Synergistic Dual-Modification Strategy of π-Conjugated Cations and Tetrahedra: Rational Design of Ultraviolet High-Birefringence Monofluorophosphates

Abstract

Modifying the birefringent active units to enhance anisotropy is crucial for improving birefringence in non-π-conjugated systems. Here, we proposed a synergistic dual-modification strategy that solves the shortcomings of single-component modifications by simultaneously engineering anisotropic anionic and cationic units to amplify polarizability anisotropy. Following this strategy, the πconjugated cation [C4N4H11] was identified as a superior ultraviolet birefringent chromophore for the first time. Two monofluorophosphates, (CN4H7)2PO3F•H2O and (C4N4H11)2PO3F•H2O were successfully synthesized. The modified π-conjugated cations ([CN4H7] and [C4N4H11]) and heteroleptic tetrahedron [PO3F] exhibit enhanced anisotropic polarizability, leading to large birefringence values of 0.116 and 0.165 at 546 nm for (CN4H7)2PO3F•H2O and (C4N4H11)2PO3F•H2O, respectively. This work not only discovers new ultraviolet birefringent materials but also provides a strategy for optimizing optical anisotropy to achieve efficient birefringence.