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. Epindolidiones are H-bonded organic pigment semiconductors with excellent operational stability, including in aqueous media. Their crystal structure, electrochemical properties, and photophysics, which are dominated by excimeric effects, are reported. Transistor and light-emitting devices are demonstrated. Routes for solution processing of epindolidiones using transient solubilizing groups are explored.