Self-doped and planar nitrogen-bay-functionalized perylene diimides: unravelling structure–property relationships

Bay-functionalization of perylene diimides (PDIs) offers a strategy for modulating electronic properties to achieve optimal n-type charge transport character, but can result in core twisting and reduced planarity, leading to compromised π-conjugation and disruption of tight π–π stacking in the solid state. Herein, we report the synthesis and characterization of two new nitrogen-bay-functionalized N-annulated PDIs, where N-annulation effectively enforces planarity of the polycyclic aromatic core thus preserving π-conjugation even with bulky bay substituents present. Both compounds exhibit intramolecular charge transfer character, tunable optical and electrochemical properties, and strong paramagnetic behaviour without external dopants present, as confirmed by UV-visible spectroscopy, cyclic voltammetry, and solid-state electron paramagnetic resonance, respectively. Guided by Hansen solubility parameters, we formulated green solvent blends that enabled concentrated ink formulations (10 mg mL⁻¹) for large-area film deposition via slot-die coating. These findings highlight the promise of bay-substituted, N-annulated PDIs as self-doped, solution-processable materials ripe for applications in organic electronics.