Precise Molecular Design of High-Tc 3D Organic–Inorganic Perovskite

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Precise Molecular Design of High‑Tc 3D Organic−Inorganic Perovskite Ferroelectric: [MeHdabco]RbI3 (MeHdabco = N‑Methyl1,4-diazoniabicyclo[2.2.2]octane) Wan-Ying Zhang, Yuan-Yuan Tang, Peng-Fei Li, Ping-Ping Shi, Wei-Qiang Liao, Da-Wei Fu,* Heng-Yun Ye, Yi Zhang, and Ren-Gen Xiong* Ordered Matter Science Research Center and Jiangsu Key Laboratory for Science and Applications of Molecular Ferroelectrics, Southeast University, Nanjing 211189, People’s Republic of China S Supporting Information *

ABSTRACT: With the flourishing development of (CH3NH3)PbI3, three-dimensional (3D) organic−inorganic perovskites with unique structure−property flexibility have become a worldwide focus. However, they still face great challenges in effectively inducing ferroelectricity. Despite the typical 3D perovskite structure and the ability of dabco (1,4diazabicyclo[2.2.2]octane) to trigger phase transition, unfortunately [H2dabco]RbCl3 adopts a nonpolar crystal structure without ferroelectricity. Within the larger RbI3 framework, we assemble N-methyl-1,4-diazoniabicyclo[2.2.2]octane (MeHdabco) obtained by reducing the molecular symmetry of dabco into a new 3D organic−inorganic perovskite. As expected, MeHdabco bearing a molecular dipole moment turns out to be vital in the generation of polar crystal structure and ferroelectric phase transition occurring at 430 K. It is the first time that the dabco component has been successfully wrapped into a 3D cage to achieve ferroelectricity even through there is intensive research on dabco. This precise molecular design strategy based on the modification of molecular symmetry provides an efficient route to enrich the family of 3D organic−inorganic perovskite ferroelectrics. Intriguingly, the iodine-doped crystal can exhibit intense saffron yellow luminescence with a high quantum yield of 17.17% under UV excitation, extending its application in the field of ferroelectric luminescence and/or multifunctional devices.

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corresponding ionic radii and τ should be in the range of 0.8− 1.5 For example, if a larger cation such as [CH3CH2NH3]+ is used, the 3D perovskite framework of [CH3NH3]PbI3 will shift to lower dimensional, leading to significant changes in physical properties.5a,6 In that case, to accommodate diverse organic cations, the lead halide can be replaced by a larger alkali halide framework. Most recently, we have successfully obtained a 3D alkali halide perovskite: (3-ammoniopyrrolidinium)RbBr3 with high-temperature ferroelectricity stemming from cation dynamics.4c For the prospect of inducing ferroelectricity in 3D alkali halide perovskites, of particularly note is the intensively studied dabco (1,4-diazabicyclo[2.2.2]octane). As a highly symmetric diamine with D3h symmetry, it is desirable for constructing ferroelectrics through conformational transformations or proton transfers.7 Several simple salts, [Hdabco]ClO4 , [Hdabco]BF4, and [Hdabco]ReO4, have been discovered as hydrogen-bonded molecular ferroelectrics, and just lately we recognized their multiaxial natures and explored the potential thin-film applications.8 Similarly, quinuclidinium derivatives analogous to dabco also have advantages in multiaxial

INTRODUCTION ABX3-type perovskites typically adopt the same three-dimensional (3D) structure as CaTiO3, where the larger A-site cation encloses the corner-sharing framework of BX6 octahedra (B and X denote the respective smaller cation and anion). Since the early 1940s, many hundreds of inorganic perovskites such as BaTiO3, LiNbO3, and Pb(Zr, Ti)O3, which constitute the biggest class of ferroelectrics, have been widely investigated for their intriguing ferroelectricity, superconductivity, colossal magnetoresistance, ionic conductivity, and dielectricity. 1 Inspired by the high photovoltaic performance of [CH3NH3]PbI3, currently organic−inorganic perovskites have become a booming field in materials science.2 Comparing with rigid inorganic perovskites, the organic−inorganic ones possess remarkable structural variability and highly tunable properties, enabling endless possibilities for achieving functional materials with applications in microelectronics, energy storage, photovoltaics, etc.3 From a structural perspective, it is the reorientation of organic cation within an inorganic framework that makes them extremely attractive as ferroelectric candidates.4 However, the selection of both organic and inorganic species is limited by the stability of 3D perovskite structure, as depicted by the Goldschmidt tolerance factor, τ = (RA + RX)/√2(RB + RX), where RA, RB, and RX represent the © 2017 American Chemical Society

