Red emitting dye in room temperature ionic liquids: A spectroscopic study

• Single exponential emission decay of NBA in ionic liquids was observed.
• The rotational relaxation decays of NBA are single exponential in nature.
• Structural organisation in RTILs affects the rotational relaxation decays of NBA.
• We have observed deviation from the stick and slip hydrodynamics.

In this article we have reported the photophysics and rotational dynamics of a red emitting dye Nile blue A (NBA) in two room temperature ionic liquids (RTILs). We have chosen two aliphatic RTILs with a common anion. In triethylsulfonium bis(trifluoromethylsulfonyl)imide ([S222][NTf2]) and trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide ([P(C6)3C14][NTf2]) absorption maximum of NBA appears at ∼635 nm. We have observed a single exponential emission decay of NBA in [P(C6)3C14][NTf2] and [S222][NTf2]. A comparison of activation energy of the non radiative decay (EnrEnr) and activation energy of rotational relaxation (ErotErot) with activation energy of viscous flow (EηEη) was made to check the dependence of the bulk viscosity of the media on the photophysics of NBA in the above RTILs. The rotational relaxation decays are also single exponential in nature. The deviations from the stick and slip hydrodynamics with changing temperature demonstrate complex structural feature of the media and specific solute solvent interaction governing the rotational diffusion.

We have observed a single exponential emission decay of a red emitting dye Nile blue A in [P(C6)3C14][NTf2] and [S222][NTf2].Figure optionsDownload as PowerPoint slide