Synthesis and Two-Dimensional Chiral Surface Self-Assembly of a π-Conjugated System with Three-Fold Symmetry: Benzotri(7-Azaindole)

Article abstract of DOI:10.1002/anie.202012100

The synthesis of a novel expanded π-conjugated system, namely benzotri(7-azaindole), BTAI, is reported. Its C_3h symmetry along with the integration of six complementary donor and acceptor N?H???N hydrogen bonds in the conjugated structure promote the 2D self-assembly on Au(111) over extended areas. Besides, a perfect commensurability with the gold lattice endows the physisorbed molecular film with a remarkable stability. The structural features of BTAI result in two levels of surface chirality: Firstly, the molecules become chiral upon adsorption on the surface. Then, due to the favorable N?H???N hydrogen bond-directed self-assembly, along with the relative molecular rotation with respect to the substrate, supramolecular chirality manifests in two mirror enantiomorphous domains. Thus, the system undergoes spontaneous chiral resolution. LEED and STM assisted by theoretical simulations have been employed to characterize in detail these novel 2D conglomerates with relevant chiral properties for systems with C_3h symmetry.

Full text of DOI:10.1002/anie.202012100

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
International Edition Chemie
www.angewandte.org
Accepted Article
Title: Synthesis and two-dimensional chiral surface self-assembly of a
novel π-conjugated system with three-fold symmetry: Benzotri(7-
azaindole)
Authors: David Curiel, Luis M. Rodríguez, Paula Gómez, Miriam Más-
Montoya, José Abad, Alberto Tárraga, Jorge I. Cerdá, and
Javier Méndez
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202012100
Link to VoR: https://doi.org/10.1002/anie.202012100

Angewandte Chemie International Edition
10.1002/anie.202012100
RESEARCH ARTICLE
Synthesis and two-dimensional chiral surface self-assembly of a
novel π-conjugated system with three-fold symmetry: Benzotri(7-
azaindole)
Luis M. Rodríguez,[a],# Paula Gómez,[b],# Miriam Más-Montoya, José Abad, Alberto Tárraga, Jorge
[b]
[c]
[b]
[
d]
[a]
[b]
I. Cerdá, Javier Méndez * and David Curiel *
[
a]
Dr. L. M. Rodríguez, Dr. J. Méndez
Department of Surfaces and Coatings
Institute of Material Science of Madrid (ICMM-CSIC)
Sor Juana Inés de la Cruz 3, 28049-Madrid (Spain)
E-mail: jmendez@icmm.csic.es
[
b]
P. Gómez, Dr. M. Más-Montoya, Prof. A. Tárraga, Dr. D. Curiel
Department of Organic Chemistry
University of Murcia
Campus of Espinardo, 30100-Murcia (Spain)
E-mail: davidcc@um.es
[c]
[d]
[#]
Dr. J. Abad
Department of Applied Physics and Naval Technology
Technical University of Cartagena
Campus Muralla del Mar, 30203-Cartagena (Spain)
Dr. J. I. Cerdá
Department of Interfaces and Nanostructures
Institute of Material Science of Madrid (ICMM-CSIC)
Sor Juana Inés de la Cruz 3, 28049-Madrid (Spain)
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of the document.((Please delete this text if not appropriate))
Abstract: The synthesis of a novel expanded π-conjugated system,
namely benzotri(7-azaindole), BTAI, is reported. Its C3h symmetry
along with the integration of six complementary donor and acceptor
N-H···N hydrogen bonds in the conjugated structure promote the 2D
self-assembly on Au(111) over extended areas. Besides, a perfect
commensurability with the gold lattice endows the physisorbed
molecular film with a remarkable stability. The structural features of
BTAI result in two levels of surface chirality: Firstly, the molecules
become chiral upon adsorption on the surface. Then, due to the
favorable N-H···N hydrogen bond-directed self-assembly, along with
the relative molecular rotation with respect to the substrate,
supramolecular chirality manifests in two mirror enantiomorphous
domains. Thus, the system undergoes spontaneous chiral resolution.
LEED and STM assisted by theoretical simulations have been
employed to characterize in detail these novel 2D conglomerates with
relevant chiral properties for systems with C3h symmetry.
