Synthesis and 2D self-assembly at the liquid-solid interface of novel H-bonding linear π-conjugated oligomers terminated by uracil and melamine units

Article abstract of DOI:10.1039/c3nj01606d

We report here on the synthesis and 2D self-assembly of novel H-bonding linear π-conjugated oligomers terminated at both ends by either two uracil moieties (compound GR1) or by two melamine groups (compounds GR2 and GR3). The bis(uracil) GR1 compound was prepared by Sonogashira coupling of an ethynyluracil with a dihalobenzene and characterized spectroscopically. The synthesis of GR2 and GR3 was performed by Suzuki coupling of the dihalogenated benzene derivatives leading to the respective bisadducts which were then converted into the target bis-melamine derivatives by treatment with dicyanodimide. Self-assembly of the GR1 derivative is investigated at the liquid/graphite interface using scanning tunneling microscopy (STM). When deposited from n-tetradecane, GR1 forms a row-like structure stabilized by multiple terminal H-bonds between neighboring molecules. Co-adsorption of two n-tetradecane molecules per unit cell is also clearly identified. In turn, when deposited from 1-phenyloctane GR1 forms a complex quasi square-shaped open structure having asymmetric sides. One possible arrangement is that four phenyloctane molecules are co-adsorbed in-between GR1 rows similar to those formed from n-tetradecane, thus forming the two other sides of the square-shaped motif. From both solvents, the row-like 2D arrangements are governed by the multiple terminal H-bonds which create long-range alignments in one direction and by the van der Waals interdigitation of the dodecyl chains of the GR1 molecules that stabilize the network in a nearly perpendicular direction. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c3nj01606d

NJC
View Article Online
View Journal | View Issue
PAPER
Synthesis and 2D self-assembly at the liquid–solid
interface of novel H-bonding linear p-conjugated
oligomers terminated by uracil and melamine
units†
Cite this: New J. Chem., 2014,
38, 2407
G. Y. Y. Chng,a X. Sun,bc S. J. Cho,a D. Rajwar,a A. C. Grimsdale*a and D. Fichou*bc
We report here on the synthesis and 2D self-assembly of novel H-bonding linear p-conjugated oligomers
terminated at both ends by either two uracil moieties (compound GR1) or by two melamine groups
(compounds GR2 and GR3). The bis(uracil) GR1 compound was prepared by Sonogashira coupling of an
ethynyluracil with a dihalobenzene and characterized spectroscopically. The synthesis of GR2 and GR3
was performed by Suzuki coupling of the dihalogenated benzene derivatives leading to the respective
bisadducts which were then converted into the target bis-melamine derivatives by treatment with
dicyanodimide. Self-assembly of the GR1 derivative is investigated at the liquid/graphite interface using
scanning tunneling microscopy (STM). When deposited from n-tetradecane, GR1 forms a row-like
structure stabilized by multiple terminal H-bonds between neighboring molecules. Co-adsorption of
two n-tetradecane molecules per unit cell is also clearly identified. In turn, when deposited from
1-phenyloctane GR1 forms a complex quasi square-shaped open structure having asymmetric sides. One
possible arrangement is that four phenyloctane molecules are co-adsorbed in-between GR1 rows similar
to those formed from n-tetradecane, thus forming the two other sides of the square-shaped motif. From
both solvents, the row-like 2D arrangements are governed by the multiple terminal H-bonds which create
long-range alignments in one direction and by the van der Waals interdigitation of the dodecyl chains of
the GR1 molecules that stabilize the network in a nearly perpendicular direction.
