Inter-Ligand Energy Transfer Process in an Ir-Complex with Expanding π-Conjugated Ligand

The inter-ligand energy transfer (ILET) process in heteroleptic iridium complex, [Ir(dfppy)₂(bpy-Im₂)]⁺ , where dfppy =2-(2,4-difluorophenyl)pyridine and bpy-Im₂ =4,4’-bis(1,2-diphenyl-1H-benzo[d]imidazole)-2,2’,-bipyridine, was investigated using a femtosecond transient absorption (fs-TA) spectroscopic technique. The photophysical properties of [Ir(dfppy)₂(bpy-Im₂)]⁺ with significantly expanding π-conjugated ligand are compared to those of [Ir(dfppy)₂(bpy)]⁺ ( bpy =2,2’-bipyridine) and a free bpy-Im₂ ligand. The emission spectrum of [Ir(dfppy)₂(bpy-Im₂)]⁺ shows no shift upon changing the solvent polarity, whereas the free ligand bpy-Im₂ showed bathochromic fluorescence shifts with increasing solvent polarity, which is attributed to intramolecular charge transfer (ICT). The unique photophysical properties of [Ir(dfppy)₂(bpy-Im₂)]⁺ are due to the fast ILET process from ³MLCT_dfppy to ³MLCT/³LC_bpy-Im2, resulting in the phosphorescence emission originating from ³MLCT/³LC_bpy-Im2. On the other hand, the TA bands of bpy-Im₂ are observed at 540 and 480 nm, corresponding to the singlet and triplet manifolds, respectively. In contrast, the TA spectrum of [Ir(dfppy)₂(bpy-Im₂)]⁺ showes broad bands centered at 420 and 600 nm, attributed to the transitions from ³MLCT_dfppy and ³MLCT/³LC_bpy-Im2, respectively. Time-resolved spectroscopic results confirm the efficient ILET dynamics from ³MLCT_dfppy to ³MLCT/³LC_bpy-Im2 in [Ir(dfppy)₂(bpy-Im₂)]⁺ . From the relaxation times determined by singular value decomposition analysis and simple sequential kinetic model, we infer that the ILET process from ³MLCT_dfppy to ³MLCT/³LC_bpy-Im2 occurs with a time constant of ca. 4 ps. The presented results in this study show that the introduction of an expanding π-conjugated ligand can lead to the efficient ILET dynamics for improving the OLED performance.     

Thiophene-Fused 1,4-Diazapentalene: A Stable C=N-Containing π-Conjugated System with Restored Antiaromaticity

A thiophene-fused 1,4-diazapentalene (TAP) was rationally designed and synthesized as a C=N-containing 4n π-electron system that exhibits restored antiaromaticity impaired by the doping with C=N bonds. X-ray crystallographic analysis and quantum chemical calculations revealed that the annulation of thiophene rings with the 1,4-diazapentalene moiety resulted in a much higher antiaromaticity than the pristine 1,4-diazapentalene. These effects can be ascribed to the reduced bond alternation of the eight-membered-ring periphery caused by stabilization of the less-stable bond-shifted resonance structure upon increasing the degree of substitution of imine moieties. Consequently, TAP underwent facile hydrogenation even under mild conditions because of its pronounced antiaromaticity and the high aromaticity of the corresponding hydrogenated product H₂-TAP. In addition, the electrophilic C=N moieties in TAP led to the formation of a dense π-stacked structure. These results highlight the effect of partial replacement of C=C bonds with C=N bonds in antiaromatic π-electron systems.     

Flexible π-Conjugated 2,5-Diarylamino-Terephthalates: A New Class of Mechanochromic Luminophores with Tunable Aggregation States

The generation of different thermodynamically (meta)stable states is crucial for the development of smart solid-state luminescent materials. However, the design of luminophores with tunable aggregation states is remaining a grand challenge. Herein, we present a family of mechanochromic luminophores with tunable metastable states, based on the dynamically controllable π–π stacking of the flexible π-conjugated structure of 2,5-diarylamino-terephthalates in the solid state. The experimental data revealed that both the kinetically controlled metastable state and thermodynamic controlled stable state can be generated via tuning the intermolecular interactions such as π–π stacking and hydrogen bonds. As a result, the highly sensitive mechano-stimuli response of these luminophores was successfully achieved.     

