A series of protonated dimethoxystyrylheterocycles containing 4-pyridine, 4-quinoline, and 2-benzothiazole residues, as well as various anions, were synthesized. The ability of these compounds to undergo the solid-phase [2 + 2] photocycloaddition (PCA) reaction was studied using 1H NMR. It was established that only 4-styrylpyridine and 2-styrylbenzothiazole hydrotosylates undergo PCA with the formation of rctt isomers of cyclobutane derivatives. X-ray diffraction studies have shown that most of the protonated styrylheterocycles form crystal packing motifs that are not suitable for the implementation of PCA. Only 4-styrylpyridine and 2-styrylbenzothiazole hydrotosylates yielded packings with a syn-head-to-tail arrangement of their cations. In the packings, the ethylene fragments of adjacent cations have antiparallel mutual arrangement and been brought closer in space. This allows the formation of centrosymmetric rctt isomers of cyclobutane derivatives upon irradiation of these substances with visible light. PCA was observed as a single crystal-to-single crystal process for dimethoxystyrylbenzothiazole hydrotosylate. The cyclobutanes were isolated in a free state and their structures were confirmed by single crystal X-ray diffraction.

A symmetrical cyclopentanone-based dienone containing two N-methylbenzoaza-15-crown-5 ether moieties was synthesized. The structures of the dienone and its bissandwich complex with barium perchlorate were investigated using X-ray diffraction and electronic spectroscopy.

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.

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

A new efficient method was proposed for the synthesis of (18-crown-6)stilbene; the structure of the product was confirmed by X-ray diffraction analysis. In MeCN, this compound forms pseudodimeric complexes with N-(2-ammonioethyl)-4-styrylpyridinium and N-(3-ammoniopropyl)-4-styrylpyridinium diperchlorates via hydrogen bonding between the ammonium group and the crown ether oxygen atoms. The ammonioethyl derivative was synthesized for the first time. The stability constants and spectral characteristics of the complexes were measured by spectrophotometric and fluorescence titration. Photoirradiation of the pseudodimeric complex of (18-crown-6)stilbene with the ammoniopropyl dye resulted in the stereospecific [2 + 2] cross-photocycloaddition reaction. The replacement of the stilbene moiety in the crown compound by a styrylpyridine moiety led to a 5-fold increase in the quantum yield of the photoprocess. The most probable cause for this effect is the presence of photoinduced electron transfer in (18-crown-6)stilbene complexes. This assumption is confirmed by fluorescence lifetime spectroscopy and density functional theory calculations.

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, NMe2) or electron-withdrawing (NO2, 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 H-1 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.

The physicochemical properties of highly stable supramolecular donor-acceptor (D-A) complexes of a bis(18-crown-6)azobenzene (weak π-donor) with a series of bis(ammonioalkyl) derivatives of viologen-like molecules (π-acceptors) in acetonitrile were studied using cyclic voltammetry, UV-vis absorption spectroscopy, 1H NMR spectroscopy, and density functional theory (DFT) calculations. The crystalline structures of the bis(crown)azobenzene and its complex with a bis(ammoniopropyl) derivative of 2,7-diazapyrene were determined by X-ray diffraction analysis. In solution, all of the supramolecular D-A complexes studied have a pseudocyclic structure owing to ditopic coordination of the ammonium groups of the acceptor to the crown ether moieties of the donor. These complexes show somewhat lower stability as compared with the previously studied complexes of the related derivative of stilbene (strong π-donor), which is explained by the relatively weak intermolecular charge-transfer (CT) interactions. Time-dependent DFT calculations predict that the low-energy CT transition in the D-A complex of the bis(crown)azobenzene with a bis(ammoniopropyl) derivative of 4,4'-bipyridine lies between the local ππ* and nπ* transitions of the azobenzene. The absorption band associated with the CT transition is indiscernible in the spectrum since it is overlapped with broad and more intense ππ* and nπ* bands. It was found that the E → Z photoisomerization quantum yield of the bis(crown)azobenzene decreases by almost an order of magnitude upon the complexation with the 4,4'-bipyridine derivative. This effect was tentatively attributed to the intermolecular electron transfer that occurs in the 1ππ* excited state of the azobenzene and competes with the 1ππ* → 1 nπ* internal conversion.

