Novel fluorene/indole-based hole transport materials with high thermal stability for efficient OLEDs

A series of novel hole transport materials based on fluorene and indole were designed, synthesized and well characterized. The carbazole and triphenylamine groups, which have excellent charge carrier mobility and low ionization potential, were introduced by coupling reactions. Ultraviolet–visible (UV–vis) spectral, photoluminescence (PL) spectral, cyclic voltammetry (CV), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements were performed to investigate the photophysical properties, thermal properties and electrochemical properties of these materials. The results implied that all these materials have excellent thermal stabilities with the 5% weight loss at 409–456 °C. The OLED devices based on the as-prepared materials were fabricated to investigate their hole transport ability. It turns out that device based on compound c exhibited the best performance with a maximum current efficiency of 3.74 cd/A and turn-on voltage at 4.0 V. The device performances indicated that the as-prepared materials can serve as highly efficient hole transport materials in OLED devices.