A combined experimental-molecular modeling study of crown ether europium complexes: Effects of the coordinated anion on structural and luminescence properties

It is reported the synthesis, characterization by elemental analysis, thermogravimetry; electronic absorption, infrared, excitation, and emission spectroscopies of the [Eu(12C4)(phen)2(X)n]X2 complexes, where 12C4 = 12-crown-4, phen = 1,10-phenanthroline, and X  = F-, Cl-, Br-, SCN-, ClO4-, and NO3-. It is verified that the polarizability of the anion X- exerts remarkable effects on the emission process. As a general trend, lower wavenumbers for the 7F0→5L6, 7F0→5D2 and 7F0→5D1 transitions are associated with the anions with higher volumes and, consequently, higher polarizability. The molecular modeling results performed with quantum methods (RHF and DFT) suggest some relationships between the calculated structures, electronic, and luminescence properties with the presence of the LMCT (ligand-to-metal charge transfer) states, which explains the differences in the emission spectra of these complexes due to the coordinated anion.

Predicting Solvation Free Energies Using Electronegativity-Equalization Atomic Charges and a Dense Neural Network: A Generalized-Born Approach

I propose a dense Neural Network, ESE-GB-DNN, for evaluation of solvation free energies ΔG°solv for molecules and ions in water and nonaqueous solvents. As input features, it employs generalized-Born monatomic and diatomic terms, as well as atomic surface areas and the molecular volume. The electrostatics calculation is based on a specially modified version of electronegativity-equalization atomic charges. ESE-GB-DNN evaluates ΔG°solv in a simple and highly efficient way, yet it offers a high accuracy, often challenging that of standard DFT-based methods. For neutral solutes, ESE-GB-DNN yields an RMSE between 0.7 and 1.3 kcal/mol, depending on the solvent class. ESE-GB-DNN performs particularly well for nonaqueous solutions of ions, with an RMSE of about 0.7 kcal/mol. For ions in water, the RMSE is larger (2.9 kcal/mol).

Base-Stabilized Phosphinidene Oxide, Imide and Sulfide

Oxidation of a base-stabilized phosphinidene (κ2 -NNP)P (12, NNP=phosphinoamidinate) with N2 O afforded a labile phosphinidene oxide (κ2 -NNP)P=O (16) which was characterized by NMR spectroscopy. Further oxidation of 16 by N2 O or reaction of 12 with two equivalents of pyridine oxide afforded the isolable dioxide (κ2 -NNP)PO2 which was characterized by NMR and SC XRD. Trapping of 16 with tolyl isocyanate resulted in P=O/N=C metathesis, eventually affording a urea-ligated phosphine (κ1 -NNP)P(NTol)2 C=O (17) The mechanism of this reaction was elucidated by DFT calculations. Reactions of phosphinidene 12 with azides generated transient imines (NNP)P=NR, which in the case of R=Tol underwent cycloaddition with tolyl Isocyanate to afford the urea product 17, and in the case of R=SiMe3 reacts with N3 SiMe3 via the addition of N-Si across the P=N bond affording, after the extrusion of dinitrogen, a P,N-heterocyclic compound. Both products of the reactions with azides have been fully characterized, both in solution and the solid-state. Finally, reaction of phosphinidene 12 with one equivalent of sulfur resulted in the isolation of the base-stabilized phosphinidene sulfide (κ2 -NNP)P=S that has also been fully characterized.

