Investigation of pyridine/propargyl bromide reaction and strong fluorescence enhancements of the resultant poly(propargyl pyridinium bromide).

Poly(propargyl pyridinium bromide), a kind of conjugated polyelectrolyte with polyacetylene as the backbone and pyridinium as side groups, was synthesized simply via reaction between pyridine and propargyl bromide under mild conditions. The resultant polymer was characterized by (1)H NMR, elemental analysis, FT-IR, and GPC-MALLS. An alkyne group was confirmed as the end group of the polymer chains by the alkyne/azide click chemistry, which reveals that the polymerization is terminated by the reaction between propargyl bromide and carbon anions. It is known that monosubstituted polyacetylenes reported have very weak fluorescence intensities, which limit their applications. As a monosubstituted polyacetylene, the freshly prepared poly(propargyl pyridinium bromide) also has a very weak fluorescence. However, we confirmed that addition of some anions to the polymer solution in DMF or DMSO leads to the fluorescence enhancements up to 25 times. Besides, heating the polymer solution at a temperature between 70 and 130 °C for longer than 0.5 h greatly enhanced the fluorescence intensity. The interaction with the anions or the heating enhances the effective exciton confinement within the conjugated backbone and thus results in the fluorescence enhancements. After the fluorescence enhancements, poly(propargyl pyridinium bromide) has relatively strong fluorescence emissions, which will make it promising in fluorescence-based applications.