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Birefringent materials are highly demanded for high‐performance polarized optics. As compared with artificial anisotropic metamaterials, anisotropic crystals have advantages of low optical losses and easy processing, but their birefringence is still limited. Herein, based on first‐principles studies, we identified a new type of functional anion units, (HxC6N9)(3−x)− (x=0, 1, 2), and then successfully synthesized a new anisotropic crystal, namely, CsH2C6N9⋅H2O (I), whose crystal structure consists of (H2C6N9)− anions. Remarkably, I is ultraviolet transparent and exhibits very large birefringence of about 0.55@550 nm, which is much larger than those of commercial birefringent crystals. These results make I a candidate for highly efficient manipulation of optics and light in optical modulation devices. Theoretical calculations reveal that large birefringence mainly arises from the cooperative π orbitals in (H2C6N9)− anions. This work provides a new insight on the underlying structure–property relationships of anisotropic crystals. [ABSTRACT FROM AUTHOR]

Birefringent materials are highly demanded for high‐performance polarized optics. As compared with artificial anisotropic metamaterials, anisotropic crystals have advantages of low optical losses and easy processing, but their birefringence is still limited. Herein, based on first‐principles studies, we identified a new type of functional anion units, (HxC6N9)(3−x)− (x=0, 1, 2), and then successfully synthesized a new anisotropic crystal, namely, CsH2C6N9⋅H2O (I), whose crystal structure consists of (H2C6N9)− anions. Remarkably, I is ultraviolet transparent and exhibits very large birefringence of about 0.55@550 nm, which is much larger than those of commercial birefringent crystals. These results make I a candidate for highly efficient manipulation of optics and light in optical modulation devices. Theoretical calculations reveal that large birefringence mainly arises from the cooperative π orbitals in (H2C6N9)− anions. This work provides a new insight on the underlying structure–property relationships of anisotropic crystals. [ABSTRACT FROM AUTHOR]

Birefringent crystals that can modulate the polarization of light play a significant role in modern optical devices including polarizing microscopes, optical isolators, and achromatic quarter‐wave plates. To date, commercial birefringent crystals are exclusively limited to purely inorganic compounds. Here we report a new organic–inorganic hybrid halide, MLAPbBr4 (MLA=melamine), which features a (110)‐oriented layered perovskite structure. Although the 6s2 lone‐pair electrons of Pb2+ cations are stereochemically inert, MLAPbBr4 exhibits a birefringence of 0.322@550 nm, which exceeds those of all commercial birefringent crystals. The first‐principles calculations reveal that this birefringence should be ascribed to the highly dislocated π‐conjugation of MLA cations and high distortion of PbBr6 octahedra. This work highlights the persistently neglected great potential of hybrid halide perovskites as birefringent crystals. [ABSTRACT FROM AUTHOR]

Birefringent crystals that can modulate the polarization of light play a significant role in modern optical devices including polarizing microscopes, optical isolators, and achromatic quarter‐wave plates. To date, commercial birefringent crystals are exclusively limited to purely inorganic compounds. Here we report a new organic–inorganic hybrid halide, MLAPbBr4 (MLA=melamine), which features a (110)‐oriented layered perovskite structure. Although the 6s2 lone‐pair electrons of Pb2+ cations are stereochemically inert, MLAPbBr4 exhibits a birefringence of 0.322@550 nm, which exceeds those of all commercial birefringent crystals. The first‐principles calculations reveal that this birefringence should be ascribed to the highly dislocated π‐conjugation of MLA cations and high distortion of PbBr6 octahedra. This work highlights the persistently neglected great potential of hybrid halide perovskites as birefringent crystals. [ABSTRACT FROM AUTHOR]

