Optoelectronic Properties of Carbon Nanorings: Excitonic Effects from Time-Dependent Density Functional Theory

TL;DR

This study uses time-dependent density functional theory to explore the unusual size-dependent optoelectronic properties of cycloparaphenylene carbon nanorings, revealing significant excitonic effects that influence their electronic behavior.

Contribution

It provides the first detailed analysis of excitonic effects in carbon nanorings, explaining their atypical electronic excitation trends through electron-hole interactions.

Findings

Lowest excitation energy increases with nanoring size, contrary to quantum confinement expectations.

Excitonic effects are crucial for understanding the photoinduced dynamics in nanorings.

Electron-hole interactions significantly influence the optoelectronic properties of the nanostructures.

Abstract

The electronic structure and size-scaling of optoelectronic properties in cycloparaphenylene carbon nanorings are investigated using time-dependent density functional theory (TDDFT). The TDDFT calculations on these molecular nanostructures indicate that the lowest excitation energy surprisingly becomes larger as the carbon nanoring size is increased, in contradiction with typical quantum confinement effects. In order to understand their unusual electronic properties, I performed an extensive investigation of excitonic effects by analyzing electron-hole transition density matrices and exciton binding energies as a function of size in these nanoring systems. The transition density matrices allow a global view of electronic coherence during an electronic excitation, and the exciton binding energies give a quantitative measure of electron-hole interaction energies in the nanorings. Based on overall trends in exciton binding energies and their spatial delocalization, I find that excitonic effects play a vital role in understanding the unique photoinduced dynamics in these carbon nanoring systems.