Ultraviolet Nonlinear Optical Single Crystals of A Three‐Dimensional Chiral Covalent Framework Containing Te−O−B−O Bonds

Abstract Extending covalent organic frameworks (COFs) into crystalline carbon‐free covalent backbones is an important strategy to endow these materials with more exotic functions. Integrating metal‐free inorganic and organic components into one covalent framework is an effective way to address the issue of poor thermal/solvent stability in the field of nonlinear optics (NLO). However, constructing such structures is very challenging. Here, we linked 3‐connected nods (BO 3 ) and 2‐connected organic building blocks (Te(Ph) 2 ) together to produce colorless single crystals (size up to 400 μm) of a three‐dimensional (3D) chiral covalent framework ( CityU‐22 ). The single‐crystal X‐ray diffraction (SCXRD) analysis reveals that CityU‐22 has a non‐carbon Te−O−B−O bond‐based network with the srs topology. The chiral CityU‐22 displays good stability under the treatment of different common solvents or heat (the decomposition temperature above 300 °C). Due to its non‐π‐conjugated backbone (−Te−O−B−O−), CityU‐22 shows an ultraviolet NLO behavior with a second‐harmonic generation (SHG) response similar to KH 2 PO 4 (KDP).