Synthesis and helical supramolecular organization of discotic liquid crystalline dibenzo[: Hi, st] ovalene

Article abstract of DOI:10.1039/c9tc03350e

Dibenzo[hi,st]ovalene (DBOV) has emerged as a new polycyclic aromatic hydrocarbon (PAH) with intriguing optical properties with strong red emission. Nevertheless, DBOV derivatives thus far synthesized either had mesityl groups that hinder the π-π stacking

Full text of DOI:10.1039/c9tc03350e

Journal of
Materials Chemistry C
View Article Online
View Journal
PAPER
Synthesis and helical supramolecular organization
of discotic liquid crystalline dibenzo[hi,st]ovalene†
Cite this:DOI: 10.1039/c9tc03350e
b
Qiang Chen,‡a Wojciech Zajaczkowski,‡a Johannes Seibel,‡b Steven De Feyter,
ac
ae
Wojciech Pisula,
*
Klaus Mullen*ad and Akimitsu Narita
*
¨
Dibenzo[hi,st]ovalene (DBOV) has emerged as a new polycyclic aromatic hydrocarbon (PAH) with
intriguing optical properties with strong red emission. Nevertheless, DBOV derivatives thus far
synthesized either had mesityl groups that hinder the p–p stacking of the aromatic cores or showed low
solubility, and the self-assembly of DBOVs has not been investigated. In this work, two 3,4,5-
tris(dodecyloxy)phenyl (TDOP) groups are introduced at the meso-positions of DBOV in order to
enhance its solubility without compromising the intermolecular interactions. The obtained DBOV-TDOP
forms at elevated temperatures a discotic liquid crystalline phase. Due to p–p-stacking interactions as
well as local phase separation between the aromatic cores and the flexible alkoxy side chains, the
DBOV-TDOP molecules self-assemble into columnar stacks. In the low temperature phase, the space
demanding TDOP substituents induce a rotation of the discs towards each other leading to an
exceptionally long helical pitch within the columnar structures. Moreover, scanning tunnelling microscopy
(STM) elucidates intriguing self-assembly of DBOV-TDOP at the interface of highly oriented pyrolytic
graphite (HOPG) and 1-phenyloctane (PO). Individual molecules are visualized by STM, revealing that the
alkyl chains protrude from the surface into the solution and suggesting that a self-assembled bilayer film
structure is predominantly formed.
Received 21st June 2019,
Accepted 27th August 2019
DOI: 10.1039/c9tc03350e
rsc.li/materials-c
columns, nanotubes, and micelles.15–23 The combination of the
rigid PAH cores with flexible aliphatic chains at the peripheral
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are attractive mole- positions can induce a phase separation between these two
cules not only because of their intriguing (opto)electronic components at the molecular level, resulting in the formation
and photophysical properties, but also for their unique self- of columnar structures due to the strong intermolecular p–p
assembly behaviour induced by the large aromatic core struc- interactions, and discotic liquid crystalline (LC) properties.24–35
tures. A wide range of applications has thus been proposed Triphenylene, perylene and hexa-peri-hexabenzocoronene
for PAHs, not only as semiconductor materials in organic (HBC) derivatives are representative examples, which have been
field-effect transistors and light-emitting devices, but also extensively studied with a variety of peripheral substituents,
as fluorescent dyes in bioimaging.1–14 The supramolecular demonstrating controllable self-assembly behaviour and high
organization of the disc-shaped PAH molecules is of particular charge-carrier mobility along the column direction.21,36–38
interest, leading to various self-assembled structures such as Their intermolecular packing can be tuned by attaching
soft chains to provide supramolecular structures with specific
a Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz,
Germany. E-mail: pisula@mpip-mainz.mpg.de, muellen@mpip-mainz.mpg.de,
narita@mpip-mainz.mpg.de
organization, such as columnar self-assemblies with controlled
rotation angle as well as intra- and intercolumnar distances.21,32
PAHs larger than HBC, as well as non-planar bowl-shaped PAHs,
such as corannulene and sumanene were demonstrated to be
also applicable as discotic LC materials.23,39–42 Nevertheless,
the LC behaviours of PAHs other than triphenylenes, HBCs
and perylenes are still underexplored and there is so far only a
limited number of PAHs that are known to show LC properties.
In particular, LC PAHs with smaller HOMO–LUMO gaps are
seldom reported, despite the interest in their longer-wavelength
absorption and emission as well as potential to achieve higher
charge-carrier mobilities.43
b KU Leuven, Department of Chemistry, Division of Molecular Imaging and Photonics,
Celestijnenlaan 200F, 3001 Leuven, Belgium
c Lodz University of Technology, Department of Molecular Physics, Faculty of Chemistry,
Zeromskiego 116, 90-924, Lodz, Poland
d Institute of Physical Chemistry, Johannes Gutenberg-University,
Duesbergweg 10-14, 55128, Mainz, Germany
e Organic and Carbon Nanomaterials Unit, Okinawa Institute of Science
and Technology Graduate University, Okinawa 904-0495, Japan
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9tc03350e
‡ These authors contributed equally to this work.
