Fluorescent probes for Cu2+, Hg2+ and amino acids in aqueous solutions based on two mechanisms

•Three new polythiophene derivatives P1, P2, and P3 were synthesized via simple methods.•P1, P2, and P3 showed high selectivity and sensitivity toward Hg2+ in methanol aqueous solutions at pH 3.•P1 showed excellent sensitive and selective Cu2+ detection in Tris–HCl buffer solutions.•Detection limit for Hg2+ and Cu2+ can be reached 10−8 M and 10−9 M respectively.•The sensing processes for Hg2+ and Cu2+ were revealed to be mediated by electrostatic effect and complexation respectively.

The new polythiophene-based conjugated polymers Poly{3-[(4-{[2-(dimethylamino)ethyl]amino}cyclohexylidene)methyl]thiophene} (P1), Poly{3-[(4-{[3-(dimethylamino)propyl]amino}cyclohexylidene)methyl]thiophene} (P2) and Poly{3-{[4-(4-methylpiperazin-1-yl)cyclohexylidene]methyl}thiophene} (P3) have been synthesized by FeCl3 oxidative polymerization. Among the common metal ions tested, P1, P2 and P3 exhibited high selectivity and sensitivity toward Hg2+ in methanol aqueous solutions at pH 3 with a turn-off mode in which the detection limit of P3 for Hg2+ reached a level of 10−8 M. Additionally, the fluorescence of P1 in Tris–HCl buffer solution could be dramatically quenched in the presence of Cu2+ with a detection limit of 10−9 M. These sensing processes for Hg2+ and Cu2+ have been shown to be mediated by electrostatic effects and complexation. In addition, the P1–Cu2+ system was also employed as a turn-on fluorescence probe for the label-free detection of amino acids.

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