Degradation Kinetics of Organic-Inorganic Hybrid Materials from Micro-Raman Spectroscopy and Density-Functional Theory: The Case of ß-ZnTe(en)0.5.

Organic-inorganic hybrid materials often face a stability challenge. ß-ZnTe(en)0.5 , which uniquely has over 15-year real-time degradation data, is taken as a prototype structure to demonstrate an accelerated thermal aging method for assessing the intrinsic and ambient-condition long-term stability of hybrid materials. Micro-Raman spectroscopy is used to investigate the thermal degradation of ß-ZnTe(en)0.5 in a protected condition and in air by monitoring the temperature dependences of the intrinsic and degradation-product Raman modes. First, to understand the intrinsic degradation mechanism, the transition state of the degradation is identified, then using a density functional theory, the intrinsic energy barrier between the transition state and ground state is calculated to be 1.70 eV, in excellent agreement with the measured thermal degradation barrier of 1.62 eV in N2 environment. Second, for the ambient-condition degradation, a reduced thermal activation barrier of 0.92 eV is obtained due to oxidation, corresponding to a projected ambient half-life of 40 years at room temperature, in general agreement with the experimental observation of no apparent degradation over 15 years. Furthermore, the study reveals a mechanism, conformation distortion enhanced stability, which plays a pivotal role in forming the high kinetic barrier, contributing greatly to the impressive long-term stability of ß-ZnTe(en)0.5 .

II-VI Organic-Inorganic Hybrid Nanostructures with Greatly Enhanced Optoelectronic Properties, Perfectly Ordered Structures, and Shelf Stability of Over 15 Years.

Organic-inorganic hybrids may offer material properties not available from their inorganic components. However, they are typically less stable and disordered. Long-term stability study of the hybrid materials, over the anticipated lifespan of a real-world electronic device, is practically nonexistent. Disordering, prevalent in most nanostructure assemblies, is a prominent adversary to quantum coherence. A family of perfectly ordered II-VI-based hybrid nanostructures has been shown to possess many unusual properties and potential applications. Here, using a prototype structure ß-ZnTe(en)0.5-a hybrid superlattice-and applying an array of optical, structural, surface, thermal, and electrical characterization techniques, in conjunction with density-functional theory calculations, we have performed a comprehensive and correlative study of the crystalline quality, structural degradation, electronic, optical, and transport properties on samples from over 15 years old to the recently synthesized. The findings show that not only do they exhibit an exceptionally high level of crystallinity in both macroscopic and microscopic scale, comparable to high-quality binary semiconductors; and greatly enhanced material properties, compared to those of the inorganic constituents; but also, some of them over 15 years old remain as good in structure and property as freshly made ones. This study reveals (1) what level of structural perfectness is achievable in a complex organic-inorganic hybrid structure or a man-made superlattice, suggesting a nontraditional strategy to make periodically stacked heterostructures with abrupt interfaces; and (2) how the stability of a hybrid material is affected differently by its intrinsic attributes, primarily formation energy, and extrinsic factors, such as surface and defects. By correlating the rarely found long-term stability with the calculated relatively large formation energy of ß-ZnTe(en)0.5 and contrasting with the case of hybrid perovskite, this work illustrates that formation energy can serve as an effective screening parameter for the long-term stability potential of hybrid materials. The results of the prototype II-VI hybrid structures will, on one hand, inspire directions for future exploration of the hybrid materials, and, on the other hand, provide metrics for assessing the structural perfectness and long-term stability of the hybrid materials.

Stepwise Assembly of an Electroactive Framework from a Co6 S8 Superatomic Metalloligand and Cuprous Iodide Building Units.

Invited for the cover of this issue is Christopher Bejger and co-workers at UNC Charlotte, Columbia University, and Donghua University. The image depicts a pair of star clusters in the constellation Perseus as the structure of two metal clusters in the reported framework. Read the full text of the article at 10.1002/chem.20201215.

Accessing new microporous polyspirobifluorenes via a C/Si switch.

Microporous spirosilabifluorene networks were synthesized via Yamamoto coupling of tetrabromospirosilabifluorene precursors. They exhibit bright fluorescence that is quenched in the presence of nitroaromatics. The C/Si switch has subtle effects on the optical properties of the spirobifluorene network and provides a convenient route to 3,3',6,6'-coupled and other polybifluorenes.

Stepwise Assembly of an Electroactive Framework from a Co6 S8 Superatomic Metalloligand and Cuprous Iodide Building Units.

The design of metal-organic frameworks (MOFs) that incorporate more than one metal cluster constituent is a challenging task. Conventional one-pot reaction protocols require judicious selection of ligand and metal ion precursors, yet remain unpredictable. Stable, preformed nanoclusters, with ligand shells that can undergo additional coordination-driven reactions, provide a platform for assembling multi-cluster solids with precision. Herein, a discrete Co6 S8 (PTA)6 (PTA=1,3,5-triaza-7-phosphaadamantane) superatomic-metalloligand is assembled into a three-dimensional (3D) coordination polymer comprising Cu4 I4 secondary building units (SBUs). The resulting heterobimetallic framework (1) contains two distinct cluster constituents and bifunctional PTA linkers. Solid-state diffuse reflectance studies reveal that 1 is an optical semiconductor with a band-gap of 1.59 eV. Framework-modified electrodes exhibit reversible redox behavior in the solid state arising from the Co6 S8 superatoms, which remain intact during framework synthesis.

Si(bzimpy)2 - a hexacoordinate silicon pincer complex for electron transport and electroluminescence.

A neutral hexacoordinate silicon complex containing two 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy) ligands has been synthesized and explored as a potential electron transport layer and electroluminescent layer in organic electronic devices. The air and water stable complex is fluorescent in solution with a λmax = 510 nm and a QY = 57%. Thin films grown via thermal evaporation also fluoresce and possess an average electron mobility of 6.3 × 10-5 cm2 V-1 s-1. An ITO/Si(bzimpy)2/Al device exhibits electroluminescence with λmax = 560 nm.