An assessment of theoretical procedures for π-conjugation stabilisation energies in enones
We introduce a representative database of 22α,β-toβ,γ-enecarbonyl isomerisation energies (to be known as the EIE22 data-set). Accurate reaction energies are obtained at the complete basis-set limit CCSD(T) level by means of the high-level W1-F12thermochemical protocol. The isomerisation reactions involve a migration of one double bond that breaks the conjugatedπ-system. The considered enecarbonyls involve a range of common functional groups (e.g., Me, NH2,OMe,F,andCN). Apart from π-conjugation effects, the chemical environments are largely conserved on the two sides of the reactions and therefore the EIE22 data-set allows us to assess the performance of a variety of density functional theory (DFT) procedures for the calculation ofπ-conjugation stabilisation energies in enecarbonyls. We find that, with few exceptions (M05-2X, M06-2X,BMK, and BH&HLYP), all the conventional DFT procedures attain root mean square deviations (RMSDs) between 5.0 and 11.7 kJ mol−1. The range-separated and double-hybrid DFT procedures, on the other hand, show good performance with RMSDs below the 'chemical accuracy' threshold. We also examine the performance of composite and standard ab initio procedures. Of these, SCS-MP2 offers the best performance-to-computational cost ratio with an RMSD of 0.8 kJ mol−1.
Fragmentation of 1,4,2-oxaselenazoles as a route to isoselenocyanates–A high-level CBS-QB3 study
In this study, the thermodynamics and barrier heights associated with the fragmentation reactions of a set of fifteen 1,4,2-oxaselenazoles into isoselenocyanates (molecules with promising anticancer activity) and carbonyl derivatives, have been studied using the high-level CBS-QB3 quantum chemical protocol. Of the systems studied, attachment of a CF3-substituent at the C5-position affords the system with the largest gas-phase free energy barrier (190.1 kJ mol–1), whilst substitution at the C5-position with two –NMe2 substituents affords a heterocycle with the lowest free energy barrier (67.8 kJ mol–1). The presence of solvent (acetonitrile) was shown to reduce the free energy barriers in all cases, with the two systems mentioned above having condensed-phase free energy barriers of 180.8 and 42.0 kJ mol–1, respectively.
Homolytic S-Cl bond dissociation enthalpies of sulfenyl chlorides – a high-level G4 thermochemical study
Numerous reactions between sulfenyl chlorides and organic molecules proceed by way of radical reactions, in which homolytic cleavage of the S-Cl bond is a key step. Owing to the lack of data concerning the quantitative effect of substituents in governing the strength of S-Cl bonds toward homolytic cleavage, the present article reports an extensive dataset of gas-phase S-Cl bond dissociation enthalpies (BDEs) obtained using the high-level G4 thermochemical protocol. The BDEs of the species in this set range from 207.2 (ONSCl) to 279.7 kJ mol−1 (tBuSCl), with HSCl having a BDE of 267.6 kJ mol−1. In addition, the gas-phase S-Cl BDEs of six sulfonyl chlorides have also been reported, and these range from 267.2 kJ mol–1 (CF3SO2Cl) to 283.0 kJ mo1-1 (FSO2Cl).
A Systematic Exploration of B–F Bond Dissociation Enthalpies of Fluoroborane-Type Molecules at the CCSD(T)/CBS Level
Fluoroborane-type molecules (R1R2B–F) are of interest in synthetic chemistry, but to date, apart from a handful of small species (such as H2BF, HBF2, and BF3 ), little is known concerning the effect of substituents in governing the strength of the B–F bonds of such species toward homolytic dissociation in the gas phase. In this study, we have calculated the bond dissociation enthalpies (BDEs) of thirty unique B–F bonds at the CCSD(T)/CBS level using the high-level W1w thermochemical protocol. The B–F bonds in all species considered are very strong, ranging from 545.9 kJ mol−1 in (H2B)2B–F to 729.2 kJ mol−1 HBF2. Nevertheless, these BDEs still vary over a wide range of 183.3 kJ mol−1 . The structural properties that affect the BDEs are examined in detail, and the homolytic BDEs are rationalized based on molecule stabilization enthalpies and radical stabilization enthalpies. Since polar B–F bonds may represent a challenging test case for density functional theory (DFT) methods, we proceed to examine the performance of a wide range of DFT methods across the rungs of Jacob’s Ladder for their ability to compute B–F BDEs. We find that only a handful of DFT methods can reproduce the CCSD(T)/CBS BDEs with mean absolute deviations (MADs) below the threshold of chemical accuracy (i.e., with average deviations below 4.2 kJ mol−1 ). The only functionals capable of achieving this feat were (MADs given in parentheses): ωB97M-V (4.0), BMK (3.5), DSD-BLYP (3.8), and DSD-PBEB95 (1.8 kJ mol−1 ).
