of single-wall nanotube DNA hybrids Optical properties of single-wall nanotube DNA hybrids Stacy E. Snyder, Slava V. Rotkin Physics Department & Center for Advanced Materials and Nanotechnology Lehigh University

SWNT DNA Modeling: Simulation Setup Charged phosphate groups of a nucleotide with a thymine base Supercell of DNA-SWNT hybrid Poisson simulation cell Integral # of wraps in integral # of UCs of bare tube; How do the partial charges on DNA atoms affect the electronic structure of the SWNT? Unit cell of bare (10,10) nanotube

Tight-binding Modeling: Computation details Self-consistent solution for the charge density of semiconductor [7,0] zigzag NT under DNA wrap perturbation

Tight-binding results: Polarization cohesion energy Self-consistent solution for the charge density of semiconductor [7,0] zigzag NT under DNA wrap perturbation Polarization interaction: for [7,0] NT and {6:1 | 4e} wrap the cohesion energy due to the NT pi-e-system polarization de ~ 0.47 eV/b.p. interaction with the image charge overestimates C.E. image charge for semiconductor

Indication of the Wrap: Optical Absorption for Perpendicular Polarization 2.0 2.5 3.0 3.5 5 10 15 20 Unperturbed SWNT ssDNA-Wrapped SWNT 1.5 Absorption (a.u.) Energy (eV) (7,0) semiconducting Nanotube Dm=+1 Dm=-1 1 >>> 1 1 >>> 2 2 >>> 1 For the helical perturbation, we expect optical selection rules to change. We obtain an increase in 1>>>1 transitions in perpendicular polarization that are prohibited for the pristine nanotube. 5

Optical Transitions: Symmetry breaking Bare SWNT Degenerate bands split Transitions prohibited for the bare SWNT are allowed in the wrapped SWNT DNA-wrapped SWNT extended bands folded band scheme 6

Absorption/Luminescence Map (7,0) SWNT 0.8 1.8 2.8 3.5 2.5 1.5 Bare tube DNA-wrapped tube Re excitons—this is 1-e- theory; Electric field is perp. to the tube; e- and hole have diff ang mom; trans suppressed?? Simulated absorption of light polarized across the SWNT axis vs. Simulated emission along the SWNT axis For the helical perturbation, we expect optical selection rules to change. We obtain an increase in 1>>>1 transitions in perpendicular polarization that are prohibited for the pristine nanotube. 7

Circular Dichroism in (8,0) SWNT Different optical selection rules for transitions in two circular polarizations result in CD, absent for the pristine nanotube. Unperturbed SWNT ssDNA-wrapped SWNT SWNT, ∆m=+1 ssDNA-wrapped SWNT SWNT, ∆m=-1 8

Summary DNA-wrapped SWNTs are widely used in optics experiments, so understanding their bandstructure is important. We developed a numerical method for modeling symmetry lowering in DNA-SWNT hybrids. We compute a self-consistent charge density for the wrapped tube We compute the polarization interaction between the DNA phosphate groups and the induced (self-consistent) charge on the SWNT Helical symmetry-breaking results in the appearance of intrinsically forbidden optical transitions in perpendicular polarization. This change in the absorption spectrum can be used for experimental detection of the wrap. A similar effect of the symmetry-breaking is predicted to result in strong circular dichroism, which is due to the SWNT itself and not to DNA optical transitions. 9