A Configurationally Confined Thermally Activated Delayed Fluorescent Two‐Coordinate Cu(I) Complex for Efficient Blue Electroluminescence

Thermally activated delayed fluorescence (TADF) from linear two-coordinate coinage metal complexes is sensitive to the geometric arrangement of the ligands. Herein we realize the tuning of configuration from coplanar to orthogonal gradually by variation of substituents. In a complex with confined twist configuration, its blue emission peaking at 458 nm presents a high Φ of 0.74 and a short τ of 1.9 μs, which indicates a fast enough k of 3.9×10  s and a depressed k of 1.4×10  s . Such outstanding luminescent properties are attributed to the proper overlap of HOMO and LUMO on Cu d orbitals that guarantees not only small ΔE but also sufficient transition oscillator strength for fast . Vacuum-deposited blue OLEDs with either doped or host-free emissive layer present external quantum efficiencies over 20 % and 10 %, respectively, demonstrating the practicality of the configurationally confined strategy for efficient linear Cu TADF emitters.