Aggregation-induced emission and large two-photon absorption cross-sections of diketopyrrolopyrrole (DPP) derivatives

In this work, a new series of triphenylamine-based diketo-pyrrolo-pyrrole (DPP) compounds (DPP-I, DPP-II, DPP-III) have been designed and synthesized by a concise route. Their one- and two-photon absorption properties have been investigated. It was found that DPP-based compounds are very weakly fluorescent in THF solution, but their intensities are increased by almost 29, 9, and 24 times in water/THF (v/v90%) mixtures, respectively, in which they exhibit a strongly enhanced red fluorescence. The result indicates that the intramolecular vibration and rotation of these dyes is considerably restricted in nano-aggregates formed in water/THF mixtures, which leads to significant increases in fluorescence. The two-photon absorption (2PA) cross-sections measured by the open aperture Z-scan technique were determined to be 188, 275 and 447GM for DPP-I, DPP-II, and DPP-III, respectively; DPP-III with the symmetrical structure shows the highest value of 2PA cross-section. The excellent properties of aggregation-induced emission (AIE) and 2PA provide an attractive alternative for the biophotonic materials.