Differently from the studies in solution and in crystal engineering,
self-assembly on surfaces is governed by the subtle balance
between molecule-molecule interactions and molecule-substrate
interactions. As expected, considering that the interactions with
the substrate surface are mainly established through van der
Waals forces,[3] the physical and chemical properties of the
substrate can condition the growth of the physisorbed adlayer.
Moreover, the structure of the self-assembled material will
depend on the molecular design and the type of non-covalent
interactions controlling the self-assembly. Among the different
interactions studied in 2D self-assembled materials, hydrogen
bonding is particularly useful due to its strength, directionality and
variety of functions that can work as hydrogen bond donor or
acceptor sites.[4] Molecules bearing carboxylic acid groups have
been by far the most explored systems.[5] Besides, the surface
[
6]
self-assembly involving compounds such as perylenediimides,
naphthalenediimides,[
7]
melamine,
[8]
cianuric acid
[9]
and
derivatives incorporating these and other building blocks have
been extensively studied.
Introduction
Two-dimensional surface self-assembly can be exploited for
several applications such as modulation of surface properties,[
10]
Control of molecular arrangement at the nanoscale has become
an exciting challenge explored from the perspective of different
research areas such as chemistry, physics, engineering or
materials science. Particularly, the organization of molecules
adsorbed on surfaces has gained attention due to the increasing
sensors[11] or catalysis,[12] among others. Nevertheless, it is worth
highlighting that investigation of 2D self-assembled materials has
gained special attention in the case of conjugated systems due to
their use as organic semiconductors in the fabrication of
optoelectronic devices.[13] In this regard, we are particularly
interested in molecular systems where hydrogen bond-directed
self-assembly is induced through interacting sites integrated in
the conjugated system itself, without needing from any peripheral
substitution, and with the additional requirement of not disrupting
interest in the development of two-dimensional self-assembled
materials.[
1]
Self-assembly through non-covalent interactions
provides the tools for a bottom-up strategy to obtain well-ordered
D supramolecular architectures.[2]
2
1
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202012100
RESEARCH ARTICLE
the conjugation, because that particular feature would benefit
charge delocalization in an eventual charge transport process.
Additionally, self-complementarity of hydrogen bond interactions
is another structural feature desirable for the self-organization of
organic compounds. Very few molecules have been reported that
meet these requirements, highlighting the results reported for the
[
14]
diketopyrrolopyrrole[15] or
characterization of quinacridone,
indigo[ self-assembly on surfaces. All these molecules have the
particularity to adsorb following a lineal self-assembly, forming 1D
rows that also establish weaker lateral interactions to obtain larger
domains with a compact surface coverage. Nevertheless, with the
aim of expanding the range of surface self-assembly, it would be
interesting to achieve the growth of the adsorbed π-conjugated
material according to a 2D hydrogen bonded network. With that
16]
2 2 3
Scheme 1. Synthesis of benzotri(7-azaindole). (i) (±)-BINAP, Pd(dba) , K CO ,
Toluene; (ii) t-BuOK, DMSO, hv.
Initially
a triple Buchwald-Hartwig reaction between 1,3,5-
benzenetriamine and 2,3-dichloropyridine leads to the formation
of three N-C bonds to obtain compound 1 in a good yield.
Subsequently, a photoinduced radical aromatic substitution
enables the triple intramolecular coupling reaction yielding the
desired product BTAI in a moderate yield. The structure of BTAI
was unequivocally elucidated by Nuclear Magnetic Resonance of
proton and carbon-13 (1H-NMR and 13C-NMR) and High
Resolution Mass Spectrometry (HRMS) techniques (see
Supporting Information). With the purpose of obtaining highly pure
material for its surface characterization, BTAI was purified using
several cycles of gradient sublimation.
objective in mind, we have synthesized a new molecule with C3h
symmetry inspired in the structure of truxene[17] and
triazatruxene[18] derivatives, that have proved to be excellent
materials with application in organic electronics. Moreover, in our
rational design we have integrated the underexplored 7-azaindole
unit to work as synthon for a complementary hydrogen bond 2D
self-assembly when physisorbed on a surface. The combination
of these appealing features leads us to the first synthesis of
benzotri(7-azaindole), BTAI.
