Halogenated Symmetrical Tetraazapentacenes: Synthesis, Structures, and Properties

We herein describe
the synthesis and property evaluation of several
brominated and chlorinated tetraazapentacenes. The targets were obtained
by thermal condensation of 2,5-dihydroxyquinone with 4,5-dichloro-,
2,6-dichloro-, and 4,5-dibromo-1,2-phenylenediamine, followed by oxidation
with hot acidic dichromate. Double alkynylation, reductive deoxygenation,
and subsequent oxidation using MnO2 furnishes the target
compounds. Absorption spectra, electrochemistry, and single crystal
structures of the targets are reported. The 1,4,8,11-tetrachlorotetraazapentacene
(1,4,8,11-tetrachloroquinoxalino­[2,3-b]­phenazine)
carrying its chlorine atoms in the peri-positions packs in a herringbone
type arrangement, while the isomer (2,3,9,10-tetrachloroquinoxalino­[2,3-b]­phenazine, with the chlorine atoms in the east and west
positions) packs in one-dimensional stacks. In all cases, the reduction
potentials and the calculated LUMO-positions are decreased by the
introduction of the halogen atoms.