News Reader.info

ABSTRACT Organic ferroelectrics, in which the constituent molecules retain remanent polarization, represent an important topic in condensed-matter science, and their attractive properties,

which include lightness, flexibility, and non-toxicity, are of potential use in state-of-the-art ferroelectric devices. However, the mechanisms for the generation of ferroelectricity in such

organic compounds remain limited to a few representative concepts, which has hitherto severely hampered progress in this area. Here, we demonstrate that a bowl-to-bowl inversion of a

relatively small organic molecule with a bowl-shaped π-aromatic core generates ferroelectric dipole relaxation. The present results thus reveal an unprecedented concept to produce

ferroelectricity in small organic molecules, which can be expected to strongly impact materials science. SIMILAR CONTENT BEING VIEWED BY OTHERS MOLECULAR FERROELECTRIC WITH

LOW-MAGNETIC-FIELD MAGNETOELECTRICITY AT ROOM TEMPERATURE Article Open access 03 June 2024 ENHANCEMENT OF PHASE TRANSITION TEMPERATURE THROUGH HYDROGEN BOND MODIFICATION IN MOLECULAR

FERROELECTRICS Article Open access 25 May 2024 ORGANIC RADICAL FERROELECTRIC CRYSTALS WITH MARTENSITIC PHASE TRANSITION Article Open access 20 September 2023 INTRODUCTION Ferroelectric

materials, which undergo reversible electric polarization upon exposure to an external electric field, are crucial components of ferroelectric devices, such as non-volatile memories,

actuators, and piezoelectric devices1. The ferroelectricity of organic molecules has attracted attention as a promising alternative to inorganic ferroelectric materials that contain precious

and/or toxic metals2,3. However, examples of organic ferroelectrics are relatively scarce, and those known typically present one of the following three mechanisms: (1) orientational change

of polar low-molecular-weight compounds4,5,6, (2) electron transfer in donor–acceptor-type charge-transfer complexes7,8,9, and (3) proton transfer in hydrogen-bonding networks10,11,12 (Fig. 

1, left). Therefore, the development of new strategies for designing organic ferroelectrics is of fundamental importance and represents a primordial step for versatile memory applications.

Chemical design strategies based on π-electron systems afford control over electrical conduction, as well as magnetic and optical properties. For instance, the charge-ordered state of the

cation radical salts of bis(ethylenedithio)tetrathiafulvalene leads to electronic polarization-type ferreoelectrics13. On the contrary, both the flexibility and the dynamics of molecular

assemblies of low-molecular-weight compounds offer an interesting dynamic environment that may allow controlling certain physical properties, such as dislocation, ferroelectricity, and

ferroelasticity. Indeed, ferroelectric responses have been observed in the flip-flop motion of a supramolecular cation and the multi-axial rotation of polar molecules in a plastic

crystalline state6,14. Such diverse motional freedom in molecular assemblies could potentially be exploited to fabricate functional ferroelectric molecular memory materials. The

supramolecular assembly of liquid crystalline compounds in a bowl-shaped structure induces dipole moments that subsequently lead to ferroelectricity (Fig. 1, middle)15,16. Although bowl

inversions have typically been observed in solution, ferroelectricity that originates from bowl inversion in supramolecular assemblies has not yet been realized, even though some advances

using bowl-shaped molecules have been reported17,18,19. For example, subphthalocyanine derivatives with strong axial dipoles have shown permanent homeotropic alignment and polarization in

columnar liquid crystals with electric fields20 and ferroelectric properties in nematic phases21. On the other hand, the use of polar oligo-(vinylidenedifluoride) and/or amide side chains

are also useful to induce ferroelectricity in solid-state columnar organic π-conjugated molecules22,23. A bowl-to-bowl inversion mechanism for the ferroelectric response is hardly designed

in solid-state columnar assembly, necessitating the utilization of highly thermal fluctuated liquid crystal or plastic crystal states. Here, we report organic ferroelectric materials based

on hexa-alkoxy trithiasumanenes (C_N_SS), which exhibit invertible bowl-shaped π-aromatic cores. We discovered that the bowl-shaped aromatic cores of these C_N_SS molecules are

one-dimensionally stacked in a columnar fashion, and that the dipole moment originating from the aligned bowl-shaped framework leads to remanent polarization in the crystals. The present

work thus describes a concept of invertible aromatic cores for materials design that provides facile access to solution-processable and low-cost single-columnar ferroelectric memory devices

with a high density (>12 TB cm−2). RESULTS MOLECULAR DESIGN AND SYNTHESIS We selected trithiasumanene (SS)24 as the bowl-shaped π-aromatic core, given its low bowl-inversion barrier. In

general, the magnitude of the bowl-inversion barrier (Δ_E_b) is closely related to the bowl depth (_l_b) of the curved π-frameworks. For the typical bowl-shaped molecule sumanene (_l_b = 

