Design of High‐Performance Organic Nonlinear Optical and Terahertz Crystals by Controlling the van der Waals Volume
Bong‐Rim Shin, Uroš Puc, Yu‐Jin Park, Dong‐Joo Kim, Chae‐Won Lee, Woojin Yoon, Hoseop Yun, Chaeyoon Kim, Fabıan Rotermund, Mojca Jazbinšek, O‐Pil Kwon
Abstract
Abstract In the development of new organic crystals for nonlinear optical and terahertz (THz) applications, it is very challenging to achieve the essentially required non‐centrosymmetric molecular arrangement. Moreover, the resulting crystal structure is mostly unpredictable due to highly dipolar molecular components with complex functional substituents. In this work, new organic salt crystals with top‐level macroscopic optical nonlinearity by controlling the van der Waals volume ( V vdW ), rather than by trial and error, are logically designed. When the V vdW of molecular ionic components varies, the corresponding crystal symmetry shows an observable trend: change from centrosymmetric to non‐centrosymmetric and back to centrosymmetric. All non‐centrosymmetric crystals exhibit an isomorphic P 1 crystal structure with an excellent macroscopic second‐order nonlinear optical response. Apart from the top‐level macroscopic optical nonlinearity, new organic crystals introducing highly electronegative fluorinated substituents with strong secondary bonding ability show excellent performance in efficient and broadband THz wave generation, high crystal density, high thermal stability, and good bulk crystal growth ability.