Rational Development of Guanidinate and Amidinate Based Cerium and Ytterbium Complexes as Atomic Layer Deposition Precursors: Synthesis,Modeling, and Application

Owing to the limited availability of suitable precursors for vapor phase deposition of rare-earth containing thin-film materials, new or improved precursors are sought after. In this study, we explored new precursors for atomic layer deposition (ALD) of cerium (Ce) and ytterbium (Yb) containing thin films. A series of homoleptic tris-guanidinate and tris-amidinate complexes of cerium (Ce) and ytterbium (Yb) were synthesized and thoroughly characterized. The C-substituents on the N-C-N backbone (Me, NMe₂, NEt₂, where Me=methyl, Et=ethyl) and the N-substituents from symmetrical iso-propyl (iPr) to asymmetrical tertiary-butyl (tBu) and Et were systematically varied to study the influence of the substituents on the physicochemical properties of the resulting compounds. Single crystal structures of [Ce(dpdmg)₃] 1 and [Yb(dpdmg)₃] 6 (dpdmg=N,N'-diisopropyl-2-dimethylamido-guanidinate) highlight a monomeric nature in the solid-state with a distorted trigonal prismatic geometry. The thermogravimetric analysis shows that the complexes are volatile and emphasize that increasing asymmetry in the complexes lowers their melting points while reducing their thermal stability. Density functional theory (DFT) was used to study the reactivity of amidinates and guanidinates of Ce and Yb complexes towards oxygen (O₂) and water (H₂O). Signified by the DFT calculations, the guanidinates show an increased reactivity toward water compared to the amidinate complexes. Furthermore, the Ce complexes are more reactive compared to the Yb complexes, indicating even a reactivity towards oxygen potentially exploitable for ALD purposes. As a representative precursor, the highly reactive [Ce(dpdmg)₃] 1 was used for proof-of-principle ALD depositions of CeO₂ thin films using water as co-reactant. The self-limited ALD growth process could be confirmed at 160 °C with polycrystalline cubic CeO₂ films formed on Si(100) substrates. This study confirms that moving towards nitrogen-coordinated rare-earth complexes bearing the guanidinate and amidinate ligands can indeed be very appealing in terms of new precursors for ALD of rare earth based materials.     

Strong Electronic Communication in Linearly Elongated Rylenes Featuring Tunable Bridges

A modified synthetic pathway towards perylene-perylene dimers and a facile purification method to obtain the regioisomerically pure syn- and anti-isomers are reported. In addition, a novel perylene-naphthalene heterodimer with 30 conjugated π-electron pairs was designed and synthesized on the basis of a previously described precursor and the resulting regioisomers were separated from each other. Thereby, the opto-electronic properties of the linearly elongated chromophores could be investigated regarding the differences in length of their aromatic system and the configuration of the isomers. Further tuning of their energy gaps was realized via protonation and methylation of the dibenzimidazole-bridging unit. Extraordinary red-shifts of the absorption maxima of 62 nm for the methylated and 92 nm for the protonated perylene-perylene anti-isomer could be achieved. Moreover, the maxima for the syn-isomer could be shifted bathochromically by 87 and 113 nm, respectively.     

Insight into the acidic behavior of oxazolidin-2-one,its thione and selone analogs through computational techniques

Deprotonation thermochemistry of Oxazolidin-2-one (OXA), Oxazolidine-2-thione (OXA-S), and Oxazolidine-2-selone (OXA-Se) has been studied in order to find the most acidic site and relative acidities of these heterocyclics at various sites. The deprotonation enthalpies at MP2/6-311++G**//MP2/6-31+G* and B3LYP/6-31+G* levels, while the free energies for deprotonation process and pKa values at B3LYP/6-31+G* level both in gas and aqueous phase (using PCM continuum model) of the anions of the three heterocyclics have been computed at 298 K. Calculated aqueous phase pKa values of OXA vary by ~6–7 units from the experimental aqueous phase pKa values of OXA and its derivatives. The deprotonation at the nitrogen is favored in OXA over the carbon atoms in contrast to the OXA-S and OXA-Se where in the deprotonation at the carbon attached to the nitrogen is most preferred. Deprotonation at this carbon induces an important C–O bond rupture in OXA-S and OXA-Se promoting an energetically favored ring-opening process. The finding offers a rare case when C–H acidity is able to dominate over the N–H acidity. In order to explain the relative stabilities, relative acidities and deprotonation enthalpies various characteristics of these molecules as well as their anions such as molecular electrostatic potential surface (MEP), frontier molecular orbital (FMO) features, chemical hardness, softness have been governed. The three dimensional MEP maps and HOMO–LUMO orbitals encompassing these molecules yield a reliable relative stability and reactivity (in terms of acidity) map displaying the most probable regions for deprotonation. The differential distribution of the electrostatic potential over the neutral and anionic species of OXA, OXA-S, and OXA-Se molecules is authentically reflected by HOMO–LUMO orbitals and NBO charge distribution analysis. The lone pair occupancies, second order delocalization energies for orbital interactions and the distribution of atomic charges over the entire molecular framework as obtained from natural bond orbital (NBO) analysis are found to faithfully replicate the predictions from the MEP maps and HOMO–LUMO band gaps in respect of explaining the relative stabilities and acidities in most of the cases. Good linear correlations have been obtained between HOMO–LUMO gap and pKa values in the aqueous phase for OXA and OXA-S molecules.     

