Long-range exciton transport in brightly fluorescent furan/phenylene co-oligomer crystals

The design of light-emitting crystalline organic semiconductors for optoelectronic applications requires a thorough understanding of the singlet exciton transport process. In this study, we show that the singlet exciton diffusion length in a promising semiconductor crystal based on furan/phenylene co-oligomers is 24 nm. To achieve this, we employed the photoluminescence quenching technique using a specially synthesized quencher, which is a long furan/phenylene co-oligomer that was facilely implanted into the host crystal lattice. Extensive Monte-Carlo simulations, exciton-exciton annihilation experiments and numerical modelling fully supported our findings. We further demonstrated the high potential of the furan/phenylene co-oligomer crystals for light-emitting applications by fabricating solution-processed organic light emitting transistors

Second-order nonlinear optical properties of composite material of an azo-chromophore with a tricyanodiphenyl acceptor in a poly(styrene-co-methyl methacrylate) matrix

© 2017 Elsevier B.V.The composite material of new synthesized 4-((4-(N,N-n-dibutylamino) phenyl)diazenyl)-biphenyl-2,3,4-tricarbonitrile (GAS dye) in commercial poly(styrene-co-methyl methacrylate) (PSMMA) was prepared, poled and its nonlinear optical properties compared with DR1 dye were studied. High thermal stability of the composite material was revealed, and the maximal concentration of the chromophore was found to reach ∼20 wt%. The dipole moment, polarizability tensor, and first hyperpolarizability tensor of the investigated dyes were calculated by within the framework of the coupled perturbed density functional theory. A nanosecond second-harmonic generation Maker fringes technique was used which is capable of providing the magnitude of the second-order nonlinearity of optical materials at a wavelength of 1064 nm. For the tested GAS–PSMMA composite material, maximal coefficient d33 was found to be 50 pm/V. The nonlinear optical response, which was achieved here, shows possible usefulness of the GAS dye as a component for molecular design of nonlinear-optical materials with advanced characteristics

Second-order nonlinear optical properties of composite material of an azo-chromophore with a tricyanodiphenyl acceptor in a poly(styrene-co-methyl methacrylate) matrix

© 2017 Elsevier B.V.The composite material of new synthesized 4-((4-(N,N-n-dibutylamino) phenyl)diazenyl)-biphenyl-2,3,4-tricarbonitrile (GAS dye) in commercial poly(styrene-co-methyl methacrylate) (PSMMA) was prepared, poled and its nonlinear optical properties compared with DR1 dye were studied. High thermal stability of the composite material was revealed, and the maximal concentration of the chromophore was found to reach ∼20 wt%. The dipole moment, polarizability tensor, and first hyperpolarizability tensor of the investigated dyes were calculated by within the framework of the coupled perturbed density functional theory. A nanosecond second-harmonic generation Maker fringes technique was used which is capable of providing the magnitude of the second-order nonlinearity of optical materials at a wavelength of 1064 nm. For the tested GAS–PSMMA composite material, maximal coefficient d33 was found to be 50 pm/V. The nonlinear optical response, which was achieved here, shows possible usefulness of the GAS dye as a component for molecular design of nonlinear-optical materials with advanced characteristics

Correction: Gostev et al. In Vivo Stability of Polyurethane-Based Electrospun Vascular Grafts in Terms of Chemistry and Mechanics. Polymers 2020, 12, 845

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Synthesis and thermomechanical properties of hybrid photopolymer films based on the thiol-siloxane and acrylate oligomers

