Structural Tuning via Chain Length for Emergent Second Harmonic Generation in Hybrid Metal Halides

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Hybrid halides are promising materials for optoelectronic applications.
• Controlling crystal structure and properties of hybrid materials is crucial for device performance.
• Pyridine-based organic cations offer versatile structural modification possibilities.

Purpose of the Study:

• To synthesize and characterize novel hybrid halides with tunable properties.
• To investigate the structure-property relationships in these materials.
• To establish a rational design strategy for multifunctional hybrid halides.

Main Methods:

• Synthesis of ten new hybrid halides using three pyridine-based organic cations (MAP, MAMP, MAEP).
• Systematic variation of cation side chain length, halide (Cl, Br, I), and metal center (Sb, Bi).
• Characterization using X-ray diffraction, optical spectroscopy, thermal analysis, and density functional theory (DFT).

Main Results:

• Discovery of six noncentrosymmetric P2₁2₁2₁ phases with strong second-harmonic generation (SHG).
• Demonstration of halide substitution effects on band gap, absorption, and emission properties.
• Observation of ns²-type broadband luminescence and high thermal stability (280-330 °C).
• DFT calculations revealed strong coupling between inorganic and organic components influencing electronic properties.

Conclusions:

• The study provides a structure-guided pathway for designing multifunctional hybrid halides.
• Tailoring organic cation structure and composition allows for controlled tuning of material properties.
• These hybrid halides show potential for applications in nonlinear optics and luminescence.