Halogen Substituent Effects on Concentration-Controlled Self

Subscriber access provided by UNIV OF LOUISIANA

C: Surfaces, Interfaces, Porous Materials, and Catalysis

Halogen Substituent Effects on Concentration-Controlled Self-Assembly of Fluorenone Derivatives: Halogen Bond versus Hydrogen Bond Meiqiu Dong, Kai Miao, Juntian Wu, Xinrui Miao, Jinxing Li, Peng Pang, and Wenli Deng J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b12176 • Publication Date (Web): 23 Jan 2019 Downloaded from http://pubs.acs.org on January 28, 2019

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 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 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.

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 34 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

Halogen Substituent Effects on Concentration-Controlled SelfAssembly of Fluorenone Derivatives: Halogen Bond versus Hydrogen Bond

Meiqiu Dong, Kai Miao, Juntian Wu, Xinrui Miao,* Jinxing Li, Peng Pang, Wenli Deng*

College of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, People’s Republic of China

*E-mail：[email protected] *E-mail：[email protected]

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 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 2 of 34

ABSTRACT: Self-assembled behaviors of three fluorenone derivatives substituted by different halogen atoms, 2-(pentadecyloxy)-6-bromo-fluorenone (Br-FC15), 2-(pentadecyloxy)-6-chlorofluorenone (Cl-FC15) and 2-(pentadecyloxy)-6-fluoro-fluorenone (F-FC15), were investigated at the 1-phenyloctane/HOPG interface by scanning tunneling microscopy (STM) combined with density functional theory (DFT) calculations in comparison to the self-assembly of 2-pentadecyloxyfluorenone (H-FC15). It is found that the different charge distribution on the halogen substituents leads to the subtle change of the molecular packing nanostructures. By varying the solution concentrations, X-FC15 (X = Br, Cl, H) can self-assemble into polymorphic nanostructures, whereas only one pattern can be observed for F-FC15 adlayer due to the stronger continuous C−H···F bonds. The intermolecular C−H···O=C hydrogen bonds are the main driving forces for all the self-assembled patterns. Particularly, the halogen-based hydrogen bonds and the type-I X···X (X = Br, Cl) bonds act as the collaborative forces to stabilize the alternate adlayers. Furthermore, the halogen bonds (C−Br···O=C and C−Cl···O=C) make the crucial contribution to the distinct lamellar and the dumbbell-like patterns. The investigation suggests that the engineering of organic nanoarchitectures can be effectively tailored by the introduction of different halogen atoms.

2


Page 3 of 34 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 As the on-surface bottom-up engineering for novel organic nanoarchitectures with specific electronic properties, molecular self-assembly has received tremendous attention for decades.1−4 With its atomic resolution, scanning tunneling microscopy (STM) has been proven to be a powerful tool to visualize the nanometer-scale self-assembled structures, giving us a better understanding of the nature of selfassembly phenomena on atomically flat conductive surfaces.5−8 It has been widely reported that twodimensional (2D) self-assembled supramolecular architectures can be tailored by exploiting intermolecular

interactions,6−8

including

molecule−molecule,

molecule−solvent,

and

molecule−substrate interactions. In addition, designing building blocks and external condition changes (such as solvent and concentration) have been demonstrated to play crucial roles in the formation of 2D nanostructures.4−8 In the field of noncovalent interactions, hydrogen bonding is widely studied for its crucial role in constructing structural polymorphism.9−14 As a weak noncovalent interaction similar to hydrogen bonding, halogen bonding, used extensively in three-dimensional (3D) crystal engineering, has been considered as an appealing tool in 2D molecular self-assembly in recent years.15−17 In general, halogen bonding arised from polarizability of the halogen atom along the C−X axis plays a crucial role in the construction of such 2D self-assembled structures.18−23 To the best of our knowledge, the effects of different halogen substituents in the 2D self-assembly have rarely been investigated.24−30 In previous studies, since the positive potential of the σ-hole along the C−X axis decreased in the order I > Br > Cl > F = 0, the tiny change of halogen substituents can drastically affect the formation of 2D nanoarchitectures, such as lattice matching,24 diversity,25, 28 type of adsorption,26 and degree of order.30 However, the internal mechanism of different halogen substituents affecting the self-assembled structure still remains obscure. Further in-depth research on the effects of different halogen substituents 3



Page 4 of 34

on the resulting intermolecular interactions should be extremely promoted for engineering novel interfacial supramolecular nanostructures. Understanding the role of intermolecular interactions dramatically affected by solution concentration and the nature of building blocks in driving the self-assembly is of particular importance in the formation of 2D nanostructures. Most of the current work associated with halogen bonding is concerned with the self-assembly of only halogen substituted molecules, while the interplay of multiple functional groups and halogen substituents has not been investigated widely.18,

20, 31

In

addition, the formation mechanism of halogen bonds in molecular self-assembly is still not clearly revealed. Previously, we have investigated the 2D self-assembly of halogen substituted thienophenanthrene derivatives. It was found that the position and type of the halogen atoms had significant influence on the final nanostructures.25,

32, 33

The competition and cooperation of the

intermolecular hydrogen bond and halogen bond between the −COOH and Br could induce different self-assembled patterns.34 Recently, we have demonstrated that the structural polymorphism in the self-assembly of fluorenone derivatives was attributed to the presence of multiple binding sites, such as hydroxyl and carboxylic acid groups and carbonyl groups.12, 35 The hydrogen bonds between −OH or −COOH and O=C are the main driving forces to thermodynamically stabilize the nanostructures. We speculate that when the −OH on the fluorenone derivative is substituted by the halogen atom, the halogen bonding could be formed between the halogen atom and O=C and acts as the dominated role in the formation of nanostructures. In order to gain a deep insight into the cooperation and the competition of the driving forces (hydrogen bonding and halogen bonding) behind these processes, a systematic study on the effects of halogen substituent on the self-assembly of fluorenone derivatives is necessary. 4


Page 5 of 34 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


Herein, three fluorenone derivatives which are substituted by different halogen atoms (X-FC15, X = Br, Cl, F) are synthesized (Figure 1a) and their self-assembled behaviors at the 1phenyloctane/HOPG interface with varying solution concentrations are investigated by scanning tunneling microscopy combined with density functional theory (DFT) calculations compared with the fluorenone derivative H-FC15 for the first time. Three types of nanostructures can be obtained by the adsorption of Br-FC15 and Cl-FC15 on the HOPG surface at different concentrations, whereas only one pattern can be observed in the assembled adlayer of F-FC15. Unexpectedly, the hydrogen bonds (C−H···O=C) instead of the X···O=C halogen bonds are the main driving forces for the self-assembly. The halogen-based hydrogen bonds (H···X) and type-I X···X bonds act as collaborative forces in the formation of the alternate patterns, while the halogen bonds (X···O=C) play an important role in the formation of the distinct nanostructures. DFT calculations provide a deeper insight into the roles of halogen substituents in the self-assembly of fluorenone derivatives at the 1-phenyloctane/HOPG interface.

