Multi‐Ion Sensing by a Tripodal N ₄ O ₃ Donor Optical Probe: Interactions with Th ⁴⁺ , Zn ²⁺ , and Fe ^2+/3+

Abstract Single crystal X‐ray structurally characterized tripodal imine (L1) has been explored for fluorescence recognition of Th 4+ and Zn 2+ and colorimetric discrimination of Fe 2+/3+ . The L1 can detect as low as 43.22 × 10 −8 M Th 4+ , 49.00 × 10 −8 M Zn 2+ , 3.681 × 10 −6 M Fe 2+ and 3.894 × 10 −6 M Fe 3+ . Strong binding interaction (10 4 M −1 order) between L1 and Th 4+ / Zn 2+ , leading to fluorescence enhancement, is attributed to the chelation‐enhanced fluorescence (CHEF) that inhibits excited‐state intra‐molecular proton transfer (ESIPT). On the other hand, the visual color change of L1 upon interaction with Fe 2+ / Fe 3+ is due to a charge transfer transition. 1 HNMR spectroscopy, mass spectrometry, FTIR spectroscopy, Job‘s plot analysis, and single crystal X‐ray structure of the [L1‐Fe (III)] complex (F1) support the interaction.