Received (in Montpellier, France)
18th December 2013,
Accepted 25th February 2014
DOI: 10.1039/c3nj01606d
www.rsc.org/njc
in substantial improvements in the performances of organic-
based devices. Two-dimensional (2D) self-assembly of appropriate
Introduction
Small p-conjugated organic molecules have been widely devel- molecular building blocks on surfaces is a widely-used strategy
oped as active materials in various electronic devices such as to prepare nanostructured functional architectures with pre-
photovoltaic solar cells, field-effect transistors, light-emitting defined geometry and properties.6–13 In particular, H-bonds
diodes, or sensors.1–5 They can easily be processed as homo- have been extensively used to direct the 2D self-assembly taking
geneous thin films either from solution or by vacuum- advantage of the lower energy compared to covalent bonds
deposition and then potentially lead to low-cost manufacturing, as well as spatial directionality. Adsorption of trimesic acid
enable the use of flexible substrates and allow fabrication of
large-area components. In contrast to polymers, small organic
molecules are prone to form highly-ordered materials resulting
a School of Materials Science and Engineering, Nanyang Technological University,
Singapore. E-mail: ACGrimsdale@ntu.edu.sg; Fax: +6567909081;
Tel: +6567906728
b
´
Sorbonne Universites, UPMC Univ Paris 06, UMR 8232, Institut Parisien de
´
Chimie Moleculaire, F-75005, Paris, France. E-mail: denis.fichou@upmc.fr;
Fax: +33144275572; Tel: +33144275080
c
´
CNRS, UMR 8232, Institut Parisien de Chimie Moleculaire, F-75005, Paris, France
† Electronic supplementary information (ESI) available: Synthetic details of the
preparation of the precursors of GR1, GR2 and GR3; 1H NMR spectra; MALDI TOF
mass spectra; UV-visible absorption and photoluminescence spectra. See DOI:
10.1039/c3nj01606d
Scheme 1 Chemical formulae of the three compounds under study here.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 2407--2413 | 2407

View Article Online
Paper
NJC
through OH00 0 0O bonds on various surfaces constitutes the and linear shape, respectively, and bearing complementary
archetype of H-bond-driven self-assembled networks.14,15 Various functional groups. Incorporation of appropriate guest organic
other types of H-bonding molecules such as N-containing molecules molecules, metallic atoms or inorganic quantum dots into the
have also been reported for the formation of NH0 0 00O or NH00 0 0
N
nanocavities within these networks would result in multi-
H-bonded 2D nanostructures.16–23 H-bonds can also allow component materials with optoelectronic properties suitable for
different molecules to clip together to form two or three- use in devices such as photovoltaic devices. These networks could
component networks.24,25 Finally, note that ‘‘weak’’ H-bonds, be made by the non-covalent interaction of two units, one trigonal
e.g. H-bonds with E o 5 kcal molꢀ1, like for example CH00 0 0O, and the other linear, bearing complementary H-bonding groups.
have also been used to build self-assembled 2D arrays.26
Along with this approach, we now report the synthesis and
We recently reported on the self-assembly of end-substituted 2D self-assembly of a linear molecule bearing a uracil moiety at
star-shaped oligophenylenes.27 In the present study, our aim is each end (GR1) as well as the synthesis of two similar molecules
to elaborate extended 2D networks by linking together suitable terminated by melamine groups (GR2 and GR3, Scheme 1).
functional molecules through non-covalent interactions such Uracil groups are capable of forming hydrogen bonds with mela-
as H-bonds. These hollow site networks might plausibly be mine units. Thus co-deposition of such a molecule with a suitable
made by the non-covalent interaction of two units of trigonal melamine derivative might produce the desired extended networks.
Scheme 2 Chemical pathway to the bis(uracil) compound GR1.
Scheme 3 Chemical pathway to the bis(melamine) compounds GR2 (R = OC12H25) and GR3 (R = C8H17).
2408 | New J. Chem., 2014, 38, 2407--2413
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
NJC
Paper
Fig. 1 STM images of the GR1 self-assembly at the n-tetradecane/HOPG interface. Left: 100 ꢁ 100 nm2, It = 20 pA, Vs = ꢀ0.6 V. Middle: 23.4 ꢁ
23.4 nm2, It = 20 pA, Vs = ꢀ1.0 V. Right: 9 ꢁ 9 nm2; It = 20 pA, Vs = ꢀ0.6 V. The unit cell is indicated by blue dashed lines.
