Properties of Dual Emissive Dendrimers Based on ThermallyActivated Delayed Fluorescence Dendrons and a Phosphorescent Ir(ppy)3 Core

Abstract Dual emission light‐emitting dendrimers composed of phosphorescent fac ‐tris[2‐phenylpyridyl]iridium(III) [Ir(ppy) 3 ] cores and thermally activated delayed fluorescence‐based (TADF‐based) dendrons have been prepared. The TADF‐based dendrons are designed to have green or blue emission. The dendrimers show solvatochromism, with the emission switching between phosphorescence and TADF depending on the medium in which the measurement is undertaken. Time‐dependent photoluminescence (PL) spectra measurements show that the TADF dendrons can act as an energy pool for emission from the phosphorescent core. The PL quantum yields (PLQYs) are found to be strongly dependent on the dielectric constant of the solvent, ranging from as high as 76% to as low as 0.3%. Neat films of the dendrimers are found to have relatively balanced hole and electron mobilities of order 10 –6 cm 2 V –1 s –1 , with bilayer organic light‐emitting diodes (OLEDs) containing neat emissive layers having a maximum external quantum efficiency ( EQE ) of 4.7% for a film having a PLQY of 12%. Finally, the solution processed OLEDs fabricated using 0.4 mol% of the dendrimers blended with 9‐[3‐(9 H ‐carbazol‐9‐yl)phenyl]‐9 H ‐carbazole‐3‐carbonitrile result in green emission with maximum EQEs of 9.8% and 15.1% for the dendrimers with green and blue emissive TADF dendrons, respectively.