Both HDPPBA-C and HDPPBA-N display aggregate bands not present in the control molecule, but differences between them were also observed. HDPPBA-C presents a bathochromic shift of the main absorption and aggregate bands in all the solvents compared to HDPPBA-N. In addition, the aggregate bands are more pronounced for the C-centered amide, as a consequence of stronger aggregation for this derivative compared to the N-centered. This effect could be observed by the naked eye since solutions of both amide derivatives in the same solvent and concentration, have different colors (Figure ). Furthermore, the disappearance of the J-aggregate band was observed either upon diluting (Figure a-b) or heating in all the solvents studied (Figure ). For HDPPBA-C, the J-aggregate band was observed at lower concentrations than for HDPPBA-N and it was present at higher temperatures (Figure ). FTIR spectra of powders at room temperature further confirm the existence of H-bonds in the bisamide derivatives. HDPPBA-C and HDPPBA-N showed a band a 3303 cm -1 assigned to the NH stretching bands of the amides. This frequency shows the amides are H-bonded (Figure ). In the region between 1600 cm -1 and 1700 cm -1 , the amide derivatives and the control show peaks at 1655 cm - 1 , corresponding to the amide I bands of the lactam rings of the DPP core. In the same area, the other peaks at 1641 cm -1 and 1637 cm -1 for HDPPBA-C and HDPPBA-N respectively, correspond to amide groups engaged in H-bonding (Figure ). The amide II bands are located at 1550 and 1548 cm -1 for HDPPBA-C and HDPPBA-N respectively, which also shows the amide groups are H-bonded. These large bands overlap with the amide II band of the lactam, visible at 1553 cm -1 for HDPPH. The difference of 4 cm -1 between the amide-containing derivatives indicates a slight difference in the strength of the H-bonds that can induce subtle differences in aggregation.