Tuning the Photochromic Properties of a Flavylium Compound by pH

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We studied the intricate pH- and light-dependent network of the thermal and photochemical reactions of the 4′-(dimethyl-amino)-7-hydroxyflavylium ion by continuous irradiation, flash photolysis; 1 H NMR spectroscopy, and stopped flow analysis. The distribution of the various forms at the pH-dependent thermodynamic equilibrium and the rates of several interconversion processes were measured. The most interesting feature of this multistate/multifunctional system is related to the possibility of pH-tuning the colour change caused by photoirradiation, because the cis-chalcone isomer, obtained from the photoisomerization of the trans-chalcone form, is spontaneously transformed into coloured species (flavylium cation and quinoidal base) at low values of pH, but reverts back to the uncoloured trans-chalcone at high values of pH because of the low energy barrier between the cis and trans chalcone isomers.

Original languageEnglish
Pages (from-to)304-312
Number of pages9
JournalEuropean Journal of Organic Chemistry
Issue number2
Publication statusPublished - 16 Jan 2004


  • Flavylium
  • Multistate/multifunctional systems
  • NMR spectroscopy
  • Photochromic properties


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