Guest-Mediated Hierarchical Self-Assembly of Dissymmetric Organic Cages to Form Supramolecular Ferroelectrics

Open AccessCCS ChemistryRESEARCH ARTICLE14 Jul 2022Guest-Mediated Hierarchical Self-Assembly of Dissymmetric Organic Cages to Form Supramolecular Ferroelectrics Xiaoning Liu†, Gucheng Zhu†, Dan He, Lehua Gu, Peiyue Shen, Guijia Cui, Shaoqiang Wang, Zhiwen Shi, Daigo Miyajima, Shiyong Wang and Shaodong Zhang Xiaoning Liu† Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Aging, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240 †X. Liu and G. Zhu contributed equally to this work.Google Scholar More articles by this author , Gucheng Zhu† Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 †X. Liu and G. Zhu contributed equally to this work.Google Scholar More articles by this author , Dan He RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198 Google Scholar More articles by this author , Lehua Gu State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), Department of Physics, Fudan University, Shanghai 200438 Google Scholar More articles by this author , Peiyue Shen Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 Google Scholar More articles by this author , Guijia Cui Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Aging, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240 Google Scholar More articles by this author , Shaoqiang Wang Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Aging, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240 Google Scholar More articles by this author , Zhiwen Shi Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 Google Scholar More articles by this author , Daigo Miyajima RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198 Google Scholar More articles by this author , Shiyong Wang Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai 200240 Google Scholar More articles by this author and Shaodong Zhang *Corresponding author: E-mail Address: [email protected] Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Aging, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240 Google Scholar More articles by this author https://doi.org/10.31635/ccschem.021.202101242 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Herein, we report on the guest-responsive hierarchical self-assembly of dissymmetric cage DC-1 with an intrinsic dipole along its C3-symmetric axis. DC-1 molecules self-assemble into supramolecular columns with the molecular dipoles aligned along the columnar axis. Mediated by different host–guest interactions of ethyl acetate (EtOAc) and chloroform (CHCl3), the columns are arranged in an antiparallel and parallel fashion, respectively, leading to a switch of the centrosymmetric and noncentrosymmetric superstructures. The symmetry of the molecular packing of DC-1 molecules of the noncentrosymmetric crystalline phase is therefore broken, producing a supramolecular ferroelectric with second-harmonic generation and piezoelectric responses. We demonstrate that cages can serve as promising building blocks for the discovery of supramolecular materials with emergent functions and properties, including but not limited to, organic ferroelectrics and nonlinear optics. Download figure Download PowerPoint Introduction Covalent organic cages have attracted considerable attention over the most recent decade.1–8 Their most important characteristic is intrinsic porosity,7 which has been applied to selective recognition/separation,2,3,9 sensing,10 catalysis,11,12 and so on. The other key characteristic of cages is the geometric diversity,6,13 which provides a panoply of polyhedra including tetrahedron,14,15 octahedron,4 cuboctahedron,16 cube,14,17 prism,18–20 and catenated structures.21–26 Cages of various shapes can be used as powerful tectons for the discovery of novel supramolecular materials that are inaccessible by conventional molecules,27 but this feature has been largely overlooked. Besides, the insofar limited examples rather focus on the structural aspects of the self-assembly of cages (capsules),28–30 and the functions of these superstructures must still be explored. Our research group have been focusing on the elaboration of hierarchical self-assembly of organic cages30 and cage catenanes.31 Recently, we found that these unique supramolecular synthons self-assembled into single-handed double helices that led to the formation of single-handed crystals with screw dislocation,30 as well as an unusual three-dimensional (3D) continuous wavelike plank with a three-level