A. M. Muzafarov

Bottom-up organic integrated circuits

Self-assembly—the autonomous organization of components into patterns and structures—is a promising technology for the mass production of organic electronics. Making integrated circuits using a bottom-up approach involving self-assembling molecules was proposed in the 1970s. The basic building block of such an integrated circuit is the self-assembled-monolayer field-effect transistor (SAMFET), where the semiconductor is a monolayer spontaneously formed on the gate dielectric. In the SAMFETs fabricated so far, current modulation has only been observed in submicrometre channels, the lack of efficient charge transport in longer channels being due to defects and the limited intermolecular π–π coupling between the molecules in the self-assembled monolayers. Low field-effect carrier mobility, low yield and poor reproducibility have prohibited the realization of bottom-up integrated circuits. Here we demonstrate SAMFETs with long-range intermolecular π–π coupling in the monolayer. We achieve dense packing by using liquid-crystalline molecules consisting of a π-conjugated mesogenic core separated by a long aliphatic chain from a monofunctionalized anchor group. The resulting SAMFETs exhibit a bulk-like carrier mobility, large current modulation and high reproducibility. As a first step towards functional circuits, we combine the SAMFETs into logic gates as inverters; the small parameter spread then allows us to combine the inverters into ring oscillators. We demonstrate real logic functionality by constructing a 15-bit code generator in which hundreds of SAMFETs are addressed simultaneously. Bridging the gap between discrete monolayer transistors and functional self-assembled integrated circuits puts bottom-up electronics in a new perspective.

Liquid crystalline carbosilane dendrimers: First generation

Abstract An approach to the synthesis of a new class of liquid crystalline (LC) compounds, dendrimers of regular structure with terminal mesogenic groups, was elaborated. LC dendrimers based on the carbosilane dendritic matrix of first generation were synthesized. Cyanobiphenyl, methoxyphenyl benzoate and cholesteryl groups were used as mesogenic fragments. Individuality and structure of all compounds obtained was proved by GPC together with 1H- and 29Si NMR methods. The mesomorphic behaviour and structure of the LC dendrimers synthesized were investigated. It is argued that different mesophases of the smectic type are realized in all cases. It is shown that the mesophase type of these compounds essentially depends on the chemical nature of the mesogenic groups.

Hyperbranched polyalkenylsilanes by hydrosilylation with platinum catalysts. I. Polymerization

Hyperbranched polycarbosilanes were synthesized by hydrosilylation addition of methyldivinylsilane, methyldiallylsilane, triallylsilane, and methyldiundecenylsilane. Molecular mass distributions of the hyperbranched polymers were investigated upon systematic variation of the reaction conditions. The formation of hyperbranched polycarbosilanes depended strongly on the reaction conditions and the monomer structure. Although cyclization reactions impeded the build up of molecular weight, crosslinking due to rearrangement reactions caused the formation of multimodal molecular weight distributions and gelation. Crosslinking could be avoided by the appropriate choice of the reaction conditions. In the case of methyldiundecenylsilane, where the distance between the double bond and silicon atom essentially was enlarged, high molecular weight polymers with remarkably narrow molecular weight distributions were obtained; the molecular mass could be controlled by subsequent addition of further monomer.

Macromolecular nano-objects as a promising direction of polymer chemistry

The main features of the manifestation of polymer characteristics of macromolecular nanoobjects are summarized and analyzed in comparison with classical linear systems. This study is primarily focused on dendrimers that exhibit qualitative changes in their characteristics after passing from lower to higher generations within the same homologous series. The above changes are shown to be typical for other representatives of a similar class of polymers.

Preparation of multi-arm star polymers with polylithiated carbosilane dendrimers†

Polyfunctional dendrimers are employed for the synthesis of multi-arm star-shaped polymers. Terminal allyl groups of a carbosilane dendrimer have been partly extended by hydrosilylation-addition of didecylmethylsilane and partly lithiated by reaction with butyllithium. Due to the peculiar structure of the dendritic polylithium compounds, the carbanionic sites were screened from intermolecular interaction and did not aggregate. Good solubility and accessibility for different monomers allowed the preparation of new star-branched poly(dimethylsiloxane), polystyrene and poly(ethylene oxide) polymers.

A biphase H2O/CO2 system as a versatile reaction medium for organic synthesis

We review activity on the usage of a biphase H2O/CO2 system in organic synthesis as a reaction medium of green chemistry. The formation of self-neutralizing carbonic acid in such a system eliminates the problem of salt disposal, typical for acid-catalyzed reactions with the usual mineral and organic acids. A large variety of different reactions to be performed in the biphase H2O/CO2 system are discussed in detail, including cyclization/cycloaddition, hydroformylation, hydrogenation, reduction, coupling, rearrangement, substitution, addition, halogenation, hydrolysis, oxidation and others. These reactions cover a significant part of modern organic synthesis. The main physical properties of carbonic acid being formed in the biphase H2O/CO2 system and their dependence on the temperature and pressure of saturating CO2 are analyzed. The problem with the search for the most optimal reaction conditions from the viewpoint of selection of appropriate pressure and temperature regions for the best yields and selectivity achievable is addressed in general. Comparison with formation and utilization of peroxycarbonic acids, alkylcarbonic acids and carbamic acids by means of saturation with pressurized CO2 of some other biphase systems is discussed in relationship to organic synthesis as well. The influence of a CO2 admixture on the unique properties of high temperature water, another promising green solvent, is also considered.

