Tunable Emissive CsPbBr3/Cs4PbBr6 Quantum Dots Engineered by Discrete Phase Transformation for Enhanced Photogating in Field-Effect Phototransistors.

Precise control of quantum structures in hybrid nanocrystals requires advancements in scientific methodologies. Here, on the design of tunable CsPbBr3/Cs4PbBr6 quantum dots are reported by developing a unique discrete phase transformation approach in Cs4PbBr6 nanocrystals. Unlike conventional hybrid systems that emit solely in the green region, this current strategy produces adjustable luminescence in the blue (450 nm), cyan (480 nm), and green (510 nm) regions with high photoluminescence quantum yields up to 45%, 60%, and 85%, respectively. Concentration-dependent studies reveal that phase transformation mechanisms and the factors that drive CsBr removal occur at lower dilutions while the dissolution-recrystallization process dominates at higher dilutions. When the polymer-CsPbBr3/Cs4PbBr6 integrated into a field-effected transistor the resulting phototransistors featured enhanced photosensitivity exceeding 105, being the highest reported for an n-type phototransistor, while maintaining good transistor performances as compared to devices consisting of polymer-CsPbBr3 NCs.

Dynamic exchange controls the assembly structure of nucleic-acid-peptide chimeras.

Recent attempts to develop the next generation of functional biomaterials focus on systems chemistry approaches exploiting dynamic networks of hybrid molecules. This task is often found challenging, but we herein present ways for profiting from the multiple interaction interfaces forming Nucleic-acid-Peptide assemblies and tuning their formation. We demonstrate that the formation of well-defined structures by double-stranded DNA-peptide conjugates (dsCon) is restricted to a specific range of environmental conditions and that precise DNA hybridization, satisfying the interaction interfaces, is a crucial factor in this process. We further reveal the impact of external stimuli, such as competing free DNA elements or salt additives, which initiate dynamic interconversions, resulting in hybrid structures exhibiting spherical and fibrillar domains or a mixture of spherical and fibrillar particles. This extensive analysis of the co-assembly systems chemistry offers new insights into prebiotic hybrid assemblies that may now facilitate the design of new functional materials. We discuss the implications of these findings for the emergence of function in synthetic materials and during early chemical evolution.

A facile post-assembly approach for the fabrication of non-close-packed gold nanocrystal arrays from binary nanocrystal superlattices.

Here, we demonstrate a novel approach for fabricating non-close-packed gold nanocrystal arrays using facile one-step post-modification of a Cs4PbBr6-Au binary nanocrystal superlattice by electron beam etching of the perovskite phase. The proposed methodology can serve as a promising approach for the scalable preparation of a vast library of non-close-packed nanoparticulate superstructures with various morphologies composed of numerous colloidal nanocrystals.

Programmable precise kinetic control over crystal phase, size, and equilibrium in spontaneous metathesis reaction for Cs-Pb-Br nanostructure patterns at room temperature.

Growth kinetics involved in spontaneous random clustering of perovskite precursors to a particular cesium-lead-bromide (Cs-Pb-Br) nanocrystal (NC) is a poorly understood phenomenon and its spectroscopic investigation is highly challenging. There is scarcely any method that has been optimized yet in which perovskites and their related NCs of a particular size can be grown, viewed, or tuned to another by reaction handling. Here, for the first time, we shed light on the largely overlooked process of growth kinetics of these transformations throughout the reaction trajectory of anionic [PbBrx]n- crystallization dictated by Cs+ cation and report a simple and direct approach to control the metathesis reaction between two precursors (specifically Cs+- and PbBr2-associated oligomeric complexes) in one solvent at room temperature to monitor the NC growth characteristics in a stepwise manner even in the early stages of nucleation. Altering the molar ratio of the two precursors up to a factor of 10 leads to the formation of three prominent phases (CsPbBr3, Cs4PbBr6, CsBr) as dictated by Cs+ to trigger distinct morphological forms (nanobelts, nanoplatelets, rhombohedral NCs, pseudo-rhombic NCs, spherical CsBr NCs, cubic CsBr NCs) including a transient phase that is formed out of linearly self-assembled CsPbBr3 clusters. Our results pave the way towards understanding spontaneous crystallization to develop well-defined, hassle-free routes for diverse perovskite NCs in a simple yet controlled manner.

