Hyperbranched blue-light-emitting alternating copolymers of tetrabromoarylmethane/silane and 9,9-dihexylfluorene-2,7-diboronic acid

The first soluble hyperbranched tetrahedral polymers were prepared by Suzuki coupling polycondensation reaction between tetrabromoarylmethane/silane and 9,9-dihexylfluorene-2,7-diboronic acid at low concentrations. The polymers exhibited high thermal stability with their decomposition temperatures (T(d)s) in the range 352-449 degreesC. The polymers emitted blue light highly efficiently in both solution and the solid state. The photoluminescence quantum efficiencies of the polymers in THF solution were in the range 73-99%, and those in thin films were 38-82%. The film PL spectra of the polymers exhibited similar spectral patterns to those determined in solutions, with 1-8 nm red shift in their emission maxima and 0-8 mn increase in their full width at half-maximum (fwhm) values being observed. No long wavelength excimer-like emissions at 500-600 nm, which were typical for polyfluorenes due to their self-aggregation in the solid state, were observed. Thus, the polymers were less prone to self-aggregation in the solid state due to their hyperbranched structures. A double-layer polymer light-emitting diode (PLED) device with a configuration of ITO/PEDOT/polymer/LiF/Ca/Ag was fabricated. The device showed bright blue emission peaking at 415 mn with an external quantum efficiency of 0.6% and a turn voltage at 6.0 V. The synthetic simplicity, good solubility and solution processability, high PL quantum efficiencies in solution and the solid state, and nonaggregating property in the solid state would make the present polymers a novel class of blue emitters.