Structure‐Property Relationship of Conjugated Polymers Utilizing Isomerized Fused Benzothiadiazole‐Based Building Blocks^†

Comprehensive Summary Only a few fused benzothiadizole (BTz) based conjugated polymers have been applied in organic field‐effect transistors (OFETs), and their performances were low, mainly due to the lack of available building blocks and in‐depth study of the relationship between structure and performance. Herein, we report two isomeric fused BTz‐based building blocks ( M1 and M2 ) and their copolymers PBTzVBTz‐T and PBTzVBTz‐TT, PTVT‐T and PTVT‐TT. DFT study showed all polymers had nearly planar backbone geometries, and PBTzVBTz‐TT exhibited the most linear backbone. PTVT‐T and PTVT‐TT exhibited red‐shift absorption spectra and deeper LUMO level than those of PBTzVBTz‐T and PBTzVBTz‐TT. Thin film microstructure study demonstrated PBTzVBTz‐TT and PTVT‐TT had edge‐on molecular orientation, while the others had the mixed molecular orientation of edge‐on and face‐on. Furthermore, PBTzVBTz‐TT had the longest coherence length in thin film. All these features of PBTzVBTz‐TT resulted in its highest carrier mobility of 0.1 cm 2 ·V –1 ·s –1 among these polymers.