Synthesis of Germanium Nanoclusters with Irreversibly Attached Functional Groups: Acetals, Alcohols, Esters, and Polymers Robin S. Tanke,* ,† Susan M. Kauzlarich,* ,‡ Timothy E. Patten,* ,‡ Katherine A. Pettigrew, ‡ Drew L. Murphy, § Mark E. Thompson, § and Howard W. H. Lee | Department of Chemistry, University of Wisconsin-Stevens Point, Stevens Point, Wisconsin 54481, Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616-5295, Department of Chemistry, University of Southern California, Los Angeles, California 90089-1062, and UltraDots Inc., 48611 Warm Springs Boulevard, Fremont, California 94539 Received December 6, 2002. Revised Manuscript Received February 13, 2003 Germanium nanoclusters of average diameter 4 nm were prepared with covalently bound termination groups. Chloride-terminated nanoclusters were reacted with a Grignard reagent to form acetal-containing surface-terminated nanoclusters. Treatment with acid yielded hydroxyl-containing surface-terminated nanoclusters, and treatment with an acid bromide and base yielded an ester-containing surface-terminated nanocluster. Atom transfer radical polymerization (ATRP) was used to graft polymer chains from the surfaces of the nanoparticles to yield hybrid nanostructures. Changes of the termination group in the nanoclusters did not alter the photophysics of the original nanoclusters, a result that is consistent with a stable nanocluster surface. The nanoclusters were characterized by HRTEM (high-resolution transmission electron microscopy), NMR, FTIR, UV-vis, and fluorescence spectroscopy. Introduction The size-dependent luminescent and nonlinear optical properties of semiconductor nanoclusters make them attractive candidates for a variety of technological applications. 1,2 Monodisperse, well-characterized samples of II-VI semiconductor nanoclusters can be readily prepared. 3-8 Consequently, many groups have demon- strated that CdS and CdSe nanoclusters 6-11 are useful in a number of technologies including light-emitting diodes (LEDs), photodiodes, photovoltaic solar cells, gas sensors, and fluorescent labeling. Nanocluster surfaces must be stabilized because the nanoclusters are unstable relative to bulk material. This is generally accomplished by covering the surface of the nanocluster with a monolayer of organic material that will be referred to as the termination group. This organic monolayer is important not only for the stabi- lization of the nanocluster but also for many of the applications of these nanoclusters. 12 For example, lu- minescent probes have been prepared 7 by attaching oligonucleotides to CdSe/ZnS nanoclusters via chemical manipulation of a thiol termination group. Photocata- lysts for the generation of hydrogen from 2-propanol have been prepared 13 by immobilizing CdS/ZnS on thiol- modified polystyrene. The use of phosphine oxides, amines, and thiols as the termination groups for II-IV nanoclusters is common; however, in many cases these termination groups can be displaced. 14,15 Furthermore, Aldana and co-workers 16 have shown that the thiols attached to CdSe undergo photocatalytic oxidation to disulfides, which eventually leads to nanocluster ag- gregation. 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