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Takahiro Kojima, Karan Patel, Shunpei Nobusue, Ahmed Mahmoud, Cong Xie, Takahiro Nakae, [Shigeki Kawai](https://orcid.org/0000-0003-2128-0120), Kazuhiro Fukami, Hiroshi Sakaguchi

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[Vectorial On-Surface Synthesis of Polar 2D Polymer Crystals](https://mdr.nims.go.jp/datasets/6959f94b-39ae-407c-90ed-cd790c5c37e6)

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Vectorial On‐Surface Synthesis of Polar 2D Polymer CrystalsRESEARCH ARTICLEEditor’s Choice www.advmatinterfaces.deVectorial On-Surface Synthesis of Polar 2D Polymer CrystalsTakahiro Kojima, Karan Patel, Shunpei Nobusue, Ahmed Mahmoud, Cong Xie,Takahiro Nakae, Shigeki Kawai, Kazuhiro Fukami, and Hiroshi Sakaguchi*The asymmetric introduction of functional groups into polymers is promisingdue to its potential to provide novel electronic and magnetic properties.Though traditional on-surface bottom-up synthesis has succeeded in creatingvarious types of polymers, it struggles at realizing asymmetry due to thedifficulty of stereoregular polymerization and the tendency for overall polaritycancellation during agglomeration. Here, enabled by the lowhalogen-contaminated metal surfaces provided by two-zone chemical vapordeposition, “compass” precursors possessing three independent bonding,edge, and dipole vectors undergo isotactic polymerization via the vectorialself-assembly of chiral precursor diradicals without the need for chiralcatalysts required in conventional in-solution polymerization. The isotacticpolymers exhibit polar 2D crystalline structures due to the hetero-edge CH–𝝅interaction between the standing phenyl and butoxy group surpassing thehomo-edge interactions of 𝝅–𝝅 and CH–CH. The developed vectorialon-surface synthetic technique not only paves the way to the realization ofstereoregular control but also unlocks unprecedented crystal engineering.1. IntroductionAsymmetric structures play crucial roles in producing particu-lar properties and functionalities in various scopes of physics,T. Kojima, K. Patel, S. Nobusue, A. Mahmoud, C. Xie, H. SakaguchiInstitute of Advanced EnergyKyoto UniversityKyoto 611-0011, JapanE-mail: sakaguchi@iae.kyoto-u.ac.jpT. NakaeSmart Materials and Devices Innovation CenterKRI Inc.Kyoto 600-8813, JapanS. KawaiResearch Center for Advanced Measurement and CharacterizationNational Institute for Materials ScienceIbaraki 305-0047, JapanK. FukamiDepartment of Materials Science and EngineeringKyoto UniversityKyoto 606-8501, JapanThe ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/admi.202300214© 2023 The Authors. Advanced Materials Interfaces published byWiley-VCH GmbH. This is an open access article under the terms of theCreative Commons Attribution License, which permits use, distributionand reproduction in any medium, provided the original work is properlycited.DOI: 10.1002/admi.202300214chemistry, and biology.[1–4] For exam-ple, ferroelectrics require the non-centrosymmetric alignment of electricdipoles, and ferromagnetism needsspins to be coupled nominally in thesame direction.[2–3] 1D carbon-basednanostructures have attracted a lot ofattention because their electronic ormagnetic properties can, in principle,be controlled by the introduction offunctional groups.[5,6] Although on-surface synthetic techniques based onchemical reactions taking place onmetal surfaces under ultrahigh vacuum(UHV) conditions have succeeded increating various types of polymers, allthose reported so far are limited tononpolar structures.