Multifunctional Hyperbranched Oligo(fluorene vinylene) Containing Pendant Crown Ether: Synthesis, Chemosensory, and Electroluminescent Properties

Abstract

Multifunctional hyperbranched oligo(fluorene vinylene) (HOFC) containing pendant crown ether was synthesized from 2,4,7-trivinyl-9,9-dihexylfluorene and 2,7-dibromo-9-(15-crown-4)-9H-fluorene via Heck coupling reaction. Their chemosensory, photophysical, and electrochemical properties were investigated and compared with those of linear oligo(fluorene vinylene) (LOFC) to elucidate the effect of hyperbranched structure. Both HOFC and LOFC exhibit selective fluorescence quenching toward Fe3+ and Ru3+, with the Stern−Volmer coefficients (Ksv) to Ru3+ being 2 × 104 and 1.9 × 104 M−1, respectively. The stability constant (Ks) of forming complex with Ru3+ are 3.1 × 103 and 5 × 103 M−1 for HOFC and LOFC. Moreover, hyperbranched HOFC reveals homogeneous film morphology due to its hyperbranched structure. After thermal treatment, the cured polymer (HFC) shows better thermal stability because of higher cross-linked density. Double-layer electroluminescent devices (ITO/PEDOT:PSS/HFC or LFC/Ca/Al), using thermally cross-linked HFC or LFC as emitting layer, were fabricated to investigate their optoelectronic properties. The turn-on voltage, maximum luminance and maximum luminance efficiency of HFC device (4.1 V, 7132 cd/m2 and 1.3 cd/A) are superior to those of LFC device (6.2 V, 331 cd/m2, 0.22 cd/A), which have been attributed to its homogeneous film morphology. Current results indicate that the hyperbranched oligo(fluorene vinylene) is a promising material for chemosensors and electroluminescent devices.