This short oligomer has a relatively large bandgap and should treatment with dicyanodimide.31,32 The optical absorption and
be capable of transferring energy or electrons to a suitable emission spectra of the dialokoxybenzene derivative GR2 are
co-monomer within the proposed networks or to a guest similar to those of GR1, with two absorption maxima in the UV
molecule deposited inside the network.
region (at 308 and 374 nm) and a single emission band peaking
We reveal by means of scanning tunnelling microscopy at B512 nm (Fig. S10, ESI†) By contrast, the dialkyl derivative
(STM) that the 2D self-assembly of the linear derivative GR1 GR3 shows only one absorption band peaking at B295 nm and a
forms long-range 2D networks when physisorbed at the HOPG/ blue-shifted emission band peaking at B430 nm (Fig. S15, ESI†).
liquid interface. When deposited from n-tetradecane, GR1 forms a
row-like structure stabilized by multiple terminal H-bonds between
neighbouring molecules. In turn, when 1-phenyloctane is used as
the solvent we observe a square arrangement where molecules are
interconnected through multiple H-bonds formed between neigh-
bouring amino-diketo terminal groups. Attempts to produce two-
component networks by combining GR1 together with melamine
or the GR2 and GR3 are currently in progress. Due to their limited
solubility, the self-assembly of the melamine derivatives and of a
mixture of the uracil and melamine-terminated molecules has not
yet been investigated by STM.
Results and discussion
Synthesis of the GR1, GR2 and GR3 compounds
The bis(uracil) derivative GR1 was prepared as shown in Scheme 2.
Uracil 1 was first alkylated and then iodinated. The iodoalkyluracil
2 was then converted into the ethynyl derivative 3 by Sonogashira
coupling with trimethylsilylacetylene followed by deprotection with
a base. Sonogashira coupling with the diiododialkoxybenzene 4
then gave the desired molecule GR1 as a yellow solid with 40%
yield. The structure of GR1 was confirmed by 1H NMR, mass
spectrometry, UV-visible absorption, fluorescence and IR spectro-
scopies (see ESI†). The GR1 molecule shows an absorption
maximum in chloroform at labs = 375 nm and a photolumines-
cence maximum at lem = 450 nm (Fig. S6, ESI†).
Compounds GR2 (R = OC12H25) and GR3 (R = C8H17) bearing
Fig. 2 Proposed model of the 2D structure of GR1 at the n-tetradecane/
two terminal melamine moieties were synthesized as shown in
HOPG interface. The unit cell is outlined by the blue dashed lines (a = 3.0 ꢂ
0.1 nm; b = 2.0 ꢂ 0.1 nm; a = 110 ꢂ 11). Co-adsorbed n-tetradecane
molecules are indicated in red (two per unit cell). Hexyl chains of GR1 are
not represented because they are not visible on the STM images.
Scheme 3. The Suzuki coupling28 of the dihalides 4 and 529,30
gave, respectively, the bisadducts 6 and 7. These were then
converted into the bis-melamine derivatives GR2 and GR3 by
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 2407--2413 | 2409

View Article Online
Paper
NJC
This is not surprising since alkoxy groups often induce a marked one GR1 molecule (Z = 1) and also two n-tetradecane molecules
red-shift of the absorption and emission spectra as compared to interdigitated with the dodecyl chains. A model of the arrange-
similar compounds bearing alkyl groups. This well-known effect ment is presented in Fig. 2. Importantly the GR1 molecules are
originates from the electron-donating nature of the alkoxy connected to each other in a head-to-head fashion through two
groups and has been extensively discussed.33 Finally, note that H-bonds occurring between terminal NH and CQO groups
the multiple hydrogen-bonding sites of the melamine groups (Scheme 4). Both the H-bonding between the neighboring GR1
make GR2 and GR3 poorly soluble in non-polar solvents.
molecules and the van der Waals interaction between the neighbor-
ing alkyl chains play important roles in forming the GR1 row-like
supramolecular network on the HOPG surface.
Self-assembly of GR1 studied by STM at the liquid/HOPG
interface
GR1 from 1-phenyloctane. Long-range ordering appears
immediately after deposition of GR1 from 1-phenyloctane on
HOPG. Highly ordered domains up to 50 ꢁ 50 nm2 in size are
observed, with the GR1 molecules forming a quasi square-
shaped structure (Fig. 3, left). Higher resolution (Fig. 3, middle
and right) allows us to visualize the main cores of the molecules
with the three interconnected rings. The two dodecyl chains are
also clearly visible, appearing as six white spots inside
the squares on the STM images. In between the two GR1
molecules aligned vertically in the STM image of Fig. 3 appear
four other bright spots having a contrast similar to that of
the three individual aromatic rings of GR1. No alkyl chain
is associated with these four bright spots but the distance
separating the two molecules corresponds roughly to the length
of a 1-phenyloctane molecule. Therefore we suggest that
these spots correspond to the aromatic benzene cores of four
co-adsorbed 1-phenyloctane molecules thus forming a bridge
between consecutive GR1 vertical rows.
