English

• Ferroelastics, as a crucial member among ferroic materials, possess the property that the spontaneous strain can be altered by the application of external pressure which makes them highly valuable in fields of sensors, actuators and so on [1-9]. Since their discovery, ferroelastics have been rapidly developed [10-17]. Currently, there are still some challenges in the development of ferroelastics, such as how to increase the dielectric switching temperature or develop ferroelastics with photoluminescent property by rational strategies.

  When discussing molecular materials [18-26], it is essential to recognize the rapid advancements in molecular ferroelectrics that have taken place in recent years. As mentioned in ferroelectrochemistry, molecular ferroelectrics have emerged due to their structural flexibility [27]. This point is also applicable to the development of molecular ferroelastics. The structural tunability of molecular materials offers tremendous potential for optimizing the properties of materials. For example, by using mono-/double-protonation strategy, Luo et al. successfully obtained the mono-protonated [Me₂N(CH₂)₂NH₃]ReO₄ and double-protonated [Me₂NH(CH₂)₂NH₃](ReO₄)₂, the result showed that the double-protonated [Me₂NH(CH₂)₂NH₃](ReO₄)₂ underwent the paraelastic-ferroelastic phase transition at 322 K while the mono-protonated [Me₂N(CH₂)₂NH₃]ReO₄ did not have the ferroelasticity [28]. Deng et al. designed high-T_c ferroelastic materials (R/S-CTA)₂SbCl₅ (CTA = 3‑chloro-2-hydroxypropyltrimethyllammonium) under the guidance of the H/OH- substitution-induced homochiral strategy [29]. Lin et al. successfully synthesized and characterized three multiaxial plastic ferroelectrics with the strategy of halogen engineering in organic part [30]. Sun et al. successfully designed two lead-based hybrid materials ([BMPD]PbBr₃ and [CMPD]PbBr₃, BMPD = N-BrCH₂—N-methylpiperidine, CMPD = NnullClCH₂—N-methylpiperidine) under the strategy of halogen engineering in inorganic part, when Cl in [CMPD]PbBr₃ is changed to Br in [BMPD]PbBr₃, the phase transition temperature for [BMPD]PbBr₃ is improved by 45 K [31].

  Here, we synthesized two multi-functional molecular ferroelastics (DMTP)PbBr₃ and (DMTP)PbI₃ under the guidance of the halogen strategy. Experimental results showed that two compounds both crystallized in the non-centrosymmetric space group Pna2₁ at room temperature and P6₃mc after the phase transition which means that they both underwent the ferroelastic–paraelastic phase transition with the Aizu notation of 6mmFmm2. (DMTP)PbI₃ underwent the phase transition at 371 K and (DMTP)PbBr₃ underwent the phase transition at a higher temperature of 390 K. Structural analysis indicated that after halogen substitution, the distance between inorganic chains decreased for (DMTP)PbBr₃, causing the organic cations are more likely to be influenced by the forces from the inorganic framework. The intermolecular interaction forces of (DMTP)PbBr₃ are stronger than those of (DMTP)PbI₃, which leads to the phase transition temperature of (DMTP)PbBr₃ is increased. In addition, they could emit orange light under the ultraviolet radiation at room temperature with the quantum yield of 2.68% for (DMTP)PbI₃ and 12% for (DMTP)PbBr₃, which is due to the inorganic framework of (DMTP)PbBr₃ exhibiting a higher degree of distortion. The luminous intensity of two compounds weakened gradually with increasing temperature and disappeared rapidly after undergoing the phase transition.

