Strain-insensitive naphthalene-diimide-based conjugated polymers through sequential regularity control

Diversified structure design is applied to donor-acceptor (D-A)-type conjugated polymers (CPs) to improve their mobility-stretchability properties. Most methods that are capable of improving mechanical durability without sacrificing charge transport performance are applicable mainly to p-type CPs and are thus not amenable to or reported for n-type CPs with limited types of backbones. In this work, we are interested in applying sequential regularity control on the n-type CP naphthalene-diimide-bithiophene (PNDI2T) to achieve intrinsic stretchability. Sequentially alternating (Alt-PNDI2T) and random (Ran-PNDI2T) CPs were synthesized accordingly through Stille coupling polycondensation. The morphologies of Alt/Ran-PNDI2Ts were investigated by using atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD), and their mobility-stretchability properties were evaluated by using a transfer/stretch technique. We found that, by inserting sequential irregularity along the polymer backbone, Ran-PNDI2T showed a near-amorphous structure and comparable charge transport performance compared to that of Alt-PNDI2T. Moreover, Ran-PNDI2T exhibited strain-insensitive mobility-stretchability properties, relating to the successfully percolation network of tie-chains. Our results indicate that the sequential regularity control of D-A-type CPs is a promising approach to achieve intrinsically stretchable CPs with high mobilities.