Consequences of a Single Double Bond within a Side Group on the

Subscriber access provided by UNIV OF NEBRASKA - LINCOLN

Article

Consequences of a Single Double Bond within a SideGroup on the Ordering of Supra-Molecular Polymers Roozbeh Shokri, Olga A. Guskova, Asad Jamal, Kaiwan Jahanshahi, Benjamin Isare, Laurent Bouteiller, Laurent Simon, Jens-Uwe Sommer, and Günter Reiter J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b07644 • Publication Date (Web): 08 Sep 2015 Downloaded from http://pubs.acs.org on September 14, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Consequences of a Single Double Bond within a Side-Group on the Ordering of Supra-Molecular Polymers Roozbeh Shokri,∗,† Olga Guskova,∗,‡,¶ Asad Jamal,†,§ Kaiwan Jahanshahi,† Benjamin Isare,k,⊥ Laurent Bouteiller,k,⊥ Laurent Simon,# Jens-Uwe Sommer,‡,@ and Günter Reiter†,§ Institute of Physics, University of Freiburg, Herman-Herder-Strasse 3, 79104 Freiburg, Germany, Institut Theorie der Polymere, Leibniz-Institut f¨ ur Polymerforschung Dresden e.V., Hohe Strasse 6, 01069 Dresden, Germany, Technische Universität Dresden, 01069 Dresden, Germany, Freiburg Materials Research Center(FMF), University of Freiburg, Stefan-Meier-Strasse 21, 79104 Freiburg, Germany, Sorbonne Université, UPMC Universite Paris 06, UMR 8232, IPCM, Chimie des Polymères, F-75005 Paris, France, CNRS, UMR 8232, IPCM, Chimie de Polymères, F-75005 Paris, France, Institut de Science des Materiaux de Mulhouse (IS2M), Mulhouse, France, and Technische Universit¨ at Dresden, Zellescher Weg 17, 01069 Dresden, Germany E-mail: [email protected]; [email protected]

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract By combining atomic force microscopy experiments and full-atomistic computer simulations, we compared the two-dimensional (2D) ordering dynamics of two variants of supra-molecular polymers of bis-urea molecules which differed only by a single cisdouble bond in their side groups. At early stages of ordering, the double bonds favored kinks at the level of individual molecules which induced transient steric constraints hindering the spontaneous formation of long supra-molecular polymers. In addition, due to these kinks, molecule-substrate interactions were disturbed. At later stages, however, due to a progressively increasing number of established directional hydrogen bonds (HBs) between molecules, the self-assembly process improved and thereby increased the length of the supra-molecular polymers. Large domains of micrometer-long and aligned supra-molecular polymers were formed, epitaxially guided by the graphite substrate and having a constant width consistent with the length of the molecule. Thus, introducing flexible (kinked) side chains can reduce the nucleation probability and slow down growth of supra-molecular polymers due to incommensurablility with the crystalline substrate. Such an elementary control of nucleation and growth via the introduction of a single double bond represents a powerful pathway for the formation of large ordered domains of aligned 1D supra-molecular polymers.

∗

To whom correspondence should be addressed Institute of Physics, University of Freiburg ‡ Institut Theorie der Polymere, Leibniz-Institut f¨ ur Polymerforschung Dresden e.V. ¶ Dresden Center for Computational Materials Science (DCMS) § Freiburg Materials Research Center(FMF) k IPCM, Chimie des Polymères, Université Pierre et Marie Curie ⊥ UMR 8232, CNRS # Institut de Science des Materiaux de Mulhouse (IS2M) @ Institut f¨ ur Theoretische Physik, Technische Universität Dresden †


Page 2 of 35

Page 3 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction Controlled tailoring of supra-molecular assemblies requires in-depth understanding of the role of competing phenomena occurring in the course of the ordering process. 1 Particularly, attractive or repulsive interactions between molecules are essentially influenced by shape, polarizability, the range of intra-molecular interactions, etc. which can be tailored through synthesis of the molecules. 2,3 At the nanoscale, even small modifications of the molecular architecture can have a substantial impact on the self-assembly process. 4 For instance, introducing double bonds in the side chains of the molecules (i.e., unsaturated molecules) can influence their dynamical and thermodynamical properties, e.g., crystallization. 5–9 Unsaturated molecules play a crucial role in biological systems: double bonds in the hydrocarbon chains of lipids have a noticeable effect on elasticity/mechanical properties of bilayers, molecular order and hydration of bio-membranes. 10–12 Design of self-assembling components with nano- to macro-scale dimensions can profit enormously by considering analogies to molecular systems. Chemists are professionally manipulating the structure of matter at the molecular scale. They focus not only at potential applications, e.g., the bottom-up fabrication of nano-electronics devices, 3,13,14 drug delivery, 15 etc., but they also provide innovative strategies for gaining in-depth understanding of natural phenomena 16–18 such as self-healing through dynamic self-assembly and disassembly of molecules. For example, inspired by self-assembly in biological systems, a series of bis-urea molecules has been synthesized. 19–21 The self-assembly leads to linear polymers, 22 somewhat analogous to the formation of actin filaments which are characterized by a long persistence length (up to 17 µm with a diameter of 7 nm). 23 Complementary to the structure formation process in solution, ordering of bis-urea-based molecules physisorbed on weakly interacting substrates such as gold, graphene and graphite has been widely investigated, with the goal to discover the role of hydrogen bonding, molecular architecture and moleculesurface interactions. 4,24–27 Apart from molecular features introduced into the self-assembling molecules through appropriate synthesis, strategies for controlling growth of supra-molecular 3 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