Received: June 10, 2017 Published: July 18, 2017 10897

DOI: 10.1021/jacs.7b06013 J. Am. Chem. Soc. 2017, 139, 10897−10902

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Journal of the American Chemical Society ferroelectric thin films, such as (R)-(−)-3-hydroxlyquinuclidinium halides, quinuclidinium periodate, and perrhenate.9 Besides, it is noteworthy that the 3D alkali halide perovskite presented by Harrison et al., [H2dabco]RbCl3, brings light to 3D organic−inorganic perovskite ferroelectrics.10 Yet, unfortunately, it belongs to nonpolar space group P3212 (point group D3), whereas ferroelectricity occurs only in the 10 polar point groups C1, C2, C1h, C2v, C4, C4v, C3, C3v, C6, and C6v. On the basis of years of research experience, we recognized that even slight changes in molecular structures can affect crystal symmetry and cause symmetry breaking.11 Hence, for permitting ferroelectricity, a molecular design strategy is proposed to induce crystallization in low-symmetric polar point groups. By adding a methyl to break the mirror plane of the dabco molecule, molecular symmetry of the resultant Nmethyl-1,4-diazoniabicyclo[2.2.2]octane ([MeHdabco]2+) is smoothly lowered to C3v and equipped with a molecular dipole moment. Then employing a RbI3 framework larger than RbCl3, as expected, [MeHdabco]RbI3 with typical 3D perovskite structure crystallizes in the polar space group R3 (point group C3) and undergoes a ferroelectric phase transition at around 430 K. As a result of the symmetry breaking with 432F3 species, the multiaxial ferroelectric nature of [MeHdabco]RbI3 has been demonstrated by piezoresponse force microscopy (PFM) and polarization−electric field (P−E) hysteresis loop. To our best knowledge, the dabco-based 3D organic−inorganic perovskite ferroelectric is unprecedented in spite of the intensive research focused on dabco. In addition, due to the iodine-doping effect, the crystal can emit bright saffron yellow light under UV excitation. Undoubtedly, such a subtle molecular design and crystal engineering within the diverse family of organic−inorganic perovskites provide fertile ground for ferroelectrics with various physical properties.

strategy is raised here. Generally, the alignment of dipole moments of polar molecules generates spontaneous polarization, whose reorientation induces ferroelectricity in crystals with polar point groups. [H2dabco]2+ is a high-symmetric molecule with spherical geometry and belongs to the D3h symmetry group, comprising symmetry elements such as a 3fold rotation axis and a σh and three σv mirror planes. Structurally, this nonpolar cation without an intrinsic dipole moment is relatively unfavorable to the formation of a polar crystal structure. To bring in a molecular dipole moment and further trigger polarity in the crystal structure, we add a methyl to one of the N atoms of the [H2dabco]2+ cation. It is the break of the σh mirror plane that results in the lower C3v symmetry of the [MeHdabco]2+ cation, which bears a dipole moment along the 3-fold rotation axis (Figure 1). Then, for the sake of

Figure 1. By applying the molecular design strategy, the σh mirror plane of the [H2dabco]2+ cation disappears in [MeHdabco]2+, with H atoms omitted for clarity.

