Speaker: Dr. Francois Leonard & Dr. Andy Vance, Sandia National Laboratory, CA
Abstract: Phototransduction plays a central role in key natural processes such as vision and photosynthesis. For these processes, natural evolution has found exquisite solutions that optimize efficiency, compactness, and self-healing. While researchers have long tried to supplant nature's successes using solid-state approaches, our ability to convert optical radiation to electrical signals with nanoscale precision still remains in its infancy. An alternative to solid-state approaches is one that more closely mimics natural processes by integrating chemical or biological materials with solid-state materials. To this end, we present a nanoscale color detector based on a single-walled carbon nanotube functionalized with azobenzene chromophores, where the chromophores serve as photoabsorbers and the nanotube as the electronic read-out. By synthesizing chromophores with specific absorption windows in the visible spectrum and anchoring them to the nanotube surface, we demonstrate the controlled detection of visible light of low intensity in narrow ranges of wavelengths. Our measurements suggest that upon photoabsorption, the chromophores isomerize from the ground state trans configuration to the excited state cis configuration, accompanied by a large change in dipole moment, changing the electrostatic environment of the nanotube. We will also present our all-electron ab initio calculations that are used to study the chromophore-nanotube hybrids and show that the chromophores bind strongly to the nanotubes without disturbing the electronic structure of either species. Calculated values of the dipole moments support the notion of dipole changes as the optical detection mechanism.