Synthesis and Properties of Nitrogen-Containing Pyrenes

We developed a short-step synthesis of 2,4,10-triazapyrenes involving two sequential C-H substitutions: Pd-catalyzed cross-coupling reactions via C-H arylation followed by intramolecular Cu-catalyzed C-H functionalization. This method was successfully applied to the preparation of 4,10-diaza-, 1,4,10-triaza-, and 1,3,4,10-tetraazapyrenes. Crystal structure analysis of 5,9-di(4-methylphenyl)-2,4,10-triazapyrene showed that planar triazapyrene cores have π-stack packing. Incorporating nitrogen atoms into the pyrene framework bathochromically shifted the lowest energy onsets of the absorption bands and increased the first reduction potentials. The nitrogen-containing pyrenes showed fluorescence with a weaker intensity (Φ_f = 0.041-0.12) than that of the parent pyrene. The number and position of nitrogen atoms influenced the extent of these effects.