semiconductors with carrier mobilities insufficient to be useful for OLET applications. Therefore, developing high-purity red-emitting materials showing a high transistor mobility at the same time is a primary challenge to embodying highperformance OLETs in display devices.We have been exploring a broad library of dicyanodistyrylbenzene (DCS)-type materials that show excellent photoluminescence (PL) quantum efficiency and/or charge carrier mobility in the solid state by virtue of their unique stacking modes and propensity for strong self-assembly. [12,[18][19][20][21][22] Recently, we have specifically demonstrated that a charge-transfer (CT) cocrystal of DCS derivatives can be a light-emitting ambipolar semiconductor, which is ideally suitable for OLET applications. [23] Aiming at finding a potentially pure red-emitting organic semiconductor, we reviewed the whole DCS library, particularly for the π-extended ones. Fortunately, we came across Hex-4-TFPTA ((2E,2′E)-3,3′-(2,5-bis(hexyloxy)-1,4-phenylene) bis(2-(5-(4-(trifluoromethyl)phenyl) thiophen-2-yl)acrylonitrile) (Figure 1a), which has reportedly shown an excellent n-type mobility in a vacuum-evaporated film (µ e ≈ 2 cm 2 V −1 s −1 ) but with an unexplored photoluminescence property. [21] In this work, we decided to first investigate the photoluminescence properties of Hex-4-TFPTA and its application in the red-emitting OLET devices. We thoroughly investigated the photophysical properties of the crystal and solid thin film, in terms of intermolecular stacking mode (J-/H-aggregation), size of the crystal, and excimeric contributions. In addition, the electrical properties of Hex-4-TFPTA were properly reevaluated by introducing different metal electrodes to ensure a small contact resistance and to prevent the probable mobility overestimation [24,25] of organic field-effect transistors (OFETs) by their nonlinear transfer curve.Subsequently, Hex-4-TFPTA single-layered OLET devices were fabricated and characterized in terms of their charge transport and electroluminescence (EL). Finally, micropatterned pixels of the Hex-4-TFPTA OLET were fabricated by using a soft-lithographic technique called "patterned taping" [26] and employing a semitransparent electrode. [27,28] This report is actually the first example of pixelated emission from an OLET which was demonstrated by patterning the organic layer with a lithographic technique.The Hex-4-TFPTA crystalline solid states (Figure 1a-c) showed a deep red (DR) emission of which the peak wavelengths were 683 and 631 nm (Figure 1d) for the single crystal A pure red-emitting organic light-emitting transistor (OLET) is successfully fabricated using a π-extended dicyanodistyrylbenzene-type organic semiconductor material (Hex-4-TFPTA), which shows outstanding charge transport and solid-state luminescence at the same time. Based on the structural (X-ray) and photophysical analyses, it is found that the appropriate molecular stacking and highly allowed S 1 →S 0 transition of Hex-4-TFPTA created the ambidextrous balance between el...
