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It has been possible to make a detailed study of photoinduced charge separation, photoconductivity and photovoltaic properties of p-Pyr-V2+-Me and p-Pyr-V2+-H in the solid-state. The photoinduced formation of long-lived charge-separated species was revealed.

Research is presented describing the use of 15N and 13C calorimetric, crystallographic and solid-state nuclear magnetic resonance techniques to investigate the phase transitions and polymorphism in 2-(2,4-dinitrobenzyl)-3-methylpyridine.

The photoinduced charge separation and subsequent transport under an external electric field is studied in the poly[bipyridine/(phenylene-vinylene)] derivatives having vinylene subunits separating the bipyridylene vinylene skeleton. The result reveals that the facile electric-field-induced separation of the electron-hole pair.

The effect of environmental factors in the control of proton transfer processes in the crystalline systems of 2-(2,4-dinitrobenzyl)-3-methylpyridine was determined through induction of proton-transfer reactions in a crystalline environment. A formation of a blue-green colored NH tautomer was indictated following exposure of the crystals to near-UV radiation. The product exhibited an unusual monoexponential decay secondary to the difference in thermal stability of the two different NH species.

Abstract: We report on the recombination kinetics of photoexcited polarons and triplet excitons in films of poly(2-methoxy-5-(2′-ethyl-hexyloxy)- 1,4-phenylene vinylene) (MEH-PPV) and MEH-PPV/C60 mixtures. Experimentally, the dependence of the polaron and exciton photoin- duced absorption bands on the excitation intensity and modulation frequency was measured, covering a dynamic range of 4–5 orders of magnitude. We have found that in all cases the recombination kinetics can be successfully described as a “bimolecular dispersive” recom- bination, with the following characteristics of the photoinduced absorption, (a) Sublinear modulation frequency dependence (ω−α , α<l) at high frequencies of both in-phase and quadrature components, (b) Sublinear excitation intensity dependence (I γ ,γ<l), with decreasing ex- ponent as the modulation frequency decreases. The exponent α and the average recombination time vary with the polymer molecular weight. [Copyright &y& Elsevier]

The molecular dyad diphenylphosphine-ethyl bromine naphthaleneimide (Br-DPPENI) emits strong fluorescence and phosphorescence. We studied the intensity and lifetime of the phosphorescence of Br-DPPENI embedded in PMMA films in atmospheres of air, He, Ar, N 2 , and O 2 as a function of pressure between vacuum and ambient pressure (1 bar). The experiment was performed in the frequency domain with a two-channel lock-in amplifier, and the data were analyzed with the polar plot or phasor technique. Reversible shortening of the lifetime due to triplet-triplet annihilation was found in the presence of atmospheric or pure oxygen. With small modulation frequencies, an additional slow component of the phosphorescence dynamics is observed, which is ascribed to the diffusion of oxygen into the sample films.

A systematic study of trends in the lipophilicity of prominent representatives of the opioid family, including natural, semisynthetic, synthetic, and endogenous neuropeptide opioids, is described. This was enabled by a straightforward 1 H NMR-based log P / D determination method developed for compounds holding at least one aromatic hydrogen atom. Moreover, the new method enables a direct simultaneous log D determination of opioid mixtures, overcoming the high sensitivity of this family to the measurement conditions, which is critical when a determination of the exact Δlog D values of matched pairs is required. Interpretation of the experimental Δlog D 7.4 values of selected matched pairs, focusing inter alia on the 3-OMe and 14-OMe motifs in morphinan opioids, is suggested with the aid of DFT calculations and may be useful for the discovery of new opioid therapeutics.

Combined molecular, physicochemical and chemical properties of electrophilic warheads can be applied to create covalent drugs with diverse facets. Here we study these properties in fluorinated diketones (FDKs) and their multicomponent equilibrium systems in the presence of protic nucleophiles, revealing the potential of the CF 2 (CO) 2 group to act as a multifaceted warhead for reversible covalent drugs. The equilibria compositions of various FDKs in water/octanol contain up to nine species. A simultaneous direct species-specific 19 F-NMR-based log P determination of these complex equilibria systems was achieved and revealed in some cases lipophilic to hydrophilic shifts, indicating possible adaptation to different environments. This was also demonstrated in 19 F-MAS-NMR-based water-membrane partitioning measurements. An interpretation of the results is suggested by the aid of a DFT study and 19 F-DOSY-NMR spectroscopy. In dilute solutions, a model FDK reacted with protected cysteine to form two hemi-thioketal regioisomers, indicating possible flexible regio-reactivity of CF 2 (CO) 2 warheads toward cysteine residues., (© 2023. Springer Nature Limited.)