Dense Neural Network for Calculating Solvation Free Energies from Electronegativity-Equalization Atomic Charges

I propose a dense Neural Network for evaluation of solvation free energies ΔG°solv for molecules and ions in water and nonaqueous solvents, Easy Solvation Energy with Electronegativity Equalization charges and Dense Neural Network (ESE-EE-DNN). As input features, it uses the Conductor-like Screening Model (COSMO) electrostatic energy, atomic cavity surface areas, total cavity volume, and induced surface charges. For the COSMO calculation, electronegativity-equalization atomic charges are employed. ESE-EE-DNN exhibits fairly high accuracy, similar or even superior to that of mainstream density functional theory-based methods. For neutral solutes in water, polar protic, polar aprotic, and nonpolar solvents, ESE-EE-DNN yields a root-mean-square error (RMSE) of 1.25, 1.36, 0.70, and 0.71 kcal/mol, respectively. ESE-EE-DNN is particularly advantageous for ionic solutes, with an RMSE of 2.82 and 1.42 kcal/mol for aqueous and nonaqueous ion solutions, correspondingly. ESE-EE-DNN is very efficient due to a fast evaluation of the electronegativity-equalization charges.

Theoretical mechanistic insights into the electrophilic addition of hydrogen halides to alkynes

The electrophilic addition of hydrogen halides to alkynes, also called polar hydrohalogenation of alkynes, is one of the most classical and important organic reactions. Mechanistic and stereoselective insights into the hydrohalogenation of various structurally different distinct alkynes, including both alkyl and aryl substituted acetylenes, in acetic acid were investigated theoretically via density functional theory (DFT) calculations. The results indicate that π-complexes between hydrogen halides and alkynes are first formed, and then all alkynes can undergo a competitive bimolecular intimate ion-pair syn-addition process and a pentamolecular concerted anti-addition process through the cyclic proton transfer mechanism for proton transfer in the absence of tetraalkylammonium halides or a termolecular electrophilic addition (AdE3) process in the presence of tetraalkylammonium halides. All aliphatic alkynes undergo slightly to obviously predominant anti-addition in hydrohalogenations both in the absence and presence of tetraalkylammonium halides. Aromatic 1-arylalk-1-ynes favour syn-additions through bimolecular intimate ion-pair processes with asynchronous concerted characteristics in the absence of tetraalkylammonium halides, while most of them generally prefer anti-addition in the presence of tetraalkylammonium halides. The stereoselectivity is significantly affected by both the electronic and steric effects of 1-arylalk-1-ynes and halides in the reaction mixture. Strongly electron-rich and bulky 1-arylalk-1-ynes generally favour syn-addition in the presence of tetraalkylammonium halides, especially arylethynes in hydrochlorination. Anti-Markovnikov hydrohalogenations of 1-arylalk-1-ynes also prefer anti-addition both in the absence and presence of tetraalkylammonium halides even in small amounts due to high activation energies. The current investigation provides deep insights into the mechanism and stereoselectivity in polar hydrohalogenations of alkynes.

Electrically Controlled Adsorptive Membranes with Tunable Affinity for Selective Chromium (VI) Separation from Water

Ionic contaminants such as Cr(VI) pose a challenge for water purification using membrane-based processes. However, existing membranes have low permeability and selectivity for Cr(VI). Therefore, in this study, we prepared an electrically controlled adsorptive membrane (ECAM-L) by coating a loose Cl--doped polypyrrole layer on a carbon nanotube substrate, and we evaluated the performance of ECAM-L for Cr(VI) separation from water. We also used electrochemical quartz crystal microbalance measurements and molecular dynamics and density functional theory calculations to investigate the separation mechanisms. The adsorption and desorption of Cr(VI) could be modulated by varying the electrostatic interactions between ECAM-L and Cr(VI) via potential control, enabling the cyclic use of the ECAM-L without additional additives. Consequently, the oxidized ECAM-L showed high Cr(VI) removal performance (<50 μg/L) and treatment capacity (>3500 L/m2) at a high water flux (283 L/m2/h), as well as reusability after the application of a potential. Our study demonstrates an efficient membrane design for water decontamination that can selectively separate Cr(VI) through a short electric stimulus.

