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The chemistry taking place in a high temperature char bed used for binding aromatic tar compounds has been studied in detail. 13 C labelled tar compounds were used to trace the incorporation into the char bed using isotope ratio mass spectrometry (IRMS) and GC–MS. Furthermore, compounds labelled with 2 H (deuterium) were used to support proposed reaction mechanisms. It was found that at 700–800 °C the aromatic tar compounds bind irreversibly to the char by a radical reaction and, hence, become an integrated part of the char. Thermally induced reactions may occur prior to the binding reaction. The findings explain the tar reducing properties of the char bed in two-stage gasifiers. A living char bed for hot gas cleaning is discussed.

It is shown to be possible to develop yacht paint with a reduction of 70% of biocide, without pigments/fillers (cuprous oxide and zinc oxide) that may cause long-term adverse effects in the aquatic environment, and to obtain application and usage properties that match present commercial anti-fouling products for yachts. To be able to reduce the amount of biocide, in this case zinc pyrithione, it is necessary to have control over the amount of biocide present in the surface layer. The control is achieved by encapsulating the biocide in a silica gel. The silica gel is dispersed together with pigments and fillers in the paint. The gel contributes to the polishing properties, where the gel particles are worn down throughout the polishing process. When a gel particle is opened by wear the biocide will be effective on the coating surface. It is also shown that zinc pyrithione is more efficient when it is encapsulated in a gel compared to a situation where it is not. This conclusion is based on the fact that the gel swells when exposed to water, and therefore the leach of zinc pyrithione is initially delayed and the biocide may start to solubilise and degrade. The result is an anti-fouling product that is formulated without introducing new compounds and with reduced amount of zinc pyrithione (1/3). Finally, it is shown that it is possible to make anti-fouling paint for yachts without zinc or copper based pigments by using other traditional pigments and fillers, which have no known long-term adverse effect in the aquatic environment, in combination with the gel. The results are documented in raft tests.

Attachment of molecules and proteins to surfaces is of great interest for the development of a large variety of applications. We present herein a novel approach to efficiently couple a molecule of choice to biological building blocks. We synthesized and employed a new derivative of 5-bromo-7-nitroindoline to attach nucleophilic molecules and proteins to gold surfaces by photochemical activation. The reaction can be seen as a photoactivated alternative to the activated ester type chemistries that are commonly used to attach proteins or molecules to surfaces. We characterize the reaction by UV-vis and NMR spectroscopy, and as test of principle experiment, we show that we can attach proteins to surfaces and demonstrate that we can functionalize gold nanoparticles by this optically induced cross-linking reaction.

A one-pot supercritical fluid (SCF) method was applied to prepare a series of silica aerogels. They were formed from alkoxysilanes by the sol–gel process directly in supercritical carbon dioxide. By this method no additional solvents are needed and the process of drying of wet gel afterwards is simplified. This method was modified by the addition of reactive polydimethylsiloxane (PDMS) chains, which yielded in organically modified silicates, the so-called “ORMOSILS” or in our case “AEROMOSILS” when prepared in the form of aerogels. The investigation of the prepared materials by atomic force microscopy (AFM) showed that they consisted mainly of particles with a diameter of 50–100 nm. 2–3 nm pores in these particles were indicated on the images. Further modification of the SCF method to yield AEROMOSILS with immobilized palladium particles was successful. This material was tested as a catalyst both for batch and continuous supercritical hydrogenation of 2,5-dihydro-2,5-dimethoxy-furane.

