Molecular design of fluorene-based polymers and oligomers for organic light-emitting diodes

Three kinds of well-defined monodisperse oligo(9.9-bis-n-hexylfluorene-2,7-diyl)s (n = 2, 3, 4) were prepared by repetitive divergent synthesis starting from 2-bromo-9,9-bis-n-hexylfluorene, 2,7-dibromo-9,9-bis-n-hexylfluorene, and 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-bis-n-hexylfluorene and using Pd(0)-catalyzed cross-coupling reaction. These oligofluorenes were fully characterized with H-1- and C-13-NMR, and FAB-MS measurement. In both solution and film, absorption and photoluminescence (PL) spectra of these oligofluorenes showed red shift as the rod length increases. In the case of PL spectrum of the tetramer (5), it showed two characteristic peaks at 422 and 438 nm in film. The PL intensity at 422 nm can be explained in terms of pi-pi stacking interaction between fluorene rings in the tetramer (5). (C) 2000 Published by Elsevier Science S.A. All rights reserved.