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. Author manuscript; available in PMC: 2020 Sep 11.
Published in final edited form as: J Am Chem Soc. 2020 Jun 9;142(25):11032–11041. doi: 10.1021/jacs.0c02796

Figure 1.

Figure 1.

Canonical ESPT scheme for avGFP with spectroscopically characterized protonation states (A, B, and I states) and their structures (with T203 shown in red). The wavelengths associated with the excitation and emission (straight and curved vertical arrows, respectively) are measured at room temperature,1,2 except for the absorption maximum of the I state, which can only be identified as a small band at low temperature.1,17 Ground-state processes, including proton transfer (GSPT) and environmental reorganization, are required to reach an equilibrium among the states. The A* emission (shown with a dashed curved arrow) is largely suppressed at steady state due to efficient ESPT.2 T203 is not the only residue that undergoes structural change following ESPT; see Figure 4 in ref 18.