Photoinduced electron transfer in [10]CPP⊃C60 oligomers with stable and well-defined supramolecular structures

Recent synthesis of a new type of polymer containing conjugated cycloparaphenylene (CPP) macrocycles interconnected by a linear conjugated backbone opens up great potential of cyclic π-conjugated materials in organic photovoltaics. In this work, I report a theoretical study of the ground and excited state properties of such polymers and investigate an effect of inclusion of fullerene molecules into polymer chains. MD simulations reveal that oligomers ([10]CPP_Fused⊃C60)24 and ([10]CPP_Fused⊃C60)32 with π-extended CPPs tend to form stable, helix-like structures. I show that photoinduced electron transfer from the CPP-based polymer to C60 fullerene is favorable and occurs on a nanosecond time scale. The hole- and excess-electron transfer rates are found to be significantly higher than the corresponding charge recombination rates.

Solv: An Alternative Continuum Model Implementation Based on Fixed Atomic Charges, Scaled Particle Theory, and the Atom-Atom Potential Method

An alternative continuum model implementation is reported. The electrostatic contribution to the solvation Gibbs free energy utilizes the noniterative conductor-like screening model of Vyboishchikov and Voityuk (DOI: 10.1002/jcc.26531) based on the fixed partial atomic charges. The nonelectrostatic solute-solvent dispersion-repulsion energy is calculated through the Caillet-Claverie atom-atom potential method employing the grid-based approach. The nonelectrostatic cavitation energy is computed within the scaled particle theory (SPT) formalism with the solute hard-sphere radius obtained via the Pierotti-Claverie (PC) scheme, from the solute molecular surface (SPT-S) or volume (SPT-V). The solvent hard-sphere radius is derived through the fitting to the experimental total solvation free energies of 2530 neutral species in 92 solvents. Application of the model to reproduce both the absolute and relative (reaction net) solvation free energies indicates that the SPT-V approach based on the CM5 charges is the best performer. The method is suggested for the solvation free energy calculation in the nonaqueous solvents.

Ferrocene/ferrocenium, cobaltocene/cobaltocenium and nickelocene/nickelocenium: from gas phase ionization energy to one-electron reduction potential in solvated medium

We propose a theoretical procedure for accurate determination of reduction potentials for three metallocene couples, Cp₂M⁺/Cp₂M, where M = Fe, Co and Ni. This procedure first computes the gas phase ionization energy (IE) using the explicitly correlated CCSD(T)-F12 method and includes the zero-point energy correction, core-valence electronic correlation, and relativistic and spin-orbit coupling effects. By means of Born-Haber thermochemical cycle, the one-electron reduction potential is obtained as the sum of the gas phase IE and the corresponding Gibbs free energies of solvation (ΔG_solv) for both the neutral and cationic species. Among the three solvent models (PCM, SMD and uESE) investigated here, it turns out that only the SMD model (computed at the DFT level) gives the best estimation of the value for "ΔG_solv(cation) - ΔG_solv(neutral)" and thus, combining with the accurate IE values, the theoretical protocol is capable of yielding reliable values (in V) for , and . These predictions compare favorably with the available experimental data (in V): , , and . We show that our theoretical procedure is reliable for accurate reduction potential predictions of Cp₂Fe⁺/Cp₂Fe, Cp₂Co⁺/Cp₂Co and Cp₂Ni⁺/Cp₂Ni redox couples in aqueous and non-aqueous media; the maximum absolute deviation is as small as ≈120 mV, which outperforms those of the existing theoretical methods.

A quick solvation energy estimator based on electronegativity equalization

ESE-EE (Easy Solvation Estimation with Electronegativity equalization) is a quick method for estimation of solvation-free energies ΔGº_solv , which uses a thoroughly fitted electronegativity equalization (EE) scheme to obtain atomic charges, which are further employed in a scaled noniterative COSMO-like calculation to evaluate the electrostatic component of ΔGº_solv . Nonelectrostatic corrections including adjustable parameters are also added. For neutral solutes, ESE-EE yields a mean absolute error (MAE) in ΔG_solv ° of 1.5 kcal/mol for aqueous solutions; 1.0 kcal/mol for nonaqueous polar protic solvents; 0.9 kcal/mol for polar aprotic solvents; and about 0.6 kcal/mol for nonpolar solvents. Since ESE-EE only requires a molecular geometry as input for a ΔGº_solv prediction, it can be utilized for a rapid screening of ΔGº_solv for large neutral molecules. However, for ionic solutes, ESE-EE yields larger errors (typically several kcal/mol) and is recommendable for preliminary estimations only. Upon a special refitting, ESE-EE is able to yield partition coefficients with a good accuracy.

