(Super)alkali atoms interacting with the σ electron cloud: a novel interaction mode triggers large nonlinear optical response of M@P4 and M@C3H6 (M=Li, Na, K and Li3O)

Abstract

Under high-level ab initio calculations, the geometrical structures and nonlinear optical properties of M@P₄ (M=Li, Na, K and Li₃O) and M@C₃H₆ (M=Li and Li₃O) were investigated; all were found to exhibit considerable first hyperpolarizabilities (18110, 1440, 22490, 50487, 2757 and 31776 au, respectively). The computational results revealed that when doping the (super)alkali atom M into the tetrahedral P₄ molecule, the original dual spherical aromaticity of the P₄ moiety is broken and new σ electron cloud is formed on the face of P₄ part interacting with the M atom. It was found that interaction of the (super)alkali atom with the σ electron cloud is a novel mode to produce diffuse excess electrons effectively to achieve a considerable β₀ value. Further, beyond the alkali atom, employing the superalkali unit can be a more effective approach to significantly enhance the first hyperpolarizability of the systems, due to the much lower vertical ionization potential. These results were further supported by the case of the (super)alkali atom interacting with the cyclopropane C₃H₆ molecule with its typical σ aromatic electron cloud. Moreover, the β₀ values of the M@P₄ series are nonmonotonic dependent on alkali atomic number, namely, 1440 au (M = Na) < 18110 au (Li) < 22490 au (K), inferring that the distance between the alkali atom and the interacting surface with the σ electron cloud in P4 is a crucial geometrical factor in determining their first hyperpolarizabilities. These intriguing findings will be advantageous for promoting the design of novel high-performance nonlinear optical materials.

Design of a Novel Series of Donor–Acceptor Frameworks via Superalkali–Superhalogen Assemblage to Improve the Nonlinear Optical Responses

“…For instance, Li-calix (4) pyrrole, which was formed by linking the Li atom into the calix (4) pyrrole, the β 0 value of complex is much higher than the pristine calix (4) pyrrole. This result is inconsistent with the C 20 F 20 M, , P 4 M, and C 3 H 6 M (M = Li, Na, K, and Li 3 O) systems. Presently, forming the charge transfer systems with the significant NLO responses by selecting the suitable D and A units have been attracting the extensive attention from the experimental and theoretical researchers. ,,,, For instance, Lin et al investigated a sets of M 3 O–Si 12 C 12 complexes (M = Li, Na, and K) with D-A building blocks.…”

Recent Progress on the Design, Characterization, and Application of Superalkalis

“…Thereafter, further endeavors have been devoted to designing NLO molecules by doping superalkalis on different nanocages, including C 24 N 24 , Si 12 C 12 , C 20 , and B 40 . In addition, NLO materials can also be obtained by interacting superalkalis with other complexants, such as graphdiyne, hexamethylenetetramine, phenalenyl,– modified graphene, and P 4 molecules . Superalkalis can also be utilized as building blocks of alkalides,– which was first revealed by Wu and co‐workers .…”

A theoretical investigation on doping superalkali for triggering considerable nonlinear optical properties of Si12C12 nanostructure

“…Recently, the design and synthesis of new materials with large second‐order nonlinear optical (NLO) response attracted much interests due to potential applications of novel materials in the area of optical and electro‐optical devices . For now, there are a great many types of promising species with considerable NLO response that have been considered as candidate of high‐performance NLO materials, such as the inorganic crystals without centro‐ symmetry, the structures with the framework of donor ‐ π bridge ‐ acceptor (DBA), the complex with diffuse excess electron, etc. In the DBA systems, the charge‐transfer path composed of π bridge connecting the electronic donor and acceptor is regarded as the trigger for considerable NLO responses, such as the carbon nanotube‐ and Möbius cyclacene‐ based systems, as well as the conjugated (porphinato)zinc(II)‐based systems .…”

“…is much larger than the undoped one (390 a.u.). The situation is the same as C 20 F 20 ‐based systems, M@P 4 , and M@C 3 H 6 (M = Li, Na, K, Li 3 O) compounds.…”

“…Due to this fact, a series of electrides with superalkali were designed theoretically and improved β 0 has been reported. For instance, in the systems of M/M 3 O@P 4 , the β 0 value of Li 3 O@P 4 is as high as 50487 a.u., not only because Li 3 O breaks the centrosymmetry more efficiently than alkali atom but also because its capacity to be an efficient electron donor is stronger than alkali atom. In addition, the C 20 F 20 ‐based studies also validated the above conclusions.…”