This journal is ©The Royal Society of Chemistry 2019
J. Mater. Chem. C

View Article Online
Paper
Further, two-dimensional (2D) self-assembly of PAHs has
Journal of Materials Chemistry C
We recently reported the synthesis of a new type of nano-
been studied at the liquid–solid interface between an organic graphene, namely dibenzo[hi,st]ovalene (DBOV) with both zigzag
solvent and highly-oriented pyrolytic graphite (HOPG). For and armchair edge structures, showing intensive absorption and
studies at the liquid–solid interface PAHs are often substituted emission in the visible light region.51,52 The molecules also
with long or bulky aliphatic groups at the periphery to increase revealed stimulated emission in a polystyrene matrix, which is
their solubility. For example, alkoxy-substituted extended crucial for potential applications in organic lasers or optical
triphenylenes were found to form ordered monolayers at the amplifiers.53 Moreover, this molecule has high chemical stability
1,2,4-trichlorobenzene (TCB)/HOPG interface with a hexagonal under ambient conditions, allowing easy processing and poten-
structure.44 A representative result with a larger PAH was tially long-term device application. However, derivatives of DBOV
reported in 1995, demonstrating that HBC substituted with that have so far been synthesized were substituted with mesityl
six alkyl chains can form 2D self-assembled structures at the groups, which prevent the p–p stacking of the aromatic cores, or
liquid–solid interface.45 The HBC core extended with four had low solubility.51,52,54,55 Packing mode in the solid state and
additional K-regions has been shown to form a highly ordered self-assembly behaviour at solid/liquid interface of substituted
monolayer at the TCB/HOPG interface, extending defect- DBOV derivatives with a new type of aromatic core remained so
free area over several hundred square nanometers, but with far unknown, although such information will be essential for
occasional molecular stacking on top of the first layer.46 In further implementation of them in (opto)electronic devices.
contrast thereto, unsubstituted HBC has been shown to form
Herein, we report a synthesis of a DBOV derivative function-
complete bilayers at the TCB/HOPG interface.47 Under ultra- alized with two 3,4,5-tris(dodecyloxy)phenyl substituents
high vacuum (UHV) conditions and at low temperatures, per- (DBOV-TDOP, Scheme 1). TDOP groups were selected in order
chlorinated HBC has been studied on the Au(111) surface, to enhance the solubility without significantly affecting the
revealing formation of islands of highly ordered supramolecu- p–p interactions between the DBOV cores, in comparison to
lar networks even at coverages lower than a full monolayer.48 the mesityl group with two ortho-methyl groups. The structure
More recently, we have observed preferential bilayer formation of of DBOV-TDOP was unambiguously characterized by a combi-
triply-fused nanographene–porphyrin–nanographene conjugates nation of nuclear magnetic resonance (NMR) spectroscopy,
at the TCB/HOPG interface.49 However, reported self-assemblies high resolution matrix-assisted laser desorption/ionization
of PAHs at liquid–solid interfaces are predominantly monolayers, time of flight mass spectroscopy (MALDI-TOF MS), and the
and formation of such self-assembled bilayers, where intermole- optoelectronic properties were studied by UV-vis absorption
cular interactions are stronger than the molecule–surface interac- and fluorescence spectroscopy. The large rigid aromatic core
tions, still remains rare.50
has strong tendency to aggregate with the long n-dodecyl chains
Scheme 1 Synthetic route towards 6,14-bis{3,4,5-tris(dodecyloxy)phenyl}dibenzo-[hi,st]ovalene (DBOV-TDOP). Reaction conditions: (a) BBr3, ꢀ78 1C
to r.t., overnight, 98% yield; (b) C12H25Br, K2CO3, N,N-dimethylformamide, 80 1C, 20 h, 63% yield; (c) Mg, I2, tetrahydrofuran, reflux, overnight; (d) 4,
tetrahydrofuran, 4 h, room temperature; (e) BF3ꢁOEt2, dichloromethane, room temperature, overnight, then p-chloranil, 2 h, 85% yield in three steps.
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2019

View Article Online
Journal of Materials Chemistry C
Paper
stretched to the periphery, enabling the formation of columnar DBOV-TDOP with a high yield of 85% in three steps. This
self-assembly structures. The phase formation and self-assembly compound showed high solubility in dichloromethane, tetra-
in the solid state was investigated by differential scanning calori- hydrofuran or toluene, which allowed unambiguous character-
metry (DSC), polarized optical microscopy (POM), and two- ization of its structure in solution.
dimensional wide- and small-angle X-ray scattering (2D-WAXS
As shown in Fig. 1a, well-resolved sharp peaks are observed
and -SAXS), which clearly indicated its packing into helical stacks in its 1H NMR spectrum, which could be assigned with two-
with an exceptionally long pitch. It has been proven that the helical dimensional NMR techniques (see Fig. S1 and S2, ESI†). High-
packing can be well controlled by attaching side alkyl chains with a resolution (HR) MALDI-TOF MS spectra (Fig. 1b) exhibited one
suitable steric demand, while a tight packing and good intra- intense peak with m/z of 1729.2822, in very good agreement with
columnar order were maintained. In addition, this molecule the calculated value of 1729.2835. The UV-vis absorption was
tends to form bilayer structures at the interface of HOPG and measured in toluene at a concentration of 10ꢀ6 M (Fig. 1c). Similar
1-phenyloctane (PO) due to strong intermolecular interactions. to other DBOV derivatives,51,52,54,55 the maximum absorption wave-
length (lmax) is located at 609 nm with very high extinction
coefficient of 3.85 ꢂ 105 Mꢀ1 cmꢀ1. Three characteristic shoulder
peaks are observed at shorter wavelength, arising from the vibronic
coupling involving CQC stretch. The solution showed very strong
red fluorescence with maximum emission peak wavelength at
Results and discussion
Synthesis and characterization of DBOV-TDOP
DBOV-TDOP was synthesized as shown in Scheme 1. First, 615 nm. Small Stokes shift of only 6 nm indicates its rigid core
5-bromo-1,2,3-tris(dodecyloxy)benzene (3) was synthesized from structure and minor energy loss in the excited state. Moreover, high
5-bromo-1,2,3-trimethoxybenzene (1) through a sequence of relative fluorescence quantum yield (F) of 0.89 was measured with
demethylation with BBr3 and three-fold nucleophilic substitution Nile blue A perchlorate as standard,57 indicating the potential of
with 1-bromododecane. Then Grignard reagent 4 was prepared by DBOV-TDOP for optoelectronic applications.
refluxing 3 and magnesium turning in tetrahydrofuran with I2 as
Solid-state self-assembly into helical columns
initiator. 5,14-Diformylbenzo[a]dinaphtho[2,1,8-cde:10,20,30,40-ghi]-
perylene (5)52,56 was subsequently treated with Grignard reagent 4 The thermal stability of DBOV-TDOP was investigated by thermo-
at room temperature followed by quenching with NH4Cl to give gravimetric analysis (TGA), which showed a high decomposition
diol intermediate 6, which was subjected to BF3ꢁOEt2 promoted temperature of up to 365 1C (5% weight loss, Fig. S3, ESI†).
