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%.