DOI: 10.1002/adma.200602002 Bicolor Pixels from a Single Active Molecular Material by Surface-Tension-Driven Deposition** By Ilenia Viola,* Fabio Della Sala, Manuel Piacenza, Laura Favaretto, Massimo Gazzano, Marco Anni, Giovanna Barbarella, Roberto Cingolani, and Giuseppe Gigli* Recently, the supramolecular organization of conjugated molecular systems has received much attention because of the increased application of conjugated materials in complex elec- tronics and optoelectronics devices, such as active matrix dis- plays, [1] plastic microelectronics circuits, [2] and large-area pan- els for lighting, [3–5] requiring high-resolution molecular patterns. The advantages of organic materials as active com- pounds for these applications lie in the low costs and ease of fabrication, and in the possibility to fine-tune the desired functional properties by minor structural modifications or conformational changes. [6–10] On the other hand, the realiza- tion of integrated devices with (sub)micrometer sizes requires the development of advanced lithography techniques suitable for soft materials; the lack of which is often a strong limitation to the use of such materials in practical applications. Several methods for controlled molecular patterning are currently under investigation, based on either top-down (soft embossing and nanoimprinting [11] ) or bottom-up lithography (spinodal dewetting, [12] micro-contact printing, [13] and surface- tension-driven (STD) techniques [14,15] ). The common goal of these approaches is to dynamically adjust the behavior of mo- lecular solutions at the solid/liquid interface. So far, bottom- up lithography looks more promising for patterning conjugat- ed macromolecules. In fact, it allows self-assembly, self-orga- nization, spontaneous aggregation, and recognition capability under suitable modulation by either external or internal stim- uli, such as surface-tension gradients, solute diffusion, and molecular weight. [16,17] Unlike the top-down approach, the bottom-up method is based on the reproduction of a molecu- lar pattern at a characteristic length scale, [18] usually without the need for expensive experimental setups, high-temperature processes, or oxygen exposure, which could damage and alter the physical–chemical properties of the materials. [19] Among the bottom-up techniques, dewetting lithography techniques are attracting growing interest owing to the simplicity of the technological processes, the possibility to realize different pat- tern resolutions, and the capability to combine and exploit pe- culiar characteristics of molecular materials, such as self-orga- nization, with dynamical properties of the fluid. Several works on controlled self-organization during dewet- ting for engineering of nano- and micrometer patterns in thin liquid films have been reported. [17,20,21] In a recent work, in particular, we demonstrated a lithography technique for the fabrication of monochromatic organic light-emitting diode (OLED) pixel arrays, [14] in which organic materials are pat- terned with defined features by exploiting the instability phe- nomena affecting a liquid thin film on a nonwetting surface. [22] Such a method allows us to exploit the organizational capabil- ity of molecules, driven by external stimuli, to define well-re- solved patterns on large-area substrates. However, all of the approaches for patterning organic mate- rials in complex structures reported thus far do not allow si- multaneous control over the supramolecular organization and the conformation of single molecules, thus strongly limiting the possibility to fully exploit the enormous potential of or- ganic conjugated materials for fine-tuning their electro-optical properties. Such a limitation necessitates the use of more than one active compound with different chemical/physical proper- ties to introduce different functionalities in a device, such as emission at different wavelengths in multicolor displays [23–26] or bipolar conductivity. [27] In this Communication we report on the realization of a bicolor organic micropixel array by a bottom-up dewetting process, exploiting for the first time the conformational flex- ibility of an oligothiophene derivative, 2,6-bis-(5′-hexyl- [2,2′]bithiophen-5-yl)-3,5-dimethyl-dithieno[3,2-b;2′,3′-d]thio- phene (DTT7Me) (Fig. 1). [28] The simultaneous control over both the molecular conformation and the supramolecular pat- tern of DTT7Me allowed us to vary its emitting properties at mi- crometer resolution, thereby realizing a well-defined pattern of red- and green-emitting pixels from a single molecular material. The lithographic approach, that is, STD lithography, [14] is il- lustrated in Figure 2. STD lithography allows us to control pattern replication by introducing a geometric confinement COMMUNICATION Adv. Mater. 2007, 19, 1597–1602 © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1597 – [*] Dr. I. Viola, Prof. G. Gigli, Dr. F. Della Sala, Dr. M. Piacenza, Dr. M. Anni, Prof. R. Cingolani National Nanotechnology Laboratory (NNL) of INFM-CNR Distretto tecnologico ISUFI via Arnesano, 73100 Lecce (Italy) and Dipartimento di Ingegneria Università degli Studi di Lecce via Monteroni, 73100 Lecce (Italy) E-mail: ilenia.viola@unile.it; giuseppe.gigli@unile.it L. Favaretto,Dr. M. Gazzano, Dr. G. Barbarella Istituto per la Sintesi Organica e la Fotoreattività (ISOF) Area di Ricerca CNR via Gobetti, 101, 40129 Bologna (Italy) [**] The authors gratefully acknowledge P. Pompa, S. Lattante, L. Martiradonna, and A. Rizzo (CNR-NNL Lecce, Italy) for PL mea- surements and useful discussions. This work has been partially funded by MIUR (FIRB RBNE03S7XZ_005 “SYNERGY”). Supporting Information is available online from Wiley InterScience or from the author.