Friedel–Crafts reaction and oxidation by p-chloranil to afford The attachment of the six dodecyloxy chains induced distinct
Fig. 1 (a) 1H NMR spectra of DBOV-TDOP in [D8]THF : CS2 = 2 : 1; (b) HR MALDI-TOF MS spectrum of DBOV-TDOP, inset: magnified spectrum showing
isotopic distribution pattern in comparison with theoretical calculation; (c) UV-vis absorption and fluorescence spectra of DBOV-TDOP measured in
toluene solution with concentration of 10ꢀ6 M, inset shows pictures of toluene solution under room light (left) and UV light (right).
This journal is ©The Royal Society of Chemistry 2019
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
thermotropic properties which were studied by DSC and POM.
The 2nd DSC heating scan showed two prominent peaks
(Fig. 2a). The first peak at 145 1C was attributed to the
reorganization of the side chains, while the second at 158 1C
was related to the melting into the liquid crystalline phase. The
clearing temperature for the compound was found at 252 1C
and was confirmed by POM. Cooling the compound between
two glass slides under cross-polarized microscopy from its
isotropic into the liquid crystalline phase resulted in a charac-
teristic birefringent fan-shaped focal conic texture (Fig. 2b).
A typical supramolecular liquid crystalline organization was
also found in the liquid crystalline phase by 2D-WAXS and -SAXS
on extruded fibers. The hexagonal liquid crystalline phase typi-
cally leads to p-stacking reflections in the wide-angle range on the
meridional plane of the 2DWAXS pattern and to equatorial
reflections in the small angle region that are related to the
hexagonal intercolumnar arrangement.58 As derived from the
pffiffi
positions at the ratio of 1 : 3 :2 of the equatorial scattering
intensities (Fig. 3a and c), the DBOV-TDOP self-assembled into
columnar stacks arranged in a hexagonal lattice. The equatorial
reflections were indexed according to a hexagonal lattice para-
meter of ahex = 3.07 nm (Fig. 3e). The meridional reflections were
assigned to the intracolumnar p-stacking distance of 0.36 nm.
In the liquid crystalline phase, the molecular dynamics are high
and the aromatic discs can perform an axial motion around
the column axes. As the thermal energy decreases at lower
temperature, this molecular motion is reduced leading to higher
intracolumnar order and the formation of a more complex
organization.59 Cooling the sample to the crystalline phase at
30 1C changed the supramolecular organization of DBOV-TDOP
as indicated by the complex pattern in Fig. 3b. The large number
of new scattering intensities confirmed the higher long-range
order in the crystalline phase. The p-stacking distance slightly
increased to 0.37 nm, while the intercolumnar arrange-
ment turned into a square lattice with asqr = 5.35 nm. The
reflections with mixed indices out of the equator and of the
meridian located on scattering lines was characteristic for helical
packing within the stacks.60–62 Additional off-meridional reflec-
tions in the small-angle region implied a helical intracolumnar
Fig. 3 2D-WAXS and -SAXS patterns of DBOV-TDOP obtained at (a), (c)
200 1C and (b), (d) 30 1C (* indicates remaining reflection from the
crystalline phase; white arrows assign reflections of the first scattering
line) and (e) equatorial integration for both measurements (reflections are
indexed by Miller indices).
Fig. 2 (a) Differential scanning calorimetry (DSC) scans (1st cooling and 2nd heating at 10 1C minꢀ1) and (b) polarized optical microscopy (POM)
photograph at 150 1C of DBOV-TDOP.
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2019

View Article Online
Journal of Materials Chemistry C
Paper
A rotation of 121 between adjacent molecules in the stack was
induced to overcome the steric hindrance of the out-of-plane
arranged TDOP group in the periphery of the aromatic DBOV
core. The strategy to control the helical organization in supra-
molecular columns of disc-shaped molecules by employing
sterically demanding substituents has been also realized for
other nanographenes,35,38,64 but for the first time for
a
dibenzo[hi,st]ovalene of this aromatic shape. Interestingly, this
concept could be applied for a DBOV core by attaching only two
bulky substituents as proven in this work. Comparison to other
core extended discotic PAHs, we confirmed the exceptionally
long helical pitch of the DBOV molecules.63 Since the corres-
ponding reflections of mixed indices are distinct and well
defined, the molecular ordering in the stacks is pronounced
and the helical twist between neighboring discs is well defined.
Fluctuations in the twist angle would lead to poor or none
reflections related to the helical packing. The high intracolumnar
order of the helical structure with such long pitch is attributed to
Fig. 4 Schematic illustration of the helical organization of DBOV-TDOP
at 30 1C. Due to p-stacking interactions, the molecules self-assemble in
columnar structures that are arranged in a hexagonal fashion. In the stacks,
the molecules are rotated by 121 with respect to each other and form a
helix. Alkoxy side chains are omitted for clarity.
packing of the molecules. The helical pitch of 5.55 nm was good intermolecular p-interactions.
determined from the first scattering line (Fig. 3d) and corre-
sponded to 15 molecules per helical pitch including a 1801
STM characterization of DBOV-TDOP
rotation (Fig. 4). This exceptionally long helical pitch, in compar- Scanning tunnelling microscopy (STM) was used to study the
ison to the typical pitch of around 1 nm for other PAHs, 2D self-assembly behaviour of DBOV-TDOP at the interface
was related to good intracolumnar packing of the molecules.63 between PO and HOPG. A solution of DBOV-TDOP in PO was
Fig. 5 STM characterization of DBOV-TDOP at the PO/HOPG interface. (a) Large-scale STM image showing the long-range order with few single-
molecule defects (red circles) and non-covered areas (c = 6 ꢂ 10ꢀ5 mol Lꢀ1). The line profile across a non-covered area reveals an apparent layer height
of approximately 0.7 nm (see inset). (b) Large-scale STM image at lower concentration (c = 6 ꢂ 10ꢀ6 mol Lꢀ1) showing an increase of disordered areas and
the same layer height (see inset). (c) STM image revealing double layer formation with an apparent height of about 0.35 nm for each layer. (d) High-
resolution STM images superimposed with a tentative model of the molecular assembly. (e) High-resolution STM image and tentative model of the
molecular assembly in the lower layer. The alkyl chains are presumably desorbed from the surface and omitted in the model for clarity. (f) Superposition
of the tentative molecular models for the first and second layer. Imaging parameters: (a) Vbias = ꢀ1.1 V, Iset = 80 pA, (b) Vbias = ꢀ1.2 V, Iset = 60 pA,
(c) Vbias = ꢀ1.1 V, Iset = 60 pA, (d) Vbias = ꢀ1.1 V, Iset = 230 pA, (e) Vbias = ꢀ0.9 V, Iset = 50 pA.
This journal is ©The Royal Society of Chemistry 2019
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
drop-casted on freshly-cleaved HOPG and subsequently imaged 0.36 nm found in the columnar stacks as is the relative orientation
by STM at room temperature, at the liquid–solid interface. of the molecules in the first and second layer.
Already at a concentration of c = 6 ꢂ 10ꢀ5 mol Lꢀ1 the HOPG
surface was found to be covered by a molecular layer, appearing
as a row-like structure, with only a few single-molecule defects
Conclusion
and small non-covered areas (Fig. 5a). The apparent height of
In conclusion, we reported the synthesis of the discotic
the layer was found to be approximately 0.7 nm (see inset in
dibenzo[hi,st]ovalene molecule functionalized with two 3,4,5-
Fig. 5a). The unit cell (a = 2.32 ꢃ 0.05 nm, b = 1.49 ꢃ 0.04 nm,
tris(dodecyloxy)phenyl groups at the meso-positions. The self-
a = 74.8 ꢃ 2.01) was determined with several drift-corrected
assembly behavior of this molecule was extensively investigated.
high-resolution STM images, i.e. by imaging first the molecular
The attachment of 1,2,3-tris(dodecyloxy)phenyl substituents
layer and subsequently the HOPG surface underneath by chan-
induced thermotropic properties and self-assembly into columnar
ging the tunnelling parameters (Fig. S4, ESI†). A tentative
structures of DBOV-TDOP. Due to the distinct steric demand of
model of the monolayer structure, based on high-resolution
the side groups, the molecules arranged in a helical fashion in the
STM images and unit cell dimensions, is shown in Fig. 5d. The
stacks. Interestingly, an especially long helical pitch is found
molecules assemble with the DBOV cores aligned in a row-like
indicating a tight molecular packing and high intracolumnar
fashion with the long molecular axes oriented perpendicular to
order despite the pronounced steric hindrance of the substitu-
the row direction. Adjacent rows are shifted half a molecular
ents. A well-defined rotation of the aromatic cores together with
width, so that interdigitation of the peripheral phenyl groups
long-range ordering in the columnar stacks are prerequisites for
allows close-packing. Single-molecule defects thereby help to
an unhindered intrinsic charge carrier transport in discotic liquid
identify the position in the assembly (Fig. 5d and Fig. S5, ESI†).
crystals. Additionally, at the liquid–solid interface, large-area
The unit cell parameters indicate that the space between
bilayer film formation was observed even at low concentrations
adjacent aromatic cores is not sufficient for the adsorption of
as a result of the strong intermolecular p–p interactions. The
the alkyl-chains. Thus, they are most likely desorbed from the
tendency to form self-organized and well-defined supramolecular
surface and back-folded in the supernatant solution. More
structures, both columns and film, makes DBOV-TDOP a promis-
dilute solutions (c = 6 ꢂ 10ꢀ6 mol Lꢀ1) lead to the formation
ing candidate for fabricating electronic devices.
of similar molecular assemblies, albeit with much lower surface
coverage, while maintaining the same apparent height
(B0.7 nm) (Fig. 5b and Fig. S6, ESI†).
Closer inspection of the molecular layers adjacent to the
uncovered areas revealed that the molecules assemble in a
Experimental methods
General
bilayer instead of a monolayer as evidenced by the STM image All reactions working with air- or moisture-sensitive compounds
provided in Fig. 5c, which clearly shows a lower molecular were carried out under argon atmosphere using standard
layer that extends beneath the second layer. Furthermore, high- Schlenk line techniques. Thin layer chromatography (TLC) was
resolution images of this lower layer show a different molecular done on silica gel coated aluminum sheets with F254 indicator
orientation, i.e. the long axes of the DBOV cores are not and column chromatography separation was performed with
perpendicular, but instead rotated by approximately 401 with silica gel (particle size 0.063–0.200 mm). Nuclear Magnetic
respect to the row propagation (Fig. 5e). A superposition of the Resonance (NMR) spectra were recorded using Bruker DPX 300
tentative molecular assembly of the first and second layer is MHz NMR spectrometers. Chemical shifts (d) were expressed in
1
shown in Fig. 5f. The DBOV cores of the molecules in the first ppm relative to the residual of solvents (CD2Cl2, H: 5.32 ppm,
and second layer are proposed to be at the same positions, 13C: 53.84 ppm; THF-d8, 1H: 3.58 ppm, 13C: 67.57 ppm). Coupling
while the long molecular axes are rotated in a way that the constants ( J) were recorded in Hertz. High resolution mass
peripheral aryl moieties, which are assumed to be out-of-plane spectra (HR MS) were recorded on a Bruker Reflex II-TOF
compared to the DBOV core, are not on top of each other, spectrometer by matrix-assisted laser decomposition/ionization
allowing a closer distance between the cores and thus increased (MALDI) using 7,7,8,8-tetracyanoquinodimethane (TCNQ) as
p–p interactions. The observed preferential double layer for- matrix and calibrated against poly(ethylene glycol). Thermo-
mation even at low concentrations indicates that the p–p interac- gravimetric analysis (TGA) was measured on a Mettler Toledo
tions between the DBOV cores are stronger than the DBOV–HOPG TGA-851 system with a heating speed of 10 K minꢀ1 under
interactions. Note that additional layers above the double layer nitrogen atmosphere. Differential scanning calorimetry (DSC)
may form, which, however, could be removed by the STM tip was recorded on a Mettler DSC 30 instrument with a heating
during the imaging process.65 Additional layers would decrease speed of 10 K minꢀ1 under nitrogen atmosphere. UV-vis
the tunnelling current and thus the STM tip would have to move absorption spectra were recorded on a PerkinElmer Lambda
closer to the surface to maintain the current setpoint, thereby 900 spectrometer at room temperature using a 10 mm quartz
removing the additional layers again while scanning. In the liquid cell. Photoluminescence spectra were recorded on a J&MTIDAS
crystalline phase, these strong p–p interactions lead to the spectrofluorometer. The fluorescence quantum yield (F) was
observed columnar structures. The apparent layer height of about measured using nile blue A perchlorate (in ethanol under air,
0.35 nm is also comparable with the p-stacking distance of F = 0.27) as a reference.57
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2019

View Article Online
Journal of Materials Chemistry C
Paper
Materials
acetate (50 mL) for three times. The combined organic layers
were washed with brine, dried with Na2SO4 and evaporated.
The residue was dried under vacuum for 2 h and dissolved in
anhydrous dichloromethane (30 mL). After bubbling with
argon saturated with dichloromethane vapour for 15 min,
BF3ꢁOEt2 (0.1 mL) was added and the stirring was continued
overnight. After quenching with methanol (2 mL), p-chloranil
(12 mg, 0.049 mmol) was added and the mixture was stirred for
2 h at room temperature. The solvent was evaporated and the
residue was purified by silica gel column chromatography
(eluent: n-hexane : dichloromethane = 3 : 1 to 0 : 1) to give the
title compound (72 mg, 85% yield) as blue solid. 1H NMR
(300 MHz, THF-d8) d 9.27 (d, J = 8.5 Hz, 2H), 9.02 (d, J = 7.7 Hz,
2H), 8.36 (d, J = 8.4 Hz, 2H), 8.10 (d, J = 8.3 Hz, 2H), 7.97
(t, J = 9.1 Hz, 4H), 7.89 (d, J = 9.3 Hz, 2H), 6.87 (s, 4H), 4.16
(t, J = 6.2 Hz, 4H), 4.05 (t, J = 6.2 Hz, 8H), 1.97–1.79 (m, 15H),
1.69–1.61 (m, 4H), 1.61–1.15 (m, 119H), 0.97–0.80 (m, 18H);
13C NMR (75 MHz, THF-d8) d 139.1, 137.5, 134.9, 132.7, 132.5,
131.3, 130.3, 130.1, 128.9, 127.9, 127.5, 127.3, 126.5, 125.5, 125.1,
124.7, 124.3, 123.6, 123.4, 122.1, 121.4, 111.0, 74.0, 70.0, 33.2,
33.1, 31.9, 31.1, 31.1, 31.1, 31.0, 30.9, 30.9, 30.8, 30.7, 30.7, 30.6,
27.6, 27.4, 23.9, 23.9, 14.9, 14.9; HRMS (MALDI-TOF): m/z calcd
for C122H168O6: 1729.2841 [M]+, found: 1729.2822.
Unless otherwise noted, all starting materials and reagents
were purchased from commercial sources and used without
further purification. The synthesis of 5,14-diformylbenzo[a]-
dinaphtho[2,1,8-cde:10,20,30,40-ghi]perylene (5) is described in
our previously report,52 and we also used an improved synthetic
route, which we have more recently developed.56
Synthesis of 5-bromo-1,2,3-tris(dodecyloxy)benzene (3)
5-Bromo-1,2,3-trimethoxybenzene (1) (2.5 g, 10 mmol) was
dissolved in dry dichloromethane (30 mL), and the solution
was cooled down to ꢀ78 1C. BBr3 (8.26 g, 33.0 mmol) was added
dropwise to the solution then the reaction mixture was gradu-
ally warmed up to room temperature and stirred overnight.
After completion of reaction, the mixture was poured into
100 mL of ice water and extracted with ethyl acetate (100 mL)
for three times. The organic layers were combined, washed with
brine (100 mL) and dried over Na2SO4. After evaporation of the
solvent and drying under reduced pressure, a crude product of
5-bromobenzene-1,2,3-triol (2) (2.0 g, 98%) was obtained as
white solid, which was used directly for the next step without
further purification. To a 100 mL Schlenk flask was added the
crude product of 5-bromobenzene-1,2,3-triol (2) (2.0 g, 9.8 mmol),
1-bromododecyl (9.92 g, 40.0 mmol) and K2CO3 (5.52 g, POM
40.0 mmol). The flask was evacuated and backfilled with argon
The optical textures of the compound were investigated using a
for three times before N,N-dimethylformamide (50 mL) was
added. After stirring at 80 1C for 20 h, the mixture was cooled
down to room temperature and diluted with ethyl acetate
(200 mL), washed with water (50 mL) and brine (50 mL), dried
over Na2SO4 and evaporated. The obtained residue was purified
Zeiss microscope with polarizing filters equipped with a Hitachi
KP-D50 colour digital CCD camera. The samples were sandwiched
between two glass slides and thermally treated on a Linkam hot
stage regulated with a Linkam TMS 91 temperature controller.
by silica gel column chromatography (eluent: n-hexane) and 2DWAXS and -SAXS
recrystallized with ethanol to give 5-bromo-1,2,3-tris(dodecyloxy)-
2DWAXS and -SAXS measurements were performed using a
benzene (3) (4.5 g, 63% yield over two steps) as white solid.
