n-Type Conjugated Dendrimers: Convergent Synthesis, Photophysics, Electroluminescence, and Use as Electron-Transport Materials for Light-Emitting Diodes

Three new electron-acceptor and light-emitting conjugated dendrimers, [G1-4Q], [G1-6Q], and [G2-12Q], based on a benzene core, poly(phenylenevinylene) dendrons, and diphenylquinoline peripheral groups have been synthesized, characterized, and used as emissive and electron-transport materials in efficient light-emitting diodes. All three dendrimers emit blue light (λmax = 414 nm) in solution with high fluorescence quantum yields in the 0.69−0.87 range and fluorescence lifetimes of 1.4−1.6 ns. In thin films the dendrimers emit yellow light with poor fluorescence efficiency, suggesting aggregation and excimer formation in the solid state. The dendrimers showed quasi-reversible electrochemical reduction with a formal potential of −2.0 V (vs SCE) and derived LUMO levels of 2.5−2.6 eV, implying that injected electrons are localized in the periphery of the dendrimers. As the emissive materials in light-emitting diodes, the dendrimers showed yellow electroluminescence the brightness and efficiency of which increa...