The analysis of time-resolved S1–Sn absorption spectra in the 0–500 ps range, together with quantum-chemical calculations, uncovered a photorecoordination reaction for the following complexes of CD6 (a bis(aza-18-crown-6)-containing dienone (ketocyanine dye) with a central cyclohexanone fragment): CD6·(Mn+)2 (M = Ba2+, Sr2+, Ca2+, K+). This process takes place over hundreds of fs and involves an “axial-to-equatorial” conformational change, with the solvation shell undergoing rearrangement as well. The characteristic photorecoordination times were found to correlate with the stability constants of the complexes. The lifetimes for the fluorescent states of CD6 and its complexes, namely CD6·(Mn+)2 (M = Ba2+, Sr2+, Ca2+, K+), are different; ergo, there is no photoejection of crowned cations into the solution. The calculated conformational profiles in the ground and excited states indicate the presence of an energy barrier in this process. A general photorelaxation pathway is suggested for CD6·(Mn+)2 metal complexes (M = Ba2+, Sr2+, Ca2+, K+). The coordination of cations via the carbonyl moiety in the dye molecule promotes photorecoordination of metal cations in the cavities of the azacrown ether fragment. Photorecoordination times were found to correlate with the degree of conjugation between the lone pairs in the N atoms of the aza-18-crown-6 ether and the π subsystem in the dye molecules (established for the CD4–CD6 metal–dye complex series, where CD4 and CD5 are related dyes with central cyclobutanone and cyclopentanone fragments, respectively).

The Z-isomer of N,N’-diammoniopropyl derivative of di(3-pyridyl)ethylene was synthesized. The structure and stability of complexes between this non-planar weak acceptor (A, (Z)-2) and a planar strong donor, the E-isomer of bis(18-crown-6)stilbene (D, (E)-1), were studied using X-ray diffraction, 1H NMR spectroscopy, and optical spectroscopy, including 1H NMR and spectrofluorimetric titrations. In MeCN, the components form a very stable pseudocyclic bimolecular complex (logKD·A = 8.48) due to homoditopic coordination of the ammonium groups of the acceptor to the crown moieties of the donor through numerous hydrogen bonds. Intrasupramolecular photo-driven electron transfer (ET) in the isomeric complexes of (E)-1 with (E)- and (Z)-2 was studied using steady-state absorption and fluorescence spectroscopy with time-resolved pulse absorption spectroscopy. It was found that back ET is approximately two times faster in complex (E)-1·(Z)-2 than in closely related (E)-1·(E)-2. Meanwhile, it is ~67 times slower in complex (E)-1·(E)-2 than in the isomeric complex based on N,N’-diammoniopropyl derivative of (E)-di(4-pyridyl)ethylene. Quantum chemical (DFT, TD-DFT) calculations suggest the actual photorelaxation pathway for the complexes under study.

The photochemistry of bis(18-crown-6)-containing 1,3-distyrylbenzene and its 2 : 2 bis-pseudo-sandwich complex with ethane-1,2-diammonium was studied. The UV irradiation of the supramolecular complex resulted in the formation of three geometric isomers of tetracrown-containing dicyclobutano[2.2]metacyclopane, differing in the orientation of the cyclobutane moieties, with the unsymmetrical isomer (>50%) predominating. The diammonium cations used as the template could be removed after photolysis by simple extraction, and the product was obtained in high yield (82%). The 1H NMR signals of a mixture of geometric isomers of [2.2]metacyclophane derivative were assigned resorting to quantum chemistry methods (DFT). The kinetic and thermodynamic parameters of thermal isomerization between the endo,endo- and exo,exo-isomers were measured. Tetracrown-containing dicyclobutano[2.2]metacyclophanes are homotetratopic ligands that contain four binding sites for metal and ammonium cations, which is of interest for the design of photo- and thermo-switchable supramolecular devices with a variable complex formation behavior and supramolecular machines owing to the butterfly-type thermal isomerization.

An overview of the main scientific achievements of Russian universities in the field of organic chemistry over the period 2018–2023 is presented.