1.143 Å; Δ_E_b = 18.2 kcal mol−1)25, these parameters are higher than those of corannulene (_l_b = 0.877 Å and Δ_E_b = 9.2 kcal mol−1)26 (Fig. 2). The introduction of large heteroatoms, such

as sulfur and selenium in curved π-molecules affords heterasumanenes, whereby the dynamic and electronic properties can be tuned by judicious choice of the inserted

heteroatom(s)27,28,29,30,31. Among these, SS molecules that bear three S atoms in the sumanene π-skeleton exhibit even smaller values (_l_b = 0.76 Å and Δ_E_b = 1.9 kcal mol−1) than those of

sumanene and corannulene25. The large atomic radius of the S-atom leads to a reduction of both parameters for the π-framework, whereas Se-atoms, which are even larger, afford the almost

planar triselenasumanenes (SSE) (Supplementary Fig. 1). The shallower bowl depth of SS should facilitate the bowl-to-bowl inversion of the aromatic core in the solid state upon applying an

external stimulus. To promote motional freedom, as well as bowl inversion, six long alkoxy chains (−OC_n_H2_n_+1) were introduced in the SS π-core, as such motional freedom should enhance

the flexibility and internal thermal energy of the molecular assembly upon heating. Herein, we report the synthesis of SS derivatives that bear −OC_n_H2_n_+1 chains (C_N_SS; _n_ = 6, 8, 10,

or 16) by dealkylation of C2SS, followed by re-alkylation of the obtained hexahydroxy intermediate C0SS (Fig. 3). The starting material (C2SS) was prepared by a modified method for the

synthesis of C4SS32. Treatment of C2SS with boron tribromide, followed by addition of water, afforded the air-sensitive hydroxy intermediate C0SS, which was treated with the corresponding

alkyl bromides (C_n_H2_n_+1–Br; _n_ = 6, 8, 10, or 16) and potassium carbonate in dimethylformamide (DMF) to obtain the C_N_SS derivatives. PHASE-TRANSITION BEHAVIOR AND MOLECULAR ASSEMBLY

The differential scanning calorimetry curves of C_N_SS (_n_ = 6, 8, 10, or 16) in the solid state show a reversible phase transition (Fig. 4a). Crystals of C6SS, C8SS, and C10SS exhibit one

reversible solid–solid (S1–S2) phase transition at 315, 299, and 280 K upon heating, and at 313, 297, and 274 K upon cooling, with melting points (S2–I phase transition) at 395, 368, and 359

 K, respectively (Table 1). The increasing length of the −OC_n_H2_n_+1 chains results in lower S1–S2 and S2–I phase-transition temperatures. In polarized optical microscopy (POM) images,

both the S1 and S2 phases exhibit birefringence under a cross-Nicol optical alignment in the absence of fluid behavior (top and middle POM images in Fig. 4b). On the contrary, fluid and

birefringence properties were confirmed for the M1 phase of C16SS (bottom POM image in Fig. 4b), suggesting the formation of a liquid crystalline phase before melting. The M1–I

phase-transition temperature and transition-enthalpy change (Δ_H_) for C16SS are 345 K and 15.1 kJ mol−1, respectively. The high structural flexibility of the −OC16H33 chains becomes

apparent in the liquid crystalline phase above the S2 phase (330–345 K). The phase-transition behavior of the C_N_SS derivatives is very similar, except for the stabilization of the M1 phase

for the C16SS derivative. Next, we determined the molecular and assembly structure of C_N_SS (_n_ = 6, 8, 10, or 16) by X-ray diffraction analyses. Although a single-crystal X-ray

diffraction analysis was successfully carried out for C2SS at 300 K, the single crystals obtained for the long-chain derivatives (_n_ = 6, 8, 10, or 16) were unfortunately of insufficient

quality. Thus, a temperature-dependent powder X-ray diffraction (PXRD) analysis was performed for each S1, S2, and M1 phase to obtain information on the molecular assembly structures. Figure

 5a shows the temperature-dependent PXRD patterns for the S1 (_T_ = 260 K) and S2 (_T_ = 320 and 346 K) phases of C10SS. C6SS and C8SS exhibit almost identical PXRD patterns (Supplementary

Fig. 2). The pattern of the S1 phase of C10SS (purple in Fig. 5a) is similar to that of the S2 phase. However, several sharp diffraction peaks at 2_θ_ ~ 20° broadened upon transition to the

S2 phase (red and green in Fig. 5a), suggesting that the crystal symmetry of the latter is probably higher than that of the S1 phase due to thermally activated molecular motion. The most

intense diffraction peak of the S2 phase at 2_θ_ = 3.960° was assigned to the 100 reflection with a periodicity of _a_ = 47.82 Å for the trigonal (or hexagonal) crystal system, which

corresponds to _a_ = 25.4783(2) Å for the single-crystal X-ray diffraction analysis of C2SS with the polar space group _P_3_c_1 at 300 K. In addition, the two weak diffraction peaks at 2_θ_ 

= 6.908 and 7.964° were assigned to the 110 and 200 reflections, respectively, which is consistent with the formation of a hexagonal lattice. A linear relationship of the _h_00 reflections

was confirmed in the C_N_SS series (_n_ = 2, 6, 8, 10, or 16) (Supplementary Fig. 3), suggesting an identical packing structure for all C_N_SS derivatives. The broad reflection at 2_θ_ ~ 20°

is probably due to the melting of the −OC_n_H2_n_+1 chains, similar to the behavior in a discotic columnar liquid crystalline phase. It should be noted that the intense reflection at 2_θ_ ~

