The Presence of Excitons in Short Single-Stranded DNA Revealed by Absorption and Circular Dichroism Spectroscopy

This paper presents a systematic absorption and circular dichroism spectroscopy study of short single strands of DNA, from 2 to 20 bases. They are composed of a sequence-specific nucleobase composition, either adenine (A), thymine (T), or AT repeats. The absorption spectra hypochromism and the circular dichroism one show butterfly-shaped spectra. Data analysis conducted on the spectra of these oligomers provides evidence for the formation of excitons and their delocalization length along the strand of DNA in relation to how many bases are involved in the excitonic coupling. In particular, the extent of this coupling is limited to adjacent nucleobases in the case of pure adenine strands but spans multiple nucleobases in the case of pure thymine strands. Predictably, AT repeats show a mixed behavior between the two.