Trans Isomerization Reaction Research Articles

Strategies to Enhance the Stability of Non‐Fullerene Acceptor‐Based Organic Solar Cells

AbstractThrough comprehensive density functional theory calculations, the photodegradation mechanisms, including cis–trans isomerization, electrocyclization, and sigmatropic rearrangement reactions are investigated in indacenodithieno [3,2‐b] thiophene (IT)‐based non‐fullerene acceptors (NFAs). Various functional group substitutions on the core (fluorine, ethyl, and cyano groups) and end groups (fluorine) of NFA are introduced to elucidate the influence of chemical modifications on photodegradation pathways. The findings reveal that the core substitution can effectively suppress electrocyclization and 1,5‐sigmatropic shift reactions, which are major contributors to photodegradation. Furthermore, the electronic, excited‐state, and charge transport properties of pristine and degraded products are studied to gain insights into the impact of degradation on photovoltaic parameters. The results suggest that photodegradation leads to the formation of shallow energy trap states, hindering charge transport and increasing charge recombination, ultimately affecting the power conversion efficiency of organic solar cells (OSCs). The study not only provides a comprehensive understanding of photodegradation mechanisms but also offers valuable molecular design strategies to enhance the stability of NFAs for future large‐scale applications of OSCs. By establishing a clear connection between the chemical structure and photostability of NFA, this research represents a pivotal contribution to the field of organic electronics and sustainable energy technologies.

Theoretical study on the isomerization mechanism of visible light-driven azobenzene-based materials

This article investigates the geometric structure and isomerization mechanism of 4,4-acetamidazobenzene molecules with halogen atoms (F, Cl, Br) substituted at four ortho positions through density functional theory (DFT) calculations. The calculation method was b3lyp/g, and the base set was def2-tzvp. According to DFT calculations, the ortho substitution of the halogen atoms differently distorted the molecular plane of the trans isomers, resulting in obvious absorption peaks in the visible range, giving them visible-light driven properties. In addition, the transition state (TS) of the cis–trans isomerization reaction in the ground state was also found. To study the molecular isomerization mechanism, the potential energy surfaces (PESs) of the ground state (S0), first excited state (S1), and second excited state (S2) of halogen substituted azobenzene derivatives were scanned separately. Through the potential energy surface curve of the ground state, the mechanism of isomerization reaction in the ground state of the four molecules is realized through a rotation-assisted inversion pathway, which is consistent with the calculation of TS. When the molecules are in the excited states, the isomerization pathways are realized through rotation pathways.

Synergy between Lewis acidic metal sites and silanols in Sn- and Ti-Beta for conversion of butenes by DRIFTS

The synergistic effect of Lewis acidic Sn/Ti sites and silanols in Sn- and Ti-Beta zeolites on the reaction pathways and mechanisms of the conversion of butenes was investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy. The double bond migration reaction of n-butene to cis-2-butene followed an AB–AD mechanism, in which hydrogen abstraction (AB) from the methylene group at Lewis acidic Sn/Ti sites afforded an allyl intermediate, followed by synergistic hydrogen addition (AD) on silanols. In contrast, the following cis–trans isomerization reaction between cis-2-butene and trans-2-butene, and the activation of isobutene, followed an AD–AB mechanism via hydrogen addition to the double bond of butenes on silanols, forming an alkoxyl group rather than allyl group as the intermediate owing to the absence of a methylene group in 2-butene and isobutene.

The trans/cis ratio of formic (HCOOH) and thioformic (HC(O)SH) acids in the interstellar medium

