Characterisation of dihydroazulene and vinylheptafulvene derivatives using Raman spectroscopy: The CN-stretching region

The effect of adding electron donating and withdrawing groups on the dihydroazulene (DHA)/vinylheptafulvene (VHF) photochromic system has been investigated using Raman spectroscopy in CS2 solutions. The photoswitching between DHA and VHF is often characterised with UV-Vis spectroscopy. However, Raman spectroscopy can also be used for this purpose and give structural insight, as the light induced ring-opening from DHA to VHF causes changes in the CN-stretching frequencies. The CN-stretching frequencies in DHA and VHF are isolated and optimal for the identification of DHA and VHF. The DHA system is also investigated in the solid state.