[Show abstract][Hide abstract] ABSTRACT: Most of the interesting physics of graphene results from the singular electronic band structure at the so-called Dirac point, where the conduction and valence bands cross in momentum space. Although graphene is very stable thermodynamically, the electronic structure at the Dirac point facilitates basal plane chemistry including pericyclic reactions such as the Diels-Alder reaction. We have discovered a series of facile Diels-Alder reactions in which graphene can function either as a diene when paired with tetracyanoethylene and maleic anhydride or as a dienophile when paired with 2,3-dimethoxybutadiene and 9-methylanthracene. In this Account, we seek to rationalize these findings using simple arguments based on considerations of orbital symmetry and the frontier molecular orbital theory. The graphene conduction and valence bands (HOMO and LUMO) cross at the Dirac point, which defines the work function (W = 4.6 eV). Thus, the HOMO and LUMO form a degenerate pair of orbitals at this point in momentum space with the same ionization potential (IP) and electron affinity (EA). Based on the importance of the energies of the HOMO (-IP) and LUMO (-EA) in frontier molecular orbital (FMO) theory, graphene should be a reactive partner in Diels-Alder reactions due to the very high-lying HOMO and low-lying LUMO (energies of -4.6 eV). Inspection of the orbital symmetries of the degenerate pair of half-occupied band orbitals at the Dirac point confirms that with the appropriate orbital occupancies, both diene and dienophile reaction partners should undergo concerted Diels-Alder reactions with graphene that are allowed based on the Woodward-Hoffmann principles of orbital symmetry.
Accounts of Chemical Research 03/2012; 45(4):673-82. DOI:10.1021/ar200302g · 22.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the present study, we have examined the interaction between a suspension of graphene in dimethylformamide and an aqueous solution of hydrofluoric acid, which was found to result in partial fluorination of suspension flakes. A considerable decrease in the thickness and lateral sizes of the graphene flakes (up to 1-5 monolayer in thickness and 100-300 nm in diameter) with increasing the duration of fluorination treatment is found to be accompanied with simultaneous transition of the flakes from conducting to insulating state. Smooth and uniform insulating films with roughness ~ 2 nm and thicknesses down to 20 nm were deposited from the suspension on silicon. The electrical and structural properties of the films suggest their use as insulating elements in thin-film nano- and microelectronics device structures. In particular, it was found that the films prepared from the fluorinated suspension display rather high breakdown voltages (field strength of (1-3)x106 V/cm), ultra low densities of charges in the film and at the interface with silicon substrate in metal-insulator-semiconductor structures (~ (1-5)х1010cm-2). Such excellent characteristics of the dielectric film can be compared only to well developed SiO2 layers. The films from the fluorinated suspension are cheap, practically feasible and easy to produce.
[Show abstract][Hide abstract] ABSTRACT: We applied ab initio computational methods based on density functional theory to study the properties of graphene and single-walled carbon nanotubes functionalized with benzyne. The calculations were carried out using the SIESTA electronic structure code combined with the generalized gradient approximation for the exchange correlation functional. Our study showed that the reaction of cycloaddition of benzyne to pristine graphene was exothermic with the possibility of formation of both [2 + 2] and [4 + 2] reaction products. The binding energies of benzyne molecules attached to semiconducting zigzag and metallic armchair nanotubes were found to be inversely proportional to the nanotube diameter. The linear fits of the binding energies between benzyne and carbon nanotubes extrapolated to the zero curvature limit were in good agreement with the binding energies of benzyne attached to graphene. Our calculations demonstrated that the cycloaddition of benzyne could open up a nonzero gap between the valence and conduction bands of graphene and metallic carbon nanotubes. The value of the band gap was significantly affected by the geometry of benzyne attachment and by the choice of the supercell.
The Journal of Physical Chemistry C 07/2015; · 4.77 Impact Factor
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