Context. Observations of the different isomers of molecules in the interstellar medium (ISM) have revealed that both low- and high-energy isomers can be present in space despite the low temperature conditions. It has been shown that the presence of these isomers may be due to tunneling effects. Aims. We carried out a theoretical study of the cis–trans isomerization reactions of two astrophysically relevant acids, formic acid (HCOOH) and thioformic acid (HC(O)SH), where the latter has recently been discovered in space. We also searched for these molecules towards the hot core G31.41+0.31 to compare their abundances with the expected theoretical isomerization results. Methods. We employed high-level ab initio calculations to study the reaction rate constants of the isomerization reactions. We used the canonical variational transition state theory with the multidimensional small curvature tunneling approximation in the temperature range of 10–400 K. Moreover, we used the spectrum obtained from the ALMA 3mm spectral survey GUAPOS (GUAPOS: G31 Unbiased ALMA sPectral Observational Survey), with a spectral resolution of ~0.488 MHz and an angular resolution of 1.′′2×1.′′2 (~4500 au), to derive column densities of HCOOH and HC(O)SH towards G31.41+0.31. Results. Our results demonstrate that these isomerizations are viable in the conditions of the ISM due to ground-state tunneling effects, which allow the system to reach the thermodynamic equilibrium at moderately low temperatures. At very low temperatures (Tkin ~ 10 K), the reaction rate constants for the cis-to-trans isomerizations are very small, which implies that the cis isomers should not be formed under cold ISM conditions. This is in disagreement with observations of the cis/trans isomers of HCOOH in cold cores where the cis isomer is found to be ~5–6% the trans isomer. At high temperatures (~150–300 K), our theoretical data not only match the observed behavior of the trans/cis abundance ratios for HCOOH (the cis form is undetected), but they support our tentative detection of the trans and – for the first time in the insterstellar medium – the cis isomer of HC(O)SH towards the hot molecular core G31.41+0.31 (with a measured trans/cis abundance ratio of ~3.7). Conclusions. While the trans/cis ratio for HC(O)SH in the ISM depends on the relative stability of the isomers, the trans/cis ratio for HCOOH cannot be explained by isomerization, and is determined by other competitive chemical processes.

Does urea modify microheterogeneous nature of ionic amide deep eutectics? Clues from non-reactive and reactive solute-centered dynamics

The impact of urea on the microheterogeneous nature of acetamide + LiNO3 deep eutectic solvents (DESs) was investigated via following the viscosity coupling of the average timescales of solute rotation, solvation and cis–trans isomerization reaction occurring in such media. Picosecond resolved fluorescence measurements were carried out to access these average relaxation timescales and the solutes employed were the non-reactive probe, coumarin153 (C153), and a reactive probe, trans- 2-[4′-(Dimethylamino) styryl]benzothiazole (DMASBT). DMASBT undergoes fast cis–trans isomerization reaction upon photo-excitation. The coupling to the solution viscosity (η) of the experimentally determined average timescales was then analyzed via the relation, 〈τx〉∝ηp, x denoting rotation, solvation or reaction, and a fractional p considered as solution microheterogeneity reflector. A comparison of the findings between the urea containing and non-urea ionic DESs revealed that addition of urea did not alter the p value for C153 rotation and DMASBT reaction times, while the C153 average solvation times showed a stronger decoupling. This stronger decoupling has been ascribed to the faster rate of solvation upon addition of urea via the participation of the amide group through the collective H-bond excitations. Addition of electrolyte at a fixed amide concentration, on the other hand, makes the fractional viscosity dependence more pronounced for both solvation and rotational dynamics, although the viscosity coupling (p value) of isomerization reaction timescale remains unchanged. DMASBT reveals, through steady state fluorescence measurements, stronger spatial heterogeneity in these solutions than that by C153, and DMASBT better senses the urea or electrolyte induced modulation of spatial heterogeneity.

Effect of cucurbituril on the primary photoprocesses in indocarbocyanine dyes in water

The effect of cucurbit[7,8]urils (CB7, CB8) on photoprocesses in indocarbocyanine dyes has been studied. Complexation with CB7 and CB8 reveals bathochromic shifts of the maxima in the absorption and fluorescence spectra. Fluorescence enhancement and decreasing have been observed for the complexes with CB7 and CB8, respectively. The dyes and their complexes are capable of trans–cis photoisomerization and hardly undergo intersystem crossing to the triplet state. The rate of the thermal cis–trans isomerization reaction is decreased due to complexation.