Scanning Tunneling Microscopy (STM) and Low Energy Electron
Diffraction (LEED) have been employed to study the surface self-
assembly under ultrahigh vacuum (UHV) conditions on
Au(111).[19] The images demonstrate the suitability of BTAI to
Homogeneous monolayers of BTAI were deposited on an Au
(
111) substrate under UHV conditions. A sharp LEED pattern was
obtained, showing a hexagonal symmetry superstructure (Figure
a) and evidencing that the molecules self-assembled on the
1
epitaxially adsorb and build highly stable self-organized
monolayers displaying long range order. Besides, the molecular
substrate surface in a highly ordered way.
The analysis of the diffraction pattern[22] presented in Figure S7
C3h symmetry of BTAI together with its confinement into a two-
7
2
reveals a superstructure characterized by a


matrix which
dimensional environment induced by the gold surface, bestows
surface chirality on the adsorbed molecules, i.e., L and R
enantiomers are expected to coexist on the surface in similar
proportions. The phenomenon of surface chirality has recently
gained much interest as a result of the applications that chiral
surfaces can have in areas as diverse as chromatographic
5
7
corresponds to a (√39x√39)±R16.1º supercell with a=18.02 Å. In
fact, the pattern in Figure 1a arises from the coexistence of two
domains that are mirror-symmetric to each other.
STM images at room temperature show the gold substrate
covered with flat lying BTAI molecules arranged as a mosaic of
triangular pieces with the molecules adopting
a face-on
stationary phases, asymmetric catalysis, non-linear optical
devices, nanoelectronics or sensors.[20]
adsorption. In the large scale image (Figure 1b) comprising two
terraces (labeled as 1 and 2), extended highly ordered molecular
domains with hexagonal motifs defining a central pore are visible
in both terraces. Only a partially disordered area is observed at
the right edge of the upper terrace close to the step (labeled as
region 3). Each terrace in the STM image corresponds to a
different domain, as their unit cells (indicated by the green and
blue parallelograms) are identical with a lattice parameter of
a=18.2 Å, but show a relative angle of 32º between them.
Furthermore, similarly to other organic molecular layers on
Au(111), the gold herringbone reconstruction is visible beneath
the molecular layer suggesting that the BTAI film remains
physisorbed on the surface. Additionally, it allows to identify the
Au(111) high-symmetry planes in the image which, in turn, reveal
In the particular case of benzotri(7-azaindole), the strategic
location of hydrogen bond donor and acceptor sites promotes
self-organized supramolecular networks where, as revealed by
theoretical calculations, complementary N-H···N hydrogen bonds
between the 7-azaindole substructures prevail. More importantly,
this reciprocal hydrogen bonding is energetically favored for
molecules with the same handedness that self-assemble to form
extended domains. Accordingly, the BTAI molecules rotate to
accommodate the hydrogen bonds, as it is readily observed in the
STM images, and the consequence of this distinctive
supramolecular surface self-assembly is the segregation of
enantiomers into homochiral mirror domains. Hence, this novel
self-assembled BTAI film represents a singular case among the
that each unit cell is rotated by ±16º with respect to the [1 ͞1 0]
selected series of molecules with three-fold symmetry that
undergo spontaneous chiral resolution.[21]
direction. Combination of the substrates p3m and the molecules
p3 symmetries dictates that both domains are mirror-symmetric.
Overall, the structural information extracted from the STM images
is in good agreement with the LEED pattern analysis.
Figures 1c and 1d correspond to zoom-in STM images at both
terraces displaying in detail the two molecular domains. The unit
cells contain two BTAI molecules which, at first sight, appear as
specular with respect to each other.[20b, 23] Individual molecules
Results and Discussion
The synthesis of benzotri(7-azaindole) is achieved using a
straightforward two-step synthetic route, as shown in Scheme 1.
2
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202012100
RESEARCH ARTICLE
are viewed as three-bladed structures, evidencing that they lie
essentially flat on the surface and hardly distorted. The domains
show a clear p3 2D space group symmetry with rotation axis
either at the center of each molecule or at the voids where six
corresponding to opposite faces of the adsorbed molecule (Figure
2). Since the three arms define a different handedness according
to the orientation of the nitrogen atoms, we ascribe the L
configuration to the surface enantiomer whose nitrogen atoms
follow a counterclockwise direction with respect to the carbon
atoms at the opposite side of each arm, and the R configuration
to the surface enantiomer having the nitrogen atoms oriented in a
clockwise direction. Nevertheless, since from the STM images
alone no specific features can be assigned to the nitrogen atoms,
it remains to unveil the chiral identity of the molecules within each
domain.
molecules meet. Furthermore, the domains show
a
supramolecular chirality (opposite at each terrace) reminiscent of
that observed for melamine and other three-fold molecules.[24]
Figure 2. BTAI surface enantiomers: L and R configurations.