EXPERIMENTAL Br-FC15, Cl-FC15, F-FC15, and H-FC15 molecules were synthesized as described in reported literature.36, 37 1-Phenyloctane (TCI, 99.9%) was used as received without further purification. The sample solutions were prepared by dissolving the compounds in 1-phenyloctane (concentration = 10−6 − 10−4 M). A droplet of the sample solutions was deposited onto the atomically flat surface of highly oriented pyrolytic graphite (HOPG) which was freshly cleaved using adhesive tape. All the STM images were collected under ambient conditions in the constant-current mode on a Nanoscope IIIa Multimode SPM (Bruker, USA) within 3 h. Tips were prepared from mechanically cut Pt/Ir wire 5



Page 6 of 34

(80/20). All of the STM measurements were repeated with different tips and samples to check the reproducibility and avoid possible artifacts at room temperature (25 − 30 °C). The corresponding tunneling parameters of each image were marked in figure captions. The STM tip was biased at positive voltage relative to the sample. The unit cell parameters were obtained through manual measurement of STM images for several times from different high-resolution STM images after performing the drift correction on them using SPIP software, and then the mean value and standard deviation were calculated. The structural models were built by Material Studio 7.0 based on the chemical structures of molecules and the high-resolution STM images. DFT calculations were carried out using the Gaussian 09 software package. The geometry optimizations were performed using the M06-2X method together with the polarized 6-31G(d) basis set. The topological properties of the electron densities in all the complexes were assessed using the Multiwfn program38 and visualized with the VMD program.39

RESULTS AND DISCUSSION

Figure 1. (a) Chemical structures of fluorenone derivatives. (b) Calculated 3D charge density maps 6


Page 7 of 34 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


and HOMO of fluorenone derivatives. The distribution of positive charges on Br and Cl atoms are reflected in the enlarged insets. The alkoxy side chain is replaced by the methoxy group. The map color scales from −5 (blue) to +5 (red) kcal mol−1. Chemical structures of fluorenone derivative molecules (Br-FC15, Cl-FC15, F-FC15, and HFC15) and their 3D charge density maps are displayed in Figure 1. Each molecule includes a fluorenone moiety substituted by different atoms (X-FC15, X = Br, Cl, F, and H) with dipole moment ranged from 4.15 to 4.66 D (Figure S1). As depicted in Figure 1b, it could be found that the distribution of electrostatic potential on the surface of the halogen atoms is different. A positive σ-hole is located on the exterior along the axes of C−X (X = Br, Cl) bonds, while the areas perpendicular to the axes are surrounded by negative charges. The σ-hole of the Br group is bigger than that of the Cl group. Thus halogen bonds (XB) might be formed through the interaction between the electrophilic region associated with a halogen (X) atom and the negative region of the same halogen on an adjacent molecule or another electronegative atom. However, only negative charges are distributed all around the F atom. This distinct charge distribution will inevitably lead to the acquisition of polymorphs. Thus, STM experiments for four fluorenone derivatives are performed at the liquid/solid interface using 1phenyloctane as the solvent. As is generally found in fluorenone systems,40 the appearance of the conjugated cores of X-FC15, (X = Br, Cl, F, and H) in the STM images under the positive bias voltage are strongly associated with the highest occupied molecular orbital (HOMO) of the molecules (Figure 1b and S2). Hence, the molecular conformations could be obtained from the STM images (ESI). Self-Assembly of Br-FC15 at the 1-Phenyloctane/HOPG Interface. By varying the solution concentrations, Br-FC15 substituted by a Br atom could self-assemble into three distinct nanostructures at the 1-phenylotane/graphite interface, as shown in the Figure 2 and S3. At high 7



Page 8 of 34

solution concentration, the entire monolayer is dominated by a lamellar pattern. STM image (Figure 2a) reveals that each trough consists of tetramer and hexamer, which alternately align along the trough randomly. All the molecules form the two-row arrangement and pack in a head-to-head fashion. The structural model is proposed in Figure 2d. As depicted in the bottom-right enlarged inset of Figure 2d, the molecules within these complexes are bonded in the same way. In each tetramer or hexamer, the Br-FC15 molecules in the same side arrange in parallel and connect through C−H···O=C and C−H···Br hydrogen bonds. The molecules in neighboring sides align in antiparallel through C−H···Br hydrogen bonds and type-I Br···Br bonds. The conjugated cores in adjacent sides of the tetramers or hexamers arrange in pairs by antiparallel dipole–dipole interaction (Figure S4a), minimizing the overall polarity of the entire monolayer. It is worth mentioning that some dark contrast horizontal lines could be observed in the STM image indicated by red arrows in Figure 2a. The corresponding molecules are marked with red color on the model in Figure 2d. This experimental phenomenon indicates that the molecules are unsteadily adsorbed on the HOPG surface.41 It can be illustrated by the bonding scheme at the joint of adjacent oligomers along the same trough, which is presented in the bottom-left enlarged inset of Figure 2d. The C−Br···O=C halogen bond and C−H···Br hydrogen bond are formed between left two molecules. The bottom-left molecule is further stabilized with the top-right one by additional C−H···O=C bond, so the bottom-left molecule is more stable than the top-left one. The right two molecules have the similar situation. The bottom-right molecule is less stable than the top-right one. Therefore, the molecules in these two positions (top-left and bottom-right) incline to move due to the lower stability and often create perturbations or dark contrast horizontal lines in the STM scanning. Furthermore, this instability may even give rise to desorption of molecules, as indicated by the green arrow in Figure 2a. These results suggest that the troughs of the complexes in the lamellar pattern are probably stabilized by delicate balance of the hydrogen bonds and the halogen bonds from the internal and joint interaction 8


Page 9 of 34 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 the complexes. The side chains in neighboring troughs are interdigitated and arranged orthogonally with respect to the troughs to maximize the intermolecular van der Waals (vdW) force. The roughly calculated molecular density is 1.51 nm2 per molecule.

Figure 2. High-resolution STM images of self-assembly of Br-FC15 at the 1-phenylotane/HOPG interface. (a) Lamellar pattern (concentration: 3.5 × 10−4 M; tunneling parameters: It = 495 pA, Vb = 681 mV; scale bar: 20 × 20 nm2); (b) Alternate-I pattern (5.4 × 10−5 M; It = 405 pA, Vb = 620 mV; 20 × 20 nm2); (c) Linear-I pattern (6.2 × 10−6 M; It = 455 pA, Vb = 631 mV; 20 × 20 nm2). (d−f) Tentative structural models for the corresponding patterns. Intermolecular interactions are reflected in the enlarged insets. With decreasing the solution concentrations, a new morphology termed as alternate-I pattern could be observed (Figure 2b and S3b). As the high-resolution STM image shown in Figure 2b, the Br-FC15 molecules self-assemble into an alternated one-row and two-row nanostructure. Neighboring two-row molecular lamellae located on both sides of the one-row lamella adopt a mirror arrangement. In addition, the cores of Br-FC15 in two-row molecular lamellae adopt an antiparallel arrangement as the green arrows indicated in Figure 2b. The side chains in neighboring troughs maintain interdigitated 9



Page 10 of 34

arrangement and keep an angle of 60° with the axes of each trough, which provide the additional vdW interaction to stabilize the alternate-I pattern. As shown in the bottom-left enlarged inset of Figure 2e, in each two-row trough, the molecules adopt parallel arrangement combined by C−H···O=C hydrogen bonds and C−H···Br hydrogen bonds. The molecules in the rows next to each other arrange in the head-to-head mode via C−H···Br hydrogen bonds. It is worth noting that the proximity of Br atoms in diagonal molecules can be attributed to the formation of type-I Br···Br bonds, acting as the significant contributor to form the stable alternate-I pattern. In each one-row molecular lamella, two Br-FC15 cores form a dimer with an antiparallel configuration bounded through C−H···O=C hydrogen bonds. Adjacent dimers are linked with C−H···Br hydrogen bonds, as highlighted by the top-right enlarged inset of Figure 2e. The structural model of the alternate-I pattern is presented based on the highresolution STM image in Figure 2e. The unit cell parameters of the alternate-I pattern are a = 1.5 ± 0.2 nm, b = 13.2 ± 0.1 nm, and γ = 90 ± 1°. The calculated molecular density is 1.65 nm2 per molecule. When the concentration is further decreased to CBr-FC15 = 6.2 × 10−6 M, the entire monolayer is covered by a new ordered morphology which is called linear-I pattern (Figure 2c and S3c). In this nanostructure, the arrangement of Br-FC15 in each trough is the same as that in the one-row packing of the alternate-I pattern. By counting the number of chains in the STM image and careful observation, we find that 1-phenyloctane molecules can coadsorb with Br-FC15 and fill in the space between alkoxy chains of Br-FC15 on the HOPG surface due to the space matching and the interchain vdW interaction. Some fuzzy bright dots corresponding to the position of phenyl rings of 1-phenyloctane could be observed in the large-scale STM image (Figure S5) confirming the coadsorption of 1-phenyloctane and desorption of the phenyl rings. The phenyl rings do not appear high contrast as bright dots in the high-resolution STM images (Figure 2c), indicating the phenyl groups of 1-phenyloctane possibly 10


