University of Washington Abstract Reversibly Reconfigurable Plasmonic Nanomaterials Soumyadyuti Samai Chair of the Supervisory Committee: Professor David S. Ginger Department of Chemistry Plasmonic nanoparticles have been extensively investigated in various fields, ranging from biosensing to nanophotonics, due to their characteristic optical features arising from localized surface plasmon resonance. A number of efforts have been made to tailor the optical properties of the nanoparticles by controlling their shape, size and chemical compositions that have advanced their applications in catalysis, molecular diagnostics, therapeutics, and designing electronic devices. Optical signatures of plasmonic nanoparticle assemblies depend on the near field coupling between the plasmon modes of the constituent particles that can be modulated by the distance and orientation between the particles. While the first-generation of plasmonic nanomaterials attempts to control the distance and directionality of the interparticle coupling by employing chemical reagents, recent developments to introduce stimulus-responsivity in the nanomaterials provide us opportunities to control the functional and optical properties of the such materials with external reagents such as light, heat, pH, electric field etc. These emerging plasmonic nanomaterials allow reversible reconfiguration of the structure that can be manipulated remotely, in a reagent-free manner, allowing reusability of the materials in all the applications. Such reconfigurable nanomaterials are obtained by combining the plasmonic nanoparticles with stimulus-sensitive materials. In this dissertation, I explore the use of photo-responsive DNA and thermo-responsive polymer poly(N-isopropylacrylamide) (PNIPAM) hydrogels, to construct reconfigurable assembly of plasmonic nanoparticles and characterize the reversible change in their optical properties in response to external stimuli. DNA has been a powerful material in nanotechnology for engineering 3D plasmonic structures, plasmon rulers and chiral nanophotonic elements. Not only the length and structural conformations of the DNA allow a precise tuning of interparticle distance and geometry of the nanostructures, but also it matches with the decay length of the near-field plasmon coupling. Recent advents of the azobenzene-phosphoramidite chemistry have facilitated the design of photo-responsive nanomaterials assembly, where the structural reconfiguration and the optical properties are controlled by the reversible trans-to-cis azobenzene photoisomerization. Such nanomaterials have found potential applications in low-cost, remote plasmonic biosensing, and optically active nanodevices. The functionality of such optically reconfigurable nanomaterials is extremely sensitive to efficiency of azobenzene photoisomerization in the DNA sequences. So, in chapter 3, we study the trans-to-cis photoisomerization of azobenzene-modified DNAs by measuring the photoisomerization quantum yields in different DNA sequences at various temperatures. Notably weAdvisors/Committee Members: Ginger, David S. (advisor).