In order to determine the molecular chirality as well as the precise
bonding geometry, we have performed extensive DFT
calculations for different molecular arrangements built from the
information obtained from the STM images. First, we examined
possible intermolecular bonding geometries by considering a
free-standing BTAI quasi-flat monolayer, placing two molecules
within the experimentally observed (√39x√39)R16.1º unit cell.
Figure 3 shows the three metastable structures found.
In the most stable one (Figure 3a), both molecules correspond to
the same enantiomer (LL, or equivalently RR after considering its
inverted image) but rotated with respect to each other so that the
upper arm of one of them faces the lower arm of the other.
Thereby, two parallel NH···N hydrogen bonds, with a length of 2.8
Å, reciprocally connect the molecules through the NH group in the
pyrrole ring and the N atom in the pyridine ring. Hereafter we
denote this bonding arrangement with the subscript NN since the
hydrogen bond donor sites correspond to two NH groups (LLNN or
RRNN). The next metastable structure (Figure 3b), only marginally
less stable, involves two different enantiomers (LR or RL)
disposed in a pseudo-specular way about the unit cell short
diagonal leading to a long NH···N interaction (2.6 Å) and a short
CH···N one (2.2 Å). Since here the intervening hydrogen bond
donor sites correspond to NH and CH groups, we denote this
assembly by LRNC or RLNC . Finally, a clearly less stable LL (or
RR) arrangement (Figure 3c) consists of two molecules facing
each other forming two parallel short CH···N bonds (2.3 Å).
However, in this case, hydrogen bond donor and acceptor sites
belong to different arms of the BTAI molecule (LLCC or RRCC).
Their bonding energies (that is, the strength of the self-assembly
between each pair of molecules) are in the order of 0.48 eV, which
Figure 1. (a) LEED pattern (inverted colour) acquired at an energy of 14 eV for
Au(111) covered with BTAI molecules. (b) Large scale STM image of a BTAI
monolayer comprising two terraces colored in light (upper) and dark (lower
terrace), labeled as 1 and 2, respectively. Region 3 corresponds to a not fully
ordered area in the upper terrace (tunneling parameters V
The herringbone gold reconstruction is barely visible in the lower terrace. The
√39x√39) unit cell in each case is indicated by a coloured parallelogram. They
form angles of +16º and -16º with respect to the substrate's [110]
b T
=0.15 V, I =10 pA).
(
͞
crystallographic direction, indicated by the white dashed line. (c) and (d) Close-
up for the upper and lower terraces, respectively.
The chirality is evidenced by the approximately ±(13±3)º rotation
of the molecular arms with respect to the axis linking the centers
of two opposite BTAI molecules in the hexamer (see Figure S8).
Subjacent to the supramolecular chirality, the C3h symmetry,
without mirror planes orthogonal to the conjugated surface,
confers the BTAI structure a prochiral character in the sense that
once deposited on the gold substrate the mirror symmetry is
broken and, hence, there are two possible surface enantiomers
roughly yields 0.24 eV per hydrogen bond, a value compatible
with typical H-bonded networks.[8] The relative energies of these
assemblies seem to follow the expected trend whereby the more
polarized NH···N hydrogen bonds are stronger than the CH···N
ones. Nevertheless, noticing the different hydrogen bond lengths,
it cannot be discarded that the effect of the CH/NH···HN/CH
repulsion between closely located hydrogen atoms may also play
3
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202012100
RESEARCH ARTICLE
a role in the relative stabilities. Indeed, as shown by the thin dotted
red lines in Figure 3, structure LLCC lineally confronts two CH with
two NH groups, LRNC presents two CH terminations facing each
other, while for LLNN two CH···HC are laterally confronted. This
preliminary analysis suggests that, considering the above
mentioned interactions, the molecular arrangement of the flat
free-standing BTAI monolayer is governed by the attractive
NH···N bonds between homochiral dimers.
angle of 13±3º. The other two structures, LRNC and LLCC, show
molecular rotations of -17º and -11º.
