N. A. Lobova

Photosensitive molecular tweezers. 3.* Synthesis and homoditopic complex formation of a bisstyryl dye containing two crown-ether fragments with diammonium salts

A new molecular tweezers, viz., bisstyryl dye containing two 18-crown-6-ether moieties and one p-phenylenedimethylene spacer group, was synthesized. Complex formation of this dye and a model monostyryl dye with ions EtNH3+ and NH3+(CH2)nNH3+ (n = 2−6) in MeCN was studied using spectrophotometry and 1H NMR spectroscopy. The homoditopic bisstyryl dye and diammonium salts form strong supramolecular complexes with pseudocyclic structure.

Synthesis and structure of bis-crown-containing stilbenes

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 1H and 13C NMR spectroscopy and by DFT quantum-chemical calculations.

Specific features of the crystal packing that enable styryl dyes of the pyridine series to undergo the solid-phase [2 + 2] photocycloaddition including the process with single crystal retention

The crystal packing of a number of styryl dyes of the pyridine series is analyzed. The structures of three dyes and three [2 + 2] photocycloaddition (PCA) products, 1,2,3,4-tetrasubstituted cyclobutanes, obtained in single crystals are determined by X-ray diffraction. Stacks of planar organic cations are characteristic of styryl dye packings. The proceeding of the PCA reaction as a single crystal-to-single crystal transformation in the syn head-to-head stacks is in principle impossible. The syn head-to-tail stacking packings are favorable for the PCA reactions resulting in the centrosymmetric rctt isomers of cyclobutane. The stacking packings, in which molecules are related by the twofold axes (the anti arrangement of molecules), are also favorable for PCA in single crystals. In this case, the products are the rtct isomers of cyclobutane. The presence of the I− counterions in a packing is a factor impeding the PCA reaction, because the secondary I…H-C bonds increase the rigidity of the crystal lattice. The conditions necessary for proceeding the PCA reactions in styryl dyes as single crystal-to-single crystal processes are as follows: (1) the stacks split into pairs of organic cations (dimers) with the d distances within 4.2 Å in a dimer and d exceeding 4.2 Å between the dimers; and (2) the dimers are surrounded by flexible shells consisting of anions, solvate molecules, or flexible moieties of the organic cations themselves.

Structural investigation of model compounds for an acceptor component of a new type of charge-transfer complexes based on viologen analogues. Characteristic features of the molecular and supramolecular structures

The crystal and molecular structures of six perchlorates (viologen analogues) are studied. These compounds serve as models of the acceptor component of new charge-transfer complexes containing bis(18-crown-6)stilbene as the donor. The polycyclic aromatic system of divalent cations is demonstrated to be virtually planar. In all cations, the side chains at the nitrogen atoms are oriented in opposite directions almost perpendicular to the plane of the cyclic system. This orientation of the spacers of these carbocations is indicative of their preorganization for the formation of 1: 2 charge-transfer complexes. Analysis of the crystal packings provides evidence that two positive charges on the conjugated systems of the organic cations and the perchlorate anions play a destructive role in the formation of stacking motifs. An increase in the size of the conjugated system and the involvement of an aromatic solvent molecule as an additional building block in a supramolecular system are favorable for the formation of a stacking supramolecular architecture.

Photonics of azacrown-containing styryl dye and its complexes with metal ions: 1. Triplet states

Photophysical processes in a styryl dye; an azacrown-containing analog; and its complexes with barium, lead, calcium, sodium, and silver cations have been studied by laser kinetic and luminescent spectroscopy. The participation of the triplet state in the degradation of photoexcitation energy has been established. Phosphorescence and delayed fluorescence of dyes and its complexes have been revealed found. It has been concluded that the molecules can exist in the excited TICT state.

