A photoresponsive Au25 nanocluster protected by azobenzene derivative thiolates.

An Au(25) cluster protected by azobenzene derivative thiolates (S-Az) ([Au(25)(S-Az)(18)](-)) was synthesized with the aim of producing a photoresponsive Au(25) cluster. The matrix-assisted laser desorption/ionization mass spectrum of the product revealed that [Au(25)(S-Az)(18)](-) was synthesized in high purity. Optical absorption spectra of [Au(25)(S-Az)(18)](-) obtained before and after photoirradiation suggest that the azobenzenes in the ligands of Au(25)(S-Az)(18) isomerize with an efficiency of nearly 100%, both from the trans to cis conformation and from the cis to trans conformation. Furthermore, the redox potential and optical absorption of Au(25)(S-Az)(18) were found to change reversibly due to photoisomerization of azobenzenes.