Triplet absorption in carbon nanotubes: a TD-DFT study

TL;DR

This study uses TD-DFT to predict triplet excited state properties in carbon nanotubes, revealing their energy levels, localization, and optical absorption features, which are similar to those in conjugated polymers.

Contribution

It provides the first detailed theoretical analysis of triplet states in CNTs using TD-DFT, highlighting their energy, localization, and optical properties.

Findings

Triplet states are 0.2-0.3 eV lower than singlet states.

Triplet states are spatially localized.

Strong optical absorption occurs at 0.5-0.6 eV.

Abstract

We predict properties of triplet excited states in single-walled carbon nanotubes (CNTs) using a time-dependent density-functional theory (TD-DFT). We show that the lowest triplet state energy in CNTs to be about 0.2-0.3 eV lower than the lowest singlet states. Like in $\pi$-conjugated polymers, the lowest CNT triplets are spatially localized. These states show strong optical absorption at about 0.5-0.6 eV to the higher lying delocalized triplet states. These results demonstrate striking similarity of the electronic features between CNTs and $\pi$-conjugated polymers and provide explicit guidelines for spectroscopic detection of CNT triplet states.