Double‐Modification Oriented Design of a Deep‐UV Birefringent Crystal Functionalized by [B12O16F4(OH)4] Clusters

Abstract

Polarization modulation of deep-UV light is of great significance to the current technologies, and to this end, birefringent crystal has emerged as an invaluable material as it allows for the effective light modulation. Herein, double-modification strategy driven by F and OH anions that makes double effects towards the critical property enhancement of deep-UV birefringent crystals is proposed. This leads to the discovery of a new hydroxyborate (NH 4 ) 4 [B 12 O 16 F 4 (OH) 4 ] with unprecedented giant cluster as a deep-UV birefringent crystal with large birefringence (Δ n exp. = 0.12@546 nm). Such a birefringence sets a record among inorganic hydroxyborates with experimentally measured birefringence. The [B 12 O 16 F 4 (OH) 4 ] cluster in near-plane arrangement is enabled by the hydrogen-bonding interactions; and it is theoretically confirmed to be optical-active for large birefringence and band gap, in which the π-conjugated modules, [BO 3 ] and [BO 2 (OH)], are the main sources of large optical anisotropy.