Physical and numerical aspects of sodium ion solvation free energies via the cluster-continuum model

Sodium cation solvation Gibbs free energies (ΔG_solv(Na⁺)) have been obtained in water, dimethylformamide, dimethyl sulfoxide, ethanol, acetone, acetonitrile, and methanol through the "monomer cycle" cluster-continuum approach where a solvent reference state is described by infinitely separated molecules. The following steps are vital for obtaining reliable ΔG_solv(Na⁺) values: (a) a meticulous conformational search involving dispersion corrected density functional theory (DFT-D) and the continuum solvation model (CSM); (b) gas-phase DFT-D geometry optimization followed by single-point (SP) domain-based local pair natural orbital coupled clusters including single, double, and partly triple excitation (DLPNO-CCSD(T)) calculations in conjunction with the complete basis set extrapolation; (c) advanced statistical thermodynamic treatment of the low harmonic frequencies (<100 cm^-1) to obtain the robust gas-phase Gibbs free energy correction; (d) gas-phase and dielectric continuum SP with non-electrostatic contributions included in the CSM; (e) an evaluation of the relative thermodynamic stability of the Na⁺(S)_n clusters to identify the number of explicit solvent molecules n to be considered. Our refined computational protocol is promising with a Pearson correlation coefficient between the predicted and experimental data, ρ, of 0.82, and the mean signed and mean unsigned errors of 0.3 and 1.4 kcal mol^-1, respectively.

Humidity-Dependent Hydration and Proton Conductivity of PFSA Ionomer Thin Films at Fuel-Cell-Relevant Temperatures: Effect of Ionomer Equivalent Weight and Side-Chain Characteristics

Studies on the hydration properties, proton conductivity, and water content of perfluorinated ionomer thin films at temperatures relevant to fuel cell operation temperatures (around 80 °C) and the effect of ionomer chemistry are scarce. In this work, we report the water content and proton conductivity properties of thin-film ionomers (30 nm) at 80 °C over a wide range of relative humidity (0-90%) for seven different ionomers differing in the side-chain structure, including the number of protogenic groups, with the equivalent weight ranging from 620 to 1100 g/mol of sulfonic acid. The results show that the acid content or equivalent weight of the ionomer is the strongest determinant of both the swelling and the proton conductivity of ionomer films at a given relative humidity. The molar water content (λ) of ionomer films normalized to the molar protogenic group is observed to be equivalent-weight-dependent, implying that the affinity for water is acid-content-dependent. At high relative humidity conditions (>70%) pertinent to fuel cell operations, the proton conductivity of low-equivalent-weight ionomers was higher than that of higher-equivalent-weight ionomers. However, upon correlating the proton conductivity with molar water content (λ), the differences reduce dramatically, highlighting that water content is the controlling factor for proton conduction. Significantly higher values of both water content and proton conductivity are observed at 80 °C compared to those at 30 °C, implying that room temperature data are not reliable for estimating ionomer properties in the fuel cell catalyst layer.

