Isomeric 1,4-Dihydropentalene-Containing Building Blocks for High Mobility Ladder-Type Conjugated Polymers

Nearly amorphous conjugated polymers, though lacking long-range order, can exhibit high charge carrier mobility and enhanced flexibility, making them ideal for flexible or stretchable OFET applications. However, research on novel structural blocks for this class of materials remains limited. We report the synthesis of two derivatives of the 5,10-dihydroindeno[2,1-a]indene (DHI) core, where two thieno groups are appended to each end to reduce torsional disorder with adjacent comonomers. The two 1,4-dihydropentalene containing isomers, anti-C16DHIT-Br and syn-C16DHIT-Br, feature distinct thieno group orientations, leading to differences in their electronic properties. The anti-isomer shows a fully delocalized conjugation pathway, whereas the syn isomer exhibits cross-conjugation, limiting delocalization along the polymer backbone. These monomers were copolymerized with benzothiadiazole (BT) to form two conjugated polymers, anti-C16DHIT-BT and syn-C16DHIT-BT, both with highly planar backbones, good solubility, and solution processability. Morphological studies reveal that anti-C16DHIT-BT exhibits more ordered stacking and higher crystallinity than syn-C16DHIT-BT. Devices based on anti-C16DHIT-BT show significantly better performance, with a hole mobility of 2.38 cm² V^-1 s^-1, slightly higher than the widely studied pIDTBT under identical conditions.