The second-harmonic generation intensification derived from localization conjugated pi-orbitals in O-2(2-)

Molecular construction with pi-conjugated groups is a favorable strategy to discover superior nonlinear optical (NLO) materials. Herein, a novel vanadium-carbonate compound K-3[V(O-2)(2)O]CO3 (KVCO), which combines two different pi-orbital groups, delocalized (CO3)(2-) pi-orbital groups and localized (O2)(2-) pi-orbital groups, was synthesized. Benefiting from the well-arranged [V(O-2)(2)OCO3] unit and dual-synergistic pi-d-pi interaction, KVCO has the largest second harmonic generation (SHG) effect (about 20 times that of KDP) among the current carbonate NLOmaterials. Moreover, first-principles calculation elucidated the coupling enhancement mechanism between (CO3)(2-), (O-2)(2-) and VOn groups.