The Heavier, the Better-Increased First Hyperpolarizabilities in M@Calix[4]pyrrole (M = Na and K)

Two promising organic electride compounds for nonlinear optical (NLO) applications, namely Na@calix[4]pyrrole and K@calix[4]pyrrole, were designed and investigated by means of density functional theory (DFT) computations. These two newly designed compounds exhibit considerably large first hyperpolarizabilities (beta(0)) (7500 and 17304 au, respectively) and are expected to be stable at room temperature. Compared with the calix[4]pyrrole (beta(0) = 390 au) and their lighter analogue Li alpha@calix[4]pyrrole (beta(0) = 7326 au), the larger first hyperpolarizabilities of M@calix[4]pyrrole (M = Na and K) are mainly due to the lower ionization potential of Na/K atom and the more easily formed diffuse excess electrons. Therefore, introducing heavier alkali atom into organic electride compounds is an efficient approach to achieve larger first hyperpolarizabilities desired for NLO materials.