Twin derivatives of fluorophenyl, difluorophenyl or trifluorophenyl substituted carbazoles as electroactive amorphous materials

• Twin derivatives of substituted carbazoles have been synthesized.
• The materials were tested as hole transporting layers.
• An OLED using one of the materials demonstrated efficiency of 3.4 cd/A.

Twin derivatives containing two 4-fluorophenyl, 3,5-difluorophenyl or 2,4,6-trifluorophenyl substituted carbazole rings were synthesized by the multi-step synthetic routes. Thermal properties and hole injecting/transport properties of the materials were examined by thermogravimetric analysis, differential scanning calorimetry, electron photoemission and time of flight techniques, respectively. Hole-transporting properties of thin amorphous layers of the derivatives were also tested in the structures of organic light emitting diodes (OLEDs) with Alq3 as the green emitter. The bilayer device based on a twin derivative composed of 3-(3,5-difluorophenyl) carbazol-9-yl blocks exhibited the best overall performance with a maximal photometric efficiency of about 2.1 cd/A and maximum brightness of 560 cd/m2. An analogous multilayer OLED with an additional PEDOT:PSS hole injecting layer demonstrated turn on voltage of 6.0 V, maximum brightness of about 6200 cd/m2 and maximal photometric efficiency of 3.4 cd/A.

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