Photoinduced Phenomena in 6,6’-Dibromoindigo (Tyrian Purple): a Theoretical Study

The compound 6,6’-dibromoindigo, which is the main component of the pigment Tyrian purple, was studied theoretically at the TD-DFT level of theory. We found that the absorption maximum of the compound about 600 nm underwent a red-shift when moving from the gas phase in solution. With the located two conical intersections S0 / S1 we investigated (TD-DFT) the mechanisms connecting these structures with the ground state equilibrium geometry. It was established that the conical intersections are not accessible along any of the excited-state reaction paths which implies optical deactivation of the first excited state of the compound. With respect to these mechanisms the pigment should exhibit high photostability when exposed to visible light. This work is licensed under a Creative Commons Attribution 4.0 International License