This study investigates the chemical structure of profoxydim, focusing on its E-isomer, the main commercial form. The research aimed to determine the predominant tautomeric forms under various environmental conditions. Using proton and carbon-13 NMR spectroscopy alongside theoretical modeling, we examined tautomers and their conformers in different solvents (MeOD, DMSO, CDCl3, benzene) to mimic gas and aqueous phases. The findings reveal that the enolic form dominates in the gas phase, while the ketonic form prevails in aqueous environments, providing key insights into the herbicide's environmental behavior. We also observed an isomeric transition from E to Z under acidic conditions, which could affect profoxydim's reactivity in natural environments. The theoretical calculations indicated that in acidic conditions, the E and Z forms are nearly degenerate, with the E form remaining dominant in neutral environments. Additionally, QSAR models assessed the toxicity of various tautomers, revealing significant differences that could impact bioactivity and environmental fate. This research offers crucial insights into the structural dynamics of profoxydim, contributing to cyclohexanedione chemistry and the development of more effective herbicides.

The sulfonylurea herbicide family has been extensively studied using computational techniques. The most stable conformer structures of the 34 molecules analyzed in gaseous, aqueous, and octanol phases have been determined. The study employed CREST conformational search methods along with the CENSO script to explore all possible conformational structures. Additional evaluations conducted at the B3LYP-D3/6-311+G(d,p) level have enabled the identification of intramolecular stability patterns across the various compounds. It has been discovered that stability is primarily determined by two factors: intramolecular hydrogen bonding involving an NH group adjacent to the sulfonyl group with either N donors or the nearby carbonyl group and potential pi-pi interactions between the aromatic rings of the molecules. These have been characterized through QTAIM and NCI population analyses. Furthermore, with the goal of developing predictive models for the physicochemical properties of pesticides that include the sulfonylurea family, a statistical analysis among the different properties of the studied molecules has been conducted. Significant correlations have been found between various properties, predicting a promising future for the prediction of characteristics that could assist laboratories in selecting among different pesticides.

Context. The assignment of the mid-infrared (mid-IR) emission features and plateaus observed in C-rich and H-rich regions of the interstellar medium (ISM) is still debated. Such mid-IR assignments must also be related to their contribution to the extinction curve in our galaxy and to the ultraviolet (UV) bump. Aims. The aim of this work is to investigate the influence of hydrogenation rate on the mid-IR spectra of populations of carbon clusters in order to constraint the n H / n C ratios in regions of the ISM where carbon is an important component. Their potential contribution to the extinction curve and in particular to the UV bump is also investigated. Methods. The absorption IR and optical spectra of tens of thousands of C 24 H n ( n = 0 , 6 , 12 , 18 , 24) isomers classified into structural families – namely flakes, branched, pretzels, and cages – were computed using the density functional based tight binding electronic structure method and its time-dependent version, respectively. Final spectra were obtained by averaging the spectra of many individual isomers. Results. The shapes and the relative intensities of the bands centered at ∼ 3.25 and 3.40 µ m and assigned to the C–H stretch of sp 2 and sp 3 carbon atoms, respectively, present a clear dependence on the n H / n C ratio. From a comparison with the astronomical spectrum from the Orion bar H2S1, the most interesting emitting candidates would pertain to the flakes population; this is the most energetically favorable family of clusters, possessing a high content of five and six carbon rings and being mostly planar, with no sp 1 carbon atoms and with a n H / n C ratio of lower than 0.5. The same conclusion is drawn when comparing the computed IR features in the [4–20 µ m] region with the observed plateaus from some C-rich and H-rich planetary nebulae objects of the Small Magellanic Cloud. The contribution of the same family could be considered for the UV bump. When n H / n C increases, only a contribution to the high-energy part of the continuum due to σ → π ⋆ excitations can reasonably be considered. Conclusions. These results bring some constraints on the structural features and on the n H / n C ratio of the hydrogenated carbon populations emitting in the mid-IR domain in interstellar objects such as protoplanetary and reflection nebulae. The flakes population, with a low n H / n C ratio, is an interesting candidate for the carbon population emitting in these regions, but not for that absorbing in the diffuse ISM. None of the populations studied in the present work can account for the UV bump, but they would contribute to a broad extinction rise in this domain. The computed features reported in this article could be used to interpret future astronomical data provided by the James Webb Space Telescope.

