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Sergei V. Voitekhovich,1 Vladimir Lesnyak,2 Nikolai Gaponik,2 and Alexander Eychmüller2
1) Research Institute for Physical Chemical Problems, Belarusian State University, Minsk, Belarus; 2) Physical Chemistry, TU Dresden, Dresden, Germany During the past decade, significant progress has been achieved in the colloidal synthesis of nanocrystals (NCs) holding great promise in the areas of catalysis, electronics, photovoltaics, biotechnology, and others. Colloidally grown nanoparticles comprise a crystalline core surrounded by a layer of a capping agent bound to the NC surface. Capping ligands play an important role in the synthesis of colloidal nanomaterials since they control the nucleation and growth of the NCs, as well as their solubility, chemical and colloidal stability. The most common ligand coatings described in the literature are based on organic hydrocarbon molecules with anchoring end groups like HS-, HOOC-, H2N-, and (HO)2(O)P-. We propose a new class of hydrophilic capping ligands, namely 5-R-tetrazoles for the stabilization of NCs in water. The presence of four nitrogen atoms in the tetrazole ring determines its hydrophilicity as well as a strong coordination ability. In addition, the tetrazol-5-yl group (CN4H) is a nonclassical isostere for the carboxylic group -COOH. These functional groups have similar physicochemical properties and may be interchangeable, resulting in similar biological properties. We found that 5-mercaptomethyltetrazole is a good substitute for thioglycolic acid which is widely used as a capping agent in the aqueous synthesis of colloidal semiconductor NCs. The employment of the tetrazole based ligand allows the preparation of highly luminescent (quantum yield of up to 60%) water-soluble semiconductor CdTe NCs.1 Moreover, the tetrazole ligand was found to replace citrate ligands on the surface of noble metal NCs. This allows the preparing of water soluble Au and Ag NCs showing sufficiently higher stability and enabling their concentration and reprecipitation without notable aggregation of the particles. Furthermore, nearly monodisperse noble metal nanoparticles were obtained by the reduction of metal salts with sodium borohydride directly in the presence of tetrazole-5-thiols in the biphasic water-toluene system.2 Tetrazole capped NCs were shown to possess the unique ability to reversibly form fine 3D networks (hydrogels) upon the addition of transition metal salts.1 The formation of the network occurs owing to the complexing properties of the cross-linking of the capping ligand through additional metal ions. The equal capping of CdTe and noble metal nanoparticles ensures the formation of hybrid semiconductor-metal gel-like structures with tunable composition under joint gelation3. Tuning the ratio of the precursors and the content of the metal salt allows for an effective control of the level of aggregation of the NCs, the composition of the assemblies, and consequently their properties. In particular, the increase of the gold content in the hybrid CdTe-Au architectures induces luminescence quenching and shortening of the emission lifetime. Acknowledgment. Financial support provided by Alexander von Humboldt Foundation and European Science Foundation (Programme PLASMON-BIONANOSENSE) is gratefully acknowledged. 1. V. Lesnyak, S. V. Voitekhovich, P. N. Gaponik, N. Gaponik and A. Eychmüller, ACS Nano 2010, 4, 4090-4096. 2. M. N. Nichick, S. V. Voitekhovich, V. Lesnyak, V. E. Matulis, R. A. Zheldakova, A. I. Lesnikovich and O. A. Ivashkevich, J. Phys. Chem. C 2011, 115, 16928-16933. 3. V. Lesnyak, A. Wolf, A. Dubavik, L. Borchardt, S. V. Voitekhovich, N. Gaponik, S. Kaskel and A. Eychmüller, J. Am. Chem. Soc. 2011, 133, 13413-13420. |
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