Cesium Lead Iodide Perovskites: Optically Active Crystal Phase Stability to Surface Engineering.

Among perovskites, the research on cesium lead iodides (CsPbI3) has attracted a large research community, owing to their all-inorganic nature and promising solar cell performance. Typically, the CsPbI3 solar cell devices are prepared at various heterojunctions, and working at fluctuating temperatures raises questions on the material stability-related performance of such devices. The fundamental studies reveal that their poor stability is due to a lower side deviation from Goldschmidt's tolerance factor, causing weak chemical interactions within the crystal lattice. In the case of organic-inorganic hybrid perovskites, where their stability is related to the inherent chemical nature of the organic cations, which cannot be manipulated to improve the stability drastically whereas the stability of CsPbI3 is related to surface and lattice engineering. Thus, the challenges posed by CsPbI3 could be overcome by engineering the surface and inside the CsPbI3 crystal lattice. A few solutions have been proposed, including controlled crystal sizes, surface modifications, and lattice engineering. Various research groups have been working on these aspects and had accumulated a rich understanding of these materials. In this review, at first, we survey the fundamental aspects of CsPbI3 polymorphs structure, highlighting the superiority of CsPbI3 over other halide systems, stability, the factors (temperature, polarity, and size influence) leading to their phase transformations, and electronic band structure along with the important property of the defect tolerance nature. Fortunately, the factors stabilizing the most effective phases are achieved through a size reduction and the efficient surface passivation on the delicate CsPbI3 nanocrystal surfaces. In the following section, we have provided the up-to-date surface passivating methods to suppress the non-radiative process for near-unity photoluminescence quantum yield, while maintaining their optically active phases, especially through molecular links (ligands, polymers, zwitterions, polymers) and inorganic halides. We have also provided recent advances to the efficient synthetic protocols for optically active CsPbI3 NC phases to use readily for solar cell applications. The nanocrystal purification techniques are challenging and had a significant effect on the device performances. In part, we summarized the CsPbI3-related solar cell device performances with respect to the device fabrication methods. At the end, we provide a brief outlook on the view of surface and lattice engineering in CsPbI3 NCs for advancing the enhanced stability which is crucial for superior optical and light applications.

Single Fluorinated Agent for Multiplexed 19 F-MRI with Micromolar Detectability Based on Dynamic Exchange.

The weak thermal polarization of nuclear spins limits the sensitivity of MRI, even for MR-sensitive nuclei as fluorine-19. Therefore, despite being the source of inspiration for the development of background-free MRI for various applications, including for multiplexed imaging, the inability to map very low concentrations of targets using 19 F-MRI raises the need to further enhance this platform's capabilities. Here, we employ the principles of CEST-MRI in 19 F-MRI to obtain a 900-fold signal amplification of a biocompatible fluorinated agent, which can be presented in a "multicolor" fashion. Capitalizing on the dynamic interactions in host-guest supramolecular assemblies in an approach termed GEST, we demonstrate that an inhalable fluorinated anesthetic can be used as a single 19 F-probe for the concurrent detection of micromolar levels of two targets, with potential in vivo translatability. Further extending GEST with new designs could expand the applicability of 19 F-MRI to the mapping of targets that have so-far remained non-detectable.

Primitive selection of the fittest emerging through functional synergy in nucleopeptide networks.

Many fundamental cellular and viral functions, including replication and translation, involve complex ensembles hosting synergistic activity between nucleic acids and proteins/peptides. There is ample evidence indicating that the chemical precursors of both nucleic acids and peptides could be efficiently formed in the prebiotic environment. Yet, studies on nonenzymatic replication, a central mechanism driving early chemical evolution, have focused largely on the activity of each class of these molecules separately. We show here that short nucleopeptide chimeras can replicate through autocatalytic and cross-catalytic processes, governed synergistically by the hybridization of the nucleobase motifs and the assembly propensity of the peptide segments. Unequal assembly-dependent replication induces clear selectivity toward the formation of a certain species within small networks of complementary nucleopeptides. The selectivity pattern may be influenced and indeed maximized to the point of almost extinction of the weakest replicator when the system is studied far from equilibrium and manipulated through changes in the physical (flow) and chemical (template and inhibition) conditions. We postulate that similar processes may have led to the emergence of the first functional nucleic-acid-peptide assemblies prior to the origin of life. Furthermore, spontaneous formation of related replicating complexes could potentially mark the initiation point for information transfer and rapid progression in complexity within primitive environments, which would have facilitated the development of a variety of functions found in extant biological assemblies.

