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

We performed the present study, aiming to clarify the influence of the combination of steric and electronic factors on both the preparation and the optical properties of diketopyrrolopyrroles. 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. 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 photophysical properties of N,N′-dialkyl-diketopyrrolopyrroles. 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 bathochromically. Two-photon absorption cross-sections had low values except for those dyes possessing a clear quadrupolar centrosymmetric nature.