The Role of Defect-Defect Interactions in Chirality Transfer of Single-Walled Carbon Nanotubes via Chemical Functionalization

Chirality transfer through the surface modification of nanomaterials is a complex process involving various proposed mechanisms. In our computational study, we focus on single- walled carbon nanotubes (SWCNTs) with sp3-defects introduced by achiral or chiral molecular adducts. Our DFT-based calculations reveal a distinct mechanism of chirality transfer from chiral adducts to the nanotube. This transfer involves the alignment of the static molecular dipoles of chiral adducts with defect-originated electronic states, leading to circular dichroism (CD) signals in the near-infrared spectral range. Notably, these signals can be up to three orders of magnitude stronger than those from chiral molecules alone, even for the achiral (11,0) SWCNT. We also observe a non-additive behavior in the CD spectra from two defects created by molecular adducts with differing chirality or positioned at various sites on the nanotube. When the defects are spaced 1 to 3 nm apart along the axial direction of the (11,0) SWCNT, the CD intensity increases by 3 to 4 times. However, at distances greater than 3 nm, the CD intensity begins to diminish. These findings significantly advance our understanding of chiroptical phenomena in nanomaterials and highlight the potential for engineering chiral nanostructures with tailored optical properties. Furthermore, the enhanced CD signals and customized chiral characteristics could greatly improve the performance of biosensors, enabling more effective detection and differentiation of chiral biomolecules, and facilitating chirality-based separation techniques for medically important molecules.