M. V. Alfimov

Supramolecular organic photochemistry of crown-ether-containing styryl dyes

The data on the molecular design, spectral properties, photochemistry and complexation of photochromic crown ethers containing a C=C bond are described systematically and generalized. Prospects for the practical application of these compounds are considered.

Molecular design, photoisomerization and complexation of crown ether styryl dyes

Abstract The structure of a new class of dyes, crown ether styryl dyes, is discussed. Quantitative data on trans—cis-and cis-trans—photoisomerization quantum yields and complexation of the obtained compounds are analyzed. The results of photoinduced and dark complexation of chromogenic 15-crown-5 ether betaine are reported. The formation of an intermolecular coordination bond between a sulfogroup and a metal cation in a crown cavity leading to cis-isomer stabilization has been established.

Molecular simulation of the complexation effects on conformations and electronic absorption spectra of crown ether styryl dyes

Abstract The structure and spectra of new styryl dyes containing a crown ether moiety and a sulfoalkyl group along with their complexes with metal cations are investigated using spectroscopic methods and computer simulation. Large differences between the absorption spectra of the cis form and its complexes with alkaline earth metals are found. The absorption maximum of the high intensity longwave band is at 429 nm for the cis form and at 321–328 nm for the complexes. We show that this difference results from a large distortion of the chromophore geometry, which arises from the formation of an intramolecular coordination bond between the sulfo group and the metal cation captured in the crown cavity. For the distorted geometry, the first electronic transition is symmetry forbidden. The disappearance of the longwave band results in a large hypsochromic shift, observed experimentally.

Crown-containing styryl dyes

Complexation of styryl dyes containing theN-phenylaza-15-crown-5 fragment (trans-2a,b) with Ca2+ ions in MeCN was studied. Unlike cationic dyetrans-2a, betainetrans-2b forms both complexes of 1∶1 stoichiometry and aggregates consisting of four dye molecules and one Ca2+ ion. Cation-induced aggregation was observed also for the analog of dyetrans-2b, which contains a dimethylamino group instead of an azacrown ether fragment (trans-3). Apparently, the interaction between a metal cation and sulfo groups of moleculestrans-2b ortrans-3 makes the main contribution to the stability of aggregates. The dependence of the stability of aggregates on the nature of the metal cation was studied.

Fluorescence of crowned butadienyl dye and its metal complexes

The absorption and fluorescence spectra of complexes of butadienyl dye (1) with lithium, sodium, magnesium, and calcium cations in MeCN were investigated. The addition of Li, Na, Mg, and Ca perchlorates to the solution of dye 1 in acetonitrile results in a significant (up to 5900-cm−1) short-wavelength shift of the absorption spectrum and a small (about 200-cm−1) short-wavelength shift of the fluorescence spectrum. The recoordination reaction in metal complexes of 1 takes place by intramolecular mechanism. The fluorescence quantum yield of 1Li+, 1Na+, and 1Ca2+ is approximately two times higher than that for 1. It was supposed that Li+ cation coordinates predominantly with oxygen atoms of macrocycle and, hence, influences weakly macrocycle nitrogen atoms conjugated with a molecule π-system.

MO calculations on the absorption spectra of organic dimers. The interaction energy between dipole moments of electronic transitions in monomers and the shape of absorption bands

Abstract The interaction energy between dipole moments of electronic transitions in the monomers and the shape of absorption bands of organic dimers are calculated by the CNDO/S-CI method. It is found that the through-space resonance interaction between π orbitals of the monomers has a strong effect on the shifts and widths of absorption bands of dimers with the structure of H -aggregates. A large intermediate region of structures is found between structures corresponding to H - and J -aggregates. In the intermediate region, the interaction energy between the dipole moments of electronic transition in the monomers is small, and the dimer has a broad unshifted spectral band similar to that of the monomers. The large size of the intermediate region is due to a violation of the point-dipole approximation.

Synthesis, structure, and characterization of chromo(fluoro)ionophores with cation-triggered emission based on N-methylaza-crown-ether styryl dyes.

