Effects of intramolecular hydrogen bonds on phosphorescence emission: A theoretical perspective

Importing intramolecular hydrogen bond in phosphorescent transition metal complexes has been considered one of the excellent approaches to improve the electroluminescence performance of organic light-emitting diodes in real applications. However, the relationships between such H-bond structure and phosphorescent properties have not been theoretically revealed yet. In this study, two types of intramolecular hydrogen bonds are introduced into the two classes of traditional materials, that is, Pt(II) and Ir(III) complexes ( 1a and 2a ) to completely elucidate their influence on the structures and properties by comparing with the original phosphors ( 1b and 2b ) using density functional theory/time-dependent density functional theory for the first time. A comprehensive analysis of the geometric structures, molecular orbitals, and luminescence properties (including phosphorescence emission wavelengths and radiative and nonradiative decay processes) has been carried out. Our theoretical model highlights that complexes 1a and 2a embedded with H-bonds significantly promote the phosphorescence emission band blue-shifted and restrict molecular deformations compared with the corresponding 1b and 2b , which can provide helpful guidance to regulate and design several aspects of highly efficient blue phosphorescent emitters.     

Heteroleptic [Cu(NN)P2]+-type cuprous complexes and their structural modulation on phosphorescent color: Synthesis,structural characterization,properties, and theoretical calculations

Four new heteroleptic [Cu(NN)P₂]⁺-type cuprous complexes— 1 -TPP, 2 -POP, 3 -Xantphos, and 4 -DPPF—were designed and synthesized using a diimine ligand 2-(2′-pyridyl)benzoxazole (2-PBO) and different phosphine ligands (TPP, triphenylphosphine; POP, bis[2-(diphenylphosphino)phenyl]ether; Xantphos, 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene; DPPF, 1,1′-bis(diphenylphosphino)-ferrocene). All complexes were characterized using single-crystal X-ray diffraction, spectroscopic analysis (infrared, UV–Vis.), elemental analysis, and photoluminescence (PL). Single-crystal X-ray diffraction revealed complexes 1 – 4 as isolated cation complex structures with a tetrahedral CuN₂P₂ coordination geometry and diverse P–Cu–P angles. Their UV–Vis. absorption spectra exhibited a blue-shift sequence in wavelength with an enlarged P–Cu–P angle from 4 to 2 then to 3 and then to 1 . The PL emission peaks of 1 – 3 also exhibited a similar blue-shift sequence ( 2 → 3 → 1 ). Their PL lifetime in microseconds (~7.5, 5.1, and 4.7 μs for 1 , 2 , and 3 , respectively) indicated that their PL behavior represents phosphorescence. Time-dependent density functional theory (TD-DFT) calculation and wavefunction analysis revealed that S₁ and T₁ states of 1 – 3 should be assigned as metal–ligand and ligand–ligand charge-transfer (ML + L'L)CT states. Their UV–Vis. absorption and phosphorescence should be attributed to the charge transfer from the P–Cu–P segment to the 2-PBO ligand. Therefore, as the P–Cu–P angle increased (lower HOMO), the energy of S₁ and T₁ states also increased, following the change of PL color.     

Electrophilic fluoroalkylthiolation induced diastereoselective and stereospecific 1,2-metalate migration of alkenylboronate complexes

A transition metal free process for conjunctive functionalization of alkenylboron ate-complexes with electrophilic fluoroalkylthiolating reagents is described, affording β-trifluoroalkylthiolated and difluoroalkylthiolated boronic esters in good yield and excellent diastereoselectivity. The potential applicability of the method was demonstrated by the preparation of a difluoromethylthiolated mimic 12 of a potential drug molecule PF-4191834 for the treatment of asthma.

A transition metal free process for conjunctive functionalization of alkenylboron ate-complexes with electrophilic fluoroalkylthiolating reagents affords β-tri- and difluoroalkylthiolated boronic esters in good yield and diastereoselectivity.

