Design of Lewis acid–base complex: enhancing the stability and first hyperpolarizability of large excess electron compound

In the present paper, a new type of Lewis acid–base complex BX 3 •••Li@Calix[4]pyrrole (X = H and F) was designed and assembled based on electride molecule Li@calix[4]pyrrole (as a Lewis base) and the electron deficient molecule BX 3 (as a Lewis acid) by employing quantum mechanical calculation. The new Lewis acid–base complex offers an interesting push-excess electron-pull (P-e-P) framework to enhance the stability and nonlinear optical (NLO) response. To measure the nonlinear optical response, static first hyperpolarizabilities ( β 0 ) are exhibited. Significantly, point-face assembled Lewis acid–base complex BF 3 •••Li@Calix[4]pyrrole (II) has considerable first hyperpolarizabilities ( β 0 ) value (1.4 × 10 6 a.u.), which is about 117 times larger than reported 11,721 a.u. of electride Li@Calix[4]pyrrole. Further investigations show that, in BX 3 •••Li@Calix[4]pyrrole with P-e-P framework, a strong charge-transfer transition from the ground state to the excited state contributes to the enhancement of first hyperpolarizability. Theory calculation of enthalpies of reaction (Δ r H 0 ) at 298 K demonstrates that it is feasible to synthetize the complexes BX 3 •••Li@Calix[4]pyrrole. In addition, compared with Li@Calix[4]pyrrole, the vertical ionization potential (VIP) and HOMO–LUMO gap of BX 3 •••Li@Calix[4]pyrrole have obviously increased, due to the introduction of the Lewis acid molecule BX 3 . The novel Lewis acid–base NLO complex possesses not only a large nonlinear optical response but also higher stability. Figure A novel Lewis acid–base complex is first proposed by the combination of usual Lewis acid and an electride. It offers an interesting push-excess electron-pull framework to enhance the stability and nonlinear optical response.