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building a stable 3D perovskite structure that can allow the motion of the large [MeHdabco]2+ cation, a suitable inorganic counterpart has been selected carefully. In view of the limitation of the Goldschmidt tolerance factor,5b for the 3D RbCl3, RbBr3, and RbI3 frameworks, the acceptable molecular radius ranges of the included organic cations are 1.96−2.90, 1.98−2.96, and 2.01−3.06 Å by assuming τ = (0.8, 1), respectively. Considering the much larger radius of the [MeHdabco]2+ cation (2.61 Å, calculated from the X-ray crystal data), by using the RbI3 framework, we successfully designed and obtained a new 3D organic−inorganic perovskite, [MeHdabco]RbI3. Similar to [H2dabco]RbCl3, it adopts the cubic perovskite structure, in which the corner-sharing anionic RbI6 octahedra constitute an extended 3D network, and the [MeHdabco]2+ cations occupy the 12-fold-coordinated cuboctahedral cavities (Figure 2a). This type of hybrid ABX3 perovskite structure has also been discovered in [CH3NH3]PbI3; however, in our case, the divalent [MeHdabco]2+ and the monovalent Rb behave as Aand B-site cations, respectively. In contrast to [H2dabco]RbCl3, the subtle molecular modifications do have a significant influence on the crystal symmetry of [MeHdabco]RbI3, matching our expectations. At 293 K, it crystallizes in rhombohedral space group R3, with cell parameters of a = b = c = 7.272(3) Å, α = β = γ = 84.810(3)°, and V = 380.0(4) Å3 (see Table S1 for detailed crystal data summary). Distinct from the nonpolar space group of [H2dabco]RbCl3, R3 belongs to one of the 10 polar point groups, 3 (C3). In this ferroelectric phase, the two N atoms and the C atom of the terminal methyl group in the ordered [MeHdabco]2+ cation are located on the crystallographic 3-fold rotation axis. After undergoing the ferroelectric-to-paraelectric

RESULTS AND DISCUSSION Just a few years ago, Harrison et al. pioneered research on 3D alkali halide perovskites based on the [H2dabco]2+ cation, representing a “missing link” between classic inorganic perovskites and layered metal halide/organic perovskites.10 This innovated work leaves much room for the exploration of 3D organic−inorganic perovskite ferroelectrics, although it is a tremendous challenge. We reinvestigated [H2dabco]RbCl3 and found a structural phase transition from nonpolar, noncentrosymmetric space group P3121 (the enantiomeric space group of P32 12 reported by Harrison et al.) to the centrosymmetric Pm3̅m at around 430 K (Figures S1 and S2). Apparently, such symmetry change does not satisfy the requirement of ferroelectrics. To further examine the possibility of ferroelectricity within this system, we prepared [H2dabco]RbBr3 and [H2dabco]RbI3 and then characterized their crystal structures as well as phase transition behaviors. Resembling [H2dabco]RbCl3, [H2dabco]RbBr3 has a 3D perovskite structure and experiences a non-ferroelectric phase transition at around 340 K accompanying the symmetry change between nonpolar, non-centrosymmetric space group P3221 and the centrosymmetric Pm3m ̅ (Figures S3 and S4). In the case of [H2dabco]RbI3, remarkably, the introduction of a heavier iodide ion even leads to a one-dimensional hexagonal perovskite structure (Figure S5). Seeing that the chemical modifications in the inorganic component are unhelpful, now what can we do to induce ferroelectricity in this system? The answer should be found in the organic cationic moiety, and a subtle molecular design 10898

DOI: 10.1021/jacs.7b06013 J. Am. Chem. Soc. 2017, 139, 10897−10902

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Figure 3. Symmetry-breaking phase transition in [MeHdabco]RbI3: (a) DSC curves and (b) temperature-dependent SHG response obtained in a heating−cooling cycle. Figure 2. Crystal structures of [MeHdabco]RbI3 in (a) the ferroelectric phase (273 K) and (b) paraelectric phase (413 K/ cooling).

3b and S11, the Tc presented by the temperature-dependent second harmonic generation (SHG) response is in accordance with the DSC results. In a heating−cooling cycle, the detectable SHG response below Tc manifests the polar point group in the ferroelectric phase. At Tc, the sudden vanishing of the SHG response confirms the nonpolar 432 point group in the paraelectric phase because not only the 11 centrosymmetric point groups but also the three non-centrosymmetric point groups 432, 422 (D4), and 622 (D6) are unable to display the SHG effect, in view of Kleinman’s symmetry transformation.13 Moreover, in the vicinity of Tc, it is the prominent anomaly of the temperature-dependent dielectric constant that proves to be a direct sign of the ferroelectricity of [MeHdabco]RbI3 (Figure S10). According to the space group R3, the crystal of [MeHdabco]RbI3 can exhibit spontaneous polarization along the polar c axis in the ferroelectric phase. Polarization reversal was investigated on a thin film capacitor with the configuration of GaIn/thin crystallite/ITO (indium−tin oxide). As shown in Figure 4, the

