Receding mechanism of NLO response of polyanion [M8O26]4− (M = Cr, Mo, W) and the closed loops theory analysis

Abstract

The second hyperpolarizability of six octa-poly-oxo anions [M₈O₂₆]⁴⁻ (M = Cr, Mo, W) were studied by DFT/TDDFT method. All of the six high symmetric anions possess moderately large γ values and the results present a receding sign of the third order NLO response as the metal element changes from Mo to Cr and W. For further knowledge of the third order NLO response mechanism, the electronic properties were studied by DFT method. The results suggest that the NLO property is closely related to the orbital closed loops of the unique electronic structure of the polyanion cage, and the direct relationship of the third order NLO response with the number and shape of the loops is presented. It is the first attempt of the analysis of NLO response mechanism by “orbital closed loops theory”.