Benchmarking Emission Energies of BODIPY Dyes using MRSF-TDDFT

We benchmarked mixed-reference spin-flip time-dependent density functional theory (MRSF-TDDFT) for predicting gas-phase fluorescence energies of ten BODIPY dyes. Because conventional approaches, such as linear-response TDDFT (LR-TDDFT) and spin-flip TDDFT (SF-TDDFT), may inadequately describe emissive states with multireference or double-excitation character, MRSF-TDDFT is explored as a more robust alternative. Several DFT functionals were evaluated alongside STEOM-DLPNO-CCSD calculations and compared with experimental data. We emphasize a doubly tuned exchange-correlation functional, DTCAM, whose parameters were optimized in this work using Latin Hypercube Sampling and Bayesian optimization, leading to improved performance over alternative functionals while preserving computational efficiency.