Porphyrin-Based Metal–Organic Framework Probe: Highly Selective and Sensitive Fluorescent Turn-On Sensor for M³⁺ (Al³⁺, Cr³⁺, and Fe³⁺) Ions

The development of porphyrin-based metal–organic frameworks (MOFs) has attracted significant interest in the scientific community in recent years because of their versatile applications particularly in optical and electronic fields. In this study, a highly selective and sensitive fluorescent turn-on sensor using a porphyrinic MOF, Tb–TCPP, is presented, which displays a 10-fold fluorescence enhancement in the presence of Al3+, Cr3+, and Fe3+ ions. The detection limit is in the nM region. For the Al3+ ion, it could be visually detected at concentrations as low as 5 mM within 15 min. Tb–TCPP could also be used as an indicator for acidic or alkaline solutions at pH values of >9 and <3. The studies on the detection mechanism illustrate that cation exchange proceed between Tb–TCPP and these M3+ ions, and consequently, energy transfer from TCPP to Tb3+ is suppressed and π*−π energy transfer of the porphyrin ligand is significantly enhanced.