Ortho-Substituent Effect on Fluorescence and Electroluminescence of Arylamino-Substituted Coumarin and Stilbene Chao-Tsen Chen,* ,² Chih-Long Chiang, ‡ Yu-Chung Lin, ² Li-Hsin Chan, ‡ Chien-Huang Huang, ² Zong-Wei Tsai, ‡ and Chin-Ti Chen* ,‡ Department of Chemistry, National Taiwan UniVersity, Taipei, Taiwan 106, R.O.C., and Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, R.O.C. chenct@ntu.edu.tw; cchen@chem.sinica.edu.tw Received February 17, 2003 ABSTRACT Newly synthesized arylamino-substituted coumarins and stilbenes show enhanced fluorescence emission (bluer and brighter) both in solution and in solid film. Pure blue efficient electroluminescence with 2.7% and 4.1% of external quantum efficiency can be achieved with MeC1 and XTPS, respectively. Many fluorescent organic compounds exhibit high fluores- cent quantum yields (Φ f ) in solution but suffer from “concentration quenching”, showing little or no fluorescence at highly concentrated solution or in the solid state. 1 The “concentration quenching” causes emission band broadening and a bathochromic shift. From a structural point of view, incorporation of bulky as well as nonplanar molecular moieties should prevent orderly molecular packing, and may alleviate the fluorescence quenching resulting from molecular interactions. 2 Structural moieties, such as bulky tert-butyl, isopropyl, and tetraphenylsilyl, 3 or sterically crowded tetra- or pentaphenylphenyl polycycle, 4 provide satisfactory effects on inhibiting molecular aggregation in the solid state. Molecules with a starburst or dendrimer shape show the effect as well. 5 Nonplanar triarylamine structural moieties have been studied in depth, 6 and have been found to be ² Department of Chemistry, National Taiwan University. ‡ Institute of Chemistry, Academia Sinica. (1) Krasovitskii, B. M.; Bolotin, B. M. Organic Luminescent Materials; Vopian, V. G., Translator; VCH: Weinheim, Germany, 1988. (2) Valeur, B. Molecular Fluorescence; Wiley-VCH: Weinheim, Ger- many, 2002. (3) (a) Rademacher, A.; Ma¨rkle, S.; Langhals, H. Chem. Ber. 1982, 115, 2927. (b) Bohnen, A.; Koch, K.-H.; Lu¨ ttke, W.; Mu¨llen, K. Angew. Chem., Int. Ed. Engl. 1990, 29, 525. (c) Geerts, Y.; Quante, H.; Platz, H.; Mahrt, R.; Hopmeier, M.; Bo¨hm, A.; Mu¨llen, K. J. Mater. Chem. 1998, 8, 2357. (d) Chen, C. H.; Tang, C. W.; Shi, J.; Klubek, K. P. Thin Solid Films 2000, 363, 327. (e) Langhals, H.; Ismael, R.; Yu¨ru¨k, O. Tetrahedron 2000, 56, 5435. (f) Chen, C. H.; Tang, C. W. Appl. Phys. Lett. 2001, 79, 3711. (g) Chan, L.-H.; Yeh, H.-C.; Chen, C.-T. AdV. Mater. 2001, 13, 1637. (4) (a) Gensch, T.; Hofkens, J.; Heirmann, A.; Tsuda, K.; Verheijen, W.; Vosch, T.; Christ, T.; Basche´, T.; Mu¨llen, K.; De Schryver, F. C. Angew. Chem., Int. Ed. 1999, 38, 3752. (b) Satayesh, S.; Grimsdale, A. C.; Weil, T.; Enkelmann, V.; Mu¨llen, K.; Meghdadi, F.; List, E. J. W.; Leising, G. J. Am. Chem. Soc. 2001, 123, 946. (c) Pogantsch, A.; Wenzl, F. P.; List, E. J. W.; Leising, G.; Grimsdale, A. C.; Mu¨llen, K. AdV. Mater. 2002, 14, 1061. (5) (a) Bettenhausen, J.; Strohriegl, P. AdV. Mater. 1996, 8, 507. (b) Katsuma, K.; Shirota, Y. AdV. Mater. 1998, 10, 223. (c) Halim, M.; Pillow, J. N. G.; Samuel, I. D. W.; Burn, P. L. AdV. Mater. 1999, 11, 371. (d) Lupon, J. M.; Hemingway, L. R.; Samuel, I. D. W.; Burn, P. L. J. Mater. Chem. 2000, 10, 867. (e) Freeman, A. W.; Koene, S. C.; Malenfant, P. R. L.; Thompson, M. E.; Fre´chet, J. M. J. J. Am. Chem. Soc. 2000, 122, 12385. (f) Wang, S.; Oldham, W. J., Jr.; Hudack, R. A.; Bazan, G. C. J. Am. Chem. Soc. 2000, 122, 5695. (g) Yeh, H.-C.; Lee, R.-H.; Chan, L.-H.; Lin, T.-Y. J.; Chen, C.-T.; Balasubramaniam, B.; Tao, Y.-T. Chem. Mater. 2001, 13, 2788. (h) Ostrowski, J. C.; Robinson, M. R.; Heeger, A. J.; Bazan, G. C. Chem. Commun 2002, 784. ORGANIC LETTERS 2003 Vol. 5, No. 8 1261-1264 10.1021/ol034268h CCC: $25.00 © 2003 American Chemical Society Published on Web 03/27/2003