Imidazolium based dicationic room temperature ionic liquids (RTILs) were synthesized, characterized, and investigated their physicochemical properties along with catalytic activity in azidation reaction. In this method two N-methylimidazolium cations were bridged with different short oligo (ethylene glycol) chains as linkers and mesylate (CH3SO3-) or tosylate (CH3C6H4SO3-) moieties as anion containing RTILs were synthesized. These RTILs were showed interesting physicochemical properties such as high thermal stability, solubility in various organic solvents, high viscosity at different temperature and efficient catalytic activity in organic transformation by tuning their cation and anion components. Catalytic activities of these RTILs were investigated for a representative reaction of alkyl halide to their corresponding azide and RTILs were reused for five times without losing their catalytic activity. The present catalytic system dicationic RTILs in methanol were showed significant high yield in short reaction time compared to the traditional monocationic ILs in azidation reaction. Moreover, we also performed theoretical study of synthesized RTILs to correlate experimental results of catalytic activity with their molecular geometry. Geometrical study and experimental results reveals that simple structural modifications of synthesized RTILs were showed major influence on their physicochemical properties as well as catalytic activity. Hence, to utilize the tunability property of these RTILs may open exciting perspectives for use in various synthetic applications in "Green" synthesis. (C) 2012 Elsevier B.V. All rights reserved.