Gradient temperature Raman spectroscopy data for DHA and DPAn-3. Colors range from white (highest signal intensity) to red, orange, yellow, green, blue, to dark blue (lowest signal intensity. The red and green represent δ-positive and δ-negatives. There is a striking contrast between DHA and DPAn-3, especially in the high-frequency vibrational modes (2100-1500). These data suggest a high probability that DHA will accept vibronic information, with the energy being absorbed by an outer orbital electron. In this wavenumber region, the only common feature between DHA and DPAn-3 is white, which refers to the C=O. Adapted from [39].