1H NMR (300 MHz, methylene chloride-d2) d 6.68 (s, 2H), 3.97–
3.83 (m, 6H), 1.85–1.72 (m, 4H), 1.72–1.62 (m, 2H), 1.51–1.39
(m, 6H), 1.39–1.22 (m, 48H), 0.94–0.82 (m, 9H); 13C NMR
(75 MHz, methylene chloride-d2) d 154.3, 137.8, 115.8, 110.3,
73.8, 69.7, 32.4, 30.7, 30.2, 30.2, 30.1, 30.1, 30.1, 30.0, 29.8, 29.8,
29.7, 26.5, 26.5, 23.1, 14.3; HRMS (MALDI-TOF): m/z calcd for
C42H77BrO3: 708.5056 [M]+, found: 708.5005.
setup consisting of copper solid-anode X-ray tube (Bruker AXS
Krystalloflex 760, operated at 35 kV and 30 mA), Osmic confocal
MaxFlux optics and a three pin-hole collimation system. The
fiber samples for the measurements were prepared by extrusion
at 25 1C and were positioned perpendicular to the incident
X-ray beam and vertical to the 2D detector. The scattering
intensity was detected on a 2-D image plate (MAR-345) with a
pixel size of 100 mm (2345 ꢂ 2345 pixels). Scattering data are
expressed as a function of the scattering vector: q = 4p/l sin(Y),
where Y is a half the scattering angle and l = 0.154 Å is the
Synthesis of DBOV-TDOP
To a 25 mL Schlenk tube was added magnesium turnings wavelength of the incident radiation. All X-ray scattering measure-
(27 mg, 1.1 mmol), I2 (3 mg, 0.01 mmol) and tetrahydrofuran ments were performed under vacuum (B20 mbar) to reduce air
(1 mL). The mixture was gently heated while approximately 1 mL scattering and beam damage to the sample. All 2DWAXS data
of 5-bromo-1,2,3-tris(dodecyloxy)benzene (3) (568 mg, 0.800 mmol) processing and analysis was performed by using the software
dissolved in tetrahydrofuran (THF) (3 mL) was added. As soon as package Datasqueeze (http://www.datasqueezesoftware.com).
the solution became colorless, the remaining solution was added
STM
dropwise under mild reflux and stirring was continued overnight.
The obtained solution of Grignard reagent (4 mL) was trans- STM measurements were performed with a Molecular Imaging or
ferred to a solution of 5,14-diformylbenzo[a]dinaphtho[2,1,8- Agilent PicoLE system in constant-current mode (PicoSPM) at
cde:10,20,30,40-ghi]perylene (5) (25 mg, 0.049 mmol) in dry THF the 1-phenyloctane/highly-oriented pyrolytic graphite (PO/HOPG)
(30 mL). After stirring at room temperature for 4 h, the reaction interface at room temperature (20–22 1C). The imaging para-
was quenched by addition of saturated NH4Cl solution (15 mL). meters Iset (tunneling current) and Vbias (substrate bias) are
After stirring for 15 min, the solution was extracted with ethyl indicated in the figure captions. STM tips were obtained by
This journal is ©The Royal Society of Chemistry 2019
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
15 B. R. Kaafarani, Chem. Mater., 2011, 23, 378–396.
mechanical cutting of
a Pt/Ir wire (80%/20%, diameter
16 S. Xiao, M. Myers, Q. Miao, S. Sanaur, K. Pang, M. L. Steigerwald
and C. Nuckolls, Angew. Chem., Int. Ed., 2005, 44, 7390–7394.
17 J. P. Hill, W. Jin, A. Kosaka, T. Fukushima, H. Ichihara,
T. Shimomura, K. Ito, T. Hashizume, N. Ishii and T. Aida,
Science, 2004, 304, 1481–1483.
18 S. Xiao, J. Tang, T. Beetz, X. Guo, N. Tremblay, T. Siegrist,
Y. Zhu, M. Steigerwald and C. Nuckolls, J. Am. Chem. Soc.,
2006, 128, 10700–10701.
19 Z. Chen, A. Lohr, C. R. Saha-Moller and F. Wurthner, Chem.
Soc. Rev., 2009, 38, 564–584.
20 E. Moulin, J. J. Cid and N. Giuseppone, Adv. Mater., 2013,
25, 477–487.
0.25 mm). Immediately before use, the HOPG substrate (grade
ZYB, Advanced Ceramics) was freshly cleaved using adhesive
tape. The solvent, 1-phenyloctane (Sigma-Aldrich, 98%), was
used without further purification. Scanning Probe Imaging
Processor (SPIP 6.5.1) software from Image Metrology ApS
was used for STM image processing.
Conflicts of interest
There are no conflicts to declare.
21 W. Jin, Y. Yamamoto, T. Fukushima, N. Ishii, J. Kim,
K. Kato, M. Takata and T. Aida, J. Am. Chem. Soc., 2008,
130, 9434–9440.
22 L. Chen, S. R. Puniredd, Y. Z. Tan, M. Baumgarten,
U. Zschieschang, V. Enkelmann, W. Pisula, X. Feng,
H. Klauk and K. Mu¨llen, J. Am. Chem. Soc., 2012, 134,
17869–17872.
