Synthesis and multistate characterization of bis-flavylium dications – symmetric resorcinol- and phloroglucinol-type derivatives as stochastic systems

Abstract

Two symmetric bis-flavylium dications were readily synthesized and further evaluated for their multistate profile. Both systems were shown fully stochastic and behave like a single compound suggesting that the two flavylium moieties do not communicate via the bridge linking them. Global pKa values of ca. 4 regarding the acid-base reaction between flavylium cation and quinoidal base were calculated by stopped flow. It was further demonstrated that the equilibrium between AH + -AH + and indistinguishable flavylium-quinoidal base isomers AH + -A (A-AH + ) can be calculated by subtracting 0.3 pH units to the observed acid-base constant. On the other hand, the equilibrium between both flavylium-quinoidal base isomers and the bis-quinoidal base A-A is obtained by adding 0.3 pH units. Moreover, both systems do not have cis-trans isomerization barrier and the rate constants of interconversion between flavylium cation and quinoidal base as a function of pH are fitted with a mono-exponential and follow a bell-shaped curve. The systems proved also to be photochromic and from the fitting of the bell-shaped curve, flash photolysis measurements and quantum yields, it is possible to calculate all rate and equilibrium constants and construct a global energy-level diagrams. It was also proved that the rate constant to form both isomers AH + -Ct from the bis-flavylium upon a pH jump from 1 to less acidic solutions is twice of the observed value and the formation of the bis-trans-chalcone from the both isomers AH + -Ct is equal to the observed rate constant. An energy-level diagram of all the multistate species was constructed from the equilibrium constants.

3‐Deoxyanthocyanidin Colorant: Nature, Health, Synthesis, and Food Applications

“…() expanded the scope and synthesized more sophisticated dicationic derivatives (Figure F), through a double condensation with two equivalents of phloroglucinols. The dicationic derivatives have shown photochromic properties, and the two cationic moieties of the system behave like a single compound and do not interact via the linking bridge (Basílio et al., ). Such compounds could have potential new properties due to the dicationic character although further investigation is needed.…”

Functionalization of 7-Hydroxy-pyranoflavylium: Synthesis of New Dyes with Extended Chromatic Stability

“…Nevertheless, all these functionalizations were selective for the glucose primary hydroxyl group present in anthocyanins. The synthesis of bis-flavylium compounds is another strategy adopted to obtain functionalized compounds that involve a variety of reactional stages, reagents, solvents, and temperatures [ 27 , 28 ]. For this, acetophenone or aldehyde, one of the initiating reagents used in the synthesis of a flavylium, undergoes one or more reactions with nucleophilic and oxidizing agents, such as magnesium bromide and 2-iodoxybenzoic acid (IBX), to produce an intermediate product.…”

“…For this, acetophenone or aldehyde, one of the initiating reagents used in the synthesis of a flavylium, undergoes one or more reactions with nucleophilic and oxidizing agents, such as magnesium bromide and 2-iodoxybenzoic acid (IBX), to produce an intermediate product. The appropriate bis-flavylium compounds are then produced by the second reagent’s highly effective acid-catalyzed aldolic condensation [ 28 , 29 ]. The addition of halogens to the flavylium core’s ring A is another form of flavylium functionalization.…”