hierarchy.31 Taking advantage of the two characteristics of cage-like compounds, namely intrinsic cavity with tunable host–guest interactions32–34 and specific geometry,6,13 herein, we show that dissymmetric cage DC-130 adopting a C3-symmetric propeller-like shape (Figure 1a) and intrinsic dipole can self-assemble into distinct crystalline phases. The molecular packing of DC-1 is simply controlled by guest molecules, switching from a centrosymmetric to noncentrosymmetric superstructure (Figure 1b). Particularly, the dipoles of all DC-1 molecules in the noncentrosymmetric superstructure are aligned in the same direction, resulting in an interesting polar supramolecular material with the properties of second-harmonic generation (SHG) and piezoelectricity, which can open a new way to develop organic cages for the potential application of nonlinear optics, ferroelectrics, bulk photovoltaics, and so on. Figure 1 | Mediation of centrosymmetric and noncentrosymmetric hierarchical self-assembly of dissymmetric cage DC-1 with different guest molecules, namely EtOAc and CHCl3. (a) Synthesis of dissymmetric cage DC-1, the red and blue panels represent the benzene and Tp-derived panel of DC-1, respectively. (b) Upon host–guest interaction with EtOAc, DC-1 self-assembled into centrosymmetric (apolar) crystalline phase DC-1•4EtOAc, while with CHCl3, DC-1 formed noncentrosymmetric (polar) crystalline phase DC-1•3CHCl3. Red and green arrows represent the alignment of dipoles of DC-1 molecules in each supramolecular column. Download figure Download PowerPoint Experimental Methods Materials A dissymmetric cage DC-1 was synthesized as in our previous work.30 Reagents and solvents were purchased from commercial suppliers, including Tansoole and Bidepharm (Shanghai, China). CHCl3 was dried with CaCl2 and freshly distilled before use. Silicon wafer and indium tin oxide (ITO) glass were also purchased from commercial suppliers. They were cleaned by distilled water, ethanol, and acetone before use. Characterization Field-emission scanning electron microscopy Field-emission scanning electron microscopy (SEM) testing was performed on a FEI Nova Nano (Thermo Fisher Scientific, Hillsboro, USA; SEM) 450 at a voltage of 10 kV. The samples are crystals grown on glass or a silicon wafer (resistivity is 0.001–0.009 Ω·cm; the crystal orientation is <100<; the type of silica wafer is N). Gold spraying treatment was carried out for 30 s before testing. Single-crystal X-ray diffractometry Single crystals were grown by slow diffusion of EtOAc into its CHCl3 solution, and slow evaporation of CHCl3 at room temperature, respectively. The single-crystal data of cage DC-1 were collected on a Bruker D8 VENTURE. The test temperature was 293 K for polymorphs DC-1·3CHCl3 and 173 K for DC-1·4EtOAc, respectively. The structures were solved by direct methods using OLEX-2 software (OlexSys Ltd, Durham, UK). All nonhydrogen atoms were refined using anisotropic thermal parameters. Details of the crystal structure solution and refinement are provided in the Supporting Information. Powder X-ray diffractometry Powder X-ray diffraction (PXRD) patterns were collected using a Bruker D8 ADVANCE Discover powder diffractometer at 40 kV and 40 mA for Cu Kα (λ = 1.54178 Å) with a scan speed of 0.10 s/step from 3° to 70° at a step size of 0.02°. The data were analyzed using the EVA program from the Bruker Powder Analysis Software package. The simulated powder patterns were calculated using Mercury (The Cambridge Crystallographic Data Centre, Cambridge, UK) based on single-crystal diffraction data of the corresponding cage. Hirshfeld surface calculations Molecular Hirshfeld surfaces were calculated and analyzed using the program CrystalExplorer.35 Each of the crystal structures in the data set was taken without modification from the Cambridge structural database (CSD) for Hirshfeld surface analysis. For the purpose of this study, all Hirshfeld surfaces were generated using a standard (high) surface resolution. Synthesis of cage DC-1 1,3,5-Tris{[3-amino(1,1′-biphenyl-3-yl)-phenyl]-3-yl}benzene (TABPB) (80.7 mg, 0.1 mmol) was dissolved in 6.7 mL anhydrous CHCl3, and 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (Tp) (21 mg, 0.1 mmol) was dissolved in a mixture of 6.7 mL anhydrous CHCl3 and a catalytic amount of trifluoroacetic acid (TFA) (268 μL). The solution of TABPB was slowly added into the Tp solution within 10 min. The mixture was then reacted without stirring for 72 h. The crude product was purified by chromatography