It was shown by 1 H NMR spectroscopy that symmetrical bis(crown)stilbenes (L) and small alkali and alkaline-earth metal cations form 1(L) : 1(M m+ ) and 1(L) : 2(M m+ ) complexes in MeCN solutions. In the case of large or hydrated metal cations such as Cs + , Rb + , K + , Ba 2+ , Sr 2+ , [Ca(H 2 O) x ] 2+ and stilbenes with a small crown-ether cavity as compared with the metal cation size, stable bis-sandwich complexes 2(L) : 2(M m+ ) can also be formed. A stable bis-pseudosandwich 2 : 2 complex is also produced from bis(18-crown-6)stilbene with the propanediammonium ion. The effect of the crown-ether size and the cation size and nature on the route of stilbene phototransformation and product composition was elucidated. The bis-(pseudo)sandwich complexes undergo effective stereoselective [2+2] photocycloaddition giving mainly rctt isomers of new 1,2,3,4-tetracrown cyclobutanes. The structures of complexes of bis(crown)stilbenes and obtained cyclobutanes were confirmed by X-ray diffraction.

An improved procedure was proposed for the synthesis of stilbenes fused to two crown ether fragments at both benzene rings. The structure of new homologous symmetric bis-crown-containing stilbenes was determined by X-ray analysis. Relations were revealed between the size of the crown ether moiety and stilbene conformation in crystal and the mode of crystal packing. Conformational analysis of the prepared stilbenes in solution and in the solid state was performed by 1 H and 13 C NMR spectroscopy and by DFT quantum-chemical calculations.In the recent years, supramolecular chemistry has become one of the most extensively developing fields of organic chemistry [1]. Components of supramolecular systems are often complex and difficultly accessible organic compounds, and their synthesis in many cases constitutes the subject of a separate study. In addition, an important problem in supramolecular chemistry is prediction of properties of compounds in supramolecular systems and development of selective procedures for their self-assembly.A promising sort of molecules for studying supramolecular organization in solution, monomolecular layers, Langmuir-Blodgett films, and polymeric matrices includes crown ether-fused azobenzenes, azomethines, styryl dyes, and related compounds [2][3][4][5] possessing double N=N, C=N, and C=C bonds. Interesting properties of these compounds are the ability to form supramolecules via host-guest-like complex formation with metal and ammonium ions, considerable variations in spectral parameters due to complex formation, and the possibility of varying their structure and properties by irradiation. The most typical photochemical processes occurring in the above selforganized systems and accompanied by considerable variation of their properties are trans-cis isomerization of the double bonds, electrocyclic reactions, and [2 + 2]-cycloaddition. Crown ether-fused stilbenes were not studied in much detail [6][7][8], though these compounds might be expected to exhibit equally interesting photochemical behavior and pronounced ability to form complexes.We recently showed that bis(18-crown-6)-stilbene Id and a number of diammonioalkyl derivatives of viologen analogs in dilute solutions give rise to unusual bi-and trimolecular complexes with effective intermolecular charge transfer due to spatial preorganization of the donor and acceptor parts of the initial molecules via hydrogen bonding [9][10][11]. Such supramolecular systems were found to be very stable; therefore, they can be regarded as convenient models for studying photoinduced intermolecular electron transfer [12] and promising species with versatile electrochemical properties [13]. However, the high potential of bis-crown-containing stilbenes as building blocks for assembly of complex supramolecular systems has not been explored to a sufficient extent. One of the main reasons is relatively difficult preparation of these compounds. Therefore, the goal of the present work was to develop a convenient procedure for the synthesis of symmetric stilbenes...