23 W. Yuan, X. K. Ren, M. Li, H. Guo, Y. Han, M. Wu, Q. Wang,
M. Li and Y. Chen, Angew. Chem., Int. Ed., 2018, 57, 6161–6165.
24 S. Laschat, A. Baro, N. Steinke, F. Giesselmann, C. Hagele,
G. Scalia, R. Judele, E. Kapatsina, S. Sauer, A. Schreivogel
and M. Tosoni, Angew. Chem., Int. Ed., 2007, 46, 4832–4887.
25 S. K. Pal, S. Setia, B. S. Avinash and S. Kumar, Liq. Cryst.,
2013, 40, 1769–1816.
26 S. Sergeyev, W. Pisula and Y. H. Geerts, Chem. Soc. Rev.,
2007, 36, 1902–1929.
27 N. Boden, R. J. Bushby, J. Clements and B. Movaghar,
J. Mater. Chem., 1999, 9, 2081–2086.
28 S. Kumar, Chem. Soc. Rev., 2006, 35, 83–109.
29 T. Wohrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum,
J. Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro, F. Giesselmann
and S. Laschat, Chem. Rev., 2016, 116, 1139–1241.
30 W. Pisula, M. Zorn, J. Y. Chang, K. Mu¨llen and R. Zentel,
Macromol. Rapid Commun., 2009, 30, 1179–1202.
31 J. M. Warman, J. Piris, W. Pisula, M. Kastler, D. Wasserfallen
and K. Mu¨llen, J. Am. Chem. Soc., 2005, 127, 14257–14262.
Acknowledgements
We are grateful for the financial support from the Max Planck
Society and the Fund of Scientific Research Flanders (FWO)
under EOS 30489208. J. S. acknowledges financial support
through a Marie Skłodowska-Curie Individual Fellowship (EU
project 789865 – EnSurf). Open Access funding provided by the
Max Planck Society.
References
¨
1 M. D. Watson, A. Fechtenkotter and K. Mu¨llen, Chem. Rev.,
2001, 101, 1267–1300.
2 A. Narita, X. Y. Wang, X. Feng and K. Mu¨llen, Chem. Soc.
Rev., 2015, 44, 6616–6643.
3 W. Pisula, X. Feng and K. Mu¨llen, Chem. Mater., 2011, 23,
554–567.
4 Q. Ye and C. Chi, Chem. Mater., 2014, 26, 4046–4056.
5 J. Li and Q. Zhang, ACS Appl. Mater. Interfaces, 2015, 7,
28049–28062.
6 L. Zhang, Y. Cao, N. S. Colella, Y. Liang, J. L. Bredas, K. N.
Houk and A. L. Briseno, Acc. Chem. Res., 2015, 48, 500–509.
7 M. Ball, Y. Zhong, Y. Wu, C. Schenck, F. Ng, M. Steigerwald,
S. Xiao and C. Nuckolls, Acc. Chem. Res., 2015, 48, 267–276.
8 R. K. Gupta and A. A. Sudhakar, Langmuir, 2019, 35, 2455–2479.
9 D. Meng, G. Liu, C. Xiao, Y. Shi, L. Zhang, L. Jiang,
K. K. Baldridge, Y. Li, J. S. Siegel and Z. Wang, J. Am. Chem.
Soc., 2019, 141, 5402–5408.
¨
32 D. Adam, P. Schuhmacher, J. Simmerer, L. Haussling,
K. Siemensmeyer, K. H. Etzbachi, H. Ringsdorf and D. Haarer,
Nature, 1994, 371, 141–143.
33 R. J. Bushby and O. R. Lozman, Curr. Opin. Colloid Interface
Sci., 2002, 7, 343–354.
10 X. Liu, M. Chen, C. Xiao, N. Xue and L. Zhang, Org. Lett.,
2018, 20, 4512–4515.
11 X. Cui, C. Xiao, T. Winands, T. Koch, Y. Li, L. Zhang,
N. L. Doltsinis and Z. Wang, J. Am. Chem. Soc., 2018, 140, 34 M. Kastler, W. Pisula, F. Laquai, A. Kumar, R. J. Davies,
´
12175–12180.
S. Baluschev, M. C. Garcia–Gutierrez, D. Wasserfallen,
¨llen, Adv. Mater.,
2006, 18, 2255–2259.
12 J. Li, K. Zhou, J. Liu, Y. Zhen, L. Liu, J. Zhang, H. Dong,
X. Zhang, L. Jiang and W. Hu, J. Am. Chem. Soc., 2017, 139,
17261–17264.
H. J. Butt, C. Riekel, G. Wegner and K. Mu
35 L. Chen, K. S. Mali, S. R. Puniredd, M. Baumgarten,
13 C. Ruiz, U. K. Pandey, R. Termine, E. M. Garcia-Frutos,
G. Lopez-Espejo, R. P. Ortiz, W. Huang, T. J. Marks, A. Facchetti,
K. Parvez, W. Pisula, S. De Feyter and K. Mu
¨llen, J. Am.
Chem. Soc., 2013, 135, 13531–13537.
¨
M. C. Ruiz Delgado, A. Golemme and B. Gomez-Lor, ACS Appl. 36 A. M. van de Craats, J. M. Warman, A. Fechtenkotter,
Mater. Interfaces, 2016, 8, 26964–26971.
14 H. A. Lin, Y. Sato, Y. Segawa, T. Nishihara, N. Sugimoto,
J. D. Brand, M. A. Harbison and K. Mu¨llen, Adv. Mater.,
1999, 11, 1469–1472.
