Quantitatively Monitoring the Size-Focusing of Au Nanoclusters and Revealing What Promotes the Size Transformation from Au 44 (TBBT) 28 to Au 36 (TBBT) 24 .

"Size-focusing" is a well-recognized process and widely employed for the synthesis of atomically monodisperse metal nanoclusters. However, quantitatively monitoring the size-focusing of Au nanoclusters has not been achieved yet, and the in-depth understanding of the size focusing is far from completed. Herein, we introduce a facile, cheap, and powerful tool, preparative thin-layer chromatography (PTLC), to quantitatively track the size-focusing process, to reveal that mainly ∼3 nm nanoparticles promote the transformation from Au44 (TBBT)28 to Au36 (TBBT)24 (where TBBT is 4-tert-butylbenzenethiolate) and to improve the syntheses of Au44 (TBBT)28 and Au36 (TBBT)24 . Our work further demonstrates the usefulness of PTLC in nanocluster research and advances one step toward understanding the "size-focusing" process of nanoclusters.