Precise Control of π-Electron Magnetism in Metal-Free Porphyrins

Abstract

The porphyrin marcocycle can stabilize a set of magnetic metal ions, thus introducing localized net spins near the center. However, it remains illusive but most desirable to introduce delocalized spins in porphyrins with wide implications, for example, for building correlated quantum spins. Here, we demonstrate that metal-free porphyrins host delocalized -electron magnetism as revealed by scanning probe microscopy and different level of theory calculations. Our results demonstrate that engineering of -electron topologies introduces spin polarized singlet state and delocalized net spins in metal-free porphyrins. In addition, the -electron magnetism can be switched on/off via STM manipulation by tunning the interfacial charge transfer. Our results provide an effective way to precisely control the -electron magnetism in metal-free porphyrins, which can be further extended to design new magnetic functionalities of porphyrin-based architectures.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

“…In 2020, Zhuang and Wang reported a method of controlling delocalized magnetism in metal-free porphyrins by peripheral fusion of ortho -dimethylphenyl substituents. 579 The three metal-free porphyrins 311.3 – 5 with different π-electron topologies were obtained from the precursor 5,10,15,20-tetrakis(2,6-dimethylphenyl)porphyrin 311.1 using on-surface synthesis on Au(111) ( Scheme 311 ). 311.3 resulted from double methyl group cleavage followed by formation of five-membered rings, whereas 311.5 was a product of incomplete dehydrogenation.…”

“… Reagents and conditions: (a) 579 Au(111), 295 °C; (b) 580 Zn(OAc) 2 , THF, reflux; (c) 580 Au(111), 300 °C; (d) 580 Au(111), 330 °C. …”

Engineering the magnetism of nanographene via co-depositing hetero precursors

“…The distributions of Kondo resonance fit well with the calculate spin density state distributed area. The Kondo peak positions are slight away from fermi level and the shapes are slight asymmetric which can be attributed to the charge transfer from substrate and the hybridization with the substate 34,35,42 . In contrast to the S = 0 ground state structure of homo-coupled NG 1a, the ground state of NG 2a, formed by hetero-coupling of two different precursors, is switched to triplet.…”

“…Secondly, quenching the spin by creating single C-metal bond, for example, bounding the radical positions to the elbow area of Au(111) surface 28 by applying positive voltage pulse 33 . Thirdly, the spin on/off could be switched due to the charge transfer by changing adsorption positions [34][35][36] . The aspects mentioned above can be considered as the tip manipulation of spin.…”

Realization of quantum nanomagnets in metal-free porphyrins

“…Recently, delocalized -electron magnetism has been introduced in porphyrins through engineering their  electron topologies [18][19][20] . Such delocalization effect allows for further realization of quantum nanomagnets with coupled spins in covalent porphyrin architectures.…”