column on silica gel with ethyl acetate/hexane = 2:1 to yield a yellow solid (15 mg, yield 15.5%). Results and Discussion Dissymmetric cage DC-1 with intrinsic dipole Dissymmetric cage DC-1 was synthesized according to our previously reported protocol,30 which was achieved by acid (TFA)-catalyzed cycloimination and subsequent keto-enol tautomerization from the precursors Tp and TABPB. The crystal structure of DC-1 revealed its propeller-like geometry with threefold C3-symmetry. The dissymmetric nature of DC-1 is clearly illustrated by the crystal structure, as it is composed of two different panels (red and blue panels in Figure 1) and three terphenyl blades, with a C3-symmetric axis as the only element of symmetry. It is also worth noting that this dissymmetric cage with two different panels endows this three-dimensional molecule with an intrinsic dipole along the C3-symmetric axis, and the alignment of the dipoles of DC-1 molecules during controlled self-assembly can provide new functions of the self-assembled superstructure (vide infra). Ethyl acetate mediating the self-assembly of DC-1 into the centrosymmetric crystalline phase As individually demonstrated by the research groups of Cooper32,33 and Banerjee,34 the molecular packing of cage-like compounds can be tuned by different host–guest interactions between the cage host and solvent guest, leading to distinct polymorphs with different porosities. Inspired by their seminal works, we first set out to probe the guest responsive self-assembly of DC-1 by slow diffusion of ethyl acetate (EtOAc) into its chloroform (CHCl3) solution, which self-assembled into triclinic space group P 1 ¯ in a solvated form DC-1·4EtOAc (Figure 2). As examined by SEM, the polymorph DC-1·4EtOAc adopts parallelepiped crystallites with a size up to 200 μm (Figure 2a). The single-crystal X-ray diffraction (SC-XRD) revealed that DC-1 molecules formed a densely packed superlattice (Figure 2c, left). Along the crystallographic a-axis (Figure 2b), DC-1s, serving as primary structures, are piled with each other to generate a supramolecular column (secondary structure, Figure 2c, right). It is worth noting that within each column the dipoles of DC-1s are aligned in the same direction, but cancelled with the dipoles in the adjacent column, as indicated with the oppositely directing arrows in brown and green (Figure 2c, right). Therefore, a pair of antiparallel supramolecular columns self-organize into a centrosymmetric crystalline phase (tertiary structure), in line with the symmetry of space group P 1 ¯ of the polymorph ( Supporting Information Table S1). Figure 2 | (a) Hierarchical self-assembly of DC-1 molecules mediated by EtOAc at the supramolecular level. (a) SEM image of the crystallites. (b) Cartoon illustration of a crystallite with the crystallographic axes assigned by SC-XRD. (c) Top (left) and side (right) views of the guest-omitted polymorph DC-1·4EtOAc. The two different panels of each DC-1 are differentiated with blue and red colors. Antiparallel brown and green arrows indicate the cancellation of dipoles of DC-1 molecules in two adjacent supramolecular columns. The crystallographic space group is given under the cartoon. Guest molecules are omitted for clarity. Download figure Download PowerPoint Chloroform mediating the self-assembly of DC-1 into a noncentrosymmetric crystalline phase When we attempted to grow the crystals by slow evaporation of CHCl3 from its solution, it yielded a different polymorph, which adopted a shape of hexagonal prism with a length up to 100 μm (Figure 3a). SC-XRD revealed that DC-1s self-assembled into trigonal space group P31c as a solvated DC-1·3CHCl3 ( Supporting Information Table S2). Contrary to the dense packing within the crystalline phase of DC-1·4EtOAc, DC-1 molecules form a honeycomb-like superlattice (tertiary structure, Figure 3c, left). Along the crystallographic c-axis (Figure 3b), DC-1s, as primary structures, are packed on top of each other to yield a supramolecular column as well (secondary structure, Figure 3c, right). In each column the dipoles of DC-1s are also aligned along the c-axis but share the same direction with those of the neighboring column, as indicated by the green arrows. It means the erstwhile centrosymmetry in polymorph DC-1·4EtOAc has been broken, which is switched to a noncentrosymmetric superstructure in polymorph DC-1·3CHCl3. This symmetry breaking leads to the alignment of dipoles of all DC-1 molecules, and this polar arrangement provides this hierarchical