IF‐ReS2 with Covalently Linked Porphyrin Antennae

Abstract

The preparation of inorganic and organic hybrid materials, of metals or semiconductor systems which are functionalized with functional molecules to fabricate devices — nanotechnology — is currently an area of intense activity in both fundamental science and applied science on an international scale. Principally, nanotechnology aims at manipulating atoms, molecules, and nanosize particles in a precise and controlled manner in order to build materials with a fundamentally new organization and novel properties. The embryonic stage of nanotechnology is atomic assembly, whereas the mature form of nanotechnology will be molecular assembly to make nano-building blocks for the design of nanocomposites or self-organizing nanodevices. In order to achieve the outstanding properties of nanomaterials, surface modification is the key to success, as any application in materials and devices is hindered by difficulties in processing and manipulation. For instance, the charge transport process across the interface between a semiconductor metal oxide and an organic dye or a biomolecule forms the basis for improving the performance of many optoelectronic devices, photovoltaic cells, and light emitting diodes (LEDS). Chalcogenide nanotubes and fullerenes are particularly useful components for inorganic hybrid structures because they find many potential applications as solid lubricants, catalysts for the hydrodesulfurization, and they are rigid and structurally well-defined. Many of the useful properties of inorganic layered metal chalcogenides are related to their crystal structures, which are characterized by weak van der Waals forces between the individual MQ2 (Q = S, Se) slabs containing metal atoms sandwiched between two inert chalcogen layers. Furthermore, they may have a broad range of chemical and physical properties that can be chosen according to the desired task. However, in order to utilize chalcogenide nanotubes and fullerenes in hybrid materials, their surfaces must be tailored with reactive groups, i. e., their surface chemistry has to be mastered. But the inertness of the chalcogen surface layer and the associated shielding of the metal atoms from nucleophilic attacks by organic ligands are the main obstacles for the functionalization of chalcogenide nanoparticles and nanotubes. Since direct anchoring of organic ligands to the surface of chalcogenides nanomaterials is difficult, we used a nitrilotriacetic acid that can be used to coordinate to Ni ions which, in turn, can use their vacant coordination sites for binding to the surface sulfur atoms of metal chalcogenides. A seemingly simple question to be addressed is the binding mode of the metal/scorpionate ligand block to the sidewalls of the metal chalcogenides nanoparticles. The most obvious model would assume a binding of the metal to defects on the chalcogenide surface. The second model assumes that the metal (e.g., Ni) is bonded to the ideally closed packed outer sulfur layer of the chalcogenide tube, and the metal is situated in a threefold hollow (or on a twofold coordinating or single site) of the closepacked sulfur layer. Herein, a step further, we report the surface functionalization of ReS2 fullerenes with polymeric ligands, the subsequent binding of protoporphyrin ligands, and the complexation of zinc. Our polymeric ligand incorporates (i) a nitrilotriacetic acid (NTA) anchor that can be used to coordinate to Ni ions which, in turn, can use their vacant coordination sites for binding to the surface S atoms of IF–ReS2; (ii) amine groups which can be used to immobilize protoporphyrins; and (iii) a piperazyl 4-chloro-7-nitrobenzofurazan (pipNBD) fluorescent dye as a recognition molecule to monitor microscopically the functionalization of the polymeric ligand to IF–ReS2. The amino groups were utilized for conjugating the protoporphyrin, which in turn complexates the Zn cation. The resulting functionalized IF– ReS2 particles can be dispersed in water and organic solvents. They were characterized by high-resolution trans-