On the singlet states of porphyrins, chlorins and bacteriochlorins and their ability to harvest red/infrared light

The decay channels of the singlet excited states of halogenated sulfonamide tetraphenylporphyrins, chlorins and bacteriochlorins were fully characterized. It was found that the radiative rates and the internal conversion rates of the bacteriochlorins are lower than expected from the Strickler-Berg equation and from the energy-gap law, respectively. It is concluded that this family of bacteriochlorins can combine long-lived singlet states with photostability, which are desired properties to harvest near-infrared light. The singlet state lifetimes of halogenated tetraphenylporphyrins, chlorins and bacteriochlorin can be related to their molecular structure and spectroscopy using the Strickler-Berg equation, the energy-gap law and spin-orbit coupling.