[7–11] To create thenovel class of electronically asymmetricpolymers, predicted to bear promisingfunctionality for new applications,[1–4]brand new synthetic methods are required since conventional on-surface synthesis techniques suffer from the difficulties of stere-oregular polymerization of the precursors and the polar inter-strand order of the polymers. To overcome these challenges, wedesigned the compass precursors, which, due to their bondingand edge vectors, are capable of aligning their reaction interme-diates in the same 2D vectorial direction that leads to isotacticpolymers with the polar 2D crystalline structures under two-zonechemical vapor deposition (CVD) (Figure 1a).2. Results and DiscussionZ-bar-linkage type precursors (molecules possessing twopolyphenylene branches linked at hinge positions that looklike the letter “z”) were used in this study. The backbone ofthese precursors allows them to adopt various conformationsdue to its flexibility at the hinge position while simultaneouslyholding rigid polyphenylene branches. Our previous workfound that two-zone CVD of the symmetric z-bar-linkage pre-cursor 4ʹʹ,5ʹʹʹ-dibromo-1,1ʹ:4ʹ,1ʹʹ:2ʹʹ,1ʹʹʹ:2ʹʹʹ,1ʹʹʹʹ:4ʹʹʹʹ,1ʹʹʹʹʹ-sexiphenylresulted in the formation of homochiral polymers and theirfollowing conversion into cove-edged graphene nanoribbons(GNRs).[12] The key to the success of this process is believed tobe the dynamic chirality of the precursor’s diradical in which theachiral (C2h) forms in the gas phase might be transformed intochiral (C1) forms when deposited on the metal surface. In thisstudy, 3-vectorial; Cs symmetry z-bar-linkage precursors withthree vectors (dynamic chirality-driven bond (polymerization)vector, unidirectional intermolecular force-inducing edge vectorAdv. Mater. Interfaces 2023, 10, 2300214 2300214 (1 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbHhttp://crossmark.crossref.org/dialog/?doi=10.1002%2Fadmi.202300214&domain=pdf&date_stamp=2023-06-16www.advancedsciencenews.com www.advmatinterfaces.deFigure 1. Concept illustration of the vectorial on-surface synthesis of polar 2D polymer crystals. a) Schematic representation of the polar 2D polymerssynthesis process indicating the 3-vectorial precursor diradical formation and consequent polymerization via two-zone CVD. b) Illustrations of thechemical compounds utilized in this study.and electronic asymmetry-inducing dipole vector) are designedto create polar polymers. The two strategies implemented in de-signing the asymmetric precursors are the length control of thepolyphenylene branches and the introduction of the electronicasymmetry-inducing butoxy (abbreviated to –BuO) functionalgroup. The n in the [n, m] notation refers to the number ofbenzene units in the z-bar-linkage precursor’s aryl branch andthe m refers to the number of benzene units in the modifierfunctional group branch. According to our strategy, two kindsof asymmetric precursors were synthesized: [2, 2-BuO] (4ʹʹ,5ʹʹʹʹ-dibromo-4-butoxy-1,1ʹʹ:2ʹʹ,1ʹʹʹʹ:2ʹʹʹʹ,1ʹʹʹʹʹʹ-quaterphenyl) and [3,2-BuO] (4ʹʹ,5ʹʹʹʹ-dibromo-4-butoxy-1,1ʹʹ:2ʹʹ,1ʹʹʹʹ:2ʹʹʹʹ,1ʹʹʹʹʹʹ:4ʹʹʹʹʹʹ,1ʹʹʹʹʹʹ’-quinquephenyl) (Figure 1b).The on-surface polymerization of [2, 2-BuO] and [3, 2-BuO]precursors was attempted using our two-zone CVD technique.[13]Two-zone CVD is based on the independent control of tempera-tures at precursor sublimation (Tpre), tube hot wall (Twall) in zone1, and Au(111) substrate (Tsub) in zone 2 to optimize the yieldof products (Figure S1, Supporting Information). To identify theproduced species, ex situ low-temperature scanning tunnelingmicroscopy (LT-STM) measurements at 77 K under UHV condi-tions were conducted on samples transferred from the two-zoneCVD apparatus. LT-STM images of two-zone chemical vapor de-posited [2, 2-BuO] precursors on Au(111) at a Tsub of 250 °C revealthe formation of linear strands with dots at their edges (Figure2a). The spacing of the dots along each strand’s side is measuredto be 0.74 nm (Figure 2b) and its width is found to be 1.72 nm(Figure 2c). These values are in good agreement with those basedon the [2, 2-BuO] polymer structure shown in Figure 2d. By an-alyzing the magnified LT-STM images as shown in Figure 2e,two kinds of dot patterns—single dots depicted in green and un-equally sized pairs of dots, referred to as “binary”, marked red—are seen at the edges along the strands. Moreover, positions of thedots appearing at one side of the strands and those on oppositesides are found to be roughly 180° out of phase relative to eachother. These results suggest that the binary dots correspond tothe butoxyphenyl group, whereas the single dots are attributed tothe edge phenyl groups (Figure 2d,e) supported by the STM sim-ulation (Figure S2d, Supporting Information). According to theresults of scanning tunneling spectroscopy (STS), the bandgap of[2, 2-BuO] is found to be 2.92 eV, as depicted in Figure 2f. Thisclosely resembles the bandgap of poly-p-phenylene on Au(111),which is 3.23 eV.