On-the-Fly Nonadiabatic Dynamics Simulations of Single-Walled Carbon Nanotubes with Covalent Defects

Abstract

Single-walled carbon nanotubes (SWCNTs) with covalent surface defects have been explored recently due to their promise for use in single-photon telecommunication emission and in spintronic applications. The all-atom dynamic evolution of electrostatically bound excitons (the primary electronic excitations) in these systems has only been loosely explored from a theoretical perspective due to the size limitations of these large systems (>500 atoms). In this work, we present computational modeling of nonradiative relaxation in a variety of SWCNT chiralities with single-defect functionalizations. Our excited-state dynamics modeling uses a trajectory surface hopping algorithm accounting for excitonic effects with a configuration interaction approach. We find a strong chirality and defect-composition dependence on the population relaxation (varying over 50−500 fs) between the primary nanotube band gap excitation E 11 and the defect-associated, single-photon-emitting E 11 * state. These simulations give direct insight into the relaxation between the band-edge states and the localized excitonic state, in competition with dynamic trapping/detrapping processes observed in experiment. Engineering fast population decay into the quasi-two-level subsystem with weak coupling to higher-energy states increases the effectiveness and controllability of these quantum light emitters.

Investigating Molecular Exciton Polaritons Using Ab Initio Cavity Quantum Electrodynamics

“…The top right panel (above Figure c,d) provides the real-space projected bare electronic transition density of the ground-to-E 11 state exciton, demonstrating its delocalized excitation character. Semiconducting SWCNTs, when functionalized with covalent adducts forming a hybridization defect, exhibit bright emission features due to the addition of a defect-associated exciton below the band edge, which have been the subject of much experimental and theoretical work over the past decade for their use as single-photon light sources and for their tunable emission at low-energy telecommunications wavelengths. − The simplicity of this system’s dipole matrix (akin to a two-level system) will lead to clear theoretical predictions and a new pathway toward the tunable manipulation of SWCNTs by coupling to optical cavities, without the need for chemical functionalization.…”

Optically active defects in carbon nanotubes via chlorination: computational insights

“…We have considered a wide range of functionalization types, including the covalent attachment of two species to a single SWCNT ring, namely at ortho and para positions of the SWCNT ring, as has been done in many previous reports. 18,38,[80][81][82][83][84][85][86] Additionally, we have simulated structures where the chlorine atoms are placed on adjacent rings (named 1,4), two rings apart (named 1,6), and three rings apart (named 1,8), as illustrated in Fig. 1c.…”

“…or become trapped by the excitonic potential energy well. Once trapped by the local defect potential, sub-picosecond thermal relaxation from the band-edge to the defect-associated excitonic state occurs, 45 followed by bright radiative emission enhanced from the pristine SWCNT by the large transition dipole between the defect-associated exciton and the ground state. 31,33,46,47 Additionally, similar to nitrogen-vacancy (NV) centers in diamonds, 48 a chemical defect in the SWCNT creates suitable conditions for single-photon emission (SPE), namely a quasitwo-level sub-system composed of ground and defect-associated states that are energetically separated from the higher-energy states.…”

Isomerization of surface functionalized SWCNTs and the critical influence on photoluminescence: static calculations and excited-state dynamics simulations

“…Many experimental and theoretical (mainly limited to the static characteristics of SWCNTs) investigations have been carried out to gain insights into the optical phenomena of as-functionalized SWCNTs, but a comprehensive understanding of their optical properties is still a prerequisite before ultimately realizing their full capabilities. 12–16 To date, the luminescence efficiency and stability are still key aspects that need to be largely improved. In experiments, chemical functionalization of SWCNTs creates defects either in sp 3 or sp 2 -preserving configuration.…”