At the CC2 level, C10, which has no substituent for AZO-2, exhibits a spectrum different from and much weaker than its nearest neighbours while the TD-DFT results indicate similar spectra for all left ring nuclei except C7. Possibly, this carbon (C10) experiences some influence from the N --N group which, in turn, is affected by the amino group in para position on C5, where the two methods produce rather different spectra. It could be that TD-DFT fails to capture some effects arising from the -NH 2 nitrogen atom which, on the other hand, are captured by the correlated CC model. This propagation of perturbation along the chain C5-C2-C7-C10 could also be an explanation for the quite different NSCD of all of these atoms between AZO-2 and AZO-3 and between TD-DFT and CC2. The difference between TD-DFT and CC2 appear to be enhanced, especially along C5-C2-C7, when comparing AZO-3 to AZO-2, suggesting that the combination of an electron-donating and electronwithdrawing group challenges the suitability of TD-DFT/BH+HLYP for this application.