A Fluorescent 1,3-Diaminonaphthalimide Conjugate of Calix[4]arene for Sensitive and Selective Detection of Trinitrophenol: Spectroscopy, Microscopy, and Computational Studies, and Its Applicability using Cellulose Strips.

A new fluorescent 1,3-diaminonaphthalimide conjugate of calix[4]arene receptor (R) was synthesized and characterized. The receptor displays good selectivity towards trinitrophenol (TNP) over other explosive aromatic- and aliphatic-nitro compounds by exhibiting changes in its fluorescence emission. Receptor-coated cellulose paper strips are equally effective in terms of their selective detection of TNP over other aromatic- and aliphatic-nitro compounds. When used in solution or on cellulose paper strips, R can detect up to submicromolar concentration of TNP by exhibiting changes in its fluorescence emission and in its supramolecular structure upon interaction. Interestingly, the microscopy features of R, TNP, and {R+TNP} are quite distinct, indicating the interactions present between R and TNP, as studied by using AFM and TEM. Computationally modeled complexes of receptor with TNP and TNT show enormous difference in their interaction energies in the favor of TNP by showing the host-guest interaction of cation⋅⋅⋅anion type in the presence of TNP but not TNT. This is because the receptor adopts an "arms-open"-type structure in the case of the TNP complex, whereas it adopts an "arms-closed"-type structure in the presence of TNT. Both the experimental and the computational studies reveal that the receptor selectively binds to TNP over TNT. Thus, R-coated Whatman No.1 filter paper strips provide easy, rapid, and economical detection of trace amounts of TNP both by visual and spectral measurement.

Versatile, Reversible, and Reusable Gel of a Monocholesteryl Conjugated Calix[4]arene as Functional Material to Store and Release Dyes and Drugs Including Doxorubicin, Curcumin, and Tocopherol.

Gels are interesting soft materials owing to their functional properties leading to potential applications. This paper deals with the synthesis of monocholesteryl derivatized calix[4]arene (G) and its instantaneous gelation at a minimum gelator concentration of 0.6% in 1:1 v/v THF/acetonitrile. The gel shows remarkable thermoreversibility by exhibiting Tgel→sol at ∼48 °C and is demonstrated for several cycles. The gel shows an organized network of nanobundles, while that of the sol shows spherical nanoaggregates in microscopy. A bundle with ∼12 nm diameter possessing hydrophobic pockets in itself is obtained from computationally modeled gel, and hence the gel is suitable for storage and release applications. The guest-entrapped gels exhibit the same microstructures as that observed with simple gels, while fluorescence spectra and molecular mechanics suggests that the drug molecules occupy the hydrophobic pockets. All the entrapped drug molecules are released into water, suggesting a complete recovery of the trapped species. The reusability of the gel for the storage and release of the drug into water is demonstrated for four consecutive cycles, and hence the gel formed from G acts as a functional material that finds application in drug delivery.

Fluorescence and piezoresistive cantilever sensing of trinitrotoluene by an upper-rim tetrabenzimidazole conjugate of calix[4]arene and delineation of the features of the complex by molecular dynamics.

A new benzimidazole-functionalized calix[4]arene receptor (R) was synthesized and characterized. The receptor R shows better selectivity toward trinitrotoluene (TNT) compared to the other nitro explosives in solution, which also retains its effectiveness for solid-phase detection. The chemical interactions of the molecule with different nitro explosive analytes were studied by fluorescence spectroscopy and by a molecular dynamics approach. The molecular dynamics studies show a 1:3 complex between R and TNT, and hence high sensitivity was imparted by fluorescence studies. The detection of explosive vapors in ambient conditions was tested by using a sensitive coating layer of R on an SU-8/CB-based piezoresistive cantilever surface. The developed device showed large sensitivity toward TNT compared to cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) in the solid state at their respective vapor pressures at room temperature. The detection sensitivity of the device was estimated to be 35 mV for TNT at ambient conditions. Moreover, the sensor does not show a response when exposed to humidity. These results demonstrate that R can be used as one of the coating materials for a cantilever for the detection of TNT using piezoresistivity measurement. R can also detect the explosives in solution with high sensitivity and selectivity by fluorescence spectroscopy.