GR1 from n-tetradecane. When deposited from n-tetradecane
on graphite the GR1 molecules form large single domains whose
size may extend well beyond 100 ꢁ 100 nm2 (Fig. 1, left). The 2D
self-organized monolayer network consists of alignments of GR1
molecules into parallel rows. In the STM images the conjugated
cores of GR1 appear as parallel bright lines separated by a
distance of B3 nm. High-resolution reveals the details of the
2D arrangement (Fig. 1, right). Single GR1 molecules are again
well-resolved, with the lateral dodecyl chains clearly resolved as
six bright spots. The hexyl chains of the GR1 molecules are not
directly observable probably because of their very short length.
The unit cell is indicated by dashed blue lines in Fig. 1, right
(a = 3.0 ꢂ 0.1 nm; b = 2.1 ꢂ 0.1 nm; a = 110 ꢂ 11). It contains
Another possibility would be that the horizontal bridges
between vertical rows are made of additional GR1 molecules.
However no additional dodecyl chains are observed, making
such a hypothesis unlikely. The unit cell of the arrangement in
1-phenyloctane is represented by the blue lines in the STM
image (Fig. 3) and in the proposed model (Fig. 4). The unit cell
parameters are a = b = 2.4 ꢂ 0.1 nm, a = 92 ꢂ 11. In this model
there is only one GR1 molecule per unit cell (Z = 1) while there are
four co-adsorbed 1-phenyloctane molecules, something rather
unusual. The complexity of this arrangement is challenging and
a more detailed analysis will be reported elsewhere.
Scheme 4 Intermolecular terminal H-bonds (red dotted lines) stabilizing
the GR1 network.
Fig. 3 STM images of GR1 at the 1-phenyloctane/HOPG interface. Left: 50 ꢁ 50 nm2; It = 10 pA, Vs = 0.8 V. Middle: 17 ꢁ 17 nm2, It = 12 pA, Vs = 0.8 V.
Right: 10 ꢁ 10 nm2, It = 20 pA, Vs = 0.8 V. The quasi-square shaped unit cell is indicated as blue dashed lines.
2410 | New J. Chem., 2014, 38, 2407--2413
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
NJC
Paper
synthetized in our lab27 in order to produce 2D open networks
with size-selected cavities.
Experimental section
Synthetic procedures
General methods. The starting compounds 1–5 (see Schemes 2
and 3) were prepared following literature procedures.22,34,35 All
other reagents and solvents were obtained commercially and used
without further purification. NMR spectra were recorded on a
Bruker Advance 400 MHz spectrometer. Mass spectra were
obtained using a Shimadzu Axima MALDI-TOF mass spectrometer.
UV-Visible absorption spectra were recorded on a Shimadzu
UV-2501PC spectrophotometer. Photoluminescence spectra
were measured on a Shimadzu RF-5301PC spectrofluorometer.
1,10-Hexyl-6,60-[(1,4-bis(dodecyloxy)-2,5-phenylene)diethynyl]-
bisuracil (GR1). To a degassed solution of dry triethylamine
(20 mL) and THF (20 mL), 1,4-bis(dodecyloxy)-2,5-diiodobenzene
(0.77 g, 1.102 mmol), palladium catalyst (0.06 g, 0.052 mmol),
and copper iodide (0.018 g, 0.095 mmol) were added and the
mixture was degassed a second time. Ethynyl uracil derivative 3
(0.6 g, 2.72 mmol) was then added, and the reaction mixture was
degassed one last time and stirred overnight at 85 1C under
nitrogen. The mixture was filtered through Celite, and then the
solvent was concentrated under vacuum. The precipitate was
purified by several precipitations from chloroform upon addition of
methanol, yielding GR1 (0.97 g, 40.3%) as a yellow solid. 1H NMR
(400 MHz, CDCl3) d 8.36 (br. s, 2H, NH), 6.97 (s, 2H), 4.10 (t, 4H),
4.01 (t, 4H) 1.78 (m, 8H), 1.44 (m, 4H), 1.30 (m, 44H), 0.86 (m, 12H).
