Tuning Optical Properties by Controlled Aggregation: Electroluminescence Assisted by Thermally-Activated Delayed Fluorescence from Thin Films of Crystalline Chromophores

Several photophysical properties of chromophores depend crucially on intermolecular interactions. Thermally-activated delayed fluorescence (TADF) is often influenced by close packing of the chromophore assembly. In this context, the metal-organic framework (MOF) approach has several advantages: it can be used to steer aggregation such that the orientation within aggregated structures can be predicted using rational approaches. We demonstrate this design concept for a DPA-TPE (diphenylamine-tetraphenylethylene) chromophore, which is non-emissive in its solvated state due to vibrational quenching. Turning this DPA-TPE into a ditopic linker makes it possible to grow oriented MOF thin films exhibiting pronounced green electroluminescence with low onset voltages. Measurements at different temperatures clearly demonstrate the presence of TADF. Finally, this work reports that the layer-by-layer process used for MOF thin film deposition allows the integration of the TADF-DPA-TPE in a functioning LED device.     

Kinetic studies of the cyclization of singlet vinylchlorocarbenes

[reaction: see text] Vinylchlorocarbenes (R = Me or Cl) cyclize to cyclopropenes with k = (2.4-5.1) x 10(7) s(-1) or (3.1-4.5) x 10(6) s(-1), respectively, in solution at room temperature. The corresponding E(a) values are 6.6 and 5.7 kcal/mol. Excited diazirines are also likely precursors of the cyclopropenes.     

Molecular‐Level Insights into the Oxidative Degradation of Grafted Amines

The oxidative degradation of CO₂ adsorbents consisting of amine‐grafted pore‐expanded mesoporous MCM‐41 silica was investigated. The adsorbents were treated under flowing air at various temperatures, and the degree of deactivation was evaluated through the measurement of their CO₂ adsorption capacity prior and subsequent to exposure to air. To decipher the chemical structure of surface species upon air‐deactivation of grafted amines, a solvent extraction procedure was developed using a deuterated basic solution. The obtained solutions were analyzed by a variety of 1D and 2D NMR spectroscopy techniques, such as ²⁹Si, ¹³C, ¹H, [¹H,¹⁵N] HMBC, [¹H,¹³C] HMQC, COSY and DOSY. The surface species generated by oxidative degradation of amine‐grafted silica were found to contain functional groups such as imine, amide and carboxylic groups. Several structural units were conclusively demonstrated.     

Guest-responsive polaritons in a porous framework: chromophoric sponges in optical QED cavities

Introducing porous material into optical cavities is a critical step toward the utilization of quantum-electrodynamical (QED) effects for advanced technologies, e.g. in the context of sensing. We demonstrate that crystalline, porous metal–organic frameworks (MOFs) are well suited for the fabrication of optical cavities. In going beyond functionalities offered by other materials, they allow for the reversible loading and release of guest species into and out of optical resonators. For an all-metal mirror-based Fabry–Perot cavity we yield strong coupling (∼21% Rabi splitting). This value is remarkably large, considering that the high porosity of the framework reduces the density of optically active moieties relative to the corresponding bulk structure by ∼60%. Such a strong response of a porous chromophoric scaffold could only be realized by employing silicon-phthalocyanine (SiPc) dyes designed to undergo strong J-aggregation when assembled into a MOF. Integration of the SiPc MOF as active component into the optical microcavity was realized by employing a layer-by-layer method. The new functionality opens up the possibility to reversibly and continuously tune QED devices and to use them as optical sensors.

A phthalocyanine-based porous material in optical cavity exhibited strong coupling and guest responsive polariton feature.     

Pd(0)-catalyzed couplings using bromide and chloride derivatives of Baylis-Hillman adducts with triarylbismuths as atom-efficient multi-coupling nucleophiles

Bromide and chloride derivatives of Baylis-Hillman adducts have been demonstrated to react efficiently with triarylbismuths affording allylic arylated products in high yields under palladium-catalyzed conditions. Triarylbismuths have been employed in sub-stoichiometric amounts as multi-coupling and atom-efficient nucleophiles in these reactions. The reactivity of both allylic bromides and chlorides was found to be facile and equally efficient in couplings with triarylbismuths.     

