Suitable helical cavity, suitable alkali metal, larger first hyperpolarizability

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.