Thin films of N , N ′-Bis(benzyl)-3,4,9,10-perylenetetracarboxylic diimide (BPTCDI, Fig. 1b) and N , N ′-Bis(benzyl)-1,4,5,8-naphthalenetetracarboxylic diimide (BNTCDI, Fig. 1d) were thermally deposited in UHV on 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA, Fig. 1a) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA, Fig. 1c) film surfaces, respectively, in order to form organic–organic interfaces so that molecules constituting the interfacing layers differ by the substituent group. The surface potential and the density of unoccupied electron states (DOUS) located 5–25 eV above the Fermi level (E F ) were measured during the film deposition using an incident beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. Analysis of the TCS data allowed us to assign the π( band located 5–7.5 eV above E F for all the four films under study and the higher located σ* 1 and σ* 2 bands and the splitting within them. In order to perform the analysis the molecules were hypothetically divided into benzene-like, conjugated and non-conjugated fragments that may individually contribute to the peaks in the DOUS bands. It was shown that a non-conjugated fragment would serve for decreasing of the energy corresponding to the σ* 1 and σ* 2 bands and the sub-bands within them while an addition of a benzene-like fragment would do the opposite. The BPTCDI/PTCDA and BNTCDI/NTCDA interfaces were found non-reacted and a 4.1±0.1 eV work function value for both BPTCDI and BNTCDI films was determined, which is about 0.25 eV lower than the work functions of the PTCDA and the NTCDA films.

The patterning of a surface using microcontact printing (μCP) generally employs a hydrophobic micropatterned stamp made from poly(dimethylsiloxane) (PDMS) to place ink molecules on a surface with spatial control. We present a simple procedure to hydrophilize PDMS stamps based on the O2 plasma oxidation of PDMS (referred to as PDMSox) and the grafting of poly(ethylene oxide) silanes (PEO−Si) to the oxidized surface. The wetting properties of a PDMSox surface derivatized with PEO having none, one, or two silanes and having chains with 7−70 EO units are inspected. All PDMSox surfaces treated with PEO−Si are hydrophilic and have advancing and receding contact angles of ∼40° and ∼30°, respectively. These surfaces remain hydrophilic for periods longer than 7 days, which saves having to hydrophilize stamps freshly prior to their usage. In particular, grafting a PEO having two triethoxysilane end groups and a molecular weight (MW) of 3400 g mol-1 enables inking and microcontact printing a polar Pd/Sn catalyst for...

Swelling of polystyrene (PS) in supercritical carbon dioxide was studied in situ. Experiments were carried out in a high-pressure cell furnished with an optical channel. This allowed to measure the dynamics of diffusion front propagation in the polymer samples during the swelling process by the use of an optical microscope supplied with a digital video camera. The measurements of this dynamics provided information about diffusion coefficients of CO 2 molecules in PS. Diffusion coefficients and equilibrium sorption degrees of the PS samples were also calculated by the use of a gravimetric method. The data were compared with the results of in situ technique. Impregnation of PS films wish ethyl-2-cyano-3(4′-dimethylaminophenyl)acrylate as a model substance for UV-filters and electrographic materials was carried out.

One-step polycyclization reaction in supercritical carbon dioxide has been carried out for the first time and a thereby set of polyimides has been synthesized. Diphenyl-2,2-hexafluoropropane-3,3′,4,4′-tetracarboxylic acid dianhydride (dianhydride 6F), 4,4′-diaminodiphenyl-2,2-hexafluoropropane (diamine 6F) and 9,9-bis(4-aminophenyl)fluorene were used as monomers. Maximum inherent viscosity of the synthesized polymers is 0.56 dl/g. It is supposed that carbon dioxide act as an acidic catalyst for the reaction in the presence of water admixture.

The article presents NMR investigations of a molecular crystalline material C60(ferrocene‒d10)2, which consists of two highly mobile molecules.13C and1H NMR line shapes and T1relaxation times are discussed and compared with results obtained for the undeuteriated compound. The mobilities of C60and ferrocene molecules were found to increase in the complex in comparison with the two components as crystalline materials.

Promising new technique of polymer deposition from solutions in supercritical carbon dioxide (sc CO2) has been applied to form ultrathin Teflon AF2400 copolymer films on substrates with different properties. Atomic force microscopy study of the coatings morphology has been performed for the first time and has revealed surprisingly high film uniformity, very low roughness, and good stability during the scanning procedure. Our findings have demonstrated the intriguing possibilities of the applied film-forming process allowing to deposit the thin-film coatings and also individual macromolecules in a controllable manner. This is because the variations of solution temperature and pressure influence significantly the dissolving power of sc CO2; therefore, the macromolecule precipitation depends strongly on the thermodynamic regime and can be easily controlled. The influence of substrate properties, exposure conditions, and deposition kinetics on the film morphology, thickness, and level of surface coverage has ...