  Synthesis: All medicines are commercially available and were used directly without further processing. The synthesis of the organic ligand for two compounds is as follows: Firstly, 0.1 mol of 1,2,3,6-tetrahydropyridine hydrochloride and 0.25 mol of iodomethane were added into the solvent mixture of acetonitrile and methanol and then 10 g of potassium carbonate was added to absorb the HCl in the 1,2,3,6-tetrahydropyridine hydrochloride and the HI produced in the reaction. Secondly, the mixed solution was moved to the oil bath to react for 24 h at 323 K then KI, KCl and excess potassium carbonate were removed by filtration. Thirdly, the solution obtained in the previous step was transferred to rotary evaporation at 325 K and the ligand which we need was made. For (DMTP)PbBr₃, at first, 3 mmol of the ligand and 1.5 mmol of silver carbonate were added in 15 mL of deionised water and then the mixed solution reacted for 2 h in the fume hood and was protected from light. Secondly, the mixed solution was filtered to remove AgI. Thirdly, 3 mmol of lead bromide was weighed and added into the mixed solution and hydrobromic acid was added continuously and at the same time, the solution was heated and stirred until lead bromide is dissolved. At last, the transparent solution was placed to the hot plate and after few days, the transparent block crystals of (DMTP)PbBr₃ were precipitated. For (DMTP)PbI₃, firstly, 2.5 mmol of the ligand was added into hydriodic acid then 2.5 mmol lead iodide was weighed and added into the solution. Secondly, the mixed solution was heated with stirring until the solution became clear and transparent. At last, the transparent solution was transferred to the hot plate at 333 K and after almost one-week, yellow needle crystals of (DMTP)PbI₃ were successfully obtained.

  Characterization: Single crystal X-ray diffraction (SXRD) was used to study the crystal structure, differential scanning calorimetry (DSC) was used for thermal analysis, and powder X-ray diffraction (PXRD) was used to verify the purity of the crystal. The more details of these measurement methods are in Supporting information.

  Thermal analysis and dielectric properties: When the structure of the crystal changes, heat-absorbing or heat-emitting phenomena usually can be observed [32-38]. DSC is often used to observe the rate of heat absorption or emission of the sample as it is heated up or cooled down. When there is an anomalous heat change, the corresponding peak can be seen from the DSC result. Figs. 1a and d show the DSC results for (DMTP)PbBr₃ and (DMTP)PbI₃, respectively. From the Fig. 1a, we can see that (DMTP)PbBr₃ has a heat absorption peak at 390 K in the heating process and correspondingly, it has an exothermic peak at 380 K in the cooling process. Similarly, for (DMTP)PbI₃, a pair of peaks is observed at 371 K (heating process) and 360 K (cooling process), respectively. For (DMTP)PbBr₃, we can get the corresponding entropy changes (ΔS) to be 13.1 and 13.4 J mol^-1 K^-1 combining the formula ΔS = ΔH/T, respectively. Similarly, for (DMTP)PbI₃, the corresponding ΔS to be 39.1 and 41.6 J mol^-1 K^-1, respectively. For ease of description, we denote the phase of the crystal before the phase transition as RTP and the phase after the phase transition as HTP. The dielectric constant of the compound near the temperature point of the phase transition usually undergoes an abrupt change [39-44]. Fig. 1b illustrates the variation of the dielectric constant of (DMTP)PbBr₃ with the temperature. In the RTP, the dielectric constant is around 7.0, as the temperature increases near the phase transition point, the dielectric constant undergoes a significant change, with the dielectric constant increasing to 8.5 in the HTP. Similarly, we can observe that for (DMTP)PbI₃ from the Fig. 1e, the dielectric constant is around 9.0 before the phase transition, and when the temperature is increased to around 371 K, the dielectric constant rapidly increases to around 11.0 and remains almost unchanged. The property that the dielectric constants of two compounds undergo an abrupt change at the point of phase transition and remain almost constant before and after the phase transition indicates the suitability of the two compounds for dielectric switching materials. The variations of the dielectric constants of two compounds with temperature at other frequencies are shown in Fig. S2 (Supporting information).

  Figure 1

  

  Figure 1.  DSC curves of (a) (DMTP)PbBr₃ and (d) (DMTP)PbI₃ in the heating and cooling process. The temperature-responsive dielectric cycles of (b) (DMTP)PbBr₃ and (e) (DMTP)PbI₃ at 1 MHz in the heating and cooling process. The second harmonic generation (SHG) intensity plots of (c) (DMTP)PbBr₃ and (f) (DMTP)PbI₃ during the heating and cooling cycle.

  DownLoad: Full-Size Img PowerPoint

  Second harmonic generation analysis: The SHG intensities of (DMTP)PbBr₃ and (DMTP)PbI₃ are about 0.32 and 0.35 times that of potassium dihydrogen phosphate (KDP) at room temperature (Fig. S3 in Supporting information). The variation curves of SHG signals of two compounds with increasing temperature are shown in Figs. 1c and f. The result indicates that two compounds both crystallize in the non-centrosymmetric space group which can be seen in the structure analysis.