Towards a transferable nonelectrostatic model for continuum solvation: The electrostatic and nonelectrostatic energy correction model

In this work, we introduce an electrostatic and non-electrostatic (ENE) correction to the solvation energy based on the Solvent-Accessible Surface Area (SASA) of the solute and the solvent static dielectric constant. The proposed correction was developed for neutral solutes in non-aqueous solvents, considering three different implicit solvation models based on a Self-Consistent Reaction Field treatment of solute-solvent mutual polarization using an Apparent Surface Charge formalism, namely the Integral Equation Formalism of the Polarizable Continuum Model using a continuous surface charge scheme (PCM), the Solvation Model based on solute electron density (SMD), and the generalized Finite-Difference Poisson-Boltzmann (FDPB) model. The proposed correction was parametrized on a diverse training set of 4980 solvation data from the Solv@tum database of experimental solvation energies, and validated on the non-aqueous subset of the MNSOL database comprising 2140 solvation energies. The performances of the proposed ENE models with minimal and extended parameters formulations have been analyzed and the latter variant has been further compared to the widely used Cavity, Dispersion, and Solvent structural effects (CDS) non-electrostatic model originally developed for the SMx family of implicit solvation models. Overall, a very good agreement between the computed solvation energies with the ENE correction and the reference experimental data has been found on both the training and test sets for all continuum solvation models considered. Furthermore, results for the ENE correction are on par with the reference CDS non-electrostatic model for both SMD and FDPB electrostatics, but with the advantage of using a lower number of parameters and thus an improved transferability between different electrostatics treatments.

Theoretical mechanistic insights into the polar hydrohalogenation of olefins

Polar hydrohalogenation of olefins, also called electrophilic addition of hydrogen halides to olefins, is an essential, classical, and important organic reaction. Mechanistic and stereoselective insights into the polar hydrohalogenations of nine structurally different distinct olefins were obtained through theoretical investigation via density functional theory (DFT) calculations. The results indicate that, after the formation of π-complexes of hydrogen halides and olefins, all olefins can undergo bimolecular intimate ion-pair syn-addition processes. However, aliphatic olefins can also undergo a pentamolecular concerted anti-addition process through a cyclic proton transferring mechanism, with a fourteen-membered cyclic transition state composed of olefins, two molecules of hydrogen halides, and an acetic acid dimer for the proton transfer. Although unsymmetric aliphatic olefins exhibit an obvious electrostatic intimate ion-pair process in their anti-addition, the process is still concerted with significantly asynchronous characteristics due to a greater hyperconjugation effect. The activation energies of anti-additions are generally lower than those of the corresponding syn-additions, especially for hydrobromination. The relative reaction rate constants of the anti-additions are always larger than those of the corresponding syn-additions on the basis of dynamics treatment according to transition state theory. Thus, in the hydrohalogenations, aliphatic olefins always give anti-adducts as major products, while aromatic olefins produce syn-adducts as major products. The substituent-controlled mechanisms and stereoselectivities are summarized and rationalized. The current investigation provides comprehensive insights into the mechanism and stereoselectivity of hydrohalogenations of olefins.

SN2 versus E2 reactions in a complex microsolvated environment: theoretical analysis of the equilibrium and activation steps of a nucleophilic fluorination

The reactivity of the fluoride ion towards alkyl halides is highly dependent on the solvating environment. In polar aprotic solvents with large counter-ions is highly reactive and produces substantial E2 product, whereas in polar protic solvents leads to slow kinetics and high selectivity for S_N2 reactions. The use of a more complex environment with stoichiometric addition of tert-butanol to acetonitrile solvent is able to module the reactivity and selectivity of tetrabutylammonium fluoride (TBAF). In the present work, we have performed a detailed theoretical analysis of this complex reaction system by density functional theory, continuum solvation model, and including explicit tert-butanol molecules. A kinetic model based on the free energy profile was also used to predict the reactivity and selectivity. The results indicated that the TBAF(tert-butanol) complex plays the key role to increase the S_N2 selectivity, whereas higher aggregates are not relevant. The E2 product is formed exclusively via free TBAF, because the solvating tert-butanol in the TBAF(tert-butanol) complex inhibits the E2 pathway. Our analysis suggests that diols or tetraols could produce an improved selectivity.

