Single-component organic semiconductors based on novel radicals that exhibit electrochemical amphotericity: Preparation, crystal structures, and solid-state properties of N,N '-dicyanopyrazinonaphthoquinodiiminides substituted with an N-alkylpyridinium unit

N,N'-Dicyanonaphthoquinodiimines fused with a pyrazine ring 1 were prepared from the corresponding quinones 4. The new accepters 1 have a planar pi -s ystem and undergo reversible two-stage 1e-reduction. Quaternization of the pyridyl substituent in 1d-f gave pyridinium derivatives 2d(+), 2e(+), and R -3(+), respectively, which are stronger accepters that undergo three-stage le-reduction. Upon electrochemical. reduction of these cations, novel radic als 2d(.) 2e(.), and R-3(.) were generated and isolated as stable solids. T he molecular geometries determined by X-ray analysis indicated that these r adicals adopt a zwitterionic structure, in which the unpaired electron is l ocated on the quinodiimine unit but not on the pyridyl group. These novel r adicals undergo facile and reversible 1e-oxidation as well as two-stage le- reduction. The observed amphotericity endows the radicals with electrical c onductivities (10(-5) to 10(-9) S cm(-1)), and these thus represent a new m otif for single-component organic semiconductors.