1D07
ボウル状トリチアスマネン誘導体の強誘電性
1東北大院工，2東北大多元研，3埼玉大院理工○呉筧筠1, 武田貴志1,2, 星野哲久1,2, 甲山雅也3,古川俊輔3, 斎藤雅一3, 芥川智行1,2

Ferroelectricity of bowl-shaped trithiasumanene derivatives○Jianyun Wu1, Takashi Takeda1,2, Norihisa Hoshino1,2, Masaya Koyama3,
Shunsuke Furukawa3, Masaichi Saito3, Tomoyuki Akutagawa1,2
1 Graduate School of Engineering, Tohoku University, Japan
2 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan
3 Graduate School of Science and Engineering, Saitama University, Japan【Abstract】Organic ferroelectric materials have been widely used in the fields of sensors,nonvolatile memory storage, and intelligent information technology.[1] In this work, a newconcept for the organic ferroelectricity was pointed in a bowl-shaped non-planar π-functional
molecule. Four kinds of alkoxy-substituted trithiasumanene derivatives (CnTSS) with n = 6,8, 10, and 16 were examined in terms of thermal stability, phase transition behavior, crystal
structure, dielectric properties, and electric filed–polarization curve. The ferroelectricity due
to bowl-inversion was firstly observed in the solid state.
【Introduction】Recent progress in organic
synthesis expands a variation of new bowl-shaped
π-molecular system such as sumanene andcorannulene. However, physical functions of these
π-curvature molecules have been insufficiently
examined form the viewpoint of electricalconductivity, magnetism, optical, and ferroelectric
Fig. 1 TTS derivatives in this study.
properties, due to the limitation of syntheticdifficulty. Herein, we focused on the bowl-shaped π-electronic system of trithiasumanene
derivative to design ferroelectric response in the solid state. The ferroelectricity oftrithiasumanene derivatives bearing six -OCnH2n+1 chains (CnTSS) was successfully
observed, which became a candidate to form new class of organic ferroelectric nonvolatileand ultra-high density memory application.
【Experimental】Four kinds of alkoxy-substituted TTS derivatives of C6TSS, C8TSS,
C10TSS, and C16TSS were synthesized. Thermodynamic responses, dielectric properties,
phase transition behaviors, and molecular assembly structures were evaluated by TG, DSC,and PXRD experiments, and the electric filed – polarization (P-E) curves were examined in
all CnTSS derivatives bearing different alkoxy chain length at –OCnH2n+1 with n = 2, 6, 8, 10,and 16 (Fig. 1). Single crystals of short-chain derivative C2TSS were obtained to clarify thebowl-shaped molecular and packing structure.[2]【Results and Discussion】Three derivatives of C6TSS, C8TSS, and C10TSS indicated
one reversible solid-solid (S1-S2) phase transition at 400, 373, and 363 K, respectively,
whereas the longest alkyl chain derivative of C16TSS showed the liquid crystalline M1 phasebefore the melting. The PXRD pattern at M1 phase of C16TSS was consistent with theformation of discotic hexagonal columnar (Colh) phase.
Single crystal X-ray structural analysis of C2TSS (Figs. 2b and 2c) indicated theformation of columnar π-stacking structure of each bowl-shaped molecule. The space groupof acentric P3c1 generated a polar axis along the c axis, corresponding to the π-stacking
direction. Each π-stack has a permanent dipole moment, and the number of polar π-stacks (Aand B) was observed at 2:1 ration with a net dipole moment, which was consistent with theferroelectric ground state. Temperature-dependent PXRD patterns of C10TSS indicated themelting state of –OC10H21 chains and same packing structure of all CnTSS derivatives to thatof C2TSS (Fig. 2a).
The frequency (f) and temperature (T) dependent dielectric constants showed theanomalies around the S1-S2 and S2-M2 phase transitions. Both ε1 and ε2 values of all CnTSS
crystals were enhanced at higher T and lower f conditions, suggesting slow molecular motions
in solid or M1 phases were thermally activated due to the melting of alkoxy chainssurrounding the π-stacking bowl columns. E Ferroelectric hysteresis in the P-E curves swere
confirmed in S2 phase of C6TSS, C8TSS, and C10TSS (Fig. 3), whereas C16TSS also
showed the ferroelectricity at liquid crystalline Colh phase. The hysteresis loops of C6TSS,
C8TSS, and C10TSS were clearly confirmed at f range from 100 to 200 Hz, whereas that ofliquid crystalline C16SS was observed at much lower f range from 10 to 100 Hz.

Fig.2 Molecular assembly structures of CnTSS derivative. (a) Temperatuer
dependent PXRD patterns of C10TSS. (b) Bowl-to-bowl inversion from down
A to up B conformation. (c) Unit cell of C2TSS viewed along the c axis.

【References】[1] Akutagawa, T. et al., Nature Mater. 8, 342-347 (2009).
[2] Xuexiang, L. et al., Angew. Chem. Int. Ed. 53, 535-538 (2014).

Fig.3 T-dependent P-E hysteresis
curves of C10TSS at f = 100 Hz.