Helical wrapping of single-walled carbon nanotubes by ionic semiconducting polymers and electronically diverse cofacial porphyrins: Spectroscopic studies of their neutral and radical ionic species

Single wall carbon nanotubes (SWNTs) possess impressive mechanical, optical, electrical, magnetic, and thermal properties. Because there exists no general method to disperse individualized SWNTs in wide range of dielectric media, development of SWNT-based materials is severely hampered. As many applications of SWNTs require preservation of the intrinsic electronic, structural, and optical properties of these species, their dispersion in variety of dielectric media calls for agents that only interact noncovalently with the nanotube surface. A key accomplishment of this work has been the development of soluble hybrids of SWNTs wrapped by ionic, semi-conducting polymers into solvents that range from water to hydrophobic tetrahydrofuran using same dispersing agent with a suitable phase transfer catalyst. AFM and TEM data of these suspended SWNTs demonstrate a self-assembled superstructure in which a highly charged semi-conducting polymer monolayer helically wraps the nanotube surface with periodic and constant morphology. In contrast to other work that has examined SWNTs enveloped by amphiphilic polymers, these systems do not exhibit polymer de-wrapping and SWNT precipitation in organic solvents. Transient optical spectroscopic studies indicate that for a fixed nanotube chirality, electronic structural homogeneity is maintained regardless of solvent; highly charged, conjugated polymers, used in combination with a suitable phase transfer agent, thus provide a general means to disperse individualized non-covalently modified SWNTs that retain their established nanotube semi-conducting and conducting properties, in a wide range of dielectric media. These ionic conjugated polymer-wrapped SWNTs were efficiently coupled with small organic molecules and chromophores into various organic solvents to develop materials which can be used in excitonic solar cell devices. Another key achievement was the utilization of chiral semiconducting polymers to drive these helically wrapped polymer-SWNT superstructures with a preferred handedness in the development of SWNT-asymmetric material.;Cofacially oriented porphyrins possess unique photo physical properties that include exciton coupling, photo induced energy and charge transfer processes, which can be fine tuned via structure modulations. However, electronically asymmetric cofacial bisporphyrin systems were not extensively studied. A series of electronically diverse cofacial-bisporphyrins were studied in their neutral and radical ionic states to interrogate the extent of interactions and charge delocalization between two face-to-face macrocyles.