assemblies through specific molecular architecture are required for tailoring the self-ordered structures over multiple lengthscales. Here, we investigated the influence of a single cis-double bond within the side chains of bis-urea substituted toluene molecules on the ordering process of these molecules on a graphite surface. Cis-double bonds were introduced in these molecules through synthesis in order to enhance the solubility. The influence of the cis-double bonds on the ordering process was determined via the differences observed in substrate-guided self-assembly of two molecules, which were identical with the exception of a single cis-double bond in each side chain. We found that at the early stage of self-assembly occurring during the deposition process from solution, cis-double bonds strongly disturbed the formation of long-range ordered assemblies. Nevertheless, allowing for sufficient time to establish four directional hydrogen bonds between molecules, long supra-molecular polymers grew in time under ambient conditions, as revealed by atomic force microscopy (AFM) experiments performed at room temperature (RT). The kinetics of self-assembly in samples containing molecules with cisdouble bonds in the side chains was conveniently slow to be observed in real time and after storing at RT for one year, allowing to detect significant changes in domain size. The growth of micrometer long polymers having a width consistent with a length of a molecule confirmed that this slow self-assembly process was governed by the formation of hydrogen bonds between adjacent molecules. Thus, we suggest that the interplay of steric constraints (kink) and reversible noncovalent hydrogen bonding interactions controls self-assembly. Kinks weaken molecular-substrate interactions and slow down the lateral growth rate while hydrogen bonds privilege to the growth of long 1D supra-molecular polymers in a defined direction.


Page 4 of 35

Page 5 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Methods Experimental setup OLUT (2,4-bis(N,N’ -oleylureido)toluene) with a melting point of 163 ◦ C and ODUT (2,4bis(N,N’ -octadecylureido)toluene) with a melting point of 183 ◦ C , both having a length of 5.6 nm for the fully extended molecules (see Supporting Information for description of synthesis and Scheme 1) were dissolved in toluene to prepare solutions with a concentration of 0.04 mg/mL. Bis-urea molecules with linear alkyl substituents are not soluble at higher concentrations in low polarity solvents. 21 Therefore, the solution were annealed at ca. 60◦ C to assure solubility of ODUT molecules. Highly oriented pyrolytic graphite (HOPG), grade ZYH, cleaved in air, was used as a substrate. Subsequently, ca. 10 µL of solution was drop-casted onto such freshly cleaved surfaces followed by drying in air. During this drying process, the concentration increased, and accordingly solutions reached the supersaturation level, where nucleation and growth of ordered domains started. In addition, adsorption of molecules at the surface enhanced the concentration close to the substrate and thus favored nucleation and growth at the graphite surface. Atomic force microscopy (AFM) experiments in the tapping mode were performed to characterize the resulting self-assembled structures under ambient conditions with a lateral resolution limited by the tip radius of ca. 2 nm. SNL Bruker sharp tips with a resonance frequency of 65 kHz were employed. The family of bis-urea substituted toluene interact through inter-urea hydrogen bonding. 21 To confirm the hydrogen bonding between the OLUT or ODUT molecules FT-IR spectroscopy on solid samples was performed. FT-IR in ATR mode displays vibration bonds at 3300 and 1630 cm−1 which are characteristic for hydrogen bonded N-H and C=O, respectively. The data is provided in Supplementary Information Figure S1. Previously, scanning tunneling microscopy and spectroscopy study together with density functional theory calculations provided evidence for hydrogen bonding between bis-urea molecules from the same family. 27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Setup for atomistic scale modelling Computer simulation of OLUT and ODUT monolayers at the vacuum-graphite interface is performed according to the previously described methodology, 28,29 in which vacuum-solid environment (dielectric permittivity is ε=1) simplifies the analysis by eliminating adsorbatesolvent interactions. The modelling of 2D structures on HOPG using methods of computer simulation allows intermolecular and adsorbate-substrate forces to be partitioned into classical force-field contributions, like Coulomb and van der Waals interactions, whereas intramolecular interactions include the standard stretching (bonds), bending (angles), dihedral and out-of-plane PCFF-type potentials. 30 The charges of the atoms are assigned according to the PCFF database and remained constant during the calculations. Modelling is carried out in an NVT ensemble at T = 298 K (Nosé-Hoover thermostat, time constant 2 fs). The electrostatic interactions are treated using Ewald summation technique with a cutoff radius of 1.25 nm; a cutoff distance of 0.95 nm is employed for Lennard-Jones interactions. Potential parameters for cross-interactions involving among others adsorbatesubstrate term are obtained by implementing Lorentz-Berthelot mixing rules. All simulations are equilibrated for 2 ns; the sampling period is 10-30 ns with time step τ =1 fs. The fully atomistic simulations are performed using both LAMMPS software 31 and Accelrys Materials Studio (MS). 32 Various initial 2D geometrical structures are created and optimized in MS, including single OLUT/ODUT molecule and predefined OLUT/ODUT assemblies on HOPG. The 2D behaviour of an isolated molecule is expected to model the conformational and dynamical properties of bis-urea ODUT/OLUT derivatives at the beginning of self-assembly, for which the role of unsaturation is highlighted. On the other hand, when applied to molecular array, simulation gives the molecular conformations that maximize intermolecular interactions, and subsequently based on predefined patterns, the stability of 2D supra-molecular lattices can be identified. Molecules on a surface can adopt a high number of possible conformations. Therefore, it is virtually impossible to achieve the minimum-energy configuration of molecular array using 6 ACS Paragon Plus Environment

