Fluorescence behavior of ethidium bromide in homogeneous solvents and in presence of bile acid hosts

Photoluminescence behavior of ethidium bromide (EB) was studied in homogeneous solvents as well as in presence of bile acid surfactants. A quantitative analysis based on Kamlet–Taft equation toward the contribution of different solvatochromic parameters like solvent polarizability (π*), hydrogen bond donor (α) and hydrogen bond acceptor (β) ability, on EB spectral properties reveals that though fluorescence quantum yield and lifetime do not show any straight forward correlation individually, the substantial decrease in these quantities is due to the increase in total nonradiative decay rate in polar protic medium. The interaction of EB with bile acid hosts gives rise to large increase in fluorescence intensity due to shielding of the probe in less hydrogen bonding environment. Global analysis of the fluorescence decay behavior indicates that more than 50% of the fluorophores get sequestered inside the micellar sub-domain with an apparent binding constant of ∼103 M−1.

The increase in ethidium bromide fluorescence intensity and lifetime in presence of bile acid hosts is due to the shielding of the sequestered probes from polar and hydrogen bonding aqueous environment.Figure optionsDownload as PowerPoint slideHighlights
► Quantitative contribution of solvent parameters on ethidium bromide (EB) fluorescence solvatochromism.
► Correlation of Kamlet–Taft parameters with total non-radiative decay rate.
► Steady state and time-resolved analysis of fluorescence quenching in different mixed solvent systems.
► Interaction of EB with three different bile acids, viz. cholic acid (CA), deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA).
► Strong interaction of EB with bile acids in comparison to the other surfactants due to facial amphiphilicity.