Alkali metal atom-aromatic ring: a novel interaction mode realizes large first hyperpolarizabilities of M@AR (M=Li, Na, and K, AR=pyrrole, indole, thiophene, and benzene).

Several new electride compounds M@pyrrole (M = Li, Na, and K), Li@AR (AR = indole, thiophene, and benzene), Li@tryptophan and Li@serotonin were designed and investigated, which exhibit considerably large first hyperpolarizabilities (β(0)) (6705, 1116, 11399, 5781, 4808, 1536, 8106, and 9389 au, respectively) by comparison with their corresponding sole molecules pyrrole (β(0) = 30 au), indole (104 au), thiophene (6 au), benzene (0 au), tryptophan (159 au) and serotonin (151 au), respectively. The computational results revealed that the interaction of the alkali metal atom with π-conjugated aromatic ring (AR) is one effectively new approach to produce diffuse excess electron to get a large β(0) value, which is advantageous for the design of the novel high-performance NLO materials with π-conjugated AR: alkali metal atoms doped nanomaterials and biomolecules.