An excess electron binding to the `purpleʹ zwitterion quinonoid

Zwitterionic and canonical isomers of a novel quinonoid species were studied using second-order Møller–Plesset perturbation theory with 6-31+G**+5(sp)4d basis sets. An experimental report on the zwitterion being the most stable isomer was confirmed. In particular, the zwitterionic isomer is lower than the lowest canonical tautomer by 1.42 kcal/mol. Binding an electron to all isomers studied was considered, and the corresponding anionic species were studied. The lowest neutral isomer (zwitterion) forms a stable dipole-bound anion as do three out of four canonical isomers. However, the electron binding energy estimated for the zwitterion (521 cm−1) is the largest among all tautomers.