Non-Adiabatic Molecular Dynamics Study of Excited States in Thermally Stimulated Delayed Phosphorescent Gold(III) Complexes

Abstract

A new class of pyrazine-based gold(III) complexes demonstrates thermally stimulated delayed phosphorescence (TSDP), an unusual emission mechanism involving higher excited states that violates Kasha's rule. Through detailed nonadiabatic molecular dynamics and quantum chemical calculations, we uncover the fundamental requirements for TSDP: appropriate energy level alignment with multiple triplet states below S1, and efficient internal conversion processes between these states. The results of these calculations reveal that TSDP efficiency is governed by the interplay between non-adiabatic coupling and ΔG descriptor , which can be tuned through molecular design. We demonstrate that C-coordinated carbazolyl auxiliaries promote TSDP through suppressed reverse intersystem crossing (rISC), while N-coordination typically leads to conventional phosphorescence or thermally activated delayed fluorescence (TADF). Based on this understanding, we successfully designed a new TSDP complex featuring an N-coordinated 4,5-diazacarbazolyl ligand, where modulated electron-donating strength enables controlled population distribution among triplet states. This work establishes a comprehensive framework for designing TSDP materials, highlighting how auxiliary ligand electronic properties can be strategically manipulated to achieve desired emission characteristics through precise control of excited state dynamics. The results presented in this work provide insights into the tailoring of emission colors and the design of phosphors with improved luminescence properties.