Poincaré–Sobolev equations in the hyperbolic space

We study the a priori estimates, existence/nonexistence of radial sign changing solution, and the Palais–Smale characterisation of the problem ${-\Delta_{{\mathbb B}^{N}}u - \lambda u = |u|^{p-1}u, u\in H^1({\mathbb B}^{N})}$ in the hyperbolic space ${{\mathbb B}^{N}}$ where ${1 < p\leq\frac{N+2}{N-2}}$ . We will also prove the existence of sign changing solution to the Hardy–Sobolev–Mazya equation and the critical Grushin problem.     

Microwave performance enhancement in Double and Single Gate HEMT with channel thickness variation

In Single Gate HEMT (SGHEMT) shortening of gate length (_Lg)$\left(L_g\right)$ below 100 nm leads to reduction in Transconductance (_gm)$\left(g_m\right)$, which reduces the unloaded voltage gain (_gm/_gd)$(g_m/g_d)$ of the device, thereby reducing the maximum frequency of oscillation (_fmax)$\left(f_{max}\right)$. The main reason for this reduction in _gm$g_m$ with _Lg$L_g$ in the Single Gate HEMT (SGHEMT) is its inability to maintain the desired channel aspect ratio (α$\alpha$). At such a miniaturization level, α$\alpha$ not only depends on the channel depth (d)$\left(d\right)$ but also on the channel thickness (_dc)$\left(d_c\right)$ of the device [5]. Moreover, the variation of _dc$d_c$ may switch the device characteristics from quantum regime to classical regime  and . The Double Gate HEMT (DGHEMT)  and  has emerged as a solution for further reduction in _Lg$L_g$ and provides enhancements over SGHEMT by virtue of its double gate and also for same _dc$d_c$ due to double heterojunctions, which virtually increases the value of α$\alpha$. In the present work, extensive simulation work has been carried out using ATLAS device simulator [35] in order to study the effect of _dc$d_c$ and _Lg$L_g$ on DGHEMT and SGHEMT. An analytical model has also been proposed for SGHEMT and DGHEMT to incorporate the effect of variation of _dc$d_c$ and _Lg$L_g$.     

Thermodynamics and kinetics of NaAlH4 nanocluster decomposition

Reactive nanoparticles are of great interest for applications ranging from catalysis to energy storage. However, efforts to relate cluster size to thermodynamic stability and chemical reactivity are hampered by broad pore size distributions and poorly characterized chemical environments in many microporous templates. Metal hydrides are an important example of this problem. Theoretical calculations suggest that reducing their critical dimension to the nanoscale can in some cases considerably destabilize these materials and there is clear experimental evidence for accelerated kinetics, making hydrogen storage applications more attractive in some cases. However, quantitative measurements establishing the influence of size on thermodynamics are lacking, primarily because carbon aerogels often used as supports provide inadequate control over size and pore chemistry. Here, we employ the nanoporous metal-organic framework (MOF) Cu-BTC (also known as HKUST-1) as a template to synthesize and confine the complex hydride NaAlH(4). The well-defined crystalline structure and monodisperse pore dimensions of this MOF allow detailed, quantitative probing of the thermodynamics and kinetics of H(2) desorption from 1-nm NaAlH(4) clusters (NaAlH(4)@Cu-BTC) without the ambiguity associated with amorphous templates. Hydrogen evolution rates were measured as a function of time and temperature using the Simultaneous Thermogravimetric Modulated Beam Mass Spectrometry method, in which sample mass changes are correlated with a complete analysis of evolved gases. NaAlH(4)@Cu-BTC undergoes a single-step dehydrogenation reaction in which the Na(3)AlH(6) intermediate formed during decomposition of the bulk hydride is not observed. Comparison of the thermodynamically controlled quasi-equilibrium reaction pathways in the bulk and nanoscale materials shows that the nanoclusters are slightly stabilized by confinement, having an H(2) desorption enthalpy that is 7 kJ (mol H(2))(-1) higher than the bulk material. In addition, the activation energy for desorption is only 53 kJ (mol H(2))(-1), more than 60 kJ (mol H(2))(-1) lower than the bulk. When combined with first-principles calculations of cluster thermodynamics, these data suggest that although interactions with the pore walls play a role in stabilizing these particles, size exerts the greater influence on the thermodynamics and reaction rates.     

Comparative study on material properties of wood-ash alkali and commercial alkali treated Sterculia fiber

Cellulose - Pulp, paper, and related industries consume large amount of commercial alkali to process raw fiber and/or recycle waste. A low-cost alternative to commercial alkali would be useful to...