Rational Design of a Narrow-Bandgap Conjugated Polymer Using the Quinoidal Thieno[3,2-b]thiophene-Based Building Block for Organic Field-Effect Transistor Applications

A new quinoidal acceptor building block (namely IQTT) is designed with directed diradical character to control and narrow the bandgap while good chemical stability is maintained with the assistance of quantum mechanics simulations. Then IQTT-based monomer and donor-acceptor (D-A) polymer (PIQTT) are synthesized as well as the isoindigo-based (IID) monomer and D-A polymer (PITT). It is found that the IQTT building block displays stronger electron-withdrawing ability and more planar backbone conformation than IID in the copolymers. Both IQTT-based monomer and PIQTT exhibit significantly red shifted absorption compared to their IID-based counterparts. In the solid state, PIQTT exhibits the superior thin film order and a decent field-effect transistor mobility. This work not only shows that IQTT is an excellent building block for organic electronics but also indicates that the quantum chemical simulation tool that developed in diradicaloid studies is a powerful approach to design novel quinoidal narrow-bandgap D-A conjugated polymers for organic electronics.