Page 6 of 35

Page 7 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


exclusively classical computer modelling methods. Generally, an initial 2D arrangement of the molecules, i.e. start configuration for all-atom MD simulation, must be either guessed on the basis of experimental findings, or taken from crystal packing predictions via translation of the predicted unit cell along two selected directions. Both approaches give molecular carpets with the periodic arrangement of the building blocks. 29,33–35 In this paper, the spatial structure within individual adsorbate domains of OLUT and ODUT is deducted from AFM (see Figures 1, 2) and previously reported STM measurements, 24–27 as well as from MD simulation of molecular self-assembly in multi-chain bis-urea systems, for which the molecules are inserted randomly near the surface. The graphite surface (xy-plane at the bottom of the simulation box with surface area A=173.2 nm2 ) is modelled as a bilayer composed of n=12096 uncharged carbons, which remain fixed in a hexagonal arrangement at interatomic distances rC−C =0.142 nm with an interlayer distance dC−C =0.340 nm (Bernal stacking). The periodic boundary conditions are assigned along x - and y-directions. The length of the box in z -direction is 14 nm to prevent the effect of the opposite side of the surface. The surface coverage Γ , which is measured as the ratio of the total mass of the molecule/molecular ensemble to the graphite surface area, is ca. Γ =0.0068 mg/m2 in case of isolated OLUT/ODUT molecule, Γ =0.082 mg/m2 for preorganized ODUT/OLUT structures composed of 12 molecules in order to mimic the most probable molecular architecture experimentally observed. The largest surface concentration is Γ =0.136 mg/m2 , which corresponds to 20 molecules inserted randomly near the substrate. Two possible motifs of H-bonding are known to be involved in the stabilization of supramolecular architectures via urea-urea interaction between neighbouring molecules in a row. 26 In this paper we use an original terminology proposed by Vonau et al. for bis-urea compounds: 26 the conformation is called parallel, if two urea groups of a given molecule are pointing in the same direction, and antiparallel, if they are directed oppositely (a sketch of the motifs is shown in Scheme 2 in Supporting Information).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Results and discussion Surface morphology and dynamics of structure formation resolved by AFM In order to gain insight into the consequence a single cis-double bond may have on a self-assembly process, we deposited molecules from solution on HOPG(0001) surfaces and scrutinized the resulting structures by AFM. Figure 1 shows characteristic AFM images of thin films of as-deposited ODUT and OLUT molecules. Directly after deposition, ODUT molecules with all-saturated bonds in the side chains formed ordered supra-molecular polymers, oriented mainly in three directions reflecting the symmetry of the underlying HOPG substrate (see the Fourier transform in Figure 1A). A similar pattern has been previously reported for other bis-urea molecules from the same family. 4 By contrast, OLUT molecules with unsaturated side chains containing a double bond in cis-conformation did not show any long-range order right after deposition (see the Fourier transform in Figure 1B). The presence of double bond introduces a kink in the side chains, and in turn, disturbs the crystallization of the molecules. Indeed, introducing kinked side chains reduces the nucleation probability and impair the crystallization and/or supra-molecular self-assembly at the early stages of ordering. Through MD simulations presented below, we will discuss two ways in detail of how cis-double bonds hamper the formation of long-range order: First, by hindering perfect atomic registry of the different molecular segments with the lattice of graphite surface. Second, by slowing down the dynamics of alignment of molecules with respect to the underlying crystalline lattice, resulting in a lower nucleation rate.

Although at the early stages of self-assembly the resulting structure for OLUT molecules did not show any long-range order, after long times the situation was completely different. Specifically, after storing the sample for one year under ambient conditions, the graphite surface was covered with long supra-molecular polymers characterized by a length up to sev8 ACS Paragon Plus Environment

Page 8 of 35

Page 9 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


A 3.53.64nm nm

0

-0.03 nm

B 3.53.83nm nm

0

0.00 nm

Figure 1: (A) and (B) AFM topographic images (665 × 330 nm2 ) of as-deposited films of ODUT and OLUT molecules on HOPG, respectively. The insets represent fast Fourier transforms (FFT) of AFM images of a larger area. The colour scale bars reflect height variations between 0 and 3.5 nm. In the models of ODUT and OLUT molecules shown above the AFM images, atoms are shown as Corey-Pauling-Koltun (CPK) spheres, carbon atoms are displayed in gray, hydrogen in white, oxygen in red and nitrogen in blue.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

