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Halide anion-mediated crystal structure engineering in guanidinoacetic acid halides for tunable birefringence
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DOI：10.1039/D6QI00843G.png)
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Abstract
En 中文
Birefringent crystals for the solar-blind ultraviolet region are essential for advanced optoelectronic applications. This work demonstrates the use of halide anions (F−; Cl−; Br−; I−; and I3−) as structural regulators to tune optical anisotropy in a series of new guanidinoacetic acid (GAA)-based halide crystals. Single-crystal XRD reveals that the chloride and bromide derivatives crystallize in non-centrosymmetric space groups; while the fluoride; iodide; and polyiodide analogues are centrosymmetric. The solar-blind ultraviolet-transparent chloride and bromide compounds exhibit moderate birefringence (Δn = 0.154 and 0.022 at 546 nm). In contrast; the centrosymmetric fluoride; iodide; and polyiodide crystals show exceptionally high birefringence (Δn = 0.227; 0.290; and 0.530 at 546 nm). The systematic variations in packing motifs and interplanar dihedral angles among GAA+ cations govern the overall crystal symmetry; concurrently; birefringence is precisely tunable via the selection of distinct halide anions. This study presents a rational crystal engineering strategy for designing birefringent materials with tailored optical performance.