Characterisation, degradation and regeneration of luminescent Ag29 clusters in solutionElectronic supplementary information (ESI) available: Absorption and emission spectra of samples with different Ag : LA ratios and old samples; SE-AUC data; tandem MS spectra; absorption, emission and ESI-MS spectra after cluster purification and cluster regeneration. See DOI: 10.1039/c6nr04958c

Luminescent Ag clusters are prepared with lipoic acid (LA) as the ligand. Using a combination of mass spectrometry, optical spectroscopy and analytical ultracentrifugation, the clusters are found to be highly monodisperse with mass 5.6 kDa. We assign the chemical composition [Ag 29 (LA) 12 ] 3− to the clusters, where LA likely binds in a bidentate fashion. The Ag 29 clusters show slow degradation, retaining their deep red emission for at least 18 months if stored in the dark. Purification or exposure to light results in faster degradation. No other cluster species are observed during the degradation process. Once degraded, the clusters could easily be regenerated using NaBH 4 , which is not usually observed for thiolate-capped Ag clusters. Bleaching of luminescent Ag 29 clusters results in non-luminescent polydisperse species. Upon reduction of bleached clusters, optical properties of the cluster are recovered.