Performance of time-dependent density functional theory on twisted intramolecular charge transfer state of emerging visible light photoswitches

Hemithioindigo dyes (HTIs) are a class of emerging visible light photoswitches. By using M06, M062X, B3LYP and BMK density functionals, we have investigated the local excited (LE) state and twisted intramolecular charge transfer (TICT) state of HTIs. Both the two excited states are located in HTIs Z1 and Z2 after combining the results of all functionals. The formation of either the LE or TICT state is found to be controlled by the direction of the C-2-C-3 single bond rotation. Different functionals are found to have intrinsic biases on LE and TICT states. Thus, a reasonable combination of various functionals is a convenient method to investigate a system possessing multiple excited-state minima. We recommend a combination of the M06 and M062X functionals