Temperature-Triggered Reversible Dielectric and Nonlinear Optical Switch Based on the One-Dimensional Organic–Inorganic Hybrid Phase Transition Compound [C₆H₁₁NH₃]₂CdCl₄

Abstract

The one-dimensional organic-inorganic hybrid compound bis(cyclohexylammonium) tetrachlorocadmate(II) (1), in which the adjacent infinite [CdCl4]n(-) chains are connected to each other though Cd···Cl weak interactions to form perovskite-type layers of corner-sharing CdCl6 octahedra separated by cyclohexylammonium cation bilayers, was synthesized. It undergoes two successive structural phase transitions, at 215 and 367 K, which were confirmed by systematic characterizations including differential scanning calorimetry (DSC) measurements, variable-temperature structural analyses, and dielectric and second harmonic generation (SHG) measurements. A precise structural analysis discloses that the phase transition at 215 K is induced by the disorder-order transition of cyclohexylammonium cations, while the phase transition at 367 K derives from changes in the relative location of Cd atoms. Emphatically, both the dielectric constant and SHG intensity of 1 show a striking change between low and high states at around 367 K, which reveals that 1 might be considered as a potential dielectric and nonlinear optical (NLO) switch with high-temperature response characterization, excellent reversibility, and obvious change of states.

Molecular Dynamics of Flexible Polar Cations in a Variable Confined Space: Toward Exceptional Two‐Step Nonlinear Optical Switches

“…The transition temperatures ( T 1/2's ) of SHG switching are consistent with the corresponding peak temperatures observed in DSC curves, suggesting the two‐step SHG switching is strongly related with the structural phase transitions. Different to the other sporadically reported two‐step SHG switches, e.g., [C 6 H 11 NH 3 ] 2 [CdCl 4 ], that reveal “low–high–low” SHG signal changes between different NLO‐active states and thus restricts a limited switching contrast (of ≈1.3), 1 affords a new type of two‐step NLO switches that exhibits a genuine “off–on–off” SHG conversion between one NLO‐active state and two NLO‐inactive states, hence exhibits a remarkable SHG switching contrast of ≈8.0. In particular, the NLO‐switching from “SHG‐on” state at ITP to “SHG‐off” state at LTP is an exceptional SHG quenching behavior by cooling, owing to an unexpected phase transition that gains inversion centers for LTP (vide infra).…”

Switchable Dielectric Phase Transition Triggered by Pendulum‐Like Motion in an Ionic Co‐crystal

“…As is wellk nown,t he order-disorder transition is one of the origins of phase transitions. [16] In our study,i ti so fn ecessity to note that the distinction betweent he LTPa nd HTP is the order-disorder transitiono ft he 2-chloro-6-hydrazinopyridine cations by ap recise analysis of the primary packingo fa nion ingredients and structural differences. In this study,t he 2chloro-6-hydrazinopyridine cations, as the switching materials, have ab istable molecular motion betweent he LTP( the ordered state) and HTP (the disordered state), namely,e very organic cation was "frozen" and perfectly ordered at LTP ( Figure 2c), and yet was orientationally disordered over two equivalent occupations (two pyridine rings locate in the same plane) at HTP.S pecifically,t he switching of the position of the terminal NH 3 group of the cation indicates ap endulum-likem otion (Figure 2d), which aims to present orientational disorder.…”

“…11)a nd point group 2/m at both LTPa nd HTP certified by the variable-temperature PXRD measurements performed witht he PANalytical X'PertP RO X-ray diffractometer in the range 123 Kt o2 93 K( Figure S4 in the Supporting Information), which is attached to centrosymmetric and reversiblyi somorphic phase transitions. [15] Herein, at LTP, the crystal cell parameters were as follows: a = 8.104(2) , b = 19.792(7) , c = 11.676(8) , a = 90.008, b = 106.72(4)8, g = 90.008, Z = 2, and V = 1793.5 (14) 3 .W hereas at HTP,t he crystal cell parameters were as follows: a = 8.029 (16) , b = 19.896(4) , c = 11.587(2) , a = 90.008, b = 106.22(3)8, g = 90.008, Z = 2, and V = 1777.3(6) 3 . The full crystallographic data of 1 are presentedi nT able S1 (see the Supporting Information).…”

“…On the one hand, from the microscopic perspective,a st he temperature increases, the Sb atom arrangementb ecomes closer,w hereas it is looser at lower temperature. For compound 1,t he Sb···Sb distance between adjacent layersc hanges from 8.1040(28) and 7.6549(26) at LTP to 8.0290 (16) and7 .6231 (14) at HTP ( Figure S5 ca nd di n the Supporting Information). As ac onsequence, the slight change of relative locations of the Sb atoms contributes to the phase transition.…”

“…[17] The simulated molecular structure may be interpreted as the average of two orientationsofthe cation. [3a] Additionally, in the LTP, the Sb···Sbd istances between the neighboring layers were 8.1040(28) and 7.6549(26) ,w hereas in the HTP, it changed to 8.0290 (16) and 7.6231 (14) .A part from that, the distortion degrees of the [Sb 2 Br 9 ] 3À octahedron at LTPa nd HTP were different, manifesting as lightd eformation of the [Sb 2 Br 9 ] 3À octahedron containing both BrÀSb bond length and Sb···Sb distance as well as the Br-Sb-Br and Sb-Br-Sba ngles, which indicated the alterations in the relative position of the Sb atoms during the phase transition ( Figure 2e,f,F igure S5 c and di nt he Supporting Information).T his is exactly that of the order-disorder transition of the 2-chloro-6-hydrazinopyridine cations coupled with the slight alteration in the relative positions of the octahedral [Sb 2 Br 9 ] 3À anions, which may afford the dominating propulsive effort for the phase transition, [18] which is probably distinct from the phase transition related to the hydrogen bonding.…”