An analysis of the results of time-resolved transient S1→Sn absorption spectroscopy studies and quantum chemical calculations of the dye (2E,5E)-2,5-bis[4-(1,4,7,10,13-pentaoxa-16-azacyclooctadecane-16-yl)benzylidene]cyclopentanone (1) and its metal complexes confirm the generality of the phenomenon of photoinduced recoordination of metal cations in the complexes of bis(aza-18-crown-6)-containing derivatives of the dibenzylidenecyclobutanone (dibenzylidenecyclopentanone) series. The results obtained confirmed the existence of the first stage of photoinduced recoordination of metal cations in the 1 • (Mn+)2 (M = Ba2+, Ca2+, K+) complexes which completes within a few hundreds of femtoseconds. The process involves cleavage of the N—M bond followed by displacement of the metal cation from its equilibrium position in the azacrown ether cavity and by transformation of the “axial” conformation of the complex to “equatorial” one. It was demonstrated that the barrier photoinduced recoordination of the cation in the 1 • (Ba2+)2 complex is accompanied by the change of the type of the solvation shell of the crowned Ba2+ cation in the following order: (2+1)MeCN, (3+1)MeCN, 4MeCN. In a low-temperature butyronitrile glassy matrix at 77 K, the photoinduced recoordination is completely suppressed. The Mg2+, Li+, and Na+ cations can form not only the inclusion complexes, but also the 1: 3 complexes ((Mn+) • 1 • (Mn+)2) of moderate stability through additional coordination to the carbonyl group of the dye. The radii, rS, of solvates of different-stoichiometry complexes containing the same metal cation determined from the data of anisotropy decay kinetics of S1→Sn absorption are about 9.2 Å for 1 • (Mg2+)2 and nearly 11.5 Å for Mg2+ • 1 • (Mg2+)2.

The complexation of the styryl dyes 1-ethyl-4-(E)-2-[4-(methylthio)phenyl]vinylpyridinium perchlorate (1) and 1-ethyl-4-[(E)-2-(4-methoxyphenyl)vinyl]pyridinium perchlorate (2) with cucurbit[6]uril (CB[6]) in aqueous solutions has been studied using steady-state and time-resolved fluorescence spectroscopy. The binding constant of the 1 : 1 inclusion complex of 1 and CB[6] is logK = 6.28, with fluorescence increasing threefold, and the 1 : 1 complex of 2 and CB[6] has logK = 5.99, with fluorescence increasing by four times. The fluorescence decay of the dyes and their complexes has two characteristic times, the short one of 2–3 ps and the long one on the order of ten picoseconds. In inclusion complexes, the latter is greater than in the free dyes. The mechanism of photobleaching of the studied dyes and their complexes with cucurbit[6]uril is considered.

The photoprocesses of diethylamino derivatives of 1,4- and 1,3-distyrylbenzenes in MeCN were studied using absorption, luminescence, 1H NMR, and laser kinetic spectroscopy. Compounds 1 and 2 undergo intersystem crossing to the triplet state and exhibit delayed fluorescence. It was concluded that dye radical anions and radical cations are formed upon dismutation of the triplet state in the presence of an electron donor or acceptor. Quantum mechanical calculations for the structures of diethylamino distyrylbenzenes in the ground and excited states were carried out, making it possible to establish the structures of isomers and the most stable conformers for both compounds.

A bis(aza-18-crown-6)-containing 2,5-di(benzylidene)cyclopentanone and a bis(ammoniopropyl) derivative of 1,2-di(4-pyridyl)ethylene in MeCN were found to form a supramolecular charge-transfer complex, which can act as an "off-on" fluorescent sensor for the Ca2+ and 1,12-dodecanediammonium ions. The molecular structure of this complex in solution was studied by density functional theory calculations.

