Bi‐polaron Transport and Magnetic Field Induced Pauli Spin Blockade in Redox‐Active Molecular Junctions

Abstract

We report the bi-polaron transport and magnetic field induced Pauli spin-blockade in solid-state molecular junctions (MJs) evidenced by a positive magnetoresistance (MR). The junction was made of thin layers of redox-active ruthenium polypyridyl-oligomers Ru(tpy) 2 sandwiched between conducting amorphous carbon (a-C) electrodes. The redox-active Ru(tpy) 2 molecule, which enables small polaron and deep traps in the charge transport of the Ru(tpy) 2 MJ as revealed by the temperature-dependent current-voltage response, leads to the formation of the bi-polaron and magnetic field induced Pauli spin blockade, resulting into the MR. At the meantime, the reliable and controllable device performance renders a rigid thickness-dependent MR evolution. The bi-polaron transport revealed in our study underscores the importance of the multi-particle transport by molecular design in MJs and laid the foundation for magnetic-electronic function in molecular-scale devices.

Probing the effect of nitro-substituents in the modulation of LUMO energies for directional electron transport through 4d6ruthenium(ii)-based metallosurfactants

“…2-Acetylpyridine, 4-octadecyloxy benzaldehyde, and 5-nitrophenanthroline were purchased from TCI Chemicals, 1,10-phenanthroline was purchased from Alfa Aesar, 2,2′:6′2″-terpyridine was purchased from GFS Chemicals, RuCl 3 •6H 2 O was purchased from Oakwood Chemical. 1 H-NMR, 13 C-NMR, COSY-NMR, and HSQC-NMR data were collected in CD 2 Cl 2 using a Varian 600 MHz spectrometer. Electrospray ionization mass spectroscopy (ESI-MS) data were collected using a Waters-ZQ 2695.…”

“…(NO 2 Ph-terpy)](PF 6 ) 2 (2), [Ru II (C 18 OPh-terpy) ( phen)Cl]PF 6 (3), and [Ru II (C 18 OPh-terpy)(NO 2 -phen)Cl]PF 6 (4) were synthesized in a stepwise way using Ru(DMSO) 4 Cl 2 as the metal precursor and introducing the heteroleptic ligand sequentially. The crude products were purified by column chromatography to yield microcrystalline species characterized by 1 H-NMR, 13 C-NMR, COSY-NMR, HSQC-NMR spectroscopy, UV-visible spectroscopy, and high-resolution ESI mass spectroscopy (Fig. S1 †), where peak clusters show the expected envelope with both ruthenium (1-4) and chloride (3-4) signatures.…”

“…The same group went on to use [Ru II (S-C x -terpy) 2 ] species with C 7 -and C 13 lengths to attain non-volatile memory elements. A recent account by Ding, Yu et al 13 describes electron transport in terms of bipolaron transport and Pauli spin blockade that relates to the consequences of spin flip. Another seminal work by Rignanese et al 14 used first-principles electronic structure calculations to confirm the mismatch between Fermi and Ru-based HOMO and to conclude that ligand involvement, rather than the inaccessible Ru-based LUMO promotes electron transfer in Ru(terpy) 2 species.…”

“…The same group went on to use [Ru II (S-C x -terpy) 2 ] species with C 7 - and C 13 lengths to attain non-volatile memory elements. A recent account by Ding, Yu et al 13 describes electron transport in terms of bipolaron transport and Pauli spin blockade that relates to the consequences of spin flip.…”

Thickness-Dependent Charge Transport in Three Dimensional Ru(II)– Tris(phenanthroline)-Based Molecular Assemblies

“…The UV–vis absorbance spectra of the thin films show two signals, one at 365 nm and the other at 570 nm, corresponding to π–π* transition and metal-to-ligand charge transfer band, respectively, ensuring the growth of molecular layers on ITO surfaces (Figure S15). Moreover, the anchorage of the Ru­(Phen) 3 thin films on the ITO substrate was estimated by cyclic voltammetry (CV). The CV curve shows a characteristic one electron oxidation peak due to Ru­(II) to Ru­(III) forming at +1.36 V vs Ag/AgNO 3 and a redox-peak due to Ru­(III) to Ru­(II) at +1.08 V vs Ag/AgNO 3 , which matches well with the previous literature (Figure S16a).…”