Two-Photon Solvatochromism II: Experimental and Theoretical Study of Solvent Effects on the Two-Photon Absorption Spectrum of Reichardt’s Dye

In this study, we report on the influence of solvent on the two-photon absorption (2PA) spectra of Reichardt’s dye (RD). The measurement of 2PA cross-sections is performed for three solvents (chloroform, dimethyl formamide, and dimethyl sulfoxide) using the Z-scan technique. The key finding of this study is the observation that the cross-section, corresponding to the 2PA of the intramolecular charge-transfer state, diminishes substantially upon increasing the solvent polarity. To unravel the solvent dependence of the 2PA cross-section, the electronic structure of RD is determined using a hybrid quantum mechanics/molecular mechanics (QM/MM) approach, in which polarization between the solute and solvent is taken into account by using a self-consistent scheme in the solvent polarization. The two-state approximation proves to be adequate for the studied system, and allowed the observed solvent-polarity-induced decrease of the 2PA cross-section to be related to the decrease of the transition moment and the increase in the excitation energy.     

Neighbourhood Sum Degree-Based Indices and Entropy Measures for Certain Family of Graphene Molecules

A topological index (TI) is a real number that defines the relationship between a chemical structure and its properties and remains invariant under graph isomorphism. TIs defined for chemical structures are capable of predicting physical properties, chemical reactivity and biological activity. Several kinds of TIs have been defined and studied for different molecular structures. Graphene is the thinnest material known to man and is also extremely strong while being a good conductor of heat and electricity. With such unique features, graphene and its derivatives have found commercial uses and have also fascinated theoretical chemists. In this article, the neighbourhood sum degree-based M-polynomial and entropy measures have been computed for graphene, graphyne and graphdiyne structures. The proper analytical expressions for these indices are derived. The obtained results will enable theoretical chemists to study these exciting structures further from a structural perspective.     

Characterization of Astaxanthin Nanoemulsions Produced by Intense Fluid Shear through a Self-Throttling Nanometer Range Annular Orifice Valve-Based High-Pressure Homogenizer

Stable, oil-in-water nanoemulsions containing astaxanthin (AsX) were produced by intense fluid shear forces resulting from pumping a coarse reagent emulsion through a self-throttling annular gap valve at 300 MPa. Compared to crude emulsions prepared by conventional homogenization, a size reduction of over two orders of magnitude was observed for AsX-encapsulated oil droplets following just one pass through the annular valve. In krill oil formulations, the mean hydrodynamic diameter of lipid particles was reduced to 60 nm after only two passes through the valve and reached a minimal size of 24 nm after eight passes. Repeated processing of samples through the valve progressively decreased lipid particle size, with an inflection in the rate of particle size reduction generally observed after 2–4 passes. Krill- and argan oil-based nanoemulsions were produced using an Ultra Shear Technology™ (UST™) approach and characterized in terms of their small particle size, low polydispersity, and stability.     

Facile synthesis of ZnS/MnS nanocomposites for supercapacitor applications

Journal of Solid State Electrochemistry - In this study, we have reported a facile fabrication of pristine zinc sulfide (ZnS), manganese sulfide (MnS), and ZnS/MnS nanocomposites (NCs) via...     

Investigations on chemical interactions between alternate cathodes and lanthanum gallate electrolyte for Intermediate Temperature Solid Oxide Fuel Cell (ITSOFC)

The doped perovskite oxides such as La_0.65Sr_0.30MnO_3-δ (LSM), La_0.70Sr_0.30CoO_3-δ (LSC), La_0.65Sr_0.30FeO_3-δ (LSF), La_0.65Sr_0.30NiO_3-δ (LSN) and La_0.60Sr_0.40Co_0.20Fe_0.80O_3-δ (LSCF) are proposed as alternate cathode materials for solid oxide fuel cells working at reduced temperature (< 1073 K). The critical requirement for their applicability is their chemical compatibility in conjunction with an alternate solid electrolyte, La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ (LSGM) without any new phase formation. To understand the chemical reactivity between these two components, thoroughly mixed different cathode and LSGM electrolyte (1:1 by wt.) powders were pressed as circular components and subjected to annealing at 1573 K for 3 h in air. XRD and SEM were used for the characterization of the annealed samples. XRD measurements revealed that no new secondary phases were formed in LSM, LSC, and LSF with LSGM mixtures whereas LSN and LSCF with LSGM resulted in the formation of new secondary phases after high temperature treatment. The sintering shrinkage for all the components (cathode + electrolyte mixture) was also estimated. For comparison of data, the individual powders (cathode/electrolyte) were also compacted and studied in the same manner. The obtained results are discussed keeping in view the requirements that the candidate cathode material must meet out with respect to its chemical compatibility to qualify for the LSGM based ITSOFC systems at 1073 K.     

Enzymatic sculpting of nanoscale and microscale surface topographies

Lithography-free etching of complex surface features is achieved by harnessing the enzyme proteinase K (PK), controlled by bovine serum albumin (BSA), to digest a biodegradable polymer. This bio-sculpting process is used to construct a membraneless filtration device for the size-based isolation and enrichment of cells from whole blood.     

NMR spin-spin coupling constants in polymethine dyes as polarity indicators

Herein, we explore the use of spin-spin coupling constants (SSCCs) in merocyanine (MCYNE) dyes as indicators of polarity. For this purpose, we use Car-Parrinello hybrid quantum mechanics/molecular mechanics (QM/MM) to determine the structures of MCYNE in solvents of different polarity, followed by computations of the SSCCs by using QM/MM linear-response theory. The molecular geometry of MCYNE switches between neutral, cyanine-like, and zwitterionic depending on the polarity of the solvent. This structural variation is clearly reflected in the proton SSCCs in the polymethine backbone, which are highly sensitive to the dielectric nature of the environment; this mechanism can be used as a "polarity indicator" for different microenvironments. This result is highlighted by computing the SSCCs of the MCYNE probe in the cavity of the beta-lactoglobulin protein. The computed SSCCs clearly indicate a non-polar hydrophobic dielectric nature of this cavity.     

Al3+ induced planarization, conformational arrest and metallochromic shift in a pyrimidine dione dye: insight from integrated hybrid quantum-classical calculations

In order to explore the possibilities of simulating metallochromism by modern molecular modeling, we apply a sequential hybrid quantum-classical approach to a prototype metallochromic system-the Al(3+) ion and pyrimidinedione (PY) dye complex. The complex shows several structural features with relevance for the metallochromism: the PY dye exhibits conformers with dynamical transitions between twisted structures, which are inhibited by the addition of the metal ion leading to planarization and a conformational arrest: the Al(3+) ion behaves like a structure-modifier for both intra and intermolecular degrees of freedom and with respect to the intermolecular solvation shell structure. The sequential approach that we have employed uses DFT/MM molecular dynamics for structure modeling and TDDFT/PCM for property modeling. The computed metallochromic shift between PY and the Al(PY)(3+) complex in DMSO solvent is obtained in excellent agreement with experiment. The results infer optimism for future use of such modeling techniques to design metallochromic indicators.