1. Two host–guest grown ether supramolecules show switchable phase transition, dielectric and second-harmonic generation effect.
- Author
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Ye, Xing, He, Wenhui, Wei, Jing, Wei, Zhenhong, You, Xiuli, and Cai, Hu
- Subjects
PHASE transitions ,SUPRAMOLECULES ,POLAR molecules ,TRANSITION temperature ,CROWN ethers ,SPACE groups - Abstract
The excellent properties of host–guest crown ether inclusions in phase transition, dielectric and second-order nonlinear optical properties have attracted much attention. In this paper, we successfully designed and prepared two novel host–guest crown ether supramolecules [(DFBA)(15-crown-5)]X (X = ClO
4 − , 1; ReO4 − , 2) by reactions of 2,6-difluorobenzylamine (DFBA) with 1,4,10,13-pentaoxacyclopentadecane (15-crown-5) in HClO4 , or HReO4 aqueous solution. By the introduction of difluoro-substituted benzylamine as a guest cation, the phase transition temperatures are greatly increased to 377 K for 1 and 391 K for 2. More importantly, the space group of 1 has changed from centrosymmetric (CS) P2/c to the non-centrosymmetric (NCS) Pca21 in 2 when substituting perchlorate (ClO4 − ) with the larger and heavier perrhenate (ReO4 − ), which leads to 2 showing a switchable and stable second-harmonic generation (SHG) effect. According to the principle of momentum matching between a cation and anion, the perrhenate group increases the energy barrier of the molecular thermal motion, which not only significantly increases the phase transition temperature of 2 but also causes it to be frozen and crystallized in a NCS space group at room temperature. This research demonstrates that a polar molecule can adjust the suitability of anions and cations inside the crystal by practical chemical means. [ABSTRACT FROM AUTHOR]- Published
- 2022
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