An N-linked disalicylaldehyde together with its caesium ion and dichloromethane sensing performances: ‘dual key & lock’ LMCT-enhanced fluorescence strategy

Abstract

The development of inexpensive, selective and rapid-response chemosensors for detecting Cs⁺ in waste water is highly desirable in the nuclear power industry. Here we demonstrate an efficient Cs⁺ optical sensor based on the N-linked disalicylaldehyde H₂Q_j with excited state intramolecular proton transfer (ESIPT), and it will transform into the ligand-to-metal charge transfer (LMCT) process in the presence of Cs⁺, resulting in dramatically enhanced fluorescence together with a distinct change of color from light-green to green-yellow. Simultaneously, it is found that CH₂Cl₂ can serve as the quencher of LMCT-enhanced fluorescence, thus enabling selective CH₂Cl₂ detection in a turn-off fluorescence approach. Further detailed studies reveal that both Cs⁺ and CH₂Cl₂ sensing processes are rapid within 60 seconds. The corresponding limit of detection (LOD) values for sensing Cs⁺ and CH₂Cl₂ are as low as 0.37 mM and 0.37%. Moreover, it was also verified that Cs⁺ sensing is applicable in the range of pH = 7–11 and the reversibility of sensor H₂Q_j can be easily achieved by modulating pH values, and H₂Q_j is also assessed for its Cs⁺ sensing performces in real water samples. This H₂Q_j-Cs sensing system must provide a valuable reference for further Cs⁺ sensors.