 24.02° corresponds to an average π-stacking distance of 3.71 Å. A single-crystal X-ray diffraction analysis of C2SS at 300 K provided insight into the solid-state structure of C2SS, and the

principal arrangements can potentially be extrapolated to the other C_N_SS derivatives with longer alkyl chains. The molecular and packing structures for C2SS based on the single-crystal

X-ray diffraction analysis are shown in Fig. 5b, c, respectively. A bowl-shaped molecular structure was confirmed, where both the up-bowl (A) and down-bowl (B) columns coexist in the unit

cell. The π-stacking columns of A and B are hexagonally arranged with respect to each other (Fig. 5c). The occupation ratio of A-column/B-column (2/1) in the unit cell is consistent with the

formation of the polar space group _P_3_c_1. Figure 5d shows the schematic arrangement of π-column A (red) and B (blue) in the trigonal (dashed green line) and hexagonal (solid black line)

lattices. The polar space group _P_3_c_1 of C2SS is consistent with a ferroelectric ground state along the _c_-axis, assuming bowl-to-bowl inversion between A and B. The PXRD patterns of the

S1 and S2 phases for liquid crystalline C16SS are very similar, and that of the M1 phase is consistent with the formation of a discotic hexagonal columnar (Colh) liquid crystal phase

(Supplementary Fig. 4b). In this Colh phase, the thermally activated melting of the six −OC16H33 chains and the free rotation of the π-stacking columns along the orientation of the director

occur simultaneously, weakening the intensity of the broad 001 reflection due to thermal fluctuation of the π-stacking _d_001-spacing. Although the Colh mesophase was not observed for C6SS,

C8SS, and C10SS, the molten state of the six −OC_n_H2_n_+1 chains was confirmed by the broad diffraction at 2_θ_ ~ 20° (Supplementary Fig. 2). The in-plane rotation of each bowl-shaped

molecule is likely suppressed in the π-stacking columns of the S2 phase, also disappearing in the Colh phase for certain C_N_SS (_n_ = 2, 6, 8, or 10). The thermally activated molten state

of the −OC_n_H2_n_+1 chains plays an important role in the phase transitions and in the ferroelectric response of such bowl-shaped C_N_SS. FERROELECTRIC RESPONSE Dielectric features arise

from the molecular motion of polar structural units within a molecular assembly. In the present C_N_SS derivatives, such polar structural units are only observed in the bowl-shaped π-plane,

whose π-stacking generates a macro dipole moment along the π-stacked column. The π-stacked columns of C_N_SS in high-temperature S2 phase were easily oriented along the direction normal to

the ITO surface after the cooling from isotropic liquid, which was confirmed in the dark POM images of the homeotropic orientation on the substrate surface (Supplementary Fig. 5). A polar

crystal structure with space group _P_3_c_1 was identified for a single crystal of C2SS, where the occupation number of the polar A and B π-stacking bowls was not balanced, producing a

ferroelectric dipole ground state. The second-harmonic generation (SHG) activity was observed at C2SS at 298 K, in which the magnitude was similar to that of sucrose (Supplementary Figs. 

6–7). Figure 6a, b shows the temperature (_T_)_-_ and frequency (_f_)-dependent real (_ε_1) and imaginary (_ε_2) components of the dielectric constants of C10SS using a sandwich-type

electrode. The _T_- and _f-_dependent _ε_1 responses around 300 K increased monotonically with increasing temperature and frequency above 330 K for the S2 phase. Dielectric anomalies were

not observed around the S1–S2 phase transition. On the contrary, the _ε_2–_T_ plots at _f_ = 1 kHz showed a dielectric peak at 349 K, i.e., a lower temperature than that of the S2–I phase

transition (356 K). Almost the same _f-_ and _T_-dependent dielectric constants were obtained for C6SS and C8SS (Supplementary Fig. 8). Interestingly, a ferroelectric polarization–electric

field (_P_–_E_) hysteresis at _f_ = 100 Hz for C10SS was confirmed in the high-temperature S2 phase (Fig. 6c), i.e., it was clearly observed at 353 and 343 K with a remanent polarization

(_P_r = 0.5–0.7 μC cm−2) and coercive voltage (_E_th ≈ 1.5 V μm−1). Time-dependent polarization behavior of C10SS at 343 K showed that the polarization was retained for 4000 ms after

applying a pulse voltage (Supplementary Fig. 9). The appearance of an _ε_2 peak at 356 K and _f_ = 100 Hz is consistent with the thermally activated molecular motion of the polar structural

units at ~100 Hz and 356 K, corresponding to a structural inversion of the π-stacking columns (Fig. 6d). The observed _P_–_E_ hysteresis curve is explained by the polling process between the

electrodes, which orients each column and domain along the sandwich direction. The homeotropic orientation of each π-stacking column aligns the direction of macro dipole moment normal to

the ITO surface without the polling process. The bowl-to-bowl structural inversion is thermally activated even in the solid S2 phase. The thermal melting of the six −OC_n_H2_n_+1 chains

around the polar π-stacking column plays an essential role in the dipole inversion of each polar column, resulting in ferroelectric dipole relaxation via structural bowl-to-bowl inversion.

