Tunable Organophosphorus Dopants for Bright White Organic Light-Emitting Diodes with Simple Structures By Omrane Fadhel, Michael Gras, Noella Lemaitre, * Vale ´rie Deborde, Muriel Hissler, * Bernard Geffroy, * and Re ´gis Re ´au* Research on the development of new emissive p-conjugated oligomers and polymers for different technological applications such as organic light-emitting diodes (OLEDs), including white organic light-emitting diodes (WOLEDs), is very active. [1] In this area, a particularly powerful strategy that has evolved for diversifying the properties and expanding the function of classical p-conjugated systems involves the incorporation of reactive heteroatoms into the conjugated chain. [2] Building blocks that are particularly amenable to this approach are phospholes, since they possess nucleophilic phosphorus centers, thus allowing direct access to a range of novel p-conjugated systems with diverse optical and electrochemical properties. [3] For example, chemical modification of the P atom of the mixed phosphole–thiophene oligomer 2a affords derivatives 3a and 4a (Scheme 1), which exhibit improved thermal stability, red-shifted photoluminescence (PL) emissions, and higher reduction/ oxidation potentials than the unmodified phospholes. [3e] The nature of the P moiety affects the bulk molecular environment and, hence, the photophysical behaviour, of these chromophores in the solid state. For example, the thiooxophosphole derivative 4a (Scheme 1) behaves as an isolated luminophore, whereas the gold(I) phosphole complex 3a forms aggregates, leading to a broad emission spectrum from both the monomer and aggregate states. [3b,e] This difference in behavior clearly highlights how the presence of reactive P atoms provides a powerful means of varying and controlling the electronic properties of p-conjugated materials at the molecular level. Exploiting this unique way of tuning the properties of p-conjugated systems readily allows for the optimization of their optoelectronic functions, something that has lead to phospholes 3a and 4a becoming the first organopho- sphorus derivatives to be used as emissive components in the fabrication of OLEDs. [3b,e] Finally, two other key advantages of phosphole-modified oligothiophenes should be noted, namely that i) they are stable in air and ii) they can be readily produced on a gram scale using zirconium-promoted coupling of diynes followed by Zr/P exchange (Scheme 1). [3a–e] Taking all these factors into account, it was tempting to further exploit the possibility of fine-tuning the optical and electro- chemical properties of phosphole-based conjugated systems, through manipulation of their chemical structure in order to tailor WOLEDs. WOLEDs have attracted much attention due to their potential for use in a variety of applications, such as flat- panel display backlights and solid-state lighting. [1g–j] Sources that produce high-quality white-light illumination are characterized by Commission Internationale de l’Eclairage (CIE) chromaticity coordinates close to (0.313,0.329), namely those of the CIE standard illuminant D65. [1g] Due to the limited spectral bandwidth achievable with emissive organic molecules (typically only about one third of the visible spectrum), it is not possible for a single molecular species to provide white-light emission. Thus, white light is generally obtained by mixing materials that give rise to either the three primary colors (red, green, and blue) [1b,c,g–j] or two complementary colors [1g,4] (cyan and red, for example) in the same OLED device. Several WOLEDs architectures can be considered for combin- ing the emissions from multiple emitters. [1g] These include multilayer devices fabricated by consecutive evaporation of organic compounds or dopants that emit different colors, [1g,5] devices in which polymer blends or multiply doped single layers are used, [6] or devices with one emissive layer that exhibits a microcavity effect. [7] WOLEDs have also been obtained using blue-light-emitting luminophores, which form excimers that emit at longer wavelengths. [8] However, each of these approaches suffers from some drawbacks. For example, the use of multiple layers often causes the need for high driving voltages and, consequently, low efficiencies. It should also be noted that problems such as color dependence on the driving voltage exist with blended polymers or multiple dopants. [9] Another serious drawback in multiply doped systems is that if one of the dopants degrades more rapidly than the others, the color of the device will change over time. Consequently, it should be clear that reducing the number of dopants and structural heterogeneities inherent in the multiple-color band architectures is of great interest. [4] In this paper, the optimization of mixed phosphole–thiophene con- jugated molecules as dopants for a blue-light-emitting host and their use in the construction of efficient WOLEDs with simple structures is reported. These devices exhibit high brightness and, COMMUNICATION www.advmat.de [*] Dr. N. Lemaitre CEA INES/DRT/LITEN/DTS/Laboratoire Composants Solaires Savoie Technolac, BP322, 73377 Le Bourget du Lac (France) E-mail: noella.lemaitre@cea.fr Prof. M. Hissler, Prof. R. Re ´au, Dr. O. Fadhel, M. Gras, V. Deborde Sciences Chimiques de Rennes UMR6226 CNRS-Universite ´ de Rennes 1 Campus de Beaulieu, 35042 Rennes Cedex (France) E-mail: mhissler@univ-rennes1.fr; rreau@univ-rennes1.fr B. Geffroy CEA Saclay/DRT/LITEN/DTNM/Laboratoire Composants Hybrides 91191 Gif-sur-Yvette Cedex (France) E-mail: bernard.geffray@polytechnique.edu DOI: 10.1002/adma.200801913 Adv. Mater. 2009, 21, 1261–1265 ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1261