On the Way to Graphane—Pronounced Fluorescence of Polyhydrogenated Graphene

Abstract

Chemistry meets graphane: a Birch-type reaction using frozen water as a gentle proton source causes the exfoliation of graphite and formation of hydrogenated graphene with electronically decoupled π-nanodomains. This highly functionalized graphene displays pronounced fluorescence.

Writing with ring currents: selectively hydrogenated polycyclic aromatics as finite models of graphene and graphane

“…Although much of the avalanche of recent research on graphene and related carbon nanostructures has been concentrated on physical properties [1][2][3], strategies for chemical functionalization of these materials are receiving increasing attention [4][5][6][7][8][9][10][11][12]. Controlled 1.…”

Highly Regioselective Alkylation of Hexabenzocoronenes: Fundamental Insights into the Covalent Chemistry of Graphene

“…[41,42] Thesecond alkylation step takes place in close proximity to the first addend and follows an S N 2-like mechanism. The free movement of alkyl radicals in the neutral vdW complex HBC-RC is akey step of the entire sequence,and is supported by electron-hole catalysis.T ransferring these insights to the extended graphene plane leads to the conclusion that the covalent alkylation of an ideal defect-free graphene surface is highly unlikely.I no ther words,o ur findings show that alkylation of reductively activated graphene can only take place at preexisting defects or close to the periphery.S uch as cenario ultimately leads to the progressive expansion of functionalized regions around intrinsic defects and the periphery.A sa lready anticipated and based on our previous studies, [11,13] no homogeneous addend binding on the graphene surface can be expected. In general, our results provide the first experimental evidence of the free migration of the trapped radical species over the graphene surface,and arises from the characteristic combination of graphene surface reactivity and the impossibility to form stable covalent adducts far away from defects.T his finding opens new avenues in the understanding of the chemistry of graphene and it could potentially extend the scope of possible applications of graphene-based nanomaterials remarkably.…”

“…[12][13][14][15][16][17][18][19][20][21] This reductive approach allows the generation of alarge variety of covalent adducts,including alkylated, arylated, and hydrogenated graphene derivatives, which exhibit comparatively high degrees of addition. Together with the reductive bulk functionalization, the addition chemistry of graphenides deposited on surfaces [18][19][20][21] has been investigated.…”

“…Thek ey point is the use of negatively charged graphites,t he so called graphite intercalation compounds (GICs), as starting materials.InGICs,alkaline metals, such as potassium, are placed between the individual carbon sheets and the graphene layers are reductively activated by electron transfer from the metal intercalates.Ageneral feature of reductive graphene functionalization protocols seems to be an inhomogeneous distribution of addends on the surface and leads to the formation of islands of highly functionalized areas next to intact nanographenes.T his distribution has been demonstrated, for example,b yh ighresolution transmission-electron microscopy (HRTEM) of polyarylated graphene, [11] and fluorescence spectroscopy of hydrogenated graphene. [13] Despite these first successful developments,many questions concerning the reaction mechanism, including the precise sequence of activation, electron transfer, and propagation steps as well as the regiochemisty of the covalent addend binding,the role of pre-existing defects, both within the basal carbon plane and at the edges,t he inertness or reactivity of the intact basal plane,and the exact nature of the electrophile (e.g.s teric demand, redox potential) remained unanswered. One reason for this lack of knowledge is the difficulty in precise and unambiguous characterization of the reaction products,a st he common powerful tools for the structure elucidation of molecules,such as NMR spectroscopy and mass spectrometry,cannot be used for these polydisperse carbon allotropes.I nstead, indirect methods such as TEM, scanning Raman microscopy (SRM), [14,18] and thermogravimetric analysis (TGA) coupled with gas chromatography and mass spectrometry [15] had to be adapted and applied for their structural characterization.…”

Mono‐ und ditope Bisfunktionalisierung von Graphen

“…Wir haben kürzlich gezeigt, dass auf diesem nasschemischen Weg alkylierte,arylierte und hydrierte Graphenderivate mit hohen Funktionalisierungsgraden -A ddition auf beiden Seiten der Basalebene -h ergestellt werden kçnnen. [16][17][18] Im Fall von vergleichbaren Funktionalisierungsreaktionena nK ohlenstoffnanorçhren und Fullerenen haben wir [19] und andere [20] nachgewiesen, dass derartige Additionsreaktionen reversibel ablaufen kçnnen. [18,21,22] Es ist anzunehmen, dass der Grad der Retrofunktionalisierung (Schema 1b)sowohl durch die Spannungsenergie des Graphenaddukts selbst als auch durch die Stabilität der Abgangsgruppe R À bestimmt wird.…”