Constructing (super)alkali–boron-heterofullerene dyads: an effective approach to achieve large first hyperpolarizabilities and high stabilities in M3O–BC59 (M = Li, Na and K) and K@n-BC59 (n = 5 and 6)

Abstract

Using DFT methods, the electronic properties and the first hyperpolarizabilities of boron-heterofullerene–(super)alkali dyads: M₃O–BC₅₉ (M = Li, Na and K) and K@n-BC₅₉ (n = 5 and 6) were systematically investigated. It is found that both M₃O and K can effectively bind to BC₅₉ with high binding energies (2.50–2.69 eV for K and 4.24–5.14 eV for M₃O). The interaction between K and BC₅₉ in K@n-BC₅₉ is identified as primarily ionic in nature, whereas that between the superalkali M₃O unit and BC₅₉ becomes much stronger owing to the formation of a strong chemical bond (B–O bond). Moreover, compared with the sole parent cluster BC₅₉ (619 au), both K@n-BC₅₉ (n = 5 and 6) and M₃O–BC₅₉ (M = Li, Na and K), possess large first hyperpolarizabilities (β₀), which are 3352, 2621 and 4921, 5440 and 7800 au, respectively, where the superalkali doped dyads (M₃O–BC₅₉) are much superior to the simple alkali exo-hedral species (K@n-BC₅₉), and heavier superalkali can be more powerful in enhancing the β₀ values of M₃O–BC₅₉. Clearly, these superalkali doped dyads M₃O–BC₅₉, formal donor–acceptor (DA) chromophores, exhibit not only excellent stability but also large first hyperpolarizability; therefore, they are expected to be potential candidates for excellent second-order NLO materials.