Mechanically-Controlled Reversible Spin Crossover of Single Fe-Porphyrin Molecules

• Published in: ACS nano Vol. 11; no. 6; pp. 6295 - 6300
• Main Authors: Kuang, Guowen, Zhang, Qiushi, Lin, Tao, Pang, Rui, Shi, Xingqiang, Xu, Hu, Lin, Nian
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 27.06.2017
• Subjects: density-functional theory; Fe-porphyrin; spin crossover; scanning tunneling microscopy; single-molecule junction
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.7b02567

Spin-crossover (SCO) molecules are thought to be ideal systems for molecular spintronics when SCO can be precisely controlled at the single-molecule level. This is demonstrated here in the single-molecule junctions of Fe-porphyrin formed in a scanning tunneling microscope. Experimentally, we find that the junctions feature a zero-bias resonance in molecular conductance associated with the Fe spin center. When mechanically stretching or squeezing the junctions by adjusting the tip height, the line shape of the zero-bias resonance varies reversibly. First-principles calculations reveal that widening the junction gap by 2 Å transforms the macrocyclic core hosting the Fe center from a saddle to a planar conformation. This conformational change shortens the Fe–N bonds by 3%, which changes the Fe spin state from S = 2 to S = 1.