pH-Induced transformation of ligated Au-25 to brighter Au-23 nanoclusters

VBK and ŽS appreciate funding from Center of Excellence (STIM) at the University of Split. This research was supported by STIM-REI, a project funded by European Union from European Structural and Investment Funds 2014–2020. Contract Number KK.01.1.1.01.0003. This work was supported by the National Science Centre under grants DEC-2013/10/A/ST4/00114 and DEC-2013/09/B/ST5/03417 and by a statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wroclaw University of Science and Technology. We would like to acknowledge the financial support from the French-Croatian project “International Laboratory for Nano Clusters and Biological Aging, LIA NCBA”. IDWS acknowledges the support from a Royal Society Wolfson Research Merit Award. Thiolate-protected gold nanoclusters have recently attracted considerable attention due to their size-dependent luminescence characterized by a long lifetime and large Stokes shift. However, the optimization of nanocluster properties such as the luminescence quantum yield is still a challenge. We report here the transformation of Au25Capt18 (Capt labels captopril) nanoclusters occurring at low pH and yielding a product with a much increased luminescence quantum yield which we have identified as Au23Capt17. We applied a simple method of treatment with HCl to accomplish this transformation and we characterized the absorption and emission of the newly created ligated nanoclusters as well as their morphology. Based on DFT calculations we show which Au nanocluster size transformations can lead to highly luminescent species such as Au23Capt17. Postprint