Synthesis and structure of indoline spiropyrans based on benzo[f]coumarin

Indoline spiropyrans containing benzo[f]coumarin moiety annulated to the 2H-pyran cycle were synthesized. The obtained compounds exist in solutions as a tautomeric mixture of their spirocyclic and merocyanine forms. The spiro form exhibits an enhanced resistance to UV irradiation and does not rearranges into the merocyanine isomer in the temperature range of 278–303 K.