Tuning Electronic Structure and Optical Properties of Li@cyclo[18]carbon Complex via Switching Doping Position of Lithium Atom

Doping alkali metal atoms, especially lithium (Li), in nanocarbon materials has always been considered as one of the most effective methods to improve the optical properties of the system. In this theoretical work, we doped a Li atom into the recently observed all-carboatomic molecule, cyclo[18]carbon (C₁₈), and finally obtained two stable configurations with Li inside and outside the ring. The calculation results show that the energy barrier of transition between the two Li@C₁₈ complexes is quite low, and thus the conversion is easy to occur at ambient temperature. Importantly, the electronic structure, absorption spectrum, and optical nonlinearity of the two configurations are found to be significantly different, which indicates that the electronic structure and optical properties of the Li@C₁₈ complex can be effectively regulated by switching the location of the doped Li atom between inside and outside the carbon ring. With the help of a variety of wave function analysis techniques, the nature of the discrepancies in the properties of the Li@C₁₈ complex with different configurations has been revealed in depth. The relevant results of this work are expected to provide theoretical guidance for the future development of cyclocarbon-based optical molecular switches.