Abstract
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.
Highlights
Compounds that combine some different photosensitive fragments in one molecule are of great interest, since various combinations of responses can be expected in them, which is controlled by the excitation wavelength and the medium
ESIPT systems represent one of the fragments often used for introducing in such complicated hybrid compounds, because they demonstrate fluorescence from the enol and/or cis-keto forms depending on substituents, geometry, media and excitation wavelength [1,2,3,4,5]
We have synthesized a hybrid compound whose molecule is built from photochromic spiropyran fragments and two fluorophores, 7-hydroxycoumarin and azomethin [16]
Summary
Compounds that combine some different photosensitive fragments in one molecule are of great interest, since various combinations of responses (including fluorescence) can be expected in them, which is controlled by the excitation wavelength and the medium (solvent, polymer nature, addition of metal ions). ESIPT-based systems have attracted attention as fluorescent sensors, bio-imaging agents and pH probes Another important component of complex hybrid photoactive molecules are photochromes [6,7,8], which have a wide range of possible applications, such as optical molecular memory units, light-transforming membranes, sensors, etc. We have synthesized a hybrid compound whose molecule is built from photochromic spiropyran fragments and two fluorophores, 7-hydroxycoumarin and azomethin [16]. The presence of a spiropyran fragment in the molecule can lead to photochromic properties due to the spiro-bond cleavage and the formation of a merocyanine form; and. The presence of a spiropyran fragment in the molecule can lead to photochromic properties due to the spiro-bond cleavage and the formation of a merocyanine form; and 7-hydroxycoumarin and azomethine fragments should provide luminescent properties. Subsequent irradiation with visible light results in the formation of the initial initial closed form, releasing free metal ions.
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