Fluorescence Lifetime Imaging and Super resolution microscopies shed light on the directed- and self-assembly of functional porphyrins onto carbon nanotubes and flat surfaces

Two new routes to functionalized SWNTs have been established using a bulky Zn(II)-porphyrin featuring thiolate groups at the periphery. We probed the optical properties of this Zinc(II)-substituted, bulky aryl porphyrin and those of the corresponding new nano-composites with single walled carbon nanotube (SWNTs) and coronene, as a model for graphene. We report hereby on: (i) the supramolecular interactions between the pristine SWNTs and Zn(II)-porphyrin by virtue of π-π stacking, and (ii) a novel covalent binding strategy based on the Bingel reaction. We investigated the nature of the porphyrin aggregates forming on flat surfaces by Steady-state and time-resolved fluorescence emission spectroscopies and imaging techniques including fluorescence lifetime imaging microscopy (FLIM) together with Atomic Force Microscopy (AFM) and Super Resolution Stimulated Emission Depletion microscopy (STED). X-ray photoelectron spectroscopy (XPS) studies highlighted the differences in the covalent versus non-covalent attachments of functional metalloporphyrins to SWNTs. Gas phase density functional theory (DFT) calculations (implemented in CASTEP) indicated that the Zinc(II) porphyrin interacts non-covalently with SWNT to form a donor-acceptor complex. The appendage of the porphyrin chromophore to the surface of SWNTs affects the absorption and emission properties of the hybrid system to a greater extent than in the case of the supramolecular functionalization of the SWNTs surface.