Substituent Effects on the Structural Features and Nonlinear Optical Properties of the Organic Alkalide Li+(calix[4]pyrrole)Li−

The effects of substituents on the structure, character, and nonlinear optical (NLO) properties of the organic alkalide Li⁺(calix[4]pyrrole)Li^? were studied by density functional theory. Natural bond orbital analysis and vertical ionization energies reveal that electron‐donating substituents strengthen the alkalide character of Li⁺(calix[4]pyrrole)Li^? and that they are beneficial for a larger first hyperpolarizability (β₀) value. However, electron‐withdrawing substituents have the opposite effect. The dependence of the NLO properties on the number of substituents and their relative position was detected in multisubstituted Li⁺(calix[4]pyrrole)Li^? compounds. For both the amino‐ and methyl‐substituted derivatives, the polarizabilities and the first hyperpolarizabilities increase as more pyrrole β‐H atoms are substituted. Moreover, distribution of the substituents so that they are as far away from each other as possible resulted in an increase in the β₀ value. The new knowledge obtained in this study may provide an effective approach to enhance the NLO responses of alkalides by employing pyrrole derivatives as complexants.     

Substituent Effects on the Photochromic Properties of Benzothiophene‐Based Derivatives

Five diarylethene photochromic derivatives, the structures of which incorporate a central benzothiophene unit, a left‐hand thiazole group, and a right‐hand benzothiophene group, have been prepared. The compound with a thiazole unit with no substituent on the reaction‐center carbon atom reveals an unprecedented transformation upon light irradiation. When the 4‐position of thiazole is protected by a methyl group, the compounds show high photosensitivity and photochromic properties. In this case, light irradiation affords new compounds with [5]helicene structures featuring the highest redshifted absorption maxima reported to date.     

Theoretical Study of the Substituent Effects on the Nonlinear Optical Properties of a Room‐Temperature‐Stable Organic Electride

Excess‐electron compounds can be considered as novel candidates for nonlinear optical (NLO) materials because of their large static first hyperpolarizabilities (β₀). A room‐temperature‐stable, excess‐electron compound, that is, the organic electride Na@(TriPip222), was successfully synthesized by the Dye group (J. Am. Chem. Soc. 2005 , 127, 12416). In this work, the β₀ of this electride was first evaluated to be 1.13×10⁶ au, which revealed its potential as a high‐performance NLO material. In particular, the substituent effects of different substituents on the structure, electride character, and NLO response of this electride were systemically studied for the first time by density functional theory calculations. The results revealed that the β₀ of Na@(TriPip222) could be further increased to 8.30×10⁶ au by introducing a fluoro substituent, whereas its NLO response completely disappeared if one nitryl group was introduced because the nitro‐group substitution deprived the material of its electride identity. Moreover, herein the dependence of the NLO properties on the number of substituents and their relative positions was also detected in multifluoro‐substituted Na@(TriPip222) compounds.     

On the Additivity of Molecular Fragment Dipole Moments of 5‐Substituted Indole Derivatives

The estimate of the magnitude and the orientation of molecular electric dipole moments from the vector sum of bond or fragment dipole moments is a widely used approach in chemistry. However, the limitations of this intuitive model have rarely been tested experimentally, particularly for electronically excited states. Herein, we find rules for a number of indole derivatives by using rotationally resolved electronic Stark spectroscopy and ab initio calculations. Based on a natural‐bond‐orbital analysis, we discuss whether the vector additivity rule can be applied in a given electronic state. From a comparison of the experimental data with ab initio calculations, we deduced that the additivity model does not apply when the flow of electron density from the substituent is opposed to that inside the chromophore.     