phase transition, the I−Rb−I angle increases from 163.835(67)° to 180°, while the distorted RbI3 framework becomes regular. The paraelectric phase adopts the nonpolar cubic space group P432 (point group 432 (O)), with cell parameters of a = b = c = 7.3827(9) Å, α = β = γ = 90°, and V = 402.39(15) Å3. In the paraelectric unit cell, the [MeHdabco]2+ cation is located on the special high-symmetry site of 432 and consequently requires a total disorder. Because of the inconsistency between crystallographic symmetry and molecular symmetry, the [MeHdabco]2+ cation was modeled with a spherical structure discarding its chemical sense (Figure 2b). This suggests that the cations with dynamic disorder are nearly freely rotating in the paraelectric phase, as usually observed for those with spherical geometries, such as dabco, tetramethylammonium, and adamantane. The symmetry change of [MeHdabco]RbI3 is described by the Aizu notation of 432F3, among the 88 possible ferroelectric species.12 In the ferroelectric phase, the distances between the two N atoms of the [MeHdabco]2+ cation and the Rb atoms at (0 0 0) and (1 1 1) are 5.162 and 6.093 Å (Figure S6). This arrangement induces a shift of 0.465 Å and a spontaneous polarization of 4.90 μC cm−2 along the [1 1 1]-direction. The rhombohedral ferroelectric lattice can be taken as elongation of the cubic paraelectric lattice along the [1 1 1]-direction. There are four equivalent ferroelectric polarization axes that can be deduced for [MeHdabco]RbI3, with respective angles of 71°, 109°, and 180° (Figure S7). The generation of spontaneous polarization can be ascribed to the order−disorder transition of the [MeHdabco]2+ cation and the distortion of the anionic framework. It is undoubted that the molecular design strategy applied on the dabco molecule indeed plays an extremely vital role in the formation of a polar crystal structure as well as ferroelectricity. In addition to the above-mentioned X-ray diffraction characterizations, detecting anomalies in the thermal properties and other representative physical properties has also long been an effective way to demonstrate ferroelectric phase transitions. Given the results of differential scanning calorimetry (DSC) and thermogravimetric (TG) analyses (Figures 3a, S9, and S11), [MeHdabco]RbI3 undergoes a reversible phase transition at around 430 K and remains stable until 530 K. Such a high Curie temperature (Tc) and excellent thermal stability make it stand out from the common molecular ferroelectrics. For example, the series of metal-formate perovskite ferroelectrics often have Tc below room temperature,4 and the simple salts of dabco, [Hdabco]ClO4 and [Hdabco]BF4, were found to possess a Tc around 380 K.7a Furthermore, as shown in Figures

Figure 4. Polarization versus voltage hysteresis loop measured at room temperature.

well-shaped rectangular P−E hysteresis loop testifies to the ferroelectric property of [MeHdabco]RbI3. The measured Ps is around 6.8 μC/cm2 at room temperature, which is much larger than a recently developed molecular perovskite ferroelectric.4c For a thin crystallite of ∼4 μm in thickness, the coercive voltage for the polarization reversal is about 39 V, corresponding to a coercive field (Ec) of 97.5 kV/cm. Such a high coercive field is due to the fact that the polarization reversal involves a great amplitude of reorientation of the cations and distortion of the inorganic framework. For ferroelectrics, the most intrinsic, and, from the application point of view, the most important feature is the switching of spontaneous polarization under an external electric 10899

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Journal of the American Chemical Society field.1 Generally, the mechanism of polarization switching is addressed to necessitate the growth and shrinking of domains, which polarize in each of the energetically equivalent polarization directions. In this respect, piezoresponse force microscopy has become an indispensable tool for nondestructive high-resolution ferroelectric domain imaging and manipulation at the nanoscale.14 For [MeHdabco]RbI3, therefore, a systematic PFM study was performed. The real spatial polarization direction in the ferroelectric domain can be constructed by three components of piezoresponse: out-ofplane PFM (OP-PFM) and two orthogonal in-plane PFM (IPPFM), i.e., the polarization vector P = (Px, Py, Pz). Meanwhile, each component is composed of the amplitude and phase signals to offer information about the piezoelectric coefficient (proportional to the local polarization) and the polarization direction, respectively. Figure 5 presents the vector PFM

(Figure 6). First, we scanned the OP-PFM signals of the initial state over an area of 20 μm × 20 μm, where the uniform phase