Similar ferroelectric relaxation processes were observed in the S2 phase of C6SS and C8SS (Supplementary Fig. 10), whereas liquid crystalline C16SS also exhibited ferroelectricity in the M1

phase (_E_th ≈ 2.2 V μm−1; _P_r ≈ 0.4 μC cm−2; _T_ = 336 K) (Supplementary Fig. 11). DISCUSSION The shallower bowl depth of the SS π-core is crucial for the bowl inversion in the solid

state. The dipole moment (_μ_) along the bowl-shaped π-plane of SS is 1.03 D25. The theoretically calculated bowl-to-bowl inversion energy (Δ_E_b) in the gas phase is relatively low (1.9 

kcal mol−1), i.e., by one order of magnitude lower than that of sumanene (Δ_E_b = 18.2 kcal mol−1)25 (Fig. 2), but higher than the room temperature energy (kB_T_ ≈ 0.58 kcal mol−1). The

bowl-to-bowl inversion of C_N_SS (_n_ = 6, 8, 10, or 16) was observed at ~350 K (~0.7 kcal mol−1) in the π-stacked one-dimensional molecular assembly, whereas such an inversion could not be

observed in the liquid crystalline phase of a –SC_n_H2_n_+1-substituted sumanene derivative19. The small curvature angle of the π-plane of SS leads to a smaller Δ_E_b, thus enabling the

bowl-to-bowl inversion even in the solid state, where the thermal melting of the alkyl chains serves as an entropy source for the polar π-stacking structure. In order to assess the

correlation between the ferroelectricity and the molecular structure, the shallow bowl-shaped selenium derivative C4SES was prepared by replacement of three S atoms by Se32. Moreover, the

π-planar triphenylene derivative C6TP was evaluated in terms of its phase transitions, _T-_ and _f_-dependent dielectric constants, and _P–E_ hysteresis curves. Although the theoretically

obtained structure of triselenasumanene (SES) is planar in the absence of alkoxy groups (Fig. 2), the structure of C4SES presents a shallow bowl shape with bowl depths ranging from 0.32 Å to

0.46 Å, as determined by a single-crystal X-ray diffraction analysis32. Crystals of C4SES exhibit a phase transition from crystalline solid (S1) to isotropic liquid (IL) at 358 K in the

absence of the intermediate thermally activated S2 and/or Colh liquid crystalline phases found for the C_N_SS derivatives (Supplementary Fig. 12a). Single crystals of C4SES with polar space

group _R_3 present one-dimensional polar bowl-to-bowl π-stacking columns along the _c_-axis, where the macroscopic dipole moment may potentially exhibit dipole inversion and ferroelectricity

upon application of an external electric field, similar to the case of the C_N_SS crystals. It should be noted here that the crystalline S1 state of C4SES does not contain thermally molten

−OC_n_H2_n_+1 chains. The temperature-dependent PXRD patterns of C4SES in the temperature range from 150 to 350 K show a highly crystalline phase with sharp diffraction peaks and the absence

of a broad diffraction at 2_θ_~20°, which suggests a non-thermally activated molten state of the −OC4H9 chains (Supplementary Fig. 12b). Furthermore, dielectric anomalies were not observed

for the _T_- and _f_-dependent _ε_1-values, which is consistent with the absence of a bowl-to-bowl inversion in the crystalline S1 state (Supplementary Fig. 13). The _P–E_ curves of the S1

phase of C4SES at 313 and 333 K revealed a linear behavior at _f_ = 100 Hz, which is consistent with a paraelectric ground state (Fig. 7). Although a polar space group was observed for

crystalline C4SES, its highly crystalline and rigid molecular assembly structure suppresses the thermally activated bowl-to-bowl inversion. On the contrary, the π-planar molecule C6TP

exhibits an S1–Colh phase transition at 343 K and a Colh–I transition at 371 K, where a thermally stable columnar liquid crystalline phase was observed within a temperature range of ~30 K

(Supplementary Fig. 14a). However, both the _T_- and _f_-dependent _ε_1 behavior of C6TP did not show any evidence for bowl-to-bowl inversion or thermally activated molecular motion of the

polar structural units within the molecular assembly (Supplementary Fig. 14b, c). Stacked structures of π-planar molecules do not exhibit a macroscale dipole moment. Therefore, linear _P–E_

hysteresis curves were obtained both in the S1 and Colh phases due to the absence of dipole inversion, despite the flexibility of the Colh phase. Therefore, thermally activated melting

and/or a dynamic state of the peripheral −OC_n_H2_n_+1 chains and the bowl-to-bowl inversion at the central SS core are both essential for the ferroelectricity exhibited by the C_N_SS

derivatives in the S2 and Colh phases. To elucidate the ferroelectric mechanism of C_N_SS, the dipole moment and _P_r values were determined by DFT calculations at the B3LYP 6–31 G(d,p)

level of theory on model compounds SS and C1SS. The macroscopic polarization, _P_r, was obtained from Eq. (1): $$P_{\mathrm{r}} \,=\, \frac{{{{\Sigma }}_{i \,=\, 1}^nP_i}}{{\Delta V}} \,=\,