Birefringent crystals that can switch light polarization have important applications in optoelectronics. In the last decades, birefringence is mostly optimized by chemical strategies. Recently, switching birefringence by physical means has attracted much attention. Here, this work reports the observation of heat switching birefringence in a 2D layered hybrid halide perovskite (C2N3H4)2PbCl4 ((C2N3H4)+=1,2,4‐triazolium). This heat switching birefringence leads to a significant change in the interference color for the crystal plate under the illumination of orthogonal polarized light. Structure analyses reveal a heat dependent structure transition in (C2N3H4)2PbCl4, whose birefringence is switched by the change in the distortion degree of PbCl6 octahedron. This discovery may be beneficial to the further development of stimuli‐responsive polarization optical devices. [ABSTRACT FROM AUTHOR]

Birefringent crystals that can switch light polarization have important applications in optoelectronics. In the last decades, birefringence is mostly optimized by chemical strategies. Recently, switching birefringence by physical means has attracted much attention. Here, this work reports the observation of heat switching birefringence in a 2D layered hybrid halide perovskite (C2N3H4)2PbCl4 ((C2N3H4)+=1,2,4‐triazolium). This heat switching birefringence leads to a significant change in the interference color for the crystal plate under the illumination of orthogonal polarized light. Structure analyses reveal a heat dependent structure transition in (C2N3H4)2PbCl4, whose birefringence is switched by the change in the distortion degree of PbCl6 octahedron. This discovery may be beneficial to the further development of stimuli‐responsive polarization optical devices. [ABSTRACT FROM AUTHOR]

Birefringent materials are vital materials to modulate the polarization of light, and play a key role in plorization devices such as linear optical devices, optical communication devices, and fiber optic sensors. It is still a challenge to design excellent birefringent materials. Herein, we report an organic–inorganic hybrid oxalate birefringent material, (CN4H7)SbC2O4F2(H2O)0.5, by introducing organic delocalized π-conjugated [CN4H7]+ and [C2O4]2− groups, and stereochemical active inorganic SbO4F2 polyhedra. (CN4H7)SbC2O4F2(H2O)0.5 exhibits a large birefringence (Δn = 0.126@546 nm) that is almost equal to that of the well-known birefringent material α-BaB2O4. Theoretical calculations reveal that the distinguished birefringence should stem from the synergistic arrangement of π-conjugated [CN4H7]+ and [C2O4]2− planar groups, and highly distorted SbO4F2 polyhedra with a stereochemically active lone pair. The synergistic effect of π-conjugated systems and the lone pair electrons greatly boosts the birefringence, which is helpful for the development of high-performance birefringent materials. [ABSTRACT FROM AUTHOR]

Antimony(III) borates with a stereochemical active lone pair remained unknown, although the first antimony borate was reported more than twenty years ago. Now, the first antimony(III) borate in a closed system is successfully synthesized, namely SbB3O6. Remarkably, SbB3O6 not only exhibits an exceptional linear optical response, that is, birefringence of Δn=0.290 at the wavelength of 546 nm, which is the largest among borates, but also has a strong nonlinear optical response of 3.5 times larger than the benchmark KH2PO4, exceeding those of most borates. Theoretical calculations reveal that the coexistence of strong linear and nonlinear optical responses in SbB3O6 should be attributable to the synergistic effect of π‐conjugated B−O anionic groups and Sb3+ with stereochemically active lone pair. This work provides a new class of optical bi‐functional materials with potential prospects in integrated optical devices. [ABSTRACT FROM AUTHOR]

Antimony(III) borates with a stereochemical active lone pair remained unknown, although the first antimony borate was reported more than twenty years ago. Now, the first antimony(III) borate in a closed system is successfully synthesized, namely SbB3O6. Remarkably, SbB3O6 not only exhibits an exceptional linear optical response, that is, birefringence of Δn=0.290 at the wavelength of 546 nm, which is the largest among borates, but also has a strong nonlinear optical response of 3.5 times larger than the benchmark KH2PO4, exceeding those of most borates. Theoretical calculations reveal that the coexistence of strong linear and nonlinear optical responses in SbB3O6 should be attributable to the synergistic effect of π‐conjugated B−O anionic groups and Sb3+ with stereochemically active lone pair. This work provides a new class of optical bi‐functional materials with potential prospects in integrated optical devices. [ABSTRACT FROM AUTHOR]