Elucidating the effects of the sidechain substitution direction on the optoelectronic properties of isomeric diketopyrrolopyrrole-based conjugated polymers for near-infrared organic phototransistors

Sidechain engineering is a powerful molecular design strategy to tune the solid-state packing and structural ordering of conjugated polymers. While the modification of the type and length of sidechains has become a key strategy in tuning the polymer properties, the effects of the sidechain direction on the optoelectronic properties of polymers have been less investigated. Herein, two new isomeric diketopyrrolopyrrole (DPP)-based conjugated polymers (namely P3BT-in and P3BT-out) with different sidechain substitution directions are designed and synthesized based on the O-alkylated DPP isomer (pyrrolo[3,4-c]pyrrol-1(2H)-one). Through comprehensive theoretical studies and experimental characterization, the effects of the sidechain-substitution direction on the optoelectronic properties of polymers and the corresponding performance of organic transistors and near-infrared organic phototransistors (NIR-OPTs) were systematically investigated. Compared to P3BT-out with sidechains spreading in the outer way, P3BT-in with sidechains in the inner way has better molecular planarity, resulting in increased crystallinity. In addition, P3BT-in has deeper LUMO energy levels and a narrower bandgap of 1.06 eV with a stronger light absorption ability, leading to increased electron mobility and n-type NIR photosensitivity. Overall, tuning the sidechain substitution direction could be a useful strategy for the rational design of functional polymers. Compared to P3BT-out, P3BT-in with sidechains in the inner way has better molecular planarity, narrower bandgap, and stronger light absorption ability, resulting in an increased electron mobility and higher near-infrared photoresponsivity.

Automated summary

Sidechain engineering is an important molecular design strategy for tuning the solid-state packing and structural ordering of conjugated polymers. The effects of sidechain direction on the optoelectronic properties of polymers and device performance were systematically investigated in this study. The results demonstrate that tuning the sidechain substitution direction can effectively improve the molecular structure and light absorption properties of polymers, providing new insights for the rational design of functional polymers.