Aggregation-induced emission enhancement (AIEE)-active donor-acceptor type fluorophores based on the 1,3-diaryl pyrazole unit: Conspicuous mechanochromic fluorescence and biosensing of iodide ions

Abstract

Two type luminophore 1 and 2, with the same triphenylamine (TPA) and malonitrile-functionalized 1,3-diaryl pyrazole (MDP) units but with different π-conjugated spacer, were designed and synthesized. The crystals solid-state emission behavior and mechanical stimuli-responsive fluorescence characteristics of 1 and 2 were investigated. Interestingly, the fluorophores 1 and 2 exhibited yellow-green and yellow crystals solid-state fluorescent, respectively. Furthermore, 1 and 2 also exhibited obvious mechanochromic fluorescence behavior with repeated four cycles. Compared to 1 with an 80 nm red-shift, 2 is more sensitive to mechanical stimuli and exhibits a large red-shift emission of 85 nm. The powder XRD experiments demonstrated that the mechanochromic fluorescence behavior of 1 and 2 were related to the morphology transformation from crystalline state to amorphous state. In addition, based on the MDP moiety as I− receptor, 1 and 2 were qualified for sensing of I− with low limit of detection (89.0 nM, 149.9 nM). The biosensing of I− based on the better detection performance of the probe 1 was achieved in A549 cells and zebrafish. These results certify the great potential of MDP as a strong electron-deficient unit for designing D-A type mechanochromic fluorescence materials and biosensors for the detection of I− in organism.