Designing functional viologen salts with colossal ionic conductivities through counterion composition and chain...

We report the synthesis, characterization, and conductivity response of five new dicationic ionic liquid (DCIL) salts featuring phenyl-extended viologen cores coupled with terminal oxyethylene groups (CH₂CH₂O)_n of two different lengths (n = 3 and 7) and paired with three distinct counter-anions: fluorosulfonylimide ((N(FSO₂)₂ ^-, FSI), trifluoromethylsulfonylimide (N(CF₃SO₂)₂ ^-, TFSI), and nonaflate (CF₃(CF₂)₃SO₃ ^-, ONf). All salts are amorphous and exhibit near- or sub-zero glass transition temperatures (T _g s), attributed to the plasticizing effect of the (CH₂CH₂O)_n chains, and show chromophore responses in organic solvents. The five salts display large dielectric responses with conductivities in the 10^-0.5 S·cm^-1 range, facilitated by the smaller counter-anion, FSI. These conductivity values are substantial for organic (non-aqueous) media, comparable to benchmark commercial electrolytes, positioning these viologen salts among the highest-performing ionic liquids reported in the literature.