A new and simple polycondensation method for the synthesis of sulfur-linked isoindole-phenylene based blue light-emitting copolymers

New isoindole containing blue light-emitting copolymers, poly[(1,2-isoindolene)-(1-sulfane-4-phenylene)] and poly[(1,2-isoindolene)-(1-sulfane-3-phenylene)] were prepared by a simple polycondensation method between ortho-phthalaldehyde and para-, or meta-aminothiophenol. The reaction proceeds under mild conditions, giving pure copolymers with high yields and does not require a catalyst. The formation of both linear and cyclic products was observed. The polymerization is largely solvent dependent and the maximum obtainable molecular weight is limited by the solubility of the copolymers. Detailed NMR study revealed orthogonal sigma–pi interactions between the chain segments of the 1,4-copolymer. The optical properties were also studied and it was found that both copolymers emitted blue light in solution with relatively narrow emission band. Unlike their simple isoindole derivatives, the copolymers proved to be stable for several weeks and can serve as model compounds for the synthesis of new and versatile isoindole-containing light-emitting polymers.