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[Display omitted] Transient absorption spectroscopy, kinetics of absorption anisotropy decay for bis-aza-18-crown-6-containing di-benzylidenecyclobutanone dye and its metal complexes, and quantum chemical calculations support the presence of the first stage in the photorecoordination mechanism for the complexes with the Ba2+, Ca2+, and K+ cations. The depolarization parameters, including the radii of solvates, are deduced from the experimental data. During the barrierless photorecoordination of the complex with two Ba2+ cations, the solvent shell of the crowned Ba2+ cation undergoes the following changes: (2 + 1)MeCN, (3 + 1)MeCN, 4 MeCN. [ABSTRACT FROM AUTHOR]

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 (Mn+) 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·(Mn+)2vs 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·(Ca2+)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. [ABSTRACT FROM AUTHOR]

[Display omitted] Complexation with strong competitors (i.e. , Ba2+, Ca2+, and K+) shortens the length of the chromophore in bis-aza-18-crown-6-containing dienones of 2,4-dibenzylenecyclo-butanone series due to the weakening of π–LP conjugation as well as disruption of the quinonoid structure in the ground state of the dye (LP is the lone electron pair of the crown nitrogen atom). In the excited state, recoordination of metal cations in the crown cavity takes place. The complexation as well as the newly discovered photorecoordination in these metal complexes may be used to control the chromophore properties of the samples. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In recent years, smart and ecological urbanism and transformations into the new models of city making have become a global mainstream. These are models of the smart city, the eco-city, and the eco-megacity. The article proposes a conceptual approach to the formation of the eco-megacity as a qualitatively new phenomenon in the post-industrial economy. The prerequisites for the transformation of a megapolis into an eco-megacity have been analyzed. The key characteristics of the new phenomenon have been revealed. The role of collaboration as the main factor in increasing the efficiency of interaction processes between ecosystem actors and between ecosystems themselves has been presented. The relationship of the formed ecosystem approaches and the groups of actors during implementation of an institutional project in the megapolis have been determined. It allows for the transformation of a megapolis into an eco-megacity. The ant colony optimization algorithm for studying the symbiosis of socio-economic ecosystems in the megapolis has been proposed. The authors have attempted to contribute to the development of theoretical and methodological aspects of the emerging eco-megacity concept as a new phenomenon of the modern economy. [ABSTRACT FROM AUTHOR]

Despite the reduction in S and N emissions, acid deposition continues to be a problem for the inland water in Northeast Asia. However, catchment-scale studies on acid deposition in the Asian part of Russia are limited. Based on the long-term data of the Acid Deposition Monitoring Network in East Asia (EANET), we evaluated the effects of acid deposition on the stream water (SW) chemistry in a catchment of the Komarovka River (KMR) located in the Far East of Russia for the period 2005–2019. The SW pH has been decreasing over the last decade, with an increase in acidifying agents, such as SO42– and NO3–. The N/S ratio increased in SW due to a rise in NO3–, which plays a key role in acidification. In contrast, the rainwater pH has been rising at the nearby EANET site. There were transition periods from a decreasing trend to an increasing trend of S and dissolved inorganic nitrogen (DIN) in 2011 and 2014, respectively. Moreover, because of changing precipitation patterns, the contribution of warm season deposition to acidification has increased, which may accelerate the leaching of S and DIN from the forested catchment. The recent increase in S and DIN deposition and increased warm-season precipitation appeared to cause acidification of SW at KMR. The N leaching at KMR was largely influenced by the precipitation patterns, while DIN deposition and forest conditions should be taken into consideration. An interlinkage between air pollution and climate change should be carefully assessed to understand the forested catchment. [ABSTRACT FROM AUTHOR]

An updated and expanded representation of organics in the chemistry general circulation model EMAC (ECHAM5/MESSy for Atmospheric Chemistry) has been evaluated. First, the comprehensive Mainz Organic Mechanism (MOM) in the submodel MECCA (Module Efficiently Calculating the Chemistry of the Atmosphere) was activated with explicit degradation of organic species up to five carbon atoms and a simplified mechanism for larger molecules. Second, the ORACLE submodel (version 1.0) now considers condensation on aerosols for all organics in the mechanism. Parameterizations for aerosol yields are used only for the lumped species that are not included in the explicit mechanism. The simultaneous usage of MOM and ORACLE allows an efficient estimation of not only the chemical degradation of the simulated volatile organic compounds but also the contribution of organics to the growth and fate of (organic) aerosol, with the complexity of the mechanism largely increased compared to EMAC simulations with more simplified chemistry. The model evaluation presented here reveals that the OH concentration is reproduced well globally, whereas significant biases for observed oxygenated organics are present. We also investigate the general properties of the aerosols and their composition, showing that the more sophisticated and process-oriented secondary aerosol formation does not degrade the good agreement of previous model configurations with observations at the surface, allowing further research in the field of gas–aerosol interactions. [ABSTRACT FROM AUTHOR]