Fig. 4 Possible model of the GR1 network with the co-adsorption of four
1-phenyloctane molecules per unit cell (in red on the scheme). The unit
cell is indicated by blue dashed lines (a = b = 2.4 ꢂ 0.1 nm; a = 92 ꢂ 11).
Conclusion
In summary we have first described the synthesis of three novel
linear p-conjugated oligomers terminated on both ends by
H-bonding uracil and melamine units. The bis(uracil) GR1
compound was prepared by Sonogashira coupling of an ethynyl-
uracil with a dihalobenzene and characterized spectroscopically.
Besides, the synthesis of GR2 and GR3 was performed by Suzuki
coupling of the dihalogenated benzene derivatives leading to the
respective bisadducts which were then converted into the target
bis-melamine derivatives by treatment with dicyanodimide.
Then, by means of STM at the liquid/graphite interface, we
have revealed that when deposited from n-tetradecane GR1
forms a row-like structure stabilized by multiple terminal
H-bonds between neighbouring molecules. Co-adsorption of two
n-tetradecane molecules per unit cell is also clearly identified.
In turn, when deposited from 1-phenyloctane GR1 forms a
complex quasi square-shaped open structure having asymmetric
sides. One possible arrangement is that four 1-phenyloctane mole-
cules are co-adsorbed in-between the GR1 rows, thus forming the
two other sides of the square-shaped motif. From both solvents,
the row-like 2D arrangements are governed (1) by the multiple
terminal H-bonds which create long-range alignments in one
direction and (2) by the van der Waals interdigitation of the
dodecyl chains of GR1 that stabilize the network in the nearly
perpendicular direction.
MALDI-TOF MS: m/z = 883.1 [M+] (calculated for C54H82N4O6
882.62). UV-Vis (CHCl3) lmax = 306, 320, 399 nm.
=
2,5-Bis(40-cyanophenyl)-1,4-didodecyloxybenzene 6. 2,5-Diiodo-
1,4-didodecyloxybenzene 4 (1.0 g, 1.43 mmol), 4-cyanophenyl-
boronic ester (0.72 g, 3.15 mmol), 30 mL of THF–water (2: 1),
and sodium carbonate (10 mL, 20 mmol) were mixed in a 100 mL
flask and degassed with nitrogen. After 10 minutes the palla-
dium catalyst (0.221 g, 0.315 mmol) was added, and the mixture
refluxed for 24 hours. The mixture was cooled to room tempera-
ture, and the organic phase was separated and filtered through
Celite. The precipitate was purified by several precipitations
from chloroform by addition of ethanol, yielding compound 6
1
as a white solid (0.28 g, 30%). H NMR (400 MHz, DMSO-d6) d
(ppm): 8.30 (d, J = 8 Hz, 4H), 7.65 (d, J = 8 Hz, 4H), 7.05 (s, 2H),
3.95 (t, 4H), 1.62–1.64 (br. m, 36H), 1.19–1.33 (br. m, 4H), 0.82
(t, 6H). 13C NMR (100 MHz, DMSO-d6) d (ppm): 166.9, 149.7,
140.5, 129.6, 128.8, 127.2, 115.4, 68.7, 39.5, 31.2, 29.0, 28.9, 28.9,
28.6, 28.5, 25.4, 22.0, 13.8.
