A curcumin-based AIEE-active fluorescent probe for Cu(2+) detection in aqueous solution

Curcuminoids have been extensively investigated as metal ion probes, but the intrinsic aggregation-caused-quenching (ACQ) characteristic of curcumin would hinder their applications in aqueous solution. Fortunately, tetraphenylethylene (TPE) could endow the compounds with aggregation-induced emission (AIE)/aggregation-induced enhanced emission (AIEE) characteristics to eliminate the ACQ effect. According to this strategy, a series of TPE-modified curcumin derivatives L1–4 were prepared and studied for their AIEE properties. Among the four TPE-curcumin analogues, only L1 particles have been successfully used as an on-off fluorescence probe for detecting Cu(2+) in aqueous solution. The fluorescence titration experiment determined its detection limit of 1.49 × 10(−7) mol L(−1), and the binding ratio between L1 and Cu(2+) was estimated as 2 : 1, which was in agreement with the results of high resolution mass spectrum and Job's plot. In addition, the binding constant was evaluated as 6.77 × 10(2) M(−1) using a Benesi–Hildebrand plot. Finally, the obtained L1-based indicator paper showed significant fluorescence response to Cu(2+) aqueous solution. This TPE-modified strategy improves the detection capability of curcumin probe in aqueous solution and provides a feasible way to obtain other probes with ACQ characteristics.