Novel 2-benzothiazole-, 4-pyridine-, and 2- and 4-quinoline-based styryl dyes containing an N-methylbenzoaza-15(18)-crown-5(6)-ether moiety were synthesized. A detailed electronic spectroscopy study revealed high performance of these compounds as optical molecular sensors for alkali and alkaline-earth metal cations. They were shown to considerably surpass analogous chromoionophores based on N-phenylaza-crown ethers regarding both the ionochromism and the cation-binding ability. In addition, they act as fluorescent sensors for the metal cations by demonstrating cation-triggered emission. Upon complexation with Ba(2+), the fluorescence enhancement factor reaches 61. The structural features of dyes and their metal complexes were studied by NMR spectroscopy and X-ray diffraction. The high degree of macrocycle preorganization was found to be one of the factors determining the high cation-binding ability of the sensor molecules based on N-methylbenzoaza-crown ethers.

Structure and ion-complexing properties of an aza-15-crown-5 ether dye: synthesis, crystallography, NMR spectroscopy, spectrophotometry and potentiometry

The perchlorate of 2-{2-[4-(13-aza-1,4,7,10-tetroxa-13-cyclopentadecyl)phenyl]ethenyl}-3-ethylbenzothiazolium (3) has been synthesised and its structure determined in the crystalline state by X-ray diffraction and in solution in acetonitrile by 1H NMR methods. Complexation with barium and silver cations in solution has been studied in comparison with other model azacrown molecules by spectrophotometric and potentiometric methods. With the exception of the puckered azacrown moiety, the structure of 3 is remarkably planar, consistent with extensive π-conjugation throughout the remainder of the molecule in both solid and solution states. Compound 3 forms a stable 1∶1 complex with Ba2+ ions in acetonitrile, with a stability constant of K1xa0=xa080xa0±xa010 dm3 mol–1; the complexation results in major changes in the electronic absorption spectrum of 3, consistent with binding to the azacrown moiety. A model compound, phenylaza-15-crown-5 (2a), was found to bind Ba2+ to form both a 1∶1 ligand–metal complex (LM), with a stability constant of K1xa0=xa0(2.0xa0±xa00.2)xa0×xa0104 dm3 mol–1, and a 2∶1 (L2M) complex, with a stability constant of K2xa0=xa0220xa0±xa020 dm3 mol–1 for binding of the second ligand. The electronic absorption and NMR spectra both indicate binding of the ‘hard’ Ba2+ cation to the azacrown oxygen atoms. However, by contrast, the evidence from NMR data shows that the ‘soft’ Ag+ cation complexes with 2a mainly through a strong interaction with the azacrown nitrogen atom, giving a 1∶1 complex with a stability constant of K1xa0=xa06xa0±xa01 dm3 mol–1, determined by potentiometry. No complexation of 3 with Ag+ is observed. Studies of the simple aza-15-crown-5 ether reveal strong complexation with both Ba2+ (K1xa0×xa0K2xa0>xa01012 dm6 mol–2) and Ag+ [K1xa0=xa0(1.15xa0±xa00.10)xa0×xa0104 dm3 mol–1 and K2xa0=xa0450xa0±xa020 dm3 mol–1].

Supramolecular assemblies of crown-containing 2-styrylbenzothiazole with amino acids

Assemblies of 2-styrylbenzothiazole containing an 18-crown-6 ether fragment with perchlorates of amino acids ClO4-NH3+(CH2)nCOOH (n = 2, 10) were studied by UV, NMR spectroscopy, time-resolved fluorescence spectroscopy and quantum-chemical calculations. The obtained data showed that complex formation of the crown-containing 2-styrylbenzothiazole with amino acids occurs through mono- or ditopic coordination. The formation of a ditopic complex influences the E-Z photoisomerization reaction of 2-styrylbenzothiazole.

CROWN ETHER STYRYL DYES : 22. SYNTHESIS AND COMPLEXATION OF THE CIS-ISOMERS OF PHOTOCHROMIC AZA-15-CROWN-5 ETHERS

New crown ether-containing styryl dyes of the benzothiazole series containing an aza-15-crown-5-ether moiety were synthesized. Thetrans-cis-photoisomerization of these dyes and their analogs was studied; the effect of metal cations on the kinetics of darkcis-trans-isomerization was elucidated. The stability constants of the complexes of thecis-isomers of these dyes with Ca(ClO4)2 were estimated. The dramatic increase (by more than three orders of magnitude) in the stability of the complexes on passing from a cationic dye to a betaine was attributed to the formation of an intramolecular bond in thecis-complexes between the sulfo group of theN-substituent and the metal cation located in the cavity of the azacrown-ether moiety.