A Deep-Ultraviolet Transparent Nonlinear Optical Hydrogen-Bonded Organic Framework

There is an urgent need for deep-ultraviolet (UV) nonlinear optical (NLO) materials for advanced cutting-edge optoelectronic applications. However, breaking through the optical nonlinearity ceiling of existing UV NLO materials has proven to be a major challenge due to the limited range of microstructural primitives and the difficulties in ensuring their uniform alignment. We report herein the first deep-UV transparent NLO crystal of O₃SCH₂NH₃ with a hydrogen-bonded organic framework. Evolving from the tetrahedral primitive by a computation-guided unit-substitution strategy, the three-dimensional (3D) framework of O₃SCH₂NH₃ consists solely of uniformly aligned [O₃SCH₂NH₃] primitives functionalized by electron-donating [CH₂NH₃] units, and exhibits deep-UV transparency (<170 nm), strong powder second-harmonic generation responses at 1064 nm (3.8 × KH₂PO₄) and 532 nm (0.7 × β-BaB₂O₄), and sufficient birefringence (Δ<i>n</i>(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover><mml:mi>1</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:math>10) = 0.060 @ 546 nm). Theoretical calculations and crystal structure analysis reveal that the uniform alignment of the [O₃SCH₂NH₃] primitives controlled by hydrogen bonding within the 3D organic framework is responsible for the exceptional NLO performance.