Ionic parachor and its application to pyridinium-based ionic liquids of {[C n py][DCA] ( n = 2,3,4,5,6)}

•Three novel ILs [Cnpy][DCA] (n=3,5,6) were synthesized successfully.•The parachors of pyridinium cations, [Cnpy]+ (n=2,3,4,5,6), were obtained.•P(Est), γ(Pred), nD(Pred) correlate quite well with P(Exp), γ(Exp), nD(Exp).•If the structure of cation or anion is the same, P+ or P− is approximately equal.