Side-Chain-Functionalized Poly(indacenodithiophene-alt-benzothiadizole)s as Stretchable High-Mobility Semiconductors with Improved Elasticity

To regulate the mechanical properties of poly(indacenodithiophene-alt-benzothiadizole) (IDT-BT), a high-mobility polymer semiconductor with high ductility but inferior elasticity (plastic deformation onset strain (PdOS) < 10%), triisopropylsilyl (TIPS), hydroxyl (OH), and 2-ureido-4[1H]-pyrimidone (UPy) groups were introduced into its side chain ends. The incorporation of bulky and neutral TIPS groups led to slightly increased ductility but had no obvious influence on the elasticity of the polymer. The presence of OH groups resulted in enhanced elasticity without sacrificing ductility. However, high-content (20 mol %) OH-functionalized side chains were necessary to improve PdOS to above 30% due to the weak and dynamic nature of formed hydrogen bonds. In contrast, incorporating a small amount of UPy groups, capable of forming strong quadruple hydrogen bonds, in side chains could significantly improve the elasticity of the polymer. A PdOS of above 40%, along with a crack onset strain of ∼100% and decent hole mobility of ∼0.6 cm2 V–1s–1, was demonstrated for polymer UPy-5% that contained 5 mol % UPy-functionalized side chains. Because of excellent elasticity, UPy-5% films displayed stable mobility against cyclic stretching, releasing up to 500 cycles at a tensile strain of 30%.