The femtosecond dynamics of photoinduced electron transfers in supramolecular donor–acceptor complexes between (E)-bis(18-crown-6)stilbene (D) and tetraperchlorates of 2,7-di(2-ammonioethyl)(2,7-diazapyrenium) (A1), 3,3′-(E)-ethene-1,2-diylbis[1-(3-ammoniopropyl)pyridinium] (A2) and 4,4′-ethane-1,2-diylbis[1-(3-ammoniopropyl)pyridinium] (A3) was studied. The acceptors A2 and A3 are weak electron acceptors whose first reduction potentials are equal to −1.0 and −1.2 V (Ag), respectively, while A1 is a strong acceptor with a reduction potential of −0.42 V. It was shown that the back electron transfer time in CT-states of the complexes D·A2 and D·A3 is 30–40 ps, which is approximately 50 times greater than the analogous time for the charge transfer complexes studied earlier. The complex D·A1 is characterized by ultrafast back electron transfer (770 fs). The relaxation pathway of excited states of D·A1 depends on the wavelength of the excitation light. When excited at 356 nm, the accumulation of a transient locally excited (LE) state with a 250 fs lifetime was observed. But when excited at 425 nm, the formation of the LE-state was not observed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Stilbene-Viologen supramolecular charge transfer complexes (D∙A) was obtained. • D∙A fluorescence ignition occurs upon adding alkanediammonium salts. • D∙A can be regarded as a possible optic sensor. • Times of electron transfer were measured by femtosecond transient spectroscopy. • Back electron transfer was described by semiclassical single-mode nonadiabatic theory. Abstract The spectral and thermodynamic properties of charge transfer complexes D∙A and D∙A∙D between (E)-bis(18-crown-6)stilbene (D) and 1,1′-bis(2-ammonioethyl)-4,4′-bipyridinium tetraperchlorate (A) in MeCN were studied. The complex D∙A is highly stable, while the complex D∙A∙D is weakly stable. D∙A does not fluoresce due to fast intramolecular processes of direct and reverse electron transfer. The efficiency of D∙A fluorescence ignition upon adding alkanediammonium salts depends on the length of a carbon chain. The spectral and kinetic characteristics of D∙A and D∙A∙D CT states were obtained by femtosecond transient absorption spectroscopy. It was established that the characteristic time of back electron transfer in the CT state of D∙A∙D (770 fs) is significantly higher than that in the CT state of D∙A (400 fs). In a number of charge transfer complexes, formed by derivatives of 4,4′-bipyridinium and di-(4-pyridinium)-ethylene with ammonioethyl and ammoniopropyl N- substituents, the rate of back electron transfer depends weakly on the acceptor nature, but is determined by the length of the carbon chain of terminal groups. [ABSTRACT FROM AUTHOR]

The formation of a supramolecular complex of bis(18-crown-6)stilbene (1) and 4,4′-bipyridine with two ammoniopropyl N-substituents (3) and the substitution reaction between 1·3 and alkali and alkaline-earth metal perchlorates have been studied using absorption, steady-state fluorescence, and femtosecond transient absorption spectroscopy. The formation of 1·(Mn+)2 complexes in acetonitrile was demonstrated. The weak long-wavelength charge-transfer absorption band of 1·3 completely vanishes upon complexation with metal cations because of disruption of the pseudocyclic structure. The spectroscopic and luminescence parameters, stability and substitution constants were calculated. The relaxation scheme of the 1·3 singlet state excited by a 25 fs laser pulse was proposed. It includes very fast vibrational relaxation and direct (τCT-d = 0.32 ps) and back (τCT-b = 0.51 ps) electron transfer resulting in complete fluorescence quenching. The quantum-chemistry calculations revealed the species taking part in the ET process and elucidated the mechanism of relaxation of the excited complex. [ABSTRACT FROM AUTHOR]

