Conjugated Polymers Based on Moderately Electron‐Deficient Biphenyl Imide for Tunable Charge Transport

A series of novel conjugated polymers ( BPIT1 ‐ BPIT4 ) based on a moderately electron‐deficient biphenyl imide (BPI) unit are designed and synthesized to systematically investigate how molecular structure influences optical and charge transport properties. By varying the BPI linkage position (5,5′‐vs. 4,4′‐) and the number of thiophene units, the solubility, energy levels, and optical properties of the polymers are effectively tuned. UV‐Vis absorption spectroscopy and cyclic voltammetry reveal tunable bandgaps and energy levels, confirming the mild electron‐withdrawing nature of the BPI unit. Atomic force microscopy (AFM) and X‐ray diffraction (XRD) analyses show that BPIT1 forms a smoother surface with more ordered molecular packing, corresponding to ambipolar transport behavior in field‐effect transistors, with average electron and hole mobilities of 1.70 and 0.33 cm 2 V −1 s −1 , respectively. In contrast, the bithiophene‐containing polymer BPIT2 exhibits only p‐type transport, highlighting the critical influence of molecular structure on charge transport characteristics. This work demonstrates that high‐performance ambipolar polymers can be achieved by precisely tuning the acceptor unit's electron‐withdrawing strength, establishing BPI as a versatile building block for advanced flexible electronic materials.