Novel chiral spirocycle coumarin-based nano fluorescence probes for selective detection of indomethacin

Two novel self-assembled fluorescent probes based on spirocoumarin, SY1 (7'-hydroxy-2',3',7,8-tetrahydro-2H-spiro[cyclopenta[h]chromene-9,1'-inden]-2-one) and SY2 (7,7',8,8'-tetrahydro-2H,2'H-9,9'-spirobi[cyclopenta[h]chromene]-2,2'-dione), were synthesized via the Knoevenagel condensation reaction. SY1 self-assembles into vesicles in ethanol due to the intermolecular hydrogen bonding and weak π-π* interactions, whereas SY2 develops cross-linked flat spherical structures solely via weak π-π* interactions. Both probes demonstrated selective fluorescence quenching for indomethacin (IND), with SY1 showing superior recognition capabilities and a lower limit of detection (LOD = 6.28 × 10^-8 M) compared to SY2 (LOD = 2.12 × 10^-7 M). The difference in the detection capabilities of SY1 and SY2 could be attributed to their distinct molecular architectures and interactions. The PET mechanism was confirmed through FT-IR spectroscopy and DFT calculations, revealing that intermolecular charge transfer occurs between the -OH group of SY1 and the CO group of IND, while SY2 facilitates charge transfer between its CO group and the -COOH group of IND. The HOMO-LUMO energy gap of SY1 is 0.3 eV smaller than that of SY2. Following its interaction with indomethacin, SY1 exhibits a reduced band gap compared to SY2, indicating enhanced recognition capability.