Novel Layer-by-layer Complexation Technique and Properties of the Fabricated Films Jaehyun Kim, Hsing-Chia Wang, Jayant Kumar, † and Sukant K. Tripathy* Center for Advanced Materials, Departments of Chemistry and Physics, University of Massachusetts, Lowell, Massachusetts, 01854 Kethinni G. Chittibabu and Mario J. Cazeca Molecular Technologies, Inc., Westford, Massachusetts, 01886 Woohong Kim Samsung Central Research Institute of Chemical Technology, Taejeon, 305-380, South Korea Received April 8, 1999 A novel layer-by-layer complex-fabrication technique for multilayer film assembly was developed by alternatively dipping desired substrates in macromolecular ligands and Eu 3+ ion solutions. A water-soluble, luminescent thiophene-based polymer, viz., poly[2,5-(3- carboxymethyl urethanyl ethyl) thiophene] (H-PURET), was prepared and used as the macromolecular ligand. Multilayer deposition was monitored using UV-visible spectroscopy by following the absorbance increase due to the deposition of the polymer layer. Multilayer thin films were characterized using infrared and fluorescence spectroscopic techniques, transmission electron microscopy (TEM), and energy-dispersive X-ray spectrometry (EDXS). The conductivity and the electroluminescence properties of the conjugated polymer-Eu 3+ complex multilayer films were also measured. The observed electroluminescence intensity of conjugated polymer-metal complex multilayer film was about 2 times higher than for the conjugated polymer by itself. The approach is general in that other macroligands and metal ions may be employed. 1. Introduction During the past several years, layer-by-layer deposi- tion techniques have attracted a great deal of attention as effective methods to prepare uniform, ultrathin structures. Since composition, thickness, and orientation of each layer can be manipulated using this technique, it provides a route for the formation of various ordered structures at the molecular level. 1-5 This manipulation at the molecular level offers many potential advantages in device applications, including use as active compo- nents in nonlinear optical devices, 2,6 employing materi- als with selective chemical responses for sensor appli- cations, 5 stable charge-separated assemblies for photo- voltaics, 7 and light-emitting diodes. 8 Since the first report of Decher and co-workers, 9 there have been numerous reports on the layer-by-layer deposition techniques based on the electrostatic attrac- tion between polycations and polyanions. Other types of intermolecular interactions, including hydrogen bond- ing, 10,11 covalent bonding, 6,12-16 and charge-transfer interactions, 17 have also been exploited for fabricating multilayer films. Coordination bonding is another type of intermolecular interaction that has been used to fabricate self-assembled monolayer and multilayer films of monomeric, multidentate ligands with transition metal ions. 18-24 Monolayer films of thiols-copper (II) and * Author for correspondence. † Department of Physics. (1) Tovar, G.; Paul, S.; Knoll, W.; Prucker, O.; Ru ¨ he, J. Supramo- lecular Sci. 1995, 2, 89. (2) Piscevic, D.; Knoll, W.; Tarlov, M. J. Supramolecular Sci. 1995, 2, 99. (3) Katz, H. E.; Sheller, G.; Putvinski, T. M.; Shilling, M. L.; Wilson, W. L.; Chidsey, C. E. D. Science 1991, 254, 1485. (4) (a) Vermeulen, L. A.; Snover, J. L.; Sapochak, L. S.; Thompson, M. E. J. Am. Chem. Soc. 1993, 115, 11767. (b) Vermeulen, L. A.; Pattanayak, J.; Fisher, T.; Hansford, M.; Burgmeyer, S. J. Mater. Res. Soc. Symp. Proc. 1996, 431, 271. (5) Rubinstein, I.; Steinberg, S.; Tor, Y.; Shanzer, A.; Sagiv, J. Nature 1988, 332, 426. (6) Li, D.-Q.; Ratner, M. A.; Marks, T. J.; Zhang, C. H.; Yang, J.; Wang, G. K. J. Am. Chem. Soc. 1990, 112, 7389. (7) Vermeulen, L. A.; Thompson, M. E. Nature 1992, 358, 656. (8) Fou, A. C.; Onisuka, O.; Ferreira, M.; Rubner, M. F. J. Appl. Phys. 1996, 79, 7501. (9) Decher, G.; Hong, J. D.; Schmitt, J. Thin Solid Films 1992, 210/ 211, 831. (10) Sun, L.; Kepley, L. J.; Crooks, R. M. Langmuir 1992, 8, 2101. (11) Stockton, W. B.; Rubner, M. F. Macromolecules 1997, 30, 2717. (12) Maoz, R.; Sagiv, J. J. Colloid Interface Sci. 1984, 100, 465. (13) Wasserman, S. R.; Tao, Y. T.; Whitesides, G. M. Langmuir 1989, 5, 1074. (14) Mormann, W.; Schmalz, K. Macromolecules 1994, 27, 7115. (15) Xing, L.; Mattice, W. L. Langmuir 1996, 12, 3024. (16) Sekkat, Z.; Wood, J.; Grrets, Y.; Knoll, W. Langmuir 1996, 12, 2976. (17) Shimazaki, Y.; Mitsuish, M.; Ito, S.; Yamamoto, M. Langmuir 1997, 13, 1385. (18) Evans, S. D.; Ulman, A.; Goppert-Berarducci, K. E.; Gerenser, L. I. J. Am. Chem. Soc. 1991, 113, 5866. (19) Li, D.; Smith, D. C.; Swanson, B. I.; Farr, J. D.; Paffet, M. T.; Hawley, M. E. Chem. Mater. 1992, 4, 1047. (20) Bell, C. M.; Arendt, M. F.; Gomez, L.; Schmehl, R. H.; Mallouk, T. E. J. Am. Chem. Soc. 1994, 116, 8374. (21) Liu, M.; Kira, A.; Nakahara, H. Langmuir 1997, 13, 779. (22) Ansell, M. A.; Zeppenfeld, A. C.; Yoshimoto, K.; Cogan, E. B.; Page, C. J. Chem. Mater. 1996, 8, 591. 2250 Chem. Mater. 1999, 11, 2250-2256 10.1021/cm990193t CCC: $18.00 © 1999 American Chemical Society Published on Web 07/14/1999