[14] The density functional theory (DFT) pre-dicted the bandgap value of [2, 2-OBu] to be 2.86 eV, as seenin Figure S2a (Supporting Information). The simulated HOMOand LUMO energy levels are located at −0.58 and +2.28 eV, re-spectively, which are akin to those of [2, 2] without the butoxygroup (Figure S2f , Supporting Information), which are −0.60and +2.34 eV, correspondingly. Furthermore, the simulation of[2, 2-BuO] revealed the appearance of the HOMO+1 peak at−1.04 eV, indicating the contribution of the butoxy group. Next,we focus on the stereoregularity of the [2, 2-BuO] polymer. In gen-eral, polymer stereoregularity is categorized into three types: atac-tic, in which the asymmetric substituents are randomly arrangedalong the polymer backbone, alternatingly arranged in syndio-tactic and�unidirectionally arranged in the isotactic conforma-tion (Figure 2g).[15] The LT-STM image shown in Figure 2e pro-vides evidence that the polymer strands are atactic because thestrand substituents appear to be joined in random orientations.Using a definition of m/(m + r), where m and r denote meso andracemo consecutive substituent ordering, respectively, as shownin Figure S2b (Supporting Information),[15] the overall isotacticityof [2, 2-BuO] polymers is assigned a value of 0.76 (Figure 2a).LT-STM images of samples produced by two-zone CVD us-ing [3, 2-BuO] precursors (Figure 2h) reveals that the dots’ spac-ing is 0.74 nm along the strand (Figure 2i) similar to that of[2, 2-BuO], however, a larger unit width of 1.61 nm (Figure 2j)is observed (compared with [2, 2-BuO]’s value of 1.38 nm asshown in Figure 2e. These values are in good agreement withthose based on the [3, 2-BuO] polymer chemical structure de-picted in Figure 2k. Different from [2, 2-BuO] polymers, high-resolution LT-STM images of [3, 2-BuO] polymers clearly showthat two kinds of dots exist exclusively at the opposite sides ofthe strands; binary dots represented in red appearing at one sideAdv. Mater. Interfaces 2023, 10, 2300214 2300214 (2 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH 21967350, 2023, 23, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/admi.202300214 by Cochrane Japan, Wiley Online Library on [26/12/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advmatinterfaces.deFigure 2. Stereoregular on-surface polymerization. a,h) LT-STM images and superimposed structures of [2, 2-BuO] (Bias voltage = −0.51 V, feedbackcurrent = 580 pA) and [3, 2-BuO] (−0.11 V, 580 pA) polymer strands. The white lines indicate strand boundaries, and the red and blue dotted lines markthe locations of the lateral and perpendicular topographic analysis paths, respectively. b,i) Topographic profiles of the red lines in (a,h). c,j) Topographicprofiles of the blue lines in (a,h). d,k) Chemical structures of [2, 2-BuO] and [3, 2-BuO] polymers. e,l) Magnified LT-STM images of single [2, 2-BuO](−0.75 V, 300 pA) and [3, 2-BuO] (−0.11 V, 580 pA) polymer strands. Green dots indicate edge phenyl groups, red binary dots indicate the butoxyphenylgroups and the twinned blue dots represent the biphenyl groups. f,m) Five times averaged STS profiles of [2, 2-BuO] and [3, 2-BuO] polymers. The insetsindicate the STS measurement locations (red dots). The bandgap is estimated from the difference in potentials of the peaks indicated by red dottedlines. g,n) [2, 2-BuO] and [3, 2-BuO] polymer tacticity. [2, 2-BuO] precursors undergo atactic polymerization while [3, 2-BuO] precursors undergo isotacticpolymerization.of the strand, while similarly sized “twinned” dots depicted inblue are seen at the opposite side (Figure 2l) supported by theSTM simulation (Figure S2e, Supporting Information). The dotsare also roughly 180° out of phase. These results suggest thatthe binary dots correspond to the butoxyphenyl group, whereasthe twinned dots are attributed to the biphenyl