Achieving an optimal performance balance in UV nonlinear optical crystals via hydrogen-bond regulation

Abstract

Non-centrosymmetric (NCS) materials underpin numerous emerging technologies, yet their targeted design remains a formidable challenge. Here, we introduce a novel “molecular modification strategy” for rationally designing ultraviolet (UV) nonlinear optical (NLO) crystals. Based on this strategy, two glycine sulfonates [C₂NO₂H₆][SO₃CF₃] (I) and [C₄N₂O₄H₁₁][SO₃CF₃] (II) were synthesized, and a transition from CS compound I to NCS compound II was successfully achieved through delicate molecular design. II achieves an optimal balance between moderate second-harmonic generation (1 × KDP), a short-UV cutoff edge (216 nm) and ideal birefringence (0.078@546 nm). In addition, compound II exhibits favorable crystal growth habits, resulting in a large single crystal measuring 18 × 4 × 2 mm³. By comparing the CS and NCS compounds, this work not only reveals the origin of symmetry breaking but also quantitatively demonstrates how fine-tuning the molecular structure can simultaneously optimize three core parameters—SHG, birefringence and bandgap—in one step. These findings provide valuable insights for the rational design of high-performance UV NLO materials.