Communications 1452 Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim,1998 0935-9648/98/1712-1452 $ 17.50+.50/0 Adv. Mater. 1998, 10, No. 17 [8] M. Aliouat, L. Mazo, G. Desgardin, B. Raveau, J. Am. Ceram. Soc. 1990, 73, 2515. [9] G. Roussy, A. Bennani, J. M. Thiebaut, J. Appl. Phys. 1987, 62, 1167. [10] D. L. Johnson, D. J. Skamser,M. S. Spotz, in Microwaves: Theory and Application in Materials Processing II (Eds: D.E. Clark, W. R. Tinga, J. R. Laia, Jr) (Ceram. Trans. 36), American Ceramic Society, Wester- ville, OH, 1993, 133. [11] B. Q. Tian, W. R. Tinga, in Microwaves: Theory and Application in Materials Processing (Eds: D.E. Clark, F. D. Gac, W. H. Sutton) (Ce- ram. Trans. 21), American Ceramic Society, Westerville, OH, 1991, 647. [12] J. Asmussen, Jr., B. Manring, R. Frintz, M. Siegel, in Microwaves: Theory and Application in Materials Processing (Eds: D. E. Clark, F. D. Gac, W. H. Sutton) (Ceram. Trans. 21), American Ceramic So- ciety, Westerville, OH, 1991, 655. [13] M.A. Janney, C. L. Calhoun, H. D. Kimrey, in Microwaves: Theory and Application in Materials Processing (Eds: D.E. Clark, F. D. Gac, W. H. Sutton) (Ceram. Trans. 21), American Ceramic Society, Wester- ville, OH, 1991, 311. [14] A. S. DØ, I. Ahmad, E. D. Whitney, D.E. Clark, in Microwaves: Theo- ry and Application in Materials Processing (Eds: D.E. Clark, F. D. Gac, W. H. Sutton) (Ceram. Trans. 21), American Ceramic Society, Westerville, OH, 1991, 319. [15] P. Komarenko, D.E. Clark, in Microwaves: Theory and Application in Materials Processing II (Eds: D.E. Clark, W. R. Tinga, J. R. Laia, Jr) (Ceram. Trans. 36), American Ceramic Society, Westerville, OH, 1993, 351. [16] A. Cherradi, Thesis, 1994, University of Caen, France. [17] A. Cherradi, G. Desgardin, J. Provost, B. Raveau, Ann. Chim. Fr. 1996, 21, 103. [18] A. Cherradi, G. Desgardin, L. Mazo, B. Raveau, Supercond. Sci. Technol. 1993, 6, 799. [19] A. Cherradi, G. Desgardin, B. Raveau, Physica C 1994, 3409, 235. [20] S. Marinel, G. Desgardin, J. Provost, B. Raveau, Mater. Sci. Eng. 1998, B52, 47. [21] S. Marinel, J. Provost, G. Desgardin, Physica C 1998, 294, 129. [22] S. Marinel, I. Monot, J. Provost, G. Desgardin, Supercond. Sci. Tech- nol. 1998, 11, 563. [23] A. Cherradi, S.Marinel, Z. Lakhdari, J. Provost, G. Desgardin, B. Ra- veau, Microwave J., 1998, 41, 84. Thin-Film Light-Emitting Devices Based on Sequentially Adsorbed Multilayers of Water-Soluble Poly(p-phenylene)s** By Jeff W. Baur, Seungho Kim, Peter B. Balanda, John R. Reynolds , and Michael F. Rubner* The discovery that conjugated polymers can be utilized as efficient emitters in thin-film electroluminescent devices has created a flurry of research effort over the past few years. [1] Current efforts have produced devices with high quantum efficiencies (1±4 %) and brightness, respectable lifetimes, and the full spectrum of colors, including white light. [2] While poly(phenylenevinylene) (PPV) and its de- rivatives are the most well-studied conjugated polymers for use in light-emitting devices; poly(p-phenylene) (PPP) based molecules have also received attention as emitting materials. [3±9] Due to its large bandgap, PPP has the desired quality of emitting in the blue region of the spectrum, which is not easily achieved with other conjugated poly- mers. However, because of the poor processibility of PPP in its underivatized form, previous workers have synthe- sized PPP ladder±type polymers with chemical bridging units between phenylene rings [10] as well as ring-func- tionalized PPPs [11] to promote solubility. The planar ladder- type structures often have to be carefully manipulated to avoid the formation of molecular aggregates, which can lead to a red-shifted component of the photolumines- cence. [12] Recently, one of us synthesized polyanionic and polycationic versions of PPP that are soluble in water, do not contain bridging units, and do not red-shift from their blue photoluminescence. [13±15] Because of their charged na- ture and related water solubility, these molecules also have the added advantage that they can be processed at the mo- lecular level by the extremely versatile layer-by-layer se- quential adsorption technique. The layer-by-layer sequential adsorption technique has been shown to produce uniform thin films with molecular- level thickness control. [16] This technique is based on the al- ternating adsorption of a positively charged molecule and a negatively charged molecule to form a bilayer building block. By repeating this adsorption cycle, a film can be made with a thickness that is determined by the thickness of the individual bilayers (typically 10±60  for polyelec- trolytes) and the total number of bilayers adsorbed. Furthermore, by adjusting simple solution parameters such as the amount of added salt [17,18] and the solution pH, [19] the thickness, composition and layer interpenetration of the bilayer building block can be systematically varied. Be- cause of the technique's flexibility and ease of use, multi- layer sequential adsorption has been successfully carried out with a variety of charged molecules, both organic and inorganic. [20] Within our research group, the ability to readily con- struct complex multilayer heterostructures and control electrode interfaces via the sequential adsorption tech- nique, has been exploited with films containing PPV to both optimize and understand the operation of light-emit- ting thin-film devices. [21,22] More recent work has focused on an optimization of the device performance of PPV and polymeric tris(bipyridyl) ruthenium(II)±containing multi- layers through manipulation of the bilayer composition. Currently, brightness levels of 1000 cd/m 2 have been achieved for sequentially adsorbed films of PPV. [23] Re- markably, these high brightness devices were created by using a relatively high work function metal, aluminum, as ± [*] Prof. M. F. Rubner Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge, MA 02145 (USA) Dr. J. W. Baur AFRL/MLBP Polymer Research Branch Wright-Patterson Air Force Base, OH 45433 (USA) Dr. S. Kim, Dr. P. B. Balanda, Dr. J. R. Reynolds Department of Chemistry Center for Macromolecular Science and Engineering University of Florida Gainesville, FL 32611 (USA) [**] This work was supported in part by the National Science Foundation, the MRSEC Program of the National Science Foundation under Award No. DMR-9400334, and the Air Force Office of Scientific Re- search (F49620-96-1-0067 and F49620-97-1-0232). The authors thank Michael Durstock, Mary Hamilton, Erika Abbas, and Jason Pinto of MIT for their contributions to this work.