A theoretical analysis of the reduction and lithiation of pillar[6]quinone

The new redox-active hexagonal macrocycle pillar[6]quinone (P[Q]6) exhibits unique electrochemical reduction behavior. This paper describes the electrochemical redox properties of P[Q]6 dissolved in an aprotic solvent in the presence of Li+ ions using density functional theory calculations. These calculations show that the multi-electron reduction behavior of P[Q]6 is determined by the electrostatic repulsion between quinone units, in agreement with the results of voltammetric measurements. The lithiation process can be divided into two stages, comprising bridging of adjacent carbonyl groups by Li+ ions followed by the formation of coordination bonds outside the macrocycle. The trend exhibited by calculated lithiation potentials was found to correspond to the voltammogram waveform. Preliminary calculations of lithiation behavior involving two macrocycles to confirm intermolecular lithium coordination are also presented herein. The results of this work are expected to provide a better understanding of the electrochemical properties of P[Q]6 and facilitate the application of this compound in redox materials.