4,8-Diallyl-2,6-dimethylnaphthalene-1,5-diyl diacetate (1) which is a highly substituted naphthalene derivative has been synthesized in two steps starting from 2,6-dimethyl-1,5-naphthalenediol (3) using a modified Claisen-rearrangement.

Swelling of poly(methyl methacrylate) and poly(butyl methacrylate) samples in supercritical carbon dioxide and propagation of diffusion fronts in the samples were studied in situ at various temperatures and pressures using direct optical observation. The difference in the appearance of diffusion fronts in these polymers with different glass transition temperatures was observed. The diffusion coefficients of carbon dioxide molecules in the polymers were determined both from swelling kinetics and from motion of diffusion fronts. A good agreement between these two values was found. The dependences of the diffusion coefficients and equilibrium swelling degrees of the polymers on pressure and temperature of supercritical carbon dioxide during sample exposure were determined and discussed.

Chiral derivatives of polythiophene (PT) were simulated using molecular dynamics (MD) procedure. The chirality introduced in the side chains of PT derivatives was shown to be responsible for helical conformation of the backbone. The magnitude of changes in helical conformation of the backbone depends crucially on the strength of chiral forces imposed by chiral side chains. The effect was studied in details by performing calculation for different structures of side chains.

Phase behaviour of hydrogen-bonded multicomponent mixtures of bipyridine, dodecyloxybenzoic acid and dicarboxylic acids with poly(acrylic acid) were studied at different compositions and temperatures. It was found that in certain composition ranges, the mixtures from a homogeneous liquid crystalline phase of smectic type with an unusually high enthalpy of transition into the isotropic state. The nature of the anisotropic phase observed in the polymers is discussed. The phase behaviour was studied using IR spectroscopy, differential scanning calorimetry and X-ray structure analysis.

Sandwich structures based on cast films of poly(3-dodecylthiophene) (PDDT) and multilayer Langmuir–Blodgett (LB) corbathiene films are studied under ambient conditions. The two types of the structures demonstrate similar photovoltaic properties. Photovoltage and photoconductivity are particularly distinguishable when n-Si substrate is used in the structures. Two photovoltaic components are observed: caused by light absorption in the film and caused by light absorption in n-Si substrate. Donor–acceptor interaction at film/n-Si interface superposed on rigid-band approach is used to suggest mechanisms of the phenomena observed. The mechanisms may be used in order to provide a low work function electrode for organic light emitting diodes.

A series of cholesteric copolymers containing combined chiral-photochromic side-groups has been obtained and their phase behaviour, optical and photo-optical properties have been studied. All copolymers are characterized by selective light reflection in the visible and IR spectral regions. It is shown that the light can be used as a very effective regulated 'external field' to control locally supramolecular structure and the optical properties of polymer films. The synthesized polymers are shown to be promising candidates for colour data recording.

The most commonly encountered form of echo planar spectroscopy involves oscillating gradients in one spatial dimension during readout. Data are consequently not sampled on a Cartesian grid. A fast gridding algorithm applicable to this particular situation is presented. The method is optimal, i.e., it performs as well as the full discrete Fourier transform for band limited signals while allowing for use of the fast Fourier transform. The method is demonstrated for reconstruction of data that are partially undersampled in the time domain. The advantages of undersampling are lower hardware requirements or fewer interleaves per acquisition. The method is of particular interest when large bandwidths are needed (e.g., for high field scanning) and for scanners with limited gradient performance. The unavoidable artifacts resulting from undersampling are demonstrated to be acceptable for spectroscopy with long echo times.