Effect of thermal decomposition on biodiesel viscosity and cold flow property

Thermal stressing experiments were performed in batch reactors at 250–425°C for 3–63min to evaluate the influence of thermal decomposition on biodiesel viscosity and cold flow properties. Dynamic viscosity was measured by a micro viscometer, and cold flow properties were characterized by differential scanning calorimetry (DSC). The crystallization onset temperature determined by DSC correlates with cold flow properties. Results showed that the cis–trans isomerization reactions had a minimal effect on both viscosity and cold flow properties of biodiesel, but polymerization and pyrolysis reactions had significant influence on both properties. Polymerization reactions resulted in increases in both viscosity and the crystallization onset temperature, while pyrolysis reactions showed the opposite effect. The current study suggests that polymerization reactions should be avoided or minimized during high-temperature non-catalytic homogeneous transesterification reactions for biodiesel production.

Highly Efficient Deep‐Blue Emitters Based on cis and trans N‐Heterocyclic Carbene PtII Acetylide Complexes: Synthesis, Photophysical Properties, and Mechanistic Studies

We have synthesized cis and trans N-heterocyclic carbene (NHC) platinum(II) complexes bearing σ-alkynyl ancillary ligands, namely [Pt(dbim)2 (CCR)2 ] [DBIM=N,N'-didodecylbenzimidazoline-2-ylidene; R=C6 H4 F (4), C6 H5 (5), C6 H2 (OMe)3 (6), C4 H3 S (7), and C6 H4 CCC6 H5 (8)] and [Pt(ibim)2 (CCC6 H5 )2 ] (9) (ibim=N,N'-diisopropylbenzimidazoline-2-ylidene), starting from [Pt(cod)(CCR)2 ] (COD=cyclooctadiene) and 2 equivalents of [dbimH]Br ([ibimH]Br for complexes 9) in the presence of tBuOK and THF. Mechanistic investigations aimed at uncovering the cis to trans isomerization reaction have been performed on the representative cis complex 5 a [Pt(dbim)2 (CCC6 H5 )2 ] and revealed the isomerization to progress smoothly in good yield when 5 a was treated with catalytic amounts of [Pt(cod)(CCR)2 ] at 75 °C in THF or when 5 a was heated at 200 °C in the solid state under an inert atmosphere. Detailed examination of the reactions points to the possible involvement, in a catalytic fashion, of a solvent-stabilized Pt(II) dialkyne complex in the former case and a Pt(0) NHC complex in the latter case, for the transformation of the cis isomer to the corresponding trans complex. Thermal stability and the isomerization process in the solid state have been further investigated on the basis of TGA and DSC measurements. X-ray diffraction studies have been carried out to confirm the solid-state structures of 4 b, 5 a, 5 b, and 9 b. All of the synthesized dialkyne complexes 4-9 exhibit phosphorescence in solution, in the solid state at room temperature (RT), and also in frozen solvent glasses at 77 K. The emission wavelengths and quantum yields have been found to be highly tunable as a function of the alkynyl ligand. In particular, the trans isomer of complex 9 in a spin-coated film (10 wt % in poly(methyl methacrylate), PMMA) exhibits a high phosphorescence quantum yield of 80 %, which is the highest reported for Pt(II) -based deep-blue emitters. Experimental observations and time-dependent density functional theory (TD-DFT) calculations are strongly indicative of the emission being mainly governed by metal-perturbed interligand ((3) IL) charge transfer.

Photoisomerization of Stilbene: A Spin-Flip Density Functional Theory Approach

The photoisomerization process of 1,2-diphenylethylene (stilbene) is investigated using the spin-flip density functional theory (SFDFT), which has recently been shown to be a promising approach for locating conical intersection (CI) points (Minezawa, N.; Gordon, M. S. J. Phys. Chem. A2009, 113, 12749). The SFDFT method gives valuable insight into twisted stilbene to which the linear response time-dependent DFT approach cannot be applied. In contrast to the previous SFDFT study of ethylene, a distinct twisted minimum is found for stilbene. The optimized structure has a sizable pyramidalization angle and strong ionic character, indicating that a purely twisted geometry is not a true minimum. In addition, the SFDFT approach can successfully locate two CI points: the twisted-pyramidalized CI that is similar to the ethylene counterpart and another CI that possibly lies on the cyclization pathway of cis-stilbene. The mechanisms of the cis--trans isomerization reaction are discussed on the basis of the two-dimensional potential energy surface along the twisting and pyramidalization angles.

