Structure-dependent fluorescence sensing of 1,10-phenanthroline by two coordination compounds with distinct metal centers

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Two coordination compounds with distinct metal centers and structural dimensionalities, CP1 and CP2, were synthesized and systematically investigated as fluorescent sensors for 1,10-phenanthroline. CP1 is a Fe(III)-based trinuclear coordination compound forming a three-dimensional dense framework, while CP2 is a Mn(II)-based compound with a zero-dimensional molecular structure. Both compounds exhibit ligand-centered luminescence originating from intraligand π→π* and n→π* transitions. In aqueous media, CP1 and CP2 show highly selective and efficient fluorescence quenching responses toward 1,10-phenanthroline, with negligible interference from common metal ions and anions. Stern–Volmer analysis revealed quenching constants of 7.69 × 104 M−1 for CP1 and 9.92 × 104 M−1 for CP2, with corresponding detection limits of 0.88 μM and approximately 0.3 μM, respectively. Both sensors also display good recyclability and sensing stability. Spectral overlap analysis indicates that excitation energy competition and inner filter effects dominate the quenching processes, while structural differences between CP1 and CP2 account for their distinct sensing efficiencies. This work demonstrates the critical role of metal centers and coordination architectures in regulating fluorescence sensing behavior and provides a useful strategy for designing coordination compound-based sensors for organic small molecules. Two structurally distinct coordination polymers (3D Fe(III)-CP1, 0D Mn(II)-CP2) were fabricated for aqueous fluorescent detection of 1,10-phenanthroline. Both sensors exhibit ligand-centered luminescence, selective fluorescence quenching via excitation energy competition and inner filter effect. The zero-dimensional Mn(II) cluster shows superior sensing sensitivity, revealing that metal center and framework dimensionality dominate recognition efficiency.

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