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IntroductionHydrogen-bonded organic pigments are a class of materials familiar from applications in the colorant industry, where they fi nd widespread use as materials for robust outdoor paints, cosmetics, and printing inks. [ 1,2 ] Indigo, a natural product, is the oldest and still most widely produced organic dye and pigment ( Figure 1 ). [ 3 ] The intermolecular -NH … O = hydrogen bonding that characterizes indigo is exploited in most of the synthetic hydrogen-bonded pigments as well. This class of materials has proven to be nontoxic and safe for humans, and is considered safer than even several classes of food dyes. [ 4 ] Hydrogen-bonding as a supramolecular engineering tool is useful to control self-assembly and highly relevant to aqueous and biochemical systems. [ 5,6 ] Recently, we have found that indigo, [ 7 ] and some of its derivatives [ 8,9 ] demonstrate ambipolar transport in organic fi eldeffect transistors (OFETs), with mobility ranging from 0.01-0.4 cm 2 V -1 s -1 . We
Epindolidiones-Versatile and Stable Hydrogen-Bonded Pigments for Organic Field-Effect Transistors and Light-Emitting DiodesEric Daniel Głowacki , * Giuseppe Romanazzi , Cigdem Yumusak , Halime Coskun , Uwe Monkowius , Gundula Voss , Max Burian , Rainer T. Lechner , Nicola Demitri , Günther J. Redhammer , Nevsal Sünger , Gian Paolo Suranna and Serdar Sariciftci 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 cm 2 V -1 s -1 can be achieved, with lower electron mobilities of up to 0.1 cm 2 V -1 s -1 . To help understand charge transport in epindolidiones, X-ray diffraction is used to solve the crystal structure of 2,8-difl uoroepindolidione 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 fl uorescence. 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.