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Photochromism of naphthoflavylium. On the role of 4-OH hemiketal in flavylium network

Paper ID Volume ID Publish Year Pages File Format Full-Text
27341 44017 2011 7 PDF Available
Title
Photochromism of naphthoflavylium. On the role of 4-OH hemiketal in flavylium network
Abstract

Flavylium compounds suffer in aqueous solution the nucleophilic addition of water at moderately acidic pH values (hydration reaction). The hydration is possible in two positions, namely at position 2, forming hemiketal B2, and at position 4, forming hemiketal B4. B2 can subsequently evolve to give the cis- and trans-chalcone species. At the present work the network of chemical reactions involving the naphthoflavylium compound in aqueous solution was studied by means pH jumps, stopped flow, continuous irradiation and flash photolysis. The equilibrium and rate constants of the system were calculated through a mathematical model. The species B4 has a kinetic effect similar to the one observed for the quinoidal base (for flavylium dyes bearing acidic groups), i.e.B4 is a kinetic product retarding the rate of equilibration. Flash photolysis experiments in comparison with reverse pH jumps results show that the appearance of the flavylium ion is faster in the photochemical-induced process than in the thermal one, suggesting an additional photochemical pathway (besides photoisomerization) after the excitation of the trans-chalcone.

Graphical abstractFormation of colored flavylium cation can be achieved by irradiation of trans-chalcone. The thermal conversion between flavylium cation and trans-chalcone depends on pH, the respective rate constant following a bell shape curve.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Kinetics and thermodynamics of the naphthoflavylium chemical network. ► Influence of the formation of hemiketal B4 on the kinetics of the system. ► Evidence for an additional photochemical pathway after excitation of trans-chalcone.

Keywords
Photochromism; Hemiketals; Multistate systems; Naphthoflavylium; Chalcones
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Photochromism of naphthoflavylium. On the role of 4-OH hemiketal in flavylium network
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 220, Issue 1, 30 April 2011, Pages 4–10
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us