Solid-state proton transfer studies on phototautomerization of 1-phenyl-3-methyl-4-furoyl-5-pyrazolone 4-methyl thiosemicarbazone

The optimized structures of the three tautomers (i.e., the enol, thiol and keto forms) for photo-induced tautomerism reaction (enol → keto) in the crystal. The proton is transferred along two different intermolecular hydrogen bonds by the effects of photoirradiation. The arrows mark the relevant proton.