\frac{{{{\Sigma }}p_{{\mathrm{mol}}}}}{{\Delta V}}$$ (1) The calculated dipole moment along the normal to the bowl-shaped π-plane of the SS molecule (_μ_ = 0.84 D) afforded a theoretical

_P_r value of 0.19 μC cm−2 for C_N_SS at 343 K, which is inconsistent with the experimental value (_P_r ≈ 0.6 μC cm−2). However, collective motion of dipole moment in the π-stacking column

effectively enhanced the macroscale dipole moment and the magnitude of the polarization33,34. Although the SHG activity was clearly confirmed in highly crystalline C2SS with polar space

group of _P_3_c_1, there were insufficient SHG signals for the other ferroelectric C_N_SS derivatives at high-temperature S2 phase. The SHG activity should be observed in the ferroelectric

ground state due to the polar space group, while highly viscous plastic crystalline S2 phase with thermally melting state of six −OC_n_H2_n_+1 chains exhibited the weak SHG activity in spite

of their _P_-_E_ hysteresis. To discuss this ferroelectric relaxation behavior of C_N_SS derivatives, we estimated a possible polarization mechanism for dipole inversion and relaxation

process of the bowl-to-bowl inversion based on the theoretical DFT calculation using a model compound of C1SS dimer (Fig. 8), where the interdimer distance and skew angle between central

benzene rings were fixed at the same as those observed in the C2SS single-crystal X-ray analysis. The bowl-depth (torsion angle at C–C–C–S bonds) was increased in a stepwise manner from the

π-planar structure (torsion angle = 180°) to the bowl-shaped one (torsion angle = 160°) of C1SS dimer (Fig. 8a). Thermally fluctuated structural transformation between the π-planar and

bowl-shaped conformations at plastic crystalline S2 phase easily activated dipole moment from 0 D at π-planar structure to 1.46 D at bowl-shaped one by the increase in the torsion angle

(Fig. 8a). The intermolecular interaction between the π-stacking columns was dominated by the hydrophobic interaction between the alkyl chains, and consequently thermal melting decreased the

magnitude of intermolecular interaction and activated the bowl-to-bowl inversion in the column. Therefore, the thermally activated structural fluctuation between the polar and the non-polar

molecular conformations in the 1D π-stacking column should be easily activated in highly temperature viscous S2 phase, where the polarity and SHG activity were thermally disturbed in bulk

due to the thermal fluctuation. The second important molecular motion is a relative skew rotation of C1SS dimer, where the rotation angle of the upper C1SS relative to the lower one changed

the magnitude of the relative energy at fixed bowl-shaped conformation with the fixed torsion angle of 175° (Fig. 8b). When the bowl-shaped C1SS dimer was directly overlapped with a

translational motion along the π-dimer with the sterically repulsive S–S interactions along the π-stack, a large relative energy around 30 kcal mol−1 was observed as a forbidden in-plane

free rotational motion. The energy minima for the skew angle rotation were observed at the angles of 30° and 90° with every 60° rotation of the upper C1SS, while the maxima of the dipole

moment of 0.84 D were also observed around 20 and 100°. The forbidden in-plane free rotation inhibited the formation of Colh liquid crystal phase. The restricted 30°-rotated π-stacking

interaction of C1SS in the π-stacking column was also thermally fluctuated in the high-temperature viscous S2 phase, where the motion was also coupled with the inversion motion of

bowl-shaped conformation via the π-planar one (Fig. 8c). Although the π-stacking distance in the π-dimer (C1SS)2 was associated with the relative energy, it did not affect the theoretical

dipole moment (Supplementary Fig. 15). Three kinds of motional freedoms of torsion, skew, and dimer separation distance were activated at S2 phase, among which the first two coupled to

generate the macroscale dipole moment under the applied electric field (Fig. 8d). When the electric field was applied to the thermally fluctuated π-stacking column of (C_N_SS)∞, the

polarized molecular conformation in the 1D assembly should be stabilized at the bowl-shaped and twisted π-stacking columnar structure keeping the maximum dipole structure. Such polar

molecular assembly was thermally relaxed after the removal of the outer electric field, which resulted in the ferroelectric _P_-_E_ hysteresis and relaxation behavior at high-temperature

viscous S2 phase. In the order-disorder type molecular ferroelectrics, the low-frequency response at _f_ = 0.1–10 Hz has been typically observed in the _P_-_E_ hysteresis curve. However, the

relatively high-frequency responses of the _P_-_E_ hysteresis curve at _f_ = 100–200 Hz for C_N_SS derivatives were consistent with the structural relaxation process from the polar

molecular assembly structure under the applied electric field. In summary, the collective dipole inversion of 1D π-stacking bowl-shaped molecules showed the ferroelectric response due to

bowl-to-bowl inversion, where the chemical design of the bowl-depth (CH2 → S → Se) tuned the suitable inversion barrier in bulk and possible dipole inversion by the application of the

electric field. C_N_SS derivatives indicated the phase transition to high viscous S2 phase, where complete melting state of alkyl chains formed the 1D plastic crystalline phase. The

thermally activated highly melting state enabled collective bowl-to-bowl inversion associated with the in-plane rotation stabilized by S•••S contacts and dipole-dipole interactions. The

