1. 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

2. 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

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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