superstructure with interesting properties such as SHG and piezoelectricity, vide infra). Figure 3 | (a) Hierarchical self-assembly of DC-1 molecules mediated by CHCl3 at the supramolecular level. (a) SEM image of the crystallites. (b) The cartoon illustration of the crystallite with the crystallographic axes assigned by SC-XRD. (c) Top (left) and side (right) views of the guest-omitted polymorph DC-1·3CHCl3. The two different panels of each DC-1 are differentiated with blue and red colors. Green arrows indicate the alignments of dipoles of DC-1 molecules in two adjacent supramolecular columns. The crystallographic space group is given under the cartoon. Guest molecules are omitted for clarity. Download figure Download PowerPoint Driving force of self-assembly of DC-1 by noncovalent interactions As mentioned earlier, two distinct superstructures self-assembled by a single type of dissymmetric cage were achieved by different guest molecules. This switch was realized by varying the noncovalent interaction between the guest molecules and DC-1s. Considering that the self-assembly of DC-1 generally results from an optimized balance between various intermolecular interactions,27 presumably including cage-to-cage, cage-to-guest, and guest-to-guest interactions, we employed Hirshfeld surfaces and two-dimensional (2D) fingerprint plots of guest molecules CHCl3 and EtOAc, respectively, to understand how different guests mediate the self-assembly of DC-1 (Figure 4).36 Figure 4 | The influence of noncovalent interaction and shape of guest molecules on the self-assembly of dissymmetric cage DC-1. Guest-filled unit cell (left), Hirshfeld surface mapped with de (middle), and two-dimensional fingerprint plot (right) of polymorphs (a) DC-1·3CHCl3 and (b) DC-1·4EtOAc, respectively. The de surfaces are mapped over the ranges of 1.000–7.644 Å and 0.095–2.450 Å for DC-1·3CHCl3, and DC-1·4EtOAc, respectively. The solvents in the left column are distinguished with different colors, as green and gray stand for CHCl3, and red and gray for EtOAc. The meaningful intermolecular interactions between the guest molecules and DC-1 are labeled with numbers, as 1 stands for C…aryl H, 2 for H…H, and 3 for O…H. (c) Relative contributions of intermolecular interactions in the self-assembled superstructures mediated by DC-1•3CHCl3, and DC-1•4EtOAc, respectively. These interactions are derived by their Hirshfeld surfaces and two-dimensional fingerprint plots. Download figure Download PowerPoint In polymorph DC-1·3CHCl3, every CHCl3 molecule resides in each window of a DC-1 (Figure 4a, left). The bright red spots on the Hirshfeld surface of CHCl3 mapped with de represent its clear interactions with the terphenyl linkers of a hosting DC-1 (Figure 4a, middle), which are mainly assigned to the meaningful C–H…Cl (strong blue spot in the area of di = 1.8–2.2 Å and de = 1.2–1.8 Å), C…aryl H (labeled 1, Figure 4a, right), and H…H (starting from di ≈ 1.7 and de ≈ 1.5 in labeled 2, Figure 4a, right) contacts between CHCl3 and DC-1 within its window. On the other hand, in polymorph DC-1·4EtOAc, four EtOAc molecules are not evenly dispersed within the void space. One EtOAc is positioned perpendicularly to the C3-symmetry axis of DC-1, and it occupies the inner cavity and one window of the cage, the second EtOAc resides in the second window, and another two EtOAc molecules share the third window of the cage (Figure 4b, left). The self-assembly of DC-1 is mediated by a cage-EtOAc-EtOAc-cage networking through a sextuple H-bond bridging ( Supporting Information Figure S2). This H-bond bridging is clearly demonstrated by the Hirshfeld surface of an EtOAc participating in the network (Figure 4b, middle), as the H-bonding acceptor is clearly shown as the striking red spot on the de surface of the guest molecule. This H-bonding is also confirmed by a 2D fingerprint plot, which is present as a strong blue spike labeled in 3 (Figure 4b, right). Due to this H-bond bridging, the distance between the two cages in DC-1·4EtOAc is brought closer compared with that in DC-1·3CHCl3, which in turn leads to tighter H…H contact (starting from di ≈ 1.1 and de ≈ 1.2 in labeled 2, Figure 4b, right) and π–π stacking ( Supporting Information Figure S3), resulting into closer packing of DC-1 molecules (Figure 2c vs 3c). The different contributions of guest molecules CHCl3 and EtOAc are summarized in Figure 4c. The contributions of π–π stacking (C…C contact) in the two self-assembled superstructures are similar, that is, about 