First-Principles Calculations of Excited-State Decay Rate Constants in Organic Fluorophores

In this Perspective, we discuss recent advances made to evaluate from first-principles the excited-state decay rate constants of organic fluorophores, focusing on the so-called static strategy. In this strategy, one essentially takes advantage of Fermi's golden rule (FGR) to evaluate rate constants at key points of the potential energy surfaces, a procedure that can be refined in a variety of ways. In this way, the radiative rate constant can be straightforwardly obtained by integrating the fluorescence line shape, itself determined from vibronic calculations. Likewise, FGR allows for a consistent calculation of the internal conversion (related to the non-adiabatic couplings) in the weak-coupling regime and intersystem crossing rates, therefore giving access to estimates of the emission yields when no complex photophysical phenomenon is at play. Beyond outlining the underlying theories, we summarize here the results of benchmarks performed for various types of rates, highlighting that both the quality of the vibronic calculations and the accuracy of the relative energies are crucial to reaching semiquantitative estimates. Finally, we illustrate the successes and challenges in determining the fluorescence quantum yields using a series of organic fluorophores.

Automated summary

In this Perspective, recent advances in evaluating excited-state decay rate constants of organic fluorophores from first-principles are discussed, focusing on the static strategy. The static strategy utilizes Fermi's golden rule to evaluate rate constants at key points of the potential energy surfaces, and the radiative rate constant can be obtained by integrating the fluorescence line shape determined from vibronic calculations. The use of Fermi's golden rule also enables the calculation of internal conversion and intersystem crossing rates, providing estimates of emission yields when complex photophysical phenomena are not present.