Synthesis of New Conjugated Polyfluorene Derivatives Bearing Triphenylamine Moiety through a Vinylene Bridge and Their Stable Blue Electroluminescence

Abstract

Two new conjugated polyfluorene derivatives bearing triphenylamine moiety through a vinylene bridge, PDPF and PBPF, have been successfully synthesized according to the Suzuki coupling method. The structures and properties of the monomers and the resulting conjugated polymers were characterized by using 1H NMR, 13C NMR, FT-IR, elemental analysis, GPC, TGA, DSC, UV−vis absorption spectroscopy, photoluminescence (PL) spectroscopy, and cyclic voltammetry (CV). The obtained polymers possess excellent solubility in common organic solvents, good thermal stability with 5% weight loss temperature of 415−448 °C, and relatively high glass transition temperature (Tg) at about 91−159 °C. The weight-average molecular weight (Mw) of PDPF and PBPF were 5.79 × 104 and 1.68 × 104 with the polydispersity index (PDI) of 2.75 and 2.69, respectively. The two-dimensional conjugated system of PFs can effectively suppress π-stacking/aggregation, improve hole injection, and facilitate intramolecular energy transfer. Single-layer PLED devices using PDPF and PBPF with the configuration of ITO/PEDOT:PSS/polymer/Ca/Al were fabricated. The maximum electroluminescence (EL) efficiency of the single-layer PLEDs based on PDPF and PBPF was about 0.19 and 0.51 cd/A, respectively. Meanwhile, the PLEDs with the optimized configuration of ITO/PEDOT:PSS/polymer/Alq3/Al showed greatly improved performance. The double-layer device based on PDPF emitted very stable greenish blue light with a low turn-on voltage of 3.6 V and showed the maximum luminance of about 2930 cd/m2 at 21.0 V. The maximum EL efficiency of the double-layer PLEDs based on PDPF and PBPF was both about 2.08 cd/A.