One of the initially surprising aspects of the experimental data is that relatively few completely new couplings are created by the folding of the G4. Although behaviour like this may be observed in our calculated spectra, such as in Figures and, it is useful to reflect on the reasons for this. Chemical moieties such as DNA bases, contain many chemical 'groups' which couple to each other in a diverse set of ways. The formation of a quartet of bases coupled by Hoogsteen hydrogen bonding might therefore primarily be characterised by the reorganisation/recombination of the vibrational states of the individual bases (and the couplings between them) rather than the emergence of altogether new couplings not characterisable in this way. This is loosely analogous to the situation in molecular exciton coupling, where electronic states are reorganised by the new couplings, rather than the number of electronic states being increased.