Effect of Electron Donating/Withdrawing Groups on Molecular Photoswitching of Functionalized Hemithioindigo Derivatives: a Computational Multireference Study

Abstract

AbstractHemithioindigos are a versatile group of molecules with the ability to undergo double bond isomerisation upon light excitation. Using electronic structure theory, a detailed description of the photoisomerisation of hemithioindigo and five of its functionalized derivatives is reported. We use a combination of Density Functional Theory (DFT), approximate second order Coupled Cluster (CC2), and multireference methods such as the complete active space self‐consistent field (CASSCF) method to probe how isomerisation capabilities of functionalized hemithioindigo derivatives are affected by functionalisation with both electron donating and withdrawing groups. We demonstrate that important properties such as the thermal barrier, electronic absorption spectra and, to an extent, the mechanism can all show pronounced differences compared to the parent hemithioindigo molecule. Our results demonstrate how the inclusion of functional groups can have important effects on its photoisomerisation capabilities, which in turn, can influence the fate of these molecules upon light excitation and their utility as molecular switches.