2-Phenyl-1-benzopyrylium (flavylium) and 2-styryl-1-benzopyrylium (styrylflavylium) cations establish in aqueous solution a series of equilibria defining chemical reaction networks responsive to several stimuli (pH, light, redox potential). Control over the mole fraction distribution of species by applying the appropiate stimuli defines a horizontal approach to supramolecular chemistry, in agreement with the customary bottom-up approach toward complex systems. In this work, we designed an asymmetric styrylchalcone able to cyclize in two different ways, producing two isomeric styrylflavylium cations whose chemical reaction networks are thus interconnected. The chemical reaction networks of 2-(2,4-dihydroxystyryl)-1-benzopyrylium (AH(+)) and 7-hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium (AH(iso)(+)) comprise the usual species observed in flavylium-derived networks, in this case, the styryl derivatives of quinoidal bases, hemiketals, and chalcones. The thermodynamics and kinetics of the crossed networks were characterized by the use of UV-vis absorption and NMR spectroscopy as well as time-resolved pH jumps followed by stopped-flow. The two styrylflavylium cations are connected (isomerize) through two alternative intermediates, the asymmetric trans-styrylchalcone (Ct) and a spiropyran-type intermediate (SP). At pH = 1, AH(+) slowly evolves (k(obs) approximate to 10(-5) s(-1)) to a mixture containing 62% AH(iso)(+),s0 through the Ct intermediate, while at pH = 5, the SP intermediate is involved. The observed rate constants for the conversion of the styrylflavylim cations into equilibrium mixtures containing essentially Ct follow a pH-dependent bell-shaped curve in both networks. While at pH = 1 in the dark, AH(+) evolves to an equilibrium mixture containing predominantly AH(iso)(+) irradiation at lambda > 435 nm induces the opposite conversion.
ISI Document Delivery No.: 985KUTimes Cited: 1
Cited Reference Count: 32
Petrov, Vesselin Parola, A. Jorge Pina, Fernando
Parola, A. Jorge/F-4048-2010; Pina, Fernando/C-8161-2011; Caparica, cqfb_staff/H-2611-2013; REQUIMTE, AL/H-9106-2013; Chaves, Pedro/K-1288-2013
Parola, A. Jorge/0000-0002-1333-9076;
Fundacao para a Ciencia e Tecnologia [PTDC/QUIQUI/104129/2008, PTDC/CTM-NAN/120658/2010, Pest-C/EQB/LA0006/2011, SFRH/BPD/18214/2004]
This work was supported by Fundacao para a Ciencia e Tecnologia through Projects PTDC/QUIQUI/104129/2008, PTDC/CTM-NAN/120658/2010, and Pest-C/EQB/LA0006/2011 and Grant SFRH/BPD/18214/2004 (V.P.). We acknowledge LabRMN at FCT-UNL and Rede Nacional de RMN, Portugal, for access to the facilities.
Amer chemical soc
Washington