Fluorine atoms play an important role in all branches of chemistry and accordingly, it is very important to study their unique and varied effects systematically, in particular, the structure-physicochemical properties relationship. The present study describes exceptional physicochemical effects resulting from a H/F exchange at the methylene bridge of gem-difunctional compounds. The Δlog P (CF2-CH2) values, that is, the change in lipophilicity, observed for the CH 2 /CF 2 replacement in various α,α-phenoxy- and thiophenoxy-esters/amides, diketones, benzodioxoles and more, fall in the range of 0.6-1.4 units, which for most cases, is far above the values expected for such a replacement. Moreover, for compounds holding more than one such gem-difunctional moiety, the effect is nearly additive, so one can switch from a hydrophilic compound to a lipophilic one in a limited number of H/F exchanges. DFT studies of some of these systems revealed that polarity, conformational preference as well as charge distributions are strongly affected by such hydrogen to fluorine atom substitution. The pronounced effects described, are a result of the interplay between changes in polarity, H-bond basicity and molecular volume, which were obtained with a very low 'cost' in terms of molecular weight or steric effects and may have a great potential for implementation in various fields of chemical sciences., (© 2022 Wiley-VCH GmbH.)

Plasticulture, the practice of using plastic materials in agricultural applications, consumes about 6.7 million tons of plastics every year, which is about 2% of the overall global annual plastics production. For different reasons, plastic material used for agriculture is difficult to recycle. Therefore, most of it is either buried in fertile soils, thereby significantly causing deterioration of their properties, or, at best case, end in landfills where its half-life is measured in decades and even centuries. Hence, developing biodegradable plastic materials that are suitable for agricultural applications is a vital and inevitable need for the global human society. In our labs, two types of potentially biodegradable plastic polymer films were prepared and characterized imidazolium in terms of their bio-degradability. In the first approach, polymers made of ionic liquid monomers were prepared using photo radical induced polymerization. The second approach relies on formation of polyethylene-like n-alkane disulfide polymers from 1,ω-di-thiols through thermally activated air oxidation. These two families of materials were tested for their biodegradability in soils by using a simulation system that combines a controlled environment chamber equipped with a respirometer and a proton-transfer-reaction time of flight mass spectrometer (PTR-TOF-MS) system. This system provides a time-dependent and comprehensive fingerprint of volatiles emitted in the degradation process. The results obtained thus far indicate that whereas the ionic-liquid based polymer does not show significant bio-degradability under the test conditions, the building block monomer, 1,10-n-decane dithiol, as well as its disulfide-based polymer, are bio-degradable. The latter reaching, under basic soil conditions and in room temperature, ∼20% degradation within three months. These results suggest that by introduction of disulfide groups into the polyethylene backbone one may be able to render it biodegradable, thus considerably shortening its half-life in soils. Principal component analysis, PCA, of the data about the total volatiles produced during the degradation in soil indicates a distinctive volatile "fingerprint" of the disulfide-based bio-degradable products which comes from the volatile organic compounds portfolio as recorded by the PTR-TOF-MS. The biodegradation volatile fingerprint of this kind of film was different from the "fingerprint" of the soil background which served as a control. These results can help us to better understand and design biodegradable films for agricultural mulching practices., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Dar, Wu, Zhang, Yu, Qin, Shen, Zou, Poh, Eichen and Achmon.)

Systematically studying the lipophilicity of phosphorus compounds is of great importance for many chemical and biological fields and particularly for medicinal chemistry. Here, we report on the study of trends in the lipophilicity of a wide set of phosphorus compounds relevant to drug design including phosphates, thiophosphates, phosphonates, thiophosphonates, bis-phosphonates, and phosphine chalcogenides. This was enabled by the development of a straightforward log P determination method for phosphorus compounds based on 31 P-NMR spectroscopy. The log P values measured ranged between -3.2 and 3.6, and the trends observed were interpreted using a DFT study of the dipole moments and by H-bond basicity (p K HB ) measurements of selected compounds. Clear signal separation in 31 P-NMR spectroscopy grants the method high tolerability to impurities. Moreover, the wide range of chemical shifts for the phosphorus nucleus (250 to -250 ppm) enables a direct simultaneous log P determination of phosphorus compound mixtures in a single shake-flask experiment and 31 P-NMR analysis.

Amino acid and peptide couplings are widely used in fields related to pharma and materials. Still, current peptide synthesis continues to rely on the use of expensive, water sensitive, and waste-generating coupling reagents, which are often prepared in multi-step sequences and used in excess. Herein is described a peptide coupling reaction design that relies mechanistically on sun-light activation of a 4-dimethylamino-pyridine-alkyl halide charge-transfer complex to generate a novel coupling reagent in situ. The resulting coupling method is rapid, does not require dry solvents or inert atmosphere, and is compatible with all the most common amino acids and protecting groups. Peptide couplings can be run on gram-scale, without the use of special equipment. This method has a significantly reduced environmental and financial footprint compared to standard peptide coupling reactions. Experimental and computational studies support the proposed mechanism., (© 2021 Wiley-VCH GmbH.)