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The synthesis of new spirooxazines linked to crown-ether entities has been largely developed. The linkage through different positions (as well as on the indolinic part as on the naphthoxazines part) and the length of the linkage-chain have been investigated.
Styryl dyes containing crown-ethers, models of photomerocyanines of spirooxazines, have also been synthesised and studied. On the other hand, the synthesis of 2H-chromenes showing improved photochromic properties has also been carried out.
Absorption spectra of spironaphthoxazines containing one crown-ether group (-OCO-18-crown-6) in different positions and their complex with Ca2+ and Ba2+ were measured in acetonitrile solution. It was shown that complex formation induces some an inherent feature in absorption spectra for all moities. The presence of Ba2+ and Ca2+ ions does not change the absorption spectra of the analogous spironaphthoxazine without crown-ether groups. Complex formation of these moities with Ba2+ and Ca2+ ions varies slightly the lifetime of the open form. Complex stability constant for investigated moities varies in the range of 106-108 dm3 mol-1.
Both ionophoric and photochromic properties of compounds have been evaluated. Concerning ionophoric properties: complexation and transfer of cations have been measured using a chloroformic phase to stimulate the cellular membrane. Without UV irradiation the properties are very similar to those of free crown-ethers, with a selectivity for the potassium. Under UV stimulation to induce the formation of photomerocyanines, very weak variations are observed for complexation and transfer.
Concerning photochromic properties evaluated by flash photolysis experiments, the complexation of the crown-ether entity led to the decrease of the colorability and in general to a weak decrease of the fading rate constants. Absorption is unchanged.
Finally, it seems that, for this kind of chromoionophores the photochrome and the ionophore entities act separately without interaction.
In addition, quantum calculations have been made to elucidate the role of the factors determining the stability of the open form on complexation.
Finally, an extended study of the kinetic and thermodynamic properties of substituted spirooxazines allowed to evaluate molar absorption coefficients of open forms, quantum yield of photocolouration, and to draw some general correlations between the structure of the molecules and their photochromic and thermochromic properties.
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