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The power of surfaces: getting meta-polyaniline from para-aminophenol

On-surface chemistry is a recent research field where the catalytic properties of surfaces are used to synthesize new materials that are not accessible with other techniques. Thus, following this bottom-up strategy, surfaces are used as a platform for enabling new low dimensional molecular networks. In this work, para-aminophenol (p-AP) molecules are used as precursors (building block) for the surface reaction. Surprisingly, we have found that these molecules, when adsorbed on Pt(111) and upon a thermal stimulus, covalently react each other forming oligomers coupled in a metaconfiguration (see Figure 1). 

Figure 1.  Top: schematic picture of the on-surface reaction occurring when depositing para-aminophenol (p-AP) molecules on a Pt(111) surface, which leads to the formation of meta-polyaniline (m-PANI). Bottom: a) experimental and b) simulated high-resolution Nc-AFM image of a m-PANI chain on Pt(111)) with the DFT optimized model superimposed on the images.


We have used a multi-technique approach that includes STM, nc-AFM, STS, XPS, and DFT calculations to study the thermal behavior of the p-AP/Pt(111) system. By STM and nc-AFM, we have observed that starting from individual molecules (see bottom right image of Figure 2) and by annealing the surface, lead to the formation of oligomer chains (top right image of Figure 2 and bottom panel of Figure 1). To unveil their chemical nature, we have investigated the thermal behavior of the p-AP/Pt(111) system by means of high-resolution XPS at the SuperESCA beamline of Elettra. Figure 2 shows high-resolution C 1s, N 1s and O 1s XPS core levels spectra of p-AP molecules on the Pt(111) when the surface reaches different temperatures. The main changes observed upon thermal annealing are the initial dehydrogenation of the alcohol group followed of oxygen elimination for higher temperatures, the partial dehydrogenation of the amino group and the formation of C-Pt and azo bonds. Combining all the experimental results we can conclude that the behavior of p-AP molecules on the Pt surface upon thermal annealing is composed of 3 steps: dehydrogenation of the alcohol groups, partial dehydrogenation of the amine groups, and intermolecular coupling between activated amine groups and carbon atoms at the meta position. This gives rise to an unforeseen result, since we have been able to synthesize meta-polyaniline oligomers starting from a para-functionalized precursor, p-AP. Thus, surprisingly the Pt(111) surface has induced an unexpected selective formal Michael addition between the precursor molecules.   
 

Figure 2.  High-resolution C 1s, N 1s and O 1s XPS core levels spectra of p-AP molecules on the Pt(111) surface at 85K (blue spectra), 300K (pink) and 525K (green). Measurements performed after cooling the system at 120 K. Left: characteristic STM images for high and room temperatures.
 

Importantly, this work has demonstrated that chemistry on 2D metallic surfaces behaves differently to that on solution (3D), where unspecific Michael addition would be expected. This reaction pathway opens a door towards the highly directional synthesis of novel nanostructures of interest in the emerging fields of nanomagnetic materials and spintronics.


 

This research was conducted by the following research team:

Nerea Ruiz del Árbol1, Carlos Sánchez-Sánchez1, Gonzalo Otero-Irurueta1,2, Jose I. Martínez1, Pedro L. de Andres1, Ana C. Gómez-Herrero1,3, Pablo Merino1,4, María F. López1, José A. Martín-Gago1, Marten Piantek5, David Serrate5,6, Paolo Lacovig7, Silvano Lizzit7, José Alemán8, Gary J. Ellis9

 

Institute of Material Science of Madrid (ICMM-CSIC), Madrid, Spain
Center of Mechanical Technology and Automation (TEMA), Aveiro, Portugal 
Institut Néel (CNRS), Grenoble, France; Université Grenoble Alpes, Grenoble, France 
Molecular Astrophysics Group, Instituto de Física Fundamental (IFF-CSIC), Madrid, Spain 
Instituto de Ciencia de Materiales de Aragón, CSIC- Universidad de Zaragoza, 50009 Zaragoza, Spain 
Departamento de Física de la Materia Condensada, Universidad de Zaragoza, Zaragoza, Spain 
Elettra - Sincrotrone Trieste S.C.p.A., Trieste, Italy
Organic Chemistry Department1, Universidad Autónoma de Madrid, Madrid, Spain 
Polymer Physics Group, Institute of Polymer Science and Technology (ICTP-CSIC), Madrid, Spain


Contact persons:

José A. Martín-Gago, email:


Reference

N. Ruíz del Árbol, C. Sánchez-Sánchez, G. Otero-Irurueta, J. I. Martínez, P. L. de Andrés, A. Gómez-Herrero, P. Merino, M. Piantek, D. Serrate, P. Lacovig, S. Lizzit, J. Alemán, G. Ellis, M. F. López and J.A. Martín-Gago, On-Surface Driven Formal Michael Addition Produces m-Polyaniline Oligomers on Pt(111), Angew. Chem. Int. Ed. 2020, 59, 23220; DOI: 10.1002/anie.202009863

Last Updated on Wednesday, 13 January 2021 11:28