Melamine derivative GR2. To a mixture of compound 6 (300
mg, 0.46 mmol), powdered potassium hydroxide (0.143 g,
2.54 mmol) and dicyanodiamide (0.1 g, 2.57 mmol) 20 mL of
2-methoxyethanolwere added. The reaction mixture was stirred
at 125 1C overnight, and then poured into dichloromethane. The
organic layer was washed with water. Ethanol was added to the
crude product to afford GR2 as a white solid (0.22 g, 58%). 1H NMR
(400 MHz, DMSO-d6) d (ppm): 8.30 (d, J = 8 Hz, 8H, NH2), 7.65
Finally, as stated in our introduction, we are presently
investigating the possibility to clip the uracil GR1 together
with either of the melamine GR2 or GR3 by means of three
complementary terminal H-bonds to form hybrid linear
rows with an alternation of two different GR molecules. We
are also mixing the GR molecules with trigonal star-shaped
planar molecules bearing complementary H-bonding motifs
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 2407--2413 | 2411

View Article Online
Paper
NJC
(d, J = 8 Hz, 8H), 7.05 (br. s, 4H), 6.70 (br. s, 12H), 3.97–3.94 (br. suspensions. The STM tips were mechanically cut from a
m, 8H), 1.63 (br. d, J = 8 Hz, 8H), 1.33–1.19 (br. m, 18H), 0.82 platinum–iridium wire (Pt–Ir 90/10, diameter 0.25 mm, Goodfellow).
(t, 12H). 13C NMR (100 MHz, DMSO-d6) d (ppm): 166.86, 149.74, The GR1 molecules were dissolved in either n-tetradecane (99 + %
140.51, 129.58, 128.77, 127.22, 115.40, 68.71, 39.50, 31.21, purity, Aldrich) or 1-phenyloctane (98 + % purity, Aldrich) as
28.96, 28.93, 28.89, 28.64, 28.53, 25.40, 22.02, 13.79.
the transfer solvents and tunnelling media. The saturated
The two dodecyl groups of GR2 are identified in the solutions were systematically diluted twice prior to deposition
chemical shift range 0.80–1.64 ppm (46 protons) while the on the substrate. Samples of highly pyrolytic graphite (HOPG,
other protons are identified in the range 3.94–3.97 ppm (4 protons). 1 ꢁ 1 cm2, Goodfellow) were freshly prepared by cleavage using
The aromatic protons are observed at 6.70 ppm and 7.05 ppm adhesive tape prior to deposition, producing clean atomically
corresponding to 10 protons. The chemical shifts in the 13C NMR flat surfaces. STM images were recorded at the liquid/HOPG
observed at 166.9, 149.7, 140.5, 129.6, 128.8, 127.2 and 115.4 ppm interface in the constant-current mode (It). Applied biases
correspond to aromatic carbons. The carbon atoms of the alkoxy were referred to the sample and Vs was noted throughout this
groups are identified by chemical shifts at 68.7, 31.2, 29.0, 28.9, study. The distance and angle values measured from the STM
28.6, 28.5, 25.4, 22.0, 13.8 ppm.
images are systematically averaged from two consecutive scans.
2,5-Bis(40-cyanophenyl)-1,4-dioctylbenzene 7. 2,5-Dibromo- All STM measurements were carried out at room temperature.
1,4-dioctylbenzene 5 (1.0 g, 2.172 mmol), 4-cyanophenyl- STM images were processed and analyzed using the software
boronic ester (1.045 g, 4.56 mmol), 30 mL of DME–water WSXM 5.0.36
(2 : 1), and sodium carbonate (2.12 g, 20 mmol) were mixed in
a 100 mL flask and degassed with nitrogen. After 10 minutes
the palladium catalyst (0.152 g, 0.217 mmol) was added and the
mixture refluxed for 24 hours. The mixture was cooled to room
Acknowledgements
temperature, and the organic phase was separated and filtered DF wishes to thank the Nanyang Technological University (NTU)
through Celite. The organic filtrate was concentrated and for a Visiting Professor position in the School of Physical and
ethanol was added to crystallize 7 as a white solid (0.39 g, Mathematical Sciences (SPMS), Division of Physics and Applied
36%). 1H NMR (400 MHz, CDCl3) d (ppm): 7.71 (d, 4H, J = 8 Hz), Physics (PAP). Funding through the Singapore Ministry of Educa-
7.44 (d, 4H, J = 8 Hz), 7.07 (s, 2H), 2.52–2.48 (br. m, 4H), tion, Academic Research Fund Tier 1 (grant RG19/07) including a
1.43–1.14 (br. m, 24H), 0.85–0.82 (br. m, 6H). 13C NMR research student scholarship for DR, and funding through the
(100 MHz, CDCl3) d (ppm): 146.47, 139.85, 137.63, 131.95, National Research Foundation CRP Grant 5-2009-04 ‘‘Towards
130.70, 130.01, 118.88, 110.87, 77.32, 77.00, 77.00, 76.68, Efficient Sunlight Harvesting’’, are gratefully acknowledged.
