The exception was the PT process for RLuc8, in which p𝐾 𝑎 (Asp162) was calculated while the emitter is in the charged phenolate form. In these calculations, the corresponding ionization configuration were used because the protonation states of nearby residues can affect the p𝐾 𝑎 of interest significantly. In each calculation, p𝐾 𝑎 value was obtained by averaging over 10 configurations sampled over 2 ps MD simulation with a 0.1 fs time step at 300K and a 0.3 kcal/(mol•Å 2 ) constraints with respect to the corresponding initial structure.