Figure 6. Topographic (left), OP-PFM amplitude (middle), and phase (right) images of the crystallite surface for [MeHdabco]RbI3. (a) Initial state. (b) After the switching produced by scanning with a tip bias of −25 V.

contrast and the nearly homogeneous amplitude signal are indicative of the single-domain state in this area (Figure 6a). Subsequently, when the box pattern in the center region was written with a tip bias of −25 V, a bidomain-pattern state appears in the phase image, and the corresponding domain wall with the signal necessarily nulling is apparent in the amplitude image, indicating the polarization switching of the ferroelectric domain (Figure 6b). Interestingly, the emerging domain shape is hexagon instead of rectangle, different from the given box pattern. This probably means that the applied voltage is a little larger than the coercive voltage, causing the domain diffusion according to the trigonal point group symmetry. Also noteworthy is that [MeHdabco]RbI3 can maintain ferroelectricity when the sample is heated to above Tc and then cooled to room temperature, revealing the stability of the switchable polarization (Figure S13). For the pure phase of colorless [MeHdabco]RbI3 crystal, no photoluminescence phenomenon is observed. Interestingly, when grown from a hot solution with an excess of hydroiodic acid, the [MeHdabco]RbI3 crystal turns yellow due to the iodine-doping effect. Under UV excitation (360 nm), the doped [MeHdabco]RbI3 crystal emits bright saffron yellow light. The emission peak maximum is located at ∼590 nm with a fwhm (full width half-maximum) of 120 nm. As shown in Figure 7, [MeHdabco]RbI3 displays several photoluminescence excita-

Figure 5. For [MeHdabco]RbI3, the OP-PFM phase and amplitude images (z direction) (a, d). The IP-PFM phase and amplitude images in the x direction (b, e) and y direction (c, f), respectively. The geometry of the cantilever is illustrated schematically. (g) Topographic image of the crystallite surface. (h, i) Phase and amplitude signals as functions of the tip voltage for a selected point, showing local PFM hysteresis loops.

images at the crystallite surface of [MeHdabco]RbI3. In the phase images, it is notable that there mainly exist three big domains with different polarization directions (as marked in Figure 5a). Also, deduced from the amplitude images, the polarizations of domains 1, 2, and 3 have relatively larger components in the y, x, and z directions, respectively. This observation unambiguously discloses the presence of non-180° domain walls and the coexistence of multiple polarization orientations in the crystallite of [MeHdabco]RbI3. To further understand the polarization switching behaviors, local PFMbased hysteresis loops were also measured. The obvious 180° reversal of the PFM phase signal (Figure 5h) and the characteristic butterfly loop of the amplitude signal (Figure 5i) actually suggest the switchable polarization of ferroelectric domains. Investigating domain dynamics during ferroelectric switching is of crucial importance to determine macroscopic responses and applications of ferroelectric materials in optics and electronics. Hence the evolution of domain structure in the presence of an electric filed was attained in [MeHdabco]RbI3

Figure 7. Photoluminescent excitation (PLE) spectrum (blue) and photoluminescent (PL) spectrum (red) under excitation with 360 nm. 10900

