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

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.