Promising Deep‐Ultraviolet Birefringent Materials via Rational Design and Assembly of Planar π‐Conjugated [B(OH)3] and [B3O3(OH)3] Functional Species

Abstract Birefringent materials play a significant role in modulating polarized light in optical communication and the laser industry. However, the discovery of deep ultraviolet (DUV, λ <200 nm) birefringent materials still faces a serious challenge. Herein, we propose hydroxylated π‐conjugated [B(OH) 3 ] and [B 3 O 3 (OH) 3 ] units for designing DUV birefringent materials. Innovatively, four new hydroxyborates have been synthesized under mild synthesis conditions. They present four novel pseudo layers that benefit from the large degree of freedom assembly modes of [B(OH) 3 ] and [B 3 O 3 (OH) 3 ] genes and large birefringence (0.057–0.123@532 nm). Moreover, the Cs 3 [B(OH) 3 ] 2 Cl 3 crystal features a short DUV cutoff edge (180 nm), which further indicates that the reported compounds are potential DUV birefringent crystals. Free and flexible assembly modes of π‐conjugated [B(OH) 3 ] and [B 3 O 3 (OH) 3 ] groups endow them a particular advantage as significant genes for exploring promising DUV birefringent materials.