Accurate Prediction of Aqueous Free Solvation Energies Using 3D Atomic Feature-Based Graph Neural Network with Transfer Learning

Graph neural network (GNN)-based deep learning (DL) models have been widely implemented to predict the experimental aqueous solvation free energy, while its prediction accuracy has reached a plateau partly due to the scarcity of available experimental data. In order to tackle this challenge, we first build a large and diverse calculated data set Frag20-Aqsol-100K of aqueous solvation free energy with reasonable computational cost and accuracy via electronic structure calculations with continuum solvent models. Then, we develop a novel 3D atomic feature-based GNN model with the principal neighborhood aggregation (PNAConv) and demonstrate that 3D atomic features obtained from molecular mechanics-optimized geometries can significantly improve the learning power of GNN models in predicting calculated solvation free energies. Finally, we employ a transfer learning strategy by pre-training our DL model on Frag20-Aqsol-100K and fine-tuning it on the small experimental data set, and the fine-tuned model A3D-PNAConv-FT achieves the state-of-the-art prediction on the FreeSolv data set with a root-mean-squared error of 0.719 kcal/mol and a mean-absolute error of 0.417 kcal/mol using random data splits. These results indicate that integrating molecular modeling and DL would be a promising strategy to develop robust prediction models in molecular science. The source code and data are accessible at: https://yzhang.hpc.nyu.edu/IMA.

Single-ion solvation free energy: A new cluster-continuum approach based on the cluster expansion method

Accurate calculation of the solvation free energy of single ions remains an important goal, involving development in the dielectric continuum solvation models, and statistical mechanics with explicit solvent and hybrid discrete-continuum methods. In the last case, many of the research studies involve a quasi-chemical approach using the monomer cycle or the cluster cycle to calculate the solvation free energy of single ions. In this work, a different cluster-continuum approach based on the cluster expansion method was tested for solvation of 16 cations and 32 anions in aqueous solution. The SMD model was used for the dielectric continuum part and three explicit water molecules were introduced in the region of the solute with the highest interaction energy. Harmonic frequency calculations and molecular dynamics sampling of configurations are not required. An empirical γ_N parameter for cations and another for anions is introduced. The method produces a substantial improvement of the SMD model with a mean absolute deviation of 2.3 kcal mol^-1 for cations and 2.9 kcal mol^-1 for anions. The analysis of the correlation between theoretical and experimental data produces a linear regression line with a slope of 1.09 for cations and 1.01 for anions. The good results of this approximated cluster expansion approach suggest that the method could be further improved by including more solvent molecules and sampling the configurations.

Photoinduced electron transfer in non-covalent complexes of C60 and phosphangulene oxide derivatives

Investigation of photoinduced electron transfer (PET) in a series of experimentally reported complexes of fullerene with phosphangulene oxides shows that the replacement of O atoms in the bridge of phosphangulene with S atoms promotes efficient and ultrafast ET from phosphangulene oxide to fullerene in PGOOSS⊃C60 and PGOSSS⊃C60 complexes. The results obtained can be useful for the development of photovoltaic devices based on phosphangulenes.

Graphical Gaussian process regression model for aqueous solvation free energy prediction of organic molecules in redox flow batteries

The solvation free energy of organic molecules is a critical parameter in determining emergent properties such as solubility, liquid-phase equilibrium constants, pK_a and redox potentials in an organic redox flow battery. In this work, we present a machine learning (ML) model that can learn and predict the aqueous solvation free energy of an organic molecule using the Gaussian process regression method based on a new molecular graph kernel. To investigate the performance of the ML model for electrostatic interaction, the nonpolar interaction contribution of the solvent and the conformational entropy of the solute in the solvation free energy, three data sets with implicit or explicit water solvent models, and contribution of the conformational entropy of the solute are tested. We demonstrate that our ML model can predict the solvation free energy of molecules at chemical accuracy with a mean absolute error of less than 1 kcal mol^-1 for subsets of the QM9 dataset and the Freesolv database. To solve the general data scarcity problem for a graph-based ML model, we propose a dimension reduction algorithm based on the distance between molecular graphs, which can be used to examine the diversity of the molecular data set. It provides a promising way to build a minimum training set to improve prediction for certain test sets where the space of molecular structures is predetermined.