Page 11 of 34 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


desorb from the HOPG surface and are rotated out of plane. The rings are fuzzy and even disappear from the STM images resulting from some motional freedom in the supernatant.42 The tentative structural model of the linear-I pattern is proposed in Figure 2f (1-phenyloctane molecules are marked with yellow color). The unit cell parameters of the linear-I pattern are a = 1.5 ± 0.1 nm, b = 5.8 ± 0.3 nm, and γ = 86 ± 2°. The calculated molecular density is 2.17 nm2 per molecule. Self-Assembly of Cl-FC15 at the 1-Phenyloctane/HOPG Interface. Three polymorphs of ClFC15 could be obtained at different solution concentrations, as shown in Figure 3 and S6. As the concentration is 4.5 × 10−4 M, the coexistence of two different morphologies (alternate-II and dumbbell-like patterns) dominates the entire monolayer on the surface (Figure S6a). Upon decreasing the solution concentrations, the alternate-II pattern (Figure 3a) disappears and the entire monolayer is covered by the dumbbell-like pattern (Figure 3b). The alternate-II pattern (Figure 3a) is similar to that observed in the Br-FC15 monolayer at high concentration. The intermolecular interactions in one-row and two-row troughs are revealed in the enlarged insets of Figure 3d. Comparing with the alternate-I pattern of Br-FC15, the difference of these two nanostructures is that the Br-based bonds in the alternate-I pattern are replaced by the Cl-based bonds in the alternate-II pattern. The tentative structural model of the alternate-II pattern is proposed in Figure 3d. The unit cell parameters for the alternate-II pattern are a = 1.5 ± 0.1 nm, b = 13.5 ± 0.2 nm, and γ = 92 ± 1°. The calculated molecular density is 1.69 nm2 per molecule.

11



Page 12 of 34

Figure 3. High-resolution STM images of self-assembled nanostructures for Cl-FC15 at the 1phenylotane/HOPG interface. (a) Alternate-II pattern (4.5 × 10−4 M; It = 445 pA, Vb = 640 mV; 20 × 20 nm2); (b) Dumbbell-like pattern (6.1 × 10−5 M; It = 485 pA, Vb = 622 mV; 20 × 20 nm2); (c) LinearII pattern (4.2 × 10−6 M; It = 465 pA, Vb = 665 mV; 20 × 20 nm2). (d−f) Tentative structural models for the corresponding patterns. Intermolecular interactions are reflected in the enlarged insets. Figure 3b shows the molecular packing details of the dumbbell-like pattern. Twelve Cl-FC15 molecules arrange with two-row and form a dodecamer. A dodecamer with a neighboring one-row tetramer in each trough form the basic unit of the dumbbell-like pattern. The chains in the neighboring lamellae are interdigitated and perpendicular to the troughs, giving rise to favorable chain–chain interaction. Similar with two-row troughs in the alternate-II pattern, in each dodecamer, two neighboring Cl-FC15 molecules adopt head-to-head arrangement and are combined by C−H···Cl hydrogen bonds. The Cl-FC15 molecules form C−H···O=C and C−H···Cl hydrogen bonds with the parallel molecules upper and lower, as displayed in the bottom-left enlarged inset of Figure 3e. The

12


Page 13 of 34 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


molecular arrangement of tetramers in the dumbbell-like pattern is similar to that of one-row trough in the alternate-II pattern. The difference is that the Cl-FC15 molecules are more dislocated when forming C−H···Cl hydrogen bonds than the arrangement in the alternate-II pattern. As shown in the top-right enlarged inset of Figure 3e, in each trough, dodecamers and tetramers which alternatively align along the lamellar direction, are linked with C−Cl···O=C halogen bonds and C−H···Cl hydrogen bonds. The tentative structural model of the dumbbell-like pattern is proposed in Figure 3e. The unit cell parameters for the dumbbell-like pattern are a = 5.1 ± 0.1 nm, b = 5.5 ± 0.1 nm, and γ = 86 ± 2°. The calculated molecular density is 1.75 nm2 per molecule. When the concentration decreases to CCl-FC15 = 4.2 × 10−6 M, the third morphology termed as linear-II pattern appears and dominates the entire scan area on the surface, as displayed in Figure 3c. As the same with the one-row packing in the alternate-II pattern, the uniform linear-II pattern of the Cl-FC15 molecule is obtained. In addition, the molecular arrangement is similar with that of Br-FC15 at low concentration. The tentative structural model of the linear-II pattern is proposed in Figure 3f. In each lamella, two neighboring Cl-FC15 molecules form a dimer via C−H···O=C hydrogen bonds, which alternately align along the trough through C−H···Cl hydrogen bonds. Similarly, the phenyl rings of 1-phenyloctane molecules stretch into the supernatant and the side chains of 1-phenyloctane molecules occupy the space between the interdigitated chains due to the space matching and the interchain vdW force. The unit cell parameters for the linear-II pattern are a = 1.6 ± 0.2 nm, b = 6.2 ± 0.1 nm, and γ = 83 ± 2°. The calculated molecular density is 2.46 nm2 per molecule. Self-Assembly of F-FC15 at the 1-Phenyloctane/HOPG Interface. Compared with the selfassembly of Br-FC15 and Cl-FC15, only one morphology named as alternate-III pattern is observed at different solution concentrations. Typical large-scale and high-resolution STM images of the adlayer 13



Page 14 of 34

for F-FC15 molecule physisorbed on the HOPG surface are presented in Figure 4. At first sight of the alternate-III pattern with one- and two-rows, the packing arrangement seems to be similar to those in the alternate patterns of Br-FC15 and Cl-FC15. However, after a careful inspection of the arrangement for F-FC15 (Figure 4b), the obvious differences can be found. Firstly, in this pattern, all the alkyl chains pack in one direction along with one of the lattices of HOPG, indicating the stronger interchain vdW interaction compared with the alternate patterns of Br-FC15 and Cl-FC15. Secondly, the conjugated cores of F-FC15 molecules in each two-row trough align in the same direction, rather than antiparallel manner in the alternate patterns of Br-FC15 and Cl-FC15. Moreover, molecules in adjacent two-row troughs adopt antiparallel arrangement to offset the dipole moment around the area. Finally, in addition to the formation of C−H···O=C hydrogen bonds, the continuous C−H···F hydrogen bonds are formed between molecules in neighboring rows of each two-row trough, as shown in the bottomright enlarged inset of Figure 4c. It is the stronger continuous C−H···F bonds stemmed from the higher polarity of C−F bond that make the alternate-III pattern differ from the alternate patterns of Br-FC15 and Cl-FC15. Similarly, in one-row lamella, two neighboring F-FC15 molecules form a dimer through C−H···O=C hydrogen bonds, which alternately align along the trough linked with C−H···F hydrogen bonds, as displayed in the bottom-left enlarged inset of Figure 4c. The unit cell parameters for the linear-III pattern are a = 1.6 ± 0.1 nm, b = 13.8 ± 0.1 nm, and γ = 90 ± 1°. The calculated molecular density is 1.84 nm2 per molecule.

