Ring currents in benzo- and benzocyclobutadieno-annelated biphenylene derivatives.

The effect of benzo and benzocyclobutadieno annelation on the current density induced in a series of biphenylene derivatives is examined at the B3LYP/cc-pVDZ level of theory, by using the CTOCD-DZ method. Angular benzo annelation increases, whereas linear benzo annelation decreases the intensity of paratropic (antiaromatic) current density along the four-membered ring of biphenylene. The opposite effect is found for benzocyclobutadieno annelation. It is shown that the extent of local aromaticity of the four-membered ring in biphenylene congeners can vary from highly antiaromatic to nonaromatic, as a result of different modes of annelation.