Organic dyes and pigments constitute a large class of industrial products. The utilization of these compounds in the field of organic electronics is reviewed with particular emphasis on organic field-effect transistors. It is shown that for most major classes of industrial dyes and pigments, i.e., phthalocyanines, perylene and naphthalene diimides, diketopyrrolopyrroles, indigos and isoindigos, squaraines, and merocyanines, charge-carrier mobilities exceeding 1 cm(2) V(-1) s(-1) have been achieved. The most widely investigated molecules due to their n-channel operation are perylene and naphthalene diimides, for which even values close to 10 cm(2) V(-1) s(-1) have been demonstrated. The fact that all of these π-conjugated colorants contain polar substituents leading to strongly quadrupolar or even dipolar molecules suggests that indeed a much larger structural space shows promise for the design of organic semiconductor molecules than was considered in this field traditionally. In particular, because many of these dye and pigment chromophores demonstrate excellent thermal and (photo-)chemical stability in their original applications in dyeing and printing, and are accessible by straightforward synthetic protocols, they bear a particularly high potential for commercial applications in the area of organic electronics.

Research on small-molecule-based organic semiconductors has undoubtedly been strongly influenced by xerographic photoconductors like triarylamines, the first important organic electronic materials in market products.[1] Their development was strongly influenced by the Bässler model, which provided a rationale for the design of amorphous organic photo-and semiconductors.[2] According to this model, only compounds that lack dipole moments are considered promising for charge-carrier transport because the increased energetic disorder associated with dipole moments is thought to impede charge hopping. Recently, we questioned this paradigm in the field of organic photovoltaics (OPV) and successfully implemented highly dipolar merocyanine dyes as active components for light harvesting as well as exciton and hole transport in solution-cast bulk heterojunction (BHJ) solar cells.[3] The rationale behind our concept [4] was that highly dipolar donor-acceptor (D-A) substituted p systems (also called push-pull dyes) self-assemble into centrosymmetric dimers, [5] thus effectively eliminating molecular dipole moments on the supramolecular and material levels.[6] Two drawbacks of our BHJ materials, however, limited the acceptance of our concept so far. Firstly, the best solar cells were obtained for merocyanine dyes whose molecular scaffolds were equipped with rather bulky substituents that interfere with close face-to-face antiparallel dimerization.[3] Secondly, the power-conversion efficiencies (h) under standard AM1.5, 100 mW cm À2 simulated solar illumination conditions for solution-cast BHJ cells with fullerenes-although significantly advanced by more sophisticated vacuum processing [7] -could not be improved beyond 2.6 %, which is significantly lower than the best solutionprocessed small-molecule-based BHJ devices fabricated with A-D-A and D-A-D chromophores, for example, acceptorsubstituted oligothiophenes (up to 3.7 %) [8] and triarylamines (up to 4.3 %), [9] diketopyrrolopyrroles (up to 4.4 %), [10] and squaraines (up to 5.2 %).[11] Herein, we introduce dipolar D-A dyes with flat structures that undoubtedly form centrosymmetric dimers [5] with perfectly cancelled dipole moments in the solid state. Solution-processed BHJ solar cells derived thereof exhibit power-conversion efficiencies up to 4.5-5.1 % (dependent on light intensity), clearly placing D-A dyes now among the top-performing small molecules in the field of organic photovoltaics.Scheme 1 outlines the synthetic route that follows our earlier work on merocyanine dyes for photorefractive materials [12] and the simple access to 5-dialkylamino-thiophene-2-carbaldehydes by Hartmann.[13] Detailed synthetic procedures and characterization data are described in the Supporting Information.The optical properties of the synthesized dyes were investigated by UV/Vis and electro-optical absorption spectroscopy.[14] Furthermore, cyclic voltammetry was performed for each dye to obtain information about their highest occupied molecular orbital (HOMO) and lowest unoccupied molecu...

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Molecular and crystal engineering rendered high‐performance organic thin‐film transistors (TFTs) based on a highly electron‐poor octachloroperylene diimide (Cl8‐PTCDI). In their Communication on F. Würthner, Z. Bao, and co‐workers report an intriguing supramolecular crystal engineering concept that directs two‐dimensional π–π‐stacked percolation paths for electron transport and affords TFTs with excellent mobilities and on‐to‐off current ratios under atmospheric conditions.

Twisted up: Perchlorination of perylene diimide afforded an exceptionally electron‐poor organic semiconductor molecule (see picture; C black, Cl green, O red, N blue, H white) that crystallizes in an ideal brickstone arrangement with close π–π and chlorine–chlorine contacts. Vapor‐deposited thin films of this molecule show excellent transistor performance, even in air (μ≈0.8 cm2 V−1 s−1, Ion/Ioff≈108).