ChemInform Abstract: Synthesis and Characterization of New Halogen-Tetramethylene Sulfoxide- Ruthenium(II) and Ruthenium(III) Complexes; Crystal Structure of cis- Dichlorotetrakis(tetramethylene sulfoxide)ruthenium(II) and Hydrogen trans-Bis(tetramethylen

In this paper we report the synthesis and characterization of the following ruthenium(II) and ruthenium(III) complexes with tetramethylene sulfoxide (TMSO): cis-RuCl2(TMSO)4 (1), trans- RuCl2(TMSO)4 (2), the corresponding dibromo derivatives cis- and trans-RuBr2(TMSO)4 (3 and 4, respectively), (TMSO)H[trans-Ru(TMSO)2Cl4] (5) and mer-RuCl3(TMSO)3 (6). Most of the reported complexes are described here for the first time, together with a new, easy synthetic path for the previously known complexes 1 and 3. The chemical behavior of 1 and 2 in solution of aprotic, non- coordinating solvents is described. Among the Ru(II) derivatives, the cis isomers are thermodynamically more stable and a photochemically driven cis to trans isomerization reaction is observed in tetramethylene sulfoxide solution. We also report the crystal structures of cis-RuCl2(TMSO)4 (1) and (TMSO)H[trans- Ru(TMSO)2Cl4] (5), as determined by three dimensional X-ray analyses. Crystal data: 1, a=9.104(2), b=11.317(2), c=21.867(6) A, β=90.62(2)°, monoclinic, space group P21/c, Z=4; 5, a=14.642(4), b=14.999(4), c=9.667(4) A, β=103.57(1)°, monoclinic, space group P1/c, Z=4. Least-squares refinement based on 3813 (1) and 4706 (5) reflections converged to R=0.032 and 0.033 for 1 and 5, respectively. In 1, all the TMSO ligands are S-bonded to Ru, with average RuS bond distances of 2.355(6) (trans to S) and 2.273(1) (trans to Cl) A. The TMSO ligands in 5 are both S-bonded to Ru (av. 2.33(1) A). The protonated TMSO molecule is hydrogen bonded to one of the two crystallographically independent anions.

Photoinduced vitrification near the surfaces of single crystals of azobenzene-based molecular materials with glass-forming ability

Photoinduced vitrification was observed to take place near the surfaces of the single crystals of azobenzene-based molecular materials with glass-forming ability. The phenomenon was caused by repetition of the trans-cis and cis-trans isomerization reactions and hence can be regarded as a kind of photomechanical effect.

Striking Differences between the Solution and Solid-State Reactivity of Iron PNP Pincer Complexes with Carbon Monoxide

Several new iron(II) complexes of the types [Fe(PNP)X2] (X = Cl, Br) containing tridentate PNP pincer-type ligands based on 2,6-diaminopyridine and 2,6-diaminopyrimidine have been prepared. They all exhibit intermolecular Fe−X···H−N hydrogen bonds, forming supramolecular networks in the solid state. In the case of X = Cl these compounds react readily with gaseous CO both in the solid state and in solution to give selectively the octahedral complexes cis- and trans-[Fe(PNP)(CO)(Cl)2], respectively, whereas with X = Br mixtures of cis and trans isomers are obtained. These transformations are accompanied by color and spin-state changes. CO binding is fully reversible in all cases, and heating solid samples of either cis- or trans-[Fe(PNP)(CO)(X)2] leads to complete regeneration of analytically pure [Fe(PNP)(X)2]. Mössbauer spectroscopy confirmed the high-spin nature of the parent five-coordinate Fe(II) complex (δ = 0.80(1) mm s−1) and the shift to two different low-spin octahedral species after reaction with CO in the solid (δ = 0.13(1) mm s−1) or in solution (δ = 0.15(1) mm s−1). Magnetization studies led to a magnetic moment close to 4.9 μB, reflecting the expected four unpaired d-electrons in [Fe(PNP)Cl2], which were confirmed by DFT calculations. The DFT study of the reaction pathway for CO capture led to low energy barriers (≤3.4 kcal mol−1). The cis−trans isomerization reaction was found to take place with a low energy barrier (10.8 kcal mol−1), after initial loss of chloride, and involves also spin-state changes

