Synthesis of Cobaltocenium Methacrylate Monomer

2-Cobaltocenium amidoethyl methacrylate hexafluorophosphate (CoAEMAPF₆) was synthesized according to our earlier report.^{51 (link)} 2-Aminoethyl methacrylate hydrochloride (90%), N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC-HCl, 98%), 4-(dimethylamino) pyridine and tetrabutylammonium chloride (TBACl) were purchased from Aldrich and used as received. Tris buffer solution was prepared from tris(hydroxymethyl)aminomethane (Tris base) (Sigma-Aldrich) and concentrated hydrochloric acid (Sigma-Aldrich). Poly(sodium styrene sulfonate) (M_n = 70,000 g/mol) was purchased from Sigma as an anionic polyelectrolyte. The fluorescent probe 5(6)-carboxyfluorescein (as a mixture of isomers) was purchased from Sigma-Aldrich. Displacer anion solutions were prepared from succinic acid (Sigma), tricarballylic acid and 1,4-cyclohexanedicarboxylic acid (Acros), 1,2,3,4-butanetetracarboxylic acid and pimelic acid (Alfa Aesar), trimesic acid and 1,3,5-cyclohexanetricarboxylic acid (TCI America). Water was from Thermo Scientific with ion conductivity at 18.20 MΩ. Azobisisobutyronitrile (AIBN) was recrystallized from methanol before use. All other chemicals were from commercial sources and used as received.