Controlling Nanoparticles with Atomic Precision: The Case of Au144(SCH2CH2Ph)60

We report a facile, two-step synthetic method for preparing truly monodiserse Au-144(SCH2CH2Ph)(60) nanoparticles with their formula determined by electrospray mass spectrometry in conjunction with other characterization. A remarkable advantage of our synthetic approach lies in that it solely produces Au-144(SCH2CH2Ph)(60) nanoparticles, hence, eliminating nontrivial, postsynthetic steps of size separation, which has proven to be very difficult. This advantage makes the approach and the type of nanoparticles generated by it of broad utility for practical applications. Unlike their larger counterparts, Au nanocrystals (typically >2 nm) that are crystalline and show a prominent surface plasmon resonance band at similar to 520 nm (for spherical particles), the Au-144(SCH2CH2Ph)(60) nanoparticles instead exhibit a stepwise, multiple-band absorption spectrum, indicating quantum confinement of electrons in the particle. In addition, these ultrasmall nanoparticles do not adopt face-centered cubic structure as in Au nanocrystals or bulk gold.