Pfeiffer effect on configurationally labile dyes within ternary complexes with metal ions and enantiopure macrocycles

A configurationally-labile helical dye, 2,4,5,7-tetranitrofluorenone oximate, is used to probe complexes made of enantiopure macrocycles and mono/divalent metal ions. Induced electronic circular dichroism (ECD) and 1H NMR responses are amplified at room temperature only in the presence of K+ and Na+ ions despite larger binding efficiency with alkaline earth metal ions.

Detecting Fe(II) Spin-Crossover by Modulation of Appended Eu(III) Luminescence in a Single Molecule

Multifunctionality in spin-crossover (SCO) devices is limited to macroscopic or nanoscopic materials because of the need for long-range effects for inducing favorable cooperativity, efficient energy migration processes, and detectable magnetization transfer. The difficult reproducibility, control, and rational design of doped materials offer some place to SCO processes, modulating the optical properties of neighboring luminescent probes in single molecules. We report here on the combination of a [FeN6] chromophore, the SCO temperature and absorption spectra of which have been tuned to induce unprecedented room-temperature modulation of Eu(III)-based line-like luminescence in the molecular triple-helical [EuFe(L2)3]5+ complex in solution.

Physicochemical approaches reveal the impact of electrolytes and hydrotropic salt on micellization and phase separation behavior of polymer polyvinyl alcohol and surfactant mixture

The polymer-surfactant mixture has usages in numerous industries mainly in the production of daily used materials. Herein, the micellization and phase separation nature of the sodium dodecyl sulfate (SDS) and TX-100 along with a synthetic water-soluble polymer-polyvinyl alcohol (PVA) have been conducted using conductivity and cloud point (CP) measurement tools. In the case of micellization study of SDS + PVA mixture by conductivity method, the CMC values were obtained to be dependent on the categories and extent of additives as well as temperature variation. Both categories of studies were performed in aq. solutions of sodium chloride (NaCl), sodium acetate (NaOAc), and sodium benzoate (NaBenz) media. The CP values of TX 100 + PVA were decreased and enhanced in simple electrolytes and sodium benzoate media respectively. In all cases, the free energy changes of micellization (∆G_m⁰) and clouding (∆G_c⁰) were obtained as negative and positive respectively. The enthalpy (∆H_m⁰) and entropy (∆S_m⁰) changes for SDS + PVA system micellization was negative and positive respectively in aq. NaCl and NaBenz media, and in aq. NaOAc medium the ∆H_m⁰ values were found negative while ∆S_m⁰ were found negative except at the highest studied temperature (323.15 K). The enthalpy-entropy compensation of both processes was also assessed and described clearly.

Computational Insights into the Aggregation Pathway of Self-Assembled Nanotubules

We performed molecular dynamics simulations of self-assembled supramolecular nanotubules constructed from amphiphiles with bent-shaped rods. By systematically examining the structure from dimeric aggregates to the fully developed nanotubule, we identified the basic building block of the nanotubule and the optimal dimensions of its stable structure which are consistent with experimental findings. Moreover, we demonstrate that the cooperative interplay of different interactions drives aggregation by selecting and stabilizing the optimal self-assembled structures for various intermediates through a complex pathway. Additionally, contraction of the nanotubule, which accompanies the dehydration process, was observed upon heating. It is suggested that the optimal stability of the self-assembled aggregates is achieved by balancing entropic and enthalpic contributions, of which the ratio is a critical factor that drives the aggregation pathway.

Tuning spin-crossover transition temperatures in non-symmetrical homoleptic meridional/facial [Fe(didentate)3]2+ complexes: what for and who cares about it?