Tuning Thiophene with Phosphorus: Synthesis and Electronic Properties of Benzobisthiaphospholes

1,4‐Dimercapto‐2,5‐diphosphinobenzene and 3,6‐bis(hexyloxy)‐1,4‐dimercapto‐2,5‐diphosphinobenzene were synthesized and combined with various acid chlorides to obtain a series of benzobisthiaphospholes. Electrochemical and photophysical properties of the substituted benzobisthiaphospholes have been evaluated, and the observed reductions are more facile than the related benzothiaphospholes and 2,6‐diphenylbenzobisthiazole. A benzobisthiaphosphole with C₆H₄‐p‐CN substituents was reduced at E_1/2=?1.08 V (vs. saturated calomel electrode (SCE)). X‐ray diffraction data for several of these phosphorus heterocycles has been obtained, and DFT calculations at the B3LYP level have been performed.     

Kinetics and thermoluminescence glow curve study of Ba2MgSi2O7:Eu3+, Dy3+

This paper reports thermoluminescence glow curves of Eu³⁺, Dy³⁺-doped Ba₂MgSi₂O₇ phosphor for different UV exposure times. Kinetic data were evaluated by the peak-shape method. The glow curves shift toward higher intensity with increasing exposure time to UV at 365 nm. When the heating rate was 5 °C s^?1, peaks were observed at 101.76, 109.69, 102.67, and 104.05 °C, respectively, after UV exposure for 5, 10, 15, and 20 min. The glow peaks are indicative of second-order kinetics. Different kinetic data, i.e. trap depth, order of kinetics, activation energy, and frequency factor were also calculated. To evaluate the persistence characteristics of the luminescence of the phosphor, the lifetime of the charge in the trap was calculated; it was 348, 660, 368, and 428 s for UV exposure of 5, 10, 15, and 20 min, which indicates the luminescence of the phosphor is persistent.     

Trace determination of parabens in cosmetics and personal care products using fabric‐phase sorptive extraction and high‐performance liquid chromatography with UV detection

A simple, fast, and sensitive analytical protocol using fabric‐phase sorptive extraction followed by high performance liquid chromatography with ultraviolet detection has been developed and validated for the extraction of five parabens including methylparaben, ethylparaben, propylparaben, butylparaben, and benzylparaben. In the present work, sol‐gel polyethylene glycol coated fabric‐phase sorptive extraction membrane is used for the preconcentration of parabens (polar) from complex matrices. The use of fabric‐phase sorptive extraction membrane provides a high surface area which offers high sorbent loading, shortened equilibrium time, and overall decrease in the sample preparation time. Various factors affecting the performance of fabric‐phase sorptive extraction, including extraction time, eluting solvent, elution time, and pH of the sample matrix, were optimized. Separation was performed using a mobile phase consisting of water:acetonitrile (63:37; v/v) at an isocratic elution mode at a flow rate of 0.9 mL/min with wavelength at 254 nm. The calibration curves of the target analytes were prepared with good correlation coefficient values (r² > 0.9955). The limit of detection values range from 0.252 to 0.580 ng/mL. Finally, the method was successfully applied to various cosmetics and personal care product samples such as rose water, deodorant, hair serum, and cream with extraction recoveries ranged between 88 and 122% with relative standard deviation <5%.     

Biofortification—A Frontier Novel Approach to Enrich Micronutrients in Field Crops to Encounter the Nutritional Security

Globally, many developing countries are facing silent epidemics of nutritional deficiencies in human beings and animals. The lack of diversity in diet, i.e., cereal-based crops deficient in mineral nutrients is an additional threat to nutritional quality. The present review accounts for the significance of biofortification as a process to enhance the productivity of crops and also an agricultural solution to address the issues of nutritional security. In this endeavor, different innovative and specific biofortification approaches have been discussed for nutrient enrichment of field crops including cereals, pulses, oilseeds and fodder crops. The agronomic approach increases the micronutrient density in crops with soil and foliar application of fertilizers including amendments. The biofortification through conventional breeding approach includes the selection of efficient genotypes, practicing crossing of plants with desirable nutritional traits without sacrificing agricultural and economic productivity. However, the transgenic/biotechnological approach involves the synthesis of transgenes for micronutrient re-translocation between tissues to enhance their bioavailability. Soil microorganisms enhance nutrient content in the rhizosphere through diverse mechanisms such as synthesis, mobilization, transformations and siderophore production which accumulate more minerals in plants. Different sources of micronutrients viz. mineral solutions, chelates and nanoparticles play a pivotal role in the process of biofortification as it regulates the absorption rates and mechanisms in plants. Apart from the quality parameters, biofortification also improved the crop yield to alleviate hidden hunger thus proving to be a sustainable and cost-effective approach. Thus, this review article conveys a message for researchers about the adequate potential of biofortification to increase crop productivity and nourish the crop with additional nutrient content to provide food security and nutritional quality to humans and livestock.     

Calix[4]arene-based ditopic receptors for simultaneous recognition of fluoride and cobalt(II) ions

A series of calix[4]arene based ditopic receptors possessing bipyridyl and hydrazone units have been synthesized and evaluated for ionic recognition. It has been observed that the synthesized derivatives function as allosteric receptors for simultaneous recognition of Co²⁺and F^? ions through non-covalent interactions. Significant bathochromic shifts in the UV–visible spectrum with a profound colour change promise their use to engineer novel applications.