Phenyleneethynylene- and Thienyleneethynylene-Based π-Conjugated Polymers with Imidazolium Units in the Main Chain

Phenyleneethynylene-based and thenyleneethynylene-based pi-conjugated polymers with imidazolium cationic units in the main chain and their model compounds were synthesized and characterized The imidazolium-containing cationic polymers were transfered to an ionic liquid by the spontaneous anion- exchange from iodide to bis(trifluoromethanesulfonyl)imide (TFSI). The fluorescence quantum yield of phynyleneethynylene-based pi-conjugated polymer in the ionic liquid, 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl)imide (emim TFSI), was higher than that of polymer based on iodide anion in pyridine because of a low degree of aggregation of the man chain and/or the absence of an external heavy- atom effect of the iodide counteranion. UV-vis and fluorescence spectra of N-methylated polymer and model compound with TFSI counteranion exhibited a significant blue shift with respect to the parent neutral molecules. Density functional theory (DFT) calculations for the model compounds showed a decrease in p-conjugation by quaternization of the N-position at the imidazole unit, supporting at the imidazole unit in the thienyleneethynylene-based pi-conjugated polymers and model compounds resulted in a ted shift of the UV-vis absorption and fluorescence spectra compared with those of neutral polymers and model compounds The DFT results suggest that the red shift comes from the contribution of coplanarization in the quaternized pi-conjugated compounds