Cis–trans isomerization of methyl cis-9-octadecenoate in the presence of cobalt tin catalysts

The isomerization of methyl cis-9-octadecenoate (cis isomer) to methyl trans-9-octadecenoate (trans isomer) was studied in the presence of CoSn/ZnO catalysts under hydrogen pressure. The cis–trans isomerization of methyl cis-9-octadecenoate over a CoSn/ZnO catalysts prepared by co-impregnation, was strongly influenced by the nature of the catalytic sites. The support ZnO did not favour this reaction but the hydrogen played an important role since it influenced the relative amount of different cobalt species. In fact cobalt-containing sites (zerovalent species as well as cobalt oxides) predominated over these reactions. The tin species, which acted as a cobalt modifier for the preferential adsorption of the carbonyl group, inhibited the isomerization of the olefinic bond. Such changes could have also been due to a significant diminution of the cobalt content at the catalyst surface especially for a bulk Sn/Co>1. Consequently, the active sites for the cis–trans isomerization reaction should be cobalt species.

Temperature dependence of the IR driven cis-trans isomerization of nitrous acid (HONO)

With the help of ultrafast time-resolved infrared spectroscopy, we investigate the temperature dependence of the IR driven cis-->trans isomerization of nitrous acid (HONO) in solid Kr. We find that the lifetime of the OH-stretch vibration, as well as the final cooling into the matrix, is affected only minimally (if at all) by temperature. Nevertheless, the quantum yield of the cis-->trans isomerization reaction increases by approximately 30% to a total of 50%-70% when lowering the temperature from 30 to 15 K, whereas the trans-->cis back yield is reduced by approximately 40%. The results are discussed in analogy to Marcus theory of nonadiabatic electron transfer for the essentially barrierless case. We present a unified view of this important prototype proton transfer reaction that can explain the high cis-->trans quantum yield of close to 1.

Optimization of the Physical Refining of Sunflower Oil Concerning the Final Contents of trans-Fatty Acids

The final contents of total and individual trans-fatty acids of sunflower oil, produced during the deacidification step of physical refining were obtained using a computational simulation program that considered cis−trans isomerization reaction features for oleic, linoleic, and linolenic acids attached to the glycerol part of triacylglycerols. The impact of process variables, such as temperature and liquid flow rate, and of equipment configuration parameters, such as liquid height, diameter, and number of stages, that influence the retention time of the oil in the equipment was analyzed using the response-surface methodology (RSM). The computational simulation and the RSM results were used in two different optimization methods, aiming to minimize final levels of total and individual trans-fatty acids (trans-FA), while keeping neutral oil loss and final oil acidity at low values. The main goal of this work was to indicate that computational simulation, based on a careful modeling of the reaction system, combined with optimization could be an important tool for indicating better processing conditions in industrial physical refining plants of vegetable oils, concerning trans-FA formation.

Solid-state cis– trans isomerization reaction of (η 5-MeC 5H 4)W(CO) 2P(O iPr) 3I

cis-(η 5-MeC 5H 4)W(CO) 2P(O i Pr) 3I ( 1) was converted to the trans isomer 2 in the solid state (90–110 °C). The reaction was monitored by heating 1 in NMR tubes for periods of time (2–60 min), cooling the tubes to room temperature and determining the conversion by solution 31P and 1H NMR spectroscopy. The data were consistent with a first-order reaction and yielded an activation energy of 59 ± 3 kJ mol −1. Comparative kinetic data were obtained from an in situ analysis of a powder-XRD study of 1. The powder-XRD study was conducted at 80–100 °C (10–60 min), yielding an activation energy of 52 ± 2 kJ mol −1 (first-order reaction). The reaction could not be monitored by single crystal X-ray diffraction as the crystal disintegrated over time on heating. This disintegration process was monitored by optical microscopy and revealed that while the bulk crystal morphology was retained the crystal surface roughened with time. The compounds 1 and 2 were also structurally characterised by X-ray crystallographic techniques.