Unexpected Disparity in Photoinduced Reactions of C60 and C70 in Water with the Generation of O2 •- or 1O2

Well-defined fullerene-PEG conjugates, C₆₀-PEG (1) and two C₇₀-PEG (2 and 3 with the addition sites on ab-[6,6] and cc-[6,6]-junctions), were prepared from their corresponding Prato monoadduct precursors. The resulting highly water-soluble fullerene-PEG conjugates 1-3 were evaluated for their DNA-cleaving activities and reactive oxygen species (ROS) generation under visible light irradiation. Unexpectedly, photoinduced cleavage of DNA by C₆₀-PEG 1 was much higher than that by C₇₀-PEG 2 and 3 with higher absorption intensity, especially in the presence of an electron donor (NADH). The preference of photoinduced ROS generation from fullerene-PEG conjugates 1-3 via the type II (energy transfer) or the type I (electron transfer) photoreaction was found to be dependent on the fullerene core (between C₆₀ and C₇₀) and functionalization pattern of C₇₀ (between 2 and 3). This was clearly supported by the electron transfer rate obtained from cyclic voltammetry data and computationally estimated relative rate of each step of the type II and the type I reactions, with the finding that type II energy transfer reactions occurred in the inverted Marcus regime while type I electron transfer reactions proceeded in the normal Marcus regime. This finding on the disparity in the pathways of photoinduced reactions (type I versus type II) provides insights into the behavior of photosensitizers in water and the design of photodynamic therapy drugs.

Initiating Electron Transfer in Doubly-curved Nanographene Upon Supramolecular Complexation of C60

The formation of supramolecular complexes between C₆₀ and a molecular nanographene endowed with both positive and negative curvatures is described. The presence of a corannulene moiety and the saddle shape of the molecular nanographene allows the formation of complexes with 1:1, 1:2, and 2:1 stoichiometries. The association constants for the three possible supramolecular complexes were determined by ¹H NMR titration. Furthermore, the stability of the three complexes was calculated by theoretical methods that also predict the photoinduced electron transfer from the curved nanographene to the electron acceptor C₆₀. Time‐resolved transient absorption measurements on the ns‐time scale showed that the addition of C₆₀ to NG‐1 solutions and photo‐exciting them at 460 nm leads to the solvent‐dependent formation of new species, in particular the formation of the one‐electron reduced form of C₆₀ in benzonitrile was observed.

Solvation Free Energies for Aqueous and Nonaqueous Solutions Computed Using PM7 Atomic Charges

We describe a simple and accurate method, ESE-PM7, for calculating solvation free energies ΔG_solv^° in aqueous and nonaqueous solutions. The method is based on a noniterative COSMO algorithm. Molecular geometries and atomic charges calculated using the semiempirical method PM7 are used to calculate ΔG_solv^°. The method has been tested on 92 different solvents and 988 solutes. The mean absolute errors (MAEs) in ΔG_solv^° in aqueous solutions estimated by the ESE-PM7 approach are found to be 1.62 kcal/mol for 389 neutral solutes and 3.06 kcal/mol for 139 ions. The MAEs for neutral molecules in organic solvents are 0.97, 0.74, and 0.51 kcal/mol in polar protic, polar aprotic, and nonpolar solvents, respectively. The developed method can be employed to quickly screen ΔG_solv^° values of extended molecular systems including pharmaceutical and biological molecules.

