Effect of halide ions on the fluorescence properties of 3-aminoquinoline in aqueous medium

Fluorescence (FL) quenching of 3-aminoquinoline (3AQ) by halide ions $\left({\mathrm{Cl}}^{?},{\mathrm{Br}}^{?}\text{and}{\mathrm{I}}^{?}\right)$ has been explored in an aqueous acidic medium using the steady-state and time-domain FL measurement techniques. The halide ions showed no significant change in the absorption spectra of 3AQ in an aqueous acidic medium. The FL intensity was strongly quenched by ${\mathrm{I}}^{?}$ ions and the order of FL quenching by halide ions was ${\mathrm{I}}^{?}>{\mathrm{Br}}^{?}>{\mathrm{Cl}}^{?}$. The decrease in FL lifetime along with the reduction in FL intensity of 3AQ suggested the dynamic nature of quenching. The obtained ${\mathrm{K}}_{\mathrm{SV}}$ values were 328 ${\mathrm{M}}^{?1}$ for ${\mathrm{I}}^{?}$ ions and 119 ${\mathrm{M}}^{?1}$ for ${\mathrm{Br}}^{?}$ ions and the ${\mathrm{k}}_{\mathrm{q}}$ values were ~ $1.66\times {10}^{10}{\mathrm{M}}^{?1}{\mathrm{s}}^{?1}$ and $6.02\times {10}^9{\mathrm{M}}^{?1}{\mathrm{s}}^{?1}$, respectively. The observations suggested that the likely governing mechanism for FL quenching may be an electron transfer process and the involvement of the heavy atom effects.