Although density functional theory is widely used in the computational chemistry community, the most popular density functional, B3LYP, has some serious shortcomings: (i) it is better for main-group chemistry than for transition metals; (ii) it systematically underestimates reaction barrier heights; (iii) it is inaccurate for interactions dominated by medium-range correlation energy, such as van der Waals attraction, aromatic−aromatic stacking, and alkane isomerization energies. We have developed a variety of databases for testing and designing new density functionals. We used these data to design new density functionals, called M06-class (and, earlier, M05-class) functionals, for which we enforced some fundamental exact constraints such as the uniform-electron-gas limit and the absence of self-correlation energy. Our M06-class functionals depend on spin-up and spin-down electron densities (i.e., spin densities), spin density gradients, spin kinetic energy densities, and, for nonlocal (also called hybrid)...

Density functionals with broad applicability in chemistry.

Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

Aggregation-Induced Emission: Together We Shine, United We Soar!

The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chemistry, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.

An overview of N-heterocyclic carbenes

A comprehensive review is presented on nucleus-independent chem. shift as a criterion for aromaticity. [on SciFinder (R)]

Nucleus-independent chemical shifts (NICS) as an aromaticity criterion.

"United we stand, divided we fall."--Aesop. Aggregation-induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non-emissive when they are dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM-based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high-tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed.

Aggregation-Induced Emission: The Whole Is More Brilliant than the Parts

The geometries, formation energies, electronic properties, and reactivities of Stone−Wales (SW) defects in single-walled (8,0) boron nitride nanotubes (BNNTs) were investigated by means of gradient-corrected density functional theory (DFT) computations. SW defects deform BNNTs severely and result in local curvature changes at defect sites. The energies of defect formation increase with increasing tube diameters and are orientation dependent. Depending on the SW defect orientations, additions to central 7-7 ring fusions can be either more or less favorable than to defect-free sites. The reaction energies of model H2 addition are mostly endothermic for defective as well as pristine BNNTs, but reactions at the most favorable sites near SW defect (homoelement N−N bonds followed by the B−B bond sites) are exothermic. This and the fact that the band structures of BNNTs are only slightly changed by SW and vacancy defects as well as by chemical additions at low modification ratios endow BNNTs with great applicati...

Stone-wales defects in single-walled boron nitride nanotubes: Formation energies, electronic structures, and reactivity

Aromatic Boron Wheels with More than One Carbon Atom in the Center: C2B8, C3B93+, and C5B11+†

On the Stability of Large [4n]Annulenes

The tetramethyl and tetra-tert-butyl derivatives of cyclobutadiene and tetrahedrane have been studied with ab initio and density functional methods. The ring in tetra-tert-butylcyclobutadiene displays very unequal bond lengths (1.354, 1.608 A) and confirms the earlier suspicion that the low-temperature X-ray structure was distorted. The C−C single bonds have the longest separations found to date between sp2-hybridized carbons. Tetra-tert-butyltetrahedrane, which prefers T over Td symmetry, is calculated to be 1.5 kcal/mol more stable than tetra-tert-butylcyclobutadiene (B3LYP/6-311+G(d)//B3LYP/6-31G(d)). The dications, C4R42+, dianions, C4R42-, and dilithiated species, Li2C4R4 (R = H, Me, t-Bu), also were studied to determine the effect of substitution on structure and stability. Finally, NICS (nucleus-independent chemical shifts) values were calculated and showed, as expected, the dications and dianions (4n + 2 π-electrons) to be aromatic (negative NICS(0)) and the cyclobutadienes to be antiaromatic (pos...

Theoretical Study of Tetramethyl- and Tetra-tert-butyl-Substituted Cyclobutadiene and Tetrahedrane

Oxidation of carbene-stabilized diarsenic, L:As–As:L [L: = :C{N(2,6-iPr2C6H3)CH}2] (1), with gallium chloride in a 1:4 ratio in toluene affords the dicationic diarsene complex [L:As═As:L]2+([GaCl4]−)2 (22+[GaCl4]2), while oxidation of 1 with GaCl3 in a 1:2 ratio in Et2O yields the monocationic diarsenic radical complex [L:AsAs:L]•+[GaCl4]− (2•+[GaCl4]). Strikingly, complex 2•+ is the first arsenic radical to be structurally characterized in the solid state. The nature of the bonding in these complexes was probed computationally and spectroscopically.

Paul von Ragué Schleyer

Papers

Stone-wales defects in single-walled boron nitride nanotubes: Formation energies, electronic structures, and reactivity

Aromatic Boron Wheels with More than One Carbon Atom in the Center: C2B8, C3B93+, and C5B11+†

On the Stability of Large [4n]Annulenes

Theoretical Study of Tetramethyl- and Tetra-tert-butyl-Substituted Cyclobutadiene and Tetrahedrane

Oxidation of carbene-stabilized diarsenic: diarsene dications and diarsenic radical cations.