Title
Photochromism of the complex between 4′-(2-hydroxyethoxy)-7-hydroxyflavylium and β-cyclodextrin, studied by 1H NMR, UV–Vis, continuous irradiation and circular dichroism
Author
Sandra Gago, Nuno Basílio, Ana Fernandes, Victor Freitas, Alexandre Quintas, Fernando Pina
Year
2014
Journal
Dyes and Pigments
Abstract
The network of chemical reactions of the compound 4′-(2-hydroxyethoxy)-7-hydroxyflavylium and its photochromic properties were studied in the absence and presence of β-cyclodextrin. The system was characterized by 1H NMR, UV–Vis, continuous irradiation and circular dichroism. In the presence of β-cyclodextrin 4.8 mM the pK′a is reduced to 2.2. The association constants with β-cyclodextrin, follow the ordertrans-chalcone > quinoidal base > flavylium cation, respectively 1.7 × 103 M−1; 5.6 × 102 M−1; ≈0. The rate of inter-conversion of the network species increases in the presence of β-cyclodextrin circa 2.6 times. The appearance of an induced circular dichroism signal of trans-chalcone inside the β-cyclodextrin is described for the first time. It gives information about the position of the guest inside the host and allows the calculation of the respective association constant.
Instrument
J-810
Keywords
Circular dichroism, Materials