IR laser manipulation of cis↔trans isomerization of 2-naphthol and its hydrogen-bonded clusters

The cis<-->trans isomerization reaction has been carried out for 2-naphthol and its hydrogen (H) bonded clusters by infrared (IR) laser in the electronic excited state (S1) in supersonic jets. A specific isomer in the jet was pumped to the X-H stretching vibration in the S1 state, where X refers to C, O, or N atom, by using a stepwise UV-IR excitation, and the dispersed emission spectra of the excited species or generated fragments were observed. It was found that the isomerization occurs only in the H-bonded clusters but a bare molecule does not exhibit the isomerization in the examined energy region of Ev< or =3610 cm(-1), indicating a reduction of the isomerization barrier height upon the H bonding. The relative yield of the isomerization was observed as a function of internal energy. The isomerization yield was found to be very high at the low IR frequency excitation, and was rapidly reduced with the IR frequency due to the competition of the dissociation of the H bond within the isomer. Density-functional theory (DFT) and time-dependent DFT calculations were performed for estimating the barrier height of the isomerization for bare 2-naphthol and its cluster for electronic ground and excited states. The calculation showed that the isomerization barrier height is highly dependent on the electronic states. However, the reduction of the height upon the hydrogen bonding was not suggested at the level of our calculation.

Cis and trans conformations in 3-substituted thietane-1-oxide

For a series of 3-substituted-thietane-1-oxide (3-R-TOX) derivatives (R=chloro, methyl, ethyl, acetate, t-buthyl, phenyl and p-chlorophenyl), the cis⇔ trans isomerization reactions have been theoretically studied in the frame of molecular orbital theory. Optimized geometries have been obtained at HF/6-31G** level, whereas the energetics and thermodynamics were calculated with basis sets that include polarization, diffuse functions and electron correlation at the second-order Møller–Plesset perturbation theory. The size and nature of the substituent seems to exert no influence on the structure of the thietane-1-oxide ring. Gas phase thermodynamics predict the cis isomers to be the preferred structure in these compounds as a result of the H10⋯O9 non-bonded interaction. The exception to this trend are the chloro and acetate derivatives where a 14 and 46% of the trans isomer, respectively, is predicted. In CCl 4 solution, the isomerization reaction would take place in large extent. The calculated 1H-NMR chemical shifts correlate well with the experimental data and demonstrate that the β-protons (H10) are magnetically sensible enough to allow the cis and trans isomeric forms to be distinguished. The β-protons chemical shifts calculated in CCl 4 do not differ appreciably from the gas phase values. The 17O-NMR signals have also been derived and the potentiality of this nucleus to be used to assign the preferred geometry as well as to follow the isomerization reaction, in this kind of compounds is pointed out. The present work also indicates that the S O stretching mode can be used to assign either a cis or trans conformation in these species, though this vibrational mode is strongly coupled with some ring and H–C–H angle deformation modes.

Novel azobenzene-containing polyamic acids as Langmuir–Blodgett–Kuhn multilayer films and for liquid crystal alignment switching

New azobenzene-containing polyamic acids (PAAs) with systematically tailored architectures were synthesized and assembled as Langmuir–Blodgett–Kuhn (LBK) multilayers. Surface plasmon resonance (SPR) spectroscopy was employed to measure the film thickness and its dependence upon the number of layers deposited. The pronounced Bragg peak in the X-ray reflectivity scans indicated the films' regularly repeated internal layer structure. Photoisomerization studies confirmed the excellent reversibility of the trans– cis and cis– trans isomerization reactions of the azobenzene sidegroups within the multilayer structures. Further, these films were found to be able to switch the orientation of liquid crystalline layers between homeotropic and planar alignment by the reversible photoisomerization of the azobenzene moieties.

Mechanism of the Cis−Trans Isomerization of Bis(glycinato)copper(II)

The cis to trans isomerization reaction of bis(glycinato)copper(II) was investigated by quantum chemical methods. An electronic reaction barrier (cis → trans) of about 7.9 kcal/mol was determined f...