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 thieno3,2‐b]thiophene and electron‐deficient thiazolo5,4‐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.