Two photoluminescent polymers based on fluorene and 2,4,6-triphenyl pyridine: Synthesis and electroluminescence

Two fluorene and triphenyl pyridine-based linear and dendronized copolymers, P1 and P2, were synthesized and fully characterized by ¹H-NMR, ¹³C-NMR, and matrix assistant laser desorption/ionization time-of-flight mass spectra, respectively. The absorption, photoluminescence (PL) behavior, and energy band gaps of P1 and P2 relative to those of polyfluorene end-capped with benzene (P0) were examined through UV-vis, photoluminescent spectra, and cyclic voltammetry. The UV-vis absorption and PL emission behavior of P0 and P1 were hardly affected by molecular architecture, while those of P2 were strongly correlated with the dendronized molecular frameworks. Cyclic voltammetry studies indicated the lower highest occupied molecular orbital energy level and wider band gap of P2 thin solid film relative to those of P0 and P1. The new polymers were thermally stable up to 410°C. The better luminance and external quantum efficiencies of P1 relative to those of P0 in polymer light-emitting diode (PLED) applications are due to improved electron injection, charge trapping and recombination at the pyridine sites. Through the experiments, it is found that the triphenyl pyridyl segments and excimers-formation make pronounced contribution to long wavelength emission in P1-based blue light-emitting materials, and the analogous materials containing 2,4,6-triphenyl pyridyl unit of P1 constitute highly attractive materials for white PLED applications.