32.48, 31.76, 31.33, 29.38, 29.16, 29.07, 22.60, 14.07.
Melamine derivative GR3. To a mixture of compound 7
(300 mg, 0.594 mmol), powdered potassium hydroxide (0.183 g,
3.27 mmol) and dicyanodiamide (0.1 g, 1.189 mmol) 20 mL of
Notes and references
2-methoxyethanolwere added. The reaction mixture was stirred
at 125 1C overnight, and then poured into dichloromethane.
The organic layer was washed with water. Ethanol was added to
the crude product to give GR3 as a white solid (0.190 g, 50%).
1H NMR (400 MHz, DMSO-d6) d (ppm): 8.32 (d, 4H, J = 8 Hz),
7.41 (d, 4H, J = 8 Hz), 7.12 (s, 2H), 6.72 (br. s, 8H), 2.57
(br. t, 4H), 1.39 (br. d, 4H, J = 8 Hz), 1.25–1.10 (br. m, 20H),
0.78 (t, 6H). 13C NMR (100 MHz, DMSO-d6) d (ppm): 139.66,
138.37, 136.81, 130.15, 128.68, 127.53, 106.43, 39.50, 31.10,
30.74, 28.77, 28.52, 28.42, 26.68, 21.92, 13.56.
1 Y. Sun, G. C. Welch, W. L. Leong, C. J. Takacs, G. C. Bazan
and A. J. Heeger, Nat. Mater., 2012, 11, 44–48.
2 A. C. Grimsdale and K. Mu¨llen, Angew. Chem., Int. Ed., 2005,
44, 5592–5629.
3 D. Fichou, J. Mater. Chem., 2000, 10, 571–588.
4 G. Xing, N. Mathews, S. Sun, S. S. Lim, Y. M. Lam,
¨
M. Gratzel, S. G. Mhaisalkar and T. C. Sum, Science, 2013,
342, 344–347.
5 J. Zhou, Y. Zuo, X. Wan, G. Long, Q. Zhang, W. Ni, Y. Liu,
Z. Li, G. He, C. Li, B. Kan, M. Li and Y. Chen, J. Am. Chem.
Soc., 2013, 135, 8484–8487.
6 J. V. Barth, G. Costantini and K. Kern, Nature, 2005, 437,
671–679.
7 R. Otero, F. Rosei and F. Besenbacher, Annu. Rev. Phys.
Chem., 2006, 57, 497–525.
8 S. Furukawa and S. De Feyter, Top. Curr. Chem., 2009, 287,
87–133.
In the 1H NMR spectrum, the two octyl groups of GR3
are identified in the chemical shift range 0.76–1.40 ppm
(30 protons) and 2.50–2.59 ppm (4 protons). The ten aromatic
protons are observed at 6.72 (8 protons) and 7.12 ppm (2 protons).
In the 13C NMR spectrum, the chemical shifts observed at 139.7,
138.4, 136.8, 130.2, 128.7, 127.5 and 106.43 ppm correspond to
the aromatic carbon atoms.
9 L. Piot, J. Wu, A. Marchenko, K. Mu¨llen and D. Fichou,
J. Am. Chem. Soc., 2005, 127, 16245–16250.
Scanning tunnelling microscopy
Scanning tunnelling microscopy (STM) was performed using a 10 H. L. Zhang, W. Chen, H. Huang, L. Chen and A. T. S. Wee,
PicoSPM (Molecular Imaging/Agilent Technology) equipped J. Am. Chem. Soc., 2008, 130, 2720–2721.
with a home-built liquid cell. The microscope was isolated 11 A. Nion, P. Jiang, A. Popoff and D. Fichou, J. Am. Chem. Soc.,
from vibrations and noise inside a closed box with mechanical 2007, 129, 2450–2451.