The [FeN₆] chromophores found in [Fe(didentate)₃]²⁺ complexes, where didentate is a non-symmetrical 2-(6-membered-heterocyclic ring)-benzimidazole ligand (Lk), exist as mixtures of two geometrical mer (C₁-symmetry) and fac (C₃-symmetry) isomers. Specific alkyl-substituted six-membered heterocyclic rings connected to the benzimidazole unit (pyridines in ligands L1-L3, pyrazines in L4-L5 and pyrimidines in L6-L7) control the ligand field strength and the electron delocalization so that [Fe^II(Lk)₃]²⁺ display tunable thermally-induced spin transitions in solution. Thermodynamic, spectroscopic (UV-Vis, NMR) and magnetic studies in solution demonstrate that [Fe(L6)₃]²⁺ (L6 = 1-methyl-2-(pyrimidin-2-yl)-1H-benzo[d]imidazole) exhibits a close to room temperature spin transition (T_1/2 = 273(3) K) combined with a high stability formation constant ( in acetonitrile), which makes this complex suitable for the potential modulation of lanthanide-based luminescence in polymetallic helicates. A novel method is proposed for assigning specific thermodynamic spin crossover parameters to fac-[Fe(L6)₃]²⁺ and mer-[Fe(L6)₃]²⁺ isomers in solution. The observed difference relies mainly on the entropic content ΔS-ΔS = 11(1) J mol^-1 K^-1, which favors the spin transition for the meridional isomer. Intermolecular interactions occurring in the crystalline state largely overcome minor thermodynamic trends operating in diluted solutions and a single configurational isomer is usually observed in the solid state. Among the thirteen solved crystal structures 1-13 containing the [M(Lk)₃]²⁺ cations (M = Fe, Ni, Zn, Lk = L6-L7), pure meridional isomers are observed six times, pure facial isomers also six times and a mixture (44% mer and 56% fac) is detected only once. Solid-state magnetic data recorded for the Fe^II complexes show the operation of slightly cooperative spin transitions in 7 (fac-[Fe(L6)₃]²⁺) and 12 (mer-[Fe(L7)₃]²⁺). For the meridional isomer in 6, a two-step spin state transition curve, associated with two phase transitions, is detected.

Nano-modified epoxy: the effect of GO-based complex structures on mechanical performance

The application of nanofillers (NFs) in multicomponent polymer systems is accompanied by important structure-directing effects that are more marked in partially miscible systems, such as polymer-modified epoxy. This study deals with rubber-modified epoxy using different combinations of GO and amine-terminated butadiene-acrylonitrile copolymer (ATBN), including in situ and pre-made grafting. Moreover, GO grafted via planar epoxy groups or solely edge-localized carboxyls was used. It is shown that the grafted ATBN chains promote the assembly of GO-g-ATBN into nacre-mimicking lamellar structures instead of usual exfoliation in thermoplastics. This complex structure of elastically embedded GO leads to the best mechanical performance. It is obvious that a small concentration of the grafted polymer exceeds the contribution of a higher concentration of separately added ATBN. The results highlight the important effect of the degree of grafted chains and geometry of the internal structure of the self-assembled arrays and their effect on the mechanical performance.

ATBN-grafted GO forms nacre-mimicking lamellar structures in epoxy; the effect of grafting geometry on the structure/property relationship is highlighted.

The origin of extrathermodynamic compensations

The way of analysis of thermodynamic systems, which takes into consideration systems’ phase volumes, is suggested. A validity of such approach was verified by the example of studying of extrathermodynamic compensations. Several types of exact linear extrathermodynamic compensations as well as their peculiar type, which peculiarity is indefinable compensation temperature, are established. The criteria that specify these types are stated. These results are illustrated by the identified exact extrathermodynamic compensations in formation of pyrene excimers.

Thermodynamic Programming of Erbium(III) Coordination Complexes for Dual Visible/Near-Infrared Luminescence

Intrigued by the unexpected room-temperature dual visible/near-infrared (NIR) luminescence observed for fast-relaxing erbium complexes embedded in triple-stranded helicates, in this contribution, we explore a series of six tridentate N-donor receptors L4-L9 with variable aromaticities and alkyl substituents to extricate the stereoelectronic features responsible for such scarce optical signatures. Detailed solid-state (X-ray diffraction, differential scanning calorimetry, optical spectroscopy) and solution (speciations and thermodynamic stabilities, spectrophotometry, NMR and optical spectroscopy) studies of mononuclear unsaturated [Er(Lk)₂ ]³⁺ and saturated triple-helical [Er(Lk)₃ ]³⁺ model complexes reveal that the stereoelectronic changes induced by the organic ligands affect inter- and intramolecular interactions to such an extent that 1) melting temperatures in solids, 2) the affinity for trivalent erbium in solution, and 3) optical properties in luminescent complexes can be rationally varied and controlled. With this toolkit in hand, mononuclear erbium complexes with low stabilities displaying only NIR emission can be transformed into molecular-based dual Er-centered visible/NIR emitters operating at room temperature in both solid and solution states.