Photophysical properties of a series of bis(arylydene)cycloalkanone dyes with various donor substituents are studied using quantum chemistry. Their capacity for luminescence and nonradiative relaxation through trans–cis isomerization is related to their structure, in particular, to the donor capacity of the substituents and the degree of conjugation due to the central cycloalkanone moiety. It is shown that cyclohexanone central moiety introduces distortions and disrupts the conjugation, thus leading to a nonmonotonic change in their properties. The increasing donor capacity of the substituents causes increase in the HOMO energy (rise in the oxidation potential) and decrease in the HOMO–LUMO gap, which results in the red shift of the absorption spectra. The ability of the excited dye to relax through fluorescence or through trans–cis isomerization is governed by the height of the barrier between the Franck–Condon and S1–S0 conical intersection regions on the potential energy surface of the lowest π-π* excited state. This barrier also correlates with the donor capacity of the substituents and the degree of conjugation between the central and donor moieties. The calculated fluorescence and trans–cis isomerization rates are in good agreement with the observed fluorescence quantum yields.

The supramolecular complex formation between donor ( E )-bis(18-crown-6)azobenzene (( E )- 1 ) and bis(ammoniopropyl) derivatives of bipyridine and dipyridylethylene acceptors ( 2 , ( E )- 3 ) was studied in MeCN using steady-state absorption and fluorescence spectroscopy, fluorescence kinetics, and quantum-chemical (DFT, TDDFT, QDPT) calculations. The complexes are quite stable, but they undergo decomposition via substitution by alkali and alkaline-earth metal cations. The formation of 1:1 and 1:2 complexes between ( E )- 1 and alkali and alkaline-earth metal cations (M n + ) was confirmed. Spectral-kinetic parameters and stability constants were calculated. The determined stability constants are generally lower than those for bis(crown)stilbene complexes due to moderate electron-donor ability of azobenzene. The plot of fluorescence quantum yields of 1· (M n + ) 2 vs charge density of the metal cation shows two separate linear relations for unipositive and dipositive ions. The results of quantum-chemical calculations supported the conclusions derived from steady-state experiments. The most stable conformations of pseudocyclic complex ( E )- 1 · 2 and two metal complexes were found. The latter involve 4 or 6 molecules of acetonitrile per each complex: ( E )- 1 ·(Ca 2+ ) 2 ·(MeCN) 4 , ( E )- 1 ·(K + ) 2 ·(MeCN) 6 . Based upon quantum-chemical calculations of model species, the character of absorption bands of crowns and their complexes with actual energy conversion pathway are discussed.

Herein, we report the synthesis and quantitative studies of novel photocontrollable ionophores.

The photophysical processes and photochemical reactions of a 15-crown-5-containing pyridine-based styryl dye and its complexes with potassium, barium, lead, and calcium perchlorates in MeCN were studied by absorption, luminescence, and laser kinetic spectroscopy. The processes of trans—cis-photoisomerization, intersystem crossing to the triplet state, and charge transfer giving the TICT state were found. Quantum chemical calculations for the structures of the dye and its complexes with metal cations were performed. It was concluded that the trans—cis-photoisomerization could proceed through the triplet state with the intermediate formation of a biradical. According to the calculations, the dye complexes with metal cations have 1:1 stoichiometry. In the case of barium cation, the possibility of formation of a 2:1 sandwich complex was also confirmed.

Complexation between (18-crown-6)stilbene and alkanediammonium ions + H 3 N(CH 2 ) n NH 3 + ( n = 2−4) resulting in the pseudo-sandwich 2:1 stilbene—dication complexes and 1:1 stilbene—dication complexes was studied by NMR spectroscopy. The stability of the complexes decreases as the methylene chain length in the alkanediammonium ion increases. UV photolysis of the bis-ligand complexes produces two major products, viz. , the rctt isomer of a biscrown-containing cyclobutane derivative formed as a result of intra-supramolecular [2+2] photocycloaddition and a crown-containing phenanthrene derivative (product of electrocyclization reaction). The effective quantum yields of both cyclization reactions occurring in the pseudo-sandwich complexes increase as the number of methylene units in the dication decreases.

Photoprocesses in aqueous solutions of the styryl dye 1-ethyl-4-{( E )-2-[4(methylthio)phenyl]vinyl}pyridinium perchlorate ( 1 ) and its complexes with cucurbit[ n ]urils (CB[ n ], n = 6–8) have been studied using the methods of stationary and time-resolved optical spectroscopy. The fluorescence intensity increases by approximately 3 times in 1 : 1 complexes of 1 and CB[6], whereas CB[7] has almost no effect on the fluorescence intensity. In 2 : 1 complexes with CB[8], the photocycloaddition reaction does not occur, with strong fluorescence quenching being associated with the formation of nonreactive dimers. The fluorescence decay kinetics of 1 has two characteristic times, 1.4 and ~130 ps, and changes little in the complexes. The photoinduced intramolecular charge transfer in 1 is an order of magnitude smaller than in the well-known dye DASPI.

