Ionic liquids display outstanding properties and have a wide range of potential uses. Their unique ionic and organic nature also identify them as good glass-forming materials. In this work, a series of imidazolium-based ionic liquids with varying functionalities from aliphatic to aromatic groups and a fixed bis((trifluoromethane) sulfonyl]amide ([NTf2](-)) anion are characterized using a commercial rapid scanning nanocalorimetry instrument, the Mettler Toledo Flash DSC. The limiting fictive temperature T-i, which is equivalent to the glass transition temperature T-f', is measured on heating as a function of cooling rate. The dynamic fragility is obtained for the series of ionic liquids, and using this data along with a compilation of data from the literature for a total of 50 ionic liquids reveals that aromatic structure increases fragility more than expected simply based on the change in T-g. Our results provide an approach to control fragility of ionic liquids through chemical modifications to the side group.