6533b834fe1ef96bd129d44c

RESEARCH PRODUCT

Benzoannulated quinone-type electron acceptors: evolution of the molecular and electronic structures upon reduction

subject

description

Abstract The molecular and electronic structures of DCNQI and its π-extended derivatives benzo-DCNQI and DCAQI have been investigated using ab initio 6-31G ∗ calculations. The steric hindrance introduced by lateral benzoannulation determines the loss of planarity of the DCNQI moiety for DCAQI. The most stable conformation of DCAQI corresponds to a butterfly-type structure, in which the DCNQI ring adopts a boat conformation and the lateral benzene rings remain planar. This structure lies 2.75 kcal mol −1 below the fully planar conformation. MP2/6-31G ∗ calculations including full geometry optimization confirm the greater stability of the butterfly structure. The geometries of the anions and dianions have also been optimized. The reduction process leads to the aromatization of the DCNQI moiety and both the anion and the dianion of DCAQI are fully planar. The stability of the anions with respect to the neutral systems is calculated to decrease along the series DCNQI > benzo-DCNQI > DCAQI, thus explaining the decrease of the electron acceptor properties along this series. For the dianions, the polycyclic skeleton is aromatic and forms a polyacenic unit substituted with two negatively charged NCN groups.