Highly Efficient Bipolar Deep‐Blue Fluorescent Emitters for Solution‐Processed Non‐Doped Organic Light‐Emitting Diodes Based on 9,9‐Dimethyl‐9,10‐dihydroacridine/Phenanthroimadazole Derivatives

Highly efficient, solution‐processed, deep‐blue fluorescent emitters are urgently required to realize inexpensive organic light‐emitting diodes (OLEDs) for full‐color displays and lighting applications. Herein, two new bipolar fluorescent emitters: 2‐(4‐(7‐(9,9‐dimethylacridin‐10(9H)‐yl)‐9,9‐diethyl‐9H‐fluoren‐2‐yl)phenyl)‐1‐phenyl‐1H‐phenanthro[9,10‐d]imidazole (AFpPPI) and 2‐(3‐(7‐(9,9‐dimethylacridin‐10(9H)‐yl)‐9,9‐diethyl‐9H‐fluoren‐2‐yl)phenyl)‐1‐phenyl‐1H‐phenanthro[9,10‐d]imidazole (AFmPPI) are rationally designed and synthesized. These two are afforded from 9,9‐dimethyl‐9,10‐dihydroacridine (DMACR) as an electron donor and phenylphenanthroimadazole (PPI) as an electron acceptor, using 9,9‐diethylfluorene as a spacer with different substitution isomers (para or meta). The photophysical, electrochemical, thermal, and charge‐transport properties, as well as the electronic distribution of AFpPPI and AFmPPI are investigated and the results are well supported by density functional theory (DFT) and semi‐classical Marcus theory. Interestingly, AFpPPI and AFmPPI display deep‐blue emission with high fluorescence quantum yields (Φ_F). Furthermore, solution‐processed, non‐doped OLEDs were fabricated with AFpPPI and AFmPPI as an emitter, in which AFpPPI delivered a maximum external quantum efficiency (EQE) of 5.76% with Commission Internationale de l'Eclairage (CIE) coordinates of (0.15, 0.10) and a maximum current efficiency (CE) of 5.39 cd A⁻¹, which is the best performance for deep‐blue, solution‐processed fluorescent OLEDs based on non‐doped bipolar emitters.