Smart ionic liquid sensory ink for ratiometric fluorescence temperature surface mapping

We report a visible-wavelength, self-referenced ratiometric thermometric platform based on co-dissolution of the molecular rotor 9-(dicyanovinyl)julolidine (DCVJ) and rhodamine 6G (R6G) in ionic liquids (ILs). DCVJ exhibits strong viscosity-dependent emission, while R6G serves as a temperature-insensitive internal reference, enabling ratiometric thermometry from 20 to 100°C. Eight ILs spanning various cations (imidazolium, pyrrolidinium, ammonium, or phosphonium) paired with bis(trifluoromethylsulfonyl)imide (Tf 2 N – ) or bis(2-ethylhexyl) sulfosuccinate (AOT – ) anion were evaluated, demonstrating that thermometric performance is tunable through IL chemistry. The ratiometric response was fully reversible with negligible hysteresis during thermal cycling. Temperature uncertainties, determined from analytically fitted calibration curves, were below 0.4°C at 100°C and decreased to < 0.1°C near room temperature, with best-case values as low as 0.06°C at 20°C. Integration into resistively heated microfabricated platforms further demonstrated rapid temporal response and real-time, non-contact surface temperature mapping across micrometer-to-millimeter length scales.