Context. The assignment of the mid-infrared (mid-IR) emission features and plateaus observed in C-rich and H-rich regions of the interstellar medium (ISM) is still debated. Such mid-IR assignments must also be related to their contribution to the extinction curve in our galaxy and to the ultraviolet (UV) bump. Aims. The aim of this work is to investigate the influence of hydrogenation rate on the mid-IR spectra of populations of carbon clusters in order to constraint the n H / n C ratios in regions of the ISM where carbon is an important component. Their potential contribution to the extinction curve and in particular to the UV bump is also investigated. Methods. The absorption IR and optical spectra of tens of thousands of C 24 H n ( n = 0, 6, 12, 18, 24) isomers classified into structural families – namely flakes, branched, pretzels, and cages – were computed using the density functional based tight binding electronic structure method and its time-dependent version, respectively. Final spectra were obtained by averaging the spectra of many individual isomers. Results. The shapes and the relative intensities of the bands centered at ~3.25 and 3.40 µm and assigned to the C–H stretch of sp 2 and sp 3 carbon atoms, respectively, present a clear dependence on the n H / n C ratio. From a comparison with the astronomical spectrum from the Orion bar H2S1, the most interesting emitting candidates would pertain to the flakes population; this is the most energetically favorable family of clusters, possessing a high content of five and six carbon rings and being mostly planar, with no sp 1 carbon atoms and with a n H / n C ratio of lower than 0.5. The same conclusion is drawn when comparing the computed IR features in the [4–20 µm] region with the observed plateaus from some C-rich and H-rich planetary nebulae objects of the Small Magellanic Cloud. The contribution of the same family could be considered for the UV bump. When n H / n C increases, only a contribution to the high-energy part of the continuum due to σ → π ✶ excitations can reasonably be considered. Conclusions. These results bring some constraints on the structural features and on the n H / n C ratio of the hydrogenated carbon populations emitting in the mid-IR domain in interstellar objects such as protoplanetary and reflection nebulae. The flakes population, with a low n H / n C ratio, is an interesting candidate for the carbon population emitting in these regions, but not for that absorbing in the diffuse ISM. None of the populations studied in the present work can account for the UV bump, but they would contribute to a broad extinction rise in this domain. The computed features reported in this article could be used to interpret future astronomical data provided by the James Webb Space Telescope.

This work aims at exploring the potential energy surfaces of C24Hn=0,6,12,18,24 using the genetic algorithm in combination with the density functional based tight binding potential. The structural diversity was analyzed using order parameters, in particular the sum of the numbers of 5- and 6-carbon rings R5/6. The most abundant and lowest energy population was designated as the flake population (isomers of variable shapes, large R5/6 values), characterized by an increasing number of spherical isomers when nH/nC increases. Simultaneously, the fraction of the pretzel population (spherical isomers, smaller R5/6 values) increases. The fraction of the cage population (largest R5/6 values) remains extremely minor while the branched population (smallest R5/6 values) remains the highest energy population for all nH/nC ratios. For all C24Hn=0,6,12,18,24 clusters, the evolution of the carbon ring size distribution with energy clearly shows the correlation between the stability and the number of 6-carbon rings. The average values of the ionization potentials of all populations were found to decrease when nH/nC increases, ranging from 7.9 down to 6.4 eV. This trend was correlated to geometric and electronic factors, in particular to carbon hybridization. These results are of astrophysical interest, especially regarding the role of carbon species in the gas ionization.

A large number of hydrogenated coronene, circumcoronene, and circumcircumcoronene isomers have been investigated by means of density functional theory calculations. The computation of their IR spectra puts forward significant differences between the different isomers in the 3 mu m region and shows that hydrogenated polycyclic aromatic hydrocarbons can account for the aromatic infrared bands resulting from the absorption of light by the interstellar medium. In particular, the intense 3.3 mu m band, as well as the weak features observed at 3.40, 3.46, 3.51, and 3.56 mu m are reasonably reproduced by the present calculations. The latter two are only observed when hydrogenation takes place in tertiary carbon atoms, showing that the frequencies at which these IR bands appear are a consequence of their position and chemical environment within the molecule.

A simple model, based on connectivity (adjacency) matrices, is introduced to study the relative stability of hydrogenated polycyclic aromatic hydrocarbons (HPAHs). The model allows us to consider a very large number of isomeric structures for HPAHs of variable size and degree of hydrogenation, by taking into account the different positions available in each hydrogenation step. The validity of our approach is demonstrated by comparing, for a few selected cases, with the predictions of Density Functional Theory calculations. We have found that aromaticity is the main factor governing the relative stability of HPAH isomers and that the most stable structures are in general those containing the maximum possible number of non-hydrogenated rings.

We present a theoretical study on the thermodynamic and kinetic reactivity of Diels-Alder cycloadditions to several empty fullerenes in order to investigate the relationship between reaction energies and energy barriers. The results show that fullerenes with large HOMO-LUMO gaps present good correlation coefficients. In all other cases, two factors are responsible for the lack of correlation. First, the formation of unexpected adducts which are not the ones resulting from a [4+2] addition and second the change in the electronic structure of some adducts due to the mixing of the ground state with excited states close in energy.