One-Pot Dual C−C Coupling Reaction via Site Selective Cascade Formation by PdII-Cryptate of an Amino-Ether Heteroditopic Macrobicycle

Selectivity of aryl iodo over ethynyl iodo toward the Suzuki cross coupling reaction is explored by utilizing a palladium complex of amino-ether heteroditopic macrobicycle. Subsequently, unreacted ethynyl iodide undergoes homocoupling reaction in the same catalytic atmosphere, thereby representing a cascade dual C−C coupling reaction. Furthermore, this approach is extended for novel one-pot synthesis of unsymmetrical 1,3-diynes.     

Generation of Selenoaldehydes via Retro Diels–Alder Reaction and Their Behavior in the Reaction with Some Enophiles

Abstract

The [4, 2] cycloadducts of selenoaldehydes and anthracene regenerate selenoaldehydes in situ quantitatively under neutral conditions via thermal retro Diels–Alder reaction. The reactions of selenoaldehydes generated by this method with 2-silyloxy-1,3-butadiene, 2-methoxyfuran, and 5-ethoxyoxazoles are described.     

Styrene Hydroformylation with In Situ Hydrogen: Regioselectivity Control by Coupling with the Low-Temperature Water–Gas Shift Reaction

The hydroformylation of olefins is one of the most important homogeneously catalyzed industrial reactions for aldehyde synthesis. Various ligands can be used to obtain the desired linear aldehydes in the hydroformylation of aliphatic olefins. However, in the hydroformylation of aromatic substrates, branched aldehydes are formed preferentially with common ligands. In this study, a novel approach to selectively obtain linear aldehydes in the hydroformylation of styrene and its derivatives was developed by coupling with a water–gas shift reaction on a Rh single-atom catalyst without the use of ligands. Detailed studies revealed that the hydrogen generated in situ from the water–gas shift is critical for the highly regioselective formation of linear products. The coupling of a traditional homogeneous catalytic process with a heterogeneous catalytic reaction to tune product selectivity may provide a new avenue for the heterogenization of homogenous catalytic processes.     

A Novel Approach for the Surface Modification of Polymeric Membrane with Phospholipid Polymer

A new economic and convenient method to modify the surface of microporous polypropylene (PP) membranes with phospholipid polymer was given. The process included the photo-irradiated graft polymerization of N,N-dimethylaminoethyl methacrylate (DMAEMA) and the ring-opening reaction of the grafted polyDMAEMA with 2-alkyloxy-2-oxide-1,3,2-dioxo-phospholanes (AOP). Four AOPs, whose alkyloxy groups consisted of dodecyl, tetradecyl,hexadecyl and octadecyl moieties, were used to convert the grafted polyDMAEMA to phospholipidpolymers. FT-IR spectra confirmed the chemical change of membrane surface. Platelets adhesion experiment indicated that PP membrane with excellent blood compatible surface could be fabricated by this method.     

A Study on the Kinetics of the Catalytic Reforming Reaction of CH4 with CO2： Determination of the Reaction Order

The kinetics of the catalytic reforming reaction of methane with carbon dioxide to produce synthesis gas on a Ni/(α-A1203 and a HSD-2 type commercial catalyst has been studied. The results indicate that the reaction orders are one and zero for methane and carbon dioxide, respectively, when the carbon dioxide partial pressure was about 12.5-30.0 kPa and the temperature was at 1123-1173 K. However, when the carbon dioxide partial pressure was changed to 30.0-45.0 kPa under the same temperature range of 1123-1173 K, the reaction orders of methane and carbon dioxide are one. Furthermore, average rate constants at different temperatures were determined.     

