Modulating donor rigidity via a lock/unlock approach in aryl-Au(I)-NHC complexes: enabling tunable photophysical properties for highefficiency green/blue emitters

Abstract

Two coordinate gold(I) complexes, comprising N-heterocyclic carbene (NHC) coordination, have shown superior performance in organic light-emitting diodes (OLEDs). While aryl-Au(I)-NHC complexes are promising, the precise influence of donor scaffold rigidity on their luminescent properties remains underexplored. Herein, a systematic investigation into this relationship is presented through the synthesis and characterization of four gold(I) complexes (Au-1-Au-4) with progressively rigidified aryl donor units. Our results demonstrate that the donor rigidity serves as a critical parameter for tuning emission decay dynamics, consequently enabling the control over the key photophysical characteristics including radiative decay rates, emission color, and photoluminescence quantum yield (Φ PL ). Flexible and moderately rigidified donor scaffolds (in Au-1/Au-2) contribute to a remarkable solid-state green/blue emission with Φ PL of 95%, far outperforming its overly rigid counterpart (Au-4, Φ PL = 18%).Temperature-dependent spectroscopic analysis reveals a dual emission mechanism involving thermally activated delayed fluorescence (TADF) and phosphorescence, where donor flexibility is shown to minimize the singlet-triplet energy gap (ΔE ST ), thereby enhancing TADF.Capitalizing on these findings, a solution-processed blue OLED employing Au-2 as the emitter achieves a high maximum external quantum efficiency (EQE max ) of 17.8% with CIE coordinates of (0.17, 0.24). This work establishes clear molecular design principles, highlighting the modulation of donor rigidity as a key strategy to engineer the excited-state dynamics and device performance of gold(I) emitters for optoelectronic applications.