Suitable helical cavity, suitable alkali metal, larger first hyperpolarizability

•Three helical complexes are designed to study structure-properties relationship.•The Na atom possesses an appropriate size to fit in the helical cavities.•The Py-pym-2Na has the smallest interaction energy.•The α0 values improve with increasing the atomic number.•The Py-pym-2Na has the largest β0 value among three helical complexes.

Three helical complexes pyridine-pyrimidine-2M (Py-pym-2M) were designed by doping two alkali metals M (Li, Na and K) into the helical cavities. Results show the structures of Py-pym-2Na and Py-pym are very similar, and the interaction energies of Py-pym-2Na is smaller than those of Py-pym-2Li and Py-pym-2K. It indicates the Na atom possesses an appropriate size to fit in the helical cavities of Py-pym. Significantly, due to the alkali-metal-doped effect, the first hyperpolarizability (β0) values of Py-pym-2M (M = Li, Na and K) enhance almost 264-620 times larger than that of Py-pym. Specially, the Py-pym-2Na has the largest β0 value.

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