Electron affinity of modified benzene

The electron affinities of organic molecules obeying Hückel's rule of aromaticity are vanishingly small, if not negative. For example, benzene, a classic example of an aromatic molecule, has an electron affinity of −1.15 eV. Using density functional theory, we have systematically calculated the electron affinities and vertical detachment energies of C₆H₆ by substituting H with halogen (F) and superhalogen (BO₂) moieties, as well as replacing one of the C atoms with B. The ground state geometries were obtained by examining about 330 isomers. The electron affinities are found to steadily increase with these substitutions/replacements, even surpassing that of Cl, the element with the highest electron affinity in the periodic table, in the case of C₅BH(BO₂)₅. In some special cases such as C₆H₅(BO₂) the electron affinity and vertical detachment energy differ by as much as 5 eV, indicating substantial changes in the geometry as the electron is removed from the anion. We hope that the ability to change the negative electron affinity of C₆H₆ to large positive values by substituting H and/or replacing C atom will motivate experimental studies.