Enhanced cation interaction in perovskites for efficient tandem solar cells with silicon

To achieve the full potential of monolithic perovskite/silicon tandem solar cells, crystal defects and film inhomogeneities in the perovskite top cell must be minimized. We discuss the use of methylenediammonium dichloride as an additive to the perovskite precursor solution, resulting in the incorporation of in situ-formed tetrahydrotriazinium (THTZ-H+) into the perovskite lattice upon film crystallization. The cyclic nature of the THTZ-H+ cation enables a strong interaction with the lead octahedra of the perovskite lattice through the formation of hydrogen bonds with iodide in multiple directions. This structure improves the device power conversion efficiency (PCE) and phase stability of 1.68 electron volts perovskites under prolonged light and heat exposure under 1-sun illumination at 85°C. Monolithic perovskite/silicon tandems incorporating THTZ-H+ in the perovskite photo absorber reached a 33.7% independently certified PCE for a device area of 1 square centimeter.

Unexpected Intermolecular C-H···O Hydrogen Bonds and 1H NMR Chemical Shifts in a Key Linker for Fluorine-18 Labeling of Dimeric Drugs

The compound 2-{[(trifluoromethyl)sulfonyl]oxy}propane-1,3-diyl bis(4-methylbenzenesulfonate) (TPB) is a crucial intermediate in the synthesis of 18F-radiolabeled cromolyn derivatives. In this work, we combine 1H NMR spectroscopy, X-ray crystallography, ab initio molecular dynamics, and NMR calculations to examine the structure, interactions, and solvation dynamics of the TPB molecule. In CDCl3, the CH2 groups within its glyceryl-derived linker exhibit a single set of proton signals in the 1H NMR measurements. However, when TPB is dissolved in DMSO-d6, distinct splitting patterns emerge despite its seemingly symmetric chemical structure. Crystallographic analysis further unveils the absence of overall symmetry in its three-dimensional arrangement. To elucidate these unique NMR features, we carry out ab initio molecular dynamics simulations and characterize the solvation structures and dynamics of TPB in CHCl3 and DMSO solutions. In contrast to the predominantly nonpolar nature of the CHCl3 solvents, DMSO directly participates in C-H···O hydrogen-bonding interactions with the solute molecule, leading to the splitting of its -CH2 chemical shifts into two distinct distributions. The comprehensive understanding of the structure and solvation interactions of TPB provides essential insights into its application in the radiofluorination reactions of cromolyn derivatives and holds promise for the future development of radiolabeled dimeric drugs.

Quantum Effects of Hydrogen Nuclei on the Nuclear Magnetic Shielding Tensor of Ice Ih

Ice is the most fundamental hydrogen-bonded system in which the hydrogen nuclear quantum effect significantly impacts the structure and relevant thermochemical and spectroscopic properties. While ice was experimentally investigated using proton nuclear magnetic resonance spectroscopy more than 40 years ago, the corresponding theoretical investigations have been rarely reported due to the difficulty in evaluating how the proton nuclear quantum effect influences the spectral characteristics of such a condensed material. In this study, we applied a combination of the ONIOM and multicomponent molecular orbital (MC_MO) methods for calculating the anisotropic and isotropic components of the nuclear magnetic shielding tensor of the hexagonal ice crystal to quantify the effects of nuclear quantum fluctuations on the spectroscopic properties of ice. The nuclear magnetic shielding values computed by incorporating the hydrogen nuclear quantum effect reasonably agree with the experimental values. The nuclear quantum effects were found to increase the anisotropic component of the magnetic shielding tensor while decreasing the isotropic component. Such a difference can be explained by their distinct dependence on the electrostatic field and hydrogen-bonding structural parameters.

Perspective: Reference-Potential Methods for the Study of Thermodynamic Properties in Chemical Processes: Theory, Applications, and Pitfalls

In silico investigations of enzymatic reactions and chemical reactions in condensed phases often suffer from formidable computational costs due to a large number of degrees of freedom and enormous important volume in phase space. Usually, accuracy must be compromised to trade for efficiency by lowering the reliability of the Hamiltonians employed or reducing the sampling time. Reference-potential methods (RPMs) offer an alternative approach to reaching high accuracy of simulation without much loss of efficiency. In this Perspective, we summarize the idea of RPMs and showcase some recent applications. Most importantly, the pitfalls of these methods are also discussed, and remedies to these pitfalls are presented.

