Characterization of quinoxolinol salen ligands as selective ligands for chemosensors for uranium

Quinoxalinol salen ligands have been characterized as selective ligands for the rapid identification of uranyl. The absorption maximum of ligand 1 presented a hypsochromic (blue) shift with the addition of UO₂²⁺ (as the acetate salt), and a bathochromic (red) shift in the presence of Cu²⁺ or Co²⁺ acetate salts, resulting in distinct, visible color changes for all three metal ions. The absorption maximum of ligand 2 was not observed to change with the addition of UO₂²⁺; however, it does present a bathochromic shift with the addition of Cu²⁺, and a hypsochromic shift with Co²⁺ added. Using TDDFT calculations, it was demonstrated that the hypsochromic shift for UO₂²⁺ ion complexation with ligand 1 is caused by a ligand‐to‐metal charge transfer, while the bathochromic shift observed with Cu²⁺ ion addition was caused by a metal‐to‐ligand charge trans