group at the edgeof the other side (Figure 2k,l). Based on STS analysis, the prod-ucts indicate a bandgap of 2.82 eV (Figure 2m) that is in goodagreement with the DFT predicted value of 2.67 eV using the[3, 2-BuO] polymer model (Figure S2c, Supporting Information).These results imply that [3, 2-BuO] polymers were successfullyformed. In stark contrast to [2, 2-BuO], analysis of the substrate’sLT-STM images (Figure 2h,l) demonstrates that the isotacticityof [3, 2-BuO] polymers is unity, as the asymmetric substituentsare arranged in a unidirectional manner, each along only oneside of the polymer backbone (Figure 2n). This perfect isotactic-ity implies that the [3, 2-BuO] precursors spontaneously organizethemselves unidirectionally—analogous to compass behavior—and then undergo radical coupling reactions to form covalentbonds.We conducted a theoretical study with practical accuracy us-ing quantum mechanics/molecular mechanics (QM/MM) simu-lations on the conformation of the precursor diradical on Au(111)as the polymer intermediate. Our aim is to understand the rea-son behind the isotactic polymerization in [3, 2-BuO] precursorscompared to [2, 2-BuO] based on our previous report.[12] The con-formation simulation on the [3, 2-BuO] and [2, 2-BuO] precursordiradicals generates eight chiral isomers in both precursor cases,categorized by two important factors: axis chirality (horizontal-axis chirality and vertical-axis chirality)[16] and enatiomerism(right-handed (R) and left-handed (S)) as shown in Figure 3aand Figure S3 (Supporting Information). Consequently, the eightisomers are named as a combination of the relative heights ofthe two hinge benzenes with regard to the Au(111) plane; if theheight of one of the benzenes at the hinge is distant from theaforementioned plane, it is denoted as “u” (up), whereas if it isAdv. Mater. Interfaces 2023, 10, 2300214 2300214 (3 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH 21967350, 2023, 23, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/admi.202300214 by Cochrane Japan, Wiley Online Library on [26/12/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advmatinterfaces.deFigure 3. Mechanism of stereoregular on-surface polymerization. a) DFT predicted conformers of [3, 2-BuO] precursor diradicals on Au(111). b,c) Energydiagrams of the optimized [2, 2-BuO] and [3, 2-BuO] precursor diradical conformers on Au(111) highlighting the energy difference between them. d) [2,2-BuO] and [3, 2-BuO] precursor diradicals’ coupling modes.located closer to character belongs the benzene of the aryl branch,which is denoted in blue, while the second letter belongs to thebutoxy-group branch benzene that is denoted in red. Horizontal-axis chirality covers the [uu] and [dd] conformers that possess achiral axis parallel to the Au(111) plane. On the other hand, thevertical-axis chirality group contains the [ud] and [du] conform-ers whose chiral axis is normal to the Au(111) plane. Addition-ally, the�energy of all conformers was calculated by QM/MM toassess their thermodynamic stability. As a result, the [2, 2-BuO]precursor diradical favors the [dd] conformer on the Au(111) sur-face (Figure 3b) while the [3, 2-BuO] precursor diradical favorsthe [ud] conformer form (Figure 3c). Due to the difference inthe metal-molecule interaction strength between the polar butoxygroup and the nonpolar phenyl groups, the butoxy group branchis expected to adhere to the metal surface in contrast to the arylbranch benzenes that may levitate above the Au(111), resultingin the driving force behind the conformation change of the pre-cursor diradicals.The coupling reactions’ modes were investigated using thepreviously generated chiral conformers to elucidate the stereo-regular polymerization. Coupling reactions cover three modes:head-to-head, head-to-tail, and tail-to-tail.