eral micrometers and a width consistent with the length of the molecule (ca. 5.6 nm) in its extended conformation (see Figure 2A). Induced by the 3-fold symmetry of the substrate, assembled polymers were oriented mainly in three directions. The significant changes induced in as-deposited film in the course of long time storage, manifest the remarkable dynamics of OLUT molecules at RT. In this context, real-time AFM imaging allowed visualizing the process of structure formation. As indicated in Figure 2C-up and down (the red rectangles mark the same areas), subsequent AFM images at a time-interval of 30 min show the formation and growth of assemblies supra-molecular polymers. We tentatively attribute this ordering process to the the progressive formation of hydrogen bonds, evidenced by the following scenario: In AFM images (for example Figure 2A), we observed 1D long (micrometer range) supra-molecular polymers having a constant width consistent with the length of the molecules, either as isolated polymers or arranged in domains of closely packed polymers. As an example, Figure 2B shows a typical individual 1D supra-molecular polymer. The huge length compared to the much smaller width of the supra-molecular polymers indicates that the growth rate of polymers is much faster than the rate of assembly of polymers in domains. The fast growth rate of supra-molecular polymers is associated with strong hydrogen bonding forces along the polymer long axis as compared to weak vdW forces which are responsible for the lateral growth. Both growth rates, however, can be slowed down through the influence of kinks induced by cis-double bonds. In comparison, for simple alkanes with a length comparable to OLUT or ODUT, which interact in all directions only through vdW forces (i.e., without directional hydrogen bonding), the formation of 2D domains rather than 1D polymers was observed. 36 In comparison to OLUT, we never observed very long (compared to their width) 1D supra-molecular polymers for ODUT molecules. Indeed, the lack of more flexible cis-double bonds allows better close packing of neighboring molecules and thus faster lateral growth and domain formation. Moreover, better registry of ODUT molecules with the HOPG substrate results in a higher adsorption strength and thus higher nucleation rate (per unit area) in


Page 10 of 35

Page 11 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


OLUT after 1 year

13 .6 6mn nm

A 0

mn 00 .0

B

C

D

Figure 2: AFM topographic images of (A)-(C) samples containing OLUT molecules after one year storage at RT under ambient conditions, and (D) thin film of as-deposited ODUT molecules. (B) An individual long supra-molecular polymer whose width is consistent with the maximum length of ca. 5.6 nm of an OLUT molecule. (C)-up and down for OLUT, and (D)-up and down for ODUT are subsequent AFM images (separated by 30 minutes, due to the acquisition time for each image) which illustrate the dynamics of the molecules at RT, i.e., representing a real-time observation of the growth and formation of the supra-molecular polymers. The size of the images are 1000 × 618 nm2 for (A), 30 × 510 nm2 for (B), 80 × 230 nm2 for (C), 26 × 30 nm2 for (D)-right and 19 × 36 nm2 for (D)-left.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

comparison to OLUT molecules. Consequently, due to rapid alignment of molecules on the surface of graphite, even at the early stages of ordering, the number of the ordered domains increased. Thus, the resulting supra-molecular polymers can only grow within the area be√ tween nucleation sites, i.e., for a distance proportional to 1/ n, where n is the nucleation rate (per unit area).

The detectable real-time dynamics of self-assembly was not exclusive to OLUT molecules. As highlighted by the dotted rectangles in Figure 2D, we also observed a similar dynamical behavior for ODUT molecules. However, there exists a remarkable difference (in comparison to the structures formed by OLUT molecules). For ODUT, no changes in the overall structure over long distances was ever observed, even after long annealing times at RT. The rather stable morphology of ODUT may be attributed to the more prominent role of the molecule-substrate interactions in controlling the self-assembly process due to a better registry of ODUT molecules with the underlying crystalline lattice of HOPG, already relevant at early stages of self-assembly. 37

To explain the observed patterns and the dynamical behavior, we have to consider a number of effects. We need to discuss and carefully evaluate the influence of molecular conformation on the self-assembly process, on molecular dynamics and the kinetics of structure formation. To this end, we have performed MD simulations, presented in the next section.

Single-chain dynamics probed by simulations Disorder induced by the molecular architecture Before modelling of the OLUT/ODUT arrays, the adsorption behaviour of single bis-urea derivatives is studied to define preferential molecular geometries and orientations of the adsorbate molecules on atomically smooth surface. This setup is important since the friction at the interface determines crystal growth. The translational dynamics can be accurately 12 ACS Paragon Plus Environment

Page 12 of 35

Page 13 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


described using a macroscopic diffusion equation with a time-dependent lateral diffusion coefficient, D(t). 38 In Supporting Information (Figure S2) we provide a set of snapshots showing typical conformations adopted by bis-urea derivatives on HOPG. The epitaxial alignment of ODUToctadecyl chains over HOPG lattice is observed, which is the result of attractive van der Waals forces between underlying surface and saturated alkyl chains being maximized. Indeed, the octadecyl chains are mostly in extended conformation, which is favoured by the coincidence between the lattice points of HOPG and saturated alkyl chain zigzag. Here the cis-double bond preserves the kinked molecular geometry. The radius of gyration calculated over the trajectory of 10 ns suggests more compact, folded conformation for OLUT and more elongated one for ODUT (see Figure S3 in Supporting Information). A single cis-double bond makes the OLUT chain more flexible: first of all, the rotation around single bonds on both sides from double bond becomes almost barrier-free. It is also less commensurate with the lattice of the graphite surface. Inspection of OLUT shape in adsorbed state suggests that association of the side chains with graphite surface is facilitated by both short terminal alkyl tails and segments located between double bond and urea residue, which leads to a weakened OLUT/HOPG coupling. To identify the orientation of individual molecules and their fragments in the adsorbed state, we characterized the pseudo-dihedral angle between the benzene ring of toluene and the graphite plane, as well as torsion angles which define the rotation around single bonds linking benzene ring and urea-groups (see Figure S4 in Supporting Information). The results indicate that deviation from a quasi planar orientation is more pronounced for OLUT than for ODUT, indicating that a substantial fraction of the molecules has tilted orientation of the central ring. To explore the mobility of OLUT/ODUT single chain on graphite, the mean square displacement (MSD, ˚ A) for a short time of 1500 ps is calculated (see Figure S5 in Supporting Information). We find that having different substituting groups saturated and with one double



