Copper(II) Complexes Based on Anthraquinone‐1,8‐Disulfonate and Application as High‐Performance pH‐Responsive Fluorescent Switch

Through ligand engineering, three Cu(II) complexes with distinct dimensionalities were successfully constructed. Among them, a dimeric Cu(II) complex ( 1 ) featuring rich intra‐ and intermolecular hydrogen bonding motifs was identified as an excellent pH‐sensitive “on–off” fluorescent molecular switch. In aqueous solution, complex 1 remained fluorescence‐silent below pH 9.6, whereas its fluorescence emission was triggered under basic conditions (pH ≥ 9.6), achieving an enhancement of up to 130‐fold. Notably, this switch exhibited complete reversibility and robust recyclability between pH 3.0 and 10.0. The development of this pH‐triggered, highly sensitive molecular switch with excellent recyclability highlights the synergistic role of ligand engineering and hydrogen‐bonding networks in modulating the photophysical behavior of metal complexes, thereby offering new insights for the design of metal‐based molecular devices.