Benzo[b]carbazole and indole derivatives as emitters for non-doped deep-blue organic light emitting diodes

Derivatives of indole and benzo[b]carbazole were prepared by employing efficient regioselective acid-catalysed synthesis of 1H, 1-methyl and 1-naphthylindole with o-phthaldialdehyde. The synthesized compounds were characterized by NMR, IR and mass spectrometries. They form molecular glasses with glass transition temperatures ranging from 86 to 116 °C. Naphthyl-substituted derivatives showed high thermal stabilities with 5% weight loss temperatures of 409 and 413 °C, while their methyl-substituted counterparts exhibited by ca. 90 °C lower 5% weight loss temperatures. Their solutions exhibited blue emission with quantum yields of 67%. Ionization potentials of the compounds estimated by cyclic voltammetry are in the range of 5.49–5.65 eV, while the values obtained using photoelectron emission in air method are in the range of 5.16–5.28 eV. The layers of the compounds exhibited ambipolar charge transport with time-of-flight charge drift mobility values well exceeding 10⁻³ cm²/(Vs) at high electric fields. Non-doped naphthylindole and benzo[b]carbazole derivative based device emitted deep-blue light with the maximum intensity at 410 nm and CIE of (0.21, 0.16), and it exhibited a maximum external quantum efficiency of 3.4%.