The above analysis for the free-standing BTAI monolayer points
to the LLNN as the preferential configuration for the BTAI
monolayer arrangement. Even so, the formation of self-
assembled nanostructures on surfaces typically results from the
interplay balance between intermolecular interactions and
molecule-substrate interaction. Thus, we have included the
Au(111) substrate in the calculations in order to assess the
stability of LLNN network, as well as to determine the adsorption
geometry and, ultimately, the nature of the BTAI-Au interaction.
An exhaustive study has been performed considering the three
intermolecular bonding configurations shown in Figure 3 and, for
each of them, three different high symmetry registries for their
aromatic central rings with respect to the substrate: top, fcc and
hcp sites. Furthermore, inversion symmetry is broken in the
presence of the substrate, so that the interchange of the
enantiomers within each model leads to a symmetry-inequivalent
structure. Accordingly, we also considered these additional three
cases again varying their registries with respect to the substrate.
In the relaxations, BTAI molecules were always placed with their
centers at the same type of site in accordance with the fact that
all free-standing geometries yielded the same intermolecular
vector (in this way all configurations preserved the experimentally
observed p3 symmetry). A summary of the tested structures and
their relative stabilities is provided in Figure S9. It is worth
recalling that all of them correspond to domain 1, that is, with the
supercell rotated by +16º with respect to the gold [1 1͞ 0] direction,
while the equivalent isoenergetic structures ascribed to domain 2
correspond to their mirror images referred to the same gold plane.
The most stable structure, with a clear DFT energy difference of
0.13 eV with respect to the next one, is depicted in Figure 4a.
Figure 3. The three metastable configurations found for a flat BTAI monolayer
containing two molecules in a (√39x√39) unit cell indicated by the parallelogram.
The structures are labelled according to the enantiomer type (L or R) of the two
molecules in the cell. The subscript refers to the nature of the hydrogen bond
donor sites: a) NN when only NH groups are involved; b) CC when only CH
groups are involved; c) NC when NH and CH groups intervene. Energies in eV
correspond to the relative stability of each phase with (a) LLNN being the most
stable. Hydrogen-bonds are indicated by the black dashed lines, with their
lengths given in Å. Thin red dotted lines refer to the confronted CH/NH groups.
The panels on the right show the resulting hexamer arrangement for each
structure together with the rotation angle of the individual molecules.
Isoenergetic structures (not shown in the figure) can be obtained for the self-
assembly of the opposite enantiomers in each case (i.e. RRNN for (a), RLNC for
(b) and RRCC for (c)).
Apart from the local point chirality, the hydrogen-bonded network
brings different rotation angles on the BTAI molecules for each
phase, thus conferring them a supramolecular chirality in
accordance with the experimental observations (Figure S8). This
is clearly seen in the right panels of Figure 3, where the three
hexamer assemblies are sketched. In the most stable LLNN
structure the BTAI molecules rotate counterclockwise by around
Figure 4. a) Top and side views of the most stable configuration found for the
Au(111)-(√39x√39)R16.1º-2BTAI system. C, N, Au and H atoms shown as
brown, blue, pale green and small white spheres, respectively. In the top view,
hydrogen bonds are indicated by black lines; b) Calculated STM image for this
model (V=0.4 V and I=1 nA); c) high resolution experimental STM image
covering the same area (V=0.15 V and I= 10 pA), with white dashed lines
indicating the substrate mirror planes. Insets in (b) and (c) contain analogous
images corresponding to the other mirror domain (V= 0.5 V and I= 10 pA).
+14º, in very good agreement with the experimentally determined
4
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202012100
RESEARCH ARTICLE
We denote it by LLNNtop, as it consists of two L enantiomers
adsorbed at top sites and arranged following the most stable free-
standing arrangement of Figure 3a, forming two complementary
NH···N bonds between each pair of molecules. As indicated in
Figure S9, there is a clear preference for adsorption at a top site,
with the hollow sites being over 0.2 meV less favorable. In all the
tested configurations the BTAI layer lies well above the surface (3
Å), as could be expected for a physisorbed regime.
phases but, due to incommensurability between the molecular
network and the substrate, the segregated phases could only be
stabilized at 120 K.[25] To our knowledge, the only reported
system presenting spontaneous resolution at RT for an adsorbed
molecular layer with chiral p3 symmetry is TTBTA on graphite.[26]
Conclusion
The influence on the molecular geometry is only minor, it induces
a buckling of 0.4 Å and a subtle 0.04 Å bond elongation. The
highest lying atoms are the carbons in the central ring, while the
three arms slightly bend towards the substrate. Inclusion of van
der Waals corrections barely modifies the physisorption height
We have synthesized an unprecedented star-shaped
polyheteroaromatic system, namely, benzotri(7-azaindole), BTAI,
that has been rationally designed to control its hydrogen bond-
directed 2D self-assembly. It is worth highlighting that the
preparation of the molecule has been achieved through a
synthetic route of two steps only. The C3h symmetry of BTAI
confers the molecule a prochiral character which leads to two
possible surface enantiomers when adsorbed flat on surfaces.
