Isomerization of free base porphyrin. Theoretical study

The photoinduced isomerization reaction of free base porphyrin molecule has been calculated using the DFT-B3LYP method combined with the 6-31G(d,p) basis set. To prove the accuracy of results, the 6-311G+(2p,2d) basis set was used. Two types of isomerization mechanisms were studied. It was found that the stepwise pathway of isomerization is the most appropriate. The geometric parameters of isomers and the transition structures of different multiplets are discussed. Zero-point energy and vibrational frequencies analysis are given.