Forcing Patterns Of Organic Molecules On Graphene Surfaces

ORIGINAL: ACS

By Prachi Patel, special to C&EN

Materials: Polymer stamps functionalize graphene surfaces by accelerating Diels-Alder reactions between inks and the material

Forced Patterns. A stamp coated in a cyclopentadiene ink and attached to an atomic force microscope created this repeating pattern of two-by-three dots of dye on a graphene surface. The inset image shows a magnification of one of these patterns.  Credit: J. Am. Chem. Soc.

To fabricate electronic devices that take advantage of graphene’s great conductivity and strength, materials scientists first need to chemically modify the material to tweak its other properties. Attaching biomolecules, for instance, could enable new types of sensors, and patterning graphene with impurities would make the material behave like a semiconductor, needed for many electronic devices.

Unfortunately, graphene often resists such functionalization. Now chemists report that a little force does the trick (J. Am. Chem. Soc. 2013, DOI: 10.1021/ja4042077).

A team led by Adam B. Braunschweig at the University of Miami and Kendall N. Houk at the University of California, Los Angeles, used pressure to accelerate Diels-Alder reactions on a graphene surface to produce patterns of covalent modifications. Other researchers had shown that graphene can participate in Diels-Alder reactions either as the diene or the dienophile, the two classes of reactants in the ring-forming reaction (J. Am. Chem. Soc. 2011, DOI:10.1021/ja200118b). It’s also well-known that high pressure accelerates the reaction.

FUNCTIONAL DRAWING. Cyclopentadiene ink pushed into a graphene surface accelerates a Diels-Alder reaction.

The chemists coated a two-by-three array of 80-nm-wide polymer tips with inks containing various molecules linked to cyclopentadiene, a classic Diels-Alder reactant. For one of the inks, they attached the dye cyanine 3 to cyclopentadiene. The researchers mounted the tip array onto an atomic force microscope and gently pushed the tips into the surface of graphene. The cyclopentadienes reacted with the graphene, resulting in 20-µm × 40-µm patches of graphene decorated with a two-by-three pattern of dye dots.

The technique works at ambient temperatures and pressures, the chemists note. They are now trying to use the method to functionalize graphene with carbohydrates to make biological sensors.

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