A high-level quantum chemical study of the thermodynamics associated with chlorine transfer between N-chlorinated nucleobases
The relative free energies of the isomers formed upon N-chlorination of each nitrogen atom within the DNA nucleobases (adenine, guanine, and thymine) have been obtained using the high-level G4(MP2) composite ab initio method (the free energies of the N-chlorinated isomers of cytosine have been reported at the same level of theory previously). Having identified the lowest energy N-chlorinated derivatives for each nucleobase, we have computed the free energies associated with chlorine transfer from N-chlorinated nucleobases to other unsubstituted bases. Our results provide quantitative support pertaining to the results of previous experimental studies, which demonstrated that rapid chlorine transfer occurs from N-chlorothymidine to cytidine or adenosine. The results of our calculations in the gas-phase reveal that chlorine transfer from N-chlorothymine to either cytosine, adenine, or guanine proceed via exergonic processes with ∆Go values of −50.3 (cytosine), −28.0 (guanine), and −6.7 (adenine) kJ mol–1. Additionally, we consider the effect of aqueous solvation by augmenting our gas-phase G4(MP2) energies with solvation corrections obtained using the conductor-like polarizable continuum model. In aqueous solution, we obtain the following G4(MP2) free energies associated with chlorine transfer from N-chlorothymine to the three other nucleobases: −58.4 (cytosine), −26.4 (adenine), and −18.7 (guanine) kJ mol–1. Therefore, our calculations, whether in the gas phase or in aqueous solution, clearly indicate that chlorine transfer from any of the N-chlorinated nucleobases to cytosine provides a thermodynamic sink for the active chlorine. This thermodynamic preference for chlorine transfer to cytidine may be particularly deleterious since previous experimental studies have shown that nitrogen-centered radical formation (via N–Cl bond homolysis) is more easily achieved in N-chlorinated cytidine than in other N-chlorinated nucleosides.
Homolytic C–Br Bond Dissociation Energies Obtained by Means of the G4 Thermochemical Protocol
Knowledge of the energies required to induce homolytic cleavage of the C–Br bonds of brominated organic molecules, a process that affords carbon-centered radicals and Br•, is of fundamental importance. Although some data pertaining to the strength of C–Br bonds can already be found in the literature, the chemical diversity of the species for which bond dissociation energies (BDEs) are available is somewhat limited. In this data article, we report a comprehensive set of homolytic C–Br BDEs, obtained using the G4 thermochemical protocol, for brominated organic molecules with wide structural diversity. The species in this set have C–Br BDEs (at 298 K) that differ by as much as 188.3 kJ mol–1, with α-bromoalanine having the lowest BDE (214.1 kJ mol–1) and 1-bromobut-1-yne having the largest (402.4 kJ mol–1). Of particular relevance to biological systems are the BDEs of 8-bromoguanine (345.3 kJ mol–1), 8-bromoadenine (345.6 kJ mol–1), 5-bromocytosine (348.8 kJ mol–1) and 5-bromouracil (350.3 kJ mol–1).
Highly accurate CCSD(T) homolytic Al–H bond dissociation enthalpies – chemical insights and performance of density functional theory
We obtain gas-phase homolytic Al–H bond dissociation enthalpies (BDEs) at the CCSD(T)/CBS level for a set of neutral aluminium hydrides (which we refer to as the AlHBDE dataset). The Al–H BDEs in this dataset differ by as much as 79.2 kJ mol−1, with (H2B)2Al–H having the lowest BDE (288.1 kJ mol−1) and (H2N)2Al–H having the largest (367.3 kJ mol−1). These results show that substitution with at least one –AlH2 or –BH2 substituent exerts by far the greatest effect in modifying the Al–H BDEs compared with the BDE of monomeric H2Al–H (354.3 kJ mol−1). To facilitate quantum chemical investigations of large aluminium hydrides, for which the use of rigorous methods such as W2w may not be computationally feasible, we assess the performance of 53 density functional theory (DFT) functionals. We find that the performance of the DFT methods does not strictly improve along the rungs of Jacob's Ladder. The bestperforming methods from each rung of Jacob's Ladder are (mean absolute deviations are given in parentheses): the GGA B97-D (6.9), the meta-GGA M06-L (2.3), the global hybrid-GGA SOGGA11-X (3.3), the range-separated hybrid-GGA CAM-B3LYP (2.1), the hybrid-meta-GGA ωB97M-V (2.5) and the double-hybrid methods mPW2-PLYP and B2GP-PLYP (4.1 kJ mol−1).
