Anomalous Optoelectronic Properties of Chiral Carbon Nanorings...and One Ring to Rule Them All

TL;DR

This paper reveals that chiral carbon nanorings exhibit unique size-dependent optoelectronic properties, with one specific chiral ring showing particularly strong and observable photoinduced transitions, challenging typical quantum confinement expectations.

Contribution

The study demonstrates anomalous optoelectronic behavior in chiral nanorings and identifies a unique chiral ring with exceptional spectroscopic properties, advancing understanding of carbon nanostructures.

Findings

Excitation energies increase with size, contrary to quantum confinement.

Chiral nanorings allow electronic excitations forbidden in armchair rings due to symmetry breaking.

One specific chiral ring (n+3,n+1)) shows large, observable photoinduced transitions.

Abstract

Carbon nanorings are hoop-shaped, {\pi}-conjugated macrocycles which form the fundamental annular segments of single-walled carbon nanotubes (SWNTs). In a very recent report, the structures of chiral carbon nanorings (which may serve as chemical templates for synthesizing chiral nanotubes) were experimentally synthesized and characterized for the first time. Here, in our communication, we show that the excited-state properties of these unique chiral nanorings exhibit anomalous and extremely interesting optoelectronic properties, with excitation energies growing larger as a function of size (in contradiction with typical quantum confinement effects). While the first electronic excitation in armchair nanorings is forbidden with a weak oscillator strength, we find that the same excitation in chiral nanorings is allowed due to a strong geometric symmetry breaking. Most importantly, among all the possible nanorings synthesized in this fashion, we show that only one ring, corresponding to a SWNT with chiral indices (n+3,n+1), is extremely special with large photoinduced transitions that are most readily observable in spectroscopic experiments.