Structure and optical properties of alkali-metal ion (Li+, Na+, K+, Rb+, and Cs+) endohedral cyclo[18]carbon.

Abstract

With growing interest in carbon-based materials for energy storage and active research in the field of advanced optoelectronic devices, we theoretically designed ten complexes by cyclo[18]carbon (C18) inside and outside complexing alkali-metal ion (M+ = Li+, Na+, K+, Rb+, and Cs+), respectively referred to as M+@C18in and M+@C18out, and performed careful analyses of their structure, binding interaction between M+ and C18, as well as optical properties of stable endohedral complexes M+@C18in. The effects of atomic number of alkali-metals on structure, binding interaction, electronic absorption spectrum, and molecular (hyper)polarizability of the M+@C18in were studied using accurate (time-dependent) density functional theory [(TD-)DFT)] calculations. The research suggests that the binding modes and strengths of different M+ with C18 are different, but there is no evident difference in electronic absorption spectra of the complexes; the polarizability and second hyperpolarizability of M+@C18in containing different alkali-metal ions are close due to the similarity of ionic properties, but their first hyperpolarizability differ greatly by reason of discrepancy in molecular symmetry. The similarities and differences in structure, fragment interaction, electronic absorption spectrum, and (hyper)polarizability of M+@C18in were explored using advanced wavefunction analysis methods.