Controlled Generation of 9-Boratriptycene by Lewis Adduct Dissociation: Accessing a Non-Planar Triarylborane

A highly bent triarylborane, 9-boratriptycene, was generated in solution by selective protodeboronation of the corresponding tetra-aryl boron ate complex with the strong Brønsted acid HNTf₂. The iptycene core confers enhanced Lewis acidity to 9-boratriptycene, making it unique in terms of structure and reactivity. We studied the stereoelectronic properties of 9-boratriptycene by quantifying its association with small N- and O-centered Lewis bases, as well as with sterically hindered phosphines. The resultant Lewis adducts exhibited unique structural, spectroscopic, and photophysical properties. Beyond the high pyramidalization of the 9-boratriptycene scaffold and its low reorganization energy upon Lewis base coordination, quantum chemical calculations revealed that the absence of π donation from the triptycene aryl rings to the boron vacant p_z orbital is one of the main reasons for its high Lewis acidity.     

Compressing a Non-Planar Aromatic Heterocyclic [7]Helicene to a Planar Hetero[8]Circulene

This work describes a synthetic approach where a non-planar aromatic heterocyclic [7]helicene is compressed to yield a hetero[8]circulene containing an inner antiaromatic cyclooctatetraene (COT) core. This [8]circulene consists of four benzene rings and four heterocyclic rings, and it is the first heterocyclic [8]circulene containing three different heteroatoms. The synthetic pathway proceeds via a the flattened dehydro-hetero[7]helicene, which is partially a helicene and partially a circulene: it is non-planar and helically chiral as helicenes, and contains a COT motif like [8]circulenes. The antiaromaticity of the COT core is confirmed by nucleus independent chemical shift (NICS) calculations. The planarization from a helically π-conjugated [7]helicene to a fully planar heterocyclic [8]circulene significantly alters the spectroscopic properties of the molecules. Post-functionalization of the [7]helicenes and the [8]circulenes by oxygenation of the thiophene rings to the corresponding thiophene-sulfones allows an almost complete fluorescence emission coverage of the visible region of the optical spectrum (400–700 nm).     

A Mechanistic Dichotomy in Two-Electron Reduction of Dioxygen Catalyzed by N,N’-Dimethylated Porphyrin Isomers

Selective two-electron reduction of dioxygen (O₂) to hydrogen peroxide (H₂O₂) has been achieved by two saddle-distorted N,N’-dimethylated porphyrin isomers, an N21,N’22-dimethylated porphyrin ( anti -Me₂P ) and an N21,N’23-dimethylated porphyrin ( syn -Me₂P ) as catalysts and ferrocene derivatives as electron donors in the presence of protic acids in acetonitrile. The higher catalytic performance in an oxygen reduction reaction (ORR) was achieved by anti -Me₂P with higher turnover number (TON=250 for 30 min) than that by syn -Me₂P (TON=218 for 60 min). The reactive intermediates in the catalytic ORR were confirmed to be the corresponding isophlorins ( anti -Me₂Iph or syn -Me₂Iph ) by spectroscopic measurements. The rate-determining step in the catalytic ORRs was concluded to be proton-coupled electron-transfer reduction of O₂ with isophlorins based on kinetic analysis. The ORR rate by anti -Me₂Iph was accelerated by external protons, judging from the dependence of the observed initial rates on acid concentrations. In contrast, no acceleration of the ORR rate with syn -Me₂Iph by external protons was observed. The different mechanisms in the O₂ reduction by the two isomers should be derived from that of the arrangement of hydrogen bonding of a O₂ with inner NH protons of the isophlorins.     

Symmetric,Unsymmetrical, and Asymmetric [7]‐, [10]‐, and [13]Helicenes

Fully aromatic helicenes with more than one pitch‐length are illustrious synthetic targets with potential applications in advanced optical devices and nano‐electronics. The task of extending the length of fully conjugated helicenes past one pitch length is challenging. Now, the synthesis of a series of azaoxa[7]‐, [10]‐, and [13]helicenes is described. The synthesis is based on iterative oxidative furan formation between 3,6‐dihydroxycarbazoles and/or 2‐naphthols. The flexibility of the presented method allows the convenient and scalable synthesis of symmetric, unsymmetrical, and asymmetric homo‐chiral structures. The [13]helicenes can be synthetically functionalized both at the termini and the periphery. The full range of helicenes were characterized using NMR and optical spectroscopy (UV/Vis, fluorescence, and CD) along with single‐crystal X‐ray crystallography. The enantiomers of the [13]helicenes are the longest optically pure helicenes isolated to date.     

