"Metal nanoparticles (NPs) have been studied intensely in the last decade due to their novel optical, catalytic and electronic properties. Because of the nanoscopic size of NPs, self-assembly has been by far the most important means of generating higher-order architectures. Light is a particularly attractive means to self-assemble of NPs because it can be delivered instantaneously and into a precise location. In order to render NPs photoactive, their surfaces need to be functionalized with photoresponsive ligands. As an incoming Independent Researcher at the Weizmann Institute of Science, the Applicant wishes to develop new nanomaterials resulting from this marriage of nanoscience and organic chemistry. The Applicant has extensive experience in the fields of nanoscience and organic chemistry, acquired during the last several years at Northwestern University, USA. In the proposed project, he would like to develop a NP-based system, in which catalysis is regulated by light. This system takes advantage of his previous research, which has shown that NPs can be reversibly assembled and disassembled using light (PNAS 2007, 104, 10305; Science 2007, 316, 261). For NPs decorated with mixed monolayers comprising photoswitches and molecular catalysts, disassembly of such aggregates will result in a drastic increase of a catalytic surface area exposed to the solvent, and therefore in effective catalysis of a model reaction. As a result, self-assembly process will be transduced into catalytic activity. The system will then be extended to include various types of NPs functionalized with mixtures of different photoswitches and catalysts. These NPs will assemble / disassemble when exposed to different wavelengths of light. The ultimate goal of the project is to demonstrate that in a complex mixture of mutually incompatible chemicals, reactions can be turned ""on"" and ""off"" using light of different wavelengths, in a way similar to enzymatic regulation of reactions in living cells."