Polyurea Modified with 4-Dihydropyrimidone-2-ketone Rings by Biginelli Reaction and its Boostered AIE Characteristic

In the synthesis of traditional AIE-active polymers with conjugate or multi-benzene system, the troublesome process is still faced such as consuming time, high temperature, catalysis, no water or vacuum, and so on. In this study, the polydihydropyrimidone derivatives (PDPMDs) with AIE properties are facilely synthesized by the introduction of 4-dihydropyrimidone rings onto non-AIE-active intermediate polyureas (PUs) in Biginelli reaction. It is found that the unsymmetrical L-lysine ethyl diisocyanate and butylenediamine played a very important role in the smooth preparation and fluorescence enhancement of PDPMDs. Compared with the intermediate PUs, the fluorescence of PDPMDs is significantly enhanced (35-fold increase), which is mainly due to the intramolecular aggregation of dihydropyrimidone rings on PUs chains. At the same time, with the increase of the content of dihydropyrimidone rings, the fluorescence intensity of PDPMDs also increases, and the emission wavelength shows an obvious red shift. The fluorescence of PDPMDs also showed obvious dependence on excitation wavelength, which further reveals the clusterization-triggering emission (CTE) mechanism. In summary, the strategy of endowing AIE properties to non-AIE active polymer by introducing heterocycles into the backbone through multi-component reaction provides useful guidance for AIE functionalization of other non-AIE materials.