Selective and differential detection of Hg2+ and Cu2+ with use of a single rhodamine hydrazone-type probe in the absence and presence of UV irradiation

A new multiple-ion-responsive chemosensor was developed for the selective and differential detection of Hg 2+ and Cu 2+ , based on the completely different ions recognition behaviors of the single rhodamine hydrazone-type probe in the absence and presence of UV irradiation. The probe was synthesized through simple chemical linkages of rhodamine B hydrazide, 4-hydroxybenzaldehyde, and acryloyl group. In the absence of UV irradiation, this probe could selectively sense Hg 2+ in the presence of other metal ions by colorimetric and fluorescent responses with considerably high sensitivity (limit of detection: 7.1 × 10 −8  M), and the process could be monitored directly by the naked eye. Intriguingly, when adding various metal ions to the probe solution under UV irradiation, only the Cu 2+ ion, even at a concentration of 1.5 × 10 −7  M, was found to induce a significant photochromism along with distinct color change. Benefiting from the high selectivity and sensitivity of such a photochromism, a convenient colorimetric sensing method for detection of Cu 2+ in presence of UV irradiation was also established. Furthermore, we demonstrated that the interference of Hg 2+ on Cu 2+ could be easily eliminated by employing Br − as a masking agent, and subsequently the discrimination of Hg 2+ and Cu 2+ under their coexistence was achieved.