The solution-processing of metal chalcogenides offers a promising route to improve the manufacturing of semiconductor devices. The amine-thiol solvent system has been deemed an "alkahest" for its ability to dissolve a wide range of metals and metal chalcogenides. Therefore, it enables convenient synthesis of metal sulfides. However, in the literature there are limited reports of analogous selenium-based "alkahest" chemistry. Here we show that solutions containing n-alkylammonium polyselenides can dissolve a wide range of metals and metal compounds through the formation of soluble metal polyselenides. These metal polyselenides can subsequently be utilized as precursors for the synthesis of a wide range of binary and multinary metal selenide thin films and nanoparticles, including Cu(In,Ga)Se-2, Cu2ZnSnSe4, and Ag2ZnSnSe4.

Solution-processed CuInSe2 films have generally relied on sulfide or sulfoselenide precursor films that, during the grain growth process, hamper the growth of thicker films and lead to the formation of a fine-grain layer. However, recent research has indicated that sulfur reduction in the precursor film modifies the grain growth mechanism and may enable the fabrication of thicker absorbers that are free of any fine-grain layer. In this work, we pursue direct solution deposition of sulfur-free CuInSe2 films from the molecular precursor approach. To this end, we tune the amine-thiol reactive solvent system and study the changes to the resulting soluble complexes through a combination of analytical techniques. We show that by reactively dissolving indium(III) selenide and selenium in solutions of n-butylamine and 1,2-ethanedithiol, a metal thiolate species is formed, and that this metal thiolate can be modified by isolation from the thiol-containing solvent via precipitation. As the quantity of selenium in the ink increases, the thiol content in the complex decreases, eventually producing soluble [InSex]- species. Extending this method to be used with copper selenide as a copper source, molecular precursor inks can be made for solution-processed, sulfur-free CuInSe2 films. We then show that these CuInSe2 precursor films can be fully coarsened without a fine-grain layer formation, even at the desired thicknesses of 2 μm and greater.

Understanding the fundamental mechanisms of chemical reactions is of great interest to scientists working in many fields as it enables the rationalization, prediction, and design of reactions. Many chemical processes involve the formation of short-lived reaction intermediates, most of which cannot be isolated and are challenging to detect. One such intermediate is the tetrahedral intermediate often proposed to be generated upon the reactions of acetyl chlorides with simple alcohols via an addition/elimination mechanism. However, the formation of this tetrahedral intermediate is a subject of controversy as it has not been detected. Furthermore, some kinetic evidence suggests the SN2 mechanism for this reaction. In the present investigation, a 266 nm pulsed Nd:YAG laser was used to evaporate and ionize reactants, reaction intermediates, and products in microdroplets of acetyl chloride and ethanol. A linear quadrupole ion trap mass spectrometer was used to detect the ions and collision-activated dissociation (CAD) experiments were employed for their structural characterization. The results demonstrate the formation of the protonated tetrahedral intermediate of the addition/elimination reaction. The protonated reaction intermediate was isolated and subjected to CAD, which resulted in the loss of water and ethylene, thus confirming its structure. These results demonstrate that the ethanolysis of acetyl chloride proceeds via an addition/elimination mechanism involving a tetrahedral reaction intermediate. However, the parallel occurrence of the SN2 mechanism cannot be ruled out.

Diagnostic gas-phase ion-molecule reactions serve as a powerful alternative to collision-activated dissociation for the structural elucidation of analytes when using tandem mass spectrometry. The use of such ion-molecule reactions has been demonstrated to provide a robust tool for the identification of specific functional groups in unknown ionized analytes, differentiation of isomeric ions, and classification of unknown ions into different compound classes. During the past several years, considerable efforts have been dedicated to exploring various reagents and reagent inlet systems for functional-group selective ion-molecule reactions with protonated analytes. This review provides a comprehensive coverage of literature since 2006 on general and predictable functional-group selective ion-molecule reactions of protonated analytes, including simple monofunctional and complex polyfunctional analytes, whose mechanisms have been explored computationally. Detection limits for experiments involving high-performance liquid chromatography coupled with tandem mass spectrometry based on ion-molecule reactions and the application of machine learning to predict diagnostic ion-molecule reactions are also discussed.

Mixed Oxides of Nitrogen (MON) are made by mixing nitrogen tetroxide (NTO) with nitric oxide (NO). Nitric oxide reacts with nitrogen tetroxide to form nitrogen trioxide, creating a mixture of oxides of nitrogen, with species the concentration of which is pressure and temperature dependent. Knowledge of the chemical composition of MONs is essential to understanding their physical and thermodynamic properties, and therefore behavior in fluid systems. The main objective of this study was to design a constant pressure feed system to get Raman spectroscopy data of different MON mixtures, from -10 to 50°C, and as a function of pressure. Using samples of known initial composition, we calibrated for N2O4 and N2O3, the major constituents in MON mixtures, to, ultimately, determine the chemical composition of any given MON. Our results include calibration for N2O4 in N2O4/NO2 mixtures and calibration curves relating the amount of N2O3 and N2O4 in various MONs. Finally, a sensitivity analysis was completed based on our results, to determine the smallest change in initial NO wt.% we can detect in unknown MON mixtures.

