An ab initio molecular orbital study of structural isomers of diketopyrrolopyrrole

Ab initio molecular orbital calculations at HF/6-31G**, HF/6-311+G**, and B3LYP/6-311+G** levels of theory for geometry optimization and RMP2-FC/6-311+G**, for a single point total energy calculation are reported for 1,4-diketo-pyrrolo[3,4-c]pyrrole (DPP, 1) and 12 structural isomers of DPP (2-13). Compounds 1-3 include 2 CCH and 2 HN-CO units. Structural isomers 4-7 include 2 CCH units, together with 2 NH and 2 CO groups. Isomers 8-13 possess 2 CH, 2 C, 2 NH, and 2 CO fragments. These calculations show that isomers 2, 4, and 8 are more stable than 1. The λmax values for 1-13 are calculated from the HOMO-LUMO energies.