Mechanochemical Synthesis of an Ionic Cocrystal with Large Birefringence Resulting from Neutral Planar π-Conjugated Groups
Xianghe Meng, Kaijin Kang, Youquan Liu, Jian Tang, Xingxing Jiang, Wenlong Yin, Zheshuai Lin, Mingjun Xia
Abstract
Birefringent materials with strong optical anisotropy are indispensable for optoelectronic devices as polarizers, isolators, and beam splitters, etc. Here, a new ionic cocrystal KBr·H3C3N3O3 (I) was synthesized by a facile and fast mechanochemical reaction. I can be described as stacking of [(H3C3N3O3)Br]− layers via hydrogen bonds separated by K+ cations along the a-axis. The experimental and theoretical results reveal that I exhibits a short ultraviolet cutoff (216 nm) and large birefringence (Δn = 0.273 at 800 nm) due to the well-aligned planar π-conjugated H3C3N3O3 molecules. In addition, I is thermally stable up to 400 °C, far higher than those of reported hydroisocyanurates. This work opens an avenue for the exploration for ionic cocrystals with π-conjugated units as prominent ultraviolet birefringent materials with strong optical anisotropy, wide band gap, easy synthesis, and good physicochemistry stability.