Excited State Processes in Supramolecular Complexes of Cyclic Dibenzopyrrolopyrrole Isomers with C Fullerene.

An approach to modulating the properties of carbon nanorings by incorporating pyrrolo[3,2-b]pyrrole units is of particular interest due to the combined effect of heteroatom and antiaromatic character on electronic properties. The inclusion of units other than phenylene leads to the formation of stereoisomers. In this work, we computationally study how the spatial orientation of monomeric units in the ring affects the properties of cyclic dibenzopyrrolo[3,2-b]pyrroles and their complexes with C fullerene. For [4]PP and [4]DHPP, the most symmetrical AAAA isomer is the most stable and forms stronger interactions with fullerene than the isomers where one or two monomeric units are flipped, mostly due to less Pauli repulsion. π-Electron delocalization in the monomeric unit is crucial for directing the electron transfer (from or to nanoring). The energy of excited states with charge transfer depends on the HOMO-LUMO gap, which varies from one stereoisomer to another only for [4]DHPP⊃C with aromatic 1,4-dihydropyrrolo[3,2-b]pyrrole units. The rates of electron transfer and charge recombination reactions are relatively weakly dependent of the spatial isomerism of nanorings.