A series of novel supramolecular multicomponent complexes of para-aminobenzoic acid (PABA) with N-containing cyclic molecules and aza-crown ethers, (H 2 PPz)

Due to hydrogen bonding, bis(18 crown 6) stilbene forms 1 : 1, 1 : 2, and 2 : 2 complexes with H 3 N + (CH 2 ) n NH 3 + 2ClO 4 -salts (n = 2-10, 12). The length of the polymethylene chain in the diammonium ions affects the phototransformation direction of stilbene and the com position of the products. In the 2 : 2 bispseudosandwich complexes with relatively short alkanediammonium ions (n = 2-4), the stereoselective reaction of [2+2] photocycloaddition proceeds to form mainly the rctt isomer of the cyclobutane derivative. The structure of rctt cyclobutane derivative as a complex with H 3 N + (CH 2 ) 4 NH 3 + 2ClO 4 -was confirmed by X ray diffraction analysis.Stilbenes and their analogs containing the 1,2 di(aryl/ hetaryl)ethylene structural fragment are objects of numerous studies, because they possess remarkable spectral fluorescence and photochemical properties, such as the ability to reversible reactions of E-Z isomeriza tion, electrocyclization, and [2+2] photocycloaddition (PCA). 1-3 These properties were used for the creation of optoelectronic media 4 and production of multiphoton absorption materials for lasers 5 and were proposed for application in information optical recording and storage systems, 6 molecular electronic devices, switchers, and machines. 7, 8 The influence on the photochemical properties of unsaturated compounds of their self assembly to supra molecular ensembles is of considerable interest because of possibility to control the direction of photoreactions in these systems, and their stereochemical result also can often be controlled. For instance, the steroselective PCA of the stilbene derivatives can occur in cavities of cucurbit[8]uril 9 and γ cyclodextrin. 10 Stilbenes contain * Dedicated to Academician A. I. Konovalov on his 75th birthday.ing the crown ether fragment also provide a possibility of comparatively easily control of their self assembly in the presence of metal cations by complexation. 11,12Ammonium ions represent wider possibilities for fine control of the structure and photochemical properties of supramolecules, 13 including those based on crown con taining stilbenes, because the assortment of ammonium compounds is much larger than the range of inorganic substrates. For example, the formation of unusually stable donor acceptor complexes between bis(18 crown 6) stilbene ((E) 1) and diammonium derivatives of viologen analogs, which can serve as fluorescent molecular sensors to alkaline earth metal cations, was observed. 14,15 The stereospecific PCA in the dimeric complex of ammo nium containing mono(24 crown 8) stilbene was stud ied. 16 The PCA reactions of biscrown containing stilbenes can be used, for example, for the creation of new photo switchable complexing agents or systems of optical record ing of information. However, photoreactions of biscrown containing stilbenes almost have not been studied up to recently, because (to a great extent) of low availability of these compounds.

Two novel compounds, (L(1)H)(2)[SiF(6)] x 2H(2)O (1) and (L(2)H)(2)[SiF(5)(H(2)O)](2) x 3H(2)O (2), resulting from the reactions of H(2)SiF(6) with 4'-aminobenzo-12-crown-4 (L(1)) and monoaza-12-crown-4 (L(2)), respectively, were studied by X-ray diffraction and characterised by IR and (19)F NMR spectroscopic methods. Both complexes have ionic structures due to the proton transfer from the fluorosilicic acid to the primary amine group in L(1) and secondary amine group incorporated into the macrocycle L(2). The structure of 1 is composed of [SiF(6)](2-) centrosymmetric anions, N-protonated cations (L(1)H)(+), and two water molecules, all components being bound in the layer through a system of NH[...]F, NH[...]O and OH[...]F hydrogen bonds. The [SiF(6)](2-) anions and water molecules are assembled into inorganic negatively-charged layers via OH[dot dot dot]F hydrogen bonds. The structure of 2 is a rare example of stabilisation of the complex anion [SiF(5)(H(2)O)](-), the labile product of hydrolytic transformations of the [SiF(6)](2-) anion in an aqueous solution. The components of 2, i.e., [SiF(5)(H(2)O)](-), (L(2)H)(+), and water molecules, are linked by a system of NH[...]F, NH[...]O, OH[...]F, OH[dot dot dot]O hydrogen bonds. In a way similar to 1, the [SiF(5)(H(2)O)](-) anions and water molecules in 2 are combined into an inorganic negatively-charged layer through OH[...]F and OH[...]O interactions.