In this equation, (𝐻𝐴) * and 𝐻𝐴 represent the phenolic -OH group of the neutral emitter in the excited state (ES) and ground state (GS), respectively, while 𝐵 -and (𝐵 * -) denote the proton acceptor Asp162 in the GS and ES, correspondingly. The PT process is based on p𝐾 𝑎 difference calculated using PDLD/S-LRA (see Section 2.2). The ∆∆𝐺 term here represent the PT correction that is added to the emission energy in Eqn. 3. The Z-axis shows the ionization configuration of the protein environment, while the diagonal axis indicates the overall incorporation of PT reaction coordinate during the bioluminescence process.