Mechanism of Color Purity Regulation in Multiresonance Thermally Activated Delayed Fluorescence Emitters: Vibronic Coupling and Nonadiabatic Dynamics Analysis

) of 97.04% within the present kinetic model while also showing the broadest adiabatic emission profile in this series with a full width at half-maximum (FWHM) of 45 nm. Through the analysis of Huang-Rhys (HR) factors and fluorescence spectra, we identified the vibrational modes contributing to this broadening. Nonadiabatic dynamics simulations further reveal that substituents modulate the degree of singlet-triplet state mixing on ultrafast time scales. By correlating the electronic structure, vibrational coupling, and nonadiabatic molecular dynamics (NAMD) simulations, this work establishes a physically consistent framework linking molecular structure to emission line width. These findings provide molecular-level guidance for achieving high color purity in MR-TADF emitters through suppression of low-frequency vibrational activation and minimization of excited-state structural relaxation.