The adequacy of the molecular design has been evidenced by the
formation of extended and close-packed mirror domains on an
Au(111) surface that have been successfully characterized by
means of LEED and STM combined with DFT calculations and
STM simulations. The interaction with the substrate is found to be
in the strong physisorption regime, whereby the molecules are
tightly bound to the surface in an almost planar geometry, but still
mobile enough to self-assemble in their most favorable
configuration. DFT reveals that such arrangement consists of two
complementary NH···N hydrogen bonds between the molecular
arms of adjacent BTAI molecules optimally oriented within the
supercell. The 2D conglomerates show a p3 symmetry and
organize in two mirror-symmetric domains, each of them
(
0
3.33 Å versus 3.35 Å) or the buckling, which is reduced by only
.05 Å. This is an indication that the gold-BTAI interaction
corresponds to a strong physisorption regime which can be
correctly described by the Generalized Gradient Approximation
(
GGA) alone. Indeed, the interaction between the self-assembled
monolayer and the substrate, estimated in 1.7 eV/molecule, is
larger than the hydrogen bonds strength. However, upon
inspection of the relative stabilities of the other metastable
structures (Figure S9), there are some of them involving different
registries or hydrogen bond configurations that energetically differ
top
from the LLNN by less than 300 meV, that is, similar to the
hydrogen bond strengths. Taking this value as an upper limit for
the energy barriers found by a BTAI molecule when diffusing
across the surface, we can conclude that the substrate presents
a reduced corrugation that confers the BTAI molecules the
mobility at RT to self-assemble with other homochiral molecules,
finally adopting their most favorable LLNN bonding configuration.
Furthermore, we also note that the difference between LLNN and
LLNC configurations increases from 70 meV in the free-standing
case (Figure 3b) to 166 meV when the substrate is considered,
indicating that the metal surface further promotes the stabilization
of the LLNN configuration.
appearing in different terraces. They correspond to
a
(
√39x√39)R±16.1º hexagonal unit cell and contain two equivalent
BTAI molecules, each three-fold self-assembled. The BTAI film
presents local organizational chirality forming highly ordered
supramolecular structures in each domain. Most interestingly, this
particular complementary NH···N linkage only involves
homochiral BTAI molecules, either LL for the +16º rotated
domains (or RR for the -16º ones). Accordingly, the system shows
an effective spontaneous resolution at each terrace. The
segregation mechanism is driven by the commitment between the
energetically allowed diffusion of each enantiomer to form
homochiral domains, and the suitable molecular structure that
results in an adlattice matching with the gold surface and three
pairs of reciprocal hydrogen bonds. This remarkably stable BTAI
structure validates our synthetic strategy to achieve the objective
of controlling the molecular arrangement at the nanoscale, as well
as their chiral properties, and opens up the possibility of studying
the reported material in different applications and further
exploiting this approach in the synthesis of innovative self-
assembled systems. The reported 2D conjugated system could
possibly find application in the area of organic electronics where
the molecular organization plays a critical role.
The validity of the LLNNtop model is corroborated by the perfect
match obtained for its associated STM image simulation (Figure
4b) and the experimental one (Figure 4c). In both images, with the
same scale, the BTAI molecules appear rotated by around 14º
clockwise. The aspect of the simulated image hardly changes with
the sign and value of the applied bias voltage (not shown), in
accordance with the experiment. The inset of Figure 4b displays
top
the simulated STM image for the mirror structure to LLNN which,
as expected, nicely matches the experimental image at the
terrace 2 (inset of Figure 4c and Figure 1d). It is an equally stable
structure but with opposite supramolecular chirality since the
molecules now appear rotated counterclockwise, as well as
opposite local point chirality, as both now correspond to R
enantiomers (Figure S10).