Two New Catalysts for the Dehydrogenative Coupling Reaction of Carboxylic Acids with Silanes—Convenient Methods for an Atom‐Economical Preparation of Silyl Esters

Tris(triphenylphosphine)cuprous chloride [Cu(PPh₃)₃Cl] has been found to be an efficient catalyst for the dehydrosilylation of carboxylic acids with silanes. In the presence of 4 mol% Cu(PPh₃)₃Cl, dehydrosilylation reactions in acetonitrile afforded the corresponding silyl esters at 80°C in good yields. It was noted that triphenylphosphine itself also functions as an adequate catalyst for the reaction.     

Understanding the Role of Solvents and Spin–Orbit Coupling in an Oxygen-Assisted SN2-Type Oxidative Transmetalation Reaction

The aerial oxidation of Pd^II to Pd^IV has emerged as an integral component of sustainable catalytic C−H functionalization processes. However, a proper understanding of the factors that control the viability of this oxidative process remains elusive. An investigation of the intricate mechanism of the transmetalation reaction of the aerial oxidative transformation of [(Me₃tacn)Pd^IIMe₂] (Me₃tacn=N,N′,N′′-trimethyl-1,4,7-triazacyclononane) to [(Me₃tacn)Pd^IVMe₃]⁺ has been conducted by using DFT, along with multireference methods, such as second-order n-electron valence-state perturbation theory (NEVPT2) with complete active space self-consistent field theory (CASSCF). The present endeavor predicts that the thermodynamics and kinetics of the oxygen activation step are primarily dictated by the polarity of the solvents, which determine the amount of charge transfer to the oxygen molecule from the Pd^II center. Additionally, it is observed that the presence of a protic solvent has a significant effect on the spin–orbit coupling term at the minimum energy crossing point of the triplet and singlet surfaces. Moreover, it is shown that the intermetal ligand-transfer phenomenon is an important instance of an oxygen-assisted S_N2 reaction.     

A General, Highly Efficient Ullmann C-O Coupling Reaction under Microwave Irradiation and the Effects of Water

A general, rapid and highly efficient method for the synthesis of diaryl ethers under the assistance of microwave irradiation was described. A series of diaryl ethers were prepared by direct coupling of phenols and aryl halides in good to excellent yields in anhydrous DMF or NMP at 150 ℃ within 20 rain. The presence of water was found to have a significant impact on the Ullmann C-O coupling reaction between aryl halides and phenols under microwave irradiation.     

Novel Photo-induced Coupling Reactions of 9-Fluorenylidenemalononitrile or 1,1-Diphenyl-2,2-dicyanoethylene with 10-Methyl-9,10-dihydroacridine. A Study on the Photophysics of the Reaction

IntroductionItwasreported1thatnovelphoto inducedcouplingre actionof 9 fluorenylidenemalononitrile (FDCN )with 10 methyl 9,10 dihydroacridine (AcrH2 )tookplaceviaanelectrontransfer protontransfer radicalcouplingpathwaytogive 9 dicyanomethyl 9 (10′ methyl 9′ acridinyl)fluo rene (1) (Scheme 1) .Similarly ,thephoto inducedreac tionof 1,1 diphenyl 2 ,2 dicyanoethylene (DPCN )withAcrH2 alsoproducedacouplingproduct .2 Thesereactionsareratherscarcewithreducednicotinamideadeninedinu cleotide …     

A Study on the Reaction Mechanism of Bromocresol Green with Bovine Serum Albumin

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Formation of Benzyl Oxazole, A Competitive Path with the Classical Bishler-Napieralski Reaction

1,2,3,4-tetrahydroisoquinoline-3-carboxylic acids (TIC) are of considerable interest due to their biological activity and as an important structural element in several important alkaloids and other medically useful products1. Moreover, TIC is a phenylalanine analogue in which the dihedral angle is limited to a very small range because of its bicyclic nature2. In connection with the design of topographically constrained peptides, TIC has been utilized in several instance as a replacement o…     

Supramolecular Catalysis of the oxa-Pictet–Spengler Reaction with an Endohedrally Functionalized Self-Assembled Cage Complex

An endohedrally functionalized self-assembled Fe₄L₆ cage complex can catalyze oxa-Pictet—Spengler cyclizations of tryptophols and various aldehyde derivatives, showing strong rate accelerations and size-selectivity. Selective molecular recognition of substrates controls the reactivity, and the cage is capable of binding and activating multiple different species along the multistep reaction pathway. The combination of a functionalized active site, size-selective reactivity, and multistep activation, all from a single host molecule, illustrates the biomimetic nature of the catalysis.     

