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 oil the sub-second time-scale, 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. ne 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 it photostationary state composed by 80% Ct and 20%, B. with a quantum yield of 0.21.
ISI Document Delivery No.: 552CSTimes Cited: 6
Cited Reference Count: 72
Leydet, Yoann Parola, A. Jorge Pina, Fernando
Pina, Fernando/C-8161-2011; Parola, A. Jorge/F-4048-2010; REQUIMTE, AL/H-9106-2013; Chaves, Pedro/K-1288-2013
Parola, A. Jorge/0000-0002-1333-9076;
Fct-mctes [ptd/qui/67786/2006, sfrh/bpd/44230/2008]
We acknowledge LabRMN at FCT-UNL and Rede Nacional de RMN (supported with funds from FCT-MCTES) for access to the facilities. The Portuguese FCT-MCTES is also acknowledged for financial support through project PTD/QUI/67786/2006 and a post-doc grant SFRH/BPD/44230/2008 (Y.L.). J. . Lima. C. Laia, and V Petrov are kindly acknowledged for fruitful discussions
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