Di(arylcarbazole) Substituted Oxetanes as Efficient Hole Transporting Materials with High Thermal and Morphological Stability for OLEDs

A group of di(arylcarbazole)-substituted oxetanes has been prepared in Suzuki reactions by using the key starting material 3,3-di[3-iodocarbazol-9-yl]methyloxetane and various boronic acids (fluorophenylboronic acid, phenylboronic acid or naphthalene-1-boronic acid). Full characterization of their structure has been presented. The low molar mass compounds represent materials having high thermal stability with 5% mass loss thermal degradation temperatures in the range of 371-391 degrees C. Glass transition temperatures of the materials are also very high and range from 107 degrees C to 142 degrees C, which is a big advantage for formation of stable amorphous layers for optoelectronic devices, i.e., organic light emitting diodes. Hole transporting properties of the prepared materials were confirmed in formed organic light emitting diodes with tris(quinolin-8-olato)aluminium (Alq3) as a green emitter, which also served as an electron transporting layer. In the device's materials, 3,3-di[3-phenylcarbazol-9-yl]methyloxetane (5) and 3,3-di[3-(1-naphthyl)carbazol-9-yl]methyloxetane (6) demonstrated superior hole transporting properties than that of material 3,3-di[3-(4-flourophenyl)carbazol-9-yl]methyloxetane (4) based device. When material 5 was used in the device structure, the OLED demonstrated rather low turn-on voltage of 3.7 V, luminous efficiency of 4.2 cd/A, power efficiency of 2.6 lm/W and maximal brightness exceeding 11670 cd/m(2). HTL of 6 based device also showed exclusive OLED characteristics. The device was characterized by turn-on voltage of 3.4 V, maximum brightness of 13193 cd/m(2), luminous efficiency of 3.8 cd/A and power efficiency of 2.6 lm/W. An additional hole injecting-transporting layer (HI-TL) of PEDOT considerably improved functions of the device with HTL of compound 4. The modified OLED with a layer of the derivative 4 demonstrated exclusive characteristics with turn-on voltage of 3.9 V, high luminous efficiency of 4.7 cd/A, power efficiency of 2.6 lm/W and maximal brightness exceeding 21,000 cd/m(2). These observations confirmed that the prepared materials have a big potential in the field of optoelectronics.

Automated summary

A group of di(arylcarbazole)-substituted oxetanes were synthesized and characterized. These compounds exhibited high thermal stability and were suitable for forming stable amorphous layers for optoelectronic devices. They also demonstrated superior hole transporting properties in organic light emitting diodes, showing great potential in the field of optoelectronics.