The Impact of the Interplay between Steric and Electronic Effects on the Synthesis and Optical Properties of Diketopyrrolopyrroles Bearing Pyridine Moieties

The influence of a combination of steric and electronic factors on both the preparation and the optical properties of diketopyrrolopyrroles was investigated. The attachment of a cyano group to the electron‐deficient pyridine ring overcame the negative influence of the flanking methyl group on the efficiency of the synthesis of diketopyrrolopyrroles. Diketopyrrolopyrroles possessing pyridine‐N‐oxide moieties were studied for the first time. We have also shown that reactions of cyanopyridines possessing an additional dialkylamino group were very capricious and depending on the relative position of all substituents, can lead to low yields of diketopyrrolopyrroles. The interplay between the dihedral angle between the diketopyrrolopyrrole core and the pyridyl substituents as well as the presence and position of electron‐donating moieties made it possible to modulate the photophysical properties of N,N′‐dialkyldiketopyrrolopyrroles. In particular, it was found that pyridine‐N‐oxides as the aryl moieties had a strong influence on the optical properties of diketopyrrolopyrroles, shifting both absorption and emission bands bathochromically. Two‐photon absorption cross‐sections had low values except for those dyes possessing a clear quadrupolar centrosymmetric nature. Good combination! The interplay between the dihedral angle between the diketopyrrolopyrrole core and the pyridyl substituents, as well as the presence and position of electron‐donating moieties, make it possible to modulate the photophysical properties of N,N′‐dialkyl‐diketopyrrolopyrroles. The oxidation of the pyridine moiety to the N‐oxide was found to be a viable strategy to obtain an increase in the two‐photon absorption cross‐section.