Synthesis and Photophysical Properties of a Series of Pyrazine-Based Push-Pull Chromophores

Eighteen push-pull pyrazine fluorophores are described. Methoxy, dimethylamino, and diphenylamino groups were used as electron-donating groups (EDGs), and six p-conjugated systems consisting of multiple bonds and 1,4-phenylene moieties were used to connect the EDGs to the pyrazine core. The chromophores were obtained by Knoevenagel condensation and palladium-catalyzed cross-coupling reactions starting from commercially available 2-methyl-or 2-chloropyrazine. The optical absorption and emission properties of these chromophores were studied in different solvents. Some proved to be highly emissive and exhibit strong emission solvatochromism, which suggests a highly polar emitting state, characteristic of compounds that undergo intramolecular charge transfer (ICT). The influences of the various electron-donating groups and pi-conjugated systems on the emission and ICT have been carefully studied.