Local Probe Structure Isomerization in a One-Dimensional Molecular Array

TL;DR

This study demonstrates controlled local probe-induced isomerization of molecular structures in one-dimensional arrays on a surface, revealing insights into their magnetic states and potential for functional device applications.

Contribution

It introduces a method to induce and control local structural isomerization in molecular arrays using STM tip pulses, combining experimental and theoretical analysis.

Findings

Tip pulses induce diradical formation and isomerization.

Diradical hosts an open-shell singlet with antiferromagnetic coupling.

Spin transition from singlet to triplet state occurs at 91 meV.

Abstract

Synthesis of one-dimensional molecular arrays with tailored stereoisomers is challenging yet has a great potential for application in molecular opto-, electronic- and magnetic-devices, where the local array structure plays a decisive role in the functional properties. Here, we demonstrate construction and characterization of dehydroazulene isomer and diradical units in three-dimensional organometallic compounds on Ag(111) with a combination of low-temperature scanning tunneling microscopy and density functional theory calculations. Tip-induced voltage pulses firstly result in the formation of a diradical species via successive homolytic fission of two C-Br bonds in the naphthyl groups, which are subsequently transformed into chiral dehydroazulene moieties. The delicate balance of the reaction rates among the diradical and two stereoisomers, arising from an in-line configuration of tip and molecular unit, allows directional azulene-to-azulene and azulene-to-diradical local probe structural isomerization in a controlled manner. Furthermore, our theoretical calculations suggest that the diradical moiety hosts an open-shell singlet with antiferromagnetic coupling between the unpaired electrons, which can undergo an inelastic spin transition of 91 meV to the ferromagnetically coupled triplet state.