Pyrazinacenes: aza analogues of acenes.

A series of edge-sharing condensed oligopyrazine analogues of acenes, the pyrazinacenes, were synthesized and characterized. X-ray crystallographic determinations revealed intermolecular interactions that affect the propensity of the molecules to undergo pi-pi stacking. Increasing heteroatom substitution of the acene framework induces shorter intermolecular pi-pi stacking distances (shorter than for graphite) probably due to lower van der Waals radius of nitrogen atoms. Hydrogen bonding is also a determining factor in the case of compounds containing reduced pyrazine rings. Combined electrochemical, electronic absorption, and computational investigations indicate the substantial electron deficiency of the compounds composed of fused pyrazine rings. The pyrazinacenes are expected to be good candidates as materials for organic thin film transistors.