  Structure analysis: In order to study the phase transition mechanism of the crystals, we performed SXRD experiments. In the LTP, (DMTP)PbBr₃ crystallizes in the Pna2₁ space group which belongs to the orthorhombic system with crystal cell parameters of a = 7.9038(16) Å, b = 16.108(4) Å, c = 10.077(2) Å, and V = 1283.0(5) ų (Table S1 in Supporting information). The inorganic framework of (DMTP)PbBr₃ exhibits a distinct one-dimensional chain structure which is same as the reported one-dimensional lead halide structures (Fig. 2a). Organic cations are located in the space between the inorganic chains. The organic cations are ordered at RTP and the carbon atoms on the six-membered ring are almost in one plane due to the limitation of the double bond, which is different from the general configuration of the six-membered ring. Inorganic chains are parallel to each other and the distance between them is 10.0770 or 9.8362 Å. Each lead atom is coordinated to six bromine atoms and the bond lengths of Pb-Br are between 2.92 Å and 3.1 Å (Fig. 2b). From the DSC result, it is clear that (DMTP)PbBr₃ undergoes a structural phase transition at around 390 K, in order to study the structure of (DMTP)PbBr₃ after phase transition, variable temperature SXRD was conducted at 403 K. In the HTP, (DMTP)PbBr₃ crystallizes in the P6₃mc space group which belongs to the hexagonal system with crystal cell parameters of a = 10.000(3) Å, b = 10.000(3) Å, c = 7.912(4) Å, and V = 685.2(6) ų (Table S1). The organic cation is in the state of severe disorder and sits on the special position with the 6 mm symmetry (Fig. 2a). The bond lengths of Pb-Br change slightly and the distance between adjacent inorganic chains is changed to 10.000 Å (Fig. 2c). The results show that the organic cation undergoes severe thermal vibration while the inorganic framework undergoes relatively weak change which leads to the phase transition of (DMTP)PbBr₃. In the LTP, (DMTP)PbI₃ crystallizes in the Pna2₁ space group which belongs to the orthorhombic system with crystal cell parameters of a = 8.2388(10) Å, b = 16.691(2) Å, c = 10.6310(15) Å, and V = 1461.9(3) ų (Table S1). Cations are in an ordered state in the LTP (Fig. 3a). Inorganic chains are parallel to each other and the distance between them is 10.6310 or 10.0073 Å. Each lead atom is coordinated to six iodine atoms and the bond lengths of Pb-Ⅰ are between 3.1919 Å and 3.2761 Å (Fig. 3b). We can see that after halogen substitution, the distance between the inorganic chains of (DMTP)PbI₃ is greater than that of (DMTP)PbBr₃, which means that the cations of (DMTP)PbI₃ would be less constrained by the inorganic framework. In the HTP, (DMTP)PbI₃ crystallizes in the P6₃mc space group which belongs to the hexagonal system with crystal cell parameters of a = 10.406(3) Å, b = 10.406(3) Å, c = 8.171(3) Å, and V = 766.3(5) ų (Table S1). The change of organic cation and inorganic framework of (DMTP)PbI₃ are similar to those of (DMTP)PbBr₃ after undergoing the phase transition (Fig. 3c). Overall, the phase transitions of these two compounds arise from the order-disorder motion of organic cations and deformation of the inorganic frameworks.

  Figure 2

  

  Figure 2.  (a) The packing structures of (DMTP)PbBr₃ and evolution of organic cation for (DMTP)PbBr₃. Evolution of inorganic part for (DMTP)PbBr₃ in the (b) RTP and (c) HTP.

  DownLoad: Full-Size Img PowerPoint

  Figure 3

  

  Figure 3.  (a) The packing structures of (DMTP)PbI₃ and evolution of organic cation for (DMTP)PbI₃. Evolution of inorganic part for (DMTP)PbI₃ in the (b) RTP and (c) HTP.

