“…Photo- and thermal excitation of the molecule lead to an excited state intramolecular proton transfer producing an excited cis-keto form, (cis-keto)*, with a possible zwitterionic structure [3,9,10,13,23,24,25]. This form then returns to the ground state enol SA conformer via either (cis-keto)*→0.277778em cis-keto deactivation or (cis-keto)*→0.277778em trans-keto isomerization followed by a conversion to the cis-keto tautomer in the ground state [5,25,26,27,28]. Results of quantum-chemical calculations generally confirm this scenario [25,29,30].…”