Dienones (ketocyanine dyes) containing two aza-18-crown-6 ether residues were synthesized. The complex formation of these dyes with the EtNH3+ and +H3N(CH2)(n)NH3+ ions (n = 2-10, 12) in MeCN was studied by electronic and H-1 NMR spectroscopy, including spectmphotometric and H-1 NMR titration. It was found that homoditopic bis-azacmwn 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 (logK(1:1) varies in the range from 2.74 to 5.62 [M-1], logK(2:2) = 2.1 [M-1], and logK(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 NH3+ groups to the azacrown ether residues of the dye. The structure of supramolecular complexes was confirmed by quantum chemical calculations.

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-dia-zapyrenium) (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.

Naphthylpyridine derivatives and cavitands form inclusive complexes of different structure and stoichiometry; the guests are capable of translocations within cucurbit[7,8]uril cavities.

The spectral and thermodynamic properties of charge transfer complexes DA and DAD between (E)-bis(18-crown-6) stilbene (D) and 1,1'-bis(2-ammonioethyl)-4,4'-bipyridlnium tetraperchlorate (A) in MeCN were studied. The complex DA is highly stable, while the complex D center dot A center dot D is weakly stable. D center dot A does not fluoresce due to fast intramolecular processes of direct and reverse electron transfer. The efficiency of DA fluorescence ignition upon adding alkanediammonium salts depends on the length of a carbon chain. The spectral and kinetic characteristics of D center dot A and D center dot A center dot 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 center dot A center dot D (770 fs) is significantly higher than that in the CT state of D center dot 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.

•Supramolecular donor–acceptor complex formed between two olefins in solution.•Complexation promotes [2 + 2]-cross-photocycloaddition and photoinduced electron transfer.•Supramolecular cross-photocycloaddition occurs stereospecifically.

A method was developed for the synthesis of nitrobenzoazacrown ethers by N-demethylation of N-methylnitrobenzoazacrown ethers on treatment with ammonium iodide, resulting in the formation of benzoazacrown ethers in 95-100 % yields. The spatial structure of nitrobenzoazacrown ethers and their complexation behaviour towards alkali and alkaline-earth metal cations, ammonium ions, and fluoride anions were investigated using X-ray diffraction and 'H NMR spectroscopy. It was shown that the stability of host-guest type complexes of nitrobenzoazacrown ethers with metal and ammonium cations in MeCN-d(3) is lower than the stability of complexes formed by N-alkyl-substituted analogues with the same macrocycle size. It was shown that fluoride anions in DMSO-d(6) or MeCN-d(3) can bind to nitrobenzoazacrown ethers via hydrogen bonding with the NH group of the macrocycle.

[2+2] Photocycloaddition of a series of styryl dyes ( a , b , and c , see text) in the cavity of cucurbit[8]uril (CB8) in aqueous solutions has been studied by optical spectroscopy. The complex formation constants were calculated for the 1 : 1 and 2 : 1 complexes of the styryl dyes with CB8. The optimal CB8 to dye molar ratios that correspond to the highest concentrations of the 2 : 1 complexes in the solution have been determined as 0.5, 0.3, and 1 for dyes a , b , and c , respectively. The quantum yields of photocycloaddition have been calculated from the results of dye photolysis in the presence of CB8: 0.06, 0.02, and 0.04 for a , b , and c , respectively. The fluorescence decay kinetics has been studied on the picosecond timescale. The lifetimes found are 1–2 ps, which correspond to the characteristic time of the solvation shell effect on the redistribution of the dye charge in the excited state. The long component of the fluorescence decay on the order of tens of picosecond is also observed. This component decreases in the presence of CB8, indicating the formation of dimeric state.

— Based on the results of authors' studies, an approach to the analysis of [2 + 2] photocycloaddition (PCA) topochemical reactions of unsaturated compounds, occurring in a single crystal with either its retention or decomposition under exposure to visible light, has been developed. The main crystal packings, favorable for photoreaction in crystal, are revealed. Conditions for PCA reaction with single crystal retention are established. The factors increasing the probability of implementing crystal packing motifs that are favorable for this reaction (by chemical modification of structural units) are analyzed. The fact of extraordinary implementation of both direct and back (under UV irradiation) photoreactions in the same single crystal is explained.

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 •(M^ n ^+)_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 (τ_CT-d = 0.32 ps) and back (τ_CT-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.