Quantifying the Role of Higher-Lying Excited States in Organic Emitters via Multistate Ab Initio Kinetic Modeling

TL;DR

This paper introduces KinLuv, a multistate kinetic model including higher excited states, to quantitatively analyze their impact on photophysical properties of organic emitters, aiding design of high-performance materials.

Contribution

The study develops KinLuv, an ab initio kinetic modeling framework that explicitly includes higher excited states and vibronic couplings, providing accurate predictions of photophysical observables.

Findings

KinLuv accurately reproduces experimental PLQY and fluorescence lifetimes.

Higher excited states significantly influence decay processes in certain organic emitters.

The framework guides the selection of simplified models without losing predictive accuracy.

Abstract

Higher lying excited states beyond S1 and T1 are widely recognized in many photophysical systems, including thermally activated delayed fluorescence (TADF). However, their explicit and quantitative impact on photophysical observables such as photoluminescence quantum yields (PLQY) and lifetimes is difficult to be attained experimentally and it has not been systematically assessed within a fully ab initio kinetic modeling framework. To address this gap, we developed KinLuv, a multistate excited state kinetic model that includes higher lying excited states (S2, T2) and all possible monomolecular interconversion processes between all the electronic states, whose rate constants were computed using Fermi golden rule explicitly including the Herzberg Teller (HT) vibronic coupling effect. We applied KinLuv to prototypical multi resonance TADF (MRTADF) emitters and their derivatives, as well as other representative organic chromophores, demonstrating its broad applicability across diverse photophysical playgrounds beyond TADF. The resulting simulations quantitatively reproduce key experimental observables, including PLQY and prompt and delayed fluorescence lifetimes. Beyond its predictive power, the present results establish clear criteria for identifying when higher lying excited states influence the excited state decay and when simplified models remain adequate. This framework enables rational selection of minimal kinetic models that balance physical insight with numerical robustness, with direct implications for the in silico design of high performance organic emitters.