Artem V. Bakirov

Thermotropic columnar mesophases of wedge‐shaped benzenesulfonic acid mesogens

The synthesis and characterisation are reported of two groups of new amphiphilic sulfonate compounds, 2,3,4‐tris(dodecyloxy)benzenesulfonates, 2,3,4‐tris(dodecyloxy)benzenesulfonamide and the isomeric 3,4,5‐tris(dodecyloxy)benzenesulfonates. As revealed by a combination of thermo‐optical microscopy, differential scanning calorimetry and X‐ray scattering techniques, the occurrence of mesophases is controlled by the radius of the cation and the symmetry of the molecule. The sulfonates exhibited a rich phase behaviour involving cubic, ordered and disordered columnar mesophases, depending on the counter ion and the type of substitution. It is proposed that the term ‘cunitic’ molecules should be introduced as a class descriptor for wedge‐shaped molecules and their columnar phases.

Effects of oligothiophene π-bridge length on physical and photovoltaic properties of star-shaped molecules for bulk heterojunction solar cells

The preparation of four different star-shaped donor (D)–π–acceptor (A) small molecules (N(Ph-1T-DCN-Me)3, N(Ph-2T-DCN-Me)3, N(Ph-2T-DCN-Hex)3 and N(Ph-3T-DCN-Hex)3) possessing various oligothiophene π-bridge lengths and their use in solution-processed bulk heterojunction small molecule solar cells is reported. Optical and electrochemical data show that increasing oligothiophene π-bridge length leads to a decrease of the optical band gap due to a parallel increase of the highest occupied molecular orbital (HOMO) level. Furthermore, subtle modifications of a molecular π-bridge length strongly affect the thermal behavior, solubility, crystallization, film morphology and charge carrier mobility, which in turn significantly change the device performance. Although the moderately increasing oligothiophene π-bridge length uplifts the HOMO level, it nevertheless induces an increase of the efficiency of the resulting solar cells due to a simultaneous improvement of the short circuit current (Jsc) and fill factor (FF). The study demonstrates that such an approach can represent an interesting tool for the effective modulation of the photovoltaic properties of the organic solar cells (OSCs) at a moderate cost.

Star-shaped D–π–A oligothiophenes with a tris(2-methoxyphenyl)amine core and alkyldicyanovinyl groups: synthesis and physical and photovoltaic properties

Synthesis of a series of star-shaped oligomers having a novel electron donating tris(2-methoxyphenyl)amine (m-TPA) core, which is linked through a bithiophene or terthiophene π-bridge with electron-deficient alkyldicyanovinyl (alkyl-DCV) groups, is described. A comprehensive study of the oligomers revealed significant dependence of their physical properties, including absorption, molecular frontier energy levels, crystal packing, and melting and glass transition temperatures, upon the chemical structure. A comparison of their photophysical properties to the nearest analog having the common dicyanovinyl (DCV) groups demonstrated a number of benefits to use alkyl-DCV units for the design of donor–acceptor small molecules: higher solubility, increased electrochemical stability, better photovoltaic performance, and possibility to control the relative physical and photovoltaic properties by a simple adjustment of alkyl and π-bridge lengths. Modification of the well-known triphenylamine (TPA) core in the star-shaped oligomers by methoxy groups increases not only solubility, but also crystallinity of the oligomers, whereas their photovoltaic performance stays on a similar level as their analogs with a TPA core. The study demonstrates that these design strategies represent interesting and simple tools for the effective modulation of properties of star-shaped molecules.

Self-assembling supramolecular systems of different symmetry formed by wedged macromolecular dendrons

The main stages of the self-assembling of supramolecular ensembles have been revealed by studying different functional wedged macromolecules: polymethacrylates with tapered side chains based on gallic acid, their macromonomers, and salts of 2,3,4- and 3,4,5-tris(dodecyloxy)benzenesulphonic acid. The first stage is the formation of individual supramolecular aggregates (long cylinders or spherical micelles) due to the weak noncovalent interactions of mesogenic groups and the subsequent ordering in these aggregates, which is accompanied by a decrease in the free energy of the system. Supramolecular aggregates, in turn, form 2D or 3D lattices. The shape of supramolecular aggregates and its change with temperature are delicate functions of the mesogen chemical structure; this circumstance makes it possible to rationally design complex self-assembling systems with the ability to respond smartly to external stimuli. X-ray diffraction analysis allows one to study the structure of supramolecular systems with different degrees of order, determine the type of mesophases formed by these systems, and reveal the phase behavior of the material. Particular attention has been paid to the method for reconstruction of electron density distribution from the relative reflection intensity. The application of a suite of experimental methods, including wide- and small-angle X-ray diffraction, molecular modeling, differential scanning calorimetry, and polarization optical microscopy, allows one to establish the relationship between the shape of the structural unit (molecule or molecular aggregate), the nature of the interaction, and the phase behavior of the material.

