A Four-position Chlorophyll-a molecular switch

Violeta Iancu and Saw-Wai Hla, "Realizing a Four-Step Molecular Switch in Scanning Tunneling Microscope Manipulation of Single Chlorophyll-a Molecules"

cond-mat/0609077

This paper combines a lot of things I like reading about: chlorophyll, STM-manipulation of molecules, and semi-empirical calculations. Basically the title says it all: you can use inelastic tunneling spectroscopy (IETS) to move the phytyl tail around into 4 distinct positions. The pictures are quite nice too, thanks to the PM3 calculations.