The non-volatility, controllable characteristics of ionic liquids (ILs) make them potential materials for various applications. The use of functionalized ionic liquids can improve their physicochemical properties. Propanenitrile imidazolium-based ionic liquids (C2CN Rim) with different functional groups, R (allyl, ethoxyl, and benzyl), and incorporating dioctylsulfosuccinate (DOSS) anion were prepared. The elemental analysis and 13C and 1H NMR results confirmed the synthesized IL structures. The density, viscosity, and refractive index of these ILs were measured over a temperature range of 293.15 to 353.15 K. Furthermore, several thermodynamic properties including the thermal expansion coefficient, molar refraction, standard molar entropy, and lattice energy were estimated for these ILs. Findings show that ILs have lower densities, similar refractive indices, higher viscosities, and lower decomposition temperature compared to their analogous incorporating only nitrile functionality. Also, the ILs showed a weak temperature dependency on the thermal expansion coefficients, α p = 4.75 � 10�4 to 5.25 � 10�4 K�1. These findings provide valuable insights into the properties and potential applications of propanenitrile imidazolium-based ionic liquids incorporating DOSS anion. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.