[17] Homo-coupling ofthe horizontally axial ([dd] + [dd]) [2, 2-BuO] precursor diradi-cals can adopt all three coupling modes due to the lack of sterichindrance between the coupling radicals, suggesting that atacticpolymerization based on randomly oriented monomers shouldtake place (Figure 3d). In sharp contrast, homo-coupling of thevertically axial ([ud]+[ud]) [3, 2-BuO] precursor diradicals exhibitsno steric hindrance in the head-to-tail and tail-to-tail modes,while the head-to-head mode is disturbed (Figure 3d). Polymergrowth can only proceed in the head-to-tail mode since the tail-to-tail mode causes strand termination, resulting in isotactic poly-merization. These considerations support the experimental re-sults, where the [2, 2-BuO] polymers are atactic (Figure 2g),while the [3, 2-BuO] polymers are isotactic (Figure 2n). Accord-ing to previous in-solution studies, isotactic polymerization ofasymmetric monomers (i.e., propylene) requires chiral catalystssuch as Zeigler–Natta or metallocene that can coordinate and di-rect monomers for polymerization.[18,19] Our on-surface isotacticpolymerization does not require chiral catalysts because the z-bar-linkage precursors spontaneously alter their shapes into chi-ral forms to unidirectionally align themselves.2.1. In Sharp Contrast to the Purely Isotactic Polymers ObtainedUsing two-zone CVD, LT-STM images of [3, 2-BuO] polymersprepared by the traditional UHV on-surface technique at 250 °Cpresent mixtures of two kinds of polymers; those possessingchain-dot spacing of 0.75 nm (isotactic) and 1.48 nm in the other(syndiotactic; alternating sequential orientation) (Figure 4a–c).It is well known that cleaved bromine atoms adhere to Au(111)under UHV on-surface synthetic techniques’ conditions[20,21] thatmight alter the conformation of [3, 2-BuO] precursor diradi-cals on Au(111),[22] resulting in a change of coupling modes.Contrary to the UHV on-surface technique, two-zone CVD canprovide large bromine-free Au(111) surfaces indicated by weakbromine XPS signals in the sample (Figure S4, Supporting In-formation). The reason behind the low bromine-Au(111) con-tamination might be the result of the separation of the molec-ular cleavage and polymer growth zones and the exhaust of thebromine atoms in the argon gas flow[12] in contrast to the UHVtechniques where the halogen is trapped. This feature of two-zone CVD makes it a prerequisite for on-surface isotactic poly-merization.After thermal annealing at 400 °C, carbon monoxide-functionalized tip constant-height LT-STM images of in situ syn-thesized polymers using the UHV apparatus reveal the forma-tion of GNRs of two kinds reflecting the tacticity of their par-ent polymers: isotactic and syndiotactic (Figure 4d,e; Figure S5,Adv. Mater. Interfaces 2023, 10, 2300214 2300214 (4 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH 21967350, 2023, 23, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/admi.202300214 by Cochrane Japan, Wiley Online Library on [26/12/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advmatinterfaces.deFigure 4. UHV on-surface synthesis of [3, 2-BuO] polymers. a) LT-STM (4K) image of [3, 2-BuO] polymer (−0.20 V, 10 pA) produced via the UHVdeposition method at a substrate temperature of 250 °C. b,c) Topographic profiles of the lines in (a) demonstrating the different dot spacing betweensyndiotactic (1.48 nm) and isotactic (0.75 nm) polymer aggregates. The expected chemical structures are illustrated. d,e) Constant-height dI/dV images(1 mV, 10 pA) using a CO-functionalized tip of selected strands of UHV deposited [3, 2-BuO] polymers annealed at 400 °C and their expected chemicalstructures.Supporting Information). The lack of functional groups in theseGNRs provides evidence for their decomposition, proving thatUHV synthesis is not suitable for creating asymmetric isotacticpolymers.[23–25]The simulated electrostatic potential mapping of [3, 2-BuO]polymers suggests that the per-monomer unit electric dipole is1.87 Debye virtually perpendicular to the strand axis (Figure 5a).As the maximum observed length of strands measured in theLT-STM images of [3, 2-BuO] Polymers (Figure S6a, SupportingInformation) is 35.3 nm (corresponding to 47 monomer units),strands are estimated to possess dipole moments of 88 Debye. Toachieve thermodynamic stability, strands of polar polymers suchas polyvinylidene difluoride (PVDF) tend to orient in an antipar-allel manner to reduce the overall polarization.