The article addresses the synthesis, structure and properties of 2-benzoylamino-1-hydroxyanthraquinone (1a), which can function as a selective colorimetric sensor for the cyanide anion in aqueous media. Compound 1a was prepared in two simple steps in good yield and its structure was confirmed by X-ray diffraction analysis. UV–Vis and NMR spectroscopy, mass spectrometry and quantum chemistry studies revealed that in MeCN–H 2 O mixtures (95:5, v/v), cyanide ionizes the hydroxyl group of the anthraquinone, which results in a strong bathochromic effect. The association constant of cyanide anion with 1a was measured to be 104.88 M–1; the detection limit is about 0.22 μM. The presence of a benzoylamino group at position 2 of the anthraquinone core has a stabilizing effect on the anionic form of 1a due to the hydrogen bonding between the amide hydrogen atom and the oxygen atom of the ionized hydroxyl group. [Display omitted] [ABSTRACT FROM AUTHOR]

The triplet state was found to involve in the photoconverion of bis(15-crown-5)-1,3-distyrylbenzene A mechanism of T-T-dismutation leading to the formation of radical photoreaction products is proposed. In the presence of Pb2+ or Ba2+, the formation of complexes 2 I ⋅2M2+ is probably accompanied by [2 + 2]-cycloaddition reaction. L.S. Atabekyan, V.G. Avakyan, A.K. Chibisov, V.N. Nuriev, A.V. Medvedko, A.V. Koshkin, S.P. Gromov "Photoprocesses in bis(15-crown-5)-1,3-distyrylbenzene and its complexes with metal perchlorates". [Display omitted] • The triplet state was found to involve in the photoconverion of bis(15-crown-5)-1,3-distyrylbenzene. • The T-T dismutation, resulting in the formation of radical products of the photoreaction (R– ⋅ + R+ ⋅). • In the presence of Pb2+ or Ba2+, the formation of complexes 2 I ∙2M2+ is probably accompanied by [2 + 2]-cycloaddition reaction. • Quantum chemical calculations indicate the formation of bis-complexes 2 I ∙2Ba2+ and their proneness to photocycloaddition. Photoprocesses in bis (15-crown-5)-1,3-distyrylbenzene (DSB) and its complexes with barium and lead perchloatewere studied in MeCN by absorption, luminescence, and laser kinetic spectroscopy. The triplet DSB molecules are involved in the degradation of electronic excitation energy, together with fluorescence processes. The most efficient intersystem crossing accompanied by a decrease in the DSB fluorescence quantum yield, occurs for the lead perchlorate complex. Using quantum chemistry methods (DFT and TDDFT), the geometry, structure, and transition energies to the S 1 state were calculated for trans - and cis -isomers of DSB in the gas phase and with allowance for the solvent and for 1:1 and 2:2 DSB complexes with barium cation in the ground and excited states. The orbital structures of the 2:2 complexes were calculated by ab initio method, and conclusions were drawn about the possibility of [2 + 2]- photocycloaddition reaction. [ABSTRACT FROM AUTHOR]

This research is dedicated to the study of bis(ammoniopropyl) derivative of (E)-4-(4-mercaptostyryl)pyridine dye (2), forming a highly stable bimolecular complex with a bis(18-crown-6 ether) derivative of (E)-stilbene (1) in solution owing to ditopic coordination via hydrogen bonds. The spectral-kinetic parameters of E isomer of the dye and its complex were obtained using steady-state absorption, fluorescence, and time-resolved absorption spectroscopy. The stability constant of the complex, quantum yields of cross-PCA and retro-PCA reactions were determined by spectrophotometric titration methods. According to density functional theory calculations, E–Z photoisomerization of dye 2 occurs via non-radiative deactivation from intermediate twisted (TICT) state. The detailed study of stereospecific [2 + 2]-cross-photocycloaddition (cross-PCA) of complex (E)- 1 ·(E)- 2 and back reaction of cross-PCA product (rctt - 3) was carried out. The complexation reaction of cyclobutane rctt - 3 with Ba2+ ions has been investigated. A highly efficient direct intrasupramolecular photoelectron transfer and the back electron transfer of a moderate efficiency were found for the complex (E)- 1 ·(E)- 2. Image 1 [ABSTRACT FROM AUTHOR]

Photoprocesses of bis(18-crown-6)-1,3-distyrylbenzene (DSB) and its complexes with barium and lead perchlorates in a MeCN–CH 2 Cl 2 (9:1, v/v) mixture were studied by absorption, luminescence, and laser kinetic spectroscopies. Unlike its strongly conjugated 1,4-isomer, 1,3-derivative shows almost independent behavior of its chromophoric subunits and is capable of phototransformations not observed in 1,4-distyrylbenzenes. Triplet DSB complexes are involved in the radiationless deactivation of the excited state along with the fluorescence processes. The most effective intersystem crossing was observed for the complex with lead perchlorate. The process is accompanied by a drastic decrease in the quantum yield of DSB fluorescence. Quantum chemistry (DFT and TDDFT) is used to calculate the geometric structure and absorption spectra of DSB and its complexes with barium and lead cations and to explain the observed results. • The nano- and microsecond kinetics of bis(18-crown-6)-1,3-distyrylbenzene and its complexes with Ba2+ and Pb2+ is studied. • 1,3-Distyrylbenzenes show independent behavior of their chromophoric subunits and are capable of novel phototransformations. • Quantum chemistry explains the experimental data. The results are useful for the rational design of photoswitches and sensors. [ABSTRACT FROM AUTHOR]

