Azulenes with aryl substituents bearing pentafluorosulfanyl groups: synthesis, spectroscopic and halochromic properties

Four regioisomeric azulenes bearing pentafluorosulfanylphenyl substituents have been prepared and characterised by various spectroscopic techniques. The absorption spectra are qualitatively similar in the visible region for all isomers, but upon protonation exhibit pronounced variation dependent on the connectivity within each molecule.