Keywords
Abstract
The photophysical and antioxidant properties of 3-hydroxyflavone (3HF) and its complexes with Mn(II), Co(II), and Zn(II) ions were investigated. Fluorescence spectra of 3HF in methanol revealed a pronounced excitation-wavelength dependence characteristic of the excited-state intramolecular proton transfer (ESIPT) process. Complexation with d-electron metal ions significantly altered the emission properties. The Zn(II) complex exhibited higher fluorescence intensity than the free ligand, consistent with the chelation-enhanced fluorescence effect and partial suppression of the ESIPT process. In contrast, Mn(II) and Co(II) complexes showed strongly reduced intensities, indicating fluorescence quenching associated with the paramagnetic character of these ions and the promotion of intersystem crossing. Antioxidant activity assessed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method showed moderate inhibition for 3-hydroxyflavone (24.0%). Among the complexes, Mn-3HF exhibited the highest activity (33.4%), while Co-3HF and Zn-3HF showed only minimal effects (7.1% and 5.9%). These results indicate that metal coordination modulates the antioxidant properties of 3HF, enhancing them in the case of Mn(II) and suppressing with Co(II) and Zn(II). The results demonstrate that coordination with d-electron metal ions exerts a strong influence on both the fluorescence properties and the antioxidant activity of 3HF.
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