Takahashi Masaki, Hoshino Norihisa, Sambe Kohei, Takeda Takashi, Akutagawa Tomoyuki
Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan.
Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
Inorg Chem. 2020 Aug 17;59(16):11606-11615. doi: 10.1021/acs.inorgchem.0c01404. Epub 2020 Jun 28.
Chiral organic ammonium cations (()-2-methylphenethylammonium (-MPhA) and ()-3,7-dimethyloctylammonium (-DMOA)) cations were combined with [MX] anions (M = Cu and Pb, X = Cl and Br) to form two-dimensional (2D) perovskites: (-MPhA)CuCl (), (-MPhA)CuBr (), (-DMOA)CuCl (), (-DMOA)CuBr (), (-DMOA)PbCl (), and (-DMOA)PbBr (). The point shearing of the MX octahedron formed 2D perovskite layers, which were sandwiched by the bilayer molecular assembly of chiral organic ammonium cations. We found that the flexible and polar organic -MPhA and -DMOA cations in the 2D perovskites played an important role in the phase transition behavior and dielectric responses. Salts - showed similar solid-solid (S1-S2) phase transitions, for which the temperatures decreased in the order of CuCl () > PbCl () > CuBr () > PbBr (). The occupation volume of one -DMOA per MX octahedron determined the dynamic crystalline space for the motional freedom of chiral ammonium in the 2D perovskite layer. Although thermally activated dielectric fluctuations were observed in salts , , and , only an order-disorder-type dielectric phase transition was observed in salt . Interband optical transitions were observed in the CuCl and CuBr 2D perovskites, whereas sharp exciton absorptions were observed in the 2D PbCl and PbBr layers in perovskite salts and .
手性有机铵阳离子（（-）-2-甲基苯乙铵（-MPhA）和（-）-3,7-二甲基辛铵（-DMOA））与[MX]阴离子（M = Cu和Pb，X = Cl和Br）结合形成二维（2D）钙钛矿：（-MPhA）CuCl（）、（-MPhA）CuBr（）、（-DMOA）CuCl（）、（-DMOA）CuBr（）、（-DMOA）PbCl（）和（-DMOA）PbBr（）。MX八面体的点剪切形成了2D钙钛矿层，这些层被手性有机铵阳离子的双层分子组装所夹。我们发现2D钙钛矿中柔性且极性的有机-MPhA和-DMOA阳离子在相变行为和介电响应中起重要作用。盐-表现出类似的固-固（S1-S2）相变，其温度按CuCl（）> PbCl（）> CuBr（）> PbBr（）的顺序降低。每个MX八面体中一个-DMOA的占据体积决定了2D钙钛矿层中手性铵运动自由度的动态晶体空间。尽管在盐、和中观察到热激活的介电涨落，但在盐中仅观察到有序-无序型介电相变。在CuCl和CuBr 2D钙钛矿中观察到带间光学跃迁，而在钙钛矿盐和的2D PbCl和PbBr层中观察到尖锐的激子吸收。
