QM/MM Calculations on Excited-State Proton Transfer and Photoisomerization of a Red Fluorescent Protein mKeima with Large Stokes Shift

Large Stokes shift red fluorescent proteins (LSS-RFPs) are of growing interest for multicolor bioimaging applications. However, their photochemical mechanisms are not fully understood. Here, we employed the QM(XDW-CASPT2//CASSCF)/MM method to investigate the excited-state proton transfer and photoisomerization processes of the LSS-RFP mKeima starting from its cis neutral isomer. Upon excitation to the bright S