Mechanistic insights into AIEE active levofloxacin for 4-nitrophenol sensing: A combined experimental and DFT/TD-DFT study with on-site applications

The photophysical properties of the FDA-approved drug levofloxacin (LFX) were studied, and its exquisite emission response at higher wavelengths prompted us to utilize it as a sensor against hazardous chemicals in the environment. LFX was fairly soluble in DMF and showed the maximum absorption (λ_abs) at 300 nm wavelength and maximum emission (λ_max) at 500 nm wavelength experimentally. Both the emission and absorption of LFX were also theoretically examined through TD-DFT calculations, and the results were compared. LFX exhibits solvatochromism as its wavelength changes in the presence of various solvents. The emission of LFX was also checked in varying water fractions (0˗90 %), and its emission response demonstrates it as an AIEE active molecule, as its emission intensity is enhanced in the presence of water. The fluorescence titration experiment of LFX was performed against various NACs, metal ions, and anions to check its sensing capability under the similar conditions DMF: H₂O (1:7, v/v) as utilized for 4-NP. The LFX intensity was quenched only upon the interaction of 4-NP and showed a limit of detection of 204 nM. UV–Vis. ¹H NMR titration experiments were also performed to investigate the type of interaction between 4-NP and LFX. Furthermore, theoretical calculations were performed to study various electronic properties of LFX and LFX@4-NP including density of state (DOS) electron density difference (EDD) and the type of interactions were elucidated by performing the non-covalent interaction (NCIs) analysis. Moreover, the sensor LFX was practically utilized in sensing the 4-NP in a real water sample, which showed a 96 % quenching efficiency.