Structurally Characterized Antipyrine‐Based Dual Fluorescent Probe: Enhanced Al III Selectivity of a Dinuclear Zn II Complex for Intracellular Sensing by a Displacement Approach

The antipyrine‐based fluorescence probe daph, structurally characterized by single‐crystal X‐ray diffraction, can recognize both Zn 2+ (at 520 nm, yellow) and Al 3+ (at 490 nm, green). However, Al 3+ selectivity is enhanced significantly when the dinuclear Zn II ‐daph complex is used as a sensor, which senses Al 3+ by a displacement approach. The binding constants of daph for Zn 2+ and Al 3+ are (4.9 ± 0.2) × 10 4 and (3 ± 0.1) × 10 5 M –1 , respectively. The higher water solubility of the Zn II ‐daph complex allows the detection of Al 3+ in a greener way (0.1 M HEPES buffer, ethanol/water = 1:9, v/v, pH 7.4). Moreover, the detection limit of the Zn II ‐daph complex for Al 3+ is higher (2.5 × 10 –9 M ) than that of free daph (4.6 × 10 –8 M ). Alkali and alkaline‐earth metal ions, Cd 2+ , Hg 2+ , and Pb 2+ , and 3d metal ions do not interfere. Both daph and the Zn II ‐daph complex are capable of intracellular Al 3+ detection.