Second-order NLO responses of two-cavity inorganic electrides Lin@B20H26 (n = 1, 2): evolutions with increasing excess electron number and various B-B connection sites of B20H26Electronic supplementary information (ESI) available: The connection B-B bond length and angle formed by the axes of the A and B cavities (Fig. S1); Frontier molecular orbitals involved in the major charge transfer transitions of 1b-4b (Fig. S2); the optimized geometries of 1c-4c (Fig. S3); spin density of 1c-4c (Fig. S4)

Confining excess electrons in a specific space is an effective strategy to design nonlinear optical (NLO) molecules. The complexants with excess electrons are usually organic compounds, but these compounds are thermally unstable and thus hardly meet the processing requirements of NLO materials. To obtain better thermostability and NLO response molecules, in this work, inorganic compounds of B 20 H 26 isomers containing two cavities were proposed. With the two included cavities, B 20 H 26 can be doped by one or two Li atoms to form electrides of Li@B 20 H 26 and Li 2 @B 20 H 26 . These electrides show larger NLO responses, with respect to the corresponding undoped complexant of B 20 H 26 . Particularly, Li 2 @B 20 H 26 has the largest β 0 value of 108 846 a.u. (MP2/6-31+G(d) level) that is 850 times as large as that of corresponding B 20 H 26 . Moreover, the change of β 0 values with excess electron number is remarkable for two of the isomers, and differences between the β 0 values among those isomers are also significant owing to various B-B connection sites between the two cavities. Therefore, the present inorganic electrides have not only better performance due to the magnitude of their β 0 values but also better behavior on the molecular-level modulation of NLO. Inorganic electrides Li n @B 20 H 26 could be NLO materials because of their better performance on the magnitude of β 0 and modulation of the NLO response.