The conformational properties of binaphthol (BN) derivatives dissolved in a pentylcyanobiphenyl liquid crystalline (LC) matrix were determined by molecular dynamics (MD) simulation. Due to the influence of intermolecular interactions between the molecules of the LC matrix and the BN molecules, the conformations of the BN molecules in LC phase are found to change in the direction from transoid to cisoid on heating that results in decrease of observed helical twisting power (HTP). The changes of molecular conformation are mainly connected with orienting potential acting on solute molecule.

Chiral derivatives of poly(3-(S-3',7'-dimethyloctyl)thiophene) embedded in either poly(methyl methacrylate) (PMMA) or poly(butyl methacrylate) (PBMA) were studied by polarization optical microscopy, UV absorption and circular dichroism (CD) spectroscopy as well as simulated using the Molecular Dynamics procedure. CD spectra change on heating to mirror spectra; for PMMA-containing blends the changes in heating/cooling cycles are reversible. The signs of CD spectra depend on free volume, the packing of side groups in particular. Since in the melt there are no restrictions on the positions of the chiral groups, those groups appears with equal probabilities at any locations with respect to the thiophene ring. By contrast, in clusters restrictions imposed by other alkyl chains result in positioning of chiral methyl groups preferentially on the left or right sides of the thiophene rings. The consequence is the formation of right or left twists in molecular backbones.

Photovoltage and photoconductivity in sandwich thin films devices based on cast regio-regular poly(3-dodecylthiophene) and multilayer LB corbathiene films were experimentally studied. n-Si and p-Si substrates and Al and Au top electrodes were used in the devices. Photovoltage values attained 0.6 V and photocurrents were 10 times bigger than dark currents under monochromatic visible light irradiation with total energy density less than 0.1 mW/cm2. The most pronounced photoresponse component was observed in the incident quanta range around 1.5 eV but only for the devices with n-Si substrate. This fact was accounted for by photovoltaic processes in the chemically formed film/n-Si interface where a negative electric charge is captured. Photovoltage vs. light intensity dependencies measured are in good agreement with this concept. Photovoltage and photoconductivity spectra of LB corbathiene film-based devices have a less pronounced peak corresponding to the films' π–π* transitions. A less pronounced peak in the spectra of poly(3-dodecylthiophene) film-based devices has a shift below the films' π–π* transition energy. That may indicate possible bipolaron formation in the polymer material. The data are further interpreted in terms of energy band diagrams of the devices.

A series of cone 5,17-bis(N-arylaminocarbonyl)calix[4]arenes were synthesized and N-methylated using an easy and high-yielding methylation procedure. The structures of the cone 5,17-bis(N-methyl-N-...

The behaviour of regioregular polypropyl-3-thiophene and polyhexadecyl-3-thiophene in poor and good solution conditions was simulated by molecular dynamics. The single chains and clusters consisting of two molecules in full atomic representation were considered. Three types of stable conformers of the single polypropyl-3-thiophene molecule were found in poor solvent conditions. One type of conformer was revealed for polyhexadecyl-3-thiophene. It was shown that the tendency to intramolecular aggregation in poor solvent conditions is much more pronounced for polythiophenes (PTs) with short substituents. The cluster of PT derivatives was shown to be very stable in poor solvent conditions. The distribution of dihedral angles along the backbone was determined to be much narrower for both intra- and intermolecular aggregates in poor solvent than for single molecules in good solvent. The calculated distribution was related to changes in the absorption spectrum in the solvatochromic transition. The agreement between calculated and experimentally observed solvatochromic changes of the absorption spectrum supports the expectation that PTs with short substituents may form the intramolecular aggregates with revealed structure.