2412 | New J. Chem., 2014, 38, 2407--2413
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
NJC
Paper
¨ ¨
12 A. Stannard, J. C. Russell, M. O. Blunt, C. Salesiotis, 24 R. Madueno, M. T. Raisanen, C. Silien and M. Buck, Nature,
M. del Carmen Gimenez-Lopez, N. Taleb, M. Schroder, 2008, 454, 618–621.
N. R. Champness, J. P. Garrahan and P. H. Beton, Nat. 25 F. J. M. Hoeben, J. Zhang, C. C. Lee, M. J. Pouderoijen,
Chem., 2012, 4, 112–117.
13 L. Piot, F. Silly, L. Tortech, Y. Nicolas, P. Blanchard, J. Roncali
and D. Fichou, J. Am. Chem. Soc., 2009, 131, 12864–12865.
M. Wolffs, F. Wu¨rthner, A. P. J. Schenning, E. W. Meijer and
S. De Feyter, Chem.–Eur. J., 2008, 14, 8579–8589.
26 A. Popoff and D. Fichou, J. Mol. Struct., 2009, 936, 156–161.
14 M. Lackinger, S. Griessl, W. M. Heckl, M. Hietschold and 27 D. Rajwar, X. Sun, S. J. Cho, A. C. Grimsdale and D. Fichou,
G. W. Flynn, Langmuir, 2005, 21, 4984–4988. CrystEngComm, 2012, 14, 5182–5187.
15 O. Ivasenko and D. F. Perepichka, Chem. Soc. Rev., 2011, 40, 28 B. Liu, T. T. T. Dan and G. C. Bazan, Adv. Funct. Mater., 2007,
191–206. 17, 2432–2438.
16 S. Griessl, M. Lackinger, M. Edelwirth, M. Hietschold and 29 A. Hilberer, H.-J Brouwer, B.-J. Van der Scheer, J. Wildeman
W. M. Heckl, Single Mol. Biol., 2002, 3, 25–31. and G. Hadziioannou, Macromolecules, 1995, 28, 4525–4529.
17 A. Popoff and D. Fichou, Colloids Surf., B, 2008, 63, 153–158. 30 K. T. Nielsen, H. Spanggaard and F. C. Krebs, Macromole-
18 A. L. Kanibolotsky, I. F. Perepichka and P. J. Skabara, Chem.
Soc. Rev., 2010, 39, 2695–2728.
19 N. Katsonis, A. Marchenko and D. Fichou, J. Am. Chem. Soc.,
2003, 125, 13682–13683.
cules, 2005, 38, 1180–1189.
31 W.-L. Tong, M. C. W. Chan, N. Zhu and S.-K. Leung, Dalton
Trans., 2009, 4741–4746.
32 P. G. A. Janssen, J. L. J. van Dongen, E. W. Meijer and
A. P. H. J. Schenning, Chem.–Eur. J., 2009, 15, 352–360.
20 J. M. MacLeod, O. Ivasenko, C. Fu, T. Taerum, F. Rosei and
D. F. Perepichka, J. Am. Chem. Soc., 2009, 131, 16844–16850. 33 A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz and
21 N. Saettel, N. Katsonis, A. Marchenko, M.-P. Teulade-Fichou
and D. Fichou, J. Mater. Chem., 2005, 15, 3175–3180.
22 A. Llanes-Pallas, C.-A. Palma, L. Piot, A. Belbakra, A. Listorti,
M. Prato, P. Samori, N. Armaroli and D. Bonifazi, J. Am.
Chem. Soc., 2009, 131, 509–520.
A. B. Holmes, Chem. Rev., 2009, 109, 897–1091.
34 L. Piot, C.-A. Palma, A. Llanes-Pallas, M. Prato,
Z. Szekrenyes, K. Kamaras, D. Bonifazi and P. Samori, Adv.
Funct. Mater., 2009, 19, 1207–1214.
35 C. Xue and F.-T. Luo, Tetrahedron, 2004, 60, 6285–6294.
23 I. Bestel, N. Campins, A. Marchenko, D. Fichou, 36 I. Horcas, R. Fernandez, J. M. Gomez-Rodriguez, J. Colchero,
´ ´
M. W. Grinstaff and P. Barthelemy, J. Colloid Interface Sci.,
2008, 323, 435–440.
J. Gomez-Herrero and A. M. Baro, Rev. Sci. Instrum., 2007,
78, 013705.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 2407--2413 | 2413