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Hydroxypyridinechromene and Pyridinechalcone: Two Coupled Photochromic Systems
Author(s) -
Leydet Yoann,
Parola A. Jorge,
Pina Fernando
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200901884
Subject(s) - photoisomerization , photochromism , chemistry , quantum yield , photostationary state , protonation , photochemistry , chalcone , yield (engineering) , isomerization , tautomer , stereochemistry , organic chemistry , materials science , fluorescence , catalysis , ion , quantum mechanics , metallurgy , physics
Abstract Substitution of the phenyl group in 2‐hydroxychalcones by a 4‐pyridine unit dramatically changes the network of chemical reactions of this compound: trans ‐chalcone‐type ( Ct ), cis ‐chalcone‐type ( Cc ), and a hemiketal (hydroxy‐4‐pyridinechromene) ( B ) and their protonated forms are formed, but the presence of a flavylium‐type cation could not be detected even at very acidic pH values. Moreover, whereas in 2‐phenyl‐2‐benzopyrylium compounds B and Cc are generally elusive species whose kinetic processes in aqueous solutions occur on the sub‐second timescale, in the present compound these species equilibrate on a timescale four orders of magnitude lower. Complete characterization of the equilibrium and kinetics of the reaction network could thus be achieved by 1 H NMR spectroscopy and UV/Vis spectrophotometry. The network of chemical reactions exhibits cis – trans photoisomerization, as well as photochromism between the hemiketal and the chalcone‐type species. The irradiation of Ct in MeOH/H 2 O (1:1) at 365 nm produces B almost quantitatively through two consecutive photochemical reactions: Ct → Cc photoisomerization followed by Cc → B photo ring closure with a global quantum yield of 0.02. On the other hand, irradiation of B at 254 nm leads to a photostationary state composed by 80 % Ct and 20 % B , with a quantum yield of 0.21.