A Simple and Strong Electron‐Deficient 5,6‐Dicyano[2,1,3]benzothiadiazole‐Cored Donor‐Acceptor‐Donor Compound for Efficient Near Infrared Thermally Activated Delayed Fluorescence

Despite the success of thermally activated delayed fluorescent (TADF) materials in steering the next generation of organic light‐emitting diodes (OLEDs), effective near infrared (NIR) TADF emitters are still very rare. Here, we present a simple and extremely high electron‐deficient compound, 5,6‐dicyano[2,1,3]benzothiadiazole (CNBz), as a strong electron‐accepting unit to develop a sufficiently strong donor‐acceptor (D?A) interaction for NIR emission. End‐capping with the electron‐donating triphenylamine (TPA) unit created an effective D?A?D type system, giving rise to an efficient NIR TADF emissive molecule (λ_em=750 nm) with a very small ΔE_ST of 0.06 eV. The electroluminescent device using this NIR TADF emitter exhibited an excellent performance with a high maximum radiance of 10020 mW Sr^?1 m^?2, a maximum EQE of 6.57% and a peak wavelength of 712 nm.     

Density functional study of the mechanism of the Beckmann rearrangement catalyzed by H-ZSM-5: a cluster and embedded cluster study

The mechanism of the Beckmann rearrangement (BR) catalyzed by the ZSM-5 zeolite has been investigated by both the quantum cluster and embedded cluster approaches at the B3LYP level of theory using the 6-31G(d,p) basis set. Single-point calculations were carried out at the MP2/6-311G(d,p) level of theory to improve energetic properties. The embedded cluster model suggests that the initial step of the Beckmann rearrangement is not the O-protonated oxime but the N-protonated oxime. The energy barriers derived from the proton shuttle of the N-bound to the O-bound isomer are determined to be approximately 99 and approximately 40 kJ/mol for the embedded cluster and quantum cluster approaches, respectively. The difference in the activation energy is due mainly to the effect of the Madelung potential from the zeolite framework. The next step is the rearrangement step, which is the transformation of the O-protonated oxime to be an enol-formed amide compound, formimidic acid. The activation energy, at the rearrangement step, is calculated to be approximately 125 and approximately 270 kJ/mol for the embedded cluster and quantum cluster approaches, respectively. The final step is the tautomerization step which transforms the enol-form to the keto-form, formamide compound. The energy barrier for tautomerization is calculated to be 123 and 151 kJ/mol for the embedded cluster and quantum cluster approaches, respectively. These calculated results suggest that the rate-determining step of the vapor phase of the Beckmann rearrangement on H-ZSM-5 is the rearrangement or tautomerization step.     

Vapor-phase Beckmann rearrangement of oxime molecules over H-Faujasite zeolite.

The Beckmann rearrangement (BR) plays an important role in a variety of industries. The mechanism of this reaction rearrangement of oximes with different molecular sizes, specifically, the oximes of formaldehyde (H₂C?NOH), Z‐acetaldehyde (CH₃HC?NOH), E‐acetaldehyde (CH₃HC?NOH) and acetone (CH₃)₂C?NOH, catalyzed by the Faujasite zeolite is investigated by both the quantum cluster and embedded cluster approaches at the B3LYP level of theory using the 6‐31G (d,p) basis set. To enhance the energetic properties, single point calculations are undertaken at MP2/6‐311G(d,p). The rearrangement step, using the bare cluster model, is the rate determining step of the entire reaction of these oxime molecules of which the energy barrier is between 50–70 kcal mol^?1. The more accurate embedded cluster model, in which the effect of the zeolitic framework is included, yields as the rate determining step, the formaldehyde oxime reaction rearrangement with an energy barrier of 50.4 kcal mol^?1. With the inclusion of the methyl substitution at the carbon‐end of formaldehyde oxime, the rate determining step of the reaction becomes the 1,2 H‐shift step for Z‐acetaldehyde oxime (30.5 kcal mol^?1) and acetone oxime (31.2 kcal mol^?1), while, in the E‐acetaldehyde oxime, the rate determining step is either the 1,2 H‐shift (26.2 kcal mol^?1) or the rearrangement step (26.6 kcal mol^?1). These results signify the important role that the effect of the zeolite framework plays in lowering the activation energy by stabilizing all of the ionic species in the process. It should, however, be noted that the sizeable turnover of a reaction catalyzed by the Brønsted acid site might be delayed by the quantitatively high desorption energy of the product and readsorption of the reactant at the active center.     

Structures and mechanisms of the dehydration of benzaldoxime over Fe-ZSM-5 zeolites: a DFT study

With considerable academic and industrial attention being focused on green chemical processes, environmentally friendly nanomaterials such as zeolites have been systemically modified and tuned to meet such requirements in various industrial chemical reactions. The dehydration of benzaldoxime over Fe-ZSM-5 zeolite has thus been systematically investigated by means of the ONIOM(M06:UFF) scheme. Three different forms of iron-oxo species are used for the active center of Fe-ZSM-5: (a) [FeO]⁺, (b) [FeO₂]⁺, and (c) [Fe(OH)₂]⁺. Both the oxidative and polar elimination mechanisms for the dehydration process were investigated. For the oxidative dehydration mechanism, this route begins with the oxygen-end benzaldoxime adsorption complex. The energy barrier is calculated to be 24.5, 31.4, and 33.6 kcal/mol for [FeO]⁺Z^?, [FeO₂]⁺Z^?, and [Fe(OH)₂]⁺Z^?, respectively. These are significantly lower than the energy barrier found for the polar elimination one. A comparison of the energetic profiles suggest that the dehydration process would take place through the oxidative dehydration mechanism in which the [FeO]⁺Z^? is the most reactive form of mononuclear Fe-ZSM-5 zeolite. Over the [FeO]⁺Z^?, an α-oxygen has the function of migrating the hydrogen of the benzaldoxime and the hydroxyl group of substrate that consecutively leads to bonding with the metal center to produce the [Fe(OH)₂]⁺Z^? and the benzonitrile product.     