14


Page 15 of 34 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 4. Large-scale (a) and high-resolution (b) STM images of F-FC15 adlayer showing the alternate-III pattern at the 1-phenylotane/HOPG interface (6.8 × 10−5 M; It = 443 pA, Vb = 682 mV; (a) 100 × 100 nm2, (b) 20 × 20 nm2). (c) Tentative structural model for the molecular packing. Intermolecular interactions are reflected in the enlarged insets.

Self-Assembly of H-FC15 at the 1-Phenyloctane/HOPG Interface. In order to confirm the crucial role of halogen substituents in the structural polymorphism of fluorenone derivatives, we investigated the self-assembly behavior of the fluorenone derivative of H-FC15 at the 1phenyloctane/HOPG interface. Alternate-IV pattern is observed at high concentration, as shown in Figure 5a. With a careful observation, the arrangement of H-FC15 in alternate-IV pattern is not strictly uniform. In each two-row trough, molecules form two types of dimers indicated by purple and yellow quadrilaterals, respectively. For brevity, others are represented by lines with different colors. Dimers with different geometries alternately align along the trough randomly. In each one-row trough, dimers and trimers (indicated by blue and pink quadrilaterals, respectively) alternately align along the lamellar direction randomly. Molecules in neighboring rows of two-row troughs arrange in an antiparallel mode as a consequence of dipole–dipole force (Figure S4d). The side chains in adjacent troughs are fully interdigitated and perpendicular to the trough to maximize the intermolecular vdW force. The arrangement of H-FC15 for these complexes in both one-row and two-row troughs is presented in Figure 5b. H-FC15 molecules are bound through weak C−H···O=C hydrogen bonds, acting as the main contributor to form the stable assembled alternate-IV pattern. The roughly calculated molecular density is 1.87 nm2 per molecule.

15



Page 16 of 34

Figure 5. High-resolution STM images of H-FC15 adlayers at the 1-phenylotane/HOPG interface. (a) Alternate-IV pattern (5.0 × 10−4 M; It = 463 pA, Vb = 622 mV; 20 × 20 nm2); (c) Linear-III pattern (5.2 × 10−6 M; It = 451 pA, Vb = 637 mV; 20 × 20 nm2). (b,d) Tentative structural models for the corresponding patterns. Intermolecular interactions are reflected in the enlarged inset.

Upon decreasing the solution concentrations, the entire monolayer is covered by the linear-III pattern, as shown in Figure 5c. The side chains keep an angle of 40° with the axes of each trough and interdigitate with the side chains of neighboring molecules. It is worth noting that there are no 1-phenyloctane molecules coadsorbed on the surface. The tentative structural model of linear-III pattern is proposed in Figure 5d. In each lamella, two molecules form a dimer as the basic unit of linear-III pattern and arrange in the antiparallel direction by C−H···O=C hydrogen bonds which dominate the formation of the structure. The unit cell parameters for the linear-III pattern are a = 1.9 ± 0.1 nm, b = 2.3 ± 0.2 nm, and γ = 63 ± 1°. The calculated molecular density is 1.95 nm2 per molecule. On the basis of above analyses, it can be inferred that in addition to interchain vdW forces and dipole−dipole interactions, only the C−H···O=C interactions are formed in the monolayers and act as the primary driving forces in the self-assembly of H-FC15. For the X-FC15 (X = Br, Cl, F) adlayers, although the C−H···O=C hydrogen bonds are still the main driving forces, the halogen-based 16


Page 17 of 34 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


interactions indeed influence the molecular packing and determine the formation of ordered nanostructures. In fact, it has been demonstrated that the structural polymorphism is related to the strength of the intermolecular interactions in our previous works.12, 38 In this system, C−H···X (X = Br, Cl) and X···X (X = Br, Cl) interactions are involved in the structural diversity of X-FC15 (X = Br, Cl). The formation of the stronger continuous C−H···F bonding limits the expression of structural polymorphism of F-FC15. Moreover, the X···O=C (X = Br, Cl) halogen bonds play an important role in the formation and transformation of distinct nanostructures. Table 1. Structural Characteristics of Different Nanopatterns Observed in the 2D Self-Assembly Nanostructures in 1-Phenyloctane with Different Solution Concentrations Structural Concentration SN a (nm) b (nm) γ (°) N 2 model (M) (nm per molecule) −4 Lamellar 3.5 × 10 1.51 −5 Alternate-I 5.4 × 10 1.5 ± 0.2 13.2 ± 0.1 90 ± 1 12 1.65 Br-FC15 −6 Linear-I 6.2 × 10 1.5 ± 0.1 5.8 ± 0.3 86 ± 2 4 2.17 −4 Alternate-II 4.5 × 10 1.5 ± 0.1 13.5 ± 0.2 92 ± 1 12 1.69 −5 Dumbbell-like 6.1 × 10 5.1 ± 0.1 5.5 ± 0.1 86 ± 2 16 1.75 Cl-FC15 −6 Linear-II 4.2 × 10 1.6 ± 0.2 6.2 ± 0.1 83 ± 2 4 2.46 −5 Alternate-III 6.8 × 10 1.6 ± 0.1 13.8 ± 0.1 90 ± 1 12 1.84 F-FC15 −4 Alternate-IV 5.0 × 10 1.87 H-FC15 −6 Linear-III 5.2 × 10 1.9 ± 0.1 2.3 ± 0.2 63 ± 1 2 1.95 The molecular densities SN for the coadsorbed arrangements do not include the solvent molecules. Molecule

Polymorphisms: Concentration and Solvent Coadsorption. It is well documented that solution concentration plays a crucial role in the expression of structural polymorphism during the selfassembly process.11, 32, 34, 43−47 Generally, the self-assembly of molecules forms toward a minimum of the overall Gibbs free energies consisted of enthalpy gain and entropy loss. To maximize the enthalpy gain derived from adsorption, molecules at the liquid/solid interface tend to organize themselves in the denser packing. Table 1 summarizes geometric characteristics and unit cell parameters of the physisorbed adlayers observed at the 1-phenyloctane/HOPG interface with different concentrations. As shown in Table 1, the experimental observations reveal that the value of SN tends to increase along 17



Page 18 of 34

with the decreasing concentrations. Hence, as the concentration decreases, the surface coverage of solute molecules decreases correspondingly. At high concentration, molecules tend to arrange in the denser packing to be favored for enthalpic gain stemmed from molecule−substrate interactions, as well as

the

intermolecules

interactions.

