The second-harmonic generation intensification derived from localization conjugated π-orbitals in O 2 2 .

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 )2 O]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 )2 OCO3 ] 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 VOn groups.