A series of symmetrical dibenzylidene derivatives of cyclohexanone were synthesized with the goal of studying the physicochemical properties of cross-conjugated dienones (ketocyanine dyes). The structures of the products were established and studied by X-ray diffraction, NMR spectroscopy, and electronic spectroscopy. All products had the E,E-geometry. The oxidation and reduction potentials of the dienones were determined by cyclic voltammetry. The potentials were shown to depend on the nature, position, and number of substituents in the benzene rings. A linear correlation was found between the difference of the electrochemical oxidation and reduction potentials and the energy of the long-wavelength absorption maximum. This correlation can be employed to analyze the properties of other compounds of this type. The frontier orbital energies and the vertical absorption and emission transitions were calculated using quantum chemistry. The results are in good agreement with experimental redox potentials and spectroscopic data.

The formation and the spectroscopic and structural properties of 1:1 and 2:1 (ligand-to-dication) complexes of an (18-crown-6)stilbene with ethane-1,2-diammonium diperchlorate in MeCN were studied by UV-vis and NMR spectroscopy and by density functional theory calculations. Prolonged UV irradiation of 2:1 mixtures of the crown stilbene and the diammonium salt led to the formation of two main photoproducts, namely, the single syn- "head-to-head" photodimer of the crown stilbene (rctt cyclobutane) due to supramolecular-assisted [2 + 2] photocycloaddition and a crown ether derivative of phenanthrene due to a photoinduced electrocyclization reaction. The rctt cyclobutane was isolated by preparative photolysis, followed by chromatography. The selectivity of the [2 + 2] photocycloaddition is explained by supramolecular pre-organization of crown stilbene molecules into the 2:1 complexes that have a pseudo-sandwich structure with stacking interactions between the stilbene moieties.

A series of symmetrical dibenzylidene derivatives of cyclobutanone were synthesized with the goal of studying the physicochemical properties of cross-conjugated dienones (ketocyanine dyes). The structures of the products were established and studied by X-ray diffraction and by NMR and electronic spectroscopy. All the products had E,E-geometry. The oxidation and reduction potentials of the dienones were determined by cyclic voltammetry. The potentials were shown to depend on the nature, position, and number of substituents in the benzene rings. A linear correlation was found between the difference of the electrochemical oxidation and reduction potentials and the energy of the long-wavelength absorption maximum. This correlation can be employed to analyze the properties of other compounds of this type. Quantum chemistry was used to explain the observed regularities in the electrochemistry, absorption, and fluorescence of the dyes. The results are in good agreement with the experimental redox potentials and spectroscopy data.

Spectroscopic, luminescent, and spectral kinetic properties of cycloalkanone-based dienones and their dieth-ylamino, methylthio, methoxy, and dimethoxy derivatives were studied. The presence of electron-donating substituents results in a red shift of the absorption and fluorescence spectral maxima. A laser pulse causes dienones to undergo intersystem crossing to the underlying triplet state with a lifetime of 0.2-40 mu s as well as results in the formation of stable photoproducts capable of photoinduced conversion to the initial dienones. It also gives rise to intermediate products resulting from redox photoreactions of 2,4-bis(4-diethylaminobenzyli-dene)cyclobutanone in methanol in the presence of electron donor (ascorbic acid) and acceptor (para-nitro-acetophenone) compounds.

Photoprocesses in 1,4-diazadistyrylbenzene (1) and 1,3-diazadistyrylbenzene derivative (2) diperchlorates in MeCN were studied by absorption, luminescence, and kinetic laser spectroscopies. For compound 1, trans-cis-photoisomerization and intersystem crossing to a triplet state are observed. For compound 2, photoelectrocyclization is suggested. Quantum chemical calculations of diazadistyrylbenzene structures in the ground and excited states were carried out. The schemes for photoreactions were proposed.