TY - JOUR
T1 - Light and pH switching between the various forms of the 4′-methylflavylium cation
AU - Maestri, Mauro
AU - Pina, Fernando
AU - Roque, Ana
AU - Passaniti, Paolo
N1 - This work was supported in Portugal by Fundação para a Ciência e Tecnologia (project PRAXIS /P/QUI/10074/1998) and Fundação Gulbenkian, and in Italy by MURST (Supramolecular Devices project) and University of Bologna (Funds for Selected Research Topics) and CNR (Sensori Fluorescenti Supramoleculari). F.P. and M.M. thank a grant from FCT (Portugal)/CNR Bologna (Italy) and A.R. a grant from FCT (BD 13330/97).
PY - 2000/10/24
Y1 - 2000/10/24
N2 -
In aqueous solution, the 4′-methylflavylium ion (AH
+
) can be interconverted into several different forms by light excitation and/or pH changes. All the observed processes are fully reversible and accompanied by strong changes in absorption and emission spectra. At pH < 1, the stable form is the coloured cationic species (AH
+
). By increasing pH, AH
+
is no longer stable and undergoes structural transformations that at pH > 3 lead to the uncoloured trans-chalcone (Ct) as a final product. This transformation occurs through the hemiacetal form (B2) and the cis-chalcone (Cc) isomer. This mixture is relatively inert due to the existence of a kinetic barrier that slows down the thermal isomerisation of Cc to the final Ct form. Ct is photosensitive and can be backconverted by light excitation into Cc which at low pH rapidly gives the AH
+
species. In basic solution, two more species were detected, the anionic forms (Cc
-
and Ct
-
) of the cis and trans-chalcone. Ct
-
is a stable, not photosensitive species, whereas Cc
-
is not stable, being converted into Ct
-
in the dark. A detailed analysis of the chemical behaviour of 4′-methylflavilium ion from the viewpoint of molecular level device shows that this compound behaves as a multistatelmultifunctional system.
AB -
In aqueous solution, the 4′-methylflavylium ion (AH
+
) can be interconverted into several different forms by light excitation and/or pH changes. All the observed processes are fully reversible and accompanied by strong changes in absorption and emission spectra. At pH < 1, the stable form is the coloured cationic species (AH
+
). By increasing pH, AH
+
is no longer stable and undergoes structural transformations that at pH > 3 lead to the uncoloured trans-chalcone (Ct) as a final product. This transformation occurs through the hemiacetal form (B2) and the cis-chalcone (Cc) isomer. This mixture is relatively inert due to the existence of a kinetic barrier that slows down the thermal isomerisation of Cc to the final Ct form. Ct is photosensitive and can be backconverted by light excitation into Cc which at low pH rapidly gives the AH
+
species. In basic solution, two more species were detected, the anionic forms (Cc
-
and Ct
-
) of the cis and trans-chalcone. Ct
-
is a stable, not photosensitive species, whereas Cc
-
is not stable, being converted into Ct
-
in the dark. A detailed analysis of the chemical behaviour of 4′-methylflavilium ion from the viewpoint of molecular level device shows that this compound behaves as a multistatelmultifunctional system.
KW - 4′-Methylflavylium salt
KW - Multistate/multifunctional systems
KW - Photochromic compounds
KW - Thermal isomerisation
UR - http://www.scopus.com/inward/record.url?scp=0346929321&partnerID=8YFLogxK
U2 - 10.1016/S1010-6030(00)00349-X
DO - 10.1016/S1010-6030(00)00349-X
M3 - Article
AN - SCOPUS:0346929321
SN - 1010-6030
VL - 137
SP - 21
EP - 28
JO - Journal of Photochemistry and Photobiology A: Chemistry
JF - Journal of Photochemistry and Photobiology A: Chemistry
IS - 1
ER -