Vibrational Circular Dichroism Spectra of 2,5-Diaminoterephtalate Macrocycles Reveal Distant Vibrational Exciton Coupling.

We applied the exciton coupling theory (ECT) to interpret the dipolar interaction mechanism of C═O stretching and N─H bending vibrations in a new class of chiral macrocycles based on the 2,5-diaminoterephthalate scaffold. VCD and FT-Raman spectra, with the support of quantum chemistry calculations, came together to disentangle the energy level diagram resulted from the vibrational coupling of the ν(C═O) and δ(N─H) vibrations on the basis of the local symmetries. The effect of the configuration of the carbonyl groups on the chiral coupling demonstrated the prevalence of the through-space dipolar interaction mechanisms, with respect to the through-bond one, between the C═O bonds, which is of interest to investigations of the biochemical activity of pharmaceutical molecules endowed with acid groups.