Luminescent Organic Semiconducting Langmuir Monolayers

In recent years, monolayer organic field-effect devices such as transistors and sensors have demonstrated their high potential. In contrast, monolayer electroluminescent organic field-effect devices are still in their infancy. One of the key challenges here is to create an organic material that self-organizes in a monolayer and combines efficient charge transport with luminescence. Herein, we report a novel organosilicon derivative of oligothiophene-phenylene dimer D2-Und-PTTP-TMS (D2, tetramethyldisiloxane; Und, undecylenic spacer; P, 1,4-phenylene; T, 2,5-thiophene; TMS, trimethylsilyl) that meets these requirements. The self-assembled Langmuir monolayers of the dimer were investigated by steady-state and time-resolved photoluminescence spectroscopy, atomic force microscopy, X-ray reflectometry, and grazing-incidence X-ray diffraction, and their semiconducting properties were evaluated in organic field-effect transistors. We found that the best uniform, fully covered, highly ordered monolayers were semiconducting. Thus, the ordered two-dimensional (2D) packing of conjugated organic molecules in the semiconducting Langmuir monolayer is compatible with its high-yield luminescence, so that 2D molecular aggregation per se does not preclude highly luminescent properties. Our findings pave the way to the rational design of functional materials for monolayer organic light-emitting transistors and other optoelectronic devices.

Cation-Controlled Excimer Packing in Langmuir–Blodgett Films of Hemicyanine Amphiphilic Chromoionophores

Supramolecular structure of ultrathin films of hemicyanine dye bearing a crown ether group (CrHCR) was tuned by lateral pressure and investigated by means of compression isotherms, UV-vis and fluorescence spectroscopies, and X-ray reflectivity. Two different types of aggregation were revealed, depending on the absence or the presence of metal cations in the water subphase. While CrHCR forms at high surface pressures head-to-tail stacking aggregates on pure water, changing the subphase to a metal-cation-containing one leads to the appearance of well-defined excimers with head-to-head orientation. The structure of monolayers transferred onto solid supports by the Langmuir-Blodgett (LB) technique was examined by use of X-ray reflectivity measurements and molecular modeling. A model of cation-induced excimer formation in hemicyanine Langmuir monolayers is proposed. Finally, fluorescence emission properties of LB films of CrHCR can be managed by appropriate changes in the subphase composition, this last one determining the type of chromophore aggregation.

Ion channel forming self-assembling systems based on benzenesulfonic acid with unsaturated aliphatic substituents

The structure and phase behavior of amphiphilic compound sodium 2,3,4-tri(dodecyl)benzenesulfonate, which is capable of self-assembling and contains methacryloyl groups in aliphatic ends, were studied by X-ray diffraction and differential scanning calorimetry. The initial samples are characterized by an ordered columnar ϕoh phase, which, during a rise in temperature to 53°C (at the expense of mobility, an increase in mesogenic groups, and a loss of order in their mutual arrangement), transforms into a disordered columnar ϕh phase. Under the action of irradiation, the cross-linking of benzenesulfonate molecules by methacryloyl groups and the formation of a continuous polymer matrix occur, which leads to a consistency of the column diameter at high temperatures. Cross linking proceeds much more intensively in the area where the disordered columnar phase exists. To analyze the structure of the columnar phase, we used an established technique: the reconstruction of electron density distribution maps in cylindrically symmetric systems from the relation of the intensities of small-angle X-ray reflections. Mutual ordering of benzenesulfonic groups in the area where the ϕoh phase exists leads to the formation of ordered ion channels; this opens up possibilities to use this material to make ion-selective membranes with controlled conductivity.

Nanocomposite nonwoven materials based on polyamide-6 and montmorillonite, prepared by electrospinning of the polymer melt

The effect of montmorillonite on the structure and properties of nonwoven microfibrous materials based on polyamide-6 and prepared by electrospinning of the polymer melt was studied. Addition of 3% montmorillonite into the melt increases its viscosity and electrical conductivity, with the mean diameter of the formed fibers increasing from 8 to 12 μm. As shown by X-ray diffraction, IR spectroscopy, and differential scanning calorimetry, pellets of the pristine polyamide are characterized by prevalence of crystals of the stable α-form, whereas in the composites and nonwoven materials the metastable γ-form prevails. Addition of montmorillonite only slightly influences the contact angles, and the resulting materials exhibit nearly superhydrophobic properties.

Structure of β-chitin from Berryteuthis magister and its transformation during whisker preparation and polymerization filling.

Models for the structures of the β-chitin-protein complex of native and deproteinized squid pen (Berryteuthis magister) based on SAXS and WAXS data are proposed. Chitin fibrils of 25 Å in diameter and persistence length of 1200 Å are immersed in protein matrix. Average distance between fibrils is 42 Å. Deproteinization of the squid pen led to disappearance of the lateral fibril order stabilized by the protein matrix of the native sample. Swelling in water and acrylic acid resulted in an increase in the chitin 010 D-spacing to 14 and 18 Å, respectively. A preparation routine for individual chitin nanofibers of few microns in length and with diameter of 40-60 Å has been developed. During exfoliation of the chitin in acrylic acid the degree of acetylation does not change. Chitin-based nanocomposites can be prepared by polymerization of acrylic acid in swelled deproteinized samples which takes place mainly in the interfibrillar space of β-chitin mainly.

Real time studies of thiophene-based conjugated oligomer solidification

The understanding of the charge transport depending on crystalline structure in organic semiconductors is an important aspect of their functionality in different organic electronic applications. For this reason we performed in situ grazing incidence X-ray diffraction (GIXD) studies to trace the solidification. Simultaneously applying the voltage to the thiophene-based oligomer system the current response was measured. The complex behaviour of the solidification process was monitored from the structure and electrical performance and the highest current was observed for the final solid film. Real time studies revealed that for the oligomers the high crystallinity is a key factor for the improvement of the charge transport.