Development of Bottom - Up Chemical Approaches to 3 - D Negative Index

The objective of this project was to develop a new approach to 3-D metamaterials. A key step was developing materials with large optical activity. A unique combination of "bottom up" and "top down" approaches to produce nanostructures was successfully applied. Multiscale modeling was used to design chiral polymers. A series of chiral polymers, based on thiophene, fluorene, and fluorene-quinoxaline motif with chiral side chains, exhibiting extremely large chirality, were synthesized, post-processed and characterized in both solution and film phases. A new concept of chirality enhancement via coupling with plasmonic, excitonic and superparamagnetic nanoparticles was introduced for the first time and verified experimentally. Theoretical models were proposed to explain the enhancement. The enhancement of nonlinear optical activity by utilizing pi-conjugated molecular building blocks was proposed and experimentally realized. Writing of sub-wavelength metal-nanoparticle-containing metamolecules was demonstrated via simultaneous photoreduction of a gold precursor and crosslinking of a photoresist using two-photon excitation, opening the way to a faster and more cost efficient "top down" manufacturing of metamaterials. Photopatternable polymer nanocomposites of chiral polymer and SU-8 photoresists were produced and photopatterning was demonstrated. Joint papers with researchers at AFRL in Dayton have been published, thus aiding in transitioning of our concepts to AFRL. Chemical synthesis and Bottom up approach: Optical properties of a series of newly synthesized chiral polythiophene polymers mixed with metallic (gold, diameter ~5nm) and nonmetallic (CdS, diameter ~5nm) nanoparticles (NPs) were studied. Absorption, reflection and circular dichroism (CD) spectra of pure polymers, polymer/Au NP and polymer/CdS NP solutions, and spinand spray-coated films were recorded. The chiral polymer and NPs were mixed in organic solvents that both dissolved the polymer and stably dispersed the NPs. In solid films, addition of Au NPs resulted in intensity redistribution among bands in the CD spectrum, while in solution the shape of the spectrum remained the same for both pure polymer and polymer/Au NP mixtures. In the case of nonmetallic NPs of similar size and surface capping, this effect was not observed. This provided clear evidence of plasmonic interaction between Au NPs and the chiral polymers. The polythiophene polymers are optically O O