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

bond leads to noticeable differences in the diffusivity. The D(t) value, as determined by the Einstein diffusion equation for 2D systems, varies from 7.15±0.087·10−5 to 5.55±0.020·10−5 cm2 /s for OLUT and ODUT derivative, respectively. Strong alkyl chain/surface interactions discussed above lead to limited ODUT mobility within the surface layer, and align the commensurable side chains along the crystallographic directions of HOPG, that corroborates our experimental findings for as-deposited films of ODUT. In contrast, OLUT molecule diffuses faster on graphite substrate, i.e. specific atomistic details of the adsorbate molecule appear to have a significant effect on the dynamics at the level of individual molecules. As a consequence, in contrast to OLUT, ODUT has side-groups which are more rapidly aligning parallel and thus ODUT molecules more rapidly form supra-molecular polymers. This faster process also translates into a higher nucleation rate (per unit area). Similar conclusions about slower dynamics of saturated chains have been drawn by Atkin et al. from quantum-chemical calculations of the adsorbed molecules on graphite surface. 39

Properties of multi-chain assemblies favored by hydrogen bonds For the multichain systems, the intermolecular interactions are coming into play, and as expected, the impact of cis-double bonds can be reduced by molecular self-assembling via HBs. As it follows from experimental findings, the organization of ODUT starts immediately and results in assemblies, whose ordering is guided by the three fold symmetry pattern of the HOPG substrate. The MD modelling of the first stages of self-assembly (30 ns after ”deposition”) of 20 randomly oriented bis-urea molecules near graphite surface is depicted in Figure 3. The separated ODUT nanorows with 3-5 hydrogen-bonded molecules in each are obtained, which form nano-assemblies containing up to 9 aligned molecules stabilized via both HBs between urea groups and registry with the substrate. For OLUT derivative the ciskink prevents rapid self-ordering, but nonetheless after 30 ns embryonic nanorows with 2-3 hydrogen-bonded molecules are observed, showing the initial self-assembly from the bottom up. Thus, hydrogen bonding overcomes the hurdles encoded in molecular constitution.


Page 14 of 35

Page 15 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


A

10 nm

B

8 nm

C

10 nm

D

8 nm

Figure 3: Snapshots of ODUT (A, B) and OLUT (C, D) self-assemblies on HOPG after 15 ns (A, C) and 30 ns (B, D) MD runs. The total number of HBs is 11 (A), 18 (B), 3 (C) and 6 (D). See Supporting Information for further details. To describe hydrogen bonding, the definition suggested by Luzar and Chandler is applied. 40



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

In addition to this important conclusion, a molecular packing scheme for nanostructures can be proposed. The width of the assemblies and the intermolecular distance within this supra-molecular polymer were calculated to be ca. 5 nm (consistent with the AFM measurements) and 0.5 nm, respectively. The latter value is in a very good agreement with the distances found for hydrogen-bonded urea moieties (0.462 ±0.005 nm, 33,41 0.47 ±0.02 nm 26 ). The preorganized motifs for further simulations include 12 bis-urea molecules, forming one polymer with two possible motifs (parallel and antiparallel) of H-bonding for each derivative. The snapshots of OLUT/ODUT assemblies after 10 ns MD annealing at 300 K on HOPG are collected in Figure 4. The radius of gyration of individual chain in assemblies indicates the previously obtained trend for isolated molecules in the adsorbed state (see Figures S3 and S6): the ODUT molecules still adopt more extended conformations as compared to the OLUT molecules, whose geometry reminds zigzag. Moreover, stripes remain closely packed (OLUT, parallel and both motifs for ODUT) due to the locking of the hydrogen bonds between the urea groups, and a collective steric effect leads to an increase in radius of gyration as compared to the isolated molecules on HOPG. The 2D character of adlayers follows from the concentration profiles (Figure 5), which describe the density changes along z -axis of the simulation box. The position of the single peak at ca. z =4 ˚ A coincides with previously obtained results for alkanes 38 and alkyl-substituted thiophenes. 28 OLUT molecules form more flattened structure on graphite, whereas the density plot for ODUT derivative shows a shoulder at ca. z =5 ˚ A. The analysis of snapshots (Figure 6) for both HB-motifs reveals a non-planar conformation of the conjugated ”ureatoluene-urea” molecular segments, in which toluene rings are tilted owing to the intermolecular hydrogen bonding, which is strong (classification of Jeffrey and Saenger 42 ) as follows from the evaluation of HB lengths. It is noteworthy that the ODUT supra-molecular assemblies have different overall geometry (Figure 4, bottom panel) depending on the motif of H-bonding involved in the stabilization of supra-molecular architectures: the molecular long axes are shifted for an-


Page 16 of 35

Page 17 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


A

B

OLUT

ODUT

Figure 4: Snapshots of OLUT and ODUT assemblies on HOPG after 10 ns MD runs starting from A - antiparallel and B - parallel motifs of preorganized supra-molecular assemblies according to Ref. 26