_P_-_E_ hysteresis responses were adequately high even in dynamic molecular system, caused by the high-speed relaxation of the polar bowl-stacking π-column under the electric field. The

present finding reveals that the wide variation of molecular designs for organic π-molecules enables us to fabricate flexible and high-density organic memory devices. METHODS MATERIALS C6TP

and C4SES were prepared following reported methods32,35. C2SS was synthesized by a modified method for the synthesis of other trichalcogenasumanene derivatives (Supplementary Information,

section 2)32. C_N_SS (_n_ = 6, 8, 10, or 16) were prepared by the following general procedure: a dichloromethane solution of boron tribromide (1.0 mol L−1, 10 equiv.) was slowly added to a

dichloromethane solution of C2SS at 0 °C, before the mixture was stirred at room temperature for 2 h. Then, water was slowly added to the reaction mixture at 0 °C. The resulting solid was

collected by filtration and washed with dichloromethane and water to furnish intermediate C0SS. The obtained solid was dissolved in DMF, and potassium carbonate (4–10 equiv.) and the

corresponding alkyl bromide (4–8 equiv.) were added to the solution. The mixture was stirred overnight at 75 °C. After cooling to room temperature, the mixture was filtered to remove an

insoluble solid. Water was added to the obtained solution, and the organic layer was extracted with a mixture of ethyl acetate and hexane (4:1, v/v). The combined organic extracts were dried

over anhydrous magnesium sulfate before the inorganic solids were removed by filtration. After evaporation of all volatiles, the crude products were purified by column chromatography on

silica gel (eluent: hexane/dichloromethane) to afford C_N_SS. MEASUREMENTS Temperature-dependent crystallographic data for a single crystal of C2SS at 300 K were collected on a Rigaku

RAPID-II diffractometer equipped with a rotating anode and a multilayer confocal optic using graphite-monochromated Cu-Kα radiation (_λ_ = 1.54187 Å). Structural refinements were carried out

using the full-matrix least-squares method on _F_2. Temperature-dependent PXRD measurements were performed on a Rigaku SmartLab diffractometer using Cu-Kα radiation (_λ_ = 1.54187 Å).

Temperature-dependent dielectric constants were determined by the two-probe AC impedance method at frequencies from 1 kHz to 1 MHz (Hewlett-Packard, HP4194A) with a liquid crystal cell

placed in a temperature control system (Linkam, LTS350). The _P_–_E_ curves were measured with a commercially available ferroelectric tester (Precision LC, Radient Technologies) using a

liquid crystalline cell with an electrode gap of 2 μm. The C_N_SS derivatives in the liquid state were introduced in the electrode gap of the liquid crystal cell. DATA AVAILABILITY All the

data generated or analyzed during this study are included in this published article (and its supplementary information files) or available from the authors upon reasonable request. The

crystallographic information for this paper has been deposited at The Cambridge Crystallographic Data Center (http://www.ccdc.cam.ac.uk) under reference number CCDC-1912824. REFERENCES *

Lines, M. E. & Glass, A. M. Principles and applications of ferroelectrics and related materials (Oxford University Press, New York, 1977). * Horiuchi, S. & Tokura, Y. Organic

ferroelectrics. _Nat. Mater._ 7, 357–366 (2008). Article  ADS  CAS  Google Scholar  * Tayi, A. S., Kaeser, A., Matsumoto, M., Aida, T. & Stupp, S. I. Supramolecular ferroelectrics. _Nat.

Chem._ 7, 281–294 (2015). Article  CAS  Google Scholar  * Solomon, A. L. Thiourea, a new ferroelectric. _Phys. Rev._ 104, 1191 (1956). Article  ADS  CAS  Google Scholar  * Goldsmith, G. J.

& White, J. G. Ferroelectric behavior of Thiourea. _J. Chem. Phys._ 31, 1175–1187 (1959). Article  ADS  CAS  Google Scholar  * Harada, J. et al. Directionally tunable and mechanically

deformable ferroelectric crystals from rotating polar globular ionic molecules. _Nat. Chem._ 8, 946–952 (2016). Article  CAS  Google Scholar  * Tokura, Y. et al. Domain-well dynamics in

organic charge-transfer compounds with one-dimensional ferroelectricity. _Phys. Rev. Lett._ 63, 2405–2408 (1989). Article  ADS  CAS  Google Scholar  * Kagawa, F. et al. Electric-field

control of solitons in a ferroelectric organic charge-transfer salt. _Phys. Rev. Lett._ 104, 227602–227604 (2010). Article  ADS  CAS  Google Scholar  * Tayi, A. S. et al. Room-temperature

ferroelectricity in supramolecular networks of charge-transfer complexes. _Nature_ 488, 485–489 (2012). Article  ADS  CAS  Google Scholar  * Horiuchi, S. et al. Above-room-temperature

ferroelectricity in a single-component molecular crystal. _Nature_ 463, 789–792 (2010). Article  ADS  CAS  Google Scholar  * Horiuchi, S. et al. Above-room-temperature ferroelectricity and

antiferroelectricity in benzimidazoles. _Nat. Commun._ 3, 1308 (2012). Article  ADS  Google Scholar  * Owczarek, M. et al. Flexible ferroelectric organic crystals. _Nat. Commun._ 7, 13108

