Evgeniya A. Svidchenko

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.

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.

Synthesis and photovoltaic effect in red/near-infrared absorbing A-D-A-D-A-type oligothiophenes containing benzothiadiazole and thienothiadiazole central units

Abstract. Two π-conjugated acceptor-donor-acceptor-donor-acceptor-type (A-D-A-D-A) oligothiophenes, TT-(2T-DCV-Hex)2 and BT-(2T-DCV-Hex)2 were designed and synthesized with thienothiadiazole (TT) or benzothiadiazole (BT) as the core and dicyanovinyl (DCV) as the terminal acceptor groups for comprehensively investigating and understanding structure–property relationships. The resulting oligomers were first characterized by thermal analysis, UV-Vis spectroscopy, and cyclic voltammetry. By simply changing the BT to TT core in these two oligothiophenes, the highest occupied molecular orbital levels were varied from −5.55  eV for BT-(2T-DCV-Hex)2 to −5.11  eV for TT-(2T-DCV-Hex)2, and the optical band gaps were varied from 1.72 eV for BT-(2T-DCV-Hex)2 to 1.25 eV for TT-(2T-DCV-Hex)2, ascribed to the stronger electron accepting character of the TT core. However, the power conversion efficiency of bulk heterojunction organic solar cells (OSCs) with TT-(2T-DCV-Hex)2 as donor and [6,6]-phenyl C70-butyric acid methyl ester (PC71BM) as acceptor was measured to be 0.04% only, which is much lower than that of BT-(2T-DCV-Hex)2:PC71BM (1.54%). Compared to the TT-(2T-DCV-Hex)2 system, the BT-(2T-DCV-Hex)2 based device shows smoother film surface morphology, and superior charge generation and charge carrier mobilities. Therefore, the results clearly demonstrate that in addition to modifying the alkyl side chains and π-bridge lengths, the design of new small molecules for high-performance OSCs should also aim to choose suitable acceptor units.

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.

Synthesis and photophysical properties of halogenated derivatives of (dibenzoylmethanato)boron difluoride

A series of (dibenzoylmethanato)boron difluoride (BF2DBM) derivatives with a halogen atom in one of the phenyl rings at the para-position were synthesized and used to elucidate the effects of changing the attached halogen atom on the photophysical properties of BF2DBM. The room-temperature absorption and fluorescence maxima of fluoro-, chloro-, bromo- and iodo-substituted derivatives of BF2DBM in THF are red-shifted by about 2-10nm relative to the corresponding peaks of the parent BF2DBM. The fluorescence quantum yields of the halogenated BF2DBMs (except the iodinated derivative) are larger than that of the unsubstituted BF2DBM. All the synthesized compounds are able to form fluorescent exciplexes with benzene and toluene (emission maxima at λem=433 and 445nm, respectively). The conformational structure and electronic spectral properties of halogenated BF2DBMs have been modeled by DFT/TDDFT calculations at the PBE0/SVP level of theory. The structure and fluorescence spectra of exciplexes were calculated using the CIS method with empirical dispersion correction.

Influence of chemical structure of branched and dendritic organosilicon luminophores on their optical and thermal properties

Abstract Synthesis and investigation of optical and thermal properties of a homologous series of highly luminescent nanostructured organosilicon luminophores (NOLs) containing different donor to acceptor ratio (D:A) are reported. Each of the NOL consists of a 1,4-bis(5-phenylthienyl-2-yl)benzene (PTPTP) acceptor unit and four, six or twelve 2,2′-bithienyl donor fragments connected to each other through two or six silicon atoms. These complex molecules show a “molecular antenna” effect with high efficiency of intramolecular energy transfer about 97-98% combined with excellent photoluminescence (PL) quantum yield of 84-91% and fast PL decay time of 0.90-0.95 ns. A significant increase of the molar extinction coefficient from 94 000 to 257 000 M−1cm−1 with increasing the D:A ratio from 4:1 to 12:1 was observed. It was found that increasing the branching extent in the NOLs prohibits their crystallization. Thermal gravimetric analysis (TGA) showed that all the NOLs reported, regardless of their branching extent, are thermally stable up to 455 °C under nitrogen. These characteristics make them promising materials for various organic photonics applications.

Fabrication of microstructured materials based on chitosan and D,L-lactide copolymers using laser-induced microstereolithography

The graft copolymers of chitosan and oligo(D,L-lactide) obtained by solid-phase synthesis have been used as the basis of photosensitive compositions for the fabrication of three-dimensional microstructures by laser-induced stereolithography. The electronic absorption spectra of the copolymers are close to the sum of the spectra of native chitosan and polylactide, which has been chosen as a model of grafted oligolactide chains. The fundamental absorption bands of the copolymers lie in a range to 500 nm, and their contribution to the absorption intensity of a photosensitive composition based on the copolymers at second harmonic laser frequency is insignificant. Depending on the macromolecular characteristics of the copolymers, the three-dimensional crosslinking of photosensitive compositions on their basis in the course of microstructuring occurs with different efficiency.

Photochemical synthesis and formation mechanisms of polyvinyl acetate–CoIII(salen) “dormant” chains during “living” radical polymerization

The formation of “dormant” chains due to the acceptance of the photodissociation products of vinyl acetate by stable CoII(salen) radicals was studied. The rate of formation of “dormant” chains was found experimentally to be considerably higher than that of initiating radicals upon the initiator-free photopolymerization of vinyl acetate. A high rate of formation of “dormant” chains is caused by supression of the cell effect in the presence of a strong inhibitor. A kinetic scheme was proposed which allowed drawing up a mechanism of formation of “dormant” chains as a mathematical model suitable for the quantitative description of the process. The comparison between the absorption spectra of the reaction system at different reaction steps and the quantum chemically calculated spectra of forming “dormant” chains showed the polymer chain initiation to afford the acyl radical. The constants for the growing radicals–CoII(salen) interaction, the quantum yield of the Co–C bond dissociation in “dormant” chains, and the quantum yield of the initiator-free vinyl acetate photopolymerization were determined.