  DownLoad: Full-Size Img PowerPoint

  Intermolecular Interaction Analysis: Intermolecular interaction forces are crucial to influencing the phase transition temperature of compounds [45-51]. Therefore, the Hirshfeld d_norm surfaces of two compounds were calculated and estimated with the help of CrystalExplorer software based on their structural files. As depicted in Fig. 4, the d_norm value for (DMTP)PbBr₃ is 0.4824, and for (DMTP)PbI₃ is 0.5153, smaller d_norm value represents larger intermolecular force so the cation for (DMTP)PbBr₃ experiences stronger restraining forces from the surrounding cations and anions, which causes that the phase transition temperature of (DMTP)PbBr₃ (390 K) is higher than that of (DMTP)PBI₃ (371 K). In addition, the C—H_(inside)⋯H—C_(outside) for (DMTP)PbBr₃ is 55.8% and for (DMTP)PbI₃ is 52.9%, which suggests that the hydrogen bonds between cations of (DMTP)PbBr₃ are stronger than that of (DMTP)PbI₃. From the structural analysis we can see that the distance between adjacent inorganic chains of (DMTP)PbBr₃ is 10.0770 Å or 9.8362 Å while that of (DMTP)PbI₃ is 10.6310 Å or 10.0073 Å, which indicates that the inorganic frameworks of (DMTP)PbBr₃ have smaller space so the organic cations are more likely to be influenced by the forces from the framework.

  Figure 4

  

  Figure 4.  Hirshfeld surface and two-dimensional (2D) fingerprint plots of (a) (DMTP)PbBr₃ and (b) (DMTP)PbI₃.

  DownLoad: Full-Size Img PowerPoint

  Ferroelasticity: For (DMTP)PbBr₃ and (DMTP)PbI₃, the space group transition from Pna2₁ to P6₃mc is occurred with an Aizu notation of 6mmFmm2 which meets one of the 94 species of ferroelastic phase transitions defined by Aizu. Figs. 5a and b show the topography of two compounds. The significant feature of the ferroelastic phase transition is that the change of ferroelastic domains can be directly observed under the polarized light. Figs. 5e-h show the change of ferroelastic domains of (DMTP)PbBr₃ under the polarized light. We can see that in ferroelastic phase there are parallel stripes on the surface of the crystal and these stripes are ferroelastic domains. With further increase in temperature, these stripes disappear when the temperature exceeded the phase transition temperature and reappear as the temperature is lowered below the phase transition temperature. Figs. 5i-l show the variation of ferroelastic domains of (DMTP)PbI₃ under the polarized light. In order to better observe the changes of ferroelastic domains for two compounds under the polarized light, we also provide relevant videos (Movies S1 and S2 in Supporting information).

  Figure 5

  

  Figure 5.  Topography of (a) (DMTP)PbBr₃ and (b) (DMTP)PbI₃. Schematic diagram of the (c) ferroelastic phase to (d) paraelastic phase. (e–h) Evolution of ferroelastic domains of (DMTP)PbBr₃ under the polarized light. (i-l) Evolution of ferroelastic domains of (DMTP)PbI₃ under the polarized light.

  DownLoad: Full-Size Img PowerPoint

  To further investigate the ferroelastic properties of the two compounds, we calculated their spontaneous strain tensor using Eq. 1 [52].

  εij=[l11l12l13l21l22l23l31l32l33]

  (1)

  Finally, the spontaneous strains for (DMTP)PbBr₃ and (DMTP)PbI₃ were calculated to be approximately 0.7 and 0.6 at room temperature (calculation details are given in Supporting information) based on Eq. 2.

  $ \varepsilon_{s s}=\sqrt{\sum\limits_{i j} \varepsilon_{i j}^2} $

  (2)