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

tiparallel motif, and remain in face-to-face position for parallel one. On the one hand we can assume that this is so-called finite size effect in simulations. Indeed, the graphite surface is large enough to accommodate many OLUT assemblies. On the other hand, the ODUT assemblies with parallel motif of HBs maintains its rectangular shape. To understand this shape variation, both the intermolecular toluene-toluene distance in rows and an averaged mutual orientation of the plane of the toluene ring and graphite surface are determined (see Figures S7 and S8). The distances between the centroids of the toluene aromatic rings is shorter for the HBs with antiparallel motif, which is caused by greater deviation of conjugated segment from planarity, when the rings stand upright with respect to the substrate. In contrast to broader distribution of angles for antiparallel motif, the counterpart is characterized by bimodal function with peaks located at 350 and 750 , showing tilted orientation of the rings, which explains larger distances between the centroids. The snapshots of both systems, which are shown in Figure S7, support our conclusion about preferential tilting of the rings for ODUT assemblies with parallel motif of HBs - all rings point out in one direction. Finally, considering the lateral diffusion of assemblies on graphite surface, we observe noticeable slowdown in dynamics as compared to the behavior of isolated molecules: the D(t) value is 1.42±0.058·10−5 and 1.09±0.019·10−5 cm2 /s for ODUT and 1.79±0.027·10−5 and 2.11±0.091·10−5 cm2 /s for OLUT derivative with anti- and parallel motif, respectively. As suggested by the AFM experiments, the simulations clearly show that OLUT ribbons have a faster diffusion on HOPG in contrast to ODUT ribbons, providing longer time to form supra-molecular polymer.

Conclusions The kinetic processes of 2D self-assembly of two bis-urea molecules, differing only by a single cis-double bond in their side groups, were investigated by AFM and computer simulation in order to explore the role of dynamic disorder induced by flexible double-bonds and the


Page 18 of 35

Page 19 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5: Density profiles C (z ) of preorganized monolayers on HOPG surface (graphite at z =0 is shown schematically).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 35

A

B

Figure 6: ODUT hydrogen-bonded supra-molecular assemblies with A - anti- and B - parallel motif according to Ref. 26 Hydrogen bonds are shown as yellow dashed lines. The average O/H length is 1.99±0.18 ˚ A for (A) and 1.98±0.14 ˚ A for (B).


Page 21 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


resulting kinks with respect to the ordering process. We demonstrated that the introduction of a single cis-double bond in the side groups of bis-urea substituted toluene resulted in drastic changes in their 2D self-assembly process on graphite. Molecules containing side chains with saturated bonds, owing to a better comensurability with the substrate lattice, formed ordered structures of supra-molecular polymers which did not change significantly over time. We attribute this difference in temporal stability to a rapid (in comparison to molecules with unsaturated bonds in the side groups) alignment of molecules on the surface and thus rapid formation of supra-molecular polymers. The faster alignment process translates into a higher nucleation rate for molecules with saturated side chains. By contrast, upon deposition molecules with unsaturated bonds in the side chains did not self-assemble into any long-range ordered structures. Cis-double bond caused distortion at a molecular level and enhanced the flexibility of the alkyl side-chains. Due to this comparatively high flexibility, perfect commensurability with the graphite lattice was less frequently established, which, in turn, resulted in a lower nucleation rate. The kink-induced perturbed moleculesubstrate interactions, in turn, emphasized the influence the hydrogen bonding (moleculemolecule interactions) on the self-assembly process. As a consequence of a low nucleation probability, domains of micrometer-long aligned supra-molecular polymers were formed in the course of time. Our study identifies a general pathway for enhancing the length of supra-molecular polymers and for generating long substrate-guided assemblies of 1D supramolecular polymers via a specific tailoring of the molecular architecture.

Acknowledgement The authors are very grateful to the Center for Information Services and High Performance Computing of the Technische Universität Dresden for providing CPU time. We acknowledge funding support from Deutsche Forschungsgemeinschaft (IRTG Soft Matter Science(GRK 1642 )).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Supporting Information Available Description of synthesis procedure, FT-IR experiments on solid samples, structural formulas of molecules, details of molecular arrangements within the self-assembled layer given by computer simulations. This material is available free of charge via the Internet at http://pubs.acs.org/.

References (1) Lehn, J.M. Perspectives in Supramolecular Chemistry−From Molecular Recognition towards Molecular Information Processing and Self-Organization. Angew. Chem. Int. Ed. Engl. 1990, 29, 1304-1319. (2) Stang, P. J.; Olenyuk, B. Self-Assembly, Symmetry, and Molecular Architecture: Coordination as the Motif in the Rational Design of Supramolecular Metallacyclic Polygons and Polyhedra. Acc. Chem. Res. 1997, 30, 502-518. (3) Shokri, R.; Lacour, M.-A.; Jarrosson, T.; L` ere-Porte, J.-P.; Serein-Spirau, F.; Miqueu, K.; Sotiropoulos , J.-M.; Vonau, F.; Aubel, D.; Cranney, M; et al. Generating Long Supramolecular Pathways with a Continuous Density of States by Physically Linking Conjugated Molecules via Their End Groups. J. Am. Chem. Soc. 2013, 135, 56935698. (4) Shokri, R.; Vonau, F.; Cranney, M.; Aubel, D.; Narladkar, A.; Isare, B.; Bouteiller, L.; Simon, L.; Reiter, G. Consequences of Varying Adsorption Strength and Adding Steric Hindrance on Self-Assembly of Supramolecular Polymers on Carbon Substrates. J. Phys. Chem. C 2012, 116, 21594-21600. (5) Levine, Y. K.; Kolinski, A.; Skolnick, J. Monte Carlo Dynamics Study of Motions in Cis-Unsaturated Hydrocarbon Chains. J. Chem. Phys. 1991, 95, 3826-3834.