Quantum mechanical effects in acid–base chemistry

Acid–base chemistry has immense importance for explaining and predicting the chemical products formed by an acid and a base when mixed together. However, the traditional chemistry theories used to describe acid–base reactions do not take into account the effect arising from the quantum mechanical nature of the acidic hydrogen shuttling potential and its dependence on the acid base distance. Here, infrared and NMR spectroscopies, in combination with first principles simulations, are performed to demonstrate that quantum mechanical effects, including electronic and nuclear quantum effects, play an essential role in defining the acid–base chemistry when 1-methylimidazole and acetic acid are mixed together. In particular, it is observed that the acid and the base interact to form a complex containing a strong hydrogen bond, in which the acidic hydrogen atom is neither close to the acid nor to the base, but delocalized between them. In addition, the delocalization of the acidic hydrogen atom in the complex leads to characteristic IR and NMR signatures. The presence of a hydrogen delocalized state in this simple system challenges the conventional knowledge of acid–base chemistry and opens up new avenues for designing materials in which specific properties produced by the hydrogen delocalized state can be harvested.

Acid-based theories do not consider the quantum mechanical nature of the acidic hydrogen shuttling potential. Here, it is demonstrated that this particularity is needed to explain the formation acid-base complex with a delocalized acidic hydrogen.

Affordable Ab Initio Path Integral for Thermodynamic Properties via Molecular Dynamics Simulations Using Semiempirical Reference Potential

Path integral molecular dynamics (PIMD) is becoming a routinely applied method for incorporating the nuclear quantum effect in computer simulations. However, direct PIMD simulations at an ab initio level of theory are formidably expensive. Using the protonated 1,8-bis(dimethylamino)naphthalene molecule as an example, we show in this work that the computational expense for the intramolecular proton transfer between the two nitrogen atoms can be remarkably reduced by implementing the idea of reference-potential methods. The simulation time can be easily extended to a scale of nanoseconds while maintaining the accuracy on an ab initio level of theory for thermodynamic properties. In addition, postprocessing can be carried out in parallel on massive computer nodes. A 545-fold reduction in the total CPU time can be achieved in this way as compared to a direct PIMD simulation at the same ab initio level of theory.

Amphiphilic chitosan-g-poly(trimethylene carbonate) - A new approach for biomaterials design

The paper presents the synthesis and characterization of poly(trimethylene carbonate) grafted chitosan as a new water soluble biopolymer suitable for in vivo applications. The synthesis was performed via ring-opening polymerization of 1,3-dioxan-2-one (trimethylene carbonate) (TMC) monomer, initiated by the functional groups of chitosan in the presence of toluene as solvent/swelling agent. By varying the molar ratio between the glucosamine units of chitosan and TMC, a series of chitosan derivatives with different content of poly(trimethylene carbonate) chains was synthetized. The structural characterization of the polymers was realized by FTIR and ¹H NMR spectroscopy and their solubility was assessed in water and in organic solvents as well. The biocompatibility was investigated by MTS assay on Normal Human Dermal Fibroblasts, and the biodegradability was evaluated in lysozyme buffer solution. Further, the surface properties of the polymer films were analyzed by polarized optical microscopy, atomic force microscopy and water-to-air contact angle measurements. It was established that, by 5% substitution of chitosan with poly(trimethylene carbonate) chains having an average polymerization degree of 7, a water soluble polymer can be attained. Compared to the pristine chitosan, it has improved biocompatibility in solution and moderate wettability and higher biodegradability rate in solid state, pointing its suitability for in vivo applications.

Helium Nanodroplet Infrared Action Spectroscopy of the Proton-Bound Dimer of Hydrogen Sulfate and Formate: Examining Nuclear Quantum Effects

The proton-bound dimer of hydrogen sulfate and formate is an archetypal structure for ionic hydrogen-bonding complexes that contribute to biogenic aerosol nucleation. Of central importance for the structure and properties of this complex is the location of the bridging proton connecting the two conjugate base moieties. The potential energy surface for bridging proton translocation features two local minima, with the proton localized at either the formate or hydrogen sulfate moiety. However, electronic structure methods reveal a shallow potential energy surface governing proton translocation, with a barrier on the order of the zero-point energy. This shallow potential complicates structural assignment and necessitates a consideration of nuclear quantum effects. In this work, we probe the structure of this complex and its isotopologues, utilizing infrared (IR) action spectroscopy of ions captured in helium nanodroplets. The IR spectra indicate a structure in which a proton is shared between the hydrogen sulfate and formate moieties, HSO₄^-···H⁺···^-OOCH. However, because of the nuclear quantum effects and vibrational anharmonicities associated with the shallow potential for proton translocation, the extent of proton displacement from the formate moiety remains unclear, requiring further experiments or more advanced theoretical treatments for additional insight.