An electrophile-induced 1,2-metalate migration of an alkenylboron “ate” complex and subsequent base-promoted β-elimination to form a functionalized cis-alkene, now the so-called Zweifel reaction, was first reported by Zweifel and co-workers in 1967 (Fig. 1A).^1–3 The reaction was proposed to proceed via an initial attack of the π electron of the alkene moiety to iodine to generate a zwitterionic iodonium ion, which then undergoes a stereospecific 1,2-metalate to afford a β-iodoboronic ester, followed by anti-elimination upon treatment with a base to afford a cis-olefin. Thus, if the iodine is replaced by an alternative electrophilic reagent and the use of a base is omitted, an interrupted-Zweifel reaction for the preparation of a stereospecific β-functionalized boronic ester could be realized. Toward this end, Aggarwal reported the first example of such a reaction by employing PhSeCl as the electrophilic reagent.⁴ It was proposed that PhSeCl first reacts with an alkenylboronate complex to form a zwitterionic seleniranium ion. Subsequent diastereospecific 1,2-metalate migration affords the stereospecific β-seleno-alkylboronate (Fig. 1B). Likewise, shortly after, Denmark and co-workers reported an analogous Lewis-base catalysed enantioselective and diastereoselective carbosulfenylation of an alkenylboronate complex using N-arylthiosaccharin as the electrophile (Fig. 1C).⁵Open in a separate windowFig. 1The interrupted Zweifel reaction.In light of these discoveries and our recent success in the development of a toolbox of electrophilic fluoroalkylthiolating reagents including three trifluoromethylthiolating reagents α-cumyltrifluoromethane sulfenate,⁶N-trifluoromethylthio-saccharin⁷ and N-trifluoromethylthiodibenzenesulfonimide,⁸ and two difluoromethylthiolating reagents N-difluoromethylthiophthalimide⁹ and S-(difluoromethyl)benzenesulfonothioate,¹⁰ we wondered whether these electrophilic fluoroalkylthiolating reagents could also trigger the proposed stereospecific 1,2-metalatation of the alkenylboronate complex to afford β-fluoroalkylthiolated borane derivatives (Fig. 1D). The trifluoromethylthio (–SCF₃) and the difluoromethylthio (–SCF₂H) groups have gained great attention recently, partially because of their high and tuneable lipophilicity¹¹ that might improve the drug candidate''s cell membrane permeability and consequently, its overall pharmacokinetics.¹² Thus, the development of new efficient reactions for the incorporation of the trifluoromethylthio¹³ or difluoromethylthio groups¹⁴ would be of vital importance in facilitating medicinal chemists'' endeavours in new drug discovery. Herein, we report that by employing electrophilic difluoromethylthiolating reagent PhSO₂SCF₂H 2a as the electrophile, the proposed difluoromethylthiolating induced stereospecific 1,2-metalate migration of alkenyl boronate complexes occurred smoothly to afford β-difluoromethylthiolated boronic esters in good yields and excellent diastereoselectivity. Likewise, when electrophilic trifluoromethylthiolating reagent N-trifluoromethylthiosaccharin 7 was used, an analogous reaction for the diastereoselective formation of β-trifluoromethylthiolated boronic esters was successfully achieved.We began our study by examining the reaction of the electrophilic difluoromethylthiolating reagent 2a with the alkenylboronate complex which was generated in situ by mixing 1a and PhLi in diethyl ether. It was found that the reaction in CH₃CN occurred in full conversion after 12 hours at room temperature, affording the corresponding product 3a in 53% yield (Table 1, entry 1). When the amount of PhLi was increased to 1.3 equivalents, the yield was increased to 76%, while the yield decreased to 66% when 2.0 equivalents of PhLi were used, likely due to the decomposition of the product under strong basic conditions (Table 1, entries 1–5). We then further investigated the effect of the reaction temperature and the solvent. It was found that the temperature did not affect the reaction significantly since the yields of the desired products were decreased slightly to 72% and 70%, respectively, when the reactions were conducted at 0 °C or −15 °C (Table 1, entries 6 and 7). Likewise, the reaction was not sensitive to the polarity of the solvent since reactions conducted in less polar solvents such as THF or CH₂Cl₂ or nonpolar solvents like toluene occurred in slightly lower 60–73% yields (Table 1, entries 9–11). We also found that reaction using N-difluoromethylthiophthalimide as the electrophilic difluoromethylthiolating reagent gave the same product in a slightly lower yield (Table 1, entry 8).Optimization of conditions for the reaction of the alkenyl boronate complex with PhSO₂SCF₂H^a

