Inducing Circular Dichroism in Carbon Nanotubes by Chemical Defects.

Chiral nanostructures are highly valued for their potential in key technologies, such as nanoelectronics, biosensing, and quantum computing. Chirality can arise from intrinsic structural asymmetry or the attachment of chiral molecules to achiral nanostructures. Our ab initio calculations uncover a mechanism where chirality and chiroptical signals are induced by a color center formed by molecules covalently bound to achiral semiconducting single-walled carbon nanotubes. In this case, both the position of structural defects at the nanotube surface and the nature of the molecular adducts forming these defects play key roles in driving the chirality transfer and enhancement of the circular dichroism (CD) response. The defects, symmetrically positioned above and below the nanotube axis, act as chiral enantiomers under circularly polarized light, exhibiting a strong CD signal at defect-related exciton energies, regardless of whether the adducts themselves are chiral or not. In contrast, the defect aligned along the nanotube axis has an achiral nature, producing insignificant CD signal even for chiral adducts. This work provides critical insights on how chemical functionalization can induce and control chiral behavior in carbon nanotubes, potentially opening new pathways in designing useful chiral nanostructures with tailored properties necessary for quantum technology and biosensing applications.