Synthesis and characterization of carbazole dendronized coumarin derivatives as solution-processed non-doped emitters and hole-transporters for electroluminescent devices

Abstract

A series of carbazole dendronized coumarin derivatives (CTmGn, m = 0–2, n = 1–3) containing oligothiophenyl coumarins as cores and carbazole dendrons up to the third generation as substituents were synthesized and characterized. Their optical, thermal, electrochemical, and electroluminescent properties as non-doped solution-processed light-emitters and hole-transporters for OLEDs were investigated. They exhibited a bright light blue to yellow fluorescence with solution fluorescence quantum yields (Φ_F) of about 0.10–0.40 and morphologically stable amorphous thin films with glass transition temperatures as high as 285 °C. As emissive layers, solution-processed OLEDs with the structure of ITO/PEDOT:PSS/CTmGn/BCP/LiF:Al emitted light blue to yellow colours with a maximum luminance efficiency as high as 7.92 cd A⁻¹ and a low turn-on voltage of 3.6 V. As hole-transporting layers, solution-processed OLEDs with the structure of ITO/PEDOT:PSS/CGn/Alq3/LiF:Al showed a bright green emission (λ_EL = 518 nm, CIE = 0.27, 0.53) with a maximum luminance efficiency as high as 6.54 cd A⁻¹ and a low turn-on voltage of 2.5 V.