C, 2008, 112, 2170–2176.
20 J. S. Lindsey, New J. Chem., 1991, 15, 153–180.
21 D. Philp and J. F. Stoddart, Angew. Chem., Int. Ed. Engl., 1996, 35,
1154–1196.
22 P. N. W. Baxter, J.-M. Lehn, B. O. Kneisel, G. Baum and
D. Fenske, Chem.–Eur. J., 1999, 5, 113–120.
23 F. J. M. Hoeben, P. Jonkheijm, E. W. Meijer and A. P. H.
J. Schenning, Chem. Rev., 2005, 105, 1491–1546.
24 P. Jonkheijm, P. van der Schoot, A. P. H. J. Schenning and
E. W. Meijer, Science, 2006, 313, 80–83.
C. Rovira, A. Lledo
´
Chem.–Eur. J., 2006, 12, 9161–9175.
33 T. Ikeda, M. Asakawa, M. Goto, K. Miyake, T. Ishida and
T. Shimizu, Langmuir, 2004, 20, 5454–5459.
34 J. Otsuki, E. Nagamine, T. Kondo, K. Iwasaki, M. Asakawa and
K. Miyake, J. Am. Chem. Soc., 2005, 127, 10400–10405.
35 M. Minguet, D. B. Amabilino, J. Cirujeda, K. Wurst, I. Mata,
E. Molins, J. J. Novoa and J. Veciana, Chem.–Eur. J., 2000, 6,
2350–2361.
36 M. Minguet, D. B. Amabilino, J. Vidal-Gancedo, K. Wurst and
J. Veciana, J. Mater. Chem., 2002, 12, 570–578.
37 A. D. Adler, J. Org. Chem., 1967, 32, 476.
38 M. Linares, P. Iavicoli, K. Psychogyiopoulou, D. Beljonne, S. De
Feyter, D. B. Amabilino and R. Lazzaroni, Langmuir, 2008, 24,
9566.
39 Y. Zhou, B. Wang, M. Zhu and J. G. Hou, Chem. Phys. Lett.,
2005, 403, 140–145.
40 D. B. Amabilino, S. De Feyter, R. Lazzaroni, E. Gomar-Nadal,
J. Veciana, C. Rovira, M. M. Abdel-Mottaleb, W. Mamdouh,
P. Iavicoli, K. Psychogyiopoulou, M. Linares, A. Minoia, H. Xu
25 R. M. Capito, H. S. Azevedo, Y. S. Velichko, A. Mata and
S. I. Stupp, Science, 2008, 319, 1812–1816.
´
and J. Puigmartı-Luis, J. Phys.: Condens. Matter, 2008, 20,
184003.
26 V. Palermo and P. Samori, Angew. Chem., Int. Ed., 2007, 46,
4428–4432.
41 D. B. Amabilino and J. Veciana, Top. Curr. Chem., 2006, 265,
253–302.
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
New J. Chem., 2009, 33, 358–365 | 365