The gaseous 2,6-didehydropyridinium cation and its derivatives transfer a proton to reagents for which the reaction for their singlet ground states is too endothermic to be observed. These reactions occur from the lowest-energy excited triplet states, which has not been observed (or reported) for other meta-benzyne analogues. Quantum chemical calculations indicate that the (excited) triplet states are stronger Brønsted acids than their (ground) singlet states, likely due to unfavorable three-center, four-electron interactions in the singlet-state conjugate bases. The cations have substantially smaller (calculated) singlet-triplet (S-T) splittings (ranging from ca. -11 to -17 kcal mol-1) than other related meta-benzyne analogues (e.g., -23.4 kcal mol-1 for the 3,5-isomer). This is rationalized by the destabilization of the singlet states (relative to the triplet states) by reduced (spatial) overlap of the nonbonding molecular orbitals due to the presence of the nitrogen atom between the radical sites (making the ring more rigid). Both the singlet and triplet states are believed to be generated upon formation of these biradicals via energetic collisions due to their small S-T splittings. It appears that once the triplet states are formed, the rate of proton transfer is faster than the rate of intersystem crossing unless the biradicals contain heavy atoms.

Diagnostic ion-molecule reactions using tandem mass spectrometry can differentiate between isomeric compounds unlike a popular collision-activated dissociation methodology for the identification of previously unknown mixtures. Selected neutral reagents, such as 2-methoxypropene (MOP) are introduced into an ion trap mass spectrometer and react with protonated analytes to produce product ions diagnostic of the functional groups present in the analyte. However, the interpretation and understanding of specific reactions are challenging and time-consuming for chemical characterization. Here, we introduce a first bootstrapped decision tree model trained on 36 known ion-molecule reactions with MOP using graph-based connectivity of analyte’s functional groups as input. A Cohen Kappa statistic of 0.72 was achieved, suggesting substantial inter-model reliability on limited training data. Prospective diagnostic product predictions were made and validated for 14 previously unpublished analytes . Chemical reactivity flowcharts were introduced to understand the decisions made by the machine learning method that will be useful for chemists.

Raman multivariate curve resolution vibrational spectroscopy and X-ray crystallography are used to quantify changes in the gauche-trans conformational equilibrium of 1-bromopropane (1-BP) upon binding to α-cyclodextrin (α-CD). Both conformers of 1-BP are found to bind to α-CD, although binding favors the unfolded trans conformation. Temperature-dependent measurements of the binding-induced change in the 1-BP conformation equilibrium constant indicate that the trans conformer is both enthalpically and entropically stabilized in the host cavity.

Combustion is the main source of power worldwide.This makes understanding combustion pathways and byproducts vital to optimizing power output and minimizing the unwanted byproducts.One of the main byproducts of the combustion process is soot, which can be accurately described as a large aggregate of polyaromatic hydrocarbons (PAHs).While the general process by which soot particles grow in size have been laid out, the incipient steps by which individual PAH molecules begin to aggregate is still a mystery.Current models of soot formation require individual PAH molecules to dimerize and π stack in PAHs significantly smaller than are thermodynamically capable of doing so.One largely untested possibility is that PAHs linked together by short chemical linkages could be responsible for the initial steps of aggregation.In particular, we propose that resonance-stabilized benzylic-like radicals could recombine to form ethyl-linked PAH dimers that are responsible for the initial stages of aggregation and π stacking.These covalently-linked dimers could withstand the high energies present in the combustion flame and provide a seed for soot aggregation.This brings us to the following question: At what sized PAH will these ethyl-linked aromatics be capable of π stacking, and if they can, will conformations leading to π stacking compete with other, more extended geometries?We begin to answer this question by studying a series of ethyl-linked naphthalene dimers in which the ethyl linkage bridges the two unique sites of substitution (shown below).These molecules are brought into the gas phase by heating, and cooled in a supersonic expansion.LIF excitation, IR-UV holeburning, fluorescence-dip infrared spectroscopy, and dispersed fluorescence are used to record conformer-specific UV and IR spectra.These dimers also have fascinating electronic spectroscopy associated with the presence of two UV chromophores that are in identical or nearly identical environments, leading to extensive vibronic coupling.The experimental results will be compared with a multi-mode theoretical model of nearresonant vibronic coupling.