(2016). Article  ADS  CAS  Google Scholar  * Lunkenheimer, P. et al. Ferroelectric properties of charge-ordered α-(BEDT-TTF)2I3. _Phys. Rev. B_ 91, 245132–1–7 (2015). Article  ADS  Google

Scholar  * Akutagawa, T. et al. Ferroelectricity and polarity control in solid state flip-flop supramolecular rotators. _Nat. Mater._ 8, 342–347 (2009). Article  ADS  CAS  Google Scholar  *

Miyajima, D. et al. Ferroelectric columnar liquid crystal featuring confined polar groups within core-shell architecture. _Science_ 336, 209–213 (2012). Article  ADS  CAS  Google Scholar  *

Sato, K., Itoh, Y. & Aida, T. Columnarly assembled liquid-crystalline peptidic macrocycles unidirectionally orientable over a large area by an electric field. _J. Am. Chem. Soc._ 133,

13767–13769 (2011). Article  CAS  Google Scholar  * Malthete, J. & Collet, A. Inversion of the cyclotribenzylene cone in a columnar mesophase: a potential way to ferroelectric materials.

_J. Am. Chem. Soc._ 109, 7544–7545 (1987). Article  CAS  Google Scholar  * Miyajima, D. et al. Liquid crystalline corannulene responsive to electric field. _J. Am. Chem. Soc._ 131, 44–45

(2009). Article  CAS  Google Scholar  * Shoji, Y. et al. Hexathioalkyl sumanenes: an electron-donating buckybowl as a building block for supramolecular materials. _Chem. Sci._ 8, 8405–8410

(2017). Article  CAS  Google Scholar  * Guilleme, J. et al. A columnar liquid crystal with permanent polar order. _J. Mater. Chem. C._ 3, 985–989 (2015). Article  CAS  Google Scholar  *

Guilleme, J. et al. Polar switching in a lyotropic columnar nematic liquid crystal made of bowl-shaped molecules. _Adv. Mater._ 27, 4280–4184 (2015). Article  CAS  Google Scholar  *

García-Iglesias, M. et al. A versatile method for the preparation of ferroelectric supramolecular materials via radical end-functionalization of vinylidene fluoride oligomers. _J. Am. Chem.

Soc._ 138, 6217–6223 (2016). Article  Google Scholar  * Gorbunov, A. V. et al. Ferroelectric self-assembled molecular materials showing both rectifying and switchable conductivity. _Sci.

Adv._ 3, e1701017 (2017). Article  ADS  Google Scholar  * Imamura, K., Takimiya, K., Otsubo, T. & Aso, Y. Triphenyleno[1,12-bcd:4,5-b′c′d′:8,9-b″c″d″]trithiophene: the first bowl-shaped

heteroaromatic. _Chem. Commun._ Issue 18, 1859–1860 (1999). * Priyakumar, U. D. & Sastry, G. N. Heterobuckybowls: a theoretical study on the structure, bowl-to-bowl Inversion barrier,

bond length alternation, structure-inversion barrier relationship, stability, and synthetic feasibility. _J. Org. Chem._ 66, 6523–6530 (2001). Article  CAS  Google Scholar  * Seiders, T. J.,

Baldridge, K. K., Grube, G. H. & Siegel, J. S. Structure/energy correlation of bowl depth and inversion barrier in corannulene derivatives: Combined experimental and quantum mechanical

analysis. _J. Am. Chem. Soc._ 123, 517–525 (2001). Article  CAS  Google Scholar  * Saito, M., Furukawa, S., Kobayashi, J. & Kawashima, T. The chemistry of heterasumanenes. _Chem. Rec._

16, 64–72 (2016). Article  CAS  Google Scholar  * Li, X. & Shao, X. Synthesis of heterasumanene. _Synlett_ 25, 1795–1798 (2014). Article  CAS  Google Scholar  * Saito, M., Shinokubo, H.

& Sakurai, H. Figuration of bowl-shaped π-conjugated molecules: properties and functions. _Mater. Chem. Front._ 2, 1–27 (2018). Article  Google Scholar  * Furukawa, S., Kobayashi, J.

