Organic molecules are rapidly finding their way into electronic architectures and photovoltaic devices. Phthalocyanines - related to the biologically important porphyrins, which includes heme and chlorophyll - are already being exploited in photovoltaic devices. However, they also display other useful bulk optical properties including dichroism and luminescence and are used in gas detection.
With this in mind, restricting phthalocyanine assemblies to 1 or 2 dimensions raises a variety of exciting issues as to what will happen to the electronic structure and hence to their physical properties. A powerful method of forming 1D-molecular arrays is the encapsulation in a carbon nanotube. Since we are dealing with planar, metallo-organic molecules the precise internal stacking order will be important when assessing the physical properties of this assembly.
For the first time near-edge X-ray absorption fine structure (NEXAFS) measurements have been used to demonstrate 1D alignment of cobalt phthalocyanine (CoPc) molecules inside carbon nanotubes. They reveal that the most probable stacking form inside the tube is consistent with the bulk α-CoPc phase. In addition, transmission electron microscope images reveal that the nanotubes have pristine surfaces, the degree of filling is near optimal, and the smallest internal diameter to host CoPc molecules is found to be 15 Å.
This new method of assembly of phthalocyanines into 1D nanostructures gives rise to a new class of nanomaterials. |