Page 22 of 35

Page 23 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6) Rey, A.; Kolinski, A.; Skolnick, J.; Levine, Y. K. Effect of Double Bonds on the Dynamics of Hydrocarbon Chains. J. Chem. Phys. 1992, 97, 1240-1249. (7) Chia, N.-C.; Mendelsohn, R. Conformational Disorder in Unsaturated Phospholipids by FTIR Spectroscopy. Biochimica et Biophysica Acta (BBA)-Biomambranes 1996, 1283, 141-150. (8) Wells, D.; Fong, C.; Drummond, C. J. Nonionic Urea Surfactants: Formation of Inverse Hexagonal Lyotropic Liquid Crystalline Phases by Introducing Hydrocarbon Chain Unsaturation. J. Phys. Chem. B 2006, 110, 12660-12665. (9) Zhang, R.; Möhwald, H. M.; Kurth, D. G.; One-Step Formation of Straight Nanostripes from a Mammal Lipid-Oleamide Directly on Highly Oriented Pyrolytic Graphite. Langmuir 2009, 25, 2290-2293. (10) Ravicz, W.; Olbrich, K. C.; McIntosh, T.; Needham, D.; Evans, E.; Effect of Chain Length and Unsaturation on Elasticity of Lipid Bilayers. Biophys. J. 2000, 79, 328-339. (11) Binder, H.; Gawrish, K.; Effect of Unsaturated Lipid Chains on Dimensions, Molecular Order and Hydration of Membranes. J. Phys. Chem. B 2001, 105, 12378-1239. (12) Smith, E. A.; Smith, C.; Tanksley, B.; Dea, P. K.; Effects of cis- and trans-unsaturated Lipids on an Interdigitated Membrane. Biophys. Chem. 2014, 190-191, 1-7. (13) Garnier, F.; Yassar, A.; Hajlaoui, R.; Horowitz, G.; Deloffre, F.; Servet, B.; Ries, S.; Alnot, P. Molecular Engineering of Organic Semiconductors: Design of Self-Assembly Properties in Conjugated Thiophene Oligomers. J. Am. Chem. Soc. 1993, 115, 87168721. (14) Barth, J. V.; Costantini, G.; Kern, K. Engineering Atomic and Molecular Nanostructures at Surfaces. Nature 2005, 437, 671-679.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(15) Li, J.; Li, X.; Ni, X.; Wang, X.; Li, H.; Leong, K. W. Self-Assembled Supramolecular Hydrogels Formed by Biodegradable PEO−PHB−PEO Triblock Copolymers and αcyclodextrin for Controlled Drug Delivery. Biomaterials 2006, 27, 4132-4140. (16) Lindsey, J. S. Self-Assembly in Synthetic Routes to Molecular Devices. Biological Principles and Chemical Perspectives: A Review. New J. Chem. 1991, 15, 153-179. (17) Zhang, S. Emerging Biological Materials Through Molecular Self-Assembly. Biotechnology Advances 2002, 20, 321-339. (18) Jahanshahi, K.; Botiz, I.; Reiter, R.; Thomann, R.; Heck, B.; Shokri, R.; Stille, W.; Reiter, G. Crystallization of Poly(γ-benzyl L-glutamate) in Thin Film Solutions: Structure and Pattern Formation. Macromolecules 2013, 46, 1470-1476. (19) Lortie, F.; Boileau, S.; Bouteiller, L.; Chassenieux, C.; Deme, B.; Ducouret, G.; Jalabert, M.; Laupretre, F.; Terech, P. Structural and Rheological Study of a Bis-urea Based Reversible Polymer in an Apolar Solvent. Langmuir 2002, 18, 7218-7222. (20) Bouteiller, L.; Colombani, O.; Lortie, F.; Terech, P. Thickness Transition of a Rigid Supramolecular Polymer. J. Am. Chem. Soc. 2005, 127, 8893-8898. (21) Simic, V.; Bouteiller, L.; Jalabert, M. Highly Cooperative Formation of Bis-Urea Based Supramolecular Polymers. J. Am. Chem. Soc. 2003, 125, 13148-13154. (22) Bouteiller, L. Assembly via Hydrogen Bonds of Low Molar Mass Compounds into Supramolecular Polymers. Adv. Polym. Sci. 2007, 207, 79-112. (23) Gittes, F.; Mickey, B.; Nettleton, J.; Howard, J. Flexural Rigidity of Microtubules and Actin Filaments Measured from Thermal Fluctuations in Shape. J. Cell Biol. 1993, 120, 923-934. (24) Vonau, F.; Suhr, D.; Aubel, D.; Bouteiller, L.; Reiter, G.; Simon, L. Evolution of Multilevel Order in Supramolecular Assemblies. Phys. Rev. Lett. 2005, 94, 066103(1-4). 24 ACS Paragon Plus Environment

