Excited State Proton Transfers in Hybrid Compound Based on Indoline Spiropyran of the Coumarin Type and Azomethinocoumarin in the Presence of Metal Ions.

Spectral-luminescence properties of a hybrid compound containing a coumarin-type spiropyran and an azomethinocoumarin fragment in toluene-acetonitrile solution in the presence of Li+, Ca2+, Zn2+ and Mg2+ ions are reported. Two excited state proton transfers can occur in the hybrid compound-the transfer of a proton from the OH group of the 7-hydroxy coumarin tautomer to the N atom of the C=N bond of the azomethine fragment leading to green ESIPT fluorescence with a maximum at 540 nm and from the OH group of the 7-hydroxy coumarin tautomer to the carbonyl group of the pyrone chromophore, which leads to the formation of the 2-hydroxyl-tautomer T of coumarin with blue fluorescence with a maximum at 475 nm. Dependence of these excited state proton transfers on the metal nature and irradiation with an external UV source is discussed.

Photochromic systems with photoinduced emission modulation of colloidal CdSe quantum wells.

A spectroscopic study of photochromic systems containing two-dimensional CdSe nanoparticles (colloidal quantum wells) and photochromic compounds of the thermally relaxing chromene and thermally irreversible diarylethene classes in solutions was carried out. First, the systems were found to exhibit modulation of emission of two-dimensional nanoparticles in accordance with the photochromic transformations of compounds due to Förster resonance energy transfer (FRET) from the two-dimensional nanoparticles to photoinduced photochromic isomers.

Photochromic and luminescence properties of a hybrid compound based on indoline spiropyran of the coumarin type and azomethinocoumarin.

A novel hybrid compound whose molecule includes the photochromic spiropyran fragment and two fluorophores - coumarin and salicylideneimine - was synthesized by the reaction of two equivalents of 8-formyl-7-hydroxy-4-methylcoumarin with 5-amino-1,3,3-trimethyl-2-methyleneindoline. Its spectral-kinetic and fluorescence properties were studied in comparison with model compounds - 7-hydroxy-4-methyl-coumarin, spiropyran of the coumarin type, and azomethinocoumarin in toluene and ethanol. It was shown that the hybrid compound exhibited photochromic transformations in both solvents. Different fluorescence emissions of the initial spirocycle and UV irradiation-induced merocyanine forms were observed. One green fluorescence emission with a maximum at 545 nm was observed for the initial closed form in toluene, and several emissions with maxima at 390 nm, 440 nm, 450 nm (violet), and 530 nm (green) appeared in ethanol. An additional red emission of the open merocyanine form in the region of 665 nm appeared after UV irradiation in both solvents. Reversible modulation of fluorescence in both the initial and photoinduced merocyanine forms in the process of photochromic transformations was discovered. It was shown that the fluorescence modulation of the hybrid compound in weakly polar toluene was caused by resonance energy transfer from the fluorescent fragment of the photochromic compound to the photoinduced merocyanine form, leading to the process of photochromic transformations. Reversible modulation of fluorescence in ethanol solutions was achieved through a photoinduced change in the ratio of the concentrations of conformers.

Synthesis and characterization of nonsymmetric cyclopentene-based dithienylethenes.

Nonsymmetric cyclopentene-based dithienylethenes, containing both thienyl and benzothienyl units, have been synthesized for the first time, employing intramolecular McMurry reaction as a key transformation to target compounds 10 and 16. Photochromic properties of these compounds were examined in toluene and acetonitrile solutions, PMMA layers, solid films, and crystal phase. To explain an unprecedented single-crystalline photochromism phenomena of 10, X-ray crystallographic analysis was performed, revealing a significant influence of strong S···S interatomic interactions on the intramolecular distance between two photochemical reaction centers in the molecule. Compound 16 could be further synthetically modified in a step-by-step manner, thus serving as potential key intermediate to various complex bifunctional photochromic molecules.