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A selective fluorescent probe based on bis-Schiff base for “turn-on” detection of Al³⁺ and cysteine by different mechanisms

Li, Yang, Liao, Caiyun, Huang, Shanshan, Xu, Hui, Zheng, Baozhan, Du, Juan, Xiao, Dan
RSC advances 2016 v.6 no.30 pp. 25420-25426
aluminum, copper, cysteine, detection limit, emissions factor, fluorescence, fluorescent dyes, phenolphthaleins
In the paper, a novel fluorescent sensor L based on phenolphthalein derivative bis-Schiff base was synthesized and characterized. Chemosensor L was found to be an excellent specific receptor for Al³⁺via significant fluorescent enhancement resulting from the inhibition of an internal charge transfer (ICT) process and an efficient chelation-enhanced fluorescence (CHEF) effect. A good linear relationship was obtained in the Al³⁺ concentration from 0 to 50 μM with the detection limit reaching below 15 nM. Moreover, the addition of 2 equiv. of Cu²⁺ can almost completely quench the emission intensity of L due to a ligand–metal charge transfer (LMCT) process. The resulting L–Cu(ii) complex showed a satisfactory sensing ability toward cysteine (Cys) through naked-eye and recovered fluorescence intensity with the detection limit of 0.36 nM. The fluorescence recovering process was caused by the stronger coordination ability of Cys with Cu²⁺ than with L and therefore free L was released from the L–Cu(ii) complex. Furthermore, the sensor was used to detect Cys in practical samples with a high accuracy.