1,3,6,8-Tetraazapyrenes: Synthesis, Solid-State Structures, and Properties as Redox-Active Materials

A series of new tetraazapyrene (TAPy) derivatives
has been synthesized by reducing 1,4,5,8-tetranitronaphthalene to
its corresponding tin salt (I) and reacting it with perfluorinated
alkyl or aryl anhydrides. The resulting 2,7-disubstituted TAPy molecules and the known parent compound 1,3,6,8-tetraazapyrene (II) have been further derivatized by core chlorination and
bromination. The brominated compounds served as starting materials
for Suzuki cross-coupling reactions with electron-poor arylboronic
acids. Single-crystal X-ray analyses established polymorphism for
some TAPy compounds. The ground-state geometries of all
new TAPy derivatives were modeled with DFT methods [B3PW91/6-31
g­(d,p) and B3PW91/6-311+g­(d,p)], especially focusing on the energies
of the lowest unoccupied molecular orbital (LUMO) and the electron
affinities (EA) of the molecules. The results of the calculations
were confirmed experimentally by cyclic voltammetry to evaluate the
substitution effects at the 2 and 7 position and the core positions,
respectively, and gave LUMO energy levels that range from −3.57
to −4.14 eV. Fabrication of organic field-effect transistors
(OFETs) with several of these tetraazapyrenes established their potential
as organic n-type semiconductors.