Phenylethenyl substituted 10-alkylphenoxazines as new electroactive materials for organic light emitting diodes

Abstract

Phenylethenyl substituted 10-alkylphenoxazines were synthesized by a multi-step synthetic route. The derivatives were characterized by thermo-gravimetric analysis, differential scanning calorimetry, electron photoemission and time of flight technique. The materials were found to show very high thermal stability having initial thermal degradation temperatures in the range of 338–354 °C. Glass transition temperatures of the low molar mass materials were in the rage of 41–49 °C. The electron photoemission spectra of thin layers of the derivatives showed ionization potentials in the range of 5.16–5.3 eV. Hole drift mobility in thin layers of these derivatives ranged from 6 × 10−4 cm2V−1s−1 to 4.5 × 10−3 cm2V−1s−1 at high electric fields at room temperature. The synthesized materials have been tested as hole transporting layers in electroluminescent bilayer organic light emitting diodes with tris(quinolin-8-olato)aluminium as an emitter. The device with hole transporting layer comprised of 3,7-di(2-phenylethenyl)-10-(2-ethylhexyl)phenoxazine exhibited the best overall performance with low turn-on voltage of 2.8 V, a maximum photometric efficiency of about 3 cd/A and maximum brightness of 2160 cd/m2. Taking the device at 1000 cd/m2, the photometric efficiency was increased by 25%, as compared with that of PEDOT:PSS-based device.