Photo- and pH-induced transformations of flavylium cation: 'Write-lock- read-unlock-erase' cycles

Fernando Pina, Maria João Melo, Mauro Maestri, Paolo Passaniti, Nadia Camaioni, Vincenzo Balzani

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

The structural transformations of flavylium ion in aqueous solutions caused by pH jumps and photoexcitation have been investigated. At pH < 1, the stable form is the colored cationic species (AH+). By increasing pH, the concentration of AH+ decreases and, at pH = 5, this form is no longer present. The species obtained immediately after a pH jump undergo transformation processes with pH-dependent rate constants. At pH = 5.2 and 20 °C, the final product is the uncolored trans-chalcone (C(t)). This form can be transformed by light excitation into the cis-chalcone (C(c)) isomer, which is in equilibrium with the hemiacetal form (B(2)). This mixture is relatively inert due to the existence of a kinetic barrier that slows down the back thermal isomerization of C(c) to the stable C(t) form. Such a back reaction to C(t) can be totally prevented if the irradiated solution is submitted to a pH jump to pH = 1, which transforms the photoproducts into the stable AH+ species. In basic solution, two more species were detected, namely the anionic forms C(c)- and C(t)- of the cis and trans chalcone. C(t)- is a stable, not photosensitive and luminescent species, whereas C(c)- is not stable, being converted into C(t)- in the dark. The photochemical and pH- induced transformations of the flavylium cation in the pH range 0-11 can be taken as a basis to design write-lock-read-unlockerase cycles for an optical molecular-level memory with multiple readout capacity.

Original languageEnglish
Pages (from-to)3199-3207
Number of pages9
JournalEuropean Journal of Organic Chemistry
Issue number11
Publication statusPublished - 1 Nov 1999

Keywords

  • Flavylium salts
  • Photochromism Reaction mechanism
  • Substituent effects

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