Previous work on similar quinoidal systems has revealed the presence of a singlet biradical ground state which affects the molecular structure and, by extension, the intermolecular interactions. Moreover, previous work on these biradical forms showed a sensitivity to temperature offering the intriguing possibility that the II-III transition occurred alongside a quinoidal to aromatic transition . The key change in molecular structure between a quinoidal and aromatic form is the alternation between the single and double bonds along the conjugated backbone, which is described by the bond length alternation (BLA) parameter, the average difference between consecutive single and double C-C bonds. A BLA < 0 defines the quinoidal structure whereas a BLA > 0 defines the aromatic form. Because of this change in bond length, Raman spectroscopy is quite sensitive to these biradical forms, due to the difference in vibrational frequency of the ECC mode in the quinoidal and aromatic systems . We simulated the Raman spectrum for this scenario by forcing the BLA into the aromatic form via substituting the cyano groups for methyl groups on the ends of the molecules and compared this to the spectra obtained from polymorph III (Figure ). This allowed us to assign the two new peaks at 1442 and 1497 cm -1 to the ECC of the aromatic form ν(C=C) ECC,A (Figure , Movie S14) and asymmetric stretching modes along the conjugated backbone (ν(C=C) asym ) (Figure , Movie S15) respectively. The complete explanation for these assignments is found in the supplementary information.