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CPP: Chemische Physik und Polymerphysik

CPP 16: Electronic Structure and Spectroscopy II

CPP 16.6: Vortrag

Mittwoch, 29. März 2006, 16:00–16:15, ZEU 160

Reduction of Noble Metal Ions to Metal Nanoparticles on J-Aggreates — •Stefan Kirstein¹, Hans v. Berlepsch², Christoph Böttcher², Dörthe M. Eisele¹, and Anna Burmistrova¹ — ¹Humboldt University of Berlin — ²Free University, Berlin

Cyanine dye molecules and their J-aggregates are well known to serve as sensitizers for photo induced electron transfer processes. Technically, this feature is utilized in photographic films where dyes are adsorbed at silver halide crystals which is reduced to elemtary silver by an electron transfer from the photoexcited dye. Here, the same mechanism is used to grow silver nanoparticles at the surface of tubular J-aggregates form AgNO₃ salt solutions.

The amphiphilic tetrachlorobenzimidacarbocyanine dye molecule C8S3 (amphipipe) forms tubular J-aggregates in aqueous solutions with a uniform diameter of 17 nm and lengths of over 100 µm. The addition of noble metal salts (Na₂PdCl₄ or AgNO₃) to a solution of C8S3 aggregates leads to the formation of metal nanoparticles at the surface of the dye aggregates. The particles are observed by cryo-TEM and also by AFM for aggregates adsorbed at solid surfaces. The particles are rather uniform in size with a mean diameter of a few nanometer and distributed along the aggregate surface. In parallel to the growth of the particles a dramatic quenching of the aggregate fluorescence is observed. Therefore, the growth of the metal nanoparticles is explained by a photoexcited electron transfer process from the J-aggrgates to the metal ions. A systematic study of this process for AgNO₃ will be presented.