1,3-Diylideneisoindolines: Synthesis, Structure, Redox, and Optical Properties

Diiminoisoindoline (DII) is a crucial reagent for the synthesis of phthalocyanine as well as related macrocycles and chelates such as hemiporphyrazine and bis­(iminopyridyl)­isoindoline. In this report, we present the synthesis and characterization of four 1,3-diylideneisoindolines prepared via the reaction of several organic CH acids and DII. These orange or red compounds exhibit intense π → π* transitions in the UV–visible region. The redox properties and electronic structures of all new compounds were investigated using cyclic voltammetry and density functional theory (DFT). The observed electrochemistry and UV–visible transitions are in good agreement with the DFT and time-dependent DFT calculations, which indicate that the HOMO is largely centered at the OC–C–CO fragments, and the lowest unoccupied molecular orbital is more extended onto the isoindoline unit.