Novel efficient green electroluminescent conjugated polymers based on fluorene and triarylpyrazoline for light-emitting diodes

Abstract

A series of novel light-emitting conjugated polymers based on fluorene and triarylpyrazoline were synthesized in good yields through Suzuki coupling reactions. The resulting polymers were characterized by NMR, FT-IR, elemental analysis, DSC, TGA and GPC. These polymers possess excellent thermal stability with glass transition temperatures (T_g) of 80–162 °C and onset decomposition temperatures (T_d) of 376–387 °C. Cyclic voltammetry studies revealed that these polymers have good hole and electron transporting properties with LUMO energy levels of −2.97 to −2.98 eV and HOMO energy levels of −5.71 to −5.81 eV. All the polymers emit green fluorescence with very high photoluminescence (PL) quantum yields of 45–59%. Polymer light-emitting diodes (PLEDs) with the configuration ITO/PEDOT/polymer/Ba/Al were fabricated. All these devices showed bright green emission peaking at 494–500 nm with high maximum external quantum efficiencies of 0.6–2.53% and low turn-on bias voltages. The good light-emitting properties indicate that these polymers are new and promising candidates for electroluminescent materials that can be used to fabricate efficient polymer light-emitting diodes.