  Photoluminescence properties: From the Fig. 6a, crystals of two compounds can both emit the orange light under the exposure of the ultraviolet radiation. In order to further describe their colours, chromaticity coordinates have been calculated and their chromaticity coordinates are (0.5386, 0.4397) and (0.5164, 0.4598) (Fig. 6d), respectively according to the standard of Commission Internationale de I’Eclairage (CIE). For better understanding the photoluminescence properties of two compounds, we measured their excitation as well as emission spectra at first. From Fig. 6b, we can see that (DMTP)PbBr₃ has two excitation peaks at 306 nm and 340 nm. Its emission peak was measured under the excitation of 340 nm wavelength and the result showed that the emission peak of (DMTP)PbBr₃ is located at 650 nm. Similarly, two excitation peaks of (DMTP)PbI₃ are located at 359 nm and 405 nm and the emission peak is located at 610 nm (Fig. 6c). The emission wavelength of the bromine substitution is somewhat red-shifted compared to that of the iodine substitution. Next, we measured photoluminescence lifetimes of two compounds. As shown in Fig. S4 (Supporting information), the lifetimes were 53.84 ns for (DMTP)PbBr₃ and 7.67 ns for (DMTP)PbI₃. They are similar to the lifetimes which have been reported so far in lead-based organic-inorganic hybrid materials. Further, the quantum yields of two compounds were measured and the yields were 12% for (DMTP)PbBr₃ (Fig. S6 in Supporting information) and 2.68% for (DMTP)PbI₃ (Fig. S5 in Supporting information). The quantum yields of two compounds varied dramatically due to the difference in halogen. This once again demonstrates that the halogen substitution strategy can effectively influence the photoluminescence properties of organic-inorganic hybrid materials. To further investigate why the quantum yields of two compounds were so different. We calculated the respective values of the ortho-octahedral distortion. The bond length distortion (Δd) and bond angle variance (β²) of two compounds were calculated based on Eqs. 3 and 4.

  $ \Delta d=\frac{1}{6} \sum\limits_{i=1}^6\left[\left(d_i-d_0\right) / d_0\right]^2 $

  (3)

  $ \beta^2=\frac{1}{11} \sum\limits_{i=1}^{12}\left(\beta_i-90^{\circ}\right)^2 $

  (4)

  Figure 6

  

  Figure 6.  (a) Photographs of (DMTP)PbBr₃ and (DMTP)PbI₃ under ambient light and UV light. Excitation and emission spectra for (b) (DMTP)PbBr₃ and (c) (DMTP)PbI₃. (d) CIE chromaticity coordinate of (DMTP)PbBr₃ and (DMTP)PbI₃. (e) Temperature-dependent PL spectra of (DMTP)PbBr₃. (f) PL trend from 303 K to 423 K of (DMTP)PbBr₃.

  DownLoad: Full-Size Img PowerPoint

  In Eq. 3, d_i is the independent bond length of Pb–X (X=Cl/Br) and d₀ is the average Pb–X bond length and β_i represents the bond angle of X–Pb–X. The quantitative values for Δd and β² were calculated to be 2.7 × 10^–4 and 63.6305 in (DMTP)PbBr₃, 1.2 × 10^–4 and 40.7984 in (DMTP)PbI₃. The result shows that the degree of distortion of bromine substitution is greater than that of iodine substitution, which explains why the quantum yield of bromine substitution is higher than that of iodine substitution. We noted that the luminous intensity of both crystals diminished with increasing temperature and disappeared near the phase transition temperature point. So we measured the temperature-dependent emission spectra of two compounds (Fig. 6e and Fig. S4a), and for ease of observation, we made plots of variation of the intensity of the emission light with temperature for fixed emission wavelengths (650 nm for (DMTP)PbBr₃ and 610 nm for (DMTP)PbI₃). From Fig. 6f, we can see that the intensity of the emission light gradually became smaller as the temperature increased, while near the phase transition temperature point, the intensity of the emitted light dropped rapidly.

  In summary, we have successfully designed and synthesized two multi-functional ferroelastics (DMTP)PbBr₃ and (DMTP)PbI₃ under the guidance of halogen substitution strategy. Two compounds both crystallized in the non-centrosymmetric space group Pna2₁ at room temperature and P6₃mc after the phase transition. They both underwent the ferroelastic–paraelastic phase transition with the Aizu notation of 6mmFmm2. The phase transitions of these two crystals arise from the order-disorder motion of organic cations and deformation of the inorganic frameworks. After halogen substitution, (DMTP)PbBr₃ exhibits a higher dielectric switching temperature compared to (DMTP)PbI₃ due to the enhanced intermolecular interactions in (DMTP)PbBr₃. Moreover, the greater distortion in the inorganic framework of (DMTP)PbBr₃ results in a higher photoluminescence quantum yield compared to (DMTP)PbI₃. This work not only validates the rationality of the halogen substitution strategy but also offers valuable insights for the exploration of multifunctional ferroelastic materials.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Zhi-Long Li: Writing – original draft. Hao-Fei Ni: Data curation. Bo Zhuang: Data curation. Kun Ding: Data curation. Da-Wei Fu: Supervision. Qiang Guo: Data curation. Meng-Meng Lun: Data curation.