Spectroscopy of surface-enhanced raman scattering of a complex with charge transfer between a bis-crown-containing stilbene and a bis-ammonium-alkyl derivative of dipyridylethylene

The structure of a charge transfer complex (CTC) formed by a bis-crown-containing stilbene (1) and a dipyridylethylene derivative (2) is studied by surface-enhanced Raman scattering spectroscopy. It is found that an excess of 2 leads to the formation of a 1: 1 CTC structure ([1·2]), whereas an excess of 1 leads to the stabilization of a sandwichlike 2: 1 CTC structure ([1·2·1]). It is also revealed that 1 and diperchlorate of 1-ammoniumpropyl-4-methylpyridinium (5) form a 1: 1 CTC structure, which is much less stable. Analysis of the surface-enhanced Raman scattering data suggests that, in complete agreement with the Mulliken theory, the CTCs under study are ordinary molecular complexes in the ground state and the interaction of a molecular complex with a photon excites the former. The excitation is accompanied by a significant transfer of the electron density from the donor 1 to the acceptor 2 (5). The structural fragments of the molecules responsible for the intermolecular interaction and charge transfer are ascertained using model compounds. The charge transfer in donor-acceptor pairs occurs between the electronic systems of trisubstituted benzene and pyridine. A CTC of the [1·2] or [1·2·1] type contains two equivalent donor-acceptor pairs; however, only one of them is involved in the charge transfer.

Study of complexation of styrylheterocycles with cavitands by spectroscopic methods

The complexation of crown-containing or dimethoxy-substituted styrylheterocycles (guest molecules) with β-cyclodextrin (β-CD), mono-6-amino-6-deoxy-β-cyclodextrin hydrochloride (β-CD-NH3Cl), and cucurbit[7]uril (CB[7]) (host molecules, cavitands) in water and water–acetonitrile solvent mixtures was studied by electronic and 1H NMR spectroscopy. Spectrophotometric, fluorescence, and 1H NMR titration, as well as 2D NMR experiments, were used to infer spectral properties, 1: 1 stoichiometry, a pseudorotaxane structure, and stability of the inclusion complexes formed. The solvent composition, the size and the charge of the heterocyclic moiety, and the size of the crown ether fragment of the guest were found to exert influence on the stability of the complexes. A synergistic effect upon complexation of 18-crown-6-containing styrylpyridines with β-CD-NH3Cl was found to be in place due to a cooperative contribution of encapsulation of the conjugated part of the guest by the cavitand cavity and hydrogen bonding between the crown ether fragment and the ammonium group. A photoinduced protonation of neutral styrylpyridines in water was demonstrated.

Photonics of N -ammonioalkyl derivatives of azacrown-containing styryl dyes

Photophysical and photochemical processes in diperchlorates of styryl dyes containing an N-ammonioalkyl substituent have been studied by the absorption, luminescence, and laser kinetic spectroscopy techniques. Participation of the triplet state in photoexcitation energy degradation processes and the ability of the dyes to enter the trans-cis photoisomerization reaction have been revealed. Dimerization and delayed fluorescence of the dyes at 77 K have been detected.

Synthesis of crown-containing and related hetarylphenylacetylenes and acetylenyl dyes

New 15(18)-crown-5(6)-containing and model methoxy-substituted 1-hetaryl-2-phenylacetylenes of the 4-pyridine and 2-benzothiazole series were synthesized using the addition of bromine to the ethylene fragment of the corresponding styrylheterocycles followed by dehydrobromination under the action of potassium tert-butoxide. The quaternization of the pyridylphenylacetylenes afforded new acetylenyl dyes. The structures of five synthesized compounds were determined by X-ray diffraction analysis.

Fluorescent and photo-optical properties of hydrogen-bonded polymer liquid-crystalline composites based on derivatives of stilbazole and crown ethers

New hydrogen-bonded photochromic stilbazole- and crown-ether-containing polymer LC composites are prepared and characterized. A smectic homopolymer with p-oxybenzoic groups, a nematic homopolymer carrying phenylmethoxy benzoate groups, and a nematic copolymer containing p-oxybenzoic and phenylmethoxy benzoate groups are synthesized and used as polymer matrices for these composites. The phase behavior and photo-optical properties of LC composites of various compositions are studied. A marked difference is observed in the fluorescence spectra for hydrogen-stabilized LC mixtures and model mixtures not forming hydrogen bonds. This effect is explained by the reversible transfer of proton of carboxyl groups involved in hydrogen bonding. It is shown that the complexation of crown-ether-containing groups of LC composites with potassium ions leads to a dramatic reduction in the intensity of fluorescence. This phenomenon may be used for creation of a new generation of sensors for metal ions.