Fine Substituent Effects in Sandwich Complexes: A Threshold Ionization Study of Monosubstituted Chromium Bisarene Compounds

Mass‐analyzed threshold ionization spectra of jet‐cooled [(η⁶‐PhMe)(η⁶‐PhH)Cr] and [(η⁶‐Ph₂)(η⁶‐PhH)Cr] reveal with unprecedented accuracy the effects of methyl and phenyl groups on the electronic structure of bis(η⁶‐benzene)chromium. These “pure” substituent effects allow quantitative experimental determination of the ionization energy changes caused by the mutual substituent influence in bisarene systems. Two types of such influence have been revealed for the first time in bis(η⁶‐toluene)chromium.     

First-Principles Investigation of the Electronic and Conducting Properties of Oligothienoacenes and their Derivatives

Herein, we calculated reorganization energies, vertical ionization energies, electron affinities, and HOMO–LUMO gaps of fused thiophenes and their derivatives, and analyzed the influence of different substituents on their electronic properties. Furthermore, we simulated the angular resolution anisotropic mobility for both electron- and hole-transport, based on quantum-chemical calculations combined with the Marcus–Hush electron-transfer theory. We showed that: 1) styrene-group substitution can effectively elevate the HOMO energy level and lower the LUMO energy level, and therefore lower both the hole- and electron-injection barriers; and 2) chemical oxidation of the thiophene ring can significantly improve the semiconductor properties of the fused oligothiophenes through a decrease of the injection barrier and an increase in the charge-transfer mobility for electrons but without lowering their hole-transfer mobilities, which suggests that it may be a promising way to convert p-type semiconductors into ambipolar or n-type semiconductor materials.     

Functionalization of Hexa‐peri‐hexabenzocoronenes: Investigation of the Substituent Effects on a Superbenzene

We have demonstrated that the iridium‐catalyzed direct borylation of hexa‐peri‐hexabenzocoronene (HBC) enables regioselective introduction of boryl groups to the para‐, ortho‐, and meta‐substituted HBCs in high yields. The boryl groups have been transformed into various functionalities such as hydroxy, cyano, ethynyl, and amino groups. We have elucidated that the substituents significantly influence the photophysical properties of HBCs to enhance fluorescence quantum yields. DFT calculations revealed that the origin of the substituent effect is the lift in degeneracy in the frontier orbitals by an interaction with electron‐donating and electron‐withdrawing substituents at the para‐ and ortho‐positions. The change in molecular orbitals results in an increase of the transition probability from the S₀→S₁ states. In addition, the two‐photon absorption cross‐section values of para‐substituted HBCs are significantly larger than those of ortho‐ and meta‐substituted HBCs.     

Adsorption Mechanism of Benzene Derivatives by Pagoda[n]arenes

Despite the widespread use in industrial production, benzene derivatives are harmful to both human beings and the environment. The control of these substances has become an important subject of scientific research. This study introduces a new approach for adsorption and separation of benzene derivatives utilizing pagoda[n]arene based supramolecular materials. Density functional theory calculations were employed to investigate the molecular recognition mechanism of benzene derivatives by pagoda[4]arenes and pagoda[5]arenes (Pa[4]As and Pa[5]As). Results indicate that Pa[4]As and Pa[5]As can effectively accommodate benzene derivatives through non-covalent interactions, leading to the formation of stable host-guest complexes. Additionally, molecular dynamics simulations revealed that both crystalline and non-crystalline supramolecular aggregates of Pa[4]As and Pa[5]As possess the ability to adsorb benzene derivatives and maintain the stability of the adsorption. Moreover, increasing the temperature causes benzene derivatives to desorb from the adsorbing aggregates, and thus the material can be reutilized.     