Preparation and in vivo imaging of a novel potential αvβ3 targeting PET/MRI dual-modal imaging agent

Journal of Radioanalytical and Nuclear Chemistry - Multi-modal biomedical imaging has played an essential role in tumor diagnosis. However, constructing a multi-modal imaging contrast agent with...     

Establishment and validation of an SIL-IS LC–MS/MS method for the determination of ibuprofen in human plasma and its pharmacokinetic study

In this work, we developed and validated a highly sensitive, rapid and stable LC–MS/MS method for the determination of ibuprofen in human plasma with ibuprofen-d3 as a stable isotopically labeled internal standard (SIL-IS). Human plasma samples were prepared by one-step protein precipitation. The chromatographic separation was achieved on a Poroshell 120 EC-C₁₈ (2.1 × 50 mm, 2.7 μm). Aqueous solution (containing 0.05% acetic acid and 5 mm NH₄Ac) and methanol were selected as the mobile phase with gradient elution. An electrospray ionization source was applied and operated in negative ion mode. Multiple reaction monitoring mode was used for quantification using target fragment ions m/z 205.0 → 161.1 for ibuprofen and m/z 208.0 → 164.0 for SIL-IS, respectively. This method exhibited a linear range of 0.05–36 μg/ml for ibuprofen with correlation coefficient >0.99. Mean recoveries of ibuprofen in human plasma ranged from 78.4 to 80.9%. The RSD of intra- and inter-day precision were both < 5%. The accuracy was between 88.2 and 103.67%. The matrix effect was negligible in human plasma, including lipidemia and hemolytic plasma. A simple, efficient and accurate LC–MS/MS method was successfully established and applied to a pharmacokinetic study in healthy Chinese volunteers after a single oral administration of ibuprofen granules.     

Langevin dynamic for the 2D Yang–Mills measure

Publications mathématiques de l'IHÉS - It is well known that a real analytic symplectic diffeomorphism of the $2d$ -dimensional disk ( $d\geq 1$ ) admitting the origin as a...     

接地式三要素型动力吸振器性能分析

利用固定点理论优化接地类型的动力吸振器得到的结果可能不是全局最优参数,在选择其他参数时主系统可以获得更小的振幅, 接地类型动力吸振器的优化问题值得进一步研究. 因此,以一种接地式三要素型动力吸振器为对象,通过研究系统参数变化对固 定点位置与主系统最大振幅的影响,得到了此吸振器的局部最优参数并分析了它的性能. 首先建立了此系统模型的运动微分方程, 得到了主系统振幅放大因子,发现系统存在3个与阻尼无关的固定点. 固定点中幅值较大点随系统参数变化的趋势可以代表最大振 幅随系统参数变化的趋势,因此利用盛金公式得到了固定点幅值的表达式. 为了更加精确,进一步使用数值算法得到了最大振幅与 系统参数的关系图,发现系统中存在局部最优参数. 通过对比接地式吸振器与接地三要素型吸振器的最大振幅随系统参数变化的趋 势,得到了接地式三要素型吸振器的局部最优参数,并发现当固有频率比小于局部最优频率比时,接地式三要素型吸振器模型主系 统的最大振幅要远小于接地式动力吸振器模型.