• Complexation of bis-aza-18-crown-6-containing dienones with EtNH 3 + and +H 3 N(CH 2) n NH 3 +. • The stability constants of the supramolecular complexes are measured. • Structures of the complexes are confirmed by 1H NMR spectroscopy and DFT calculations. • Fluorescence is decreased in the presence of EtNH 3 + and +H 3 N(CH 2) n NH 3 + (n = 2–8). • Fluorescence is enhanced in the presence of +H 3 N(CH 2) n NH 3 + (n = 9, 10, 12). Dienones (ketocyanine dyes) containing two aza-18-crown-6 ether residues were synthesized. The complex formation of these dyes with the EtNH 3 + and +H 3 N(CH 2) n NH 3 + ions (n = 2–10, 12) in MeCN was studied by electronic and 1H NMR spectroscopy, including spectrophotometric and 1H NMR titration. It was found that homoditopic bis-azacrown dienones and alkanediammonium ions with a short polymethylene chain form 1:1, 2:2, and 1:2 complexes, whereas alkanediammonium ions with a long polymethylene chain form only pseudocyclic 1:1 complexes. The stability constants of the resulting complexes were determined (log K 1:1 varies in the range from 2.74 to 5.62 [M–1, log K 2:2 = 2.1 [M–1, and log K 1:2 varies in the range from 2.03 to 2.96 [M–1). The most stable complexes are formed by diammonium ions with a long polymethylene chain owing to simultaneous binding of both NH 3 + groups to the azacrown ether residues of the dye. The structure of supramolecular complexes was confirmed by quantum chemical calculations. [ABSTRACT FROM AUTHOR]

The study addresses the spectral and photochemical properties of N -(3-ammoniopropyl)-4-styrylpyridinium diperchlorate and its substituted analogs containing either electron-donating (OMe, SMe, NMe 2) or electron-withdrawing (NO 2 , Cl) groups on the benzene ring. These styryl dyes in MeCN form pseudodimeric complexes with uncharged 18-crown-6-containing 4-styrylpyridine due to hydrogen bonding between the ammonium group and the crown ether oxygen atoms. The stability constants of the complexes were determined by spectrophotometric and 1H NMR titration methods. Owing to complexation, the dyes containing OMe or SMe groups and the dye with unsubstituted benzene ring undergo a stereospecific [2 + 2]-cross-photocycloaddition to the crown-containing styrylpyridine to give unsymmetrical cyclobutane derivatives as single rctt isomers. The structure of cyclobutanes was confirmed by X-ray diffraction analysis. The most probable conformations of the pseudodimeric complexes in MeCN were determined by density functional theory calculations. The cross-photocycloaddition quantum yields, measured upon selective excitation of the styryl dye, and other relevant data suggested that the barrier for this photoreaction increases with an increase in the reorganization energy of the singlet excited state of the dye. Image 1 • Photochemical properties of ammoniopropyl derivatives of 4-styrylpyridinium dyes. • Complexation of the styrylpyridinium dyes with a crown-containing 4-styrylpyridine. • DFT calculated structures of the pseudodimeric complexes in solution. • Supramolecular [2 + 2]-cross-photocycloaddition affording rctt cyclobutanes. • Stereochemistry of the cyclobutanes was confirmed by X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

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 Ca 2+ and 1,12-dodecanediammonium ions. The molecular structure of this complex in solution was studied by density functional theory calculations., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Gromov, Fomina, Zdorovenko, Fakhrutdinov and Ushakov.)

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., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

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., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

[reaction: see text] A novel oxidative photodehydrocyclization of indolinylphenylethenes to a polycyclic heteroaromatic cation with good yields was described. Starting from the trans derivative, the phototransformation is a multistep process. The process includes two photochemical reactions and a trans-cis isomerization reaction, followed by an 1-aza-1,3,5-hexatrienic electrocyclic reaction involving the formation of a C-N bond. The cyclized product gives the stable heteroaromatic cations from hydride elimination with oxygen from air or iodine.