Highly Air-Stable Thieno[3,2-b]thiophene-Thiophene-Thiazolo[5,4-d]thiazole-Based Polymers for Light-Emitting Diodes

A series of highly air‐stable, low‐bandgap poly(3‐alkylthiophene)s containing electron‐rich thieno[3,2‐b]thiophene and electron‐deficient thiazolo[5,4‐d]thiazole rings were synthesized by the Stille coupling reaction. The polymers exhibited good thermal stability and solubility with excellent film forming properties when drop‐ or spin‐cast from solution. A strong absorption at 564–568 nm and a shoulder at 614–616 nm were observed. The optical bandgap of the polymers was found to be 1.82–1.85 eV. The IP of the polymers was found to be 5.62–5.65 eV. All polymers showed strong fluorescent emission both in solution and in the solid state. EL devices were fabricated using the polymers as an emissive layer and red emission was observed with the emission range of 649–679 nm. A series of new thieno[3,2‐b]thiophene‐, alkylthiophene‐ and thiazolo[5,4‐d]thiazole‐based low‐bandgap semiconducting polymers have been synthesized by Stille coupling. The polymeric films showed a strong absorption peak at 564–568 and emission at 671–678 nm with a bandgap of 1.8 eV. The IP of the polymers were estimated to be 5.6 eV. Because of their high IP, the polymers are expected to be stable in air. Solution‐processed polymer LEDs fabricated from these polymers showed red emission in the range 649–679 nm.