Optimization of nonlinear properties of C₆O₆Li₆-doped alkalides <i>via</i> group I/III doping for unprecedented charge transfer and advancements in optoelectronics

The design and synthesis of nonlinear optical (NLO) materials are rapidly growing fields in optoelectronics. Considering the high demand for newly designed materials with superior optoelectronic characteristics, we investigated the doping process of Group-IIIA elements (namely, B, Al and Ga) onto alkali metal (AM = Li, Na and K)-supported C₆O₆Li₆ (AM@C₆O₆Li₆) complexes to enhance their NLO response. The AM-C₆O₆Li₆ complexes retained their structural features following interaction with the Group-IIIA elements. Interaction energies as high as -109 kcal mol^-1 demonstrated the high thermodynamic stability of these complexes. An exceptional charge transfer behavior was predicted in these complexes, where the electronic density of the Group-III metals shifted toward the alkali metals, making these complexes behave as alkalides. The π conjugation of C₆O₆Li₆ was found to withdraw excess electrons from the Group IIIA metals in these alkalides, which were subsequently transferred to the Group IA metals. The energy gap of the frontier molecular orbitals (FMOs) in the AM-C₆O₆Li₆ complexes was notably reduced upon alkalide formation. UV-visible analysis explicitly showed a bathochromic shift in the alkalides. The first hyperpolarizability (<i>β</i>₀) was calculated to confirm the NLO properties of these alkalides. B-C₆O₆Li₆-K exhibited the highest <i>β</i>₀ value of 1.75 × 10⁵ au. The vibrational frequency-dependent first and second hyperpolarizability values illustrated an increase in hyperpolarizability at a frequency of 532 nm. A higher <i>n</i>₂ value of 8.39 × 10^-12 cm² W^-1 was obtained for B-C₆O₆Li₆-Na at 532 nm. These results highlight the promising NLO response of the designed alkalides and their potential applications in the field of optics.