Dipicolylamine-Based Fluorescent Probes and Their Potential for the Quantification of Fe(3+) in Aqueous Solutions

[Image: see text] We have synthesized two ligand systems, N(SO(2))(R(1))dpa (L1) and N(SO(2))(R(2))dpa (L2), where R(1) = biphenyl and R(2) = azobenzene, which are sulfonamide derivatives of the NNN-donor chelating dipicolylamine. Both L1 and L2 can be used as sensors for detecting Fe(3+) and are highly sensitive and selective over a wide range of common cations. Time-dependent density functional theory (TDDFT) calculations confirmed that the key excitations of L2 and the [Fe(L2)(H(2)O)(3)](3+) model complex involve −R(2)-unit-based π and π* charge transfer. L2 demonstrates a relatively high photostability, a fluorescence turn-on mechanism, and a detection limit of 0.018 μM with 1.00 μM L2 concentration, whereas L1 has a detection limit of 0.67 μM. Thus, both ligands have the potential to be used as fluorosensors for the detection of Fe(3+) in aqueous solutions.