Functionalized Phenanthrene Imide‐Based Polymers for n‐Type Organic Thin‐Film Transistors

High‐performing n‐type polymer semiconductors are crucial for the applications of organic electronics, however strong electron‐deficient building blocks with optimized physicochemical properties for constructing them are still limited. The imide‐functionalized polycyclic aromatic hydrocarbons (PAHs) with extended π‐conjugated framework, high electron deficiency and good solubility serve as promising candidates for developing high‐performance n‐type polymers. Among these PAHs, phenanthrene (PhA) features a well‐delocalized aromatic π‐system with multiple active sites to functionalize. However, the PhA‐based imides are seldom studied, mainly attributed to the synthetic challenge. Herein, we reported two functionalized PhA moieties, CPOI and CPCNI, by simultaneously incorporating imide with carbonyl or dicyanomethylene onto PhA. Notably, the dicyanomethylene‐modified CPCNI exhibits a well stabilized LUMO energy level (‐3.84 eV), attributed to the synergetic inductive effect from imide and cyano groups. Subsequently, based on CPOI and CPCNI, two polymers PCPOI‐Tz and PCPCNI‐Tz were developed. Applied to organic thin‐film transistors, owing to the strong electron‐deficient character of CPCNI, polymer PCPCNI‐Tz shows an improved electron mobility and largely decreased threshold voltage compared with PCPOI‐Tz. This work affords two structurally novel electron‐deficient building blocks and highlights the effectiveness of dual functionalization of PhAs with strong electron‐withdrawing groups for devising n‐type polymer semiconductors.