Conformational Editing Drives Covalent Hybridization for Nonlinear Optical Crystals

Abstract

ABSTRACT The covalent integration of planar organic molecules with inorganic tetrahedra into crystalline solids is fundamentally constrained by steric repulsion. Open‐chain organic moieties predominantly adopt thermodynamically stable trans ‐conformations, which spatially hinder close approach and covalent bond formation, often leading to centrosymmetric architectures. Here, we first report a solvent‐driven conformational editing strategy that overcomes this long‐standing synthetic challenge. By modulating HBF 4 concentration, we reprogram biuret from a sterically hindered trans ‐conformer into a spatially accessible cis ‐conformer. This in situ conformational switching, validated by interacting region indicator analysis and Raman spectroscopy, providing a general kinetic pathway for previously inaccessible bond formations. The resulting non‐centrosymmetric hybrid crystal, [C 2 O 2 N 3 H 5 BF 2 ][BF 4 ], features [C 2 O 2 N 3 H 5 BF 2 ] units that represent the first synthesis of a covalently linked biuret–[BO 2 F 2 ] hybrid. This compound achieves an outstanding combination of key properties for short‐wavelength ultraviolet nonlinear optical applications. Through this conformational editing approach, we further synthesized 14 additional compounds, establishing biuret as a versatile platform for hybrid assembly. Our work demonstrates solvent‐mediated conformational control as a general synthetic paradigm for overcoming steric hindrance and accessing previously inaccessible organic–inorganic architectures with tailored optical functionality.