Poster presentation

Interplay between π–conjugation and exchange magnetism in one-dimensional porphyrinoid polymers
Kalyan Biswas¹, Maxence Urbani¹, Ana Sánchez-Grande¹, Diego Soler², Koen Lauwaet¹, Adam Matěj², Pingo Mutombo², Libor Veis³, Jiri Brabec³, Katarzyna Pernal⁴, José M. Gallego⁵, Rodolfo Miranda¹, David Écija¹, Pavel Jelínek², Tomás Torres¹, and José I. Urgel¹

1 IMDEA Nanoscience, C/ Faraday 9, Campus de Cantoblanco, 28049 Madrid, Spain
2 Regional Centre of Advanced Technologies and Materials, Czech Advanced Technology and Research Institute (CATRIN), Palacký University Olomouc, 771 46 Olomouc, Czech Republic
3 Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, 182 23 Prague, Czech Republic
4 Institute of Physics, Lodz University of Technology, 90-924 Lodz, Poland
5 Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain

The field of carbon magnetism has gained an increased attention in view of the recent progress made in the synthesis and characterization of open-shell polycyclic aromatic hydrocarbons following a bottom-up synthetic approach[1,2]. Under this scenario, the comprehensive fabrication of magnetic porphyrinoid-based polymers emerges as a highly appealing field of research. However, the vast majority of the porphyrinoid species and polymers studied to date exhibit a closed-shell ground state [3].

In this work, we introduce an exemplary approach toward the bottom-up fabrication of unprecedented magnetic porphyrinoid-based polymers homocoupled via surface-catalyzed [3 + 3] cycloaromatization of isopropyl substituents studied on Au(111) under ultra-high vacuum (UHV) conditions. The chemical structure of the polymer, formed by thermal-activated intra- and intermolecular oxidative ring closure reactions followed by controlled tip-induced hydrogen dissociation from the porphyrinoid units, have been clearly elucidated by scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). Scanning tunneling spectroscopy (STS), complemented by computational investigations reveals the open-shell character, i.e. antiferromagnetic singlet ground state (S=0) of the formed polymers, which display singlet−triplet inelastic excitations observed between spins of adjacent porphyrinoid units only along a specific π-conjugation pathway, thus revealing the interplay between π-conjugation and magnetic exchange. We envision that our approach can be a highly relevant step towards the on-surface synthesis of covalently linked 1D magnetic organic polymers with prospects in nanoscale spintronic devices.

Figure 1. On-surface reaction scheme toward the synthesis of one-dimensional porphyrinoid polymers starting from precursor 1 to magnetic porphyrinoid polymer 3 with intermediate non-magnetic porphyrinoid-based polymer 2.

[1] Auwärter, W. et al., Nat Chem. 7 (2), 105–120, (2015)
[2] Gottfried, J. M., Surf. Sci. Rep. 70 (3), 259–379, (2015)
[3] Shimizu, D et al., Chem. Sci. 9 (6), 1408–1423, (2018)