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

• The CN-stretching frequencies in DHA and VHF dissolved in CS2 were not affected by substitution.
• CN-stretching frequencies in DHA redshift upon ring-opening to VHF.
• CN-stretching frequencies in DHA split into two separate bands upon ring-opening to VHF.
• The calculated frequency shifts and intensity changes upon ring-opening are in agreement with the experimental observations.

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.

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