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was refined in the nonpolar, non-centrosymmetric space group P3121, which is the enantiomeric space group of P3221 reported by Harrison et al.10 The high-temperature crystal structure was refined in the centrosymmetric space group Pm3̅m, while only one independent atom corresponding to the atoms of the [H2dabco]2+ cation can be found in the Fourier difference map. Due to the high site symmetry, the modeled cation has a spherical geometry, which means that the [H2dabco]2+ cations are dynamically disordered because of the motion of tumbling (Figure S1b). The case of [H2dabco]RbBr3 is similar to this, while the room-temperature and high-temperature crystal structures were refined in the space groups P3221 and Pm3̅m, respectively. At room temperature, [H2dabco]RbI3, consisting of infinite columns of face-sharing RbI6 octahedra separated by the [H2dabco]2+ cations, was refined in the nonpolar, non-centrosymmetric space group P6̅2c (Figure S5). Such a structure has been described as a hexagonal perovskite structure, as found in hexagonal 2H BaNiO3. There are a few hybrid metal halide compounds having hexagonal perovskite structures, such as [N(CH3)4]CdBr3,15 (3pyrrolinium)MnCl3,16 and (3-pyrrolinium)CdCl3.17 Measurements. Differential scanning calorimetry measurements were performed on a Netzsch DSC 200 F3 instrument under a nitrogen atmosphere with a heating and cooling rate of 10 K min−1, where the crystalline samples were placed in aluminum crucibles. For second harmonic generation measurements, an unexpanded laser beam with low divergence (pulsed Nd:YAG at a wavelength of 1064 nm, 5 ns pulse duration, 1.6 MW peak power, 10 Hz repetition rate) was applied. The instrument model is FLS 920, Edinburgh Instruments, and the laser is Vibrant 355 II, OPOTEK. Powder X-ray diffraction data were obtained on a Rigaku D/MAX 2000 PC X-ray diffractometer in the temperature range from 273 to 443 K. Diffraction patterns were collected in the 2θ range of 5−52° with a step size of 0.02°. Complex dielectric permittivity was measured with a Tonghui28 impedance analyzer at the frequency range from 50 Hz to 1 MHz with an applied electric field of 0.5 V. P−E Hysteresis Loop Measurements. A thin-film crystal capacitor was fabricated for the P−E hysteresis loop measurement. The detailed process is described as follows. First, a commercial ITO-coated glass substrate (Φ = 15 mm) was sequentially ultrasonically cleaned in toluene, acetone, ethanol, and deionized water 20 min at a time. A drop of an aqueous solution of [MeHdabco]RbI3 was carefully spread on a newly cleaned ITO-coated glass (conductive ITO was used as the bottom electrode). With controlled substrate temperature and solvent evaporation rate, small isolated crystals grown by slow evaporation were formed as the evaporation was completed. To a crystallite, GaIn eutectic was used as the top electrode. The whole ferroelectric hysteresis measurements were conducted with this capacitor architecture (GaIn/sample film/ITO) under the double wave method. The film thickness was measured by AFM. Nanoscale polarization imaging and local switching spectroscopy were carried out using a resonant-enhanced piezoresponse force microscope (MFP-3D, Asylum Research). Conductive Pt/Ir-coated silicon probes (EFM-50, Nanoworld) were used for domain imaging and polarization switching studies. Photoluminescence Measurements. The emission and excitation spectra together with the emissive lifetimes in solid states were measured on an Edinburgh FLS-920 fluorescence spectrometer. The luminescent quantum yields of powder samples in sealed quartz cuvettes were determined by the integrating sphere (142 mm in diameter) using an Edinburgh FLS-920 spectrofluorophotometer.

tion bands ranging from 250 to 410 nm, which are responsible for the yellow light emission. Considering the rather long lifetime of 0.84 μs (Figure S14) and the distinguishable discontinuity interband between photoluminescence excitation (PLE) and photoluminescence (PL) spectra, the yellow emission of the doped [MeHdabco]RbI3 crystal is typical phosphorescence. The detailed process for the absorption and emission of phosphorescence is described as follows: the absorbed photon energy undergoes an unusual intersystem crossing into a triplet state. As a result, the energy can become trapped in the triplet state with only “forbidden” transitions available to return to the lower energy state. These transitions will still occur in quantum mechanics but are kinetically unfavored and thus progress at significantly slower time scales. It is worth mentioning that the photoluminescence behavior is positive correlated to the iodine-doped concentration (Figure S15), and the photoluminescence quantum yield (PLQY) of such phosphorescence can be as high as 17.17% (Figure S16), indicating that iodine-doped [MeHdabco]RbI3 can be used as high-efficient yellow phosphor. In addition, the iodine-doped sample also displays SHG activity at room temperature and has the same symmetry-breaking behaviors as the pure [MeHdabco]RbI3 (Figure S17), and the temperature dependence of the dielectric constant of both the iodine-doped and pure sample are basically overlapped (Figure S10, inset), strongly indicating that both of them display similar ferroelectric behavior. In view of the exotic 3D framework of [MeHdabco]RbI3, the doped high-efficient phosphorescence makes [MeHdabco]RbI3 a promising multifunctional ferroelectric-luminescent material through a crystal engineering design strategy.