Theoretical investigation on reaction pathways for ethylene epoxidation on Ti-decorated graphene

The activities of atomic Ti-decorated graphene (Ti/dG) for ethylene epoxidation and competitive paths for acetaldehyde (AA) formation are investigated by means of density functional theory together with the D3 dispersion correction (UM06-L-D3). Two reaction mechanisms for ethylene epoxidation, namely concerted and stepwise mechanisms, were considered. The computational results reveal that the electron transfer from graphene can effectively enhance the catalytic activity of Ti atom. Without graphene support, atomic Ti becomes an inert metal for this reaction. Strong adsorption and significant activation of the reactant O₂ molecule were observed on the Ti-decorated graphene material. Over the O₂-adsorbed Ti/dG, the direct attack of the olefin on an peroxo oxygen center is preferred. The activation for this step is 10.9 kcal mol^?1. After the reaction, an ethylene oxide is formed with one atomic oxygen on top of Ti. Consequently, a gaseous ethylene reacts with the remaining O atom of TiO moiety for the formation of the second ethylene oxide molecule. The formation of ethylene oxide over the TiO/dG involves a two-step process which is the formations of oxametallacycle intermediate and EO, respectively. The calculated barriers for these two steps are 9.9 and 18.9 kcal mol^?1, respectively. Furthermore, the Ti/dG showed a lower activation barrier toward EO formation than that of AA. Therefore, our theoretical study suggests that atomic Ti-decorated graphene could possess catalytic activity for ethylene epoxidation comparable to that of potential catalysts.     

Comparison of Cu‐ZSM‐5 Zeolites and Cu‐MOF‐505 Metal‐Organic Frameworks as Heterogeneous Catalysts for the Mukaiyama Aldol Reaction: A DFT Mechanistic Study

The density functional theory (DFT) model ONIOM(M06L/6‐311++G(2df,2p):UFF was employed to reveal the catalytic activity of Cu^II in the paddle‐wheel unit of the metal‐organic framework (MOF)‐505 material in the Mukaiyama aldol reaction compared with the activity of Cu‐ZSM‐5 zeolites. The aldol reaction between a silyl enol ether and formaldehyde catalyzed by the Lewis acidic site of both materials takes place through a concerted pathway, in which the formation of the C? C bond and the transfer of the silyl group occurs in a single step. MOF‐505 and Cu‐ZSM‐5 are predicted to be efficient catalysts for this reaction as they strongly activate the formaldehyde carbonyl carbon electrophile, which leads to a considerably lower reaction barrier compared with the gas‐phase system. Both MOF‐505 and Cu‐ZSM‐5 catalysts stabilize the reacting species along the reaction coordinate, thereby lowering the activation energy, compared to the gas‐phase system. The activation barriers for the MOF‐505, Cu‐ZSM‐5, and gas‐phase system are 48, 21, and 61 kJ mol^?1, respectively. Our results show the importance of the enveloping framework by stabilizing the reacting species and promoting the reaction.     

Reaction Mechanism of Methanol to Formaldehyde over Fe‐ and FeO‐Modified Graphene

We employed periodic DFT calculations (PBE‐D2) to investigate the catalytic conversion of methanol over graphene embedded with Fe and FeO. Two possible pathways of dehydrogenation to formaldehyde and dehydration to dimethyl ether (DME) over these catalysts were examined. Both processes are initiated with the activation of methanol over the catalytic center through O?H cleavage. As a result, a methoxo‐containing intermediate is formed. Subsequently, H‐transfer from the methoxy to the adjacent ligand leads to the formation of formaldehyde. Conversely, the activation of the second methanol over the intermediate gives DME and H₂O. Over Fe/graphene, the dehydration process is kinetically and thermodynamically preferable. Unlike Fe/graphene, FeO/graphene is predicted to be an efficient catalyst for the dehydrogenation process. Oxidative dehydrogenation over FeO/graphene takes place through two steps with free energy barriers of 5.7 and 10.2 kcal mol^?1.     

Mechanistic Studies on the Transformation of Ethanol into Ethene over Fe‐ZSM‐5 Zeolite

Ethanol, through the utilization of bioethanol as a chemical resource, has received considerable industrial attention as it provides an alternative route to produce more valuable hydrocarbons. Using a density functional theory approach incorporating the M06‐L functional, which includes dispersion interactions, a large 34T nanocluster model of Fe‐ZSM‐5 zeolite in which T is a Si or Al atom is employed to examine both the stepwise and concerted mechanisms of the transformation of ethanol into ethene. For the stepwise mechanism, ethanol dehydration commences from the first hydrogen abstraction of the ethanol OH group to form the ethoxide‐hydroxide intermediate with a low activation energy of 17.7 kcal mol^?1. Consequently, the ethoxide‐hydroxide intermediate is decomposed into ethene through hydrogen abstraction from the ethoxide methyl carbon to either the OH group of hydroxide or the oxygen of the ethoxide group with high activation energies of 64.8 and 63.5 kcal mol^?1, respectively. For the concerted mechanism, ethanol transformation into the ethene product occurs in a single step without intermediate formation, with an activation energy of 32.9 kcal mol^?1.