Timescale of π‐Stacking Formation in a Benzene Trimer Cation Formed by Ionization of the Parent Neutral Trimer: A Direct Ab Initio Molecular Dynamics Study

Abstract

AbstractThe π‐stacking interaction plays a crucial role in structural arrangements and molecular assemblies in several molecular systems. In the present study, π‐stacking formation in the benzene trimer cation, (Bz)3+, following ionization of the parent neutral benzene trimer, (Bz)3, was investigated using direct ab initio molecular dynamics to elucidate the timescale of π‐stacking formation and reaction mechanism in the ionized state. Cyclic (Bz)3 was chosen as the benzene cluster. After ionizing (Bz)3, the structure drastically changed to a double π‐stacking form. The (Bz)3+ product vibrated between two structural forms, (Bz‐Bzc)+—Bz ↔ Bz—(Bzc‐Bz)+, where Bzc is a benzene molecule located in the central position of (Bz)3+ and (Bzc‐Bz)+ represents a dimer core composed of the benzene dimer cation. The timescale of π‐stacking formation was calculated as 300–380 fs. The absorption spectrum of (Bz)3+ was blue‐shifted as a function of time. We discuss the reaction mechanism based on the theoretical results.