Upon

decreasing

the

solution

concentrations,

the

molecule−substrate interactions are weakened because of the lower solute surface coverage. Taking the adsorption–desorption equilibrium into consideration, 1-phenyloctane molecules can interact with Br-FC15 or Cl-FC15 molecules by coadsorption resulting in the favorable solvent−substrate and molecule−solvent interactions to stabilize the linear adlayers of Br-FC15 and Cl-FC15 at low concentrations. In the linear-III pattern of H-FC15, H-FC15 molecules can be better adsorbed on the substrate surface by decreasing the angle between the chain and the axis of each trough to increase the surface coverage (SN linear-III < SN linear-I, SN linear-II), giving rise to the stable molecular packing without the coadsorption of 1-phenyloctane. Self-Assembly Mechanism: Computing Simulation. On account of the particular potential distribution around the halogen atoms, halogen substituents play a crucial role in the self-assembly adlayers of fluorenone derivatives. Due to the high polarizability and strong electronegativity which lead rearrangement of electronic density on the surface, the region of positive electrostatic potential called “σ-hole” is formed on the top of Br and Cl atoms along the C−X axes, while the areas perpendicular to the axes are surrounded by negative charges.17 The bigger the halogen atoms, the bigger the positive area at the “σ-hole”. The bigger “σ-hole” might give rise to the stronger intermolecular interactions. In this system, except for the interchain vdW forces and dipolar interactions, the hydrogen and halogen bonds are involved in the self-assembly of Br-FC15 and ClFC15, whereas only the hydrogen bonds are the driving forces in stabilizing the 2D self-assembled 18


Page 19 of 34 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


structures of F-FC15 and H-FC15. A detailed analysis of the high-resolution STM images reveals that all the alternate patterns consist of two representative models (tetramer and trimer), as shown in Figure 6. The trimer is also involved in the formation of linear patterns. As shown in Figure 6a and b, BrFC15 molecules arrange in the same way as Cl-FC15. Molecules form the two-row arrangement with an antiparallel direction and pack in a head-to-head fashion connected through C−H···X (X = Br, Cl) hydrogen bonds and the type-I bonds (Br···Br and Cl···Cl), while the molecules in the same side form C−H···O=C and C−H···X (X = Br, Cl) hydrogen bonds. Unlike the packing of Br-FC15 and Cl-FC15, all F-FC15 molecules in tetramer align in parallel through C−H···O=C and C−H···F hydrogen bonds, as shown in Figure 6c. Continuous C−H···F bonds are formed between molecules in neighboring rows. Similarly, trimers in Figure 6d−f are composed of three molecules with parallel or antiparallel manner connected through C−H···O=C and C−H···X (X = Br, Cl, F) hydrogen bonds.

Figure 6. DFT optimized intermolecular interactions for representative models of two-row and onerow lamellae in alternate patterns. (a,d) Br-FC15. (b,e) Cl-FC15. (c,f) F-FC15. The intermolecular 19



Page 20 of 34

bonds are labelled by dashed lines with different colors, respectively.

Table 2. Optimized Geometries, Structural Parameters, Topological Properties of the Electron Density at the Critical Points, and Dipole−Dipole Forces Relative to the Complexes in Two-Row Lamellae of Alternate Patterns of Monolayers for X-FC15 (X = Br, Cl, F) Br-FC15 Dimer-I’

Cl-FC15

Dimer-II’

Dimer-III’

H···Br

H···Br

Br···Br

2.78

2.82

3.50

159

156

170

−0.75

−0.19

0.063

0.045

−0.191

−0.071

Dimer-I’’

F-FC15

Dimer-II’’

Dimer-III’’

H···Cl

H···Cl

Cl···Cl

2.91

3.00

3.94

166

164

178

−0.99

−0.19

0.0340

0.011

−0.075

−0.039

Dimer-I’’’

Dimer-II’’’

Molecule Block Bond

H···O

Distance

2.31

(Å)

2.41

Angle

165

(°)

161

ΔE

−3.66

(kcal/mol) ρBCP (e

Å−3)

0.077 0.067

ΔED−D

0.067

−0.157

(kcal/mol)

H···O 2.34 2.38 164 162

−3.90 0.074

0.040

0.070

−0.194

H···O 2.38 2.39 163 160

H···F

H···F

3.29

2.44

179

159

−3.87 0.069 0.068

0.007

−0.197

Table 3. Optimized Geometries, Structural Parameters, Topological Properties of the Electron Density at the Critical Points, and Dipole−Dipole Forces Relative to the Complexes in Linear Patterns and One-Row Lamellae of Alternate Patterns of Monolayers for X-FC15 (X = Br, Cl, F) Br-FC15

Cl-FC15

F-FC15

Dimer-IV’

Dimer-V’

Dimer-IV’’

Dimer-V’’

Dimer-III’’’

Dimer-IV’’’

H···O

H···Br

H···O

H···Cl

H···O

H···F

2.42

2.72

175

140

−2.89

−1.19

0.056

0.028

−0.228

−0.376

Molecule Block Bond Distance (Å) Angle (°) ΔE (kcal/mol) ρBCP (e

Å−3)

ΔED−D (kcal/mol)

2.40 174 −2.91 0.058 −0.277

3.00 2.95 126 128 −1.04 0.039 0.053 −0.586

2.42 174 −2.92 0.056 −0.224

3.16 3.08 127 130 −1.42 0.022 0.032 −0.355

20


−0.67 0.044 0.069

Page 21 of 34 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


To gain a deeper insight into the intermolecular interactions mechanism within the 2D adlayers, density functional theory (DFT) calculations were performed. Furthermore, theoretical calculations based on the quantum theory of atoms in molecules (QTAIM) of Bader were performed by Multiwfn program. As shown in Figure 6 and Table 2, 3, and S1−3, the geometry optimization dimers32 which used to illustrate the intermolecular interactions are closely consistent with two representative models of the observed molecular packings in the alternate and linear patterns. Since the dipole−dipole interaction is not considered in the DFT calculations, we further conduct the calculation by the semi−𝑢 𝑢

empirical equation48 𝑤(𝑟, 𝜃1 , 𝜃2 , φ) = 4π𝜀1ε𝑟23 [2𝑐𝑜𝑠𝜃1 𝑐𝑜𝑠𝜃2 − 𝑠𝑖𝑛𝜃1 𝑠𝑖𝑛𝜃2 𝑐𝑜𝑠𝜑] to determine its 0

role in the formation of dimer complexes and the results are given in Tables 2 and 3. Unsurprisingly, the energies of dipole−dipole interaction (ΔED−D) are much higher than the ΔE for all the complexes, which indicates that the dipole−dipole interactions only act as the complementary forces to stabilize the self-assembled adlayers. Dimer-I’ to dimer-III’ are involved in the formation of two-row trough. Dimer-IV’ and dimer-V’ are the basic units of one-row trough for the alternate-I pattern and the coadsorbed linear-I pattern of Br-FC15. Similarly, five dimers (dimer-I’’ to dimer-V’’) are involved in the formation of polymorphs of Cl-FC15 adlayers, while the self-assembled pattern of F-FC15 consist of four elementary structural units (dimer-I’’’ to dimer-IV’’’). As the most stable geometry for dimer-I (ΔE = −3.66 kcal/mol for Br-FC15, −3.90 kcal/mol for Cl-FC15, and −3.87 kcal/mol for FFC15) in two-row troughs, C−H···O=C and C−H···X (X = Br, Cl, F) hydrogen bonds are mainly formed. It is worth mentioning that, as an indicator for the bond strength, the larger ρBCP value corresponds to a stronger bond.49, 50 The ρBCP values for C−H···O=C interactions (0.067 ~ 0.077 e Å−3) are larger than that for C−H···X (X = Br, Cl, F) interactions (0.007 ~ 0.067 e Å−3), respectively, which indicates that the stronger C−H···O=C interactions are the primary driving forces to form two-row 21