  Acknowledgments

  This work was financially supported by the National Natural Science Foundation of China (No. 22371258) and the research fund of Southeast University.

  Supplementary materials

  The supplementary crystallographic data for this paper have been uploaded in the Cambridge Structural Database. The number of CCDC are 2400546-2400549. Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2024.110755.

  
  
• 1. [1]

     F.F. Di, H. Peng, H. Zhang, et al., Mater. Chem. Front. 5 (2021) 2842–2848. doi: 10.1039/d1qm00007a

  2. [2]

     D.W. Fu, J.X. Gao, P.Z. Huang, et al., Angew. Chem. Int. Ed. 60 (2021) 8198–8202. doi: 10.1002/anie.202015219

  3. [3]

     P.Z. Huang, H.F. Ni, C.Y. Su, et al., CCS Chem. 5 (2023) 1942–1951. doi: 10.31635/ccschem.022.202202332

  4. [4]

     Q.Q. Jia, H.F. Lu, J.Q. Luo, et al., Small 20 (2023) 2306989.

  5. [5]

     H.F. Ni, J.H. Lin, C.F. Wang, et al., Inorg. Chem. Front. 10 (2023) 7231–7237. doi: 10.1039/d3qi01650a

  6. [6]

     S.E. Park, H.T. Jeong, Y.C. Cho, et al., Phase Transit. 70 (2006) 231–242.

  7. [7]

     J.L. Schlenker, G.V. Gibbs, M.B. Boisen, Acta. Crystal. A 34 (1978) 52–54. doi: 10.1107/S0567739478000108

  8. [8]

     C.Y. Su, M.M. Lun, Y.D. Chen, et al., CCS Chem. 4 (2022) 2009–2019. doi: 10.31635/ccschem.021.202101073

  9. [9]

     H. Yan, H. Yang, J. Luo, et al., Chin. Chem. Lett. 32 (2021) 3825–3832. doi: 10.1016/j.cclet.2021.05.017

  10. [10]

      W.L. Yang, X. Yan, M. Wang, et al., Inorg. Chem. Front. 11 (2024) 6874–6879. doi: 10.1039/d4qi01780c

  11. [11]

      J.T. Mo, Z. Wang, Chin. Chem. Lett. 35 (2024) 109360. doi: 10.1016/j.cclet.2023.109360

  12. [12]

      J.C. Qi, Y. Qin, H. Peng, et al., Sci. China. Chem. 67 (2024) 4167–4174. doi: 10.1007/s11426-024-2175-2

  13. [13]

      H. Peng, L. Qin, Y.H. Liu, et al., Chin. Chem. Lett. 34 (2023) 107980. doi: 10.1016/j.cclet.2022.107980

  14. [14]

      S.Y. Zhang, Z.C. Zhang, T. Zhang, et al., Dalton Trans. 52 (2023) 10415–10422. doi: 10.1039/d3dt01574b

  15. [15]

      Q.Q. Jia, T. Shao, L. Tong, et al., Chin. Chem. Lett. 34 (2023) 107539. doi: 10.1016/j.cclet.2022.05.053

  16. [16]

      Z.X. Zhang, C.Y. Su, J. Li, et al., Chem. Mater. 33 (2021) 5790–5799. doi: 10.1021/acs.chemmater.1c01699

  17. [17]

      L.L. Chu, T. Zhang, Y.F. Gao, et al., Chem. Mater. 32 (2020) 6968–6974. doi: 10.1021/acs.chemmater.0c02223

  18. [18]

      D.W. Fu, J.X. Gao, W.H. He, et al., Angew. Chem. Int. Ed. 59 (2020) 17477–17481. doi: 10.1002/anie.202007660

  19. [19]

      J.X. Gao, W.Y. Zhang, Z.G. Wu, et al., J. Am. Chem. Soc. 142 (2020) 4756–4761. doi: 10.1021/jacs.9b13291

  20. [20]

