Molecular Ferroelectric Exhibiting a 10-Fold Enhancement in Second Harmonic Generation over KDP

Second-order nonlinear optical (NLO) switches are highly promising for next-generation intelligent optoelectronic devices. Herein, a zero-dimensional organic–inorganic hybrid ferroelectric, [Me3NEt][FeCl4] (1), was designed and synthesized via a quasi-spherical molecular strategy. Concurrent endothermic/exothermic peaks in differential scanning calorimetry (DSC) and step-like dielectric anomalies jointly corroborate the fully reversible structural transition. Strikingly, it exhibits a strong second-order NLO response with a second harmonic generation (SHG) intensity approximately 10 times greater than that of the benchmark KDP (KH2PO4). Its ferroelectric properties were further confirmed through piezoresistive force microscopy (PFM) observations and polarization–electric field (P–E) hysteresis loop testing. This study not only presents a high-performance NLO switch but also offers a viable design strategy for advanced ferroelectric and photonic materials.