The synthesis of hybrid oligomers for photopolymer compositions was carried out based on the thiol-ene reaction between the tetraacrylate dihydroxydiphenylsulfide derivative and thiol-siloxane oligomer. Thiol-siloxane oligomer was synthesized by condensation of diphenylsilanediol and 3-(mercaptopropyl)-trimethoxysilane. The thiol-siloxane oligomer structure was identified by 1H, 13C, 29Si NMR spectroscopy including COSY, HSQC, and HMBC methods and by MALDI-TOF mass spectrometry. The hybrid oligomers were obtained at different tetraacrylate:thiol-siloxane oligomer ratios (1:2, 1:1, 2:1). The obtained compositions are resistant to the oxygen inhibition of photopolymerization and give flexible, thermostable, and rigid polymer films under UV light at air atmosphere. The degree of the film photopolymerization was monitored by IR spectroscopy. The thermomechanical properties of photopolymer films were determined using thermogravimetric, differential scanning calorimetric, and dynamic mechanical analyses. The storage modulus (E′) at room temperature (1.16–1.88 GPa) and the glass transition temperatures (78–133 °C) were determined for photopolymer films obtained at different ratios of acrylate and thiol-siloxane units. The photocured hybrid films exhibit high stability to thermal decomposition in the inert (T10% over 321 °C) and oxidizing (T10% over 314 °C) atmospheres

Continuous Wave and Time-Resolved Electron Paramagnetic Resonance Study of Photoinduced Radicals in Fluoroacrylic Porous Polymer Films

Fluoroacrylic polymers with inherent micro/nanoporosity are promising media for incorporation of fluorescent molecules and following application as pressure-sensitive paints (PSPs), and UV photostability of PSPs is critically important for their long-term performance. Although photodegradation mechanisms of fluoroacrylic polymers have been studied previously in solutions, they have never been addressed in practically relevant for PSPs solid-state porous films. In this work we combined continuous wave (CW) and time-resolved (TR) electron paramagnetic resonance (EPR) to study UV photodegradation of thin porous films of a few representative fluoroacrylic polymers. Different types of spectra were detected using CW and TR EPR and assigned to the species formed on the inner surface of the pores and in the bulk of the polymer, respectively. The radical pairs formed in the bulk are short-lived, as is evidenced by TR EPR, and most likely recombine back to the initial polymer. On the contrary, the radicals formed on the surface of the pores are metastable in the absence of oxygen; they can be studied by CW EPR and clearly assigned to the radicals of type ·C­(CH₃)­CH₂– (so-called propagating radicals) formed via the cleavage of the C–C bond of the ester side chains and consecutive β-scission. Remarkably, their CW EPR spectra closely resemble solution-state spectra, indicating that these radicals are localized in the pores where the mobility of methyl and methylene protons is not suppressed. Thus, based on complementary results of CW and TR EPR, we conclude that UV photodegradation of porous fluoroacrylic polymer films mainly occurs on the inner surface of the pores, which needs to be considered in future development of this type PSPs

Probing Gas Adsorption in Metal–Organic Framework ZIF‑8 by EPR of Embedded Nitroxides

Metal–organic frameworks (MOFs) are being increasingly considered as promising materials for gas separation and storage, yet specific interactions between gas molecules and the inner surface of pores are still not well understood. In this work, we propose a new approach for investigation of such interactions by Electron Paramagnetic Resonance (EPR). We use stable nitroxide radicals as multifunctional agents embedded into the pores of a MOF prior to the gas sorption. They act as EPR-active reporters, and simultaneously as competitor molecules during the gas adsorption process. We exemplify this approach using a ZIF-8 framework, nitroxide TEMPO ((2,2,6,6-tetra­methyl­piperidin-1-yl)­oxyl), and CO₂, N₂, and O₂ gases. The mobility of nitroxide monitored by continuous wave EPR behaves differently upon adsorption of each of these gases. In particular, a noticeable increase of mobility in the presence of CO₂ reveals the weakening of guest–host interactions TEMPO–MOF induced by CO₂, which was qualitatively supported by molecular dynamic calculations. The nitroxides can be embedded in MOFs postsynthetically, and their negligible amounts (≤1 per 1000 cells) are required due to a high sensitivity of EPR. Therefore, the proposed approach is sufficiently versatile and might find broad applications for various MOFs