Page 22 of 34

troughs of X-FC15 (X = Br, Cl, F). Furthermore, the binding energy for C−H···O=C bond in dimerIV’, -IV’’, and -III’’’ (−2.92 ~ −2.89 kcal/mol) is lower than that for C−H···X (X = Br, Cl, F) in dimerV’, -V’’, and -IV’’’(−0.053 ~ −0.022 kcal/mol), indicating that the C−H···O=C bonds make the primary contribution to the formation of one-row troughs for the alternate patterns and the coadsorbed linear patterns of X-FC15 (X = Br, Cl, F). These results demonstrate that the C−H···O=C hydrogen bonds are the primary driving forces to stabilize the alternate and linear patterns of X-FC15 (X = Br, Cl, F). Other interactions, such as X-based bonds (X = Br, Cl, F), vdW forces, and dipolar interactions, act as the collaborative factors. As mentioned before, only the C−H···O=C interactions are formed and act as primary driving forces in the self-assembly of H-FC15, thus the X-based bonds (including C−H···X hydrogen bonds (X = Br, Cl, F) and X···X bonds (X = Br, Cl)) determine the organized uniform arrangement of X-FC15 (X = Br, Cl, F) molecules rather than “disordering” of H-FC15. As shown in dimer-III’ and dimer-III’’, the binding energy for the Br···Br (−0.19 kcal/mol) and Cl···Cl (−0.19 kcal/mol) are higher than that for the C−H···F interaction (−0.67 kcal/mol) in dimer-II’’’, indicating that the continuous C−H···F hydrogen bonds are obviously stronger as compared to the X···X (X = Br, Cl) interactions and account for the critical contribution in the alternate-III pattern of F-FC15. The stronger C−H···F hydrogen bonds also result in the only one nanostructure of F-FC15. As a consequence, the alternate-III pattern of F-FC15 distinguishes itself from the alternate patterns of X-FC15 (X = Br, Cl) due to the formation of the X···X bonds (X = Br, Cl) and the C−H···F hydrogen bond which display obvious disparity in strength. These results are consistent with our STM observations, which are the reason why similar structures with subtle difference could be obtained by Br-FC15, Cl-FC15, F-FC15, and H-FC15 physisorbed at the 1-phenyloctane/HOPG interface.

22


Page 23 of 34 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 7. DFT optimized intermolecular interactions for representative models of the joint of adjacent complexes along the same trough. (a) Tetramer in the lamellar pattern of Br-FC15. (b) Trimer in the dumbbell-like pattern of Cl-FC15. The intermolecular bonds are labelled by dashed lines with different colors, respectively. Table 4. Optimized Geometries, Structural Parameters, and Topological Properties of the Electron Density at the Critical Points Relative to Intermolecular Interactions in the Lamellar Pattern of Br-FC15 and the Dumbbell-Like Pattern of Cl-FC15 Br-FC15 Tetramer

Cl-FC15 Trimer

Molecule Block Bond Distance (Å)

Angle (°) ΔE (kcal/mol) ρBCP (e Å−3)

H···Br Br···O H···O H···Cl Cl···O 3.09 2.82 2.96 2.34 3.57 3.05 2.97 177 149 176 146 164 177 150 −8.18 −1.93 0.027 0.058 0.087 0.082 0.008 0.061 0.034

As described above, both Br-FC15 and Cl-FC15 can self-assemble into the alternate and 23



Page 24 of 34

coadsorbed linear nanostructures. However, two distinct structures can be obtained, that is the lamellar pattern for Br-FC15 and the dumbbell-like pattern for Cl-FC15. In each trough, a tetramer and a hexamer form the elementary structural units of lamellar pattern, whereas a dodecamer with a neighboring tetramer with one-row packing involved in the formation of the dumbbell-like pattern. The arrangement of the molecules within these complexes is similar to that in the two-row troughs of the alternate patterns. The difference is how these complexes are connected, as shown in Figure 7. In the tetramer, the Br atoms form the C−Br···O=C halogen bonds and C−H···Br hydrogen bonds, along with the formation of two C−H···O=C hydrogen bonds. The molecules in the trimer are connected through a C−Cl···O=C halogen bond and C−H···Cl hydrogen bonds. As shown in Table 4, the observed C−Br−O angle in the tetramer of the lamellar pattern and C−Cl−O angle in trimer of the dumbbell-like pattern are close to 180° (176° and 177°), which is the ideal C−X−O (O=C) angle widely recorded in the research of halogen bonding,51, 52 indicating the strongest electrostatic attraction between halogen and oxygen. Furthermore, the ρBCP value for the C−Br···O=C halogen bond (0.087 e Å−3) is larger than that for C−H···Br (0.058 e Å−3) and C−H···O=C (0.082 e Å−3) hydrogen bonds in the tetramer of the lamellar pattern and accounts for the critical role in the lamellar pattern of Br-FC15. Similarly, for the dumbbell-like pattern of Cl-FC15, the ρBCP value for the C−Cl···O=C halogen bond (0.061 e Å−3) is larger than that for C−H···Cl (0.008 ~ 0.034 e Å−3) at the joint between dodecamers and tetramers. This means that the C−Cl···O=C interaction plays a significant role in the formation of the dumbbell-like pattern. In our study, the ρBCP value for the C−Br···O interaction (0.087 e Å−3) is larger than that for the C−Cl···O=C interaction (0.061 e Å−3), reflecting a stronger XB for the larger halogen. This can be further illustrated by the shorter C−Br−O bond length of 2.96 Å versus the C−Cl−O bond length of 3.05 Å. Although the ρ BCP 24


Page 25 of 34 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


values of C−X···O=C (X = Br, Cl) are the biggest among that of the interactions in tetramer and trimer, respectively, the binding energy density per unit area of C−H···O=C bond in the lamellar and the dumbbell-like structures is obviously higher than that of C−X···O=C (X = Br, Cl) bonds. Thereby, it is further confirmed that the C−H···O=C bonds are the driving forces of the lamellar and the dumbbelllike patterns, while the C−X···O=C (X = Br, Cl) bonds act as the critical factor in the formation of these two distinct structures.

CONCLUSION

In summary, the self-assembled behaviors of Br-FC15, Cl-FC15, F-FC15, and H-FC15 were investigated at the 1-phenyloctane /HOPG interface by STM combined with DFT calculations. By varying the solution concentrations, the polymorphic self-assembled nanostructures were obtained in the adlayers of Br-FC15, Cl-FC15 and H-FC15. The solvent molecules could significantly stabilize the adlayers by coadsorption to form the linear patterns of X-FC15 (X = Br, Cl) at low concentration. Only one pattern was observed for the self-assembly of F-FC15, due to the stronger continuous C−H···F hydrogen bonds. It was found that the C−H···O=C hydrogen bonds played the primary role in driving the formation of all the patterns, while the halogen-based interactions significantly influenced the molecular packing and determined the formation of ordered nanostructures. Particularly, on account of the formation of C−H···X hydrogen bonds (X = Br, Cl, F) and type-I X···X bonds (X = Br, Cl), the alternate patterns of X-FC15 (X = Br, Cl, F) distinguish themselves from the “disordering” of H-FC15. Furthermore, owing to the X···X type-I bonds (X = Br, Cl) and C−H···F hydrogen bond which display obvious disparity in strength, the alternate-III pattern of F-FC15 keeps its unique in contrast to the alternate patterns of X-FC15 (X = Br, Cl). The halogen bonds (C−Br···O=C and 25



Page 26 of 34

C−Cl···O=C) play a significant role in the formation of the distinct nanostructures (the lamellar pattern for Br-FC15 and the dumbbell-like pattern for Cl-FC15). Moreover, the vdW forces, as well as dipole−dipole interactions, act as the complementary forces to stabilize the self-assembled adlayers. This work can give a deep insight in better understanding of competition and cooperation mechanism of the hydrogen and halogen bonds, and provide an effective approach to construct the polymorphic self-assembled structures.

Supporting Information The supporting information is available free of charge on the ACS Publications website at DOI: xxx/acs.jpcc.xxx. Molecule syntheses, Spectral data, and additional images (PDF)

The authors declare no competing financial interest.

Acknowledgements Financial supports from the National Natural Science Foundation of China (21573077 and 51373055), the Natural Science Foundation of Guangdong Province (2018A030313452), and the Fundamental Research Funds for the Central Universities (SCUT) are gratefully acknowledged.

26


Page 27 of 34 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


REFERENCES 1.

