Probes based on diketopyrrolopyrrole and anthracenone conjugates with aggregation-induced emission characteristics for pH and BSA sensing

Two new diketopyrrolopyrrole (DPP)-based compounds were synthesized and their fluorescence properties were investigated. DPP1 containing two diethylamino groups possess a typical aggregation-induced emission (AIE) property. Namely, when fraction of water (fw, by volume) reaches 90%, the emission intensity is 13.7 times higher than that in THF. Owing to the AIE effect and chemical reactivity of diethylamino group towards H+ ions, DPP1 starts to aggregate at basic conditions (pH = 10.59). At a pH of 12.36, the emission intensity of DPP1 is 6.67-fold compared to that at pH 2.53, which indicates that DPP1 can work as a fluorescent pH sensor. On the other hand, DPP2 is an ammonium-salt containing compound and has no AIE phenomenon in solution, but shows emission enhancement in solid state and in the increasing viscosity system. DPP2 can interact strongly with BSA to amplify its emission with 7.65-fold fluorescence enhancement in presence of 100 μM BSA. Therefore, DPP2 is a fluorescent “turn on” biological probe for BSA detection. In addition, DPP2 can be utilized as a fluorescent probe for cellular imaging of HeLa cells, where red fluorescence is observed in the cytoplasm. The CCK-8 assay shows that the cytotoxicity of DPP2 is low.