Room‐Temperature On‐Spin‐Switching and Tuning in a Porphyrin‐Based Multifunctional Interface

Abstract

Molecular interfaces formed between metals and molecular compounds offer a great potential as building blocks for future opto-electronics and spintronics devices. Here, a combined theoretical and experimental spectro-microscopy approach is used to show that the charge transfer occurring at the interface between nickel tetraphenyl porphyrins and copper changes both spin and oxidation states of the Ni ion from [Ni(II), S = 0] to [Ni(I), S = 1/2]. The chemically active Ni(I), even in a buried multilayer system, can be functionalized with nitrogen dioxide, allowing a selective tuning of the electronic properties of the Ni center that is switched to a [Ni(II), S = 1] state. While Ni acts as a reversible spin switch, it is found that the electronic structure of the macrocycle backbone, where the frontier orbitals are mainly localized, remains unaffected. These findings pave the way for using the present porphyrin-based system as a platform for the realization of multifunctional devices where the magnetism and the optical/ transport properties can be controlled simultaneously by independent stimuli.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202104779.

Disproportionation of Nitric Oxide at a Surface‐Bound Nickel Porphyrinoid

“…By comparing the STM images acquired before and after the NO uptake, we note that the dark depression at the macrocycle center, which is associated with the Ni atom, [33,35] is replaced with a bright protrusion (Figure 1c), similarly to what has been observed upon direct exposure to NO 2 (Figure S4). [35] The NO 2 ligand coordinates to the Ni atom at the center of the macrocycle, as further confirmed by the STM d 2 I/dV 2 maps. Inelastic Electron Tunneling Spectroscopy localizes indeed the mode low-frequency mode (Figure 1d) and the mode detected by means of both IR-Vis SFG and IRAS (Figure 1f) on top of the Ni atoms, whereas no vibrational feature was localized at intermediate bias (Figure 1e).…”

Distortion-driven spin switching in electron-doped metal porphyrins

“…Indeed, the adsorption on the highly reactive copper surface implies the filling of the adsorbate lowermost unoccupied MOs (up to the LUMO+3) and the concomitant TM(II) -TM(I) reduction. 18,19,23,24 Charge injection into the metal complex may also be induced by exploiting alternative pathways such as AM doping. Aimed to look into the TM reduction process, a NiTPP layer deposited on the Au(111) surface has been stepwise K doped.…”

“…Such a remarkable charge transfer (up to the LUMO+3) has already been revealed for the aforementioned NiTPP/Cu(100) and CoTPP/Cu(100) interfaces. 18,19,23 As a final remark, the peculiar work function (WF) trend as a function of the K dose (see Fig. 1(a)) deserves to be highlighted: (i) a significant WF drop, indicative of the formation of a new surface dipole induced by the adsorption of the K atoms at the interface, is present at the lower K doping level; such WF change is accompanied by a HOMO blue shift with respect to the Fermi level; (ii) a plateau region leading to the complete filling of the gas-phase unoccupied MOs up to LUMO+3 characterizes the intermediate K coverage; this range corresponds to the region of interest for the electron doping of the molecular layer; (iii) a further, less pronounced, WF drop determining a blue-shift of low-lying empty MO (LUMO/+1 and LUMO+3) takes place at higher K doses, which corresponds to the appearance of neutral K species in the K 2p XPS spectrum (see Fig.…”

“…In this respect, it has been shown that axial coordination may be exploited to modulate the TM oxidation and spin states. [17][18][19] In fact, the spin state of the Mn ion in the tetra-pyrrolic pocket may sweep across different configurations by subtle modification of the N ligand field, e.g., by changes of the Mn-ligand distance (HS in Mn-porphyrins, 20 IS in Mn-Pc 15 ) or of the ligand peripheral coordination (HS in Mn-TCNQ 4 metal-organic covalent networks). 21 Interestingly, it has been recently demonstrated that ruthenium tetraphenylporphyrin (RuTPP) on Ag(111) can be stabilized in two different conformations, saddle-shaped and planar, and only the former may axially interact with CO as a consequence of its greater molecular flexibility.…”

“…In this respect, it has been shown that axial coordination may be exploited to modulate the TM oxidation and spin states. 17–19 In fact, the spin state of the Mn ion in the tetra-pyrrolic pocket may sweep across different configurations by subtle modification of the N ligand field, e.g. , by changes of the Mn–ligand distance (HS in Mn–porphyrins, 20 IS in Mn–Pc 15 ) or of the ligand peripheral coordination (HS in Mn-TCNQ 4 metal–organic covalent networks).…”