Efficient Synthesis of Phenoxathiines via the Cascade C–H Hydroxylation–C–S Coupling–C–O Cyclization Reaction

Russian Journal of General Chemistry - The ligand-free and simple cascade C–H hydroxylation–C–S coupling–C–O cyclization reaction has been used as the synthetic...     

A New Rearrangement Reaction of 2-Phenyl Substituted Benzothiazepine with Ethoxycarbonyl Carbene─Mechanism of the Reaction and Structure of the Product

Intheprevi0usaFticlesl-2wehavereportedthatthereacti0n0fbenz0diazepinewithethoxycarbonylcarbenemayobtainnormal[2 l]cycIoadditi0npr0ductsregardlessthe2-substitUentismethyl0rphenyl.Howeverunderthesamec0nditi0nsthereaction0fbenzothiazepinewithethoxycarbonylcarbeneunderwentrearrangementreacti0n.Forexample,whenthe2-substituentismethyl,thereacti0nofbenzothiazepinewithethoxycarbonylcarbenegivearing-openingproductIIatroomorhightemperature'.Whenthe2-substituentisphenyl,weunexpectedlyfoundan0thernewrea…     

Perturbing π-clouds with Substituents to Study the Effects on Reaction Dynamics of gauche-1,3-Butadiene to Bicyclobutane Electrocyclization

The conical intersection (CI) governs the ultra-fast relaxation of excited states in a radiationless manner and are observed mainly in photochemical processes. In the current work, we investigated the effects of substituents on the reaction dynamics for the conversion of gauche-1,3-butadiene to bicyclobutane via photochemical electrocyclization. We incorporated both electron withdrawing (−F) and donating (−CH₃) groups in the conjugated system. In our study, we optimized the minimum energy conical intersection (MECI) geometries using the multi-configurational state-averaged CASSCF approach, whereas, to study the ground state reaction pathways for the substituted derivatives, dispersion corrected, B3LYP-D3 functional was used. The non-adiabatic surface hopping molecular dynamics simulations were performed to observe the behaviour of electronic states involved throughout the photoconversion process. The results obtained from the multi-reference second-order perturbation correction of energy at the XMS-CASPT2 level of theory, topography analysis, and non-adiabatic dynamics suggest that the −CH₃ substituted derivatives can undergo faster thermal conversion to the product in the ground state with a smaller activation energy barrier compared to −F substituted derivative. Our study also reveals that the GBUT to BIBUT conversion follows both conrotatory and disrotatory pathways, whereas, on substitution with −F or −CH₃, the conversion proceeds via the conrotatory pathway.     

The Application of Suzuki Coupling Reaction on the Preparation of Carbosilane Dendrimers with 4-（Naphthalen-l-yl）phenyl Core

Carbosilane dendrimers with p-bromophenyl core were synthesized by alternating Grignard and hydrosilylation reaction. And the α-naphthalenyl was connected to the core by the Suzuki coupling reaction. A new carbosilane dendrimer with big π-conjugated structure [4-（naphthalen-l-yl）phenyl core] was given. It shows Suzuki coupling reaction is an effective and powerful core-functionalization method and the satisfactory result can be obtained through prolonging the reaction time with the increase of the generation of dendrimer.     

Oxidative Coupling Reaction of N,N‐Dialkylanilines with Cerium(IV) Ammonium Nitrate in the Solid State

Oxidative coupling reactions of N,N‐dialkylanilines with cerium(IV) ammonium nitrate can be achieved by grinding at room temperature in the absence of solvents.