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CONCLUSION In summary, on account of a precise molecular design strategy, we have successfully designed a 3D organic−inorganic perovskite ferroelectric with a considerably high Tc of 430 K. After the molecular symmetry is lowered by introducing a methyl to the dabco, the formation of a polar crystal structure and ferroelectricity is triggered by the addition of molecular dipole moment. According to the PFM results, the static domain structure and the polarization switching of domains provide solid evidence for the ferroelectric nature. This work points to a new way of constructing 3D organic−inorganic perovskite ferroelectrics by the symmetry reduction of spherical moieties and thus the induced crystallization in polar point groups. The combination of molecular design, crystal engineering, and domain engineering within this diverse family of 3D organic−inorganic perovskites contributes to not only the understanding of the ferroelectric mechanisms but also the acceleration of practical utilizations. Moreover, the iodinedoped [MeHdabco]RbI3 crystal can display intense saffron yellow luminescence with a high quantum yield of 17.17% under UV excitation, promoting the practical use in ferroelectric luminescence.

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ASSOCIATED CONTENT

S Supporting Information *

EXPERIMENTAL SECTION

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.7b06013. Figures S1−S14, Table S1, and discussion (PDF) Crystallographic data for [MeHdabco]RbI3, 293 K (CIF) Crystallographic data for [MeHdabco]RbI3, 413 K (CIF) Crystallographic data for [H2dabco]RbBr3, 293 K (CIF)

Materials. [MeHdabco]RbI3, [H2dabco]RbCl3, [H2dabco]RbBr3, and [H2dabco]RbI3 were prepared by the literature method.10 The crystal structures of [H2dabco]RbCl3 and [H2dabco]RbBr3 can be described as three-dimensional (3D) perovskites with the general formula ABX3, where the [H2dabco]2+ cation site in the cavities is enclosed by the corner-sharing RbCl6 or RbBr6 octahedra (Figures S1 and S3). The room-temperature crystal structure of [H2dabco]RbCl3 10901

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Crystallographic Crystallographic Crystallographic Crystallographic

data data data data

(10) Paton, L. A.; Harrison, W. T. Angew. Chem., Int. Ed. 2010, 49, 7684. (11) Shi, P.-P.; Tang, Y.-Y.; Li, P.-F.; Liao, W.-Q.; Wang, Z.-X.; Ye, Q.; Xiong, R.-G. Chem. Soc. Rev. 2016, 45, 3811. (12) Aizu, K. J. Phys. Soc. Jpn. 1969, 27, 387. (13) Kleinman, D. Phys. Rev. 1962, 126, 1977. (14) (a) Garcia, V.; Fusil, S.; Bouzehouane, K.; Enouz-Vedrenne, S.; Mathur, N. D.; Barthelemy, A.; Bibes, M. Nature 2009, 460, 81. (b) Lee, D.; Lu, H.; Gu, Y.; Choi, S.-Y.; Li, S.-D.; Ryu, S.; Paudel, T. R.; Song, K.; Mikheev, E.; Lee, S.; Stemmer, S.; Tenne, D. A.; Oh, S. H.; Tsymbal, E. Y.; Wu, X.; Chen, L.-Q.; Gruverman, A.; Eom, C. B. Science 2015, 349, 1314. (15) Gesi, K. J. Phys. Soc. Jpn. 1990, 59, 432. (16) Ye, H. Y.; Zhou, Q.; Niu, X.; Liao, W. Q.; Fu, D. W.; Zhang, Y.; You, Y. M.; Wang, J.; Chen, Z. N.; Xiong, R. G. J. Am. Chem. Soc. 2015, 137, 13148. (17) Ye, H. Y.; Zhang, Y.; Fu, D. W.; Xiong, R. G. Angew. Chem., Int. Ed. 2014, 53, 11242.

for [H2dabco]RbBr3, 353 K (CIF) for [H2dabco]RbCl3, 293 K (CIF) for [H2dabco]RbCl3, 458 K (CIF) for [H2dabco]RbI3, 293 K (CIF)

AUTHOR INFORMATION

Corresponding Authors

*[email protected] *[email protected] ORCID

Wei-Qiang Liao: 0000-0002-5359-7037 Ren-Gen Xiong: 0000-0003-2364-0193 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (21422101, 91422301). REFERENCES

