Trans-diaxial complex of Sn(IV)-2,3,7,8,12,13,17,18-octaethylporphyrin with fluorescein was obtained and identified by means of UV-vis, NMR, IR spectroscopy and ESI-HRMS spectrometry. Using one- and twodimensional NMR spectroscopy and quantum chemical calculations, it was found that the Sn(IV) cation in the macrocycle is bound to fluorescein through the hydroxo group of the xanthene dye. The spectral, acid-base and fluorescent properties as well as photoresistant to UV-radiation of the synthesized compounds were studied by spectrophotometric method. It was also described possible protolytic and tautomeric processes occurring in the Sn(IV)-2,3,7,8,12,13,17,18-octaethylporphyrin extra-complex with two fluorescein molecules, which has proved to be resistant to degradation into separate fragments in the wide range of medium pH. Given that the synthesized porphyrin-fluorescein triad exhibits a high sensitivity of fluorescence and photostability to the molecule ionization it can be considered as pH-dependent photoactive arrays that simultaneously possess both rotary [due to the Sn(IV) cation] and pH sensing (due to the fluorescein fragments) properties.
