CdF(C6H4NO2)(H2O): A UV Nonlinear Optical Material with Unprecedented SHG and Birefringence via a π-Conjugated Rings and Unique "Warren Truss Structure"

Abstract

We report the design and synthesis of a novel ultraviolet (UV) nonlinear optical (NLO) material, CdF(C6H4NO2)(H2O), featuring a unique "Warren truss structure". This material exhibits a two-dimensional (2D) layered architecture structure composed of highly polarized [CdF3NO2] octahedra and π-conjugated organic rings (C6H4NO2). Notably, CdF(C6H4NO2)(H2O) demonstrates exceptional second-harmonic generation (SHG) response, with an intensity 3.2 times that of KH2PO4 (KDP), and a large birefringence of 0.26 @ 546 nm, which is highly unusual for UV fluorides with a bandgap >4.2 eV. Theoretical calculations and structural analysis reveal that the introduction of (C6H4NO2)- into CdF2 induces significant structural distortion and polarization, leading to the formation of non-centrosymmetric "Warren truss structure". This structure aligns [CdF3NO2] octahedra and organic rings in a highly ordered manner, which is crucial for the enhanced SHG and large birefringence. Our findings provide a new strategy for designing high-performance UV NLO materials by leveraging organic-inorganic hybrid structures.