Blue electroluminescent polymers with dopant–host systems and molecular dispersion features: polyfluorene as the deep blue host and 1,8-naphthalimide derivative units as the light blue dopants

Abstract

We developed a series of highly efficient blue electroluminescent polymers with dopant–host systems and molecular dispersion features by selecting 1,8-naphthalimide derivatives as the light blue emissive dopant units, choosing polyfluorene as the deep blue emissive polymer host and covalently attaching the dopant units to the side chain of the polymer host. The polymers' EL spectra exhibited both deep blue emission from the polymer host and light blue emission from the dopant units because of the energy transfer and charge trapping from the polymer host to the dopant units. By modifying the chemical structures of the dopant units, we controlled the energy transfer and charge trapping from the polymer host to the dopant units and consequently tuned the emission colors of the resulting polymers. Thermally annealed single-layer devices (ITO/PEDOT/polymer/Ca/Al) based on these polymers emitted deep blue light with a luminous efficiency of 2.89 cd A⁻¹, a power efficiency of 2.01 lm W⁻¹ and CIE coordinates (0.16, 0.17), or emitted sky-blue light with a luminous efficiency of 6.84 cd A⁻¹, a power efficiency of 4.28 lm W⁻¹ and CIE coordinates (0.15, 0.22). Their excellent EL performances were due to the energy transfer and charge trapping from the polymer host to the highly fluorescent dopant units.