The spectral and luminescent properties of a new Schiff base obtained from 2,3-diaminopyridine with two different (benzo and naphtho) azomethine moieties have been studied. A comparison has been made with the properties of both a bisazomethine of similar benzene structure obtained from 1,2-phenylenediamine and azomethines with identical azomethine moieties. The absorption and luminescence spectra of the new pyridine compound indicate that the naphthoazomethine moiety is in the keto form, while solutions of benzene azomethine contain isomers with two tautomeric forms of the naphtho unit and, as such, determine the difference in luminescence between these compounds.

К числу важных материалов для новых технологий, безусловно, относятся органические люминесцентные материалы, которые широко используются в связи с прогрессом искусственного освещения, дисплеев, разработкой флуоресцентных биомедицинских инструментов, люминесцентной дефектоскопии и для многих специальных целей.

Исследованы спектрально-люминесцентные свойства растворов бисгидроксифенилазометинов (I и II) и бисгидроксинафтилазометинов (III и IV) бензольного и пиридинового ряда в толуоле и этаноле. Кето-енольное равновесие в пиридиновом азометине II в основном состоянии слабо зависит от наличия атома N пиридина, в то время как для пиридинового азометина IV влияние пиридина значительно. В растворах I и II в обоих растворителях наблюдаются две полосы люминесценции от енольной (Е*) и кето-формы (К*), соотношение которых зависит от длины волны возбуждения. Люминесценция в растворах III и IV определяется образованием К*, только в растворе III в толуоле при коротковолновом возбуждении в спектре люминесценция добавляется преобладающая коротковолновая люминесценция от E*. Наблюдается влияние растворителя и атома пиридина на положение полос эмиссии, причем более выраженное для соединения II, чем для IV. Для всех соединений I-IV люминесценция в спирте на порядок эффективнее, чем в толуоле.

The spectral and luminescent properties of solutions of bis(hydroxyphenylazomethine)s (I and II) and bis(hydroxynaphthylazomethine)s (III and IV) of the benzene and pyridine series in toluene and ethanol have been studied. The keto–enol equilibrium in pyridine azomethine II in the ground state weakly depends on the presence of the pyridine N atom, whereas the influence of pyridine is significant for pyridine azomethine IV. In solutions of I and II in both solvents, two luminescence bands are observed from the enol (E*) and (K*) keto forms, the ratio of which depends on the excitation wavelength. Luminescence in solutions of III and IV is determined by the formation of K*, and predominant short-wavelength luminescence from E* is added to the luminescence spectrum only in a solution of III in toluene in the case of short-wavelength excitation. The solvent and the pyridine atom were found to affect the position of the emission bands, with the influence being more pronounced for compound II than for IV. For all compounds I–IV, luminescence in alcohol is an order of magnitude more intense than in toluene.

The luminescent properties of an organic dyad that combines two different luminophores, hydroxy-substituted 2,4,5-triarylimidazole and 8-azomethine-7-hydroxycoumarin, in its molecule have been studied in seventeen polymer matrices obtained by photocuring, which are represented by linear poly(meth)acrylates differing in the amount of hydroxyl groups and acrylic network polymers differing in the nature of crosslinking oligomeric blocks. The dependence of the luminescent properties of materials on the wavelength of excitation light, as well as on the presence and amount of hydroxyl groups in polymers; the presence of urethane groups, ether bonds, and aromatic moieties (individually or in combination); and flexibility and conditional polarity of the matrix, has been established.

Spectral-kinetic and fluorescence properties of hybrid compound, whose molecule includes the photochromic spiropyran fragment and two fluorophores—coumarin and salicylideneimine, were studied in comparison with model compounds—7-hydroxy-4-methylcoumarin, spiropyran of coumarin type and azomethinocoumarin in mixed toluene–acetonitrile solution in the presence of Tb3+ ions. It was shown that the hybrid compound exhibited direct photochromic transformations. Different fluorescence of complexes of the initial spirocycle and UV irradiation-induced merocyanine forms were observed. One green fluorescence emission with a maximum at 570 nm was observed for the initial closed form in mixed solvent solution and the additional red emission of the open merocyanine form in the region of 640 nm appeared after UV irradiation. The merocyanine form fluorescence in the presence of Tb3+ ions extremely increased after irradiation with visible light.

The conditions to prepare luminescent acrylate polymers containing the organic dyad, molecule of which combines two different emitting fragments, hydroxyl-substituted 2,4,5–triarylimidazole and 8-azomethine-7-hydroxycoumarine moieties, via photocuring have been optimized. The effect of the nature of the photocured network acrylate polymers on luminescent properties of the dyad has been investigated. The prepared aliphatic network polymers have exhibited independent fluorescence of both molecule fragments, dependent on the excitation wavelength. At the same time, the aromatic network polymers and the aliphatic network polymers containing ether links have revealed only the imidazole fragment fluorescence. The fluorescence nature has been stronger dependent on the polymer repeat unit structure and the content of the aromatic fragments in the polymer matrix than on the presence of the hydroxyl groups in the polymer. It has been shown that the emission of the imidazole fragment of the dyad in the aliphatic network polymers depends on the internode distance and conditional polarity of the medium.

The title compound, 1,1′-((1E,1′E)-(pyridine-3,4-diylbis(azanylylidene))bis(methanylylidene))bis (naphthalen-2-ol) (1), was synthesized and structurally characterized. The compound cocrystallized with one MeCN molecule. Interestingly, one of two salicylaldehyde Schiff base fragments exists in enol form, while the other one - in a ketone form. Moreover, cocrystallized acetonitrile molecule forms hydrogen bonding with three hydrogen atoms of the dye molecule. The nature and energies of intermolecular and intramolecular hydrogen bonds were studied theoretically using DFT calculations and topological analysis of the electron density distribution within the formalism of Bader′s theory (QTAIM method).

The absorption and fluorescent, as well as photochromic properties exhibited by hybrid spiropyran during formation of complexes between its molecules with metal ions were studied.

The spectral and luminescent properties of solutions of bis(hydroxynaphthoazomethine) of the pyridine family have been studied in comparison with the analogue of the benzene family. The presence of the pyridine nitrogen atom in the ortho position to the azomethine group favors the formation of the keto form of the azomethine moiety in the ground state of the molecule. The position of the luminescence maxima of solutions weakly depends on the presence of a nitrogen atom in the heterocycle and is more determined by the solvent polarity. Longer-wavelength and more efficient luminescence is observed in polar media.

Synthesis and structure of two novel dyads including two fluorophores - 1,2,4,5-tetraarylimidazole and azomethine fragments of different nature, have been studied targeting compounds with tunable luminescence. The presence of multiple fluorescence in both dyads has been established, and switching in one of the compounds is controlled by the excitation wavelength.

The spectral and luminescent properties of compounds A3–SA, A4–o–SA, and A4–o–K have been studied, whose structures include moieties of triphenylimidazole A3, tetraphenylimidazole A4, and hydroxyazomethines salicylideneaniline SA and coumarin-substituted azomethine K. Due to electronic conjugation of moieties, the compound A3–SA exhibits switchable luminescence only in alcohol solutions, whereas independent behavior of the moieties is observed in the case of linking of these luminophores by an oxygen bridge and luminescence switching by changing the excitation wavelength is possible both in solutions and polymeric media.