Near-infrared fluorescent probe for ratiometric Al3+ signaling and imaging through combined PET and ICT mechanisms

A porphyrin dimer (BPD) was introduced for selective detection of aluminum ions (Al3+) in a fully aqueous system. BPD produces a ratiometric emission profile in the near-infrared (NIR) region upon Al3+ complexation. The sensing mechanism involves photoinduced electron transfer (PET) and intramolecular charge transfer (ICT). The binding mode of BPD/Al3+ was fully examined based on spectroscopic titration, time-resolved fluorescence decay, NMR spectroscopy, mass spectrometry, and IR analyses. In aqueous media, the strong interaction between Lewis acid Al3+ and nitrogen atoms allows BPD to conquer the high energy barriers of the solvent for only Al3+, resulting in the high selectivity and low detection limit (2.65 × 10–8 M) of the probe. Practical applications of BPD for Al3+ monitoring in real samples and fluorescent prints were further investigated with satisfactory results. With its organic solvent-free sensing medium, good biocompatibility, and NIR ratiometric emission properties, the designed BPD probe is appropriate for ratiometric visualization of Al3+ in living cells.