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Tuning the Photochromic Properties of a Flavylium Compound by pH
Author(s) -
Moncada Margarida C.,
Pina Fernando,
Roque Ana,
Parola A. Jorge,
Maestri Mauro,
Balzani Vincenzo
Publication year - 2004
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200300508
Subject(s) - chemistry , photoisomerization , chalcone , photochromism , photochemistry , flash photolysis , photodissociation , cis–trans isomerism , organic chemistry , isomerization , reaction rate constant , kinetics , catalysis , physics , quantum mechanics
We studied the intricate pH‐ and light‐dependent network of the thermal and photochemical reactions of the 4′‐(dimethylamino)‐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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)