7%. The directional H-bonding in DC-1•4EtOAc is stronger, comprising 11.2% of the intermolecular interactions. As a result, it leads to a tighter packing of cages in DC-1·4EtOAc than in DC-1·3CHCl3, which in turn results in a stronger H…H interaction in the former (46.2% in DC-1·4EtOAc vs 32% in DC-1·3CHCl3). Monitoring crystal growth of DC-1 with different guest molecules After we gained insight into the guest-mediated hierarchical self-assembly of DC-1 at the supramolecular level, we extended the investigation to the mesoscopic level with crystal growth under different solvent conditions. To acquire a direct visualization of the crystal growth we created a concentration gradient of the solute by vertically immersing the silica wafer into the CHCl3 solution of DC-1, and slowly evaporating CHCl3 six “snapshots” taken at different stages ( Supporting Information Figure S4 and Figure 5). DC-1 molecules first formed sheet-like structures (Figures 5a and Supporting Information Figure S5), which might serve as mesoscopic building units (MBUs). With further evaporation of CHCl3, the MBUs were stacked into brochette-like structures (Figure 5b, Supporting Information Figure S6a, and step (i) in Figure 5h), which subsequently self-organized with each other, forming a “brochette bundle” intermediate (Figure 5c, Supporting Information Figures S6b–S6d, and step (ii) in Figure 5h). The first two steps of crystal growth can be considered as the self-templating phase (Figure 5h), where MBUs and brochette-like structures served as their own templates, respectively. This was followed by the self-perfection phase, where the as-formed bundle intermediate served as a template on which MBUs or DC-1 molecules were attached until the formation of crystallites with the perfect shape of a hexagonal prism (Figure 5d–5f, illustrated by steps (iii–v) in Figure 5h). The crystalline structural resolution of the bulk mixture composed of all the aforementioned intermediates was conducted by PXRD (Figure 5g). Together with the Pawley refinements, the PXRD results revealed a trigonal unit cell (a = 21.58, b = 21.58, c = 11.38 Å) with space group P31c, which is identical to that derived from the single-crystal X-ray structural analysis of polymorph DC-1·3CHCl3. It confirmed that the molecular packing of DC-1 remained identical during the crystal evolution process. Therefore, this observation provides an unusual yet plausible step-wise crystallization mechanism of DC-1 at the mesoscopic level. Figure 5 | In situ evolution of crystal growth induced by concentration gradient of dissymmetric cage DC-1 in CHCl3 solution. (a–f) SEM images during the crystal evolution process: (a) sheet-like structure, (b) brochette-like structure, (c) brochette-bundle intermediate, (d–e) crystal intermediates during the self-perfection steps, (f) crystallite with the perfect shape of hexagonal prism. (g) Powder X-ray pattern of the mixture of crystals at different stages, with experimental (gray line) and refined patterns after Pawley refinement (blue circled line, Rwp = 8.28%, Rp = 6.35%) at 298 K (a = 21.58, b = 21.58, c = 11.38 Å, P31c). The simulated pattern from its single crystals is presented with a red line, reflection positions marked in green, and the difference from experimental and refined patterns with a black line. (h) The schematic illustration of the crystal growth process at different stages: (i) self-assembly of sheet-like structure into brochette-like structure, (ii) self-organization of brochette-like structure into a “brochette bundle” intermediate, (iii–v) self-perfection steps with a brochette-bundle as the template. Download figure Download PowerPoint We also attempted to monitor the crystal growth by slowly diffusing EtOAc into the CHCl3 solution of DC-1 ( Supporting Information Figures S9 and S10), but the step-wise crystallization of DC-1·4EtOAc was less conclusive. Nevertheless, it allowed us to postulate a layer-by-layer growth mechanism, followed by surface perfection of the crystals, similar to that of DC-1·3CHCl3. SHG and piezoelectric properties of the noncentrosymmetric crystalline phase of DC-1·3CHCl3 As mentioned earlier, the alignment of dipoles of DC-1 molecules in the noncentrosymmetric crystalline phase of DC-1·3CHCl3 might make it a good candidate for supramolecular ferroelectrics and electronics.37–41 The symmetry breaking between DC-1·4EtOAc and DC-1·3CHCl3 was first investigated with SHG (also called frequency doubling) experiments, as SHG can be observed only in crystals of