Naphthalene‐Functionalized,Photoluminescent Room Temperature Ionic Liquids Bearing Small Counterions

Obtaining π‐conjugated room temperature ionic liquids (RTILs) is difficult because of the relatively strong π–π interaction among the π‐moieties. Existing strategies by using bulky counterions greatly hindered further property optimization and potential applications of these intriguing functional fluids through simple ion exchange. Herein, four naphthalene‐functionalized, π‐conjugated RTILs with small counterions (Br^?) have been facilely synthesized with high yields. Our strategy is to attach branched alkyl chains to the cationic backbone of the target compounds ( 2 a – d ), which effectively tune inter‐ and intramolecular interactions. Compounds 2 a – d have satisfactory thermal stability (up to 300 °C) and low melting points (<?19 °C). Rheological measurements revealed the fluid character of 2 a – d , whose viscosity decrease with the increase of the alkyl chain length and temperature. The presence of the π‐conjugated naphthalene moiety imparts 2 a – d photoluminescent properties in bulk solutions. Moreover, the absence of strong π–π stacking among the naphthalene units in solvent‐free states enables them to be used as a new generation of photoluminescent inks.