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 BX3...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 BX3 (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 BF3...Li@Calix[4]pyrrole (II) has considerable first hyperpolarizabilities (β 0) value (1.4  ×  106 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 BX3...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 (ΔrH0) at 298 K demonstrates that it is feasible to synthetize the complexes BX3...Li@Calix[4]pyrrole. In addition, compared with Li@Calix[4]pyrrole, the vertical ionization potential (VIP) and HOMO-LUMO gap of BX3...Li@Calix[4]pyrrole have obviously increased, due to the introduction of the Lewis acid molecule BX3. The novel Lewis acid-base NLO complex possesses not only a large nonlinear optical response but also higher stability.