(1) (a) Scott, J. F. Science 2007, 315, 954. (b) Lines, M. E.; Glass, A. M. Principles and Applications of Ferroelectrics and Related Materials; Clarendon Press: Oxford, UK, 1977. (c) Tejuca, L. G.; Fierro, J. Properties and Applications of Perovskite-Type Oxides; CRC Press: New York, 2000. (2) (a) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. J. Am. Chem. Soc. 2009, 131, 6050. (b) Burschka, J.; Pellet, N.; Moon, S. J.; Humphry-Baker, R.; Gao, P.; Nazeeruddin, M. K.; Gratzel, M. Nature 2013, 499, 316. (3) (a) Saparov, B.; Mitzi, D. B. Chem. Rev. 2016, 116, 4558. (b) Li, W.; Wang, Z.; Deschler, F.; Gao, S.; Friend, R. H.; Cheetham, A. K. Nat. Rev. Mater. 2017, 2, 16099. (c) Kagan, C.; Mitzi, D.; Dimitrakopoulos, C. Science 1999, 286, 945. (d) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Science 2012, 338, 643. (4) (a) Jain, P.; Ramachandran, V.; Clark, R. J.; Zhou, H. D.; Toby, B. H.; Dalal, N. S.; Kroto, H. W.; Cheetham, A. K. J. Am. Chem. Soc. 2009, 131, 13625. (b) Jain, P.; Dalal, N. S.; Toby, B. H.; Kroto, H. W.; Cheetham, A. K. J. Am. Chem. Soc. 2008, 130, 10450. (c) Pan, Q.; Liu, Z. B.; Tang, Y. Y.; Li, P. F.; Ma, R. W.; Wei, R. Y.; Zhang, Y.; You, Y. M.; Ye, H. Y.; Xiong, R. G. J. Am. Chem. Soc. 2017, 139, 3954. (d) Fu, D. W.; Zhang, W.; Cai, H. L.; Zhang, Y.; Ge, J. Z.; Xiong, R. G.; Huang, S. D.; Nakamura, T. Angew. Chem., Int. Ed. 2011, 50, 11947. (e) Xu, W.-J.; Li, P.-F.; Tang, Y.-Y.; Zhang, W.-X.; Xiong, R.-G.; Chen, X.-M. J. Am. Chem. Soc. 2017, 139, 6369. (f) Xu, G.-C.; Ma, X.-M.; Zhang, L.; Wang, Z.-M.; Gao, S. J. Am. Chem. Soc. 2010, 132, 9588. (5) (a) Mitzi, D. B. J. Chem. Soc., Dalton Trans. 2001, 1, 1. (b) Goldschmidt, V. M. Naturwissenschaften 1926, 14, 477. (6) (a) Cheng, Z.; Lin, J. CrystEngComm 2010, 12, 2646. (b) Mitzi, D.; Wang, S.; Feild, C.; Chess, C.; Guloy, A. Science 1995, 267, 1473. (7) (a) Katrusiak, A.; Szafrański, M. Phys. Rev. Lett. 1999, 82, 576. (b) Szafrański, M.; Katrusiak, A.; McIntyre, G. Phys. Rev. Lett. 2002, 89, 215507. (c) Zhang, Y.; Zhang, W.; Li, S. H.; Ye, Q.; Cai, H. L.; Deng, F.; Xiong, R. G.; Huang, S. D. J. Am. Chem. Soc. 2012, 134, 11044. (8) (a) Tang, Y.-Y.; Zhang, W.-Y.; Li, P.-F.; Ye, H.-Y.; You, Y.-M.; Xiong, R.-G. J. Am. Chem. Soc. 2016, 138, 15784. (b) Shi, P.-P.; Tang, Y.-Y.; Li, P.-F.; Ye, H.-Y.; Xiong, R.-G. J. Am. Chem. Soc. 2017, 139, 1319. (9) (a) Li, P. F.; Tang, Y. Y.; Wang, Z. X.; Ye, H. Y.; You, Y. M.; Xiong, R. G. Nat. Commun. 2016, 7, 13635. (b) You, Y. M.; Tang, Y. Y.; Li, P. F.; Zhang, H. Y.; Zhang, W. Y.; Zhang, Y.; Ye, H. Y.; Nakamura, T.; Xiong, R. G. Nat. Commun. 2017, 8, 14934. (c) Harada, J.; Shimojo, T.; Oyamaguchi, H.; Hasegawa, H.; Takahashi, Y.; Satomi, K.; Suzuki, Y.; Kawamata, J.; Inabe, T. Nat. Chem. 2016, 8, 946. 10902

DOI: 10.1021/jacs.7b06013 J. Am. Chem. Soc. 2017, 139, 10897−10902