Excited-state properties of 6-methoxyflavone in the presence of halide ions in aqueous media.

The present work investigated the influence of different halides on the excited state dynamics of 6-methoxyflavone (6MF) in an aqueous solution with steady-state and time-resolved techniques. On successive addition of I^-and Br^-ions, the fluorescence of 6MF quenched significantly, whereas the respective ions do not change the maximum fluorescence band. Fluorescence of 6MF was quenched 66% by I^-ions and 34% by Br^-ions. In a pure aqueous medium, both the H-bonded: CT and protonated species of 6MF participate in the quenching of fluorescence. The quenching process was categorized by Stern-Volmer (S-V) and Lehrer equations. Quenching parameters such as K_SV, K_SV-Land k_qwere higher for I^-ions than Br^-ions. The decrease in fluorescence intensity and a reduction in fluorescence lifetime suggested the dynamic nature of quenching by I^-ions following the electron transfer mechanism. Fluorescence quenching of 6MF has also been observed in the acidic medium in the presence of different halides. Thus, the study reveals that 6MF is responsive towards I^-ions in a wide range of pH, specifically in a purely aqueous environment (pH∼7), hence important for sensing/detection applications.