Gutzler, R.; Walch, H.; Eder, G.; Kloft, S.; Heckl, W. M.; Lackinger, M. Surface Mediated

Synthesis of 2D Covalent Organic Frameworks: 1,3,5-Tris(4-Bromophenyl)Benzene on Graphite(001), Cu(111), and Ag(110). Chem. Commun. 2009, 29, 4456−4458. 2.

Kesanli, B.; Lin, W. Chiral Porous Coordination Networks: Rational Design and Applications in

Enantioselective Processes. Coord. Chem. Rev. 2003, 246, 305−326. 3.

Smith, B. H.; Clark, M. B., Jr.; Kuang, H.; Grieco, C.; Larsen, A. V.; Zhu, C.; Wang, C.; Hexemer,

A.; Asbury, J. B.; Janik, M. J.; et al. Controlling Polymorphism in Poly(3-Hexylthiophene) through Addition of Ferrocene for Enhanced Charge Mobilities in Thin-Film Transistors. Adv. Funct. Mater. 2015, 25, 542−551. 4.

Zhang, S. Q.; Liu, Z. Y.; Fu, W. F.; Liu, F.; Wang, C. M.; Sheng, C. Q.; Wang, Y. F.; Deng, K.;

Zeng, Q. D.; Shu, L. J.; et al. Donor−Acceptor Conjugated Macrocycles: Synthesis and Host−Guest Coassembly with Fullerene toward Photovoltaic Application. ACS Nano 2017, 11, 11701−11713. 5.

Wan, L. J. Fabricating and Controlling Molecular Self-Organization at Solid Surfaces: Studies by

Scanning Tunneling Microscopy. Acc. Chem. Res. 2006, 39, 334−342. 6.

De Feyter, S.; De Schryver, F. C. Self-Assembly at the Liquid/Solid Interface: STM Reveals. J.

Phys. Chem. B 2005, 109, 4290−4302. 7.

Chen, Q.; Chen, T.; Wang, D.; Liu, H. B.; Li, Y. L.; Wan, L. J. Structure and Structural Transition

of Chiral Domains in Oligo(P-Phenylenevinylene) Assembly Investigated by Scanning Tunneling Microscopy. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, 2769−2774. 8.

Elemans, J. A. A. W. Externally Applied Manipulation of Molecular Assemblies at Solid−Liquid

Interfaces Revealed by Scanning Tunneling Microscopy. Adv. Funct. Mater. 2016, 26, 8932−8951. 27



Page 28 of 34

9. Kawai, S.; Nishiuchi, T.; Kodama, T.; Spijker, P.; Pawlak, R.; Meier, T.; Tracey J.; Kubo, T.; Meyer, E.; Foster, A. S. Direct Quantitative Measurement of the C=O···H−C Bond by Atomic Force Microscopy. Sci. Adv. 2017, 3, e1603258. 10. Silly, F.; Aratsu, K.; Yagai, S. Two-Dimensional Chiral Self-Assembly of Barbituric-AcidFunctionalized Naphthelene Derivatives. J. Phys. Chem. C 2018, 122, 6412−6416. 11. Ciesielski, A.; Szabelski, P. J.; Rzysko, W.; Cadeddu, A.; Cook, T. R.; Stang, P. J.; Samori, P. Concentration-Dependent Supramolecular Engineering of Hydrogen-Bonded Nanostructures at Surfaces: Predicting Self-Assembly in 2D. J. Am. Chem. Soc. 2013, 135, 6942−6950. 12. Miao, K.; Hu, Y.; Zha, B.; Xu, L.; Miao, X. R.; Deng, W. L. Hydroxyl versus Carboxyl Substituent: Effects of Competitive and Cooperative Multiple Hydrogen Bonds on Concentration-Controlled SelfAssembly. J. Phys. Chem. C 2016, 120, 14187−14197. 13. Xu, L.; Miao, X. R.; Zha, B.; Deng, W. L. Hydrogen-Bonding-Induced Polymorphous Phase Transitions in 2D Organic Nanostructures. Chem. Asian J. 2013, 8, 926−933. 14. Lackinger, M.; Griessl, S.; Heckl, W. M.; Hietschold, M.; Flynn, G. W. Self-Assembly of Trimesic Acid at the Liquid−Solid Interfaces — a Study of Solvent-Induced Polymorphism. Langmuir 2005, 21, 4984−4988. 15. Cavallo, G.; Metrangolo, P.; Milani, R.; Pilati, T.; Priimagi, A.; Resnati, G.; Terraneo, G. The Halogen Bond. Chem. Rev. 2016, 116, 2478−2601. 16. Gilday, L. C.; Robinson, S. W.; Barendt, T. A.; Langton, M. J.; Mullaney, B. R.; Beer, P. D. Halogen Bonding in Supramolecular Chemistry. Chem. Rev. 2015, 115, 7118−7195. 17. Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Terraneo, G. Halogen Bonding in Supramolecular Chemistry. Angew. Chem. Int. Ed. 2008, 47, 6114−6127. 28


Page 29 of 34 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


18. Abdel-Mottaleb, M. M. S.; Götz, G.; Kilickiran, P.; Bäuerle, P.; Mena-Osteritz, E. Influence of Halogen Substituents on the Self-Assembly of Oligothiophenes — a Combined STM and Theoretical Approach. Langmuir 2006, 22, 1443−1448. 19. Mukherjee, A.; Teyssandier, J.; Hennrich, G.; De Feyter, S.; Mali, K. S. Two-Dimensional Crystal Engineering Using Halogen and Hydrogen Bonds: towards Structural Landscapes. Chem. Sci. 2017, 8, 3759−3769. 20. Gutzler, R.; Fu, C.; Dadvand, A.; Hua, Y.; MacLeod, J. M.; Rosei, F.; Perepichka, D. F. Halogen Bonds in 2D Supramolecular Self-Assembly of Organic Semiconductors. Nanoscale 2012, 4, 5965−5971. 21. Makoudi, Y.; Beyer, M.; Jeannoutot, J.; Picaud, F.; Palmino, F.; Cherioux, F. Supramolecular SelfAssembly of Brominated Molecules on a Silicon Surface. Chem. Commun. 2014, 50, 5714−5716. 22. Silly, F. Concentration-Dependent Two-Dimensional Halogen-Bonded Self-Assembly of 1,3,5Tris(4-Iodophenyl)Benzene Molecules at the Solid−Liquid Interface. J. Phys. Chem. C 2017, 121, 10413−10418. 23. Zheng, Q. N.; Liu, X. H.; Chen, T.; Yan, H. J.; Cook, T.; Wang, D.; Stang, P. J.; Wan, L. J. Formation of Halogen Bond-Based 2D Supramolecular Assemblies by Electric Manipulation. J. Am. Chem. Soc. 2015, 137, 6128−6131. 24. Oison, V.; Koudia, M.; Abel, M.; Porte, L. Influence of Stress on Hydrogen-Bond Formation in A Halogenated Phthalocyanine Network. Phys. Rev. B 2007, 75, 035428. 25. Zha, B.; Dong, M. Q.; Miao, X. R.; Miao, K.; Hu, Y.; Wu, Y. C.; Xu, L.; Deng, W. L. Controllable Orientation of Ester-Group-Induced Intermolecular Halogen Bonding in a 2D Self-Assembly. J. Phys. Chem. Lett. 2016, 7, 3164−3170. 29



