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Unlocking Strong Second-Harmonic Generation in Deep-UV-Transparent Polar Organic Sulfonates through Connectivity
Feiyuan Gong1, Xingxing Jiang2, Kaining Duanmu1
1China-Australia Joint Research Center for Functional Molecular Materials, School of Chemical Science and Engineering, Tongji University, Shanghai, 200092, China.
Angewandte Chemie (International Ed. in English)
|November 10, 2025
Summary
Researchers developed a new method to create polar organic salts for high-performance ultraviolet nonlinear optical (UV NLO) applications. This approach controls anion alignment, enhancing optical properties and enabling efficient UV NLO crystal development.
Area of Science:
- Materials Science
- Crystallography
- Nonlinear Optics
Background:
- Developing high-performance ultraviolet nonlinear optical (UV NLO) crystals is challenging due to the need for efficient NLO-functional groups and their precise non-centrosymmetric alignment.
- Existing methods struggle to simultaneously achieve both high NLO efficiency and optimal structural organization in UV NLO materials.
Purpose of the Study:
- To introduce a connectivity-regulation approach for synthesizing polar organic salts with tailored NLO properties.
- To investigate how structural connectivity influences the alignment of NLO-functional anions and subsequent optical performance.
- To develop novel UV NLO materials with enhanced linear and nonlinear optical characteristics.
Main Methods:
- Systematic variation of counter-cations and anionic alkyl tails in aliphatic sulfonates to control crystal structure.
- Experimental verification of compositional evolution's effect on sulfonate anion alignment (antiparallel, staggered antiparallel, parallel).
- Optical property characterization, including bandgap measurement and second-harmonic generation (SHG) evaluation.
- Theoretical calculations and crystal structure analysis to elucidate structure-property relationships.
Main Results:
- A connectivity-regulation strategy successfully induced changes in sulfonate anion alignment from antiparallel to parallel.
- The compound Li[SO3(CH2)2OH] exhibited an ultrawide bandgap (> 6.53 eV) and superior SHG (3.0 × KH2PO4) among deep-UV sulfonates.
- This material demonstrated sufficient birefringence for phase-matched fourth-harmonic generation at 266 nm.
- Parallel anion alignment, driven by hydrogen and ionic bonding, was identified as key to the enhanced optical performance.
Conclusions:
- Structural connectivity is a critical factor in tuning the NLO properties of organic salts.
- The developed approach offers a new pathway for designing high-performance UV NLO organic materials.
- Li[SO3(CH2)2OH] represents a promising candidate for deep-UV NLO applications.
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