Theoretical Investigation of Chemical Spin Doping into Single Porphyrin Junctions toward Ultrahigh-Sensitive Nitric Oxide Sensor

We theoretically study chemical spin doping into single porphyrins connected to nanoelectrodes via benzenethiols, ethynyl-benzenethiols, and vinyl-benzenethiols using the adsorption of a nitric oxide (NO) molecule. For all three anchoring groups, the adsorption of a NO molecule injects one spin into single-molecule junctions and produces antiferromagnetic interactions between the injected spin and the original spins at the junctions, resulting in a decrease in the spin-polarized currents. We found that the magnitude of change in the spin-polarized current significantly depends on the type of anchoring groups; the magnitude is ordered by the following anchoring group: vinyl-benzenethiol $>$ ethynyl-benzenethiol $>$ benzenethiol. In particular, for vinyl-benzenethiol, spin doping causes not only $\pi$ electron localization on molecular orbitals but also structural change.