Identifying the "true" repeat unit of a copolymer using time-resolved electron paramagnetic resonance spectroscopy: a case study involving PNDIT2, NDI-T2 and T-NDI-T

Semiconducting polymers promise to revolutionise the way electronic devices can be built and deployed for a vast array of applications ranging from light-energy conversion to sensors to thermoelectric generators. Conjugated push-pull copolymers consisting of alternating donor and acceptor moieties are at the heart of these applications, due to the large tunability of their electronic structure. Hence, knowing the repeat unit and thus the chromophore of these materials is essential for a detailed understanding of the structure--function relationship of conjugated polymers used in organic electronics applications. Therefore, spectroscopic tools providing the necessary molecular resolution that allows to discriminate between different building blocks and to decide which one actually resembles the electronic structure of the polymer are of utmost importance. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy is both, perfectly suited for this task and clearly superior to optical spectroscopy, particularly when supported by quantum-chemical calculations. This is due to its molecular resolution and unique capability of using light-induced triplet states to probe the electronic structure as well as the impact of the local environment. Here, we demonstrate the power of this approach for the polymer PNDIT2 (poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)}) revealing NDI-T2 unambiguously as the "true" repeat unit of the polymer, representing the chromophore. The alternative building block T-NDI-T has a markedly different electronic structure. These results are of high importance for the rational design of conjugated polymers for organic electronics applications.

Effective prediction of short hydrogen bonds in proteins via machine learning method

Short hydrogen bonds (SHBs), whose donor and acceptor heteroatoms lie within 2.7 Å, exhibit prominent quantum mechanical characters and are connected to a wide range of essential biomolecular processes. However, exact determination of the geometry and functional roles of SHBs requires a protein to be at atomic resolution. In this work, we analyze 1260 high-resolution peptide and protein structures from the Protein Data Bank and develop a boosting based machine learning model to predict the formation of SHBs between amino acids. This model, which we name as machine learning assisted prediction of short hydrogen bonds (MAPSHB), takes into account 21 structural, chemical and sequence features and their interaction effects and effectively categorizes each hydrogen bond in a protein to a short or normal hydrogen bond. The MAPSHB model reveals that the type of the donor amino acid plays a major role in determining the class of a hydrogen bond and that the side chain Tyr-Asp pair demonstrates a significant probability of forming a SHB. Combining electronic structure calculations and energy decomposition analysis, we elucidate how the interplay of competing intermolecular interactions stabilizes the Tyr-Asp SHBs more than other commonly observed combinations of amino acid side chains. The MAPSHB model, which is freely available on our web server, allows one to accurately and efficiently predict the presence of SHBs given a protein structure with moderate or low resolution and will facilitate the experimental and computational refinement of protein structures.

Encapsulation of anticancer drug Ibrance into the CNT(8,8-7) nanotube: A study based on DFT method

In this research, a DFT calculation was performed for study to investigate the encapsulation of the anticancer drug Ibrance into CNT(8,8-7) by using M062X/6-311G * level of theory in the solvent water. TD-DFT method was used to compute the electronic spectra of the Ibrance drug, CNT(8,8-7) and complex CNT(8,8-7)/Ibrance in aqueous medium for the study of non-bonded interaction effect. The non-bonded interaction effects of Ibrance drug with CNT(8,8-7) on the electronic properties and natural charges have been also studied. The results display the change in title parameters after process adsorption. According to NBO results, the molecule Ibrance and CNT(8,8-7) play as both electron donor and acceptor at the complex CNT(8,8-7)/Ibrance. Charge transfer, on the other hand, occurs between the bonding, antibonding, or nonbonding orbitals of Ibrance drug and CNT (8,8-7). According to QTAIM analysis and the LOL and ELF values, all intermolecular bonds in the complex are non-covalent in nature. As a result, CNT(8,8-7) can be thought of as a drug delivery system for transporting Ibrance as an anticancer drug within biological systems.

Combined nanoarchitectonics with self-assembly and electrosynthesis for flexible PTCDIs@PEDOT films with interpenetrating P-N heterojunction

A novel synthesis method for fabricating large area, uniform bulk-heterojunction film with electron donor and acceptor materials homogeneously distributed each other forming a bicontinuous network morphology is reported. The acceptor...

Nanometer-Scaled Landscape of Polymer:Fullerene Blends Mapped with Visible s-SNOM

Bulk heterojunction is one key concept leading to breakthrough in organic photovoltaics. The active layer is expectantly formed of distinct morphologies that carry out their respective roles in photovoltaic performance. The morphology-performance relationship however remains stymied, because unequivocal morphology at the nanoscale is not available. We used scattering-type scanning near-field optical microscopy operating with a visible light source (visible s-SNOM) to disclose the nanomorphology of P3HT:PCBM and pBCN:PCBM blends. Donor and acceptor domain as well as intermixed phase were identified and their intertwined distributions were mapped. We proposed energy landscapes of the BHJ active layer to shed light on the roles played by these morphologies in charge separation, transport and recombination. This study shows that visible s-SNOM is capable of profiling the morphological backdrop pertaining to the operation of high performance organic solar cells.