      X.J. Song, T. Zhang, Z.X. Gu, et al., J. Am. Chem. Soc. 143 (2021) 5091–5098. doi: 10.1021/jacs.1c00613

  21. [21]

      C.Y. Su, Z.X. Zhang, J. Yao, et al., Chin. Chem. Lett. 34 (2023) 107442. doi: 10.1016/j.cclet.2022.04.040

  22. [22]

      Y. Wang, T. Zhang, M.M. Lun, et al., Inorg. Chem. Front. 8 (2021) 4230–4238. doi: 10.1039/d1qi00736j

  23. [23]

      Y.F. Xie, Y. Ai, Y.L. Zeng, et al., J. Am. Chem. Soc. 142 (2020) 12486–12492. doi: 10.1021/jacs.0c05372

  24. [24]

      Y.Y. Zhang, J.Q. Luo, Y. Han, et al., Chin. Chem. Lett. 36 (2024) 109530.

  25. [25]

      T. Zhang, J.Y. Li, G.W. Du, et al., Inorg. Chem. Front. 9 (2022) 4341–4349. doi: 10.1039/d2qi00964a

  26. [26]

      Y. Zhang, X.J. Song, Z.X. Zhang, et al., Matter 2 (2020) 697–710. doi: 10.1016/j.matt.2019.12.008

  27. [27]

      H.Y. Liu, H.Y. Zhang, X.G. Chen, et al., J. Am. Chem. Soc. 142 (2020) 15205–15218. doi: 10.1021/jacs.0c07055

  28. [28]

      J.Q. Luo, M.M. Lun, Q.Q. Jia, et al., Chin. J. Chem. 42 (2024) 1706–1712. doi: 10.1002/cjoc.202400076

  29. [29]

      B.W. Deng, Z.P. Rao, M.J. Shen, et al., J. Mater. Chem. C 12 (2024) 6098–6105. doi: 10.1039/d4tc00428k

  30. [30]

      J.H. Lin, J.R. Lou, L.K. Ye, et al., Inorg. Chem. 62 (2023) 2870–2876. doi: 10.1021/acs.inorgchem.2c04295

  31. [31]

      X.T. Sun, H.F. Ni, Y. Zhang, et al., Chin. J. Struc. Chem. 43 (2024) 100212.

  32. [32]

      Y.Y. Chen, C.H. Gao, T. Yang, et al., Chin. J. Struc. Chem. 41 (2022) 2204001–2204011.

  33. [33]

      K. Ding, H.S. Ye, C.Y. Su, et al., Nat. Commun. 14 (2023) 2863. doi: 10.1038/s41467-023-38590-7

  34. [34]

      J.Y. Li, T. Zhang, M.M. Lun, et al., Small 19 (2023) 2301364. doi: 10.1002/smll.202301364

  35. [35]

      M.M. Lun, H.F. Ni, Z.X. Zhang, et al., Angew. Chem. Int. Ed. 63 (2024) e202313590. doi: 10.1002/anie.202313590

  36. [36]

      M.M. Lun, C.Y. Su, J. Li, et al., Small 19 (2023) 2303127. doi: 10.1002/smll.202303127

  37. [37]

      M.M. Lun, J.Q. Luo, Z.X. Zhang, et al., Chem. Eng. J. 475 (2023) 145969. doi: 10.1016/j.cej.2023.145969

  38. [38]

      M.M. Lun, C.Y. Su, Q.Q. Jia, et al., Inorg. Chem. Front. 10 (2023) 5026–5034. doi: 10.1039/d3qi01037f

  39. [39]

      J.Q. Luo, Q.Q. Jia, G. Teri, et al., ACS Mater. Lett. 6 (2023) 452–460.

