AbstractAcceleration of singlet‐triplet intersystem crossings (ISC) is instrumental in bolstering triplet exciton harvesting of multi‐resonance thermally activated delayed fluorescent (MR‐TADF) emitters. This work describes a simple gold(I) coordination strategy to enhance the spin‐orbit coupling of green and blue BN(O)‐based MR‐TADF emitters, which results in a notable increase in rate constants of the spectroscopically observed ISC process to 3×10⁹ s⁻¹with nearly unitary ISC quantum yields. Accordingly, the resultant thermally‐stable Au^Iemitters attained large values of delayed fluorescence radiative rate constant up to 1.3×10⁵/1.7×10⁵ s⁻¹in THF/PMMA film while preserving narrowband emissions (FWHM=30–37 nm) and high emission quantum yields (ca. 0.9). The vapor‐deposited ultrapure‐green OLEDs fabricated with these Au^Iemitters delivered high luminance of up to 2.53×10⁵ cd m⁻²as well as external quantum efficiencies of up to 30.3 % with roll‐offs as low as 0.8 % and long device lifetimes (LT₆₀) of 1210 h at 1000 cd m⁻².