The unambiguous determination of the atomic structure of the
current Au(111)/BTAI system, confirming the LLNN intermolecular
arrangement (or its RRNN mirror domain), leads to one of the main
conclusions of this work, namely, BTAI molecules self-assemble
on Au(111) into segregated homochiral domains, revealing their
(
(Note: Please place comprehensive details in the Supporting
ability to achieve
a
spontaneous resolution of surface
Information.))
enantiomers. Although this chiral segregation has been observed
for different types of molecule-on-surface systems,[21] very few
precedents have been reported for C3h molecules. Zhang et al.
observed spontaneous resolution for chiral TPTZ molecules on
the same gold surface and for different coverage dependent
Acknowledgements
5
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202012100
RESEARCH ARTICLE
Authors are grateful to the Ministry of Science, Innovation and
Universities for funding the projects MAT2015-66888-C3-1R,
MAT2017-85089-C2-1-R, RTI2018-101092-B-I00 and RTI2018-
[19] a) D. Cui, J. M. MacLeod, F. Rosei, Chem. Commun. 2018, 54, 10527-
10539; b) S. De Feyter, F. C. De Schryver, Chem. Soc. Rev. 2003, 32,
139-150.
[
[
20] a) F. Zaera, Chem. Soc. Rev. 2017, 46, 7374-7398; b) R. Raval, Chem.
Soc. Rev. 2009, 38, 707-721.
0
97895-B-C41 and "Programa Estatal de Fomento de la
Investigación Científica y Técnica de Excelencia" (RED2018-
02815-T). Authors also thank "Fundación Séneca - Agencia de
21] a) S. Dutta, A. J. Gellman, Chem. Soc. Rev. 2017, 46, 7787-7839; b) L.
Pérez-García, D. B. Amabilino, Chem. Soc. Rev. 2007, 36, 941-967; c)
L. Pérez-García, D. B. Amabilino, Chem. Soc. Rev. 2002, 31, 342-356.
1
Ciencia y Tecnología de la Región de Murcia" for funding the
project 20959/PI/18. M. M.-M. acknowledges Fundación Séneca
for a postdoctoral Saavedra Fajardo contract.
[22] LEEDpat, version 4.2, utility by K.E. Hermann and M.A. Van Hove, Berlin
Hong Kong, 2014; see also http://www.fhi-
berlin.mpg.de/KHsoftware/LEEDpat/index.html
23] S. M. Barlow, R. Raval, Surf. Sci. Rep. 2003, 50, 201-341.
/
[
[
24] a) B. Baris, V. Luzet, E. Duverger, P. Sonnet, F. Palmino, F. Cherioux,
Angew. Chem. Int. Ed. 2011, 50, 4094-4098; b) N. Jiang, Y. Wang, Q.
Liu, Y. Zhang, Z. Deng, K.-H. Ernst, H.-J. Gao, Phys. Chem. Chem. Phys.
Conflict of interest
2010, 12, 1318-1322; c) W. Xu, M. Dong, H. Gersen, E. Rauls, S.
The authors declare no conflict of interest.
Vázquez-Campos, M. Crego-Calama, D. N. Reinhoudt, I. Stensgaard, E.
Laegsgaard, T. R. Linderoth, F. Besenbacher, Small 2007, 3, 854-858.
25] J. Zhang, B. Li, X. Cui, B. Wang, J. Yang, J. G. Hou, J. Am. Chem. Soc.
2009, 131, 5885-5890.
Keywords: surface self-assembly • 2D materials •
supramolecular surface chirality • spontaneous resolution •
benzotri(7-azaindole)
[
[26] J. M. MacLeod, O. Ivasenko, C. Fu, T. Taerum, F. Rosei, D. F.
Perepichka, J. Am. Chem. Soc. 2009, 131, 16844-16850.
[
1]
a) D. P. Goronzy, M. Ebrahimi, F. Rosei, Arramel, Y. Fang, S. De Feyter,
S. L. Tait, C. Wang, P. H. Beton, A. T. S. Wee, P. S. Weiss, D. F.
Perepichka, ACS Nano 2018, 12, 7445-7481; b) M. Gobbi, E. Orgiu, P.
Samori, Adv. Mater. 2018, 30, 1706103.
[
2]
a) L. Sosa-Vargas, E. Kim, A.-J. Attias, Mater. Horizons 2017, 4, 570-
583; b) K. S. Mali, N. Pearce, S. De Feyter, N. R. Champness, Chem.
