Reversible photo-switching of single azobenzene molecules in controlled nanoscale environments.

We drive reversible photoinduced switching of single azobenzene-functionalized molecules isolated in tailored alkanethiolate monolayer matrices on Au{111}. We designed molecular tethers to suppress excited-state quenching from the metal substrate and formed rigid assemblies of single tethered azobenezene molecules in the domains of monolayer to limit steric constraints and tip-induced and stochastic switching effects. Single molecules were reversibly photoisomerized between trans and cis conformations by cycling exposure to visible and UV light. Trans and cis conformations were imaged as high (2.1 +/- 0.3 A) and low (0.7 +/- 0.2 A) protrusions in STM images and were assigned to the on and off states of the molecule, respectively.