Constructing thermally activated delayed fluorescence dendrimers for solution processable blue OLEDs by molecular engineering of peripheral dendrons

Thermally activated delayed fluorescence (TADF) dendrimers with definite chemical structure are ideal candidate to fabricate high-efficiency organic light emitting diodes (OLEDs) using lower-cost solution processing techniques. Nevertheless, there still remains a challenge to construct molecular architectures of dendrimer-based TADF emitters that show easily controlled photophysical properties and superior carrier transporting capability simultaneously. Herein, we integrate peripheral dendrons possessing bipolar transmission capability with donor-acceptor skeleton through spiro junction to construct newly designed dendritic TADF emitters, TrzSpiroAc-tmCP and TrzSpiroAc-tmCPCN. By precisely regulating peripheral dendrons in these newly designed molecules, the lifetime and proportion of delayed components for TrzSpiroAc-tmCPCN are meticulously modulated to be 3.1 μs and 26.0 %, respectively, and thus exhibiting enhanced reverse intersystem crossing process with rate constant of 3.2 × 105 s−1 and excellent photoluminescence quantum yield over 70 %. Solution processable OLEDs based on TrzSpiroAc-tmCPCN with blue emission are achieved, and the external quantum efficiency value can exceed 10 %. Overall, this work manifests a valid strategy to tackle the imperative need for further exploring high-efficiency TADF dendrimers by integrating molecular engineering of peripheral dendritic units with constructing spiro junction between emission core and dendritic units.