Indolo[3,2-b]carbazole-based functional derivatives as materials for light emitting diodes

Derivatives of indolo[3,2-b]carbazole containing reactive oxetanyl groups were characterized using 1H NMR, IR spectroscopy and mass spectrometry. The synthesized materials were examined using various techniques including differential scanning calorimetry, thermogravimetry, electron photoemission spectrometry and xerographic time of flight technique. The electron photoemission spectra of layers of the derivatives showed ionisation potentials of 5.2–5.45 eV; hole drift mobilities in layers of the derivatives dispersed in the polymeric host Bisphenol Z polycarbonate (50%) ranged from 6.2 × 10−6 to 6.9 × 10−4 cm2 V−1 s−1 at high electric fields at room temperature. The compounds were tested as hole transporting materials in bilayer OLED's using Alq3 as emitter; devices comprising phenyl substituted indolo[3,2-b]carbazole exhibited best overall performance with a turn-on voltage of ∼5 V, maximum luminance efficiency of 3.64 cd A−1 and maximum brightness of ∼5700 cd m−2. The compounds were also used for the preparation of cross-linked hole transporting layers by photoinduced polymerization, the ensuing layers being employed in light emitting diodes.