[26] On the con-trary, the [3, 2-BuO] polymers’ structure was discovered to belongto the unusual non-centrosymmetric 2D crystalline symmetrygroup in which every domain’s strands’ electric dipoles align uni-directionally virtually perpendicular to the strands (Figure 5b).In addition, the observed “inter-strands” uniform 1.61 nm spac-ing (Figure 2j) also supports the proposed polar 2D-crystal do-mains model. Consequently, the 2D polar polymer agglomeratescan be categorized into the P1 space group. It is well knownthat dielectric materials can be categorized according to the pointgroups of their crystals.[27] Among the 32 crystal symmetry pointgroups, 21 are non-centrosymmetric and can further belong tothe special property classes of piezoelectric, pyroelectric and fer-roelectric materials.[27] Thus, the 2D crystals of [3, 2-BuO] poly-mers are believed to be pyroelectric since their structure is non-centrosymmetric and polar. A theoretical study based on theinter-chain interaction energies of two molecular groups (aryland alkyl) was conducted on [3, 2-BuO] polymers to identify thereason for the overall polar inter-chain arrangement of the [3,2-BuO] polymers. Three modes of inter-chain interactions canbe considered, CH-𝜋 interactions (Figure 5c), 𝜋–𝜋 (Figure 5d)and CH–CH interactions (Figure 5e).[28–30] The energy for thethree interaction modes was calculated by DFT using the gener-alized gradient approximation of the Perdew–Burke–Ernzerhof(GGA-PBE) functional that accounts for the noncovalent molec-ular interactions without solid surfaces.[31] In this calculation,one strand’s coordinates were fixed, and the second’s was placedin close proximity to the fixed one and its location adjusted insmall increments in the X and Y directions (Figure 5c). DFT en-ergy calculations were performed at all secondary strand coordi-nates. Assigning the energy minimum value (CH-𝜋, Figure 5f)to zero, the relative energy landscapes based on this model re-veal the energy difference for the other two interaction modes’minimum values to be 39.92 kcal mol−1 for 𝜋–𝜋 (Figure 5g), and66.40 kcal mol−1 for CH–CH (Figure 5h). The optimized strands’geometry at the minimum energy for the three modes is repre-sented in Figure 5c–e. Among the three modes of interaction,the CH-𝜋 mode possesses the least energy, suggesting that thestructure resulting from it—the polar crystalline structure—isthe most energetically favorable. The theoretical study also esti-mates that the inter-strand distance in the optimized CH-𝜋 con-figuration is 1.61 nm (Figure 5c). In principle, 𝜋–𝜋 interactionsare known to be stronger than CH-𝜋 interactions and CH–CHinteractions in solutions.[28] However, the results we obtained de-viate from the norm. The reason behind this phenomenon pre-sumably originates from steric hindrance; narrow spaces result-ing from the massive edge-phenyl groups hinder 𝜋–𝜋 inter-chaininteraction by forbidding the approach of neighboring strands’phenyl groups (Figure 5d). As a result, [3, 2-BuO] polymers ex-press the unusual CH-𝜋 chemical interaction rather than that of𝜋–𝜋 or CH–CH.3. ConclusionTo summarize, the alignment of polymer strands in their crys-tal domains is a result of two of the precursors’ three vectors.The bond vector aligns the diradicals along the polymerization“latitude” based on the energetic stability of the precursors’ chi-ral conformities. The asymmetry vector of the edge butoxy andAdv. Mater. Interfaces 2023, 10, 2300214 2300214 (5 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH 21967350, 2023, 23, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/admi.202300214 by Cochrane Japan, Wiley Online Library on [26/12/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advmatinterfaces.deFigure 5. Polar 2D polymer crystals. a) Simulated electrostatic potential map of a [3, 2-BuO] 5mers. The green arrow indicates the per-monomer electricdipole of 1.87 Debye. b) Illustration of a polar 2D polymer crystal domain. The red, blue, and green arrows represent the bonding, edge, and dipole vectors,respectively. c–e) Illustrated interaction models