& Kawashima, T. Development of a sila-Friedel−Crafts reaction and its application to the synthesis of dibenzosilole derivatives. _J. Am. Chem. Soc._ 131, 14192–14193 (2009). Article  CAS

  Google Scholar  * Furukawa, S. et al. Triphosphasumanene trisulfide: High out-of-plane anisotropy and Janus-type π-surfaces. _J. Am. Chem. Soc._ 139, 5787–5792 (2017). Article  CAS  Google

Scholar  * Li, X. et al. Non-pyrolytic, large-scale synthesis of trichalcogenasumanene: a two-step approach. _Angew. Chem. Int. Ed._ 53, 535–538 (2013). Article  Google Scholar  * Louis, L.

et al. Polarization canting in ferroelectric diisopropylammonium-halide molecular crystals: a computational first principles study. _J. Mater. Chem. C._ 6, 1143–1152 (2018). Article  CAS 

Google Scholar  * Horiuchi, S., Kobayashi, K., Kumai, R. & Ishibashi, S. Proton tautomerism for strong polarization switching. _Nat. Commun._ 8, 14426 (2017). Article  ADS  CAS  Google

Scholar  * Gupta, M. et al. A new strategy towards the synthesis of a room-temperature discotic nematic liquid crystal employing triphenylene and pentaalkynylbenzene units. _Chem. Commun._

53, 3014–3017 (2017). Article  CAS  Google Scholar  Download references ACKNOWLEDGEMENTS This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas “π-System

Figuration: Control of Electron and Structural Dynamism for Innovative Functions” from the Japan Society for the Promotion of Science (JSPS) (JP26102006 to M.S. and JP26102007 to T.A.) and

“Stimuli-responsive Chemical Species for the Creation of Functional Molecules” (15H00918 to S.F.) from the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT).

This work was also supported by JSPS KAKENHI grant (16K13945 to S.F., JP20H05865 to T.A., JP20K05442 and JP20H04655 to T.T.), JST CREST (JPMJCR18I4 to T.A.), and the ‘Dynamic Alliance for

Open Innovation Bridging Human, Environment and Materials’ from MEXT (T.A.). M.S. gratefully acknowledges a research grant from the Yamada Science Foundation. AUTHOR INFORMATION AUTHORS AND

AFFILIATIONS * Department of Chemistry, Graduate School of Science and Engineering, Saitama University, Shimo-okubo, Sakura-ku, Saitama-city, Saitama, 338-8570, Japan Shunsuke Furukawa, 

Masaya Koyama, Keisuke Hayashi & Masaichi Saito * Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan Jianyun Wu, Norihisa Hoshino, Takashi Takeda & Tomoyuki

Akutagawa * Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan Norihisa Hoshino, Takashi Takeda &

 Tomoyuki Akutagawa * Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 1677-1 Yoshida, Yamaguchi, 753-8512, Japan Yasutaka Suzuki & Jun Kawamata Authors *

Shunsuke Furukawa View author publications You can also search for this author inPubMed Google Scholar * Jianyun Wu View author publications You can also search for this author inPubMed 

Google Scholar * Masaya Koyama View author publications You can also search for this author inPubMed Google Scholar * Keisuke Hayashi View author publications You can also search for this

author inPubMed Google Scholar * Norihisa Hoshino View author publications You can also search for this author inPubMed Google Scholar * Takashi Takeda View author publications You can also

search for this author inPubMed Google Scholar * Yasutaka Suzuki View author publications You can also search for this author inPubMed Google Scholar * Jun Kawamata View author publications

You can also search for this author inPubMed Google Scholar * Masaichi Saito View author publications You can also search for this author inPubMed Google Scholar * Tomoyuki Akutagawa View

author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS M.K. and K.H. conducted the synthetic experiments and analyzed the data. J.W. performed thermal

and electrical measurements. N.H. carried out the single-crystal X-ray diffraction analysis. T.T. performed DFT calculations. J.K. and Y.S. conducted SHG measurement. S.F., M.S. and T.A.

prepared the manuscript. S.F. and T.A. conceived the project, which was directed by S.F., M.S. and T.A. CORRESPONDING AUTHORS Correspondence to Shunsuke Furukawa, Masaichi Saito or Tomoyuki

Akutagawa. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing interests. ADDITIONAL INFORMATION PEER REVIEW INFORMATION _Nature Communications_ thanks Stephen Ducharme

and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available. PUBLISHER’S NOTE Springer Nature remains neutral with

regard to jurisdictional claims in published maps and institutional affiliations. SUPPLEMENTARY INFORMATION SUPPLEMENTARY INFORMATION PEER REVIEW FILE RIGHTS AND PERMISSIONS OPEN ACCESS This

article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as

you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party

material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s

Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Furukawa, S., Wu, J., Koyama, M. _et al._

Ferroelectric columnar assemblies from the bowl-to-bowl inversion of aromatic cores. _Nat Commun_ 12, 768 (2021). https://doi.org/10.1038/s41467-021-21019-4 Download citation * Received: 24

May 2019 * Accepted: 08 January 2021 * Published: 03 February 2021 * DOI: https://doi.org/10.1038/s41467-021-21019-4 SHARE THIS ARTICLE Anyone you share the following link with will be able

to read this content: Get shareable link Sorry, a shareable link is not currently available for this article. Copy to clipboard Provided by the Springer Nature SharedIt content-sharing

initiative