A DFT investigation of the anti- and syn-fused isomers of difuropyridines, difuropyrazines, and their dithieno analogues

Density functional theory calculations have been performed on the anti- and syn-isomers of a series of difuropyridines and difuropyrazines, as well as their dithieno analogues, and the results compared with those of the corresponding benzodifurans and benzodithiophenes. When the central ring in these systems was changed from benzene to pyridine and finally to pyrazine, the difference in the energy levels of the lowest unoccupied molecular orbitals (E_LUMO) of the anti- and syn-isomer became smaller, irrespective of the fused rings. Furthermore, the difference in the E_LUMO values of the furan- and thiophene-fused systems decreased as the central ring became increasingly electron deficient. In contrast, rather complicated trends were observed between the energy levels of the highest occupied molecular orbitals.