of the optimized [3, 2-BuO] polymers indicating the optimum strand spacing for each interaction mode.The secondary polymer displacement axes are illustrated in (c). The red dotted circles indicate the typical interacted position. f–h) Contour maps ofedge-group interaction energy as a function of X and Y displacement. The red dotted circles indicate the energy minima at the optimum inter-stranddistances.phenyl groups provides “longitudinal” inter-chain forces due tointer-strand edge group interaction, which we call “2D vecto-rial self-assembly.” This process is capable of producing polarcrystals (as shown in Figure 5b). These findings open up thepossibility of creating polar 2D assemblies of 3-vectorial build-ing blocks, which could lead to a new approach in polar crystalengineering.[32]4. Experimental SectionSTM Measurements: STM measurements except Figure 4 were per-formed under the constant-current mode with a commercially avail-able UNISOKU low-temperature scanning tunneling microscopy system(USM-1100SA-2C) at 77 K. An electrochemically etched tungsten wire wasused as the tip. Before conducting LT-STM and XPS measurements, allsamples underwent pre-treatment in UHV conditions at 150 °C for 1 h toeliminate any adsorbed species. dI/dV spectra were acquired using the fol-lowing conditions: Vsample =−0.5 V, I= 200 pA under the reduced feedbackloop during voltage sweep. Additionally, STM measurements for Figure 4were performed with commercially available Omicron low-temperaturescanning tunneling microscopy and a homemade STM system, operatingin ultra-high vacuum at temperatures below 5 K. High-resolution dI/dVimaging was performed with a CO-terminated tip, the differential conduc-tance map was recorded by a digital lock-in amplifier with a modulationfrequency of 510 Hz and an AC voltage of 10 mV. Obtained images wereanalyzed using the SPIP software.Calculations: For the adsorption simulation of precursor on Au (111)surface, 100 different adsorption structures were calculated by the MonteCarlo method with a unit cell (46.24 × 40.05 × 49.72 Å) containing athree-layer gold substrate and a vacuum layer of 45 Å. The adsorptionsimulation was performed with the Adsorption Locator module basedon the MM method, and COMPASS III was used for the force field. Theprecursor molecule was used as the initial structure. The obtained 100structures were classified into four types, “ud”, “du”, “dd”, and “uu”, ac-cording to the difference in height between the two benzene rings at themolecule’s hinge. One of each of the four structure types was optimized bythe quantum mechanics/molecular mechanics (QM/MM) method (withthe QMERA module).[33] The DMol3 module[34] and GGA-PBE exchangecorrelation functional were used to calculate the properties of the QMatoms and GULP was used to calculate the properties of the MM volumesemploying the ReaxFF 6.0 force field.Hydrogen-terminated GNR trimer models were used for the chargedensity and dipole estimation calculations. In the DMol3 module, a hybridB3LYP functional with an all-electron core DN basis set was used. The gridinterval was set to 0.25 Å, the orbital cutoff distance was set to 3 Å and themultipolar expansion was set to hexadecapole.Regarding polymer inter-chain interaction energy, a unit cell(7.40 × 80.00 × 30.00 Å) was prepared, and two GNR strands wereplaced. Fine structural optimization calculation was performed byCASTEP module. DFT structural optimization and STM calculations,the Perdew–Burke–Ernzerhof generalized-gradient approximation (GGA-PBE)[35] was used as the exchange correlation functional employingon-the-fly-generated (OTFG) Ultrasoft pseudopotentials. The energylandscapes were constructed from the energy calculations performed atAdv. Mater. Interfaces 2023, 10, 2300214 2300214 (6 of 7) © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH 21967350, 2023, 23, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/admi.202300214 by Cochrane Japan, Wiley Online Library on [26/12/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advmatinterfaces.deeach GNR strand coordinate. 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