A Rational Study of the Origin and Generality of Anti-Enthalpy–Entropy Compensation (AEEC) Phenomenon

In addition to enthalpy–entropy compensation (EEC), anti-enthalpy–entropy compensation (AEEC) phenomenon is also found in literature. The reports on the latter are limited, and analyses and justifications are so far unclear. Herein we present demonstration on the nature and possibility of the AEEC phenomenon. Although literature reports so far have mostly shown linear AEEC, we have found both linear and non-linear dependences. The non-linearity we consider arises from large “free energy window” (FEW) like EEC, recently presented and discussed. Attempts have been made to rationalize the observations in terms of solvation–desolvation phenomenon of the involved processes anticipated in previous studies. We have found that enthalpy and entropy of formation of gaseous and solid materials may also exhibit AEEC, it can be thus classified as a global phenomenon. In addition to AEEC, the phenomenon of no-enthalpy–entropy compensation (NEEC) is also reported. Thus, the phenomena EEC, AEEC and NEEC are thermodynamic puzzles that require close attention and analysis. With the help of wide range of physical chemical processes, an elaborate general understanding of the linear and non-linear AEEC phenomena has been attempted. The experimental data herein used are collected from literature reports, new measurements were not done. A variety of examples have supported possible generality of AEEC.

Controlled Bulk Properties of Composite Polymeric Solutions for Extensive Structural Order of Honeycomb Polysulfone Membranes

This work provides additional insights into the identification of operating conditions necessary to overcome a current limitation to the scale-up of the breath figure method, which is regarded as an outstanding manufacturing approach for structurally ordered porous films. The major restriction concerns, indeed, uncontrolled touching droplets at the boundary. Herein, the bulk of polymeric solutions are properly managed to generate honeycomb membranes with a long-range structurally ordered texture. Water uptake and dynamics are explored as chemical environments are changed with the intent to modify the hydrophilic/hydrophobic balance and local water floatation. In this context, a model surfactant such as the polyoxyethylene sorbitan monolaurate is used in combination with alcohols at different chain length extents and a traditional polymer such as the polyethersufone. Changes in the interfacial tension and kinematic viscosity taking place in the bulk of composite solutions are explored and examined in relation to competitive droplet nucleation and growth rate. As a result, extensive structurally ordered honeycomb textures are obtained with the rising content of the surfactant while a broad range of well-sized pores is targeted as a function of the hydrophilic-hydrophobic balance and viscosity of the composite polymeric mixture. The experimental findings confirm the consistency of the approach and are expected to give propulsion to the commercially production of breath figures films shortly.

A quantitative assessment of chemical perturbations in thermotropic cyanobiphenyls

The cohesion Gibbs free energy densities (CFEDs) measured in cyanobiphenyl-containing liquid crystals transform chemical perturbations into pressure increments, which can be analyzed within the frame of standardP–Tdiagrams using the Clapeyron equation.

Chemical Programming of the Domain of Existence of Liquid Crystals

This work illustrates how enthalpy and entropy changes responsible for successive phase transitions of cyanobiphenyl-based liquid crystals can be combined to give cohesive free energy densities. These new parameters are able to rationalize and quantify the demixing of the melting and clearing processes that occur in thermotropic liquid crystals. Minor structural variations at the molecular level can be understood as pressure increments that alter either the melting or clearing temperatures in a predictable way. This assessment of microsegregation operating in amphiphilic molecules paves the way for the chemical programming of the domain of existence of liquid-crystalline phases.

Controlling the assembly of cyclotriveratrylene-derived coordination cages

Ligand-functionalised cyclotriveratrylene derivatives self-assemble to afford coordination cages and topologically non-trivial constructs, including controlled assembly of M₃L₂ metallo-cryptophane and M₆L₈ cages.

Tuning the coordination chemistry of cyclotriveratrylene ligand pairs through alkyl chain aggregation

Propylated cyclotriveratrylene ligands with N-donor groups form coordination polymers where the propyl groups aggregate or form a Pd₆L₄ cage.

Resolution of microscopic protonation enthalpies of polyprotic molecules by means of cluster expansions

Cluster expansion techniques are used to obtain microconstants and microenthalpies of protonation reactions. The approach relies on the analysis of macroscopic protonation constants and protonation enthalpies within a homologous series. Various linear aliphatic polyamines are considered, including 3,4-tri (spermidine), 3,4,3-tet (spermine), and 2,2,2,2-pent. Besides the full resolution of the microscopic protonation equilibria, one obtains information on the temperature dependence of the microstate probabilities. We find that the concentrations of the dominant microspecies increase with increasing temperature. Due to the large negative protonation enthalpies that are typical for amines, higher temperatures generally favor the less protonated species.