Tetradentate Cyclometalated Platinum(II) Complexes for Efficient and Stable Organic Light-Emitting Diodes

As one of the most important phosphorescent emitters, tetradentate cyclometalated platinum(II) complexes have attracted much attention in recent years, because of the high luminescent efficiency, emission spectra, and color tuned easily, especially for the development of high-efficient deep-blue and “pure” blue emitters and single-doped white organic light-emitting diodes (OLEDs). Also, some platinum(II)-based OLEDs exhibited superior operational stability, indicating their potentials in full-color display and solid-state lighting applications. In this chapter, we will introduce the recent advances of the tetradentate cyclometalated platinum(II) complexes, including pyrazole, N-heterocyclic carbene, imidazole and pyridine-based complexes, molecular design, photophysical properties, and some of their device performances

Substituent effects on geometric and electronic properties of iron tetraphenylporphyrin: a DFT investigation

To investigate the effects of the substituents, substituent positions and axial chloride ligand on the geometric and electronic properties of the iron tetraphenylporphyrin (FeTPP), a series of the substituented iron tetraphenylporphyrins and their chlorides, FeT(o/p-R)PP and FeT(o/p-R)PPCl (R = -H, -Cl, -NO2, -OH, -OCH3), were systematically calculated without any symmetry constraint by using DFT method. For geometric structure, the substituent position and axial Cl ligand change the configuration of the iron porphyrin obviously. The ortho-substituents prefer making the phenyls perpendicular to the porphyrin ring; the axial chloride draws the central Fe ion similar to 0.500 out of the porphyrin plane toward the ligand. With regard to electronic properties, it is found that E-LUMO could be related to the catalytic activity. The electron-withdrawing group always lowers the energies of both frontier orbitals, while the electron-donating one heightens them simultaneously, but they affect the E-HOMO and E-LUMO in the same sequence, -NO2 < -Cl < -H < -OH < -OCH3. The substituent effects on the central Fe ion were explored by calculating NBO charge distribution, spin density and natural electron configuration

Exploring Deep Learning for Metalloporphyrins: Databases, Molecular Representations, and Model Architectures

Metalloporphyrins have been studied as biomimetic catalysts for more than 120 years and have accumulated a large amount of data, which provides a solid foundation for deep learning to discover chemical trends and structure-function relationships. In this study, key components of deep learning of metalloporphyrins, including databases, molecular representations, and model architectures, were systematically investigated. A protocol to construct canonical SMILES for metalloporphyrins was proposed, which was then used to represent the two-dimensional structures of over 10,000 metalloporphyrins in an existing computational database. Subsequently, several state-of-the-art chemical deep learning models, including graph neural network-based models and natural language processing-based models, were employed to predict the energy gaps of metalloporphyrins. Two models showed satisfactory predictive performance (R2>0.94) with canonical SMILES as the only source of structural information. In addition, an unsupervised visualization algorithm was used to interpret the molecular features learned by the deep learning models

Metal-Free Aerobic Oxidation of Nitro-Substituted Alkylarenes to Carboxylic Acids or Benzyl Alcohols Promoted by NaOH

Efficient and selective aerobic oxidation of nitro-substituted alkylarenes to functional compounds is a fundamental process that remains a challenge. Here, we report a metal-free, efficient, and practical approach for the direct and selective aerobic oxidation of nitro-substituted alkylarenes to carboxylic acids or benzyl alcohols. This sustainable system uses O₂ as clean oxidant in a cheap and green NaOH/EtOH mixture. The position and type of substituent critically affect the products. In addition, this sustainable protocol enabled gram-scale preparation of carboxylic acid and benzyl alcohol derivatives with high chemoselectivities. Finally, the reactions can be conducted in a pressure reactor, which can conserve oxygen and prevent solvent loss. The approach was conducive to environmental protection and potential industrial application

Metal-Free Aerobic Oxidation of Nitro-Substituted Alkylarenes to Carboxylic Acids or Benzyl Alcohols Promoted by NaOH

Efficient and selective aerobic oxidation of nitro-substituted alkylarenes to functional compounds is a fundamental process that remains a challenge. Here, we report a metal-free, efficient, and practical approach for the direct and selective aerobic oxidation of nitro-substituted alkylarenes to carboxylic acids or benzyl alcohols. This sustainable system uses O₂ as clean oxidant in a cheap and green NaOH/EtOH mixture. The position and type of substituent critically affect the products. In addition, this sustainable protocol enabled gram-scale preparation of carboxylic acid and benzyl alcohol derivatives with high chemoselectivities. Finally, the reactions can be conducted in a pressure reactor, which can conserve oxygen and prevent solvent loss. The approach was conducive to environmental protection and potential industrial application

A DFT investigation of the effects of doped Pb atoms on Pd-n clusters (13 <= n <= 116)

Basic properties of cuboctahedral Pd-Pb clusters ranging from 13 to 116 atoms were studied by computational analysis, and the effects of doped Pb atoms on Pd clusters were investigated. The average bond length of Pd-Pb clusters was found to be similar to 0.1 A longer than pure ones, but doped Pb atoms did not constantly expand the Pd-Pd bond lengths in Pd-Pb clusters owing to size effect. In addition, doped Pb atom changed the thickness of surface phase and surface morphology of Pd cluster. The chemical activity of Pd clusters could be enhanced by the doped Pd atoms, although an enough size was required. Lead atoms essentially changed the surface charge population of Pd clusters. The Pd atoms in Pd-Pb clusters were seen to become more electrophilic than in pure Pd clusters, and the probability of being attacked by nucleophilic reagent could be comparable with that of being attacked by electrophilic reagent. Total electron density and deformation electron density revealed that the nature of interaction between metal atoms was metal bond. Weak covalent bond might exist when clusters were in small size. (C) 2011 Elsevier B.V. All rights reserved

Aqueous-phase hydrodechlorination of 4-chlorophenol on palladium nanocrystals : identifying the catalytic sites and unraveling the reaction mechanism

Hydrodechlorination (HDC) catalyzed by palladium has important applications in the disposal of chlorinated organic pollutants (COPs), yet the associated catalytic sites and the underlying reaction mechanism have not been clearly revealed. Here, we use Pd nanocrystals (Pd NCs) as the probe catalyst to investigate the HDC catalytic sites as well as the reaction mechanism in aqueous solution with 4-chlorophenol as the model COP. It was found that the numbers of edge and corner atoms (defect atoms) on cubic Pd NCs with varying sizes (6.3–18.4 nm) showed linear correlation with the HDC activity, suggesting that these defect atoms are the main catalytic sites for HDC. The production of chloride ion, the absence of Ullmann coupling product in the absence of H2, and the positive effect of electron-withdrawing substituents on HDC demonstrate that the HDC should include an oxidative addition process that follows the nucleophilic aromatic substitution.MOE (Min. of Education, S’pore

Synthesis of substituted meso-tetraphenylporphyrins in mixed solvent systems

An efficient synthetic method of substituted meso-tetraphenylporphyrins with better isolated yields was proposed by using propionic acid, valeric acid and m-nitrotoluene as mixed-solvent systems. The porphyrin yields in mixed solvent systems were obviously higher than those in the single propionic acid or valeric acid as solvents. The further investigation showed that the acidity, polarity, viscosity and the property of oxidant played an important role to the synthesis of porphyrin. Compared with other oxidants, m-nitrotoluene as an excellent oxidant could completely transform tetraphenylporphyrinogen to tetraphenylporphyrin