HXeBr与苯和苯的衍生物弱相互作用的理论研究

采用MP2/aug-cc-pVDZ (对于Xe和I原子采用aug-cc-pVDZ-PP基组)优化了复合物HXeBr…C₆H₅X (X=H, CH₃, NH₂, N(CH₃)₂, NHCH₃, OH, OCH₃, CN, F, Cl, Br, I, COOH, SO₃H, CF₃)及单体的几何构型, 详细分析了π…H键和双齿氢键两种弱相互作用类型的特征, 以及不同的取代基对这两种弱相互作用能的影响. 对14个双齿氢键型复合物, 我们发现复合物的相互作用能与苯环衍生物(C₆H₅X)的偶极矩, 复合物中Xe-Br键键长的变化, H-Xe键键长的变化和H-Xe键振动频率的变化, 以及双齿氢键上Br原子和两个H原子范德华表面相互穿透距离之和均有较好的线性关系. 另外, 我们还发现复合物的相互作用能与双齿氢键上两个键临界点的电子密度之和, 电子密度Laplacian值之和, 静电势之和, 以及双齿氢键和苯环碳原子形成环的环临界点处的电子密度, 电子密度Laplacian值以及静电势均有着较好的线性关系.     

高能化合物热解机理和撞击感度的理论研究-苯和苯胺类硝基衍生物

在DFT-B3LYP/6-31G*水平求得苯和苯胺类硝基衍生物的全优化分子几何和电子结构。通过非限制性 (U) B3LYP/6-31G*计算求得标题物各化学键离解能(BDE)。用UHF-PM3 MO方法求得引发键C-NO2键均裂反应的活化能(Ea)。以静态指标(键集居数、前线轨道能级差和硝基上净电荷)和动态理论指标(BDE和Ea) 阐明了热解引发机理,关联了实验撞击感度。运用SPSS程序关联静态和动态理论指标,表明它们可平行或等价地用作预示标题物的热解引发机理和撞击感度。     

Substituent Effects of Tetracoordinate Boron in Organic Synthesis

The present review focuses on recent examples of tetracoordinate boryl groups greatly influencing reactions in organic synthesis. Electron-rich tetracoordinate boryl groups stabilize or activate reactive intermediates such as cations, radicals and π-conjugation systems, and interaction of the intermediates with carbon-boron or heteroatom-boron bonds is the origin of such substituent effects. Unique substituent effects of tetracoordinate boryl groups often promote desired reactions and affect results of reactions such as yield and selectivity of products.     

A Density Functional Theory Investigation of the Cobalt‐Mediated η5‐Pentadienyl/Alkyne [5+2] Cycloaddition Reaction: Mechanistic Insight and Substituent Effects

Alkyl‐substituted η⁵‐pentadienyl half‐sandwich complexes of cobalt have been reported to undergo [5+2] cycloaddition reactions with alkynes to provide η²,η³‐cycloheptadienyl complexes under kinetic control. DFT studies have been used to elucidate the mechanism of the cyclization reaction as well as that of the subsequent isomerization to the final η⁵‐cycloheptadienyl product. The initial cyclization is a stepwise process of olefin decoordination/alkyne capture, C? C bond formation, olefin arm capture, and a second C? C bond formation; the initial decoordination/capture step is rate‐limiting. Once the η²,η³‐cycloheptadienyl complex has been formed, isomerization to η⁵‐cycloheptadienyl again involves several steps: olefin decoordination, β‐hydride elimination, reinsertion, and olefin coordination; also here the initial decoordination step is rate limiting. Substituents strongly affect the ease of reaction. Pentadienyl substituents in the 1‐ and 5‐positions assist pentadienyl opening and hence accelerate the reaction, while substituents at the 3‐position have a strongly retarding effect on the same step. Substituents at the alkyne (2‐butyne vs. ethyne) result in much faster isomerization due to easier olefin decoordination. Paths involving triplet states do not appear to be competitive.     

9,9‐Dimethylxanthene Derivatives with Room‐Temperature Phosphorescence: Substituent Effects and Emissive Properties

Room‐temperature phosphorescence (RTP) emitters with ultralong lifetimes are emerging as attractive targets because of their potential applications in bioimaging, security, and other areas. But their development is limited by ambiguous mechanisms and poor understanding of the correlation of the molecular structure and RTP properties. Herein, different substituents on the 9,9‐dimethylxanthene core (XCO) result in compounds with RTP lifetimes ranging from 52 to 601 ms, which are tunable by intermolecular interactions and molecular configurations. XCO‐PiCl shows the most persistent RTP because of its reduced steric bulk and multiple sites of the 1‐chloro‐2‐methylpropan‐2‐yl (PiCl) moiety for forming intermolecular interactions in the aggregated state. The substituent effects reported provide an efficient molecular design of organic RTP materials and establishes relationships among molecular structures, intermolecular interactions, and RTP properties.     

