High Quality Dispersions of Hexabenzocoronene in Organic Solvents

作者：Hughes J Marguerite; Hernandez Yenny; Aherne Damian; Doessel Lukas; Muellen Klaus; Moreton Ben; White Thomas W; Partridge Cerianne; Costantini Giovanni; Shmeliov Aleksey; Shannon Mervyn; Nicolosi Valeria; Coleman Jonathan N^*

来源：Journal of the American Chemical Society, 2012, 134(29): 12168-12179.

DOI：10.1021/ja303683v

We have studied the exfoliation and dispersion of hexabenzocoronene (HBC) in 28 different solvents We see a wide range of dispersed concentrations and aggregation states, all of which can be related to the solvent properties. To a first approximation, the dispersed concentration is maximized for solvents with Hildebrand solubility parameter close to 21 MPa1/2, similar to graphitic materials such as nanotubes and graphene. We have also studied the concentration dependence of the absorbance and photoluminescence of HBC for both a good solvent, cyclohexyl pyrrolidone (CHP), and a poor solvent, tetrahydrofuran (THF). In both cases, we observe features that can be associated with either individual molecules or aggregates, allowing us to establish metrics both for aggregate and individual molecule content. While the aggregate content always increases with concentration, good solvents disperse individual Molecules at relatively. high Concentrations while poor solvents display aggregation even at low concentrations Using these metrics; we determine that large populations of individual molecules are present at low concentrations in certain solvents with Hildebrand solubility parameters close to 21 MPa1/2. However, the aggregation state of HBC is considerably more sensitive to solvent Hildebrand parameter for halogenated solvents than for amide Solvents. We find a Combination of high overall concentrations and large populations of individual molecules in four solvents cyclohexyl pyrrolidone, 1-chloronaphthalene, 1-bromonaphthalene, and 1,2,4-trichlorobenzene. Scanning tunnelling microscopy (STM) measurements show the formation of self-assembled rnonolayers at the interface between a HBC-solvent dispersion and a highly oriented pyrolytic graphite (HOPG) substrate. Similar structures were observed on ultrathin supports by aberration-corrected transmission electron microscopy (TEM). Also observed were graphitic objects of size similar to 1 nm consistent with monomers or aggregated stacks of very few monomers. We believe this is strong evidence of the presence of individual molecules in dispersions prepared with appropriate solvents.

• 出版日期2012-7-25