Aggregation and photoisomerization of amphiphilic crown-ether styryl dye in monolayers at the interface

The molecules oftrans-isomer of styryl dye1a, containing the benzo-18-crown-6 moiety and the methoxybenzothiazole residue with theN-octadecyl substituent, were shown to form stable, highly ordered monolayers at the water/air interface. Increasing the surface pressure of the monolayer results in the formation of the H-aggregated molecules of compound1a. The H-aggregates tend to dissociate to the monomerictrans-form, when the monolayer forms in the Langmuir-Blodgett film (LB film). The light irradiation of the LB films leads to the partially reversibletrans-cis-photoisomerization of compound1a, whose efficiency is much lower than that observed in an acetonitrile solution of1a. The aggregation of cis-1a isomers in the LB film is suggested to hamper the reversecis-trans-isomerization. The aggregation oftrans-1a molecules in the LB films does not occur in air, but, after dipping in an aqueous solution, molecules of the LB film slowly form J-aggregates. A model of the structural organization oftrans-1a molecules in the LB films was proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2490–2496, October, 1996.     

Influence of metal cations on spectral characteristics of crown ether vinylogs with different terminal polar groups

Complexation of crown ether vinylogs containing different terminal polar groups with alkali and alkali-earth metal ions in solutions was studied by spectrophotometry. The hypsochromic shift of absorption band maxima in the UV-Vis absorption spectra indicates that the ligands containing the monobenzocrown ether fragments interact with metal ions. The scheme of complexation was proposed, and the stability constants of the complexes were determined. The efficiency of complexation depends on the metal cation size and the structure of the ionophoric fragment.     

Driving forces of the solute self-organization in an evaporating liquid microdroplet

A method is proposed for preparing solid phases of desired morphologies from microscopic droplets on solid substrates with a GMS 417 Arrayer, which is commonly used for biochip production. The initial droplet of an aqueous solution is about 100 pl (about 100 μm in diameter), and the evaporation time is about 0.5 s. Such small solution volumes are first considered from the viewpoint of the solute self-organization. Aqueous solutions of inorganic molecular and ionic substances, organic dyes, and latex colloid particles in the evaporating droplets are experimentally studied. Various substrates and solute concentrations are used. The morphology of the solid phase formed on the substrate after water evaporation is analyzed with the use of computer simulation of dynamics of the latex particles within the evaporating microdroplet. Elucidating the self-organization mechanisms will facilitate producing of the desired morphology of the solid phase, which can find an application in nanotechnology.     

Crystallographic Approach to the [2 + 2] Photocycloaddition Topochemical Reactions of Unsaturated Compounds with Single Crystal Retention

Crystallography Reports - Based on the results of authors' studies, an approach to the analysis of [2 + 2] photocycloaddition (PCA) topochemical reactions of unsaturated compounds, occurring in...     

Crown-containing spirooxazines and spiropyrans

Methods for the synthesis of new spironaphthooxazines containing an aza-15-crown-5 fragment in two different positions (5′ and 9′) were developed. The spectral and photochemical properties of these compounds suggest that two competitive complexation processes occur with alkaline-earth or rare-earth metal cations differing in efficiency and selectivity. A metal cation occupies the optimum position in the crown-ether cavity with respect to the donor oxygen atom of the merocyanine form of the dye and thus can affect more strongly its spectral and photochemical properties than in the case of intermolecular interaction. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1974–1983, October, 1999.     

Effect of cucurbit[8]uril on the spectral and luminescent properties of alkyl-substituted thiacarbocyanines

In the presence of cucurbit[8]uril, polymethine dyes 3,3’-dimethylthiacarbocyanine (DMCy) and 3,3’-diethylthiacarbocyanine (DECy) in aqueous solution can form both nonfluorescing D@CB8 and fluorescing D@2CB8 dimer complexes. The D@2CB8 complexes with DMCy have a symmetrical narrow absorption band. The substitution of the СН₃ group in DMCy for the С₂Н₅ group in the DECy molecule results in a difference in the absorption spectra of the dimeric dye complexes. Quantum chemical calculations show a difference in structure between the dimeric complexes for DMCy and DECy. The enthalpies of dimerization of DMCy and DECy in water and of the formation of complexes D@CB8 and D@2CB8 are close.     

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 -system.     

Novel photoswitchable receptors: synthesis and cation-induced self-assembly into dimeric complexes leading to stereospecific [2+2]-photocycloaddition of styryl dyes containing a 15-crown-5 ether unit

Styryl dyes 4a-e containing a 15-crown-5 ether unit and a quinoline residue with a sulfonatoalkyl or sulfonatobenzyl N-substituent were synthesized. The relationship between the photochemical behavior of these dyes and their aggregates derived from complexation with Mg(2+) in MeCN was studied using (1)H NMR and absorption spectroscopy. The E-isomers of 4a-e were shown to form highly stable dimeric (2:2) complexes with Mg(2+). Upon irradiation with visible light, the dimeric complexes undergo two competing photoreactions, viz., geometric E --> Z isomerization, resulting in an anion-capped 1:1 complex of the Z-isomer with Mg(2+) and stereospecific syn-head-to-tail [2+2]-cycloaddition, affording a single isomer of bis-crown-containing cyclobutane. The N-substituent in the dye has a dramatic effect on the photochemical behavior of the dimeric complex. Molecular dynamics and semiempirical quantum-chemical calculations were carried out to interpret the observed photocycloaddition in the dimer. Conformational equilibria for the dimer of (E)-4b were analyzed using (1)H NMR spectroscopy.     

Complexation of Nitroxide Radicals with Cyclodextrins: Kinetics of Crystal Complex Formation

Using the ESR method in combination with the stop-flow technique the kinetics of crystal complex formation of hydrophobic nitroxide radicals with cyclodextrins has been studied upon mixing cyclodextrin aqueous solutions with nitroxides emulsified in aqueous milieu. The - and -cyclodextrins and the piperidine nitroxide radicals with a OC(O)C_mH_2m+i (m = 7, 10, and 17) substituent in a para-position were used. It was established that the complexation process in the system emulsion of probe–cyclodextrin solution consists of two mainstages. The first stage is the transfer of probes from drops into aqueous solution and the formation of complexes RC_n, where R is the probe, C is cyclodextrin, n = 1, 2 and 3. The second stage is crystal complex formation and growth from solution of RC_n complexes. The results obtained indicate that mainly RC₃ complexes take part in crystallization. It was observed that the characteristic time of crystallization is approximately inversely proportional to the concentration of RC₃ complexes.Equilibrium constants of the processes R + C RC, RC + C RC₂ have been determined. It was found that complexation and further crystallization lead to the formation of monodispersed microcrystals.