Alkali Metals-Substituted Adamantanes Lead to Visible Light Absorption: Large First Hyperpolarizability

Adamantane (Ad) is the parent molecule of diamondoids, which has been the subject of much chemical interest because of its highly symmetric cage structure. Many valuable papers demonstrated that the H atom of the methine position in Ad is highly reactive. Compared with highly symmetric carbon structures such as graphene and single-walled carbon nanotubes (SWCNTs), Ad only possesses σ bonds. In this work, we report a quantum chemical calculation on three complexes (Ad-Li, Ad-Na, and Ad-K), which were obtained by substituting the H atom of methine position in Ad with alkali metal (Li, Na, and K). Interestingly, the substitution by alkali metals leads to absorption within the visible region. The maximum absorption wavelengths of the complexes show a red shift trend from the Li to the K complex. This trend indicates that the crucial transition energy becomes smaller, which might lead to a larger nonlinear optical response. Among the three structures, the largest first static hyperpolarizability (βtot) of the ...