Determination of Glyphosate and AMPA in Food Samples Using Membrane Extraction Technique for Analytes Preconcentration

The method for determining glyphosate (NPG) and its metabolite AMPA (aminomethyl phosphonic acid) in solid food samples using UAE-SLM-HPLC–PDA technique was developed. Firstly, ultrasonic-assisted solvent extraction (UAE) and protein precipitation step were used for the analyte isolation. Then, the supernatant was evaporated to dryness and redissolved in distilled water (100 mL). The obtained solution was alkalized to pH 11 (with 1 M NaOH) and used directly as donor phase in SLM (supported liquid membrane) extraction. The SLM extraction was performed using 2 M NaCl (5 mL) as an acceptor phase. The flow rate of both phases (donor and acceptor) was set at 0.2 mL/min. The membrane extraction took 24 h but did not require any additional workload. Finally, the SLM extracts were analyzed using the HPLC technique with photo-diode array detector (PDA) and an application of pre-column derivatization with p-toluenesulfonyl chloride. Glyphosate residues were determined in food samples of walnuts, soybeans, barley and lentil samples. The LOD values obtained for the studied food were 0.002 μg g−1 and 0.021 μg g−1 for NPG and AMPA, respectively. Recoveries values ranged from 32% to 69% for NPG, 29% to 56% for AMPA and depended on the type of sample matrix. In the case of buckwheat and rice flour samples, the content of NPG and AMPA was below the detection level of a used analytical method.

TEMPERATURE DEPENDENCE OF OPTICAL TRANSMISSION OF GERMANIUM SINGLE CRYSTALS

Проведены исследования оптического пропускания в диапазоне длин волн 2 - 14 мкм монокристаллов германия, легированных донорными и акцепторными примесями (удельное сопротивление германия 1 - 3 Ом⋅см), в интервале температур от 86 К до 523 К. Рассчитаны значения коэффициентов ослабления α для исследуемых кристаллов; минимальные значения коэффициентов ослабления (0,0015 - 0,0231 см) в интервале температур от 86 К до 323 К характерны для монокристаллов германия, легированных сурьмой, в диапазоне 2 - 11 мкм. Исследования показали, что низкие значения α и коэффициента пропускания на длине волны 3,39 мкм для кристаллов Ge: Sb и Ge: Bi позволяют применять эти низкоомные кристаллы германия для газовых гелий-неоновых лазеров при температурах от 86 К до 323 К. Исследованы температурные изменения геометрии поверхности кристалла на наноразмерном уровне. Показано, что нагрев кристаллического германия приводит к увеличению диффузного отражения излучения от поверхности. Сделан вывод о возможности использования низкоомных кристаллов германия, легированных сурьмой, в качестве элементов инфракрасной оптики в интервале температур 86 - 373 К. In this work, we investigated optical transmission in the wavelength range of 2-14 μm of low-resistance germanium crystals (1 - 3 Ω⋅cm) doped with donor and acceptor impurities in the temperature range from 86 K to 523 K. The values of the attenuation coefficients for investigated crystals are obtained. Minimum attenuation coefficients α of 0,0015 - 00231 cm in the temperature range from 86 K to 323 K are characteristic for germanium single crystals doped with antimony in the range 2,1-11 μm. Studies have shown that the low values of α and the transmittance at a wavelength of 3,39 pm for Ge: Bi and Ge: Sb crystals make it possible to use these low-resistance germanium crystals for gas helium-neon lasers at temperatures from 86 K to 323 K. The temperature changes in the geometry of the crystal surface are investigated at the nanoscale level. It is shown that heating crystalline germanium leads to an increase in the diffuse reflection of radiation from the surface. The possibility of using the low-resistance germanium crystals doped with antimony as elements of infrared optics in the temperature range 86 - 373 K has been demonstrated.

Virtual Screening of TADF Emitters for Single-Layer OLEDs

Thermally-activated delayed fluorescence (TADF) is a concept which helps to harvest triplet excitations, boosting the efficiency of an organic light-emitting diode. TADF can be observed in molecules with spatially separated donor and acceptor groups with a reduced triplet-singlet energy level splitting. TADF materials with balanced electron and hole transport are attractive for realizing efficient single-layer organic light emitting diodes, greatly simplifying their manufacturing and improving their stability. Our goal here is to computationally screen such materials and provide a comprehensive database of compounds with a range of emission wavelengths, ionization energies, and electron affinities.

The Halogenation Effects of Electron Acceptor ITIC for Organic Photovoltaic Nano-Heterojunctions

Molecular engineering plays a critical role in the development of electron donor and acceptor materials for improving power conversion efficiency (PCE) of organic photovoltaics (OPVs). The halogenated acceptor materials in OPVs have shown high PCE. Here, to investigate the halogenation mechanism and the effects on OPV performances, based on the density functional theory calculations with the optimally tuned screened range-separated hybrid functional and the consideration of solid polarization effects, we addressed the halogenation effects of acceptor ITIC, which were modeled by bis-substituted ITIC with halogen and coded as IT-2X (X = F, Cl, Br), and PBDB-T:ITIC, PBDB-T:IT-2X (X = F, Cl, Br) complexes on their geometries, electronic structures, excitations, electrostatic potentials, and the rate constants of charge transfer, exciton dissociation (ED), and charge recombination processes at the heterojunction interface. The results indicated that halogenation of ITIC slightly affects molecular geometric structures, energy levels, optical absorption spectra, exciton binding energies, and excitation properties. However, the halogenation of ITIC significantly enlarges the electrostatic potential difference between the electron acceptor and donor PBDB-T with the order from fluorination and chlorination to bromination. The halogenation also increases the transferred charges of CT states for the complexes. Meanwhile, the halogenation effects on CT energies and electron process rates depend on different haloid elements. No matter which kinds of haloid elements were introduced in the halogenation of acceptors, the ED is always efficient in these OPV devices. This work provides an understanding of the halogenation mechanism, and is also conducive to the designing of novel materials with the aid of the halogenation strategy.