Substituent effect on the electronic properties of pyrazino[2,3-g] quinoxaline molecules

We report the synthesis and characterization of pyrazino[2,3-g]quinoxaline derivatives with a systematic change in the substituents at the 2, 3, 7 and 8 positions and with or without 2-thienyl at the 5 and 10 positions to study the substituent effect and quinoid character of such a system. We performed density functional theory calculations using the B3LYP functional and 6-31G* basis set under the geometry optimization condition, together with the resonance effect of a valence bond theory to understand the electronic structures of these molecules. It was found that a combination of conjugation and cross-conjugation effects is responsible for the observed trends in their electronic properties, thus giving insights into designing molecules utilizing such effects.