Tuning Spin-Orbit Coupling in (6,5) Single-Walled Carbon Nanotube Doped with sp3 Defects

Single-walled carbon nanotubes (SWCNTs) containing s p 3 defects are a promising class of optoelectronic materials with bright photoluminescence and demonstrated single-photon emission. Using density functional theory simulations, complemented by measurements, we investigate the electronic structure of a series of quantum defects attached to (6,5) SWCNT with the goal of tuning the spin–orbit coupling by introduction of a heavy atom in the defect structure. We characterize the ground state electronic and spin properties of four synthesized and three potential defects on the tube and find that all of the synthesized defects considered introduce a localized midgap defect-centered state containing a single electron, ≈ 0.2–0.3 eV above the valence band. The spin density is located at the s p 3 defect site with negligible spin–orbit coupling even with the presence of a Pd atom. Three additional functional groups were tested via computation to increase spin localization near the metal, thereby increasing spin–orbit coupling. We predict that only the chlorodiphosphanepalladium(II)– [Cl(PH 3) 2Pd(II)–] defect results in increased spin–orbit splitting of the defect state and the conduction band associated with the pristine-like SWCNT, a measure of the spin–orbit coupling of excited state transitions. This study suggests that for unpassivated s p 3 defects in (6,5) SWCNT, forming a direct bond between a heavy atom and the s p 3 carbon allows for tuning of spin–orbit coupling.