Researchers at the Technical University of Munich (TUM) have succeeded in linking graphene with a chemical group called porphyrins, which are well-known because of their notable functional properties (for instance, playing a central role in chlorophyll during photosynthesis). These new hybrid structures could be used in the field of molecular electronics, catalysis or even as sensors.
Many researchers focus on wet-chemical methods for attaching the molecules to the surface of the material. The TUM team, however, decided to take a different approach: The researchers were able to link porphyrin molecules to graphene in a controlled manner in an ultra-high vacuum using the catalytic properties of a silver surface on which the graphene layer rested. When heated, the porphyrin molecules lose hydrogen atoms at their periphery and can thus form new bonds with the graphene edges.The team explains that this method creates a clean and controllable environment, in which it is possible to see exactly how the molecules bond and what types of bonds occur. The researchers used advanced atomic force microscopy to depict the chemical structure of individual molecules. For the first time the scientists have succeeded in attaching functional molecules to the edges of graphene covalently, i.e. with a stable chemical bond.
The researchers chose the porphyrin molecules as the partner for graphene because of their special properties. The molecules change their properties depending on which metals are at their center and can take on various different tasks, e.g. specifically bonding with gas molecules such as oxygen and carbon dioxide.
In the future this new method may make it possible to bond other molecules to graphene as well. The researchers also want to take even better control of the reaction, achieving targeted modifications by attaching molecules to carbon nanostructures such as graphene ribbons.