Rational design of superalkali-based novel calix[4]pyridine alkalides as high performance nonlinear optical materials

In the present work, novel superalkali-based calix[4]pyridine alkalides have been designed as excess electron compounds using DFT simulations. The computed interaction energies (-32.3 to -64.5 kcal mol^-1) and vertical ionization energies (2.51 to 2.79 eV) indicate the stability of the designed alkalides. The highest charge at Li^- alkalide in the K₃O⁺CXP[4]Li^- is -0.486 |e| as analyzed by natural population analysis. The investigated complexes exhibit reduced HOMO-LUMO energy gaps (0.30-0.50 eV) in comparison to pure calix[4]pyridine (5.69 eV). The IRI and QTAIM analyses indicate that the CXP[4] interacts with superalkali clusters and Li metal via non-covalent interactions. These superalkali-based alkalides possess absorption maxima (727-1096 nm) in the visible to NIR region. The Na₃O⁺CXP[4]Li^- alkalide displays a significantly higher static first hyperpolarizability of 2.5 × 10⁶ au as compared to the β _o (3.4 × 10⁴ au) for superalkali-based calix[4]pyrrole alkalides. The β _vec and β _TL values show a similar trend to the static β _o values. Furthermore, the highest dynamic NLO responses for second harmonic generation, hyper-Rayleigh scattering and electro-optical Pockel's effect are 1.8 × 10⁸ au, 1.1 × 10⁸ au and 7.7 × 10⁷ au, respectively. These findings imply that designed alkalides offer a novel perspective on the rational designing of stable high-tech NLO materials.