Page 30 of 34

26. Cunha, F.; Sá, E.; Nart F. In Situ STM Study of the Adsorption of Halogen Derivatives of Uracil on Au(111). Surf. Sci. 2001, 480, L383−L388. 27. Gatti, R.; MacLeod, J. M.; Lipton-Duffin, J. A.; Moiseev, A. G.; Perepichka, D. F.; Rosei, F. Substrate, Molecular Structure, and Solvent Effects in 2D Self-Assembly via Hydrogen and Halogen Bonding. J. Phys. Chem. C 2014, 118, 25505−25516. 28. Dobrin, S.; Harikumar, K. R.; Polanyi, J. C. STM Study of the Conformation and Reaction of Long-Chain Haloalkanes at Si(111)-7 × 7. J. Phys. Chem. B 2006, 110, 8010−8018. 29. Pflaum, J.; Bracco, G.; Schreiber, F.; Colorado Jr, R.; Shmakova, O. E.; Lee, T. R.; Scoles, G.; Kahn, A. Structure and Electronic Properties of CH3- and CF3-Terminated Alkanethiol Monolayers on Au(111): a Scanning Tunneling Microscopy, Surface X-Ray and Helium Scattering Study. Surf. Sci. 2002, 498, 89−104. 30. Müller, T.; Werblowsky, T. L.; Florio, G. M.; Berne, B. J.; Flynn, G. W. Ultra-High Vacuum Scanning Tunneling Microscopy and Theoretical Studies of 1-Halohexane Monolayers on Graphite. Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 5315−5322. 31. Yasuda, S.; Furuya, A.; Murakoshi, K. Control of a Two-Dimensional Molecular Structure by Cooperative Halogen and Hydrogen Bonds. RSC Adv. 2014, 4, 58567−58572. 32. Zha, B.; Dong, M. Q.; Miao, X. R.; Peng, S.; Wu, Y. C.; Miao, K.; Hu, Y.; Deng, W. L. Cooperation and Competition between Halogen Bonding and Van der Waals Forces in Supramolecular Engineering at the Aliphatic Hydrocarbon/Graphite Interface: Position and Number of Bromine Group Effects. Nanoscale 2017, 9, 237−250. 33. Zha, B.; Miao, X. R.; Liu, P.; Wu, Y. C.; Deng, W. L. Concentration Dependent Halogen-Bond Density in the 2D Self-Assembly of a Thienophenanthrene Derivative at the Aliphatic Acid/Graphite 30


Page 31 of 34 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


Interface. Chem. Commun. 2014, 50, 9003−9006. 34. Wu, Y. C.; Li, J. X.; Yuan, Y. L.; Dong, M. Q.; Zha, B.; Miao, X. R.; Hu, Y.; Deng, W. L. Halogen Bonding versus Hydrogen Bonding Induced 2D Self-Assembled Nanostructures at the Liquid–Solid Interface Revealed by STM. Phys. Chem. Chem. Phys. 2017, 19, 3143−3150. 35. Miao, K.; Hu, Y.; Xu, L.; Dong, M. Q.; Wu, J. T.; Miao, X. R.; Deng, W. L. Chiral Polymorphism in the Self-Assemblies of Achiral Molecules Induced by Multiple Hydrogen Bonds. Phys. Chem. Chem. Phys. 2018, 20, 11160−11173. 36. Chen, X. Y.; Ozturk, S.; Sorensen, E. J. Synthesis of Fluorenones from Benzaldehydes and Aryl Iodides: Dual C−H Functionalizations Using a Transient Directing Group. Org. Lett. 2017, 19, 1140−1143. 37. Ivanov, A. V.; Lyakhov, S. A.; Yarkova, M. Y.; Galatina, A. I.; Mazepa, A. V. Synthesis and Liquid Crystal Properties of 2,7-Dialkoxy-9-Fluorenones. Russ. J. Gen. Chem. 2002, 72, 1435−1438. 38. Lu, T.; Chen, F. Multiwfn: a Multifunctional Wavefunction Analyzer. J. comput. Chem. 2012, 33, 580−592. 39. Humphrey, W.; Dalke, A.; Schulten, K. VMD: Visual Molecular Dynamics. J. Mol. Graphics 1996, 14, 33−38. 40. Hu, Y.; Miao, K.; Dong, M. Q.; Xu, L.; Zha, B.; Miao, X. R.; Deng, W. L. Exploration of Chirality and Achirality of Self-Assembled Monolayer Formed by Unsymmetrically Substituted Fluorenone Derivative at the Liquid/Solid Interface. Adv. Mater. Interfaces 2018, 5, 1700611. 41. Bertrand, H.; Silly, F.; Teulade-Fichou, M. P.; Tortech, L.; Fichou, D. Locking the Free-Rotation of a Prochiral Star-Shaped Guest Molecule inside a Two-Dimensional Nanoporous Network by Introduction of Chlorine Atoms. Chem. Commun. 2011, 47, 10091−10093. 31



Page 32 of 34

42. Mamdouh, W.; Uji-i, H.; Ladislaw, J. S.; Dulcey, A. E.; Percec, V.; De Schryver, F. C.; De Feyter, S. Solvent Controlled Self-Assembly at the Liquid−Solid Interface Revealed by STM. J. Am. Chem. Soc. 2006, 128, 317−325. 43. Miao, K.; Hu, Y.; Zha, B.; Xu, L.; Dong, M. Q.; Miao, X. R.; Deng, W. L. Polymorphic SelfAssemblies of 2,7-Bis(Decyloxy)-9-Fluorenone at the Solid/Gas Interface: Role of C−H···O=C Hydrogen Bond. J. Phys. Chem. C 2017, 121, 3947−3957. 44. Cai, Z. F.; Yan, H. J.; Wang, D.; Wan, L. J. Potential- and Concentration-Dependent Self-Assembly Structures at Solid/Liquid Interfaces. Nanoscale 2018, 10, 3438−3443. 45. El Garah, M.; Dianat, A.; Cadeddu, A.; Gutierrez, R.; Cecchini, M.; Cook, T. R.; Ciesielski, A.; Stang, P. J.; Cuniberti, G.; Samori, P. Atomically Precise Prediction of 2D Self-Assembly of Weakly Bonded Nanostructures: STM Insight into Concentration-Dependent Architectures. Small 2016, 12, 343−350. 46. Kudernac, T.; Lei, S. B.; Elemans, J. A.; De Feyter, S. Two-Dimensional Supramolecular SelfAssembly: Nanoporous Networks on Surfaces. Chem. Soc. Rev. 2009, 38, 402−421. 47. Lei, S. B.; Tahara, K.; De Schryver, F. C.; Van der Auweraer, M.; Tobe, Y.; De Feyter, S. One Building Block, Two Different Supramolecular Surface-Confined Patterns: Concentration in Control at the Solid−Liquid Interface. Angew. Chem. Int. Ed. 2008, 47, 2964−2968. 48. Israelachvili, J. N. Intermolecular and Surface Forces; Academic Press: Burlington, U.S.A., 2011. 49. Arnold, W. D.; Oldfield, E. The Chemical Nature of Hydrogen Bonding in Proteins via NMR: JCouplings, Chemical Shifts, and AIM Theory. J. Am. Chem. Soc. 2000, 122, 12835−12841. 50. Politzer, P.; Murray, J. S.; Clark, T. Halogen Bonding: an Electrostatically-Driven Highly Directional Noncovalent Interaction. Phys. Chem. Chem. Phys. 2010, 12, 7748−7757. 32


Page 33 of 34 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


51. Riley, K. E.; Murray, J. S.; Politzer, P.; Concha, M. C.; Hobza, P. Br···O Complexes as Probes of Factors Affecting Halogen Bonding: Interactions of Bromobenzenes and Bromopyrimidines with Acetone. J. Chem. Theory Comput. 2009, 5, 155−163. 52. Pigge, F. C.; Vangala, V. R.; Swenson, D. C.; Rath, N. P. Examination of Halogen Bonding Interactions in Electronically Distinct but Structurally Related Tris(Haloarenes). Cryst. Growth Des. 2010, 10, 224−231.

33



TOC Graphite

34


Page 34 of 34

Halogen Substituent Effects on Concentration-Controlled Self

Recommend Documents