The second-harmonic generation intensification derived from localization conjugated π-orbitals in O22−

Abstract

Molecular construction with π-conjugated groups is a favorable strategy to discover superior nonlinear optical (NLO) materials. Herein, a novel vanadium-carbonate compound K₃[V(O₂)₂O]CO₃ (KVCO), which combines two different π-orbital groups, delocalized (CO₃)²⁻ π-orbital groups and localized (O₂)²⁻ π-orbital groups, was synthesized. Benefiting from the well-arranged [V(O₂)₂OCO₃] unit and dual-synergistic π–d–π interaction, KVCO has the largest second harmonic generation (SHG) effect (about 20 times that of KDP) among the current carbonate NLO materials. Moreover, first-principles calculation elucidated the coupling enhancement mechanism between (CO₃)²⁻, (O₂)²⁻ and VO_n groups.