The triplet state decay kinetics and deactivation funnel geometry of a series of nonplanar saddle-shaped porphyrins

It is found that the triplet state lifetimes of the series of nonplanar saddle-shaped porphyrins are much shorter than those of their planar analogs (hundreds of nanoseconds vs. several milliseconds). As our calculations show, two low-lying conformations with strongly different triplet-ground singlet state energy gap ΔETS exist for each molecule in its triplet state. An energy inversion of these conformations for the most distorted porphyrin molecule is found to be responsible for the observed non-monotonic dependence of the triplet state deactivation rate on the degree of nonplanar distortion.