Actual Symmetry of Symmetric Molecular Adducts in the Gas Phase, Solution and in the Solid State

This review discusses molecular adducts, whose composition allows a symmetric structure. Such adducts are popular model systems, as they are useful for analyzing the effect of structure on the property selected for study since they allow one to reduce the number of parameters. The main objectives of this discussion are to evaluate the influence of the surroundings on the symmetry of these adducts, steric hindrances within the adducts, competition between different noncovalent interactions responsible for stabilizing the adducts, and experimental methods that can be used to study the symmetry at different time scales. This review considers the following central binding units: hydrogen (proton), halogen (anion), metal (cation), water (hydrogen peroxide).

Symmetry/Asymmetry of the NHN Hydrogen Bond in Protonated 1,8-Bis(dimethylamino)naphthalene

Experimental and theoretical results are presented based on vibrational spectra and motional dynamics of 1,8-bis(dimethylamino)naphthalene (DMAN) and its protonated forms (DMANH+ and the DMANH+ HSO4− complex). The studies of these compounds have been performed in the gas phase and solid-state. Spectroscopic investigations were carried out by infrared spectroscopy (IR), Raman, and incoherent inelastic neutron scattering (IINS) experimental methods. Density functional theory (DFT) and Car–Parrinello molecular dynamics (CPMD) methods were applied to support our experimental findings. The fundamental investigations of hydrogen bridge vibrations were accomplished on the basis of isotopic substitutions (NH → ND). Special attention was paid to the bridged proton dynamics in the DMANH+ complex, which was found to be affected by interactions with the HSO4− anion.

Proton-responsive naphthyridinone-based RuII complexes and their reactivity with water and alcohols

We report the synthesis and reactivity of RuII complexes with a new naphthyridinone-substituted phosphine ligand, 7-(diisopropylphosphinomethyl)-1,8-naphthyridin-2(1H)-one (L-H), which contains two reactive sites that can potentially be deprotonated by a strong base: an NH proton of naphthyridinone and a methylene arm attached to the phosphine. In the absence of a base, the stable bis-ligated complex Ru(L-H)2Cl2 (1) containing two NH groups in the secondary coordination sphere is formed. Upon further reaction with a base, a doubly deprotonated, dimeric complex is obtained, [Ru2(L*-H)2(L)2] (2), in which two of the four ligands undergo deprotonation at the NH (L), while the other two ligands are deprotonated at the methylene groups (L*-H) as confirmed by an X-ray diffraction study; intramolecular hydrogen bonding is present between the NH group of one ligand and an O-atom of another ligand in the dimeric structure, which stabilizes the observed geometry of the complex. Complex 2 reacts with protic solvents such as water or methanol generating aqua Ru(L)2(OH2)2 (3) or methanol complexes Ru(L)2(MeOH)2 (4), respectively, both exhibiting intramolecular H-bonded patterns with surrounding ligands at least in the solid state. These complexes react with benzyl alcohols to give aldehydes via base-free acceptorless dehydrogenation.

Quantum effects and 1H NMR chemical shifts of a bifurcated short hydrogen bond

The monoprotonated compound N,N',N''-tris(p-tolyl)azacalix[3](2,6)pyridine (TAPH) contains an intramolecular hydrogen bond that is formed from three N atoms in its cavity. Constrained by the macrocyclic molecular structure, the separations between the N atoms in this bifurcated hydrogen bond are about 2.6 Å, considerably shorter than those typically observed for hydrogen bonded systems in the condensed phases. As such, TAPH exhibits significantly elongated N-H lengths in its hydrogen bond and a downfield ¹H NMR chemical shift of 22.1 ppm. In this work, we carry out ab initio molecular dynamics and ab initio path integral molecular dynamics simulations of TAPH in the acetonitrile solution to reveal the geometry and proton sharing conditions of the bifurcated short hydrogen bond and uncover how the interplay of electronic and nuclear quantum effects gives rise to its far downfield ¹H chemical shift. Taking a linear short hydrogen bond as a reference, we demonstrate the distinct features of competing quantum effects and electronic shielding effects in the bifurcated hydrogen bond of TAPH. We further use the degree of deshielding on the proton as a measure of the hydrogen bonding interactions and evaluate the strength of the bifurcated short hydrogen bond as compared to its linear counterpart.