Unusual Pathways of Triplet State Dynamic Relaxation in Meso-Aryl-Substituted Porphyrins and Their Chemical Dimers at 295 K

It was found that mono- and di-meso-phenyl substitution in octaethylporphyrins (OEP)and their chemical dimers with the phenyl ring as a spacer manifests itself in the dramatical shortening of T₁ state lifetimes at 295 K (from 1.5 ms down to 2–5 s in degassed toluene solutions). On the other hand, this substitution does not influence spectral-kinetic parameters of S₀ and S₁ states. The enhancement of the T₁ state non-radiative deactivation is explained by torsional librations of the phenyl ring around a single C-C bond in sterically encumbered OEP molecules leading to non-planar dynamic distorted conformations in the excited T₁ states. For these compounds with electron-accepting NO₂-groups in the meso-phenyl ring the strong non-radiative deactivation of S₁ and T₁ states (by 2–3 orders of magnitude) is observed upon the displacement of NO₂-group from para-to ortho-position of the phenyl ring. The S₁ state quenching is caused by the direct intramolecular electron transfer to low-lying CT state of the radical ion pair (the normal region, non-adiabatic case presumably, V = 130–190 cm^–1 in dimethylformamide). The additional deactivation of the T₁ state is connected with thermally activated transitions to upper-lying CT states as well as the strengthening of intersystem crossing probabilities.     

用MOCVD方法生长的GaAs/GaAsP量子线及其特性

本实验采用普通的光刻和湿法腐蚀技术,将GaAs基片刻蚀成具有W形沟槽样的非平面结构,基片表面为(100)面,沟槽的侧斜面为(111)B面.在此基片上用低压MOCVD设备外延生长了GaAs/GaAsP多层膜,通过扫描电镜和微区拉曼光谱,研究它们的生长特性,发现GaAs和GaAsP的生长速率与基片的晶向及基片上的生长位置有关.根据这一生长特性,选择合适的W形沟道形状,用常规的量子阱外延方式,在W形沟道中央顶部突起的线条状平面上形成宝塔形生长,从而在尖端长出量子线.低温荧光光谱中观察到相应的能量峰,从而证实量子线的存在.     

单块非平面环形腔激光器的强度噪声抑制技术研究

研究了LD泵浦1319nm单块非平面环形腔(NPRO)激光器的强度噪声特性,发现随着输出功率的增加,弛豫振荡峰频率从100kHz向280kHz移动,同时弛豫振荡峰宽度增加但幅度降低,且在弛豫振荡峰处发生π相位跃变,在600kHz以上频率区域,噪声已经接近量子噪声极限。自行设计的噪声抑制电路在实现足够大增益的同时,在500kHz附近获得了约65°的相位超前,由此获得了优于通常同类实验的噪声抑制结果:当弛豫振荡峰频率为230kHz时,弛豫振荡峰处和低频区域的强度噪声幅度分别被抑制了45dB和20dB。     

Shock waves in reactive hydrodynamics

Using the weakly non-linear geometrical acoustics theory, we obtain the small amplitude high frequency asymptotic solution to the basic equations in Eulerian coordinates governing one dimensional unsteady planar, spherically and cylindrically symmetric flow in a reactive hydrodynamic medium. We derive the transport equations for the amplitudes of resonantly interacting waves. The evolutionary behavior of non-resonant wave modes culminating into shock waves is also studied.      

Controlled Generation of 9‐Boratriptycene by Lewis Adduct Dissociation: Accessing a Non‐Planar Triarylborane

A highly bent triarylborane, 9‐boratriptycene, was generated in solution by selective protodeboronation of the corresponding tetra‐aryl boron ate complex with the strong Brønsted acid HNTf₂. The iptycene core confers enhanced Lewis acidity to 9‐boratriptycene, making it unique in terms of structure and reactivity. We studied the stereoelectronic properties of 9‐boratriptycene by quantifying its association with small N‐ and O‐centered Lewis bases, as well as with sterically hindered phosphines. The resultant Lewis adducts exhibited unique structural, spectroscopic, and photophysical properties. Beyond the high pyramidalization of the 9‐boratriptycene scaffold and its low reorganization energy upon Lewis base coordination, quantum chemical calculations revealed that the absence of π donation from the triptycene aryl rings to the boron vacant p_z orbital is one of the main reasons for its high Lewis acidity.