alpha-BBO-like pi-Conjugated Crystal with Large Birefringence

Birefringent crystals are in great demand for high performance polarizing devices. Designing new birefringent crystals with large birefringence remains a challenge. Herein, we successfully synthesized a new alpha-BBO-like pi-conjugated birefrin-gent crystal, K2HC3N3S3.1.5H(2)O (I). I exhibits a relatively large birefringence of 0.31@550 nm; such a birefringence is larger than those of most present commercial birefringent crystals. This result indicates that I might be a potential candidate for polarization modulation components in optical devices. First-principles calculations reveal that the planar pi-conjugated [HC3N3S3](2-) anions make dominant contributions in the large birefringence of I.