Optical Pd2+ sensing by rhodamine hydrazone ligands: different stoichiometries in aqueous/nonaqueous environments

A series of rhodamine spiro-leuco compounds have been developed as fluorescence-enhanced sensors for optical sensing of palladium ion (Pd2+). The initial rhodamine hydrazone derivatives, RPd1-a, RPd1-b, and RPd1-c, display a good coordination to Pd2+ inducing the spirolactam-open reaction with a significant fluorescence enhancement and color generation. Different stoichiometry results, 1:2 in EtOH/H2O and 1:1 in MeOH/DCM were observed for Pd2+/RPd1-c complexation.

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