Poly(pyridinium salt)s with organic counterions derived from 3,3′-dimethylnaphthidine: Thermal, liquid crystalline, and optical properties

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A poly(pyridinium salt) was synthesized from 4,4′-(1,4-phenylene)bis(2,6-diphenylpyrilium)tosylate and 3,3′-dimethylnaphthidine. Tosylate counterion was exchanged with other organic counterions such as triflimide, 1-napthalenesulfonate, and 2-napthalenesulfonate in DMSO to yield a total of four poly(pyridinium salt)s. Their chemical structures were established by using various spectroscopic techniques. Gel permeation chromatography showed that their number-average molecular weights (Mn) were in the range of 56–76 kg/mol and polydispersities in the range of 1.09–1.32. Their thermal stabilities ranged from 290 to 425 °C, under nitrogen atmosphere. Even though these polymers didn’t show thermotropic liquid crystalline phases, counterion-dependent lyotropic liquid-crystalline phase were observed in some polar aprotic solvents above their critical concentrations. Each of these polymers emitted green light (500–572 nm) both in solutions and solid states as observed by UV–vis and photoluminescent spectroscopies.