Physical review / E 57(3), 3153 - 3163 (1998). doi:10.1103/PhysRevE.57.3153, We report a detailed structural analysis of the phases of 1,2−sn-dipalmitoylglycerol Langmuir monolayers at room temperature. Pressure-induced transitions have been investigated by combination of molecular-dynamics simulations and grazing-incidence x-ray diffraction (XRD). The diglyceride film undergoes two phase transitions occurring at 38.3 and 39.8Å2/molecule. Simulation indicates that the first transition involves a reorientation of the headgroups while simulation and XRD show that in the second transition the order parameter is the tilt angle of the alkyl chains. A methodology for Fourier analysis of simulated Langmuir monolayers is presented. According to the simulation, in the two states of higher surface pressure the alkyl chains are vertical and pack in a centered-rectangular (nearly hexagonal) lattice. In the second phase transition the alkyl chains start tilting. At the lowest pressure the tilt angle reaches ≈14° in a direction close to a nearest neighbor direction. Both arrangements of the alkyl chains are confirmed by XRD. For higher order and fractional order Bragg peaks, simulations predict higher intensities than observed with XRD. This may indicate that in the simulated monolayer the finite size with periodic boundary conditions imposes a higher degree of order., Published by Inst., Woodbury, NY

The paper is devoted to investigations of spin-lattice relaxation processes in 99% 13C-enriched diamonds. Relaxation time measurements were performed as a function of orientation, magnetic field, and temperature. Both experimental results and theoretical discussion are presented. Multiexponential behavior of nuclear magnetization recovery was observed. There was found no significant influence of the diamond orientation on the nuclear spin-lattice relaxation. The field dependence of the spin-lattice relaxation time was found to be proportional to the second power of the magnetic field. The temperature measurements showed a weak increase of the spin-lattice relaxation time with decreasing temperature. Possible mechanisms of impurity relaxation are considered and compared with the experimental data. Copyright 1998 Academic Press. Copyright 1998 Academic Press

Novel comb-shaped liquid crystalline acrylic copolymers consisting of nematogenic methoxy-phenylbenzoate acrylic monomers (A) together with novel chiral binaphthol (BN) methacrylic monomers (MB-m) were synthesized in this study. The prepared copolymers differ in spacer lengths of MB-m (m = 3, 5, 11) and in their compositions. The homopolymers of the three new chiral BN monomers MB-m were also prepared. Copolymers with a low concentration of BN monomeric units (less than 16 mol %) display a cholesteric mesophase. The induced chirality in the polymers is due to atropisomerism (chirality due to hindered rotation around single bonds) of the BN molecules. The helical twisting power β (HTP) caused by the atropisomeric units in the synthesized copolymers was shown to decrease significantly on heating. The unusually high negative temperature coefficient of HTP observed above the glass transition temperature (T g ) could be explained in terms of conformational changes of the BN molecules in the copolymers.

Photovoltage investigations were performed on Langmuir–Blodgett (LB) corbathiene film (∼100 nm thick) deposited onto silicon substrate using the total current spectroscopy technique under UHV conditions. High photovoltage sensibility (of about 104 V W−1 cm2) was observed under visible-light illumination. The dependence of the photovoltage signal on both the light intensity and the wavelength was examined, and transient characteristics were measured in different spectral ranges. The nature of the observed phenomena is discussed and it is found to be the sum of photovoltage components which are generated at both interfaces: silicon/LB corbathiene film and LB corbathiene film/vacuum. © 1997 Elsevier Science S.A.

Novel liquid crystalline (LC) acrylate side group copolymers, which consist of nematogenic phenyl 4-methoxybenzoate acrylate monomer (A) and novel chiral binaphthyl (BN) methacrylate monomers (MB-n) have been synthesized. The copolymers prepared differ in the spacer lengths of MB-n (n 3,5,11) and in their compositions. The homopolymers of the three new chiral binaphthyl monomers MB-n were also prepared. Copolymers with a low concentration of binaphthyl monomer units (less than 16 mol%) display a cholesteric mesophase. The induced chirality in the polymers is due to atropoisomerism (C2-symmetry) of the molecules. The helical twisting powers (beta), caused by the atropoisomeric units in the synthesized copolymers, were determined, and their temperature dependencies studied. The unusually high negative temperature coefficient of beta observed above the glass transition temperature is explained in terms of conformational changes of the BN molecules in the copolymers.

