2,2′-bipyridine-functionalized single-walled carbon nanotubes: The formation of transition metal complexes and their charge transfer effects

There is presently a great interest in the development of versatile nanohybrid systems that are based on the covalent functionalization of carbon nanotubes. Covalent functionalization of the single walled carbon nanotubes (SWCNTs) enhances their processability and functionality, allowing them to be further used in different applications. However, at the same time this leads to a disturbance of the nanotube π-network, thus reducing its intrinsically distinct physical and chemical properties of nanotubes. In the optimal situation, covalently functionalized SWCNT nanohybrid materials could be formed in a way where both of these wanted properties would exist; Good processability and the electronic properties nanotubes had before the functionalization. In this work, we describe the formation of nanohybrid materials by covalently grafting bipyridyl ligands directly onto the sidewall of the SWCNT. This is followed by addition of several different transition metals to form organometallic complexes. The systems we describe here does not utilize linker molecules between the ligands and the nanotubes allowing a better electronic communication between them. The covalent addition of the ligand onto the sidewall first causes p-type doping which is reversed to n-type doping after the addition of a transition metal. This technique offers a possibility to tune the electronic properties through reversing doping in charge transport between substrates and SWCNT. All new nanotube hybrids were fully characterized with the help of FTIR, XPS, Raman spectroscopy and HRTEM.