Theoretical Study on Intramolecular Proton Transfer of Perylenequinonoid Derivatives

In the past two decades, perylenequinonoid derivatives (PQD), such as hypocrellin A (HA), hypocrellin B (HB) and hypericin (HYP) have attracted considerable attention owing to their excellent properties of photosensitization and great advantages over the investigation of intramolecular proton transfer (IPT)1-5. Previous researches demonstrated that IPT both in the ground state and excited states exists in PQD and is critical for PQD to reserve their photosensitive activity3,6. Altho…     

Some Novel Conducting Polythiophene Derivatives: Theoretical Analysis,Synthesis, Characterization and Electroreological Properties

A series of alternating phylene and symmetrically bithiophene containing repeat units and the respective homopolymers have been synthesized and characterized by combining FTIR, UV-Vis spectroscopy, four probe conductivity measurement, TGA and SEM analysis. Quantum mechanical calculations of the structures and infrared spectra of the monomers and respective dimers were compared with experimental results. The polymers are soluble in N-methyl-pyrrolidone (NMP). The samples have conductivities of 10^?5 S/cm levels. Thermal degradation analysis results indicated that poly-bithiophene derivatives have higher thermal stabilities than poly-monothiophene derivatives. All samples exhibited different surface morphologies. The electrorheological (ER) properties of polymer suspensions in silicone oil were prepared and ER behavior was investigated as a function of shear rate, electric field strength and frequency.     

Can Variations of 1H NMR Chemical Shifts in Benzene Substituted with an Electron‐Accepting (NO2)/Donating (NH2) Group be Explained in Terms of Resonance Effects of Substituents?

The classical textbook explanation of variations of ¹H NMR chemical shifts in benzenes bearing an electron‐donating (NH₂) or an electron‐withdrawing (NO₂) group in terms of substituent resonance effects was examined by analyzing molecular orbital contributions to the total shielding. It was found that the π‐electronic system showed a more pronounced shielding effect on all ring hydrogen atoms, relative to benzene, irrespective of substituent +R/?R effects. For the latter, this was in contrast to the traditional explanations of downfield shift of nitrobenzene proton resonances, which were found to be determined by the σ‐electronic system and oxygen in‐plane lone pairs. In aniline, the +R effect of NH₂ group can be used to fully explain the upfield position of meta‐H signals and partly the upfield position of para‐H signals, the latter also being influenced by the σ‐system. The position of the lowest frequency signal of ortho‐Hs was fully determined by σ‐electrons.     

苯的硝基和叠氮基衍生物的理论研究

在密度泛函理论B3LYP/6-31G*水平下优化了91个苯的硝基(NO₂)和叠氮基(N₃)衍生物的分子几何构型, 预测了它们的密度和生成热, 采用Kamlet-Jacobs方法计算了爆速和爆压, 筛选得到11种爆轰性能较好的高能量密度化合物(HEDC), 计算了它们的多个可能的热解引发键的键离解能(BDE)以及按“氧化呋咱机理”分解时的活化能(E_a). 结果表明, 当分子中有NO₂与N₃相邻时, 分解按“氧化呋咱机理”进行, 分解反应的E_a均大于100 kJ/mol|分子中没有NO₂和N₃相邻时, 热解始于C-NO₂或C-N₃均裂, 裂解的BDE都大于200 kJ/mol. 只含NO₂或N₃的7个物质的稳定性好于同时含NO₂和N₃的物质, 而只含N₃的物质的稳定性又好于只含NO₂的物质, 五叠氮苯和六叠氮苯具有很出色的爆轰性能和稳定性. 无论是能量还是稳定性方面, 筛选得到的11种物质基本符合HEDC的要求.