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. 2001 Jan 16;98(2):410–414. doi: 10.1073/pnas.98.2.410

Figure 4.

Figure 4

A four-level scheme that represents the ultrafast rearrangement during a enol-keto isomerization. The transfer times are experimental (19). The Tinuvin molecule shown (2-(2′-hydroxy-5′ methylphenyl)benzotriazole) is special among the systems exhibiting proton transfer in the excited state in that it undergoes the complete cycle within less than a picosecond.