Structure–property relationships in noncentrosymmetric solid-state materials

Noncentrosymmetric (NCS) solid-state materials play a vital role in modern photonic and optoelectronic technologies attributable to their ability to exhibit second-order nonlinear optical (NLO) phenomena such as second-harmonic generation (SHG), the bulk photovoltaic effect (BPVE), and directionally selective photoluminescence. The design of such materials requires a nuanced understanding of how structural asymmetry at the atomic and molecular levels translates into macroscopic physical properties. This tutorial review introduces a selection of representative NCS compounds—CsScP₂S₇, [Zn(pvb)₂]·(DMF) (pvb = trans-2-(4-pyridyl)-4-vinylbenzoate), (4AMPY)(MA)Ge₂I₇ (4AMPY = 4-(aminomethyl)pyridinium; MA = methylammonium), and (MIPA)₂PbI₄ (MIPA = N-methyliodopropylammonium)—each synthesized via distinct routes, including solid-state reaction, hydrothermal synthesis, and solution-phase crystallization. Through structural analyses, we illustrate how features such as asymmetric coordination geometries, layered or chain-type connectivity, and the incorporation of polar organic cations govern key functional behaviors. By systematically correlating synthetic strategies, crystallographic features, and physical responses such as SHG efficiency, optical anisotropy, and photoreactivity, we highlight the critical role of structural design in achieving desirable NLO and optoelectronic performance. This review serves as an accessible guide for students and early-career researchers, offering both theoretical foundations and practical insights into the rational design of NCS materials through solid-state chemistry.