  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.
