Anthocyanin Color Stabilization by Host-Guest Complexation with p-Sulfonatocalix[n]arenes

Flavylium-based compounds in their acidic and cationic form bring color to aqueous solutions, while under slightly acidic or neutral conditions they commonly bring discoloration. Selective host-guest complexation between water-soluble p-sulfonatocalix[n]arenes (SCn) macrocycles and the flavylium cationic species can increase the stability of the colored form, expanding its domain over the pH scale. The association constants between SCn and the cationic (acid) and neutral basic forms of flavylium-based compounds were determined through UV-Vis host-guest titrations at different pH values. The affinity of the hosts for synthetic chromophore was found to be higher than for a natural anthocyanin (Oenin). The higher affinity of SC4 for the synthetic flavylium was confirmed by 1H NMR showing a preferential interaction of the flavylium phenyl ring with the host cavity. In contrast with its synthetic counterpart, the flavylium substitution pattern in the anthocyanin seems to limit the inclusion of the guest in the host’s binding pocket. In this case, the higher affinity was observed for the octamer (SC8) likely due to its larger cavity and higher number of negatively charged sulfonate groups.

Спектральное исследование протонирования фотохромных хроменов в полимерных матрицах

For the first time, proton complexes of the photoinduced colored form of chromene have been obtained in polymer binders. It is shown that UV irradiation of photochromic chromene leads to spectral changes due to the structure of the compounds and the nature of the polymer binder.

Preparation and Photochromic Performance of Homogeneous Phase Nitrocellulose Membrane Grafting Spirooxazine Moieties

The synthesis of 1,3,3-trimethyl-9′-acryloxyspiro[indoline-2,3′(3H)naphtho[2,1-b][l,4]-oxazine] (AISO) was carried out by catalytic esterification of 1,3,3-trimethyl-9′-hydroxyspiro-[indoline-2,3′(3H)naphtho[2,1-b][l,4]oxazine] (SO–OH) and acrylic acid in the presence of 1,3-dicyclohexylcarbodiimide (DCC) and N-dimethylaminopyridine (DMAP). Then, the synthesis of the target copolymer (NC-g-AISO) was was carried out by benzoyl peroxide (BPO)-induced graft copolymerization of the AISO monomer onto nitrocellulose (NC) in a homogeneous methyl isobutyl ketone medium. The structure of NC-g-AISO was characterized by Fourier transform infrared (IR) spectroscopy, 13C Nuclear Magnetic Resonance (NMR) spectra and thermogravimetric (TG) analysis. The photochromic properties of NC-g-AISO were investigated by examining UV–Vis spectra in ethyl acetate solution and solid membrane. Compared with the AISO monomer in ethyl acetate solution, the thermal color decay stability of the colored form of NC-g-AISO in ethyl acetate solution and in solid membrane improved significantly. The thermal color decay reaction rate constants in ethyl acetate solution and membrane at 25 °C were 1.77 × 10–2 and 1.36 × 10–3 s–1, respectively, fitted using the first-order reaction equation. After ten photochromic cycles, the relative absorption intensity of the colored form of NC-g-AISO decreased by 0.85%, indicating that the NC-g-AISO membrane has good reversible photochromic behavior.

Synthesis and Photochromic Properties of Poly(4-vinylpyridine-co-styrene) with Pendant Spiroxazine Moieties

An ionic polymer with pendant photochromic moieties was prepared by the reaction of poly(4-vinylpyridine-co-styrene) and 1,3,3-trimethyl-6′-bromohexyloxyspiro[2H]-indol-2,3′-[3H]-naphth[2,1-b][1,4]oxazine. The photochromic reaction in question is caused by the reversible heterolytic cleavage of the C(spiro)—O bond under UV irradiation, yielding the colored form that can return to the colorless form by ring closure under visible light irradiation or in dark. The visible range absorption of the corresponding polymer increased gradually by UV irradiation which is ascribed to the generation of the open merocyanine form from the closed spiro form. The ionic conductivity of polymer increased upon UV irradiation, which brought about the generation of zwitterions form, and subsequently decreased in dark, which brought about the generation of closed spiro form. Sufficient reversibility was found in this polymer and this response was completely synchronized with that in the absorbance changes.

Photochromism of indolino-benzopyrans studied by NMR and UV-visible spectroscopy

The synthesis of photochromic 3,3-di(4′-fluorophenyl)-3H-benzopyrans fused to an indole moiety is described. The structures of photomerocyanines elucidated by NMR spectroscopy and spectrokinetic data (λmax⁡of colored form, colorability, and rate constant of bleaching) obtained by UV-visible spectroscopy are reported.