  40. [40]

      H.F. Ni, L.K. Ye, P.C. Zhuge, et al., Chem. Sci. 14 (2023) 1781–1786. doi: 10.1039/d2sc05857j

  41. [41]

      J.Q. Wang, G. Teri, H.F. Ni, et al., Inorg. Chem. Front. 10 (2023) 3860–3866. doi: 10.1039/d3qi00594a

  42. [42]

      Z.J. Wang, H.F. Ni, T. Zhang, et al., Chem. Sci. 14 (2023) 9041–9047. doi: 10.1039/d3sc02652c

  43. [43]

      Q.Q. Jia, J.Q. Luo, Z.Y. Xue, et al., Chin. Chem. Lett. 36 (2025) 110471. doi: 10.1016/j.cclet.2024.110471

  44. [44]

      Q.Q. Jia, G. Teri, J.Q. Luo, et al., J. Am. Chem. Soc. 30 (2024) 21120–21128. doi: 10.1021/jacs.4c06929

  45. [45]

      J.Y. Liu, M.M. Lun, Z.J. Wang, et al., Chem. Sci. 15 (2024) 16612–16617. doi: 10.1039/d4sc03571b

  46. [46]

      J.Y. Liu, M. Zhu, F.W. Zhang, et al., Inorg. Chem. Front. 11 (2024) 6418–6424. doi: 10.1039/d4qi01774a

  47. [47]

      J.Q. Luo, H.F. Lu, Y.J. Nie, et al., Nat. Commun. 15 (2024) 8636. doi: 10.1038/s41467-024-53031-9

  48. [48]

      C.F. Wang, Y. Yang, Y. Hu, et al., Angew. Chem. Int. Ed. 63 (2024) e202413726. doi: 10.1002/anie.202413726

  49. [49]

      Z.J. Wang, M.J. Shen, Z.P. Rao, et al., Inorg. Chem. Front. 11 (2024) 2290–2299. doi: 10.1039/d4qi00303a

  50. [50]

      Z.X. Zhang, H. Wang, H.F. Ni, et al., Angew. Chem. Int. Ed. 63 (2024) e202319650. doi: 10.1002/anie.202319650

  51. [51]

      Z.X. Zhang, H.F. Ni, J.S. Tang, et al., J. Am. Chem. Soc. 146 (2024) 27443–27450. doi: 10.1021/jacs.4c07268

  52. [52]

      J. Li, T. Zhang, M.M. Lun, et al., Chem. Commun. 59 (2023) 4644. doi: 10.1039/d3cc00776f

• 

  Figure 1  DSC curves of (a) (DMTP)PbBr₃ and (d) (DMTP)PbI₃ in the heating and cooling process. The temperature-responsive dielectric cycles of (b) (DMTP)PbBr₃ and (e) (DMTP)PbI₃ at 1 MHz in the heating and cooling process. The second harmonic generation (SHG) intensity plots of (c) (DMTP)PbBr₃ and (f) (DMTP)PbI₃ during the heating and cooling cycle.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  (a) The packing structures of (DMTP)PbBr₃ and evolution of organic cation for (DMTP)PbBr₃. Evolution of inorganic part for (DMTP)PbBr₃ in the (b) RTP and (c) HTP.

  下载: 全尺寸图片 幻灯片
  

  Figure 3  (a) The packing structures of (DMTP)PbI₃ and evolution of organic cation for (DMTP)PbI₃. Evolution of inorganic part for (DMTP)PbI₃ in the (b) RTP and (c) HTP.

  下载: 全尺寸图片 幻灯片
  

  Figure 4  Hirshfeld surface and two-dimensional (2D) fingerprint plots of (a) (DMTP)PbBr₃ and (b) (DMTP)PbI₃.

  下载: 全尺寸图片 幻灯片
  

  Figure 5  Topography of (a) (DMTP)PbBr₃ and (b) (DMTP)PbI₃. Schematic diagram of the (c) ferroelastic phase to (d) paraelastic phase. (e–h) Evolution of ferroelastic domains of (DMTP)PbBr₃ under the polarized light. (i-l) Evolution of ferroelastic domains of (DMTP)PbI₃ under the polarized light.

  下载: 全尺寸图片 幻灯片
  

  Figure 6  (a) Photographs of (DMTP)PbBr₃ and (DMTP)PbI₃ under ambient light and UV light. Excitation and emission spectra for (b) (DMTP)PbBr₃ and (c) (DMTP)PbI₃. (d) CIE chromaticity coordinate of (DMTP)PbBr₃ and (DMTP)PbI₃. (e) Temperature-dependent PL spectra of (DMTP)PbBr₃. (f) PL trend from 303 K to 423 K of (DMTP)PbBr₃.

  下载: 全尺寸图片 幻灯片
•