1. General Qualitative Scheme for ESIPT .

^a Photoexcitation populates the enol excited state (*E), which may directly decay 1) radiatively (solid black arrow) or 2) non-radiatively (dashed grey arrow) to the ground state, or instead 3) tautomerize to the monoketo (*K1) or diketo (*K2) excited state, with the two processes occurring simultaneously, sequentially, or both. These keto excited states may also decay radiatively or non-radiatively (4 and 5) to their respective keto ground state(s) (K), which eventually relax back to the enol (E).