noncentrosymmetric space groups. As compared with DC-1·4EtOAc without any SHG response, clear evidence of symmetry breaking of DC-1·3CHCl3 was confirmed with the frequency change of the incident laser (820 nm), whose output light was doubled (410 nm) when passing through the latter (Figures 6a–6c). Figure 6 | SHG and piezoelectric properties of the thin film of DC-1·3CHCl3. (a) SHG signal (410 nm) of the single crystal of DC-1·3CHCl3 with excitation of an 820 nm femtosecond laser with an (b) optical image and (c) SHG mapping image of the crystal without poling. (d) Atomic force microscopy (AFM) topographic image, (e) vertical PFM amplitude image and (f) phase image within a 5 × 5 μm region in the thin film of DC-1·3CHCl3. (g) Vertical PFM amplitude (butterfly) and phase (hysteresis) loops as a function of dc bias. Domain switching of this thin film presented with (h) PFM amplitude image and (i) phase image within a 10 × 10 μm region, recorded after applying a voltage of +50 V on the left side and −50 V on the right side of the region. Download figure Download PowerPoint We further probed the centrosymmetric (apolar) and noncentrosymmetric (polar) nature of DC-1·4EtOAc and DC-1·3CHCl3, respectively, by scanning their corresponding spin-coated thin film samples with piezoresponse force microscopy (PFM). When the samples were scanned with a conductive tip with a voltage of ca. 300 mV in a vertical mode, it allowed us to observe the out-of-plane polarization domains pointing up- or downward. The topographic imaging revealed that both DC-1·4EtOAc and DC-1·3CHCl3 thin films were rather smooth, exhibiting a roughness of ca. ±5 nm (Figure 6d and Supporting Information Figure S16a).42 It therefore facilitates the record of local lattice deformation of a ferroelectric sample, namely amplitude and phase signals, that correspond to the piezoresponse intensity and polarization orientation, respectively.42,43 No obvious amplitude and phase signals were noticed with the sample of DC-1·4EtOAc ( Supporting Information Figure S16b, S16c, and S16d), which indicated this superstructure was not a polarized material, in line with its centrosymmetric nature. On the other hand, the sample of DC-1·3CHCl3 displayed obvious piezoelectric response, particularly with a 180° reversal of two oppositely directing polarization domains (Figure 6e and 6f), which confirmed this noncentrosymmetric sample of a polarized material.42,44 We continued to investigate the polarity switch of both samples by applying a voltage bias (Figure 6g–6i and Supporting Information Figure S17). To do so, an initial state was set up by scanning a 10 × 10 μm region of the thin film with a uniform domain, which was then written by the probing tip with a bias of +50 and −50 V on the left and right sides of the region, respectively.42 As expected, no piezoelectric signal was observed for the centrosymmetric and nonpolar DC-1·4EtOAc thin film ( Supporting Information Figure S17). A successful polarization switching of DC-1·3CHCl3 sample was confirmed with a 180° PFM phase difference with a well-defined boundary between the two opposite polarization areas (Figure 6i). When varying the dc voltage bias of the conductive tip, characteristic butterfly and hysteresis loops of ferroelectrics were observed by PFM (blue and red curves in Figure 6g). The butterfly (amplitude) loop shows the strain variation along an external field change, and the hysteresis loop presents an approximately 180° phase reversal with the voltage bias reversal.41–44 When applying different voltages, a constant coercive voltage at ca. 75 V was determined for the DC-1·3CHCl3 thin film ( Supporting Information Figure S15). These two piezoelectric signals therefore showed a typical polarization switching of the polar DC-1·3CHCl3 thin film, confirming its ferroelectric feature. Inducing ferroelectric polarization of the single crystals of DC-1·3CHCl3 were unsuccessful, due to the crystals cracking under high voltage. Conclusions We have demonstrated that dissymmetric cage DC-1 could self-assemble into various hierarchical superstructures with different packing modes. The different molecular packing of DC-1 molecules were mediated by specific noncovalent host–guest interactions of the guest molecules, which in turn changed the overall balances of various intermolecular interactions such as H-bonding, π–π stacking, C…aryl H contact, H…H interactions, and so on. It led to switching of the centrosymmetric ( P 1 ¯ space group) and noncentrosymmetric superstru