The density functional theory method (M05-2X/6-31G(d)) was used to investigate reaction mechanisms for deoxygenation of graphene oxides (GOs) with hydrazine or heat treatment. Three mechanisms were identified as reducing epoxide groups of GO with hydrazine as a reducing agent. No reaction path was found for the hydrazine-mediated reductions of the hydroxyl, carbonyl, and carboxyl groups of GO. We instead discovered the mechanisms for dehydroxylation, decarbonylation, and decarboxylation using heat treatment. The hydrazine de-epoxidation and thermal dehydroxylation of GO have opposite dependencies on the reaction temperature. In both reduction types, the oxygen functionalities attached to the interior of an aromatic domain in GO are removed more easily, both kinetically and thermodynamically, than those attached at the edges of an aromatic domain. The hydrazine-mediated reductions of epoxide groups at the edges are suspended by forming hydrazino alcohols. We provide atomic-level elucidation for the deoxyge...

Hydrazine and Thermal Reduction of Graphene Oxide: Reaction Mechanisms, Product Structures, and Reaction Design

In this review, we discuss the most recent progress on graphene-related nanomaterials, including doped graphene and derived graphene nanoribbons, graphene oxide, graphane, fluorographene, graphyne, graphdiyne, and porous graphene, from both experimental and theoretical perspectives, and emphasize tuning their stability, electronic and magnetic properties by chemical functionalization.

Graphene-related nanomaterials: tuning properties by functionalization

Graphene has attracted great interest for its superior physical, chemical, mechanical, and electrical properties that enable a wide range of applications from electronics to nanoelectromechanical systems. Functionalization is among the significant vectors that drive graphene towards technological applications. While the physical properties of graphene have been at the center of attention, we still lack the knowledge framework for targeted graphene functionalization. In this critical review, we describe some of the important chemical and physical processes for graphene functionalization. We also identify six major challenges in graphene research and give perspectives and practical strategies for both fundamental studies and applications of graphene (315 references).

Chemistry and physics of a single atomic layer: strategies and challenges for functionalization of graphene and graphene-based materials

Understanding the properties of electronically excited states is a challenging task that becomes increasingly important for numerous applications in chemistry, molecular physics, molecular biology, and materials science. A substantial impact is exerted by the fascinating progress in time-resolved spectroscopy, which leads to a strongly growing demand for theoretical methods to describe the characteristic features of excited states accurately. Whereas for electronic ground state problems of stable molecules the quantum chemical methodology is now so well developed that informed nonexperts can use it efficiently, the situation is entirely different concerning the investigation of excited states. This review is devoted to a specific class of approaches, usually denoted as multireference (MR) methods, the generality of which is needed for solving many spectroscopic or photodynamical problems. However, the understanding and proper application of these MR methods is often found to be difficult due to their comp...

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Multireference Approaches for Excited States of Molecules.

Graphene oxide shows stress-induced toxicity properties in vivo under different pathophysiological conditions. A dual-path chemical mechanism, involving the overproduction of hydroxyl radicals and the formation of oxidizing cytochrome c intermediates, is responsible for the toxicity properties.

Unraveling Stress‐Induced Toxicity Properties of Graphene Oxide and the Underlying Mechanism

When an all-benzenoid nanographene is linearly unzipped into oxygen-joined fragments, the oxidized benzenoid rings (aromatic sextets) selectively adopt the low-spin (ΔS = 0) or high-spin conformation (ΔS = 1) to yield the thermally most stable isomer. The selection of the conformation depends simply on the position of the aromatic sextets: the inner ones prefer the high-spin conformation, whereas the peripheral ones prefer the low-spin conformation. Therefore, the resulting most stable isomer has a total spin whose value equals the number of inner aromatic sextets (ni) along the oxidizing line. The nanographene fragments contained in this isomer have a ferromagnetic spin coupling. Due to the tautomerization between the high-spin and low-spin conformations, there also exist other possible isomers with higher energies and with spins at ground state ranging from 0 to (ni − 1). The rich geometrically correlated spins and the adjustable energy gaps indicate great potential of the graphene oxides in spintronic ...

Oxidation Unzipping of Stable Nanographenes into Joint Spin-Rich Fragments

Projector Monte Carlo method based on configuration state functions. Test applications to the H4 system and dissociation of LiH

Projector Monte Carlo method based on Slater determinants: Test application to singlet excited states of H2O and LiF

A new sampling method is proposed for projector Monte Carlo (PMC) calculations based on Slater determinants (SD) in singlet states. Using the symmetry of the α and β electron determinants, the number of configurations to be considered can be about one-half of the original sampling. We applied the new sampling to the PMC-SD calculations of the H2O molecule in the ground state. The results were always improved by the new sampling method both for the equilibrium and for bond-stretched structures.

Projector Monte Carlo method based on Slater determinants: a new sampling method for singlet state calculations

Mechanisms of the cycloaddition reactions of singlet difluorocarbene (CF2) to alkenes and disilene were studied using CASSCF, MR-MP2, CR-CC(2,3), and UB3LYP methods in combination with basis sets up to 6-311++G(3d,p). The CASSCF(4,4) energies suggest that the cycloadditions all follow the stepwise mechanism. However, energies calculated using the MR-MP2(4,4) and CR-CC(2,3) methods in combination with the 6-311G(d) or larger basis sets consistently show that the reactions follow a concerted mechanism. The stepwise mechanisms predicted at the CASSCF level are “artificial” because of their neglect of dynamic electron correlation effects. The importance of dynamic electron correlation in determining the mechanistic nature of the reactions is explained through knowledge of the reacting system’s geometries and charges along the reaction path.

Yuhki Ohtsuka

Papers

Oxidation Unzipping of Stable Nanographenes into Joint Spin-Rich Fragments

Projector Monte Carlo method based on configuration state functions. Test applications to the H4 system and dissociation of LiH

Projector Monte Carlo method based on Slater determinants: Test application to singlet excited states of H2O and LiF

Projector Monte Carlo method based on Slater determinants: a new sampling method for singlet state calculations

Mechanism and dynamic correlation effects in cycloaddition reactions of singlet difluorocarbene to alkenes and disilene.