The photophysical properties of aqueous solution of styryl dye, 4-[(E)-2-(3,4-dimethoxyphenyl)ethenyl]-1-ethylpyridinium perchlorate (dye 1), in the presence of cucurbit[7]uril (CB[7]) was studied by means of fluorescence spectroscopy methods. The production of 1:1 host-guest complexes in the range of CB[7] concentrations up to 16 μM with K = 1.0 × 10(6) M(-1) has been observed, which corresponds to appearance of the isosbestic point at 396 nm in the absorption spectra and a 5-fold increase in fluorescence intensity. The decay of fluorescence was found to fit to double-exponential functions in all cases; the calculated average fluorescence lifetime increases from 145 to 352 ps upon the addition of CB[7]. Rotational relaxation times of dye 1 solutions 119 ± 14 ps without CB[7] and 277 ± 35 ps in the presence of CB[7] have been determined by anisotropy fluorescence method. The comparison of the results of quantum-chemical calculations and experimental data confirms that in the host cavity dye 1 rotates as a whole with CB[7].

Three styryl dyes of the 4-pyridine series that form syn-headto-tail dimeric pairs in polycrystalline films were synthesised. NMR and UV/Vis spectroscopic studies showed that this promotes stereospecific [2+2]-autophotocycloaddition (PCA) in the dimeric pairs to give rctt-isomers of cyclobutane derivatives. For the dye with an N-ammoniopropyl substituent, this transformation was accomplished according to the singlecrystal-to-single-crystal pattern. In aqueous solutions, the dyes and cucurbit[n]urils (CB[n], n = 7, 8) form complexes with a pseudorotaxane structure. CB [7] tends to form 1:1 complexes, and CB[8] forms 1:1 and 2:1 complexes. The structure of the termolecular complex formed by the betaine of the N-sulfonatopropyl styryl dye and CB[8] was determined by X-ray diffraction. The stability of the complexes

No abstract

A procedure was developed for the synthesis of a 18 crown 6 containing styryl dye of the pyridine series. Phototransformation products of the dye that formed upon irradiation with visible light in solution, films, and crystals were studied by 1 H and 13 C NMR spectroscopy and spectrophotometry. Irradiation of solutions of this dye in acetonitrile leads only to reversible E-Z photoisomerization of the C=C bond. Irradiation of a film of the dye induces stereospe cific [2+2] photocycloaddition to form exclusively the rctt isomer of tetrasubstituted cyclobutane. The latter was found to undergo base catalyzed isomerization giving rise to the rcct isomer. X ray diffraction study showed that photocycloaddition occurs in single crystals without their destruction. The structures of the E isomer of the dye and the resulting rctt isomer of the cyclobutane derivative were established. The characteristic features of the molecular packing of the dye favorable for topochemical photocycloaddition in the crystal and the structural changes that accompany the cyclobutane formation are discussed.

New styryl dyes of the pyridine and benzothiazole series were synthesized with the aim of investigating the solid state [2+2] autophotocycloaddition (PCA) reaction. The 1 H NMR spectroscopy showed that for most of the compounds under study, the visible light irradiation of thin polycrystalline films of the dyes affords cyclobutane derivatives. The rate of the photo reaction depends on the structure of the dye and is higher for compounds, which contain a short N substituent in the heterocyclic moiety and have strong absorption in the visible region. Dyes bearing electron releasing substituents in the benzene ring undergo the stereospecific PCA in the syn head to tail dimeric pair to give the only rctt isomer of cyclobutane derivatives. Electron withdrawing and bulky substituents in the benzene fragment of styryl dyes extend the range of the mutual orientations of the molecules in the dimeric pairs, resulting in the forma tion of two or even four isomeric cyclobutanes in the PCA reactions. The structures of some dyes were established by X ray diffraction. In the overwhelming majority of the structures, one of two packing modes, either syn head to tail or syn head to head, with extensive stacking interactions is observed. A rare example of the anti head to head stacking mode was found for the dicationic dye containing the bulky N + (Et)Me 2 substituent in the benzene ring. The syn head to tail and anti head to head stacking modes can facilitate the PCA reaction due to the close spatial proximity of the ethylenic bonds and their parallel orientation in the dimeric pairs of the dye molecules.