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Organic σ‐Hole Containing Crystals with Enhanced Nonlinear Optical Response and Efficient Optical‐to‐THz Frequency Conversion
Author(s) -
Kim SeIn,
Kim Won Tae,
Seok JinHong,
Jazbinsek Mojca,
Yoon Woojin,
Yu In Cheol,
Yun Hoseop,
Kim Dongwook,
Rotermund Fabian,
Kwon OPil
Publication year - 2020
Publication title -
advanced optical materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.89
H-Index - 91
ISSN - 2195-1071
DOI - 10.1002/adom.201901840
Subject(s) - chromophore , hyperpolarizability , materials science , terahertz radiation , intermolecular force , crystal (programming language) , nonlinear optics , optoelectronics , nonlinear optical , molecular physics , chemical physics , optics , nonlinear system , molecule , photochemistry , chemistry , physics , organic chemistry , laser , quantum mechanics , computer science , programming language
A new approach for the molecular design of highly efficient nonlinear optical organic crystals is proposed by introducing substituents that form σ‐holes on both nonlinear optical cationic chromophores and aromatic anions. Introducing chlorinated substituents, in which a relatively positive σ‐hole and a negative belt coexist, provides selective reduction capability of specific π–π intermolecular interactions and simultaneous multiple secondary bonding capabilities. This leads to a crystalline state with enhanced first‐order hyperpolarizability β crystal of chromophores that favors parallel chromophore alignment and suppression of molecular vibrations, which are optimal characteristics for electro‐optic and nonlinear optical applications, including efficient THz wave generation. Compared to benchmark nonhalogenated and fluorinated analogous crystals with state‐of‐the‐art macroscopic optical nonlinearity, σ‐hole containing chloro‐quinolinium crystals exhibit up to two times higher macroscopic nonlinear optical response and remarkably different crystal characteristics. As a result, a 0.16 mm thick chloro‐quinolinium crystal exhibits ≈22 times higher optical‐to‐THz conversion efficiency than the widely used 1.0 mm thick ZnTe inorganic crystal. Moreover, chloro‐quinolinium crystals exhibit very broad THz spectra, up to 8 THz with significantly different THz spectral shape compared to benchmark organic crystals, which is attributed to different phase matching between optical and THz frequencies and molecular vibration motions.