Using a density functional theory approach, we explore the emission properties of a family of bis-cyclometallated cationic iridium(iii) complexes of general formula [Ir(C^N)2(CN-tert-Bu)2]+ that have tert-butyl isocyanides as neutral auxiliary ligands. Taking the [Ir(ppy)2(CN-tert-Bu)2]+ complex (Hppy = 2-phenylpyridine) as a reference, the effect of replacing the pyridine ring in the cyclometallating ppy ligand by a five-membered azole ring has been examined. To this end, two series of complexes differing by the nature of the atom (either nitrogen or carbon) linking the azole to the phenyl ring of the cyclometallating ligand have been designed. Each series is composed of three molecules having an increasing number of nitrogen atoms (2 to 4) in the azole ring. The emission energies computed for the azole-containing [Ir(C^N)2(CN-tert-Bu)2]+ complexes show a generalized blue-shift compared to [Ir(ppy)2(CN-tert-Bu)2]+, in agreement with the experimental data available for two of the six complexes designed here. The electronic nature of the lowest-lying triplet (T1) is clearly established as a ligand-centred (3LC) state associated with the cyclometallating ligands, and cannot be described as a simple HOMO → LUMO promotion. Therefore, no clear trend based on the sole use of molecular orbital energies can be inferred to predict the emission properties. The significant oscillation in the emission quantum yield (ranging from 0.1% to 52%) experimentally reported is rationalized by the energy gap between the emitting T1 state and a non-radiative triplet state having metal-centred (3MC) d-d* nature. On the basis of such a model, two of the here proposed systems are expected to display significant emission quantum yields in the blue region of the visible spectra, which make them good candidates for electroluminescent applications.

We present an extensive and systematic study on the regioselectivity of Diels-Alder (DA) cycloadditions to empty fullerenes, covering the whole range of cage sizes from C60 to C180. Reaction energies obtained from DFT calculations, which correlate with activation barriers, can be well reproduced by using a simple Hückel model, indicating that π electronic effect is the key factor determining the relative stability of DA adducts. Based on these results, we propose a couple of simple rules of thumb, in terms of a set of bond patterns, as a visual guide for approximate prediction of DA reactive sites. Moreover, we suggest two quantitative descriptors for the stability of DA regioadducts of empty fullerenes; one combines the π free valences and bond orders involved in the DA addition, and the other characterizes the local π aromaticity around the addition site. The latter criterion allows us to easily rationalize the proposed rules.

The association behavior of an electron-donating, bowl-shaped, truxene-based tetrathiafulvalene (truxTTF) with two corannulene-based fullerene fragments, C32H12 and C38H14, is investigated in several solvents. Formation of 1:1 complexes is followed by absorption titrations and complemented by density functional theory (DFT) calculations. The binding constants are in the range logK(a)=2.9-3.5. DFT calculations reveal that the most stable arrangement is the conformation in which the 1,3-dithiole ring of truxTTF is placed inside the concave cavity of the corannulene derivative. This arrangement is confirmed experimentally by NMR measurements, and implies that a combination of - and CH- interactions is the driving force for association. Time-dependent DFT calculations reproduce the experimental UV/Vis titrations and provide a detailed understanding of the spectral changes observed. Femtosecond transient absorption studies reveal the processes occurring after photoexcitation of either C32H12 or C38H14 and their supramolecular associates with truxTTF. In the case of truxTTFC(38)H(14), photoexcitation yields the charge-separated state truxTTF(.+)C(38)H(14)(.-) with a lifetime of approximately 160ps.

A theoretical density functional theory study has been performed on different families of cationic cyclometallated Ir(III) complexes with the general formula [Ir(C^N)2(N^N)](+) and azole-based ligands. The goal was to investigate the effect that the number and position of the nitrogen atoms of the azole ring have on the electronic structure and emission wavelength of the complex. The increase in the number of nitrogen atoms changes the relative energy of the HOMO and LUMO levels and leads to a gradual shift in the emission wavelength that can be larger than 100 nm. The direction of the shift however depends on the ligand in which the azole ring is introduced. The emission shifts to bluer wavelengths when the azole forms part of the cyclometallating C^N ligands, whereas it shifts to the red when the 5-membered ring is incorporated into the ancillary N^N ligand. The position of the nitrogen atoms in the azole ring also plays an important role in determining the emission energy. Complexes with phenyl-azole C^N ligands bearing a nitrogen in the azole position to which the phenyl is linked show a markedly blue-shifted emission compared to complexes with the same number of nitrogen atoms in the azole ring and bearing a carbon atom in that position. Therefore, when comparing the emission properties of azole-based [Ir(C^N)2(N^N)](+) complexes, not only the number of nitrogen atoms of the azole but also their position in the ring and the ligand where the azole ring is incorporated should be taken into account.