Polycondensation of alkoxysilanes in an active medium as a versatile method for the preparation of polyorganosiloxanes

Hydrolytic polycondensation of functional derivatives of silicon is an important method for preparation of polysiloxanes of different structure ranging from organocyclosiloxanes to high-molecular-weight linear, cyclolinear, or branched polymers. The most widely used version of hydrolytic polycondensation is based on the use of organochlorosilanes. More than a five decade history of the industrial use of this process resulted in a broad range of organosilicon compounds without which modern technology cannot even be imagined [1]. However, until now, it was impossible to solve two fundamental problems, namely, eliminate the use of chlorosilanes in polysiloxane preparation processes and carry out hydrolytic polycondensation under homogeneous conditions. The significance of the first issue is obvious in view of the need to decrease the environmental pressure. Currently, the use of alkoxy derivatives instead of organochlorosilanes is held up not only by the lack of industrial direct synthesis of organoalkoxysilanes but also by the difficulty to control the polymer production processes from these raw materials. The solution of the latter problem would markedly increase the process controllability, most of all, through control of the product structures. A study of the reaction of organoalkoxysilanes with an excess of anhydrous acetic acid has shown that the process can be accompanied by complete conversion of alkoxysilyl groups within polyfunctional oligomers or their mixtures with alkoxysilanes. Acetic acid was used as the active reaction medium. A fundamental difference between the active medium and common organic solvents is that the former does not merely dissolve the reactants and products but is also a coreactant. Analysis of the literature concerning this pair of reactants has shown that acetic acid either functioned as an active solvent [2‐4] (in this case, water was added to the reaction mixture for hydrolysis) or as a reactant [5] (in this case, complete conversion of alkoxysilyl groups could not be attained). The authors were the first to demonstrate that an excess of anhydrous acetic acid induces the process to follow the hydrolytic polycondensation mechanism, the required water being generated in the reaction system in amounts needed for complete conversion of the alkoxysilyl groups. The key studies were performed for the reaction of acetic acid with dimethyldimethoxysilane. For the convenience of monitoring the reaction, it was carried out in deuterated acetic acid ( CD 3 COOD ). In this case, the variation of the reactant concentrations could be monitored by recording the 1 H NMR spectra of samples taken directly from the reaction mixture without any additional treatment. The signals for different methoxygroup protons (Fig. 1) were assigned on the basis of preliminary experiments including measuring the individual spectra of the major components of the reaction mixture. The absence of acetic acid protons in the spectrum made it possible to calculate the relative concentrations of functional groups in the reactants and products from the intensities I of the proton signals of these groups in the methoxy region (3.3‐3.7 ppm). In view of the fact that the sum of integral intensities in this region ( Σ I ) remains constant during the reaction, the relative concentrations of functional groups ( c rel ) in this spectral region were calculated using the formula c rel = I / Σ I .

Carbosilane dendrimers with diundecylsilyl, diundecylsiloxane, and tetrasiloxane terminal groups: Synthesis and properties

Three derivatives of poly(allylcarbosilane) dendrimers of the fifth generation with different terminal groups are synthesized. The influence of terminal groups on the properties of the dendrimers in bulk and solution is investigated by viscometry, precision adiabatic vacuum and differential scanning calorimetry, dynamic light scattering, and atomic force microscopy. It is shown that the surface layers of the dendrimers substantially affect their properties and behavior. The existence of the second relaxation transition and its dependence on the nature and structure of terminal groups are established. The experimental data indirectly confirm the assumed formation of intermolecular entanglement networks for higher generation dendrimers.

Complementarity of small-angle neutron and X-ray scattering methods for the quantitative structural and dynamical specification of dendritic macromolecules

The structural characteristics of polycarbosilane dendrimers with different molecular architecture were determined in solutions by small angle neutron and X-ray scattering. The same linear dimensions were sized up for the dendrimers both in benzene and chloroform. A solvent molecules penetration inside dendrimer structure in amount up to 30 vol.-% was found from the comparison of the partial and effective scattering volume for the dendrimers in solution.

Nanostructured organosilicon luminophores and their application in highly efficient plastic scintillators

Organic luminophores are widely used in various optoelectronic devices, which serve for photonics, nuclear and particle physics, quantum electronics, medical diagnostics and many other fields of science and technology. Improving their spectral-luminescent characteristics for particular technical requirements of the devices is a challenging task. Here we show a new concept to universal solution of this problem by creation of nanostructured organosilicon luminophores (NOLs), which are a particular type of dendritic molecular antennas. They combine the best properties of organic luminophores and inorganic quantum dots: high absorption cross-section, excellent photoluminescence quantum yield, fast luminescence decay time and good processability. A NOL consists of two types of covalently bonded via silicon atoms organic luminophores with efficient Förster energy transfer between them. Using NOLs in plastic scintillators, widely utilized for radiation detection and in elementary particles discoveries, led to a breakthrough in their efficiency, which combines both high light output and fast decay time. Moreover, for the first time plastic scintillators, which emit light in the desired wavelength region ranging from 370 to 700 nm, have been created. We anticipate further applications of NOLs as working elements of pulsed dye lasers in photonics, optoelectronics and as fluorescent labels in biology and medical diagnostics.