Effects of heterocyclic ring and amino‐ethyl‐amino group on the electronic and photophysical properties of a triphenylamine‐pyrimidine dye

Introduction of a heterocyclic ring and an amino‐ethyl‐amino group to donor‐acceptor (D‐A) type photosensitive dyes can modulate the lifetime of the charge separation generated in the D‐A dyes as well as their electronic and UV‐vis absorption properties. Here we perform density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) calculations to study 11 derivatives of a triphenylamine‐pyrimidine, namely MTPA‐Pyc, in order to improve the performance of MTPA‐Pyc as solar cell sensitizers. Five heterocyclic rings and an amino‐ethyl‐amino group were introduced on the styryl moiety of MTPA‐Pyc. The results show that the introduction of heterocyclic rings generally causes an absorption red shift, but the absorption intensity reduces as a result of the increase in the dihedral angle between the donor and acceptor. Further, introduction of an amino‐ethyl‐amino group to these dyes with a heterocyclic ring modification disrupts the conjugation between the donor and acceptor, which does not benefit the absorption but may have the potential to increase the lifetime of charge separation of the dyes. We identify 2 out of 11 dyes that have the best potential for solar cell applications. Eleven photosensitizing dyes were designed by introducing a heterocyclic ring or an amino‐ethyl‐amino group to the styryl moiety of a triphenylamine‐pyrimidine dye. Studies based on density functional theory and time‐dependent density functional theory predicted that the addition of the heterocyclic ring causes an absorption red shift, which benefits solar energy absorption. The modification using an amino‐ethyl‐amino group disrupts the conjugation, which has the potential to increase the lifetime of charge separation.