Conductivity and photoconductivity properties of multilayer Langmuir-Blodgett (LB) films of corbathiene ( ∼ 100 nm thick) have been investigated. The conductivity exhibits anisotropic behaviour, i.e. it is different for lateral and transverse directions. Measurements of lateral photoconductivity and its dependence on wavelength and intensity of exciting light have been performed. The time-resolved decay of the photoinduced conductivity is indicative of more than one recombination mechanism. The results are related to the optical absorption features and discussed in terms of semiconducting concepts. Lateral photoconductivity has been found to be essentially a bulk property of the films. All data obtained arc well reproducible which means that the LB corbathiene films arc stable at room temperature in the current density range investigated ( 10 −7 to 10 −6 A cm −2 ) when subjected to illumination in the wavelength range 300–900 nm (10 16 –10 17 photons cm −2 s −1 ).

Ny rapport og analysekoncept fra en tværfaglig projektgruppe hjælper trykkerier til at dokumentere om emballager af trykt pap til fødevarer lever op til lovgivningens og fødevareindustriens krav.

A number of new chiral binaphthol (BN) derivatives with different substituents R,R′ in the 6,6′-positions in open (BN-diethylethers) and bridged forms (BN-acetals) have been synthesized. The syntheses of the chiral 6,6′-disubstituted-2,2′-diethoxy-1,1′-binaphthyls (R,R′ = -CH'CHCHO, -CH'CH-(p-BrPh), -CH'CH-(p-CHOPh)) and the chiral 9,14-disubstituted-dinaphtho [2,1-d:1′,2′-f][1,3] dioxepins with R,R′ = -CH'CH-(p-BrPh), -CH'CH-(p-CHOPh) are reported for the first time. The possible liquid crystalline properties and molar twisting powers (βM) in three different nematic liquid crystals (LCs) of the BN derivatives were investigated. Derivatives with spatially extended substituents in the 6,6′-positions (e.g. styryl or vinyl) show unusually high molar twisting power (up to 124.5μm−1). A direct correlation between the magnitude of βM and the length of the substituents was found. Bridged forms, in which the dihedral angle θ between the naphthyl moieties is ≊ 54°, show higher twisting power than the corr...

Insoluble deposit formed in aromatic bitters produced from alcoholic extracts of about 30 different botanical materials with a dry matter content of 1.67% and 38 vol% alcohol and a characteristic astringent flavour was shown by13C NMR spectroscopy to be a coprecipitate of plant polyphenols, proteins and carbohydrates. The polyphenols in the deposit were flavonoids such as anthocyanidins and anthocyanins, with glucose as the principal carbohydrate and derivatives of cinnamic acid. The deposit formation in the aromatic bitters was accelerated by addition of the radical initiator 2,2′-azobis(2-amidinopropane) dihydrochloride or by addition of hydrogen peroxide in combination with iron(III) nitrate and ascorbic acid as a Fenton reagent. Polymerization of catechin and pelargonidin was shown, in model experiments, to be oxidative and to be accelerated by exposure to light. A mechanism involving oxidative polymerization of polyphenols followed by coprecipitation of polymerized polyphenols, proteins and carbohydrates is proposed for formation of deposits in alcoholic beverages of the bitters type.

Important new information about the crystal structure of dicalcium phosphate (DCP) powders was obtained using the 31P NMR technique. There were two types of powders under investigation. One type includes pure DA (CaHPO4) and DH (CaHPO4· 2H2O) powders, and their mixtures in different proportions. The other includes powders from an industrial production. They were obtained by DH heating. An effective and fast method of identification of the structure of the nuclear nearest surroundings is presented. Determination of the concentration of nearest surroundings corresponding to DA or DH types for the 31P nuclei was demonstrated on examples taken from production powders. Good agreement was found in comparison with data obtained by chemical analysis. Especially interesting information is obtained by using the CP MAS NMR technique. This method allows the following conclusions about the production sample structure to be drawn: it is a powder consisting of DH-type microcrystals, but with numerous vacancies at the positions of water molecules which disappeared during heating.