Consecutive Ligand-Based Electron Transfer in New Molecular Copper-Based Water Oxidation Catalysts

Water oxidation to dioxygen is one of the key reactions that need to be mastered for the design of practical devices based on water splitting with sunlight. In this context, water oxidation catalysts based on first‐row transition metal complexes are highly desirable due to their low cost and their synthetic versatility and tunability through rational ligand design. A new family of dianionic bpy‐amidate ligands of general formula H₂LNⁿ⁻ (LN is [2,2′‐bipyridine]‐6,6′‐dicarboxamide) substituted with phenyl or naphthyl redox non‐innocent moieties is described. A detailed electrochemical analysis of [(L4)Cu]²⁻ (L4=4,4′‐(([2,2′‐bipyridine]‐6,6′‐dicarbonyl)bis(azanediyl))dibenzenesulfonate) at pH 11.6 shows the presence of a large electrocatalytic wave for water oxidation catalysis at an η=830 mV. Combined experimental and computational evidence, support an all ligand‐based process with redox events taking place at the aryl‐amide groups and at the hydroxido ligands.

Fast non-iterative calculation of solvation energies for water and non-aqueous solvents

We propose an efficient and accurate non-iterative method, dubbed uESE, for calculating solvation free energies. Apart from a COSMO-like electrostatic term, the model takes into account non-electrostatic contributions, which depend on atomic surfaces, induced surface charge densities, and the molecular volume. uESE is tested on 35 polar and 57 non-polar solvents. The calculated and experimental solvation free energies are compared for 2892 systems. The method exhibits an excellent performance, which is superior to major solvation methods. The mean absolute error of predicted solvation energies is found below 1 kcal/mol for neutral solutes and below 3 kcal/mol for ions. The calculated data are almost independent of the quantum-chemical method or/and basis sets employed.

How Do Defects in Carbon Nanostructures Regulate the Photoinduced Electron Transfer Processes? The Case of Phenine Nanotubes

Photoinduced electron transfer is studied in a series of inclusion complexes of structurally modified phenine nanotubes (pNT) with C70 using the TD-DFT method. Analysis of electronic properties of the complexes shows that the electron transfer is infeasible in pNT_4d⊃C70 built on the tetrameric array of [6]cyclo-meta-phenylene ([6]CMP) units. However, replacing one or more [6]CMP units with a coronene moiety enables electron transfer from pNT to C70 . The generation of the charge separated states from the lowest locally excited states occurs on a sub-nanosecond time scale. Depending on the number of the [6]CMP units, the charge recombination rate varies from 1.8 ⋅ 107 to 3.1 ⋅ 102  s-1 , i. e., five orders of magnitude.

Ambiguities in solvation free energies from cluster-continuum quasichemical theory: lithium cation in protic and aprotic solvents

Gibbs free energies for Li+ solvation in water, methanol, acetonitrile, DMSO, dimethylacetamide, dimethoxyethane, dimethylformamide, gamma-butyrolactone, pyridine, and sulfolane have been calculated using the cluster-continuum quasichemical theory. With n independent solvent molecules S initial state forming the "monomer" thermodynamic cycle, Li+ solvation free energies are found to be on average 14 kcal mol-1 more positive compared to those from the "cluster" thermodynamic cycle where the initial state is the cluster Sn. We ascribe the inconsistency between the "monomer" and "cluster" cycles mainly to the incorrectly predicted solvation free energies of solvent clusters Sn from the SMD and CPCM continuum solvation models, which is in line with the earlier study of Bryantsev et al., J. Phys. Chem. B, 2008, 112, 9709-9719. When experimental-based solvation free energies of individual solvent molecules and solvent clusters are employed, the "monomer" and "cluster" cycles result in identical numbers. The best overall agreement with experimental-based "bulk" scale lithium cation solvation free energies was obtained for the "monomer" scale, and we recommend this set of values. We expect that further progress in the field is possible if (i) consensus on the accuracy of experimental reference values is achieved; (ii) the most recent continuum solvation models are properly parameterized for all solute-solvent combinations and become widely accessible for testing.