Advancements in Carbazole-Based Sensitizers and Hole-Transport Materials for Enhanced Photovoltaic Performance
Carbazole-based molecules play a significant role in dye-sensitized solar cells (DSSCs) due to their advantageous properties. Carbazole derivatives are known for their thermal stability, high hole-transport capability, electron-rich (p-type) characteristics, elevated photoconductivity, excellent chemical stability, and commercial availability. This review focuses on DSSCs, including their structures, working principles, device characterization, and the photovoltaic performance of carbazole-based derivatives. Specifically, it covers compounds such as 2,7-carbazole and indolo[3,2-b]carbazole, which are combined with various acceptors like benzothiadiazole, thiazolothiazole, diketopyrrolopyrrole, and quinoxaline, as reported over the past decade. The review will also outline the relationship between molecular structure and power-conversion efficiencies. Its goal is to summarize recent research and advancements in carbazole-based dyes featuring a D-π-A architecture for DSSCs. Additionally, this review addresses the evolution of carbazole-based hole-transport materials (HTMs), which present a promising alternative to the costly spiro-OMeTAD. We explore the development of novel HTMs that leverage the unique properties of carbazole derivatives to enhance charge transport, stability, and overall device performance. By examining recent innovations and emerging trends in carbazole-based HTMs, we provide insights into their potential to reduce costs and improve the efficiency of DSSCs.
Tailoring the Optoelectronic Properties of Soybean-Derived Nitrogen Self-Doped Carbon Dots through Composite Formation with KCl and Zeolite, Synthesized Using Autogenic Atmosphere Pyrolysis
This article investigates the environmentally friendly synthesis and characterization of carbon dots (CDs) derived from soybean biomass, in conjunction with their composites containing potassium chloride (KCl) or zeolite. By using an environmentally sustainable synthetic approach, this study sought to unlock the potential of these materials for various applications. The physicochemical properties of the CDs and composites were comprehensively analyzed using various techniques including scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. In addition, various optical properties such as UV–Vis absorption, band gap, and excitation–emission behavior were investigated. A key finding to arise from this study was that the inclusion of a doping agent such as KCl or zeolite significantly reduced the size of the resulting CDs. In this light, whereas the undoped species are associated with average sizes of 8.86 ± 0.10 nm, those doped with either zeolite or KCl were associated with average sizes of 3.09 ± 0.05 and 2.07 ± 0.05 nm, respectively. In addition, it was shown that doping with either zeolite or KCl resulted in an alteration of the elemental composition of the CDs and influenced their optical properties, especially their excitation-dependent emission. These promising results point to potential applications in environmental sensing and energy-related fields.
A high-level G4(MP2) thermochemical study of the relative energies of the N-chlorinated isomers formed upon chlorination of cytosine
Although the relative energies of the various tautomers of cytosine and 5-chlorocytosine have been studied in detail, little is known about the relative energies of the N-chlorinated isomers of cytosine. N-chlorination of cytosine is known to occur when cytosine is exposed to hypochlorous acid, a potent oxidant that is formed during the inflammatory process, and is presumed to have consequences concerning, for example, the structural integrity of DNA and RNA. In this study, the high-level G4(MP2) thermochemical protocol has been employed in studying the relative gas-phase free energies of thirty isomers that may be formed upon N-chlorination of cytosine. Using free energy of solvation corrections obtained by way of continuum models (CPCM and SMD), an approximation of the effect of aqueous solvation on the relative energies of the isomers has also been taken into account. In both the gas- and aqueous-phases, the lowest energy isomer is an exocyclic N-chloroimino derivative.