The design of fluorescent molecules represents a major application of electronic structure theory, broadly important for the displays, solid-state lighting, and fluorescence probes for cell biology. Time-dependent density functional theory (TD-DFT) using approximate exchange-correlation functionals is now widely used for predicting vertical excitation energies, and is becoming widely available for full fluorescence spectra. The present contribution benchmarks several state-of-the-art TD-DFT approximations for the emission spectrum and Commision Internationale de l'eclairage (CIE) color of fluorescent dyes. The results are a "rainbow of error", with the green-fluorescing perylene diimide Pigment Red 179 predicted to be anywhere from deep red to bright blue. Tradeoffs in performance for vertical excitations vs. ground- and excited-state frequencies leave significant differences in predicted emission, even when spectra are shifted to match experiment. The results motivate further development of density functionals possessing combined accuracy for excited states and geometric properties.

Time-dependent density functional theory simulations of emission spectra and CIE Color: A rainbow of error?

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ACS Fall 2022

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