Page 24 of 35

Page 25 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25) Vonau, F.; Suhr, D.; Aubel, D.; Bouteiller, L.; Reiter, G.; Simon, L. Cooperative Rearrangements Leading to Long Range Order in Monolayers of Supramolecular Polymers. Phys. Rev. Lett. 2007, 99, 086103(1-4). (26) Vonau, F.; Linares, M.; Isare, B.; Aubel, D.; Habar, M.; Bouteiller, L.; Reiter, G.; Geskin, V.; Zerbetto, F.; Lazzaroni, R.; et al. Branched Substituents Generate Improved Supramolecular Ordering in Physisorbed Molecular Assemblies. J. Phys. Chem. C 2009, 113, 4955-4959. (27) Vonau, F.; Shokri, R.; Aubel, D.; Bouteiller, L.; Guskova, O.; Sommer, J.-U.; Reiter, G.; Simon, L. Tunneling Spectroscopy Measurements on Hydrogen-Bonded Supramolecular Polymers. Nanoscale 2014, 6, 8250-8256. (28) Guskova, O.A.; Mena-Osteritz, E.; Schillinger, E.; Khalatur, P.G.; Bäuerle, P.; Khokhlov, A.R. Self-Assembled Monolayers of β−Alkylated Oligothiophenes on Graphite Substrate: Molecular Dynamics Simulation. J. Phys. Chem. C 2007, 111, 7165-7174. (29) Guskova, O.A.; Khalatur, P.G.; Bäuerle, P.; Khokhlov, A.R. Silk-inspired ”Molecular Chimeras”: Atomistic Simulation of Nanoarchitectures Based on Thiophene-Peptide Copolymers. Chem. Phys. Lett. 2008, 461, 64-70. (30) Sun, H. Ab initio Calculations and Force Field Development for Computer Simulations of Polysilanes. Macromolecules 1995, 28, 701-712. (31) Plimpton, S.J. Fast Parallel Algorithms for Short−Range Molecular Dynamics. J. Comput. Phys. 1995, 117, 1-19. (32) Materials Studio Release Notes, Release 7.0; Accelrys Software, Inc.: San Diego, CA, 2014.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(33) Gesquière, A.; Abdel-Mottaleb, M.M.S.; De Feyter, S.; De Schryver, F.C.; Schoonbeek, F.; Van Esch, J.; Kellogg, R.M.; Feringa, B.L.; Calderone, A.; Lazzaroni, R.; et al. Molecular Organization of Bis-urea Substituted Thiophene Derivatives at the Liquid/Solid Interface Studied by Scanning Tunneling Microscopy. Langmuir 2000, 16, 10385-10391. (34) Miao, X.; Chen, C.; Zhou, J.; Deng, W. Influence of Hydrogen Bonds and Double Bonds on the Alkane and Alkene Derivatives Self-assembled Monolayers on HOPG Surface: STM Observation and Computer Simulation. Appli. Surf. Sci. 2010, 256, 4647-4655. (35) Copie, G.; Cleri, F.; Makoudi, Y.; Krzeminski, C.; Berthe, M.; Cherioux, F.; Palmino, F.; Grandidier, B. Surface-Induced Optimal Packing of Two-Dimensional Molecular Networks. Phys. Rev. Lett. 2015, 114, 066101(1-5). (36) Magonov, S. N.; Yerina, N. A. High-Temperature Atomic Force Microscopy of Normal Alkane C60 H122 Films on Graphite. Langmuir 2003, 19, 500-504. (37) Hooks, D. E.; Fritz, T. Ward, M. D. Epitaxy and Molecular Organization on Solid Substrates Authors. Adv. Mater. 2001, 13, 227-241. (38) Park, J.H.; Aluru, N.R. Surface Diffusion of n−Alkanes: Mechanism and Anomalous Behavior. Chem. Phys. Lett. 2007, 447, 310-315. (39) Page, A.J.; Elbourne, A.; Stefanovic, R.; Addicoat, M.A.; Warr, G.G.; Vo¨ıtchovsky, K.; Atkin, R. 3-Dimensional Atomic Scale Structure of the Ionic Liquid−Graphite Interface Elucidated by AM-AFM and Quantum Chemical Simulations. Nanoscale 2014, 6, 81008106. (40) Luzar, A.; Chandler, D. Hydrogen-Bond Kinetics in Liquid Water. Nature 1996, 379, 55-57. (41) van Esch, J.; De Feyter, S.; Kellogg, R.M.; De Schryver, F.; Feringa, B.L. Self-assembly


Page 26 of 35

Page 27 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of Bisurea Compounds in Organic Solvents and on Solid Substrates. Chem. Eur. J. 1997, 3, 1238-1243. (42) Jeffrey, G.A; Saenger, W. Hydrogen Bonding in Biological Structures. Springer-Verlag, New York, 1991.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Graphical TOC Entry

Formation of long Supra-molecular polymers on graphite as a consequence of a single double bond within the side -groups


Page 28 of 35

Page 29 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


A 3.53.64nm nm

0

-0.03 nm

B 3.53.83nm nm

ACS Paragon Plus Environment

0

0.00 nm


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

OLUT after 1 year

Page 30 of 35

13 .6 6mn nm

A 0

mn 00 .0


B

C

D

Page 31 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58

A


10 nm

B

8 nm

C

10 nm

D


8 nm

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

A


OLUT

ODUT ACS Paragon Plus Environment

B

Page 32 of 35

Page 33 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42




1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Page 34 of 35

A

B


Page 35 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15


Formation of long Supra-molecular polymers on graphite as a consequence of a single double bond within the side -groups ACS Paragon Plus Environment

Consequences of a Single Double Bond within a Side Group on the

Recommend Documents