Modulating the thermodynamics, kinetics and photochemistry of 7-diethylamino-4'-dimethylaminoflavylium in water/ethanol, SDS and CTAB micelles.

The thermodynamics and kinetics of compound 7-diethylamino-4'-dimethylaminoflavylium were studied in water : ethanol (1 : 1) and water in the presence of SDS and CTAB micelles. The blue flavylium cation is in equilibrium with the pink protonated flavylium cation defined by p K _{AH ²⁺ /AH ⁺} and the yellow trans -chalcone, defined by p K _{AH ⁺ /Ct} . The difference between these two p K s gives the pH domain of the flavylium cation, Δp K = 1.95 in CTAB, Δp K = 5.6 in water/ethanol (1 : 1) and Δp K = 8.5 in SDS micelles. On the other hand, the pH domain of the trans -chalcone is limited by p K _{AH ⁺ /Ct} and p K _{Ct/Ct ^-} . It is lower in SDS micelles Δp K = 2.7, increases in ethanol/water (1 : 1) Δp K = 5.1 and is maximum in CTAB micelles, Δp K = 6.8. All these effects can be explained by the electric charge present at the micellar surface. Relative energy level diagrams that allow for the explanation of the driving forces for any pH stimuli or light absorption were constructed from the calculated equilibrium constants. Irradiation of the trans -chalcone at 466 nm leads to the formation of the flavylium cation. In water : ethanol (1 : 1), the photochemistry is residual with Φ < 0.00002, while in SDS micelles at pH = 7 light increases the rate of the spontaneous conversion of trans -chalcone to the flavylium cation, with quantum yield Φ = 0.002; photochromism from trans -chalcone to give the flavylium cation with the same quantum yield is also observed in CTAB micelles.