L. T. Scott, T. Higashiyama and K. Itami, Angew. Chem., Int. 37 X. Feng, W. Pisula, T. Kudernac, D. Wu, L. Zhi, S. De Feyter
Ed., 2018, 57, 2874–2878.
and K. Mu¨llen, J. Am. Chem. Soc., 2009, 131, 4439–4448.
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2019

View Article Online
Journal of Materials Chemistry C
Paper
38 W. Pisula, Z. Tomovic, M. D. Watson, K. Mu¨llen, J. Kussmann, 51 G. M. Paterno, Q. Chen, X. Y. Wang, J. Liu, S. G. Motti,
C. Ochsenfeld, T. Metzroth and J. Gauss, J. Phys. Chem. B, 2007,
111, 7481–7487.
A. Petrozza, X. Feng, G. Lanzani, K. Mu¨llen, A. Narita and
F. Scotognella, Angew. Chem., Int. Ed., 2017, 56, 6753–6757.
39 T. Nagano, K. Nakamura, Y. Tokimaru, S. Ito, D. Miyajima, 52 D. M. Coles, Q. Chen, L. C. Flatten, J. M. Smith, K. Mu¨llen,
T. Aida and K. Nozaki, Chem. – Eur. J., 2018, 24, 14075–14078. A. Narita and D. G. Lidzey, Nano Lett., 2017, 17, 5521–5525.
40 Y. Shoji, T. Kajitani, F. Ishiwari, Q. Ding, H. Sato, H. Anetai, 53 A. J. Kuehne and M. C. Gather, Chem. Rev., 2016, 116,
T. Akutagawa, H. Sakurai and T. Fukushima, Chem. Sci.,
2017, 8, 8405–8410.
41 D. Miyajima, K. Tashiro, F. Araoka, H. Takezoe, J. Kim,
12823–12864.
54 Q. Chen, D. Wang, M. Baumgarten, D. Schollmeyer, K. Mu¨llen
and A. Narita, Chem. – Asian J., 2019, 14, 1703–1707.
`
K. Kato, M. Takata and T. Aida, J. Am. Chem. Soc., 2009, 131, 55 G. M. Paterno, L. Nicoli, Q. Chen, K. Mu¨llen, A. Narita,
44–45.
G. Lanzani and F. Scotognella, J. Phys. Chem. C, 2018, 122,
42 A. Idelson, C. Sterzenbach, S. S. Jester, C. Tschierske,
25007–25013.
¨
U. Baumeister and S. Hoger, J. Am. Chem. Soc., 2017, 139, 56 Q. Chen, S. Thoms, S. Stottinger, D. Schollmeyer, K. Mu¨llen,
´
A. Narita and T. Basche, 2019, under review.
4429–4434.
43 C. Aumaitre and J. F. Morin, Chem. Rec., 2019, 19, 1142–1154. 57 R. Sens and K. H. Drexhage, J. Lumin., 1981, 24–25, 709–712.
44 T. Yatabe, M. A. Harbison, J. D. Brand, M. Wagner, 58 K. Ban, K. Nishizawa, K. Ohta, A. M. van de Craats, J. M.
´
K. Mu¨llen, P. Samorı and J. P. Rabe, J. Mater. Chem., 2000,
10, 1519–1525.
Warman, I. Yamamoto and H. Shirai, J. Mater. Chem., 2001,
11, 321–331.
¨
45 A. Stabel, P. Herwig, K. Mu¨llen and J. P. Rabe, Angew. Chem., 59 I. Fischbach, T. Pakula, P. Minkin, A. Fechtenkotter,
¨
Int. Ed. Engl., 1995, 34, 1609–1611.
K. Mu¨llen, H. W. Spiess and K. Saalwachter, J. Phys. Chem. B,
46 T. Dumslaff, B. Yang, A. Maghsoumi, G. Velpula, K. S. Mali,
2002, 106, 6408–6418.
´
C. Castiglioni, S. De Feyter, M. Tommasini, A. Narita, X. Feng 60 R. Martın-Rapu´n, D. Byelov, A. R. A. Palmans, W. H. de Jeu
and K. Mu¨llen, J. Am. Chem. Soc., 2016, 138, 4726–4729. and E. W. Meijer, Langmuir, 2009, 25, 8794–8801.
47 P. Samorı, N. Severin, C. D. Simpson, K. Mu¨llen and 61 E. Beltran, E. Cavero, J. Barbera, J. L. Serrano, A. Elduque
J. P. Rabe, J. Am. Chem. Soc., 2002, 124, 9454–9457. and R. Gimenez, Chem. – Eur. J., 2009, 15, 9017–9023.
48 Y. Zhang, Y. Zhang, G. Li, J. Lu, X. Lin, Y. Tan, X. Feng, 62 M. Peterca, M. R. Imam, C. H. Ahn, V. S. Balagurusamy,
´
S. Du, K. Mu¨llen and H. J. Gao, J. Chem. Phys., 2015,
142, 101911.
D. A. Wilson, B. M. Rosen and V. Percec, J. Am. Chem. Soc.,
2011, 133, 2311–2328.
49 Q. Chen, L. Brambilla, L. Daukiya, K. S. Mali, S. De Feyter, 63 W. Pisula, X. Feng and K. Mu¨llen, Adv. Mater., 2010, 22,
M. Tommasini, K. Mu¨llen and A. Narita, Angew. Chem., Int.
Ed., 2018, 57, 11233–11237.
3634–3649.
64 X. Feng, W. Pisula and K. Mu¨llen, J. Am. Chem. Soc., 2007,
129, 14116–14117.
´
¨
¨
¨
50 P. Samorı, A. Fechtenkotter, F. Jackel, T. Bohme, K. Mu¨llen
and J. P. Rabe, J. Am. Chem. Soc., 2001, 123, 11462–11467.
65 W. Azzam, Appl. Surf. Sci., 2016, 371, 562–570.
This journal is ©The Royal Society of Chemistry 2019
J. Mater. Chem. C