Nikolay M. Surin

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.

Highly Luminescent Solution-Grown Thiophene-Phenylene Co-Oligomer Single Crystals

Thiophene-phenylene co-oligomers (TPCOs) are among the most promising materials for organic light emitting devices. Here we report on record high among TPCO single crystals photoluminescence quantum yield reaching 60%. The solution-grown crystals are stronger luminescent than the vapor-grown ones, in contrast to a common believe that the vapor-processed organic electronic materials show the highest performance. We also demonstrate that the solution-grown TPCO single crystals perform in organic field effect transistors as good as the vapor-grown ones. Altogether, the solution-grown TPCO crystals are demonstrated to hold great potential for organic electronics.

Detection of scintillation light in liquid xenon by multipixel avalanche Geiger photodiode and wavelength shifter

A multipixel avalanche Geiger photodiode with a p-terphenyl wavelength shifter in front of it has been tested in the liquid xenon to detect the 175-nm scintillation light. The detection efficiency of about 10% is obtained. A poly-para-xylylene film was used for protection of the liquid xenon detection medium from p-terphenyl pollution. The film has shown very good and stable adhesion at the low temperatures both to the p-terphenyl surface and to the surface of the stainless steel flange.

Microwave plasma in liquid n-heptane: A study of plasma-chemical reaction products

It has been found that a microwave discharge in liquid n-heptane leads to the formation of a solid phase in the form of carbonaceous nanoparticles. The composition and size of the particles have been determined by means of scanning electron microscopy with energy dispersive analysis and Raman spectroscopy. Using electronic absorption and luminescence spectroscopy, it has been shown that the discharge treatment results in the formation of polycyclic aromatic hydrocarbons in liquid n-heptane.

Luminescence spectral properties of dendritic oligothiophenesilane macromolecules

The luminescence spectral properties of oligothiophenesilane dendrite macromolecules were studied. It was found that the chromophores responsible for the formation of the absorption and luminescence spectra were dendrimer fragments separated by silicon atoms; all the chromophores are equally involved in the formation of the absorption spectra of dendritic macromolecules of the zero, first, second, and third generations. It was shown that for dendrites of the first, second, and third generations, the luminescence spectrum is mainly formed by the chromophore fragments lying in the internal layers of the dendritic macromolecule due to the induction resonance energy transfer of electronic excitation from peripheral to internal chromophore fragments. The conclusion was drawn that synthesis of dendritic macromolecules with internal chromophore fragments possessing a high quantum yield of fluorescence can give actively luminescing nanosized objects with the molar extinction coefficient proportional to the number of fragments ɛmax ≈ 106 l/(mol cm). These compounds can find wide application in transducers for converting various types of ionizing radiation into optical radiation in electroluminescent devices.

A novel highly efficient nanostructured organosilicon luminophore with unusually fast photoluminescence

Synthesis and theoretical and experimental investigations of a novel nanostructured organosilicon luminophore (NOL) containing six 2,2′-bithienyl donor units connected via silicon atoms to a 1,4-bis(5-phenylthienyl-2-yl)-benzene acceptor unit with efficient intramolecular Forster resonance energy transfer are reported. The NOL shows a unique combination of optical properties: a high photoluminescence (PL) quantum yield of up to 91%, a fast PL decay time of down to 800 ps, a large pseudo-Stokes shift of 101 nm and a huge molar extinction coefficient of 1.4 × 105 M−1 cm−1. These peculiarities caused by the specific arrangement of the donor and acceptor fragments at the nanoscale distance within the NOL were correlated with the molecular structure of the NOL using theoretical calculations, which for the first time allowed successful prediction of the oscillator strength, PL decay time and intramolecular energy transfer efficiency. A comparison of the photophysical properties of the NOL with the standard laser dye POPOP in THF and toluene solutions revealed its huge application potential in organic photonics and high energy physics.

Novel Cross-Linked Luminescent Silicone Composites Based on Reactive Nanostructured Organosilicon Luminophores

New functional silyl hydride and vinyl containing methylphenylsiloxane oligomers were synthesized by a polycondensation reaction in the active medium being the solvent, the catalyst and the reactant simultaneously. Hydrosilylation of them in the presence of 0.1 - 3 wt. % of novel reactive nanostructured organosilicon luminophores (NOLs) containing different central luminescent and 2,2’-bithienyl peripheral light harvesting fragments with terminal undecylenic groups led to crosslinked silicone composites with valuable luminescence in different regions of the visible spectrum (blue, yellow or red). Investigation of their optical properties revealed that their absorption and luminescence spectra correspond to those of the diluted solutions of the reactive NOLs used. These findings indicate the absence of any aggregation of NOLs in the crosslinked silicon composites confirming their excellent optical quality. High thermal stability of the reactive NOLs (up to 370 ∘C in argon) and the silicones themselves indicate their great potential for creation of highly efficient thermo and radiation resistant plastic scintillators.

Solid state synthesis of chitosan and its unsaturated derivatives for laser microfabrication of 3D scaffolds

Chitosans with various degrees of deacetylation and molecular weights and their allyl substituted derivatives were obtained through a solvent-free reaction under shear deformation in an extruder. Structure and physical-chemical analysis of the samples were carried out using nuclear magnetic resonance (NMR), ultraviolet (UV) and infrared radiation (IR) spectroscopy. Photosensitive materials based on the synthesized polymers were successfully used for microfabrication of 3D well-defined architectonic structures by laser stereolithography. Study on the metabolic activity of NCTC L929 cultured in the presence of the cured chitosan extracts indicates that the engineered biomaterials could support adhesion, spreading and growth of adherent-dependent cells, and thus could be considered as biocompatible scaffolds.

Effect of electrolytes on the slow aggregation of TiO2 nanocrystals

We studied the slow aggregation of dilute TiO2 hydrosols containing narrow fractions of nanocrystals separated from polydisperse sol by the stepwise coagulation with portions of HCl. It is shown that the kinetics of this process and the structure of formed aggregates greatly depend on the ionic strength and the pH of a medium. It is suggested that, in the presence of various electrolytes, the aggregation proceeds by an identical mechanism. In this case, highly ordered aggregates are formed in which there are thin layers of medium between TiO2 nanocrystals.

Chitosan-g-lactide copolymers for fabrication of 3D scaffolds for tissue engineering

Chitosan-g-oligo (L, D-lactide) copolymers were synthesized and assessed to fabricate a number of 3D scaffolds using a variety of technologies such as oil/water emulsion evaporation technique, freeze-drying and two-photon photopolymerization. Solid-state copolymerization method allowed us to graft up to 160 wt-% of oligolactide onto chitosan backbone via chitosan amino group acetylation with substitution degree reaching up to 0.41. Grafting of hydrophobic oligolactide side chains with polymerization degree up to 10 results in chitosan amphiphilic properties. The synthesized chitosan-g-lactide copolymers were used to design 3D scaffolds for tissue engineering such as spherical microparticles and macroporous hydrogels.