Synthesis and characterization of novel cross-linking light-emitting polyfluorene derivatives

Abstract

Polyfluorene derivative with amine side groups, namely, P1 was synthesized by the palladium-catalyzed coupling reaction of 2,5-dibromoaniline with 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9′-dioctylfluorene. Cross-linked polyazomethine P1-TPD (cross-linked polymer, P1/ terephthalic aldehyde) was obtained by the reaction of P1 with terephthalic aldehyde. Given that replacement of the phenylene ring by a thiophene ring can improve π-electron delocalization, we also synthesized P1-TPCD (cross-linked polymer, P1/ 2,5-thiophenedicarboxaldehyde) whose cross-linking bridge was a thiophene ring. The ultraviolet–visible spectra of P1-TPD showed that there was a little hypsochromic shift to its pristine polymer P1, however, the maximum emission wavelength was changed to the second peak in the photoluminescence spectra. Besides, the band gap energy (E _g) of P1-TPD was a little narrower than that of P1. The maximum absorption wavelength and the maximum emission wavelength of P1-TPCD was almost the same with P1, but its E _g was narrower than P1 and P1-TPD. Most notably, azomethine-linked P1-TPD and P1-TPCD were fluorescent with measured fluorescent quantum yields of 22% and 44%.