Soc. Rev. 2017, 46, 2520-2542; c) D. B. Amabilino, Supramolecular
Chemistry at Surfaces, 2016.
[
[
3]
4]
T. Tian, C.-J. Shih, Ind. Eng. Chem. Res. 2017, 56, 10552-10581.
A. G. Slater, L. M. A. Perdigão, P. H. Beton, N. R. Champness, Acc.
Chem. Res. 2014, 47, 3417-3427.
[
[
5]
6]
a) C. Fu, F. Rosei, D. F. Perepichka, ACS Nano 2012, 6, 7973-7980; b)
M. Lackinger, W. M. Heckl, Langmuir 2009, 25, 11307-11321.
A. J. Pollard, E. W. Perkins, N. A. Smith, A. Saywell, G. Goretzki, A. G.
Phillips, S. P. Argent, H. Sachdev, F. Müller, S. Hüfner, S. Gsell, M.
Fischer, M. Schreck, J. Osterwalder, T. Greber, S. Berner, N. R.
Champness, P. H. Beton, Angew. Chem. Int. Ed. 2010, 49, 1794-1799.
C. Fu, H.-p. Lin, J. M. Macleod, A. Krayev, F. Rosei, D. F. Perepichka,
Chem. Mater. 2016, 28, 951-961.
[
[
[
[
7]
8]
9]
F. Silly, A. Q. Shaw, M. R. Castell, G. A. D. Briggs, M. Mura, N.
Martsinovich, L. Kantorovich, J. Phys. Chem. C 2008, 112, 11476-11480.
V. V. Korolkov, M. Baldoni, K. Watanabe, T. Taniguchi, E. Besley, P. H.
Beton, Nat. Chem. 2017, 9, 1191-1197.
10] a) F. Huttmann, A. J. Martínez-Galera, V. Caciuc, N. Atodiresei, S.
Schumacher, S. Standop, I. Hamada, T. O. Wehling, S. Blügel, T.
Michely, Phys. Rev. Lett. 2015, 115, 236101; b) Q. Zhou, Y. Li, Q. Li, Y.
Wang, Y. Yang, Y. Fang, C. Wang, Nanoscale 2014, 6, 8387-8391.
11] M. H. Chang, N.-Y. Kim, Y. H. Chang, Y. Lee, U. S. Jeon, H. Kim, Y.-H.
Kim, S.-J. Kahng, Nanoscale 2019, 11, 8510-8517.
[
[
12] D. Nguyen, G. Kang, N. Chiang, X. Chen, T. Seideman, M. C. Hersam,
G. C. Schatz, R. P. Van Duyne, J. Am. Chem. Soc. 2018, 140, 5948-
5
954.
13] F. Yang, S. Cheng, X. Zhang, X. Ren, R. Li, H. Dong, W. Hu, Adv. Mater.
018, 30, 1702415.
[
[
[
[
2
14] T. Wagner, M. Györök, D. Huber, P. Zeppenfeld, E. D. Głowacki, J. Phys.
Chem. C 2014, 118, 10911-10920.
15] C. Fu, P. J. Beldon, D. F. Perepichka, Chem. Mater. 2017, 29, 2979-
2987.
16] C. J. Villagomez, O. Guillermet, S. Goudeau, F. Ample, H. Xu, C. Coudret,
X. Bouju, T. Zambelli, S. Gauthier, J. Chem. Phys. 2010, 132, 074705.
17] F. Goubard, F. Dumur, RSC Adv. 2015, 5, 3521-3551.
[
[
18] A. Connell, Z. Wang, Y.-H. Lin, P. C. Greenwood, A. A. Wiles, E. W.
Jones, L. Furnell, R. Anthony, C. P. Kershaw, G. Cooke, H. J. Snaith, P.
J. Holliman, J. Mater. Chem. C 2019, 7, 5235-5243.
6
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202012100
RESEARCH ARTICLE
Entry for the Table of Contents
The synthesis of benzotri(7-azaindole), BTAI, aims at the control of molecular arrangement in the nanoscale. The rational design and
location of hydrogen bond donor and acceptor sites promotes the two-dimensional self-assembly of this novel conjugated system
with C3h symmetry. STM experiments on Au(111) and computational models prove the formation of extended homochiral domains
resulting from the spontaneous resolution of the surface enantiomers.
7
This article is protected by copyright. All rights reserved.