Accurate Prediction and Understanding of ECD Spectra Through Jahn-Teller or Exciton-Exciton Effects in Symmetric Cyclic Systems.

Abstract

Strong chiroptical responses are a requirement for the development of chiral electronics devices. A promising design strategy utilizes repetitive monomeric units in a cyclic and symmetric chiral arrangement assembled into a molecular system. This strategy is inspired by the exciton coupling mechanism of electronic circular dichroism.1,2 However, the computational prediction of optical and chiroptical properties is challenging because such properties are ruled by nonadiabatic effects beyond the widely used Born-Oppenheimer approximation. In the particular case of systems with symmetry axis of order equal or larger than 3, symmetry imposes degenerate state whose potential energy profile is largely affected by nuclear coordinates and determined by Jahn-Teller (JT) and pseudo Jahn-Teller (pJT) effects. The present study focuses on trigonal systems showing that JT and particularly pJT effects must be properly accounted to reproduce the experimental spectra since such effects are responsible of the optical and chiroptical properties. Our approach applies diabatization procedures combined with quantum dynamical wavepacket propagations,3 according to two possible alternative pictures: 1) a delocalized approach defining diabatic states coincident with the adiabatic states of the trimeric system in the equilibrium geometry and 2) a localized approach based on idealized monomers and their excitonic coupling. The predictions provided by both approaches converge in remarkable agreement with the experimental results. The proposed method is easily extensible to other symmetries, allowing to estimate the most favorable arrangements in the search of strong chiroptical responses