Epindolidiones—Versatile and Stable Hydrogen‐Bonded Pigments for Organic Field‐Effect Transistors and Light‐Emitting Diodes

Hydrogen-bonded pigments are remarkably stable high-crystal lattice energy organic solids. Here a lesser-known family of compounds, the epindolidiones, which demonstrates electronic transport with extraordinary stability, even in highly demanding aqueous environments, is reported. Hole mobilities in the range 0.05–1 cm2 V–1 s–1 can be achieved, with lower electron mobilities of up to 0.1 cm2 V–1 s–1. To help understand charge transport in epindolidiones, X-ray diffraction is used to solve the crystal structure of 2,8-difluoroepindolidione and 2,8-dichloroepindolidione. Both derivatives crystallize with a linear-chain H-bonding lattice featuring two-dimensional π–π stacking. Powder diffraction indicates that the unsubstituted epindolidione has very similar crystallinity. All types of epindolidiones measured here display strong low-energy optical emission originating from excimeric states, which coexists with higher-energy fluorescence. This can be exploited in light-emitting diodes, which show the same hybrid singlet and low-energy excimer electroluminescence. Low-voltage FETs are fabricated with epindolidione, which operate reliably under repeated cyclic tests in different ionic solutions within the pH range 3–10 without degradation. Finally, in order to overcome the insolubility of epindolidiones in organic solvents, a chemical procedure is devised to allow solution-processing via the introduction of suitable thermolabile solubilizing groups. This work shows the versatile potential of epindolidione pigments for electronics applications.