Steric and substituent effects on the photoreversibility of novel indolospirobenzopyrans: Acid deuterolysis, UV and 1H NMR spectroscopy

The photoreversibility of several novel indolospirobenzopyrans was investigated using temperature studies – monitored using 1H NMR spectroscopy, qualitative UV studies and acid deuterolysis (trifluorodeuterioacetic acid (TFA-D)) catalysed isomerisation studies. Derivatives that contained appropriately placed electronically modifying substituents on both the indole and benzopyran-rings; also variants possessing sterically hindering (with regard to spiropyran-opening ↔ closing reaction) groups, within the spirocyclic ring-system were prepared. In addition, compounds that contained both sterically restricting and electronically biasing substituents, were investigated, simultaneously.