Fig. 3.

Suggested mechanisms for the formation of the PAmCherry1 dark chromophore (OFF state) and its light-induced conversion into the fluorescent state (ON state) are shown. The cyclized form is the chromophore with the non-oxidized bond between p-hydroxyphenyl and imidazolone moieties and without N-acylimine. Hydrogen bonds are shown with dashed lines. Intermediate compounds are shown in parentheses. The chromophore in the excited state is denoted with asterisk. hv, indicates the illumination with violet light. Migration of the electron density is shown with curved arrows.