Phenyl-, carbazolyl- and fluorenyl-substituted derivatives of indolo[3,2-b]carbazole as hole-transporting glass forming materials

A series of new derivatives of indolo[3,2-b]carbazole containing phenyl, fluorenyl and carbazolyl substituents at the nitrogen atoms were synthesized by Ullmann coupling of 6-pentyl-5,11-dihydroindolo[3,2-b]carbazole with the different aryl halogenides. The optical, photophysical, photoelectrical and thermal properties of the materials obtained were studied. All the synthesized compounds can be transformed into the amorphous phase with the glass transition temperatures ranging from 0 to 154 °C. The ionization potentials of the newly synthesized derivatives of indolo[3,2-b]carbazole are in the range of 5.22-5.48 eV. The lowest energy absorption edges and the lowest ionization potentials were observed for carbazolyl-substituted derivatives. Charge transport properties of the synthesized materials were estimated by the time-of-flight technique. The highest hole drift mobilities were observed for the fluorenyl-substituted derivative. For the molecular glass of 5,11-bis(9,9-dibutyl-9H-fluoren-2-yl)-6-pentyl-5,11-dihydroindolo[3,2-b]carbazole they exceed 10−3 cm2/V s at an electric field of 3.6 × 105 V/cm.