(Invited) Triplet Excitons in sp3-Functionalized Single-Walled Carbon Nanotubes by Optically-Detected Magnetic Resonance

Abstract

Controlled sp3-functionalization of single-wall carbon nanotubes (SWCNTs) has become a common route to enhance their emission efficiency [1], indispensable for their integration in various applications.[2] While a lot of research focused on the effect of the functionalization on the singlet excitons, little information is available on how the triplet excitons are affected by the creation of these sp3-defects along the CNT wall. Here we investigate such triplet excitons by optically detected magnetic resonance, a technique combining the sensitivity of emission spectroscopy with magnetic resonance transitions between the triplet sublevels in an external applied magnetic field. We preform ODMR experiments on a series of samples with different functionalization density and functional groups, and find significant differences in zero-field splitting, ODMR intensity and triplet spin density distribution. While pristine SWCNTs hold triplet excitons with a purely axial symmetry and a zero-field splitting inversely proportional to the diameter of the SWCNT [3], the spin-density distribution of triplet excitons trapped in the sp3-defects changes significantly, losing the axial symmetry of the CNTs. Moreover, we will show how intersystem crossing can be tuned by changing the functional group that is attached to the SWCNT. These results show first steps towards exploiting sp3-functionalization to tune intersystem crossing in CNTs.[1] Y. Piao et al, Nature Chem 5, 840 (2013)[2] J. Zaumseil et al, Adv. Opt. Mater. 10, 2101576 (2022)[3] I. Sudakov et al, ACS Nano 17, 2190 (2023)