Probing the DNA–ionic liquid interaction using an ultrafast molecular rotor

The interaction of imidazolium based ionic liquids with calf thymus DNA has been investigated using a benzothiazole based ultrafast molecular rotor, Thioflavin-T, as a local reporter. It has been found that the addition of ionic liquid causes large reduction in the emission yield of the DNA bound probe indicating a strong interaction between the ionic liquids and DNA. Detailed studies show that the interaction between ionic liquids and DNA is sufficiently strong to remove the bound probe from the DNA. The excited state lifetime of the DNA bound probe measured by femtosecond fluorescence upconversion technique also corroborate with the above proposition. To understand the nature of the interaction between ionic liquids and DNA, photophysical properties of Thioflavin-T in DNA was investigated in the presence of imidazolium based ionic liquids having alkyl side chain of different lengths in the cationic moiety and the results indicate that apart from electrostatic interaction, the hydrophobicity of ionic liquid also plays a significant role in the ionic liquid–DNA interaction.