The structures of colorless, red, and yellow-orange fluorescein have been investigated by a combination of solution and solid state13C NMR. It is demonstrated that the three forms have lactonic, zwitterionic, and quinoid structures, respectively. Conflicting X-ray, NMR, and IR structural evidence is discussed for samples of red fluorescein which cannot readily be obtained in definite crystalline form. It is concluded that solid-state13C NMR spectroscopy is superior by revealing primarily the molecular structure but being fairly insensitive toward lattice variations.

We have analysed scanning tunnelling microscope (STM) images of self-assembled didodecybenzene (DDB) molecules physisorbed on graphite from a DDB solution using octylbenzene as solvent. The DDB images were obtained alternating with images of the graphite substrates using two different bias voltages. The well-known lattice constant of the graphite substrate was used for an accurate determination of the calibration factors and drift of the STM. The DDB unit cells were detected and measured in the Fourier domain and corrected by the calibration data. The commensurability between the graphite lattice and the DDB lattice was analysed. Although the graphite lattice and the DDB lattice planes are parallel, incommensurability was observed as superstructures in the Fourier pattern. The molecules dioctadecyldiselenide and dioctadecyldisulphide also form well-ordered monolayers when adsorbed on graphite from solution. Dioctadecyldiselenide extent the molecules form mmixed structures when physiorbed on the substrate. Theoretical and experimental observations show that S and Se atoms yield markedly different contrasts in the STM images. When imaging mixed surface layers, the dynamic adsorption and dissolution of individual molecules can be followed. A time scale of around 1 s was found for this process. The ratio between fractions of adsorbed molecules of different species was found to be very similar to the ratio in solution, indicating a small difference in bonding energy.

1,2-sn-diglyceride monolayers exhibit unique and complex phase transitions as a function of surface pressure. The dynamical response of the layer on expanding the film has been investigated by computer simulations, (π-A) isotherms and grazing-incidence X-ray diffraction. Good agreement is found between the simulations and experiments. The Langmuir film undergoes two phase transitions occurring at 38.3 and 39.8 A2/molecule. The transition at low surface density is associated with a tilt of ≈14° in the direction close to nearest neighbour. The first transition is unique for the diglyceride molecules and has not been observed for other amphiphilic molecules. It is driven by a competition of hydrophobic/hydrophilic and intra/intermolecular forces and can be pictured as a «seesaw» mechanism. Due to the close packing of the chains at high surface pressure, the sn-1 ester group aligns with the alkyl chain, and only the sn-2 ester group is favoured to lay at the aqueous interface. Hydrophilic forces attract the sn-1 ester group, but its motion towards the aqueous subphase is hindered by intra- and intermolecular chain interactions. On expansion, the intermolecular interaction decreases, and at the first transition, the intramolecular interaction between the two chains is strong enough to cause a «swelling» of the molecules. The diffraction pattern determined in the different mesophases reveals that the layer maintains its hexagonal structure up to the second phase. Concomitant with the tilt, the structure relaxed from a hexagonal to a distorted hexagonal lattice.

Synthesis and properties of new pH-sensitive cholesteric polymer composites are described. Polymer composites, consisting of low molar mass liquid crystal and chiral molecules entrapped in the polymer network, responded to changes in the chemical environment by increasing the pitch of the cholesteric helix. Hydrogen bonding between components of composites stimulates the formation of frozen-in cholesteric structure. Disruption of hydrogen bonds between components by changing the pH results in increasing the pitch of the cholesteric structure and shifting the selective reflection band.

Bianthrones, which are based on two anthrone moieties connected by a double bond, are proposed as a molecular switch involving large conformational changes. Upon substitution, the electronic properties change significantly. Time-resolved optical measurements, such as picosecond excited state spectroscopy and nanosecond time-resolved fluorescence, investigate the excited state relaxation of both the substituted and unsubstituted molecule. Large differences are found in the transient spectra, recorded over the visible region, and their temporal behaviour. Comparison to similar measurements on anthracene identify local electronic states in the spectra. Additional electronic states are induced by substitution. The time decay shows a higly stabilized excited state in the substtuted form. However, fine structure in the relaxation and the dependences of the fluorescence decay indicate complex decay mechanisms. These results are discussed in terms of the proposed conformational change.