An oxacalix[4]arene-derived dual-sensing fluorescent probe for the relay recognition of Hg2+ and S2− ions

A novel rhodamine–tren-appended oxacalix[4]arene architecture, viz. RTOC, has been introduced as a dual-readout sensor for the selective recognition of mercury (Hg2+) and sulphide (S2−) ions. The designed probe showed a significant change in colour from yellow to pink and a corresponding ‘turn-on’ fluorescence response was observed upon interaction with Hg2+ ions, whereas the lower limit of detection was determined to be 20.5 nM. A theoretical study further discloses that the enhancement of the fluorescence intensity may be due to the Hg2+-induced spirolactam ring opening at rhodamine B sites. Moreover, the RTOC–Hg2+ system has been successfully utilized for the sensing of sulphide (S2−) anions up to submicromolar range.