NANOLANTA · Nanoengineering of functional lanthanide tetrapyrrole systems

Nanoengineering of functional lanthanide tetrapyrrole systems

The project NANOLANTA has addressed the nanoengineering of lanthanide-tetrapyrrole architectures on atomistically clean surfaces in vacuum conditions and measured their geometrical and electronic properties by Scanning Tunneling Microscopy (STM) and Spectroscopy (STS), with the aim of creating novel supramolecular nanostructures that provide application potential relevant for photovoltaics, biosensors and magnetic recording. To this aim, we have explored self-assembly protocols combining atom and molecules on surfaces to yield specific nanopatterns. Phase I. In Phase I, the goal was focused on designing a 2D lanthanide tetrapyrrole monolayer on metal surfaces by dosing different lanthanides on top of a stable tetrapyrrole monolayer at room temperature, exposing the Cerium to vacuum to exploit the rich lanthanide chemistry. First, we have selected Cerium as the lanthanide and 2H-TPP (free base porphyrin) as the tetrapyrrole molecular species. Herein, we have been successful in creating an assembly of 2H-TPP on Ag (111) which is stable at room temperature at one monolayer coverage. Subsequently, we have metallated this assembly with Cerium, which seems to go underneath the porphyrins, contrary to our initial expectations. Secondly, to prevent the former behavior of Cerium, we have studied the growth of another flatter tetrapyrrole (2H-P: free base porphine, the smallest of all porphyrins) on Ag (111). Subsequent sublimation of Cerium results in the formation of CeP (porphines metallated with Cerium), in which the Cerium seems to be facing the substrate, like in the former case. Phase II. In this phase, we have designed novel routes to achieve double and triple-deckers complexes of 2H-TPP (Ce (TPP) 2 and Ce2 (TPP) 3) and of 2H-P (CeP2 and Ce2P3) on Ag (111). For the in-situ synthesis of Ce (TPP) 2 and Ce2 (TPP) 3, we have directly exposed a porphyrin 2H-TPP multilayer to an atomic beam of cerium, followed by a temperature-programmed reaction promoting the interaction of Ce with the porphyrin macrocycles under the removal of hydrogen and desorbing any unreacted 2H-TPP material. A formation of arrays of Ce (TPP) 2 with embedded Ce2 (TPP) 3 species was observed. Herein, the direct sublimation of Ce (TPP) 2 on Ag (111) confirmed the in-situ synthesis of Ce (TPP) 2 by our novel route. In addition, rotational motions of the top porphyrin of the Ce (TPP) 2 and Ce2 (TPP) by molecular STM manipulation were addressed. For the in-situ synthesis of CeP2 and Ce2P3 we have followed a derived simpler recipe, which is based on growing one monolayer of 2H-P on Ag (111), subsequent deposition of Cerium and a final gently annealing to 230?C. Herein, results show the formation of hexagonal arrays of CeP2 complexes, with embedded Ce2P3 species. Conclusions. In summary, we have in-situ synthesized Cerium double-decker tetrapyrrole assemblies on a metallic substrate and characterised them geometrically and electronically, addressing via STM tip stimulation their rotational properties. Remarkably, we have opened new avenues towards the design of a variety rare-earth porphyrinatos sandwich complexes, extending surface-based supramolecular coordination protocols into the third dimension. In addition, we have addressed with exquisite resolution new insights regarding the performance of molecular rotors on surfaces. The double-decker complexes synthesized in this proposal stand out due to their expected applications. The proximity of the two rings of the porphyrins and their rotatibility make them promising as basic units for: molecular semiconductors, optical gas sensors (including artificial noses), electrochemical sensors and mass sensors, organic field-effect transistors (mainly used for liquid crystal displays) and molecular rotors. Finally, an extension of our synthesis recipes to another lanthanide atoms (like dysprosium and terbium) could lead to the formation of novel molecular magnets species on surfaces.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз