Thienoisoindigo-based recyclable conjugated polymers for organic electronics

In transient electronics, imine-based semiconducting polymers based on thiophene-flanked diketopyrrolopyrrole (TDPP) are widely used to realize naturally disposable electronic devices. However, TDPP units easily decomposed even under mildly acidic conditions in the biodegradation of electronic devices. Herein, we have designed and synthesized two chemically recyclable thienoisoindigo (TII)-based polymers bearing an imine bond at the depolymerized position, in which these polymers were prepared from polycondensation reactions of dialdehyde-functionalized monomer TII-(CHO)2 with p-phenylenediamine (PPD) to produce p(TII-PD) and 2,6-naphtalenediamine (2,6ND) to produce p(TII-2,6ND), respectively. Especially, we have examined the recyclability of both polymers. In the degradation process under mildly acidic conditions, our polymers showed excellent degradability within one day, and the TII-(CHO)2 monomer was retrieved with over 90% yield and exhibited remarkable chemical stability over 6 months under the degradation conditions. We prepared the same recycled polymers as p(TII-PD) and p(TII-2,6ND) by utilizing the recovered TII-(CHO)2 monomer. The recycled polymers displayed almost the same physicochemical properties and field-effect mobilities in the order of 10-2-10-3 cm2/Vs as the pristine polymers. These reproducible results suggest that the TII-based monomer unit is an excellent building block for developing fully recyclable semiconducting polymers.