Chirality-Driven Polar Lattice Engineering for High-Performance Organic Nonlinear Optical Crystals
High-performance organic second-order nonlinear optical (NLO) crystals face a persistent challenge: molecular designs that enhance hyperpolarizability often crystallize into centrosymmetric or nonpolar arrangements, suppressing bulk second-order response, while simultaneously reducing optical bandgaps, enforcing a trade-off between nonlinearity and transparency. We report a chirality-driven polar lattice engineering strategy that couples molecular asymmetry with directional intermolecular interactions to promote polar ordering. A binaphthyl-based chromophore (S-3) crystallizes in the polar space group P2₁, exhibiting strong second-harmonic generation (~3.53 × KDP), wide transparency (3.91 eV), phase-matchable birefringence (Δn = 0.15), high laser damage threshold (742.6 MW cm⁻²), and thermal stability up to 210 °C. Theoretical calculations reveal a 69% enhancement in first-order hyperpolarizability (β_tot) relative to the unfunctionalized derivative, with a net intramolecular electron transfer of 0.16 e⁻ from the chiral scaffold to the benzoate acceptor. Crucially, enantiomeric crystals exhibit identical NLO responses, confirming that bulk nonlinearity is governed by engineered lattice polarity, not molecular handedness. This work establishes chirality as an active tool for crystal engineering and provides a general design paradigm for high-performance organic NLO materials.