resumo
Engineering sublattice imbalance is an intuitive way to induce high-spin ground states in bipartite polycyclic conjugated hydrocarbons (PCHs). Such molecules can be employed as building blocks of quantum spin chains, which are outstanding platforms to study fundamental models in quantum magnetism. This is exemplified by recent reports on the bottom-up synthesis of antiferromagnetic spin chains that provided insights into paradigmatic quantum phenomena such as fractionalization. In contrast to antiferromagnetism, demonstration of ferromagnetic coupling between PCHs has been scarce. Previous attempts in this direction were limited by the formation of nonbenzenoid rings leading to spin quenching or the use of spacer motifs that weaken the magnitude of ferromagnetic exchange. Here, we demonstrate the on-surface synthesis of short ferromagnetic spin chains based on dibenzotriangulene, a triplet PCH. Our synthetic strategy centers on the concept of achieving a direct (without spacer motifs) majority-minority sublattice coupling between adjacent molecules. This leads to a global sublattice imbalance in spin chains scaling with the chain length and therefore a ferromagnetic ground state with a strong intermolecular ferromagnetic exchange. Through scanning probe measurements and quantum chemical calculations, we analyze the electronic and magnetic properties of ferromagnetic dimers and trimers of dibenzotriangulene and confirm their quintet and septet ground states, respectively, with an intermolecular ferromagnetic exchange of 7 meV. Furthermore, we elucidate the role of sublattice coupling on magnetism through complementary experiments on antiferromagnetic dibenzotriangulene dimers with majority-majority and minority-minority sublattice couplings. We expect our study to provide impetus for the design of organic ferromagnetic materials.
palavras-chave
SCANNING TUNNELING MICROSCOPE; MOLECULES; STATE
categoria
Chemistry
autores
Paschke, F; Ortiz, R; Mishra, S; Vilas-Varela, M; Albrecht, F; Peña, D; Melle-Franco, M; Gross, L
nossos autores
Manuel Melle-Franco
Investigador Principal
Ricardo Ortiz Cano
Investigador JúniorProjectos
CICECO - Aveiro Institute of Materials (UIDB/50011/2020)
CICECO - Aveiro Institute of Materials (UIDP/50011/2020)
Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)
agradecimentos
R.O. would like to thank Karol Strutynski for fruitful discussions. This work was supported financially by the European Research Council Synergy grant MolDAM (grant no. 951519). Furthermore, support within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI 10.54499/UIDB/50011/2020), UIDP/50011/2020 (DOI 10.54499/UIDP/50011/2020), and LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020), financed by national funds through the FCT/MCTES (PIDDAC) is gratefully acknowledged. This project has received funding from the European Union's Horizon 2020 research and innovation program, under grant agreement Nos. 958174 and 101046231, and from the Foundation for Science and Technology (FCT) under grant agreement M-ERA-NET3/0006/2021 through the M-ERA.NET 2021 call. Financial support from the Spanish Agencia Estatal de Investigacion (PID2022-140845OB-C62), the Xunta de Galicia (Centro de Investigacion do Sistema Universitario de Galicia, 2023-2027, ED431G 2023/03), and the European Union (European Regional Development Fund-ERDF) is gratefully acknowledged.