Rational design of local electric fields: an effective strategy to modulate thermally activated delayed fluorescence in carbene–gold(i)–amide complexes

Abstract

Carbene–metal–amide-based thermally activated delayed fluorescence (CMA–TADF) compounds are promising emerging metal–organic materials for OLEDs. However, there is a lack of systematic studies on the influence of external electric fields (EEFs) on the underlying photophysical mechanisms of conformationally distinct CMA complexes. In this work, we employ density functional theory (DFT) and time-dependent DFT (TD–DFT) methods to elucidate how EEFs of specific orientation and magnitude govern the excited-state properties and dynamics of coplanar (CAAC-Au-Ptz-1) versus perpendicular (CAAC-Au-Ptz-2) conformations. The results indicate that in the CAAC-Au-Ptz-1 conformation, the delayed fluorescence quantum yield (Φ_DF) increased by 16.41%. This is primarily due to EEF-induced elevation of triplet energy, which reduced the singlet–triplet energy gap (ΔE_ST) by 0.052 eV and enhanced the spin–orbit coupling (SOC) effect. In combination with other contributing factors, these alterations collectively drove a series of corresponding modulations in both radiative and non-radiative rates. For the perpendicular conformation (CAAC-Au-Ptz-2), although ΔE_ST increases under an EEF, this effect is counterbalanced by a concurrent increase in the SOC matrix element (SOCME). Consequently, the resulting Φ_DF remains around 95%, matching the performance observed in the absence of an EEF. These findings on conformational and EEF effects pave the way for developing high-performance luminescent materials and novel design strategies.