  We present some computational simulations of graphene-based nanoribbons with
a number of half-twists varying from 0 to 4 and two types of defects obtained
by removing a single carbon atom from two different sites. Optimized geometries
are found by using a mix of classical-quantum semiempirical computations.
According with the simulations results, the local curvature of the nanoribbons
increases at the defect sites, specially for a higher number of half-twists.
The HOMO-LUMO energy gap of the nanostructures has significant variation when
the number of half-twists increases for the defective nanoribbons. At the
quantum semiempirical level, the first optically active transitions and
oscillator strengths are calculated using the full configuration interaction
(CI) framework, and the optical absorption in the UV/Visible range (electronic
transitions) and in the infrared (vibrational transitions) are achieved.
Distinct nanoribbons show unique spectral signatures in the UV/Visible range,
with the first absorption peaks in wavelengths ranging from the orange to the
violet. Strong absorption is observed in the ultraviolet region, although
differences in their infrared spectra are hardly discernible.
