Why is indigo photostable over extremely long periods?

Izumi Iwakura, Atsushi Yabushita, Takayoshi Kobayashi*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


This experimental work clarifies the mechanism for the ultra-photostability of indigo carmine by direct observation of a transition state using a sub 5-fs laser pulse. The molecular structural changes during the photoexcited proton-transfer process were traced as the time-dependent instantaneous frequency of molecular vibrations. The mono-alcohol intermediate generated by proton transfer via stepwise path was found to be unstable, and it immediately reverted to indigo carmine. This regression to the reactant